I would love to tap into your collective wisdom for a moment to help me choose the nearest 'correct' bike size.

I had a bike fit a couple of years ago and am due another one but before I do, I am looking to purchase a new bike, namely 3T Strada Pro.

The geometry is as follows (from https://www.3t.bike/en/products/bikes/strada-551.html#/269-bikes_size-xs...)
Size XS S M L XL
Fork axle-crown 355 355 355 355 355
Headtube angle 69.5 71.2 73 73.5 73.5
Seattube angle 72.5 72.5 72.5 72.5 72.5
Toptube length 507 529 550 571 592
Seattube length 487 500 506 518 533
Headtube length 119 119 143 172 202
BB drop 71 71 71 71 71
Stack 501 507 536 565 594
Reach 349 369 381 393 405
Front center 567 567 573 589 609
Rear center 405 405 405 405 405
Fork rake 50 43 43 43 43

My measurements were based around a 'sportive' fit so happier to go a bit racier.
Height: 188 cm
Flexibility: high
Target Knee Angle: 150° to 152°
Recommended Measurements:
W 50mm - handlebar drop - vertical distance from underside of the noise to the hood trough
X 820mm - vertical saddle height - from BB to underside of nose of the saddle
Y 200mm - pedal to saddle setback - horizontal distance between pedal axle (175mm cranks) pointing forward to tip of saddle
Z 660mm - horizontal reach - horizontal distance from tip of saddle to hood trough

Now I've drawn diagrams, done my best maths but can't fathom whether a L or XL is best. Needless to say this is made more complicated by the fact I can't try either size before I order one in. I can return for a different size but that would be at my expense, which I'd rather avoid having already agreed to hand over a kidney and my testicles to my wife to be given permission to buy a nice bike.

Any help is greatly appreciated.


madcarew [1002 posts] 7 months ago

If you feel you're on the cusp of 2 sizes, if you like a sportier experience it is generally better (and more adaptable)to go for the smaller frame. 

From these figures we couldn't give you an accurate match as we would need to know how long your handlebar stem is, what your height from the bottom of your head tube to top of your handlebar stem is, angle of your handlebar stem, set back of saddle from bottom bracket centre, height of saddle itself (how thick is your saddle from underside of nose to top of saddle).

HOwever, if you measure on your existing frame Front-centre, Stack, Reach, seat tube length, and top tube length as shown on the diagram, if they are within a few mm of each other  then you will likely be able to achieve your current position on the new frame.



Rod Marton [125 posts] 7 months ago

Are you sure this is the right bike for you? Your sportive postion is quite upright and this is an out-and-out race bike - you won't be able to duplicate that position on it. In particular your bars will need to be lower and further from the saddle.

From this information it's really not possible to say which will be frame will be better for you, though with your height I would guess it would be the larger one. I think your best option would be to have a bike fit based on a racing position and see what that tells you.

vonhelmet [1350 posts] 7 months ago

The geometry is a bit of a nightmare. Stack/reach varies wildly up the sizes. XL is way more stretched out than L, for example.

pablo [213 posts] 7 months ago

whats your current bikes stack and reach? i went from a sportive fit to a race fit with something like 30mm drop in stack.  The only way to really know is try one or get a fit with a recommendation.  I'm top of a 54 bottom of 56 I road a 54 for 100+ miles but couldn't use the drops on the flat so went 56 which has been fine. Fit is a really personal thing.

melliott [24 posts] 7 months ago

Thanks for your responses. Unfortunately I'm not in a position to actually try out the bike before buying (not ideal).

My main bike currently is a 58 GT Grade, but I have a 130mm stem and a 400mm seat post fitted. Reach: 382mm, stack: 627mm. I think the Strada comes with a 110mm stem. When I overlay the geometries, the setup looks very similar to my current bike setup.

I have sized myself on a Giant Propel, which is pretty similar in geometry and it looks like the XL Strada is probably the closest.

I'm looking forward to getting into a racier position.