Thoughts on 27.5+ on front and 29er on rear

[triton189]

Looking for peoples thoughts and advice on whether a 27.5+ rim and tire on the front and a 29er on the back of a 29 bike is a positive idea or not.  I am an older rider of average ability looking for stability on terrain but like the idea of less rolling resistance on the back.  Anybody tried this yet?  Thanks

[Jeff Barber]

I haven’t tried this but now I’m going to do it! I’ll let you know how it goes…

[triton189]

Thanks Jeff!

[jaron7]

following

[Jeff Barber]

Aaron pointed out that the head tube angle will be effectively increased which is a negative in terms of descending. But hey, maybe it’ll climb even better!

The bottom bracket will be lowered compared to a bike running 29er wheels front and back but fortunately for me, I’m converting UP from 27.5+ wheels front and back. So my bottom bracket should be slightly raised which is good–I definitely notice the lower BB on my conversion.

Stay tuned…

[Jeff Barber]

Ok, I did this a while ago but forgot to post back. Thanks Rick for reminding me. 🙂

Let me start by saying my experience is specific to this particular tire/wheel/bike configuration and won’t apply to every situation. For reference, I tested this out on my Santa Cruz Tallboy (100mm f/r) with WTB Scraper rims (45mm) and WTB Trailblazer tires (2.8″).

On paper, placing a plus tire up front makes a lot of sense because the front is where you want good traction for handling. However, the Trailblazer tires, especially on wide, 45mm rims, cut a squarish profile, rendering the cornering knobs all but ineffective. As a result, I found handling was sketchy at best, and dangerous at worst. But that’s not really different from running Trailblazers front and rear (which I did for the better part of a year.)

The real problem was the head tube angle, which I mentioned in my last post. Running the smaller diameter plus tire up front slackened steepened the front end, meaning the bike didn’t climb descend as well as before. Add the extra rolling resistance of a plus tire up front, and I found it wasn’t a good combo.

Now, here’s the really interesting part. I broke my rear 29er wheel just before a ride several weeks back, and in a pinch, I threw the 27.5+ wheel on the back, keeping a 29er wheel up front. This turned out to be one of my best rides on that bike in a long time, and I’m still rocking the mullet configuration! The smaller wheel in the back makes the head angle a bit steeper more slack, cornering is great, and I still get most of the stability of a plus setup. I’m even finding it works well for wheelie practice.

 

[Alvin Mullen]

No, not a good idea. It makes the bike more prone to flipping forward.    27.5 rear 29 front can work well, and several companies actually do that.   One that gets great reviews is the Foes Racing Mixer.

[Jeff Barber]

Alvin, the Foes Mixer uses a traditional 27.5 wheel in the back, not a 27.5+ like triton asked about. With a 27.5+ tire, the diameters are a bit more closely matched.

Here’s a photo I snapped last night of my current configuration with the plus wheel in back, and a regular 29er wheel up front. Not sure if it’s the slope or what, but the rear wheel actually looks bigger than the front!

[Alvin Mullen]

I’m sorry, I did not catch the +.  I would say if they are very close to the same overall diameter or if the rear+ is taller it would be fine.

[microwaveric]

Jeff, I couldn’t help but chime in that a smaller diameter wheel (27.5+) in the front will effectively steepen your head angle, the same way a shorter travel fork would. To account for this, bikes like the Pivot Switchblade have some sort of way to adjust/maintain the geometry (like head tube angle and bottom bracket height). The Pivot includes a 17mm taller lower headset cup (roughly the size difference between 27.5+ and 29 wheels) to keep the geometries consistent when using 27.5+ wheels.

Conversely, the smaller 27.5+ wheel in the back will slacken the head angle.

Granted, a 17mm lower/higher front end will equal less than 1 degree in head tube angle, which may or may not be noticeable to all riders, especially with the traction and other changes in ride characteristics that come along with a 27.5+ tire.

[Greg Heil ✓ supporter]

The smaller wheel in the back makes the head angle a bit steeper (I dig climbing),

Conversely, the smaller 27.5+ wheel in the back will slacken the head angle.

I was just going to say this myself, but you beat me to it 😉

[Jeff Barber]

My bad. I had actually edited my June 10 post earlier this week, because for some reason I thought it sounded backward. Apparently I should have left it alone. 🙂

Ok, so just to make sure I have this straight:

•  27.5+ front, 29er rear: increased HTA
• 29er front, 27.5+ rear: decreased HTA

 

[Robash]

Jeff, how did this experiment turn out with the 27.5 plus on the back and 29 up front? I’m thinking about doing this on a santa Cruz chameleon for a bit more comfort in the rear.

[Jeff Barber]

Still running the 27.5+ on the rear, 29er up front. It feels good, and make wheelies easier. 🙂

[mongwolf]

I can’t imagine why one would want a smaller tire on front for mountain biking.  I think John has some valuable experience and knowledge related to the doing just the opposite.  He has ridden the Foe for a while now, I believe.  Triton, can you explain conceptually what benefits you are looking for with a smaller diameter on front?  It sounds scary to me =) at least on the trails I ride.

[azdb]

Mongwolf, howz it going……Big D here…haha…..I was googling 27.5+ rear and 29er front and this popped up…wow…..I have a hard tail 27+/29 either or, norco torrent, and the bearings are going out on  the 275+ wheel in front, so I threw on my 29er wheel, have yet to ride, will try it out….29er 2.4 tire front, 275+ 2.8 in back……….while I am here,  found really cool bikepacking video, 25 min or so………….they start in Ulanbaater, and spend a month biking, here you go………………https://vimeo.com/152236240 hope all is well in outer mong….

D.

 

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