Lennard Zinn on the Physics of Mountain Biking, Bike Fitting, and Fitness

Lennard Zinn is a bike designer and frame builder, and is the author of Zinn and the Art of Mountain Bike Maintenance. We talk about bit fit, repair, tire rolling resistance, and fitness in this wide-ranging interview.

Lennard Zinn is a bike designer and frame builder with a shop in Louisville, Colorado. He was a member of the U.S. Olympic cycling team and worked with Tom Ritchey on some of the earliest mountain bikes. He’s also the author of Zinn and the Art of Mountain Bike Maintenance, one of the world’s best selling guides to mountain bike repair.

In this episode we ask:

  • How did you get into designing and building bikes?
  • Zinn and the Art of MTB Maintenance was first published in 1996, and it’s now in its 6th edition. What’s changed over the years?
  • Are today’s bikes easier to work on than bikes were 10, or 20 years ago? Why?
  • What are the challenges involved in fitting taller riders?
  • What have you learned about crank lengths over the years?
  • Do tall cyclists have any particular advantages when it comes to power or bike handling?
  • What are the considerations in terms of frame design for bigger and heavier riders? Is any of this applicable to more aggressive mountain bike designs, and vice versa? 
  • What are the main factors that influence a bike tire’s rolling resistance? 
  • What led you to write about heart conditions in athletes in your latest book, heart conditions in athletes? What did you learn through researching the book? Did your own heart condition influence your decision to build your first e-bike?
  • Is there room for further bike fit improvements in the future? Which tech trends are you excited about?

Find out more at zinncycles.com or order Haywire Heart from Amazon.

The following transcript has been lightly edited.


Jeff 0:00
Hey everybody, welcome to the Singletracks podcast. My name is Jeff and today my guest is Lennard Zinn. Lennard is a bike designer and frame builder with a shop in Louisville, Colorado. He was a member of the US Olympic Cycling Team and worked with Tom Ritchie on some of the earliest mountain bikes. He’s also the author of Zinn and the Art of Mountain Bike Maintenance, which is one of the world’s best selling guides to mountain bike repair. Thanks for joining me, Lennard.

Lennard 0:28
Thank you.

Jeff 0:30
So tell us a bit about your background, how’d you get into designing and building bikes?

Lennard 0:36
Well, as you said, I was on national cycling team and you know, once that happens, you generally have sponsors providing you with your equipment. And I had one — there’s a race called the Iron Horse classic in Durango — and the classic stage race with the the main event is the race from Durango to Silverton, where you’re actually racing, the — it’s called Iron Horse, because you’re racing the narrow gauge train that runs from Durango to Silverton.

And I won that race in 1980. And I set the course record by like, more than five minutes. I was kind of a heavy favorite to win it again in 81. And by then, you know, I was on a little tiny team when I won in 1980 and and so now I was on a strong trade team and had a sponsor that provided my kit that I just got. And there’s two 11,000 foot passes in that stage and, and coming down the backside of the first pass, my bike just started shaking uncontrollably. And, you know, there was nothing I could do except put the brakes on and just let the group go and, and then the same thing happened on the even steeper descent down into Silverton. And it was sort of at that moment that, you know, I used to make jewelry when I was in high school.

And then when I was in college I actually taught jewelry making with the leisure program at Colorado College and I had a degree in Physics and I had done my senior seminar on the stability of the bicycle I’d written these computers computer programs and this ancient computer language called Fortran about determining the stability of a bike.

And so I figured I have the craft, from jewelry making to be able to do it and that I had knowledge and interest from my physics background to to be able to do it as well. And so that’s when I decided I could I could make a better bike than this myself. So that’s what sort of started that started the whole process.

I guess I already had started, I had made one bike in the the year after I graduated from college while I was training at the Olympic Training Center, Colorado Springs. I was also working in the physics department at Colorado College as a paraprofessional and in those days, you want a lot of bike parts, because you didn’t you didn’t win much money. And, and I really wanted my girlfriend who’s now my wife of 39 years to to have a nice bike. And so I built her a frame while I was in the physics shop there.

And then I had Bill Whittle, who was this really famous mechanic of the national team and I had him help me with all the finishing stuff over at the Olympic Training Center and put all those parts that I’d want over time on the bike. So I I had that little experience of this one thing and making this frame and and then really what happened was late in that season in 1981 I tore my gastrocnemius muscle racing in the Tour of Ireland stage race.

After I got back from Ireland, it just got worse and worse and worse. It calcified and stuff and it was just, I couldn’t stand being around Boulder where everything for me was — other than my girlfriend — was about bikes, you know, and I moved to Northern California and started working for a geophysics company. I got laid off, and then just was flipping through the phonebook and saw Tom Ritchey’s name and I called him up.

