I am about to go from 175 to 170 cranks on my Scott Spark. I am 180cm with 82cm inseam and spark is medium.
What is yout exp with going shorter with the cranks?
170mm cranks… if you know, you know. First, it was the way people looked at me. It made me feel a bit self conscious at first, but gradually I started to enjoy it. Initially I thought I had done my hair differently as it was mainly women who were looking at me, then I knew it was some deeper as men started to do it too too. Children looked at me wonderingly like I was a ray of light through a forest canopy, and dogs queued up in front of me expecting to be petted.
Next, it was my riding. I expected something to change but it was like I had discovered another gear - I even wondered if I had inadvertently taken some gear as I danced up climbs barely feeling the chain. FTP gradually began to dissipate as a concept and I was able to estimate speed, power and time elapsed using new sensory powers rather than my Garmin.
Finally, and I’ll be careful what I say here with it being a decent forum, but let’s just say things with my wife and I have never been better. She’s insatiable and I’m having to work so hard I’m using 120g of carbs per hour in the bedroom.
But really, I prefer 170mm cranks, it won’t be a panacea to whatever issue you’re looking to fix. I still clip rocks but I don’t feel like I have to over torque in the same way I did with 175mm. If you’re committed to going to shorter cranks, try to find a way to try 165mm before committing to buying, you might even prefer them and you’ll probably feel the 10mm difference more than 5mm, which everything considered equally is quite a small change.
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I went from 175 to 165. I’m 188cm, 92cm inseam and I can confirm what @swgregg claimed above. It even grew the 1cm I took off my cranks. Makes all the difference wearing thight bibs
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Haha
so throwing 500+ euros seems like a god bang for the buck
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I went from 175 to 170 on my MTB and couldn’t notice anything different. I did so for less pedal strikes and it was a big improvement.
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so nothing in the stroke? No powert improvement, no fatigue reduction?
Not that I noticed. Maybe if I had done some back to back test runs comparing the two there’d be something small, but nothing I concerned myself with. The goal was to avoid pedal strikes, so that’s what focused on.
I changed to 170 on mtb and 165 on roads bike a few years ago and didn’t notice anything different.
On the road you can get a bit lower on the drops but on the mtb I didn’t notice anything
I have 175 on my xc bike and 170 on my enduro bike - 190cm with 86cm inseam. the 170 cranks drive me nuts. I don’t understand the hype of smaller cranks and probably never will. It’s okay, in 5 years we’ll be back to long cranks 
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I am a big fan of shorter cranks. I never felt I could get a smooth spin with 175 on my mountain bike and switched to 170 which feel much better. I had 172.5 on my gravel bike and also switched that to 170 so everything is the same. I have even thought about going 165. My inseam is 82cm and 183cm tall.
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It does depend on your style a bit. My feeling is if your a bit of a grinder, longer can be better, or atleast fine. I really like my 180mm xtr race cranks, unfortunately they don’t fit great on most bikes. 175 is fine, but I don’t notice a huge difference. I do notice when I step down to 170s on the enduro though, not too much worse for me, but 175 is better for me. 6’4” with 34” inseam.
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I went from 175 to 165 on my road bike. I’m a little over 185cm tall. At first it felt maybe slightly more difficult to push at the same cadence, but that feeling went away after about 5 rides. I run a 1x setup with a large chainring and have still been able to climb in the mountains. I don’t plan on changing back. Pedal strikes in crits have gone to a constant danger to basically no need to even think about it. If anyone wants some 175mm SRAM Red D1 cranks let me know!
I’d love to change to 165 on my MTB, I just can’t really find them easily I guess.
I changed from 172,5 to 170 mm on the gravel/road bike and from 175 to 170 on the mountain bike before the 24 season. Noticed less hip issues on the gravel bike with better position and more comfort riding in the drops. On the MTB the differences in actual pedaling is less notable, but the improvement in ground clearance and hip comfort is. Still ride 175 cranks on the trainer with noticable hip and leg issues and more difficulty finding the perfect fit on the bike. Power not comparable to outside riding, but that’s more of an trainer/outside-issue than crank length.
This has been covered ad nauseum.
Everyone agrees that shorter is better. Except for a tiny rare few who don’t agree. I’m one of those few.
I did a blind experiment. I prefer longer cranks. Here was my test:
My trail bike came with 165’s. I destroyed the cranks in a wreck, and asked my friend at the LBS to order me some more. He accidentally ordered and installed 175’s. I thought the pedal strikes were from lazy riding technique, but felt better overall. I adjusted my riding, and all was good. Several months later I ended up noticing the 175 written in the cranks, and figured it out.
My first gravel bike came with 165’s. I could never get comfortable on that bike, always had knee discomfort. Every bike I’ve had since then has had 170-175 and I am fine.
I’m 5’7" (171cm in the civilized world), as a reference.
I am in the camp of those who had 175 on the XC bike and 170 on the eduro bike. I hated the 170s. I put 175s on the enduro bike and all was good… Then I started trying the 170s on the xc bike and hated it. Then I did Breck Epic and the torque killed me. So, desperate for a quick solution, I tried the 170s again on the xc rig and hated it. Upon great reflection, I realized my riding style on the MTB relied on the instant torque that is easier to get from the 175s.
It is important to note that I have 165s on my road/grave bikes and love it. I am 190cm tall.
So I waited until the off season, bought a new mtb and asked the shop to spec it with 170s. The bike was new, I wasn’t worried about results, etc. and bamb, after 2 weeks everything clicked.
Long story short, It took me three attempts to switch from 175s to 170s before I loved it.
MTB, you need to consider both pedaling efficiency and rock/root strike clearance - with rock strike clearance likely being far more important. I moved from 175mm to 170mm and it was no big deal because my MTB fit was so different than my road fit. I was having issues with my shoe barely clipping hidden stuff and causing crashes.
Keep in mind that they likely just move the drilling on a 170 - 175 arm rather than the whole metal casting being different. When you get into the 160s you might get a different length arm.
I’d say a set of used crankarms are cheap and only take 10mins to swap out if you have all the tools.