TT bike sizing

Matthewfalle

Morning all

Just a quick one - after doing some research, there seems to be two schools of thinking re TT bike sizing:

1. Same as your road bike and adjust to suit
2. Go a size smaller due to different riding position.

Any opinions?

I'm normally a 57 with huuuuge seat post to slammed bar drop as I'm all legs and still flexible and never had a problem, so whether this plays a part in potential aero position on TT bike I really don't know.

Many thanks

M

simon_masterson

You will need a shorter top tube, I don't have a modern road bike but I suspect I would want a 55-56 top tube whereas my TT bikes are 53.

Position wise, I go for a big drop but even if you are flexible enough, in the ratio of aero benefit to power compromise, lower is not always better.

Grill

The idea of sizing down a TT bike is a misconception. Unless you know your ideal S+R for a TT position then you'll want to go the same size as your road bike. That said, typically top tubes will be a bit shorter on the same brand TT frame, but not by much. Make sure to get bars and stem that are highly adjustable as you'll be playing with your position for a while (adjustable stem + PDQ bars are a good shout).

In regards to drop, lower is not necessarily faster (in my testing dropping 20mm off the front gave me a massive hit in CdA), but the only way to know for certain is to test (Chung method or AeroCoach sessions if you have the cash). There are very few, if any, universal truths when it comes to fitting in regards to comfort and aerodynamics (eyeballing doesn't work) so you'll need to spend time validating any changes.

iron-clover

^This^

Just to throw a spanner in the works, the top tube on my TT bike is longer than on my road bike for the same seat tube length. Although it is an old school frame- maybe they've changed from the 'long and low' mentality of the past with modern frames.

Grill

Unfortunately long and low TT bikes are becoming more difficult to find. I blame triathletes.

Matthewfalle

Brilliant - thank you very much indeed for your time and posts.

I've done some measuring and the large frame I had my eye on seems to fit the bill quite nicely - maybe a cm nip and tuck here (enough to compact it all up) but not enough to make it too small. Until my famed flexibility goes then it seems the way to go.

Again, many thanks.