It just so happened that his second employee ever had quit that day. And so I became the third employee ever, and me and this guy, Devin and Tom, we made 100 frames a month. I’d heard about mountain bikes, but I’d never seen them. But you know, Richie was the only one making that kind of scale of mountain bikes in the world. And so I learned an enormous amount from him.

He’s a good friend, and he’s only a year older than me or something. It’s just that he’d started his company when he was 16. So last October I went out to his place for celebrating the 50th anniversary of Ritchey bicycles. Whereas this past summer, we celebrated the 40th anniversary of Zen cycles. So he just started his business a lot sooner.

Anyway, in order to heal this knee injury, it just wasn’t healing out there in California. So I came back to Boulder to be treated by Andy Pruitt, who’s famous in the bike world as the sort of the orthopedist of cycling’s elite and who created what Retül came out of and all the bike fitting systems basically are based on Andy Pruitt’s work.

My grandmother left me $10,000 when she died about that same time, and I used that to start Zinn Cycles and never really thought it would become a career. I wanted to build some bikes and ended up you know, being 40 years now, almost 41 years into it.

Jeff 6:49
Yeah, that’s great. So Zinn and the Art of Mountain Bike Maintenance was first published in 1996. And from what I see, it’s now in the sixth edition. What’s changed over the years in the book?

Lennard 7:05
I wrote the book in 1996. I remember the cover for that one, the first edition, was the only one that had a picture of me on it. The other ones are all just a picture of a bike, really, and on that [first one] I was holding up an early, like Rockshox Judy suspension fork, so suspension forks had just come in. So that was one reason to write the book, because nobody knew how to work on those.

But otherwise, you know, you had cantilever brakes. There was certainly no rear suspension. I don’t think there were even any carbon bikes. All bikes were made out of metal, you know, a few titanium, basically steel and aluminum was where that was at. There was no such thing as a threadless headset, at the time. Threaded headset with a stem with a quill/

Jeff 8:05
Yeah, so a lot of changes. Would you say today’s bikes are easier to work on than they were 10 or 20 years ago? Are things getting more complicated?

Lennard 8:15
Well, it depends on if you actually want to completely overhaul things. Like at the time, you know, there was no such thing as like one of these cranks where the crank arm and the spindle are one piece. And then, you know, it’s a sealed, sealed bearing in the bottom bracket. At that time, it was all loose ball bearings, and, you know, separate crank arms. And so those were harder to work on in the sense that you needed more tools in order to take them apart.

But then you could completely take everything apart, down to, you know… Now you just replace the bearing and a cartridge bearing or even, you don’t even a lot of times do that you replace the entire bottom bracket, the whole cups with the bearings in them. Or you don’t have the ability to work on the individual parts also. Like a cantilever brake, you could replace individual pieces of the cantilever brake. And now modern disc brakes, you’re not even allowed to get into that other than tape. I don’t even think they’re designed so that you can’t can overhaul much of anything inside of them, you just can change the pads and stuff.

And then of course electronic shifting. And even the STI… because in 1996 I guess there was click shifting already then but those are thumb shifters, you know, on the mountain bike. But you really don’t do that anymore. You’ve kind of replaced the shifter and all.

Jeff 10:00
Right, yeah. On the one hand, things are easier because we don’t have to work on them, we just replace them. But, you know, on the other hand, maybe it’s kind of wasteful, and we’re losing out on kind of understanding our bikes from a different level. Do you think one way is better than the other? Or are they kind of good trade offs to have?

Lennard 10:22
Well, from a purist perspective, which, I’ve always kept everything as long as I possibly could and always make everything as long as I can possibly even it is clothing, cars, anything, you know. Bikes and are no exception. And I do find it frustrating, like with a ski bindings, you know, that if you break one little dinky part on the ski binding, there’s nothing you can do it.

But on the other hand, in terms of your time invested, if your main focus is on riding the bike, then you can get back on the bike much faster today, because you just replaced this whole modular unit, whatever it is, that was failing, boom, put it back in. And removing cranks, for instance, is a lot quicker process. So I can’t say one’s better than the other.

Jeff 11:28
Yeah, there’s trade offs either way, and like you mentioned, depends on kind of who you are, and where you have that trade off between time and money and where your interests lie in terms of biking.

I think for a lot of people, it is about just being able to get out and ride again as quickly as possible. And at the same time, there are those who enjoy tinkering and you know, figuring that stuff out.

So I want to talk about building bikes for tall riders. How did you get into building mountain bikes and bicycles for taller folks?

Lennard 12:03
Well, you know, I told you that story about coming down. The descents in the Durango to Silverton Iron Horse Race and getting mad, well, that’s a function of being tall. You know, I’ve always been a pretty lean guy. At the time, I was six foot six and 156 pounds.

And the taller the bike, the more torsional flex it has. It just can’t control the twisting motion very well. All bikes had the same diameter tubing because there was all lugged, lug construction. So the lugs dictated not only that the tubes are round but also what size they were. And those were really quite skinny. That’s just what bikes looked like at the time.

