TT bike fit experts, sizing advice

[Wayne77]

I’ve pretty much figured out road bike fit but know nothing about fitting a TT bike. Here’s why I’m asking: I have an opportunity to get an older model Pinarello Montello TT frame. I ride a 57cm effective top tube road bike, though I can make a 58 work and usually can work with a 56 as well. I’ve heard that you size down a couple sizes. In any case I can chose from 2 sizes. These Pinarello TT frames seem to run a little longer than the listed size. For example, one option is their “53” which has a 54.5cm effective top tube, and the other is their “55” which has a 56cm effective top tube. Both have a a relatively old-school 76.5 deg seat tube angle. Given the ‘size down’ thing with TT/Tri frames it almost feels like either would work...but I really can’t be sure. They are within 1.5cm of each other. Wondering if it’s better to err on the shorter end of the spectrum or longer end of the spectrum.

Thoughts?

[el cheapo]

Youtube it! There's loads of fitting vids for Tri and TT.

[John H.]

Fit matters a lot on a tt bike.
Either spend some time dialing yourself in- or if there is a tt fit guru near you...

Also consider helmet as part of tt fit- The fastest helmet is very individual and you want to integrate this into the program.

Then you want to test this on the road. Because speed is the nexus of aerodynamics and power.
Sometimes you can lose a few watts and still be faster.
Sometimes an aero position makes it impossible to do what you need to do to go fast.

[echappist]

Hard to generalize, as this depends on both brand and the particular cyclist.

The road bikes I used for road racing have the following ETT (in chronological order): 54.5, 52.5, 53.5, 54.5 (last one being the ETT of my current road bike).

My TT bike has a ETT of 52.0. Technically, it should be okay, and for the most part, I do like the bike, but the head tube is so short that I feel stretched on the bullhorns, and it has an effect on bike handling (can't get enough weight on the front wheel to really rail corners). The next size up has ETT of 55.0, and I'm not sure if that one would have been appropriate. If I were to do this all over again, I'd have gone to a different brand (with ETT and HT both slightly larger than what I'm currently using).

All this is a long winded way of suggesting you find someone who could give you the stack & reach numbers you need, and then find a bike that satisfy those requirements.

The other thing is that if you want to be anywhere near competitive in the TT, you should probably look at something a bit more modern than the Montello.

[Wayne77]

Thanks, this is helpful information. I forgot to mention that is is more about getting a TT bike just as ‘another kind of bike to have’...not remotely concerned on being competitive. I do a lot of road and gravel racing and that’s where my focus is. But having a TT bike that when I’m the mood to go out and kill it on a flat course somewhere just for fun sounds appealing.

In any case none of this is about incremental aero gains, competitiveness, etc. I just want to pick the one out of the two sizes available that will allow me to ride most comfortably. I will say this though...the Montello is one of very few TT frames that I personally find aesthetically pleasing. There are so many ugly TT frames out there these days.