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how do I know what TT length is for me?(6 posts)

how do I know what TT length is for me?chahny
Apr 3, 2001 1:24 PM
from what I've been reading, the bias on the board is definitely toward getting the right top tube length for proper fit. My question is how do you find out what is the correct TT length is for each person. If it helps, I'm 5'9", 31.5" inseam and my arms are longer than I am tall(not sure by how much). Is it more of a qualitative feeling or is it a quantitative measurement?

thanks
re: how do I know what TT length is for me?PsyDoc
Apr 3, 2001 1:43 PM
The TT length can be a quantitative measurement or a qualitative feeling. If you want a good starting point, then go to:

http://www.bsn.com/Cycling/

Then click on "Ergobike: Competition Bicycle Size/ Proportions Analysis" and at the bottom of the new page that opens, you can choose your inseam measurement. The program then calculates all the other measurements that are "average" for someone with your inseam. You will get a plethora of information back. You can also input your exact information as well. The measurement process will require a friend and a good bit of time if you choose to enter your specific measurements.

You can also go to: http://www.wrenchscience.com/WS1/guest1.asp which will give you a good starting point as well. The important thing to remember is to use the information as a guide. Do not let the information "pigeon hole" you into thinking that particular size is the one you need because some computer program told you it was. Once you have that information, then go out and ride a bike with that TT size and other bikes that have the same head angle and seat angle with TT lengths that are 1-2 cm different. See which bike feels right for you and go with that bike. OR, you could spend some $$$ and have a fit -kit done for you. Good luck!
vertical & horizontal fit....dave
Apr 3, 2001 2:38 PM
The "ideal" top tube length should allow the use of a mid-sized stem, and yield some knee-to-elbow clearance with your hands in the drops (on the brake levers) and the knee at top of it's stroke. Riders that lack flexibility or back and abdominal strength may use a shorter stem to feel comfortable, and tolerate some knee-to-elbow overlap. I usually need a stem ranging from 10 to 12cm in length on 54-55cm frames.

Both top tube length and seat tube angle must be considered to optimize horizontal fit. The ideal seat tube angle will provide adequate fore-aft saddle adjustment to place the knee-over-pedal spindle at the point of best efficiency, and still have some saddle adjustment available. One of the problems for beginners, is determining the "optimum" knee-over-pedal position. Only a lot of riding and experimentation will determine the position that produces the optimum combination of torque and spin to maximize power output. When experimenting, keep in mind that moving the saddle forward from the neutral position increases cadence, and moving it back increases torque. Keep in mind that power = torque x cadence. If cadence is reduced, torque must be increased to maintain the same power (and vice-versa).

You'll notice that most manufacturers only change the top tube length about half as much as the seat tube length, between the different sizes. It's not wise to ignore vertical fit in the search of that "perfect" top tube length, especially when stems are readily available in 9-13cm sizes, in almost any brand. Vertical fit is just as important, to avoid the need for high rise stems or lots of steering tube spacers, when using threadless headsets. I always consider the head tube length, when purchasing a frame today. I also keep my standover clearance in the 2-4cm range to keep the saddle to bar height at 9cm or less.
dont worry too muchjohn de
Apr 3, 2001 3:54 PM
its ok to get a ball park top tube just dont be afraid to change your stem length if you feel to cramped or streached... ive recently changed from a 53 top tube to a 54.5 and i kept the same stem and bars and i wouldnt want to change anything
Don't worry too much? Bad advice!Kerry Irons
Apr 3, 2001 4:52 PM
Don't worry if you don't care how your bike fits. Don't worry if you "got lucky" on your original sizing. Worry if you get a "normal" TT length but the bike happens to have a slack seat angle and now no length of stem is long enough to allow you to stretch out. Worry if you have a steep seat tube angle and you have to use a very short stem to get fit, screwing up the bike's weight distribution and handling. With so much information available

http://www.bsn.com/cycling/ergobike.html
http://www.coloradocyclist.com/BikeFit/index.cfm
http://www.sheldonbrown.com/harart-frames.html
http://www.electriciti.com/~bikelane/sizing.html
http://www.rivendellbicycles.com/frameinfo/Frame_Sizing.htm
http://www.peterwhitecycles.com/fitting.htm

to properly size a frame, why on earth would you be willing to take what comes and hope for the best?
from my experience it'll be okjohn de
Apr 3, 2001 7:07 PM
ive owned a 61cm, 53, 52,and a 50..and they were all fine with a bit of tweaking...it depends on the type of ride you want, the bigger the more stable, smaller more aero...if its so important why does giant sell small, medium, and large....even though there are formulas which match bike sizes to body demensions, once you throw in a bit of personality and personal preferances the formula is no longer a formula its only a guideline...as to weight distribution, i think shorter stems than the norm (9 or 10) enable you to sit farther back and better control the bike, thats a personal preferance which seems to go in the face of the supposed science of weight distribution and handling...the whole usps team rides stock bikes, and they only come in 2cm increments....can you come up with anything on earth that applies the human body to such a ludicrious formula for fit, not pants,shoes,suits,cars....its only a guideline..also each bike company recomends a different fit..