But now you look at bikes like that, and you’re like ‘whoa, what skinny little tubes,’ right? They control the bike from twisting back and forth too much. And I knew from a physics perspective that basically that high speed shimmy is a resonance frequency on whatever you’re hitting on the road. The little bumps and the wind and whatever environmental effects that you’re dealing with are at a similar frequency to the frequency of vibration of the frame, the frequency of twisting one back and forth oscillation.

And the bigger the frame, the longer that period and so the lower the frequency because it takes longer to twist it back and forth and one twisting thing, whereas a small, much higher frequency, shorter period of oscillation. And so you’d never encounter the the environmental effects that would make a small frame do that. And so that was really the impetus was like, ‘Jesus Christ, these guys don’t know anything about big people.’ Because you know, at the time, everybody was racing on an Italian bike, you know, and Italians are smaller people than Northern Europeans and so that was how it started.

Then as time progressed I sponsored a women’s racing team for a decade or so and for a long time that was a really good market for me making really small bikes for women. Because the bikes for women in the 80s, if you if you were a small person, you ended up like on a kid’s bike kind of a thing, not a bike of similar quality to the high end racing bikes from the big manufacturers. I had a very loyal following among women bike racers. But then at some point the big companies just realized that women actually spend a lot of money on bike stuff.

Those initial attempts at women’s specific designs were just literally shrink it and pink it, and that didn’t provide a good performance advantage. But now… everybody is small smile at some point in their life, so you know, kids are racing today. There are pretty sweet [smaller] bikes these days so that whole market kind of dried up for me, but the tall bike market was just a natural, obviously, being so tall myself and I just sort of veered that way. And then as time went on I continued to build bikes for any size people. But I don’t have any competition in that [tall rider] niche.

Jeff 15:54
It sounds like the impetus for that was actually like structural for lack of a better term. I mean, the performance of the bike just wasn’t what you wanted, or what you would expect as a tall rider.

What about like the bike fit? Are there challenges to fitting a taller rider? What what are the things that you need to do that are maybe a little bit different for a tall rider, than for somebody who’s more average height?

Lennard 16:23
Well, yes, if you’re sticking with stock components, which is what I would have been doing when I was racing on national team. Eddie Davis was the national team coach at the time, he did the fitting for me, and I had 180 millimeter cranks, which I’d gone to great lengths to find at the time. And it just made sense to me that I should have the longest cranks that you could make.

And he said you need longer cranks. And I’m like, they don’t make any longer than this. So he’s like, Oh, sure, they make, they make. But, they didn’t. And there was no other alternative for me other than the 180 millimeter, but even that, most other riders are like, ‘Oh my god 180 millimeters.’

But if you think of it as a percentage of leg length, my inseam is almost 1000 millimeters, and the crank is 180mm. So that’s 18% of my leg length. Okay, well, most people on, you know, 172.5 millimeter crank with a 820 millimeter inseam. That’s like 22%. So that means that the taller rider on the stock size crank, the angles that the hip and knee are going through are much less than the angles compared to a person with a much higher percentage of their leg length being in the crank is going through.

So that means that the angle between the hip and the thigh, when the when the foot is at the top of the crank circle, that that angle at the hip is more open on the tall rider. They can fold over further. That’s that you definitely see in the pro ranks when you see really tall, tall guys in the Tour de France, there’s this tremendous amount of drop from their saddle to their handlebars. It’s maybe six to 10 inches, a huge amount that most never tolerate. Well, it’s a function of the fact that that crank is disproportionately short compared to their leg length. It’s not that there’s anything different about the physiology of a really tall person that they can fold over more.

And that’s what most fitters are dealing with when they’re fitting. They’re fitting them with standard sized cranks. And so that’s a fundamental differences that you need to be like, ‘whoa, you can have a whole lot of drop from this saddle to the bar.’

Other issues are that as the saddle goes, the seat angle is angled somewhere, you know, 73 degrees, 72 degrees, something like that on most [road] bikes and as the seat goes angled up more and more, it gets taller and taller. That means that the seat is literally further and further back over the rear wheel, which the bikes tend to wheelie. And you know, you have tall riders, that’s a problem all the time on road bikes. It’s certainly on mountain bikes, but also on road bikes just of being in the saddle pedaling hard, and the front wheel gets super light.

Jeff 19:47
Yeah, mountain bikers might like that. I’m tall, and I wish I could do better wheelies, but that’s that’s a personal problem.

Lennard 19:57
There are definitely advantages for climbing on technical terrain. For that reason, there are other times when it’s, you know, more mixed terrain rolling. Or you want to have more some more weight on the front.

On mixed terrain, it’s definitely an advantage to have decent traction with your front tire. A tall rider fundamentally feels more vulnerable, they’re just higher off the ground. Sort of high-siding situations dropping down steep, steep things, feeling like they’re more likely to pitch over because so much of them is sticking up in the air. Something that didn’t exist of course when I first wrote Zinn and the Art of Mountain Bike Maintenance, is the dropper post, was was a giant boon to tall riders.

