Forcing a bike to fit, Am I nut or OK, need advice

[stefs]

Hi all, here is my situation.





The size for me for a road bike is 53cm.



I just spot a titanium bike at really a good deal, but is is a 55cm.



I compare the geometry of the bike I want to buy with the one I have right now



For the titanium 55cm bike, I notice that if I put a shorter stem, move/adjust forward about 0.5 to 1 cm the saddle (because the top tube is slightly longer than my actual bike) and move down a little bit the seat post then I get in theory the same position on the bike.



Arms/torso angle should be the same, my inseam on the bike will still left me some standover clearance inches.



Am I right saying that I should feel as comfortable on this bike than a one that is exactly in theory my size? Is it forcing too much the fit?



Please let me know you point of view.

 

[dabac]

(Assuming seat tube angle etc are the same between bikes..)

Pushing the saddle forward on the post will change the saddle position vs the cranks, which might affect your riding comfort. Changing to a shorter stem OTOH should only have a marginal effect on how the steering feels.

 

[Bro Deal]

Two centimeters is not that much. There are three or four different ways to measure a frame, so 53cm on one frame may not be the same as 53cm on another. You might want to check how each frame is measure to see if it is truly a 2cm difference.

If you can achieve the right knee position relative to the BB that you want then the frame will probably work for you. People have varied thigh lengths, so they will use different saddle fore-aft positions. Aside from thigh length differences, people have different preferences for being fore or back from KOPS. Anyway the point I am trying to make is that even though two people might ride the same size frame, they may have quite different saddle positions; so your position may not be any different than some of the people who normally ride the 55cm frame and the handling would not be any different.

Normal stem extension is usually from 10 - 13cm. If you can use a stem in that range then again you won't be using anything that is out of the ordinary.

In some cases a rider might choose a slightly larger frame. I for one like a long top tube, so if I am in between two sizes I would usually buy the slightly large frame to stretch me out a bit more.

 

[PeterF]

Hi all, here is my situation.





The size for me for a road bike is 53cm.



I just spot a titanium bike at really a good deal, but is is a 55cm.



I compare the geometry of the bike I want to buy with the one I have right now



For the titanium 55cm bike, I notice that if I put a shorter stem, move/adjust forward about 0.5 to 1 cm the saddle (because the top tube is slightly longer than my actual bike) and move down a little bit the seat post then I get in theory the same position on the bike.



Arms/torso angle should be the same, my inseam on the bike will still left me some standover clearance inches.



Am I right saying that I should feel as comfortable on this bike than a one that is exactly in theory my size? Is it forcing too much the fit?



Please let me know you point of view.

Three questions:

1. Are both frames measered c-c on the seat tube? I only ask because some companies like Trek or Colnago measure c-t.

2. What are the top tube lengths of each frame? For example, Pinarello's 53 frame has a 54.3 cm top tube and the 55 frame has a 55 cm top tube. Personally, when I buy a frame I pay less attention to the seat tube length than the top tube. You may find that very slight modifications will need to be made to the saddle position and stem lenght.

3. How does your 53 fit? If you're already stretch out, or you don't have much room left in standover height, you might need to pass on the 55.

FWIW, I jumped up a size from my lifelong 56 size to 57. I'm more comfy now on the 57 and the only modification is that there's 1 cm less seatpost showing. I would try and demo a 55 if you get a chance.

 

[mikeyp123]

If you are comfy on your 53cm. Take some measurments. Fill out the relvant stuff on this form:
http://parktool.com/repair/readhowto.asp?id=130

Try to transfer those measurments to your 55. I would not recommend moving your saddle forward. Measure how far the tip of your saddle is behind the center of the BB (on your 53), make any adjustment for a difference in seat-tube angle.. and setup your 55 with that correct offset.

As already mentioned in the thread, you could probably go with a shorter stem.. if the top-tube is exactly 2cm longer on the 55, get a 2cm shorter stem.

If you ride the 53 with lots of drop on the handlebars, you may have problems replicating that with the 55.

 

[Zoopeda]

If you are comfy on your 53cm. Take some measurments. Fill out the relvant stuff on this form:
http://parktool.com/repair/readhowto.asp?id=130

Try to transfer those measurments to your 55. I would not recommend moving your saddle forward. Measure how far the tip of your saddle is behind the center of the BB (on your 53), make any adjustment for a difference in seat-tube angle.. and setup your 55 with that correct offset.

As already mentioned in the thread, you could probably go with a shorter stem.. if the top-tube is exactly 2cm longer on the 55, get a 2cm shorter stem.

If you ride the 53 with lots of drop on the handlebars, you may have problems replicating that with the 55.

Along these lines...

How much clearance (inches/cm) should there be when you straddle and stand over the top tube of a road bike?

Thank you,
Zoop

 

[mikeyp123]

Along these lines...

How much clearance (inches/cm) should there be when you straddle and stand over the top tube of a road bike?

Thank you,
Zoop

Hmm.. I suppose if you can straddle it without hurting your privates, in a situation where you'd have to come to a quick stop and un-clip.. well I guess that would be ok.

It also depends on the geomertry.. on compact geometry there would be lots of stand-over almost regardless of frame size... so it would be more important to get the top-tube length correct.

Top-tube length and how it affects your reach is probably more important, assuming you can comfortably straddle the frame.