Sorry! Another Bike Size Question

sods_law
Posts: 161
Hi all, apologies for another bike size question, I have ordered a bike based on the seat tube dim, but on closer inspection of other dimensions, am worried I have got the wrong size.
I am 5' 10", and currently ride a 54cm bike with a 57.6cm top tube (size L).
I have just ordered a bike (Boardman TC) which is 53cm, but which has a 55.5cm top tube (size M). The size L is 55.5cm high, and 57cm top tube.
I obviously made the decision based on the nearest matching seat tube dimension, but the top tube length is a bit different, how big a difference will the 2cm make?
I am tempted to stick with the M, as the original bike was a guess at the size I needed, and went solely on the Seat tube length. I have suffered with a sore back (across shoulder blades) on longer rides, and wondered if this is because being tired i start overreaching on the bars etc, so a shorter bike may suit me anyway? I have also had a couple of comments that I look slightly stretched on my current bike, though others disagree.
My current view is that I stick with it, and if I struggle, I could put a 1cm longer stem on, but was wondering if 2cm difference will be that noticable, and might even help me if im slightly stretched...
My saddle height is 76cm ish, if this makes any difference re: bike sizing...
Thanks
I am 5' 10", and currently ride a 54cm bike with a 57.6cm top tube (size L).
I have just ordered a bike (Boardman TC) which is 53cm, but which has a 55.5cm top tube (size M). The size L is 55.5cm high, and 57cm top tube.
I obviously made the decision based on the nearest matching seat tube dimension, but the top tube length is a bit different, how big a difference will the 2cm make?
I am tempted to stick with the M, as the original bike was a guess at the size I needed, and went solely on the Seat tube length. I have suffered with a sore back (across shoulder blades) on longer rides, and wondered if this is because being tired i start overreaching on the bars etc, so a shorter bike may suit me anyway? I have also had a couple of comments that I look slightly stretched on my current bike, though others disagree.
My current view is that I stick with it, and if I struggle, I could put a 1cm longer stem on, but was wondering if 2cm difference will be that noticable, and might even help me if im slightly stretched...
My saddle height is 76cm ish, if this makes any difference re: bike sizing...
Thanks

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Comments
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boardman geometry is quite low and long. im 6ft and ride a large. i have put a longer seatpost to get high enough 82cm from bb to top of seat.definately dont need any more reach.120mm stem.0
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A 55.5cm top tube sounds spot-on for 5' 10''. Unless you have unaturally small legs and long body.0
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morrisje wrote:A 55.5cm top tube sounds spot-on for 5' 10''. Unless you have unaturally small legs and long body.
Cheers morrisje, no, i am pretty evenly proportioned, looking at the geometry, my current bike is very long for its size, think a M will be a more comfortable size.redddraggon wrote:sods_law wrote:I obviously made the decision based on the nearest matching seat tube dimension
Why'd you do that?
Because everyone talks about bikes in frame size in regards to height. Now I have looked at it in more detail, surely top tube length is a more sensible measurement, as bike height is somewhat less useful as your saddle height is adjustable!rake wrote:boardman geometry is quite low and long. im 6ft and ride a large. i have put a longer seatpost to get high enough 82cm from bb to top of seat.definately dont need any more reach.120mm stem.
Ok, thanks, looks like my current GT is very long for its size. Looks like the M will fit me fine0 -
Worst case scenario, fit a longer stem.Cycling weakly0
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maybe a seatpost as well. my large only had a 30cm post. maybe for weight or money save may be normal i dont know. bit shorter than me you may struggle for reach on a large so i think medium is good.0
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morrisje wrote:A 55.5cm top tube sounds spot-on for 5' 10''. Unless you have unaturally small legs and long body.
Kin ell mate, I'm 5'11 and I've got a Boardman Comp in large and my BB to seat recommended measurement is 71cm!0 -
BB to seat= seat tube NOT top tube0
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Cheers all, sounds like M will do the job0