Jeff 21:27
Right, for sure. Talking about crank links, I think you started making custom crank lengths in like 2008. And I saw that you have some that are as long as 220 millimeters long. Is that the limit, would you say for mountain biking, specifically in terms of like a long crank and getting hung up on rocks and things like that?

Lennard 21:54
Well, the limitation for getting hung up on rocks is the combination of the crank length and the bottom bracket height. If you make the bike, design the bike for the longer crank, then you don’t have any different clearance issues. I mean, that’s what we do with our bikes, both Zinn and the custom ones. And the Clydesdales are designed with quite a bit higher bottom bracket than standard because we’re planning on the pedal at the bottom of the stroke being no lower to the ground than I an average bike would have.

So from that perspective, you know, obviously, if you’re just buying a crank from us and sticking it on your existing bike, yeah, you’re gonna have some clearance issues. You don’t want to go up very much, you know, maybe 10 millimeters on crank length for that reason. There are some fundamental things that people don’t think about that that long crank really benefits.

As a tall mountain biker [with longer cranks], one advantage is that when you’re descending in technical terrain, your feet are much further apart, you have a much longer stance. For example, if you’re playing football, and somebody’s zooming at you, you don’t keep your feet close together to avoid getting knocked over. You increase the length of your stance, so that you can brace yourself. So when you’re standing out of the saddle and descending technical stuff, it’s great having that long platform.

On a long sustained climb, assuming you have the legs long enough to handle the long crank, you get tremendous leverage. Like when you’re really up a little bit and do a single oomph over a rock or a root, or a stump, or something, that’s benefited by standing out on the end of a long crank and making that one stroke really make a difference.

Where I think it’s not a great thing is when there’s, with a mountain bike, there’s much more change in cadence. Dropping down into gullies and up and down and in all that sort of stuff, and to be able to spin up and down and in in terms of cadence that’s enhanced with the shorter crank.

It depends on physiology, your style of riding, and the kind of rides that you do. Even though like a downhiller, a lot of the downhil riding is coasting and would benefit from this longer stance, on the other hand, there’s all this spinning up and spinning down. And so, on balance, I think a downhiller is going to be better off with a shorter crank.

Jeff 25:12
Okay. Yeah, that makes sense. How tall is the tallest rider you’ve you’ve built a bike for?

Seven foot two.

Jeff 25:12
Wow. Was that particularly difficult? Are you able to kind of scale up what you do for riders of others heights?

Lennard 25:27
Well, yeah, it’s particularly difficult. To make that bike not shimmy, you got to use enormously large diameter tubes. You know, when I started this business, even mountain bikes had level top tubes. The tubes were a lot longer for a given height of handlebar. If you have a level top tube, your seat tube is a lot longer, stand over height is high. And you know, BMX bikes were the only bikes with a sloping top tube back then.

And then fortunately, mountain bikes really pushed a lot of things that that benefited everybody and that are benefiting everybody in all types of bikes now whether it’s road, gravel, cyclocross, track, everything. Those are getting away from lugs because people wanted the sloping top tube and wanted all these different angles that didn’t exist in lugs. Then you can go to welded construction or fillet braze construction, like we were doing at Tom Ritchey’s. That allows you to use different tube shapes, different tube diameters, any angle you want, all that sort of thing.

So those are things, all of which I took advantage of. We were the first ones to use one and 1/8 inch diameter steering tube on a road bike because that bikes, and it made sense for tall riders that we knew we wanted to have a bigger head tube so that we got a bigger top tube that wouldn’t twist and be so flimsy. Shortening the seat tube, and sloping the top tube meant that for the same effective horizontal top tube, the actual tube was shorter. Until it gets to become a perpendicular bisector, that the shortest distance between those lines, you know, between those points is reduced by dropping that top tube.

The stiffness of anything and stiffness of a tube or anything goes as the cube of its length. So if you can decrease the length of the tube, but have the same effective fit, then you’ve made a huge difference in the stiffness. And so then we are incorporating more of the height of the seat height in the crank length which means that we can shorten the seat tube from the bottom to and raise the bottom bracket higher, which shortens the tube as well and shortens the chainstays a little bit too.

And so every tube we’re able to make shorter, other than the head tube. And then we make the seat tube as big as we can. So mountain bikes push the limits with the diameters of the seat posts, and we could get posts that were stiff enough, even though there was a lot more of it sticking out of the bike.

But the limitation, you know, and back in the day, we were making the forks too, so it wasn’t really all the bike. But then then once everybody wanted a carbon fork, then you’re limited by the length of this. And with a mountain bike it’s a suspension fork, then you’re limited by the by the length of the steering tube that the manufacturer provides, which on mountain bikes is getting shorter and shorter and shorter. It’s getting hard to deal with that problem for really tall bikes because you know, Fox just this past year again, just shortened all the tubes so much and it’s like it’s very frustrating.

