In my case, it was instantly noticeable. I have limited range of motion in my left leg from an old accident, and 170mm cranks are right at the very limit of what I can ride. 172.5s (which are what normally come stock on 54cm/mediums) are slightly outside my range, and painful to ride, even in an upright position (I can't quite get over the top of the stroke, and can just barely manage with 170s). Switching from 170s to 165s gave me a bit of breathing room. Comfort, plus a slightly flatter back, just by changing the crank and raising the saddle 5mm. My very first ride, I was faster and more comfortable...

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"I'm thinking of a number between 1 and 10, and I don't know why!"

What puzzles me, and what the esteemed Hanginon is probably referring to, is that someone was selling small-sized bikes with 172.5 mm cranks.

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"FTP is a bit 2015, don't you think?" - Gustav Iden

I fit the US womens road race champion a few weeks before the race last year. She had 165mm on her road bike. I recommended 160s but no big deal. On the fit bike for a time trial fit she strongly preferred 145s, as most riders with sub 650mm saddle height tend to choose when in aerobars. Her team gave her a tt bike with 170s a week before the race. She bought (her own funds) the shortest thing she could buy that honored the sponsorship.... Shimano 105s in 160mm. We gave up 4-5cm of drop from the fit bike position. 1st in the rr, 5th in the tt.

It’s a real mystery to me why the industry specs what they spec, and why it never changes.

People come to me for TT fits with German bikes that have 175mm stock!!!

E

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Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

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So a crank that was 15 mm longer (160 vs 145) forced you to raise the cockpit / lower the saddle by 4-5 cm?

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"FTP is a bit 2015, don't you think?" - Gustav Iden

Yes.

I can't think of any new TT/Tri bike that will properly fit anyone with a saddle height less than 650mm.

[/quote] If I put the 170's back on, it feels better with a much more balanced effort feeling between my thighs and calf's, and my legs feel better overall after the ride.

Has anyone else noticed this?[/quote]

Yes! Back about 10 years ago when short cranks were a new thing on ST, I went from 170's to 155's (I think). I tried it for a a season, not terrible. However, after the race season I was using an older TT bike that still had 170's on it, and just felt SO much better. Power, rhythm, feel throughout the power phase, just clicked. Never looked back and use 170's now. For info, I moved my seat height all over the place with no big difference. I also used to ride fixed gear on the roads, for that 165mm cranks is what I use there: right tool for the job in that case.

I have been planning on going from 165s to 175s since last summer but didn't get around to it. Finally switched over this weekend. My desire has been to lower centre of gravity for descending as I had a few speed wobbles and twitching moments. Otherwise, I have been very happy fit wise.

Did an easy zwift 30min ride before and after switching. 1 hour time difference between spins. Went up the climb portal. Some anecdotal evidence and some caveats below.

My average watts increased 146>153w while my HR was lower with 175s. I would not take these results as 100% accurate as I use garmin vector 2s and I find them sensitive to the torque they are installed at. But I would confidently say there was no real impact in my power/RPE switching to 175s. This may be different riding at higher wattages and struggling with the more closed hip angle.

What I thought was more interesting is that my self selected cadence was higher (86 vs 79) with the 175s than the 165s. Completely counterintuitive but I'll monitor this over the next few rides.

All I did was lower the saddle, I didn't mess with fore/aft position. Felt good riding in the position but one thing I did notice was a bit more rocking in the hips.

6'5" here, never got rid of my 175's.

Nice! I was wrong about my earlier "Ganna" comment. At 6'4" tall, he used 175's to set the new Hour Record.

Besides my move back to 170's (from 165's), I also started moving my foot back on the pedal, as opposed to slamming the cleat as far rearward as possible on the shoe. I'm essentially back to the position I rode as a young man - and it feels good.

I'm starting to think that much of what is currently thought of as "good position" is negatively influenced by Triathlon - they are in fact two different disciplines. Tri riders need to be more comfortable since the ride is longer, and they need to run when they get off the bike. TT rides are usually one hour (25 miles) or less, and you should be in so much pain that actual "comfort" is completely secondary - plus if you did your split correctly, you might not even be able to walk when dismounting!!

Unfortunately, the number of riders who specialize in TT's who get "fitted" is probably a very small percentage vs Tri riders.

IM 70.3 Pucón, Sam Long blasted the course record with 175 mm cranks.

Was he on 165s previously?

This thread has been really informative.

FWIW then at 6'4" and all legs (body of a 6 footer) then I ride 175mm on road and my tt is 172.5mm. For full disclosure US12.5/48 feet. But, my natural cadence is 96-97rpm and has been for over 20 years, going higher if I'm doing high power stuff. On hills I'll almost certainly spin rather than stand - and whilst I'm not CAT A racer, then I am very much mixing it with the wiry mountain goats on the club climbs, albeit using a totally different approach. The biggest leap forward in my cycling came from a move to a compact chainset as that meant I had more appropriate gears for my cadence.

And so noting the talk about the logic of smaller being to help the cadence increase means I am even less inclined to try going shorter.

Cadence can be controlled by simply changing gears.

Gears can be changed to keep power and cadence steady