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Size up or down?(11 posts)

Size up or down?tempete
Jan 14, 2002 1:59 PM
Say you're gonna buy a frame/ complete bicycle and they come in one cm increment...

You'd fit a 53.5 but can only get a 53 or a 54 (similar size difference in top and seat tube) which one do you get? Size up or down?

Also is it the same if you fit a 62 or a 48? Please don't answer "get a custom"...

I would always take the smaller frame and deal with seat post/railing and stem... What do you do?
re: Size up or down?axlebasher
Jan 14, 2002 2:30 PM
Most will say go down. I say go up. One cm is not going to affect the weight or stiffness significantly. I personally have found over the years that a slighly larger frame is more comfortable at no performance loss.

down for me nmDog
Jan 14, 2002 2:35 PM
Up for me--but it's rare to have a choiceRetro
Jan 14, 2002 3:31 PM
I'm at (or just above) the fit limit on most stock frames, so I rode for years on bikes I now believe were too small ("It'll fit you fine once you put on an 18-inch seat post"). I feel a lot better on a bike 1-2cm big than one that's 1-2cm small.
too little difference to matter....C-40
Jan 14, 2002 4:26 PM
How do you figure that you fit a 53.5? All frame size gives you is a dimension that mainly affects standover clearance, which is very non-critical.

You should judge the frame by head tube length, top tube length and seat tube angle. Head tube length determines how much spacer will be required to get the bars up to the desired height. The STA determines the nominal saddle position that is best suited to your femur length and desired KOP position. Top tube length (in conjunction with STA) determines the stem length required.

Get the frame that produces the best result. On many frames the STA will be the same on both sizes. The TT length will typically be .5cm shorter on the smaller size and the head tube length will be 1cm shorter. The wheelbase will also be a little shorter on the smaller frame.
I have a question.....nellie
Jan 14, 2002 4:39 PM
How much real difference is there with 2 cm on a TT? I am buying a used IF and need to decide between a 57cm TT and a 59cm TT. The advantage of the bigger size is bigger (i.e. stiffer) tubing which may make a difference with my size - 225 lbs.. But the guys at my LBS and the Fit-Kit system tell me that a 57cm TT with 110 stem is right. Do i go with the 2cm larger TT and get a stiffer frame? How much would i notice the 2 cm? Or, do i go with the 57cm TT?
I have a question.....dolmencc
Jan 14, 2002 4:55 PM
the smaller frame size is stiffer. thats the idea with the compact frames, with shorter tubes.
typical dimensions...C-40
Jan 14, 2002 6:50 PM
It is "typical" to make the top tube .5cm longer for a 1cm increase in frame size, but it's not a hard & fast rule. A 2cm larger frame may have a 1cm longer top tube and would require a 1cm shorter stem, if (and only if) the STA is the same. The head tube on the 59 would a lot longer and reduce the required amount of steering tube spacers. I wouldn't buy a frame unless I knew it's head tube length to determine the bar height that I could get without a lot of spacers (assuming it's a threadless setup).

If the guys who did the fit kit didn't use the same general type of saddle that you intend to use or didn't know your preferred KOP setting, then the fit can't be extremely accurate.

The larger 59cm frame would not be stiffer unless it used a different tube set with larger diameter or differently shaped tubes than the 57.
typical dimensions...nellie
Jan 15, 2002 12:05 PM
Let me ask you how much difference you think there would be with this info...the fit-kit tells me that my ideal ST is 57.5, STA is 72 and TT is 57.5 with a 110 stem (i'm not sure what a KOP is or what my preferred setting is).

after checking into it, my 2 options are this:
1) Bike 1 - 56cm ST, 57cm TT, 72.5 STA & 139mm Head Tube Length

2) Bike 2 - 58cm ST, 59cm TT, 72.5 STA and a head tube length of 158mm.

The guys that i talked to at IF tell me that they increase the tube diameters and thickness (he couldn't tell me exactly how much but approximated by about 10%) on the 58 as compared to the 56.

I am 6'3", 225 lbs and have about an 88.5 cm inseam with a 64 cm torso.

So my question is really this, can i get away with the bigger bike so that i can have a little stiffer frame? Would the 2 cm difference in TT length be that much of an issue? Or, do i go with the 56?
I have long arms so I size up.dzrider
Jan 15, 2002 5:32 AM
I used to size down to get a lighter, stiffer frame, but found that the longer stem made me feel less centered and balanced on the bike. Now I size up. Probably more personal preference than anything.
I would go up ...tarwheel
Jan 15, 2002 6:18 AM
Most of the fit formulas that are popular now (eg, colorado cyclist) tend to err toward the smaller size frame. This can be a mistake, particularly with the threadless stems/forks that are standard now. With a threadless system, it is difficult raising your bars without adding a bunch of spacers and/or a positive rise stem. So, I would go with the larger frame to minimize the amount of spacers and rise needed to get the handlebars to a comfortable height.

Some cyclists are comfortable riding in a very aggressive position,with handlebars 3-5" inches below the saddle. For many others, including me, low handlebars cause a bunch of problems -- ranging from numb hands to sore necks and backs. Personally, I prefer my handlebar about 1" below the saddle. This may be freddish to some cyclists, but if I go any lower than that I have problems. But if you have no problems with an aggressive position and low bars, the smaller frame might work. I bought a bike last fall that was the exact right size according to the colorado cyclist fit formula that is often touted here. It had a threadless stem/fork and the highest I could raise the bars was about 3" below the saddle. As a result, I developed serious numbness in my hands that took months to cure. It only got better after I got smart and bought a larger frame and raised my handlebars.