Jeff 29:01
Why is that? I mean, that’s something that people are going to cut anyway. So it seems like they could just make it as long as they want or do you actually have to adjust where the taper portion of it is?

Lennard 29:11
Oh it’s entirely to save money. Less material and you’re smaller everything you know your warehouse space is greater because the boxes aren’t as big and all that

Jeff 29:28
That seems like not a big advantage. You’re saving a few pennies but making it tough on the tall riders.

Lennard 29:34
Early suspension forks actually had pinch bolts that helped pinch the crown onto the steering tube. Anything like that is long since gone, you know they’re gonna they’re gonna make these assemblies of the of the fork crown and steering tube in massive quantities. They’re not going to say oh, we’ll make a couple thousand of them with a longer steerer. That’s just not gonna happen.

With carbon forks, finally, after three years of development, we just come up with our own fork, which,we went way beyond the ISO standards. You know, ISO sets these standards for safety. To be able to sell a fork, you have to show that it that it withstands a certain number of cycles at a certain load level. And different things at the brake; with a disc brake, that part of the fork is particularly vulnerable, because it’s trying to, you know, break the bottom of the left leg off, basically. There’s all these things required by ISO.

But since we’re making bikes for really huge people, and the ones that we want to have these, you know, we have a 500 millimeter long steering tube on that, on that fork, well, 300 millimeters is standard now, maybe 350mm. Now with gravel bikes, that’s become so. But we know that not only are people buying our bikes but also people that are likely to buy those aftermarket are going to be taller and heavier and using it on a stock size bike. [In that case] they’re going to be stacking up a bunch of spacers, too. So a lot of that steering is unsupported above the top headset cup. All those things keep me awake at night.

So we took the ISO standards and went 50% higher to handle all these things. You’ll see it’s just a lot bigger blades than you see on anybody else’s carbon fork and the wall thickness of the steering tube is greater, since we don’t get to change that diameter that’s fixed by the headsets and everything.

Jeff 32:03
You mentioned that taller riders tend to be heavier. And so you also designed bikes for big riders. Is that kind of the same approach and the same thing that you’re looking at in terms of like, the strength of the frame and those sorts of things for heavier riders?

Lennard 32:23
Yes. And we have been through the wringer with this over the four years. We have a few six foot eight, 350 pound customers who even though 350 pounds, they can put an enormous number of miles on their bikes and go up in the mountains. You know some may drop for a while over the summer to 320 or something, but it’s not like they’re dropping pounds. There are just big man, and incredibly strong. And all these things I wouldn’t think would happen, but the torque is extremely high in a really low gear.

People are probably familiar with mountain bikers breaking chains and things like that, and here, but when you go to, you know, a really small front chainring and larger cog, and you stomp on that, the torque at the rear wheel is tremendous. Well, if you’re 350 pounds, and you can put out 2,000 watts of power, well, you’re gonna find that these guys will rip the spokes right out of the hub flange, or yank the spoke nipples right out of the rims, or they just break the freehub body so that the freewheel just spins straight forward. All the kinds of things that you hear about happening with people on tandems… people on a tandem weigh about the same as one of these guys, you know, and their power is probably similar.

And so the braking issues, all those sorts of things. We have a customer who is six foot and a 350 pound customer, and would go on six week long tours in the Pyrennes and in the Alps and stuff. And when disc brakes came out, he thought that was great because he was no longer exploding the tires because his rims would get hot from the brakes, you know? He was on the original Shimano road disc brakes. He was going through pads every single day. Things have improved, things have gotten better but the kind of stuff that these guys deal with, most people don’t have any idea about.

We say with our cyldesdale bikes that these will take riders up to 450 pounds, we really mean it. We select all the components and we know the frame is going to take it and we know the fork is gonna take it, but we also put parts on there, the seat posts and the stems and the handlebars and, and the hubs and the rims and the spokes and everything. We’ve thought about in terms of what’s going to happen.

We have anecdotally heard about guys who are trying to, you know, live a healthier life, they get into their 40s and 50s. And they discovered that they’re 500 pounds, you know, and they realize there’s no such thing as an 80 year old that’s 500 pounds. If you want to live on, you got to do something about it. And so they’ll be too embarrassed to be seen on the scene out riding, bulk hanging off the bike. So they go two AM. So a guy riding at 2am, who breaks a bunch of crap on his bike, he’s not going to be a biker very long if he’s got to call us, right at 2am to rescue him. And so that’s the customers that we’re thinking of that we we want to make sure that these things hold up to them.

Jeff 36:34
Yeah, and I imagine a lot of this is applicable to like, more aggressive bikes, like mountain bikes in particular. And downhill, like you’re kind of mentioning, I mean, those bikes need to be very strong, very reliable. And it seems like a lot of that there’s a lot of crossover between the two.

