Trying 170 Crank Arm Length

[reidsvillebikes]

Since I started back mountain biking this Spring I’ve used 175 Crank Arms, pretty much the standard on Mountain Bikes. I just put on 170’s to see what the difference is. Planning a ride tomorrow so I’ll give you my impressions after. I’m a 30+ year roadie and always rode 170’s, I’m 5’9" and once tried 175’s, it sounds funny but it was too hard to turn the bigger circle.

[Greg Heil ✓ supporter]

Cool, let us know what you think!

[reidsvillebikes]

Here’s what I learned about switching from 175 to 170 cranks. First let me say that I rode a trail that I ride at least once a week and know well. Second I changed nothing else on the bike. For sure I could tell a difference in leverage. When needing to get up a short quick incline it was noticeable. In fact I had to quickly get off twice because I was in the wrong gear to get up this short uphill that I would have gone up with the 175’s. I’m thinking on the remainder of the trail that I could spin the pedals up faster and get to the next gear sooner. After a couple miles I was anticipating the uphills better and shifting sooner. I did ride the trail in my fastest average time to date but let me say that the trail was fast today and it was cold which is when I’m the strongest. I’m gonna raise my saddle about 1/4" to compensate for the shorter cranks and see. I’m leaving the 170’s on for a bit and ride some more of the trails I normally hit. Hope this all helps. I’ll keep you posted. 😃

[reidsvillebikes]

One last bit of info I found on 170 cranks. I raised my saddle to see if it helped with the loss of leverage, it did not help, so my saddle height is back where it’s been. I am faster with the 170’s based on times for routes I ride. Just need to anticipate hills better and change gears.

[herlsy]

In that instance it seems raising your seatpost 5mm would just put your riding position to the original ‘degree of knee’ when the leg is at 6 o’clock. I’m not sure how much of an angle change the 5mm makes, but it will definitely change something.

I bought a crankset that was 170mm just because it was on sale. I thought ‘ahh it’s only 5mm’. I couldn’t tell much difference but i’m wondering if i could tell by going back to 175mm.

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