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Another sizing ? - would 2cm +/- in TT lengh make a diff?(7 posts)

Another sizing ? - would 2cm +/- in TT lengh make a diff?nellie
Jan 15, 2002 4:20 PM
Sorry, I know that there have been a couple of different sizing questions posted over the past few days but i am a newbie and need to make a decision on a frame. I wonder how much difference you all think there would be based on my info......

I went to my local LBS and was fitted using the "Fit-Kit". It 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).
My 2 frame options are this:
1) Bike 1 - IF, 56cm ST, 57cm TT, 72.5 STA & 139mm Head Tube Length

2) Bike 2 - IF, 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 on the 58 as compared to the 56 to make it stiffer (they couldn't tell me exactly how much but approximated by about 10%).

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?

Thanks in advance for your help!!!
Go biggerKerry Irons
Jan 15, 2002 4:49 PM
KOP is Knee Over Pedal, a starting point in placing your saddle relative to the BB. You sit on the bike with the cranks horizontal, and a plumb bob from the boney projection of your forward knee drops through the center of the pedal axle. If you like to push and/or have long femurs, you tend to move the saddle rearward. A TT bike would have the saddle forward, as would someone who likes to spin more or sprint a lot. It's a good reference point as you start finding your preferred position on the bike.

I have to assume that these seat tube lengths are center-to-center, because at your inseam you would have your seat post at max height on a 59 cm center-to-top frame. I can't imagine that a 56 would fit you - seat tube and top tube too short.

You are relatively long in the torso for your height, so a longer top tube seems the direction to go. I think the larger frame is your choice. Add in the 72.5 STA on the bike, and that means that the TT needs to be about .5-1 cm longer than that on a 73 STA frame to keep the h'bar in the same place.

Forget about the tube diameter stuff - you have to have a frame that fits and you shouldn't get a smaller frame (that can't be made to fit) because you're worried about this issue. Good builders will always tweak their larger frames in order to maintain stiffness. You aren't really getting a stiffer frame with the larger size - you're getting a frame that is stiffer than it would be if the builder didn't change it. It might (or might not) be flexier than the smaller frame. It really doesn't matter, since the bigger bike is what you need.
re: Another sizing ? - would 2cm +/- in TT lengh make a diff?ishmael
Jan 15, 2002 5:42 PM
id say go systems dont take into account the real road after an hour in the saddle...even the kops thing isnt the best, its a good guide but there are alot of people who disregard it or are a bit fore or back and they are fine...what if you find the bigger frame seems a bit too streached out and you want to shorten your reach, you cant get much shorter with a stem without it starting to handle strangely......i have a 13cm stem on my bike and its very nice, my other bike with the 9cm isnt as secure feeling..also smaller frames feel snappier and more fun, maybe a bit scarier for the first month or two but you grow to like its agility as aposed to the staid and stable large frame...i dont think the increased headtube is an issue for you, you could always raise the stem or get a better angled one...the stiffness thing probably isnt a worry either, ill bet they are both strong enough, unless you plan to race its not an issue.... im not sure if you said you were new to riding or not but i think you should try out the smaller one for a good hour with a nice seat, shorts, good bike shoes, and the bars positioned where you want them, and then make a decision...dont go on anyone elses advice...yes 2cm makes a huge difference
the 56 is too small...C-40
Jan 15, 2002 6:02 PM
and the head tube is way too short. I have a 134mm head tube on my 55cm. My inseam is 5.5cm shorter, but I still have a 10cm distance from the top of the saddle to the top of the bars (with an 80 degree stem and no spacers). You would have a 15-16cm distance which is almost certainly too much.

Don't even consider the 56cm frame.
the 56 is too small... unless...Elefantino
Jan 15, 2002 6:15 PM
Remember my brother in law. (OK, so he's 6-1, about 165 pounds, 32-inch inseam, you do the conversions). But he likes to ride that little roller skate Giordana of his (54 cm).

However, I will add this: At your weight, on a 56cm steel bike, I wonder about frame stress. You're a Clydesdale on a frame built for a greyhound. And the fact that IF admits that it strengthens the frame for the 58 should tell you something.


PS: If the person who "fit" you suggests wheels with ti spokes, run out of the store immediately.
Jan 15, 2002 7:00 PM
None of the numbers stuff is as important as the ride and feel. You need to ride both and see how it feels and how you settle in. With the bigger frame you could drop to a 100 cm stem and the you'd only be off by 0.5 cm form "ideal". If you go smaller then your seat will be higher and you'll need a longer (0.5 cm) stem WITH 2 cm of increased height to hit "ideal." Frankly I can't see a 6'3" guy at 225 lbs. being correctly fit on a 56 cm frame - I'm 5'10" and ride a 56 cm - and you've got 5" of height on me which is about 12.5 cm and a 34" inseam vs. my 32". If they need to order you and extra long seat post (and they will) consider this a warning.

What you need to do is use the third option: get some more opinions from other shops and fitters. Don't tell them what kind of bike you want or what size you think you should be on - or else that's what they'll sell you - even if it's wrong. Hey, the customer is *always* right - especially in this economic climate - and if not maybe we can sell him another bike. Ride lots of bikes and talk to many fitters to understand their approach - you'll be surprised at the great differences in philosophy. You may find that brand "X" is a better bike for you. Don't even think about buying it if you can't ride it and aren't convinced that this is THE best bike for you. Keep an open mind and learn as much as you can. Don't rush the process. In the end if nothing seems right consider a custom frame, but this isn't the best advice since it really helps if you know exactly what works for you. Recognize that the "ideal" position that they put you in may not work for you over time. Consider buying a less expensive bike until you sort everything out - it's a bummer if you blow the bank on something like an IF and then you come to realize isn't right - after a few thousand miles and dollars.
why not pay a little extra an have a consult/custom by IF...koala
Jan 16, 2002 5:19 AM
Your dropping a lot of dough on it anyway, it might as well be perfect. If you could go there it(factory) it would be best.