Lennard 36:55
There is. We’ve we’ve certainly benefited from the existence of those extreme uses of the bike. Downhill, you know, has created the development of, of wider hubs, for instance, that can support the destruction better and stronger freehub bodies and, spoke technology. The spokes that you see on a lot of wheelchairs always had these really, really thick 12-gauge spokes. And that was sort of the assumption you made was that a really, really strong wheel, you’re gonna get a really, really fat spoke.

Well, if you look at downhillers’ wheels, they’re not like that; they’re double butted spokes. And the reason is that you want, if the spoke is too stiff, it puts much more strain on the rim. Because as you put a tremendous load on that wheel, and as it rolls along, it gets slightly D-shaped at the bottom. Well, if this isn’t able to sort of stretch a little bit and move with that, then it loses contact, the spoke nipple loses contact with the rim for that instant and gets flattened out. And then when it comes past that, past the bottom dead center, it springs back, and it goes Whap against that spoke nipple. And then that constant boop boop boop boop which fatigues a rim really fast and ends up on the drive side spoke nipples.

Whereas a double butted spoke, you think well, they make that for lightness. Well, they make that actually for longevity. For the wheel to then stretch and move with the wheel, you get a longer lasting wheel.

All these things that we see happening in downhill helps us. And you know when the fork steerers get ridiculously short, our only alternative for really tall people to see is a super long travel fork, because we can’t get along enough steerer tube. So thank God those exists, you know?

Jeff 39:17
Given your background and knowledge of physics, it’s clear, the way you describe these things, that you’re looking at it from that physics perspective. And one of the topics that I know you’ve written a good bit about is bike tire rolling resistance. And so I’m curious to know, and I think a lot of our listeners too, want to know, what are the kind of the main factors that influence a bike tire’s rolling resistance?

Lennard 39:44
Well, I’d say there’s four things. One is something you can do something about, which is tire pressure. The others are built into the tire: the casing, the tread compound, and the tread design.

Jeff 39:59
And is that sort of the order that it goes in terms of importance?

Lennard 40:05
Yeah, I think so. Yes. Okay. It’d be argued between tread design; if the tread design is really huge, you have really big knobs, compared to another tire, obviously, that’s going to absorb more energy. So right gray area there.

The other thing too is tire diameter. The casing is really critical, because, you know, it’s cheaper to make a tire with much thicker threads and and the cord. The carcass of the tire, you know, it’s listed in TPI, threads per inch. So if you have a low TPI, it means that those threads are fat, because if they’re stacked, right next each other, not very many threads are going to fit in one inch. That means the thread is stiffer, and thicker so it’s going to be stiffer. So as that casing encounters a bump, if the threads can’t move properly with the casing, the casing is stiffer, which means that it will force the entire bike and rider up. It it were a more supple one with much thinner threads in the casing, it will be able to absorb — assuming the same tire pressure — more of that bump, and it will lift the rider less. Obviously the more you lift the bike and ride it, that was energy — except when you’re going downhill — when you’re going uphill or flat, that energy came out of the rider’s legs.

And the more that you send the bike up and down, the more energy loss it takes to get the bike up to that speed. And back when I was racing, a national team, you know, we believe that, you know, the bike just felt really lively. When you pumped the tires to like 135 you had these really skinny 19 millimeter tires, 135 pounds, and it felt like it was really fast because it was really bouncy, but it was the opposite. Because it was bouncing along the road, you know, and that energy that could have been absorbed in the tire if you’d had a bigger tire at lower pressure, even with racing construction and everything you could have gone much faster. And you know, it’s a shame that I didn’t realize that.

Jeff 42:49
Right. It’s kind of counterintuitive. And it’s also it’s interesting, because I think for a lot of us, we tend to focus on the tread pattern and just, you know, we think we can look at a tire and have an idea of like, whether it’s going to roll fast or not. But it sounds like there are a lot of factors involved and some of them, maybe are even more important than the tread pattern itself.

Lennard 43:14
So basically your thread per inch, but you kind of got to look at the casing, you know, just get a sense of looking at casings and looking at, oh, those are really fine threads because some manufacturers, you know, a tire is made standard clincher tire, the casing starts basically on one side and wraps around the bead and over the side of the tire around the bead up over the top of the tire around the bead on the other back across the center. So that means a crooked, you got three layers of casing and on the sides, you got two layers of casing.

So threads per inch is supposed to be the number of threads per inch in one layer of that casing, but some tire manufacturers, because they know that people don’t buy their tires, because if they know that the threads per inch, they’ll say oh, well they’ll multiply by three because they’ll say well under the tread, it’s seven times three or whatever that is, you know, 200. And so you go like wow, that’s a 200 TPI tire. Well, it’s not apples to apples comparison. So you need to get a sense for looking at the casing and seeing, and you can feel it too. You go into a store and you feel a cheap tire and you just feel the casing feels like compared to a really expensive one for the same application.

