172.5mm cranks on TT bike or 165mm?

Basically in a bit of a rush - I’m selling off some bike kit and part of it is the missus’ 165mm Inpower crankset.

When I was building my TT bike I saw a really good deal on an Inpower Flow, but it was 172.5mm. Price was too good to resist so I grabbed it. Now I usually ride 170mm on the road bike and know a lot of TT guys say to go even lower on the TT bike than road.

Just hit me as I was talking to the buyer for the 165mm power meter that I could keep it for my TT bike and sell off the Flow which only has a handful of rides on it. Flow looks cooler than the 3D+ style but I’d maybe get more watts out of the better cadence than I would from the aero style.

What do you guys think, I’m sort of time limited on this and not sure which way to go. I’m 5ft 10.5inch by the way if that helps (179cm). 32inch (81cm) inseam roughly.

I’m 189cm and use 170mm cranks on my TT Bike, I find it helps me spin it up faster and reduce muscle fatigue.

Still use 175mm on my road bike and don’t have any trouble switching between the two.

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I’m long-legged 6’4 and use 170s on the tt bike. It might depend on your position but shorter cranks allow you to open the hip angle/get lower on the bike. I don’t see any downside really.

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Definitely depends on a lot of factors, especially hip angle. Most likely though either way the most efficient crank arm length for tt will be shorter than one’s road setup.
I’m have a similar body as Coach Johnathan
I run 175mm on my road bike and 170mm on tt

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I switched to 165mm cranks a few years ago from the 172.5mm which I had beforehand. Obviously it’s completely subjective but I remember feeling that it was more comfortable at the time and that I felt less cramped at the top of the pedal stroke. I still use longer cranks on my road bikes, from memory one is 175mm and one 172.5mm

I don’t even think about it now but if I were changing my crankset again I’d definitely keep to 165mm on the TT bike. I’m 174cm FWIW and I use a Rotor aero chainring.

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Thanks guys, that made my mind up last night. Keeping the 165mm, really looking forward to trying it too. Was never totally happy on the 172.5.

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I don’t think it makes a huge difference but I use 165s on my TT bike, and it does help with position. I like to think I notice in my knees when using my roadie with 172.5s but it may be in my head.

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I use 165 on the fixed TT bike (track cranks) and 172.5 on the road. I don’t really notice the difference (too many other things going on), but reprogramming the crank length on the (P1) pedals each time I switch is a complete PITA!

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I have a 29.5-30" leg. On my TT bike I swapped from 170 to 165 and immediately noticed it was easier to get my leg over the top. I would at least try it before you sell them.

I ride 165 on my winter road bike and 170 on my summer bike - no problem.

The TT bike came with 172.5 and i rode them for a while, but quickly swapped. Did not notice that change so much, but it was a while ago and my position at the time was far worse.

One possible side effect - my cadence has increased this year over last year. I now do TTs at 92 rather than 88. However I have trained on TR over the winter and been cycling on a velodrome, so both of those might have had some effect. In theory you do pedal slightly faster for the same power (Force x speed I think) but the difference between 165 and 170 as a percentage is small. The height difference at the top of the pedal stroke is a whole cm. (and your saddle comes up 5mm to compensate of course).

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Similar thing for me - except that I have 172.5 mm on my TT… and these 2.5 mm actually makes a lot of difference in regards to cadence - and reduced muscle fatigue.

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Not being a pro they were a waste of money for me for me. Besides being worse for sprinting which doesn’t happen on the TT bike, there is simply no noticeable change in performance. If I could do it over I’d have never switched from the 172.5’s.

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