What size frame to choose

[Peter Salt]

Yeah, I guess if I was 5'5'' there would be no debate on the 'S', likewise if I was 5'9'' it would have to be an 'M'.

At 5'7'' it looks as though you can make both work with some adjustments to bar height and stem length. As a newbie I think I should go with a smaller one as getting a longer stem on a smaller frame will result in less 'twitchiness' then a shorter stem on a larger frame.

 

[CanucksTraveller]

I rode a TCR for some years until I sold it recently. I'm 6'0 and I was on a M/L frame on the TCR, just right, and bang in the middle of Giant's sizing guide.

when the saddle got adjusted to my leg length it didn't look very high

- family jewels were less than half an inch away from the top tube when standing up (in trainers)

A TCR should have masses of seatpost showing and your groin should be a LONG way over the top tube when standing, it's a compact frame with a sloping top tube. If the seat looks fairly low on a TCR it's the wrong size frame for that rider, probably by 2 orders of magnitude.
The saddle should (as a rough guide) be about level with the bars, or a little above. Not down near the frame's seat cluster.

Edit: I see you're on the right lines now but thought I'd leave this up just to help confirm it in your mind.

 

[Jody]

Yeah, I guess if I was 5'5'' there would be no debate on the 'S', likewise if I was 5'9'' it would have to be an 'M'.

Might not be much use but I'm 5'5 and my small Giant road bike still feels a little bit too big.

 

[CanucksTraveller]

Just to give you an idea of what a TCR looks like seat post wise when it's the correct size for the rider, this was mine:

 

[cyberknight]

I have ridden bikes with a 56 TT aka medium and i had to compromise with 70/80 mm stems

 

[Peter Salt]

Got an idea: Will go to the gym a try different positions on an exercise bike. I believe the ones in my local leisure centre have both horizontal and vertical adjustments on the seat and handlebar. Anything I should have in mind when comparing an exercise bike to the real thing in terms of position?

 

[cyberknight]

https://wheel-easy.org.uk/wp-content/uploads/bike-set-up-2017a.pdf

 

[SkipdiverJohn]

The problem with many smaller modern road frames is the head tube lengths are too short to give a comfort-oriented bar height. Pros want to be as aero as possible, so they tend to size on the small side because the riding position of a short head tube frame is inherently more aggressive. Small frames also tend to be shorter wheelbase, so they feel more sporty to ride but less stable.
Most leisure riders, however, are not interested in crippling themselves just to be able to squeeze out 1extra mph on their max speed. Therefore if you have long legs you need a frame with a tall head tube, which normally means choosing one of the larger sizes. If that makes the reach uncomfortable, then you compensate for it by shortening the stem.
My inside leg is about 33 1/2" and I mostly ride frames of around 23"-23 1/2".

 

[rivers]

It all depends on what you want from a bike. If you don't want an aggressive riding position, maybe the TCR isn't the bike for you and something more endurance oriented is. My road bike and my gravel bike are both 46cm/XS bikes with a top tube length around 50.8cm. Put them side by side, it doesn't look like there is much between them. However, my gravel bike has a shorter stem, slightly longer head tube, and higher stack and less reach, giving my a slightly more upright position. My road bike is a bit more aggressive. I can ride both bikes all day long. I'm 5'2" with a 31" inseam, and have roughly 8 inches of seat post showing on each bike.

 

[Sittingduck]

Reach more important than inseam length. You will be an S or maybe a M but probably the former. Need to test ride one of the appropriate size. Don’t forget you can easily swap the stem for a different length one. I do this for most road bikes and am 5 9 with a short leg of 29 or 30 tops. default M in Giant bikes with a 90mm stem instead of typical 100 as stock. Cranks 172.5