Say it’s cross country. It’s a little different to tell where you’re trying to have more toughness of the tire but you know, a really fine, fast cross country tire can have a really supple casing. Generally the casing will be thinner because of the thinner threads as well, which means that it will also be lighter, which that’s another benefit.

The tread compound is something that you cannot look at, you cannot tell how fast the tire is. In general, what I will say is that, you know, as the CAFE standards, which are the mileage standards that the government sets for cars, as the CAFE standards get higher, one of the things that the car manufacturers do is put greater pressure on the tire manufacturers to make faster rolling tires to save them from having to do as much engineering of the engine and whatever it takes to get that. That’s why the really, the tire brands that are known to have really fast tread compounds, often, they’re German guys doing it, who started it, because Continental is one of the only brands in the bike business that is a car tire brand as well. A premium car tire brand that’s been under pressure from the car manufacturers to get lower rolling resistance. So then they have all these engineers who’ve really worked on these tread compounds.

The experimental thing is called hysteresis. It’s basically, you know, if you have a super ball and you drop it, the thing that makes it a super ball is that it’ll bounce almost as high you dropped it. That means it’s got very low hysteresis. So as it goes through a cycle of elasticity of being deformed and then returning to its original shape, very little energy is lost. Most rubber balls are not super balls. That’s why super balls are super.

Jeff 47:09
Yeah, that’s why they’re super.

Lennard 47:11
The same thing goes with a tread compound that as the tread gets deformed by the road, how much energy is lost in heating that compound versus, you know, before it returns to its original shape. If you took a super ball compound and put it on a tire, there’d be very little hysteresis loss. On the other hand, it would probably be really poor traction too, because it’d be too bouncy. So there’s this balancing act you have to go through, and what always is done with tires, bike tires is they, you know, sort of took available rubbers, and that’s just the deal. You picked a softer rubber if you wanted better traction, while the softer rubber is going to be slower rolling, because you got more hysteresis loss.

So then, it wasn’t until you know, all these smart guys started figuring out all these different compounding things they could do, where you could get a little bit of both, you could have it soften, still have lower hysteresis loss. And so Continental, then Schwabe, Specialized, you know, take engineers at Continental and they develop, you know, the Specialized Gripton tread. And, you know, those were the guys that worked on the Continental Black Chili tread compound. And then, and then you’ve got the one that Schwabe, which I can’t remember what that compound is called.

Those are generally, in my testing for my articles for Velo News, I’ve done a lot of rolling resistance testing sending to the best independent rolling resistance testing lab in the world, which is Wheel Energy in Nastola, Finland. Those compounds, if you’re able to make all the other variables the same, compounds will rise to the top that Continental Black Chili, Specialized Gripton, and the Schwalbe, whatever it’s called. Then the next thing is tread design, which, if you want the fastest rolling tire, then you’re going to make it slick, but but that’s not going to give you much traction. So you have this trade off. The more tread you’ve got on it, individual knobs are going to flex and the more energy is going to be absorbed. The lower the slower the tire will roll, the more rolling resistance.

Jeff 49:54
So finally, I want to ask you about your latest book, The Haywire Heart which examines heart conditions in athletes. What led you to write about this subject?

Lennard 50:05
Well, I developed a heart arrhythmia. I tended to race year round — I raced cyclocross in the fall and winter, I raced early winter, and then I raced, cross country ski racing, doing these ski marathons all over the world out into March. And then I’d be doing training for cyclocross, I’d be doing a little number of hill climbs and road races, some mountain bike races. And I was under the impression that I think a lot of masters endurance athletes are that if you’re 55, and you’re beaten all the 35 year olds, you are somehow immune from your body falling apart in ways that you didn’t expect.

And, you know, just like, even though you’re 55, and you’re super fit, you grab your skin on your hand, and it’s super thin, and compared to a baby, or then even a 20 year old. That kind of process is happening all over your body, that you’re losing the the elasticity of your tissues all over your body.

And with your heart, you know, if you’re a 20 year old, and you ask for this tremendous amount of blood volume from your heart in order, because you’re going to, you know, do all sorts of endurance training and racing, or you’re going to climb Mount Everest, without oxygen, or whatever you’re going to do, your heart will get bigger in response to that. And the things that we all know about where your resting heart rate goes down, because you’re pushing out so much blood with each pump, that you’re at a lower heart rate, and all these things that we associated with being better fitness and all that, right.

If you’re 20, and you then de-train yourself and go, you stopped doing those things, your heart will return to its original shape. If you’re in your 50s, 60s, and you’re asking for that similar kind of blood volume, in answering that demand to get bigger, your heart being less flexible, there will be micro tearing, that’s going to be happening in the, in the heart. And then as that heals, there will be scarring in the heart, you’ll have little scars in there.

