Yep. Absolutely. And, changing crank length dramatically probably is best done with the help of a fitter. Becuase, if everything isn't adjusted right...then, yeah it feels exactly like you described. My Road boke is 175mm, TT 150mm. Once I got the TT bike fitted properly, I couldn't tell the difference between them. YMMV, of course.


Yep. It's ~1 cog per 10mm change in length. All else staying the same. More or less.

Yep. It's ~1 cog per 10mm change in length. All else staying the same. More or less.[/quote]
Personally, I’d rather change the chain rings, rather than the cassette, But thats mainly for consistency with my Road bike, unless I need a different cassette, which I dont - flat country here, so 12-25 is usually the choice

Just to weigh in one more time... I had a respected Tampa area fitter, Roy Foley, do a pre-purchase fit before I bought the bike. That came about from recommendations from my fellow St Pete Bicycle Club members and it made a lot of sense to me to avoid buying a bunch of components and then swapping them out later. This all happened before I ever read a post on Slowtwitch. I ordered the bike and got it 6 weeks later.

In the meantime I happened upon this site and dove in to the minutia and of course second guessed all my prior decisions. Roy and I didn't really discuss crank length during the first Retul fit but Trek will send you a 172.5 (50 / 34) crank with a size L Speed Concept frame so that's what I ended up with. When I went back to Roy for the follow up I made a point of addressing the crank length issue. His view was that I looked good on the bike aero wise, angle wise and I felt comfortable so let's not worry about it.

Since I had never owned a TT bike before it took a while to keep it between the ditches but after a while I felt pretty good. When it came time to add a power meter I had a chance to revisit the crank / gearing issue. One of my bike club buddies was adamant that I swap the inner chainring to 36 and swap the cassette to 12-25. I also wanted to change the crank length due to the prevailing opinion here on ST that shorter is better. I kind of hedged my bets going down to 165 and not lower. There were inventory issues and 165 was available so I ended up with a Stages 2 sides 50/36 set up in front and the 12-25 in back. For my power range it's perfect because there are no big jumps, perfect overlap and I mostly live on the 50 x 15,16,17 which keeps me off the smaller cogs.

I'm a diligent consumer of the fit assistance threads on ST. Since I last left Roy's shop and become more confident on the bike I've dropped 15mm in pad stack, maximized the reach and shortened the crank length by 7.5mm. It took a lot of riding, reading and fussing but I was pretty happy when I posted these videos and I'm happier now.

Cheers

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"They know f_ck-all over at Slowtwitch"
- Lionel Sanders