jonathanf2

Just a little background: I originally had 170mm cranks on my gravel bike, but then I swapped them out to 165mm crank arms and they ride perfect for me. On the flats I feel like there's decent torque for me to accelerate and when hill climbing I can spin at high cadence far easier. So I decided to try the same with my road bike, but went from 170mm to 160mm thinking I'd have similar handling characteristics and the 160mm option wasn't available on my gravel crankset. I noticed a few pros and cons starting with the cons first. When in the saddle while hill climbing, I notice a lack of torque and my lowest gear feels more like one gear up. It felt significantly harder to do the same climb I did with ease with my 170mm crank arms. Regarding the pros, when out of the saddle though I feel like I can sustain a faster and harder climb especially when sprinting up. It spins with better efficiency from what I could feel. I think with the 170mm crank arms out of the saddle, it was much harder.

I'm now undecided on what to do? Should I try adjusting my saddle position and seat post height on my bike to slightly change my hip positioning and leg extension? Is this something that might need a break-in period where I would eventually adjust? I could go back to my 170mm crankset, but the 160mm crankset also shifts smoother (went from an FSA Gossamer to a Shimano 105 R7000), so there's that. BTW - I'm running an 11-32t rear and 50:34t front. - OR - Is this just another step on my cycling journey to help me get stronger and I should just stick it out with the 160mm cranks until it feels easier?

Thanks for any advice!

shelbyfv

For the cost of a crank you might be close to a session with a fitter who has the ability to measure power. Otherwise you are just subjectively fooling around. Not surprised the Shimano crank works better than the FSA.

Iride01 

When you change your crank length you have to change your saddle height. Unless if was wrong before and just happens to now be correct.

Yes you do loose torque on the crankshaft with shorter cranks. That's why you have to ensure you have the proper gearing to make up for that loss and if you can't spin that lower ratio faster, then you'll be slower climbing the hill. So several things that you might need to correct. One, just get use to the new torque and cadence you'll have to use to be equal to before. And do you have a gear ratio that lets you spin fast as you go up the hills in question?

I'm not claiming you have to climb at 80 plus RPM. But you should have that option available for times it's needed.

I use 165 cranks on my road bike with a 36/52 front and 11-30 rear. 34.5" inseam. I go up most hills at the same cadences I use for flatter parts, unless I'm really trying to best a personal KOM. Then I might be a slower cadence or even a faster cadence. It just depends.

ThermionicScott 

If you went from 170mm cranks to 160mm and didn't raise your saddle by about 10mm, then it's probably the wrong height now! I'm not surprised you feel like it's harder to make power now.

jonathanf2

I'm on an 11-32t cassette on my road bike and don't really plan on going bigger since I have a gravel bike with much lower gearing. I'm using the road bike primarily for fitness training and speed. According to my computer data, I was spinning at an average of 75 rpm for a 30-40 minute hill climb and where I felt the difference was on the particular steep sections that were still hard on the 170mm crank. The one thing I really liked is I didn't feel the same muscle fatigue when out of the saddle on the 160mm crank while doing hard sprint climbs. I even felt less winded. So I'm wondering if doing some seat post and saddle adjustments might make up the difference when doing the seated climbing?

jonathanf2

When I got home, I did exactly that. I'll give it another go later today and report back.

Iride01 

If you measure your proper saddle height from the saddle to the pedal when at the bottom of the stroke furthest away from the saddle, then that measurement should be good for any crank length on any road bike you get on.

I do vary my saddle height at various times between 106 - 109% of my inseam measured snug in the crotch to the floor.

My experiences between longer and shorter cranks are much like you wrote:
Even in the saddle, I feel much less fatigued pedaling a high cadence than I do on long cranks. While I can tolerate 170 mm cranks, 172 and longer just make me feel like I'm thrashing about and tire my legs quickly.

ThermionicScott 

Cool, hope that does the trick.

I can tell pretty quickly when a saddle is just a couple mm too low -- it feels harder to make power, and before too long, one or both knees start to hurt from the effort.

Carbonfiberboy 

Practice spinning faster in a lower gear on climbs. Lower gears at the same speed work your lungs harder and your legs less. My guess is that you might best climb at over 80 cadence with the 160 cranks. That takes practice. One can economically do a heckuva lot of deep breathing to keep the legs operational. As long as you're aerobic, there's really no cost to breathing more. Try 95 on the flat. If you have a trainer or rollers, a fun thing is to spin 120 in a very low gear for a long period. Fixes your coordination right up.

jonathanf2

I just took the bike out for a 10 mile spin primarily on all hills. At first the saddle felt a bit high and then I got used to it. It feels much different than the 170mm crank arms when riding. Looking at my bike now, the seat post looks comically tall, but for these cranks the fit is just right.

What's interesting is just how less winded I feel, especially out of the saddle climbing. I did some segments I would normally sit, but standing and climbing, and I still had O2 in the tank by the time I reached the top!

AnthonyG

As well as moving the saddle up with shorter cranks, try moving the saddle a little further back on the rails as well in order to get the most advantage of the shorter cranks.

phtomita

I have a 160mm on my fast road bike and a 165mm on my steel commuter.
When I first move the road bike from 165mm (105 5800 to 105 R700) to 160mm, the feel was that I was slower for a 40 miles ride, specially on the flats - actually some 5 mins - but there are all other factors that comes to the equation.
Two weeks ago, I participated on a 53 miles organized ride with 4k feet elevation and since forecast was a bit of rain, took my commuter one (165mm) that has fenders on it (got rain after the ride when getting out of ferry to the car) and honestly don't feel much difference.
My main goal is to get easy on my knees since I'm a short rider.