Advice on Crank Length and Bike Size on a Build

I’m getting ready to ask to add 1 to N (where N is the number of bikes we own). I’m looking at picking up a frame via EBay an older model but unused Tarmac (from a trusted source “my” bike shop confirms is good) frame. I buy components as I find them on deals, specials, or used. My current road bike went through a similar process.

My CX bike is a specialized at 58 cm and the frame I’m looking at is 60 cm. I’m 6’2" (188 cm) in height. Looking at the Specialized charts I see I should be okay on either the 58 (confirmed) or the 60 frame. IIRC, my current road is a 60 cm Trek Madone 5.9 and is fine.

So, is it too much thought to worry about the varying size frame, does that present an issue for fitting, or do we just take it one bike at a time and it fits as it fits?

Second question, both my CX and current road bike have 175 mm cranks. Given what we have been hearing on the Podcast of late and the overall trend, is it best for me to keep things standard at 175 on the cranks or would moving to 170 on the build be okay? Again, I wonder if the feel would throw me for a loop as I switch from bike to bike.

I plan to keep the current road bike and use it for training – both in and out. The new bike would be more for racing or more spirited group riding.


Are you wanting to go with 170s because its what you have laying around or are you curious about shorter cranks?

FWIW Im 5’7 on smaller frame bikes that came with 170s. I switched this year to 165s on both of my roadbikes to improve fit. As I got in the drops with the 170s my knees came too high and it was hard to get over the top on the pedal stroke. I had to raise the seat to compensate which means your front will be even lower relative to your saddle. I also use a larger rear cassette to compensate for the loss of leverage on the shorter cranks. I have 175s on my mountain bike and getting on it after a break, you most definitely feel the difference. Lot more torque available. ie acceleration. On a MTB that ability to turn the crank and generate speed is a good thing as often times there is not a lot of time to accelerate between corners or trail features. Im guessing that is the same benefit put forward by crit racers favoring long cranks as they are better for acceleration. Bottom line. If you are doing it to improve bike fit, go for it. I didnt see higher cadences ect. Going from 170s to 165s on the road wasnt very noticeable as far as the pedaling goes but I do feel it going from 165 road to 175 MTB.

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Which Tarmac model? There isn’t a 60, only a 61…

That being said, you should likely be fine on the larger size and should be able to make it fit unless you have weird proportions for your size

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As far as crank length goes, GENERALLY speaking it comes to a fit issue.

All the studies that I have seen basically shows a trivial to not statistically significant difference in power due to crank length change in of itself.

That said, if changing the crank length allows you to get better rotation of the pelvis for a more powerful position, or gets your quads out of your chest, allowing you to breathe better, then they may prove useful.

If you have a very low aggressive position and find your legs and torso trying to take up the same space, then going short could well be worth the change. I find this to be MUCH more common on either time trial bikes, or guys using their road bike almost like a time trial bike ( eg breakaway specialists etc. )

If this isn’t an issue, then you might not even notice a difference.

TL;DR, going shorter might help, might make no difference, but I can’t see it being harmful.

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DOH! Why I had 60 in my head, IDK, but now that I look at it again it is plain as day. No matter. Thanks! Its an SL5 from 2016, which is about 11 years newer than the frame on my current ride.

No, this is a greenfield build – I have some spare parts laying about but none of them are suitable for this project. Looking for advice.

On my first build I went for the longer 175 cranks – using the extra length to gain mechanical advantage. However, I know people tell me it is better to have a smaller crank to get to higher cadence more quickly. Then there is the fit issue, I’ll have to pay close attention on the trainer to see how low I can go before I start bring my quads into my torso. I do have some spacers on the bars – spacers I’ve been thinking of removing (at least 1 and then see how that goes), but I still can lower myself and see if that is reasonable.

Since this bike would be a road bike and most of the racing here is CRIT style that argument you make about having a bit longer lever arms makes sense until you think about pedal strikes – which I have done once (just enough to make noise but not enough to crash me – plus I was actually “time trialing” at the time).

Hmmmm, probably putting more thought into this than it is worthfor a masters FAT 5 racer!