The way that the electrical impulse moves through the heart to cause the contraction, it moves like a smooth wave across it. If you have water moving smoothly across sand, like flowing smoothly across sand, and then you throw a rock in it, it will suddenly get eddy currents around that rock. And that’s the same thing that happens with this scarring that’s happening in your heart that the electrical current can’t just move through smoothly, there’ll be there’ll be eddy currents formed around these things. And that’s the substrate for arrhythmia, and some of these arrhythmias can be very, very dangerous.

There type of cardio that killed Phidippides when he came and ran to bring the news of the Battle of Marathon. We know the word marathon because Phidippides died running 26.2 miles to bring the news of that, and we know him as having been, well, he just didn’t know how to pace himself.

Well, he was a full 43 year old full time running messenger. That’s what he did, ran. He was the quintessential masters endurance athlete, and he died from V-tach. Most arrhythmias are more mellow atrial fibrillation; you’re not going to die from it but it’s going to cause you other problems. You can know you can get a stroke from it and things like that.

When I developed arrhythmia, I looked around and realized some of the guys that I’ve been racing with, particularly cross country ski racing, who just disappeared and there was this rumor about them, they had been super, super fast. And all of a sudden, they were just gone. I was like, how could they stop? And there had been these rumors about something with their heart and I followed up with them, like what happened with you? There was no data in this country. That’s why I wrote the book because because any data, American data at the time, about a arrhythmias was all on cardiac patients. These are people that have the risk factors, you know, smoking, diabetes, overweight, lack of exercise, all those sorts of things.

But in Scandinavia, there were studies done of over 50,000 people, people doing these two ski races. I used to do one in Sweden, a 90k, called the Vasa lopud, another 60k called the Birkebeiner in Norway, and those studies showed that competitors had 30% higher incidence of atrial fibrillation than the rest of the Scandinavian population.

Secondly, the faster they were, the higher the rate of atrial fibrillation. And thirdly, the more times they done the race, the higher the rate of atrial fibrillation. These races, 16,000 people do them each year. So you could follow a lot of people. And so that was very eye opening for me. And that’s what got me to write that book, because I was like, people need to know this.

You know, people who are overweight and couch potatoes are shunned by our society. You know, they don’t get acknowledged when they go to go to parties for Wow, that’s so awesome. But the person in their 50s and 60s, they’re winning bike races. They’re like, Wow, that’s amazing. But the risk factor is similar.

In the U-shaped curve of activity level versus versus morbidity, you know, you have very high morbidity at very low activity levels, but then as you increase your activity level as well. It comes down to the trough where your lowest morbidity tends to be, you know, people may be walking an hour a day, not people doing, you know, extreme exercise. For them it starts going back up again and never reaches maybe as high as the other side but you get similar morbidity from continuing beyond the throttle your whole life.

Jeff 57:18
So in writing the book and doing research did that cause you to change your habits or your fitness routine or anything?

Lennard 57:27
It sure did because my arrhythmia has something called multifocal atrial tachycardia, which feels like a fish flopping around in my chest when I go into the arrhythmia. But I have AFib which AFib is where it’s uncontrolled. The upper upper chambers of the heart allows clots to happen on the top of the surface of the blood, and then those can be sent to your brain and get a stroke and so the way that that’s combated is by they give you anticoagulants, blood thinners, to prevent that from happening. Well, you can’t be a mountain biker and be on blood thinners. Because you hit your head, you can have a closed bleed inside your head that won’t stop and you’ll die from that. You could bang your hip really hard and you end up with a bruise that won’t end you know, and so yeah, so I don’t want any of those things.

I certainly no longer race at anything. I do cross country skiing you know, I no longer ski skate at altitude I just classic ski or now most of the time is backcountry ski and not with 30 year olds. I go with people my age and rather than always being the first one at the top like I used to be I’m always the last one.

And, and as far as bike riding, you know, I still want to go on these great rides in the mountains. But if I do it on a regular bike, I get in a rhythm. So I ride and eat. And that tremendous boon for my business too, because I started building e-bikes five years ago in order to make one for myself, and had a huge head start on everybody. Because we’ve been doing it for a while we understand it. We know how to make e-bikes, we were, you know, we just know all about it. And now it’s become a big thing in this country. It’s been in Europe a long time, but it’s starting to be big in this country.

And and you know, there are the user conflicts that are happening with trail access and stuff and mountain biking that we’ll be dealing with for some time to go. But it’s opened up this whole thing to me and and all these climbs that I used to do a thousand times that I’ve done some of these climbs around here. And now I noticed things that I never noticed before, like ‘look at the grain in that granite on this road cut.’ I mean, it’s really quality of life, and I’m doing the things I want to do. They’re just different. And I think I’m gonna last longer because I’ve made those changes

Jeff 1:00:37
Yeah that’s awesome. Well, Lennard, thanks so much for taking the time to chat with us. You’re a wealth of knowledge on a number of topics

You can find out more about Zinn Cycles on the website zinncycles.com

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