ldesfor1@ithaca

hi, just a general question. i am 6' 3.5" and seem to prefer a very short top tube. based i bikes i have ridden i think that a 64cm frame with a 58cm top tube and a long steerer tube would be ideal. this is with drop bars and a 90mm stem and a very setback saddle. if i was to have a custom frame built up (for light touring/audax/road) are there any handling problems/overlap problems that would arise from this frame sizing? have you encountered anyone who prefers a frame sized like this? thanks for replying to this awkward question.

potus

overlap would not be a problem. handling is dependent upon head-tube angle and fork rake. having a 64cm ST and 58cm TT can work. sounds like you have long legs. have you ever been fit by a professional? may be interesting to hear what they would prescribe.

Dave Moulton

If you are considering a custom frame you can safely leave the design in the hands of the builder. You might however consider this, the same 58cm. top tube with a shallower seat angle. The saddle can then be set central rather than set back, and a longer handlebar stem used, which might improve handling.

Toe overlap should not be an issue on a frame this size. You might consider longer chainstays so you are not sitting directly over the rear hub as this may cause shimmy problems, especially if you plan to use panniers. See my blog “Shimmy re-visited.”

ldesfor1@ithaca

thanks for the replies. i really dont trust fitting experts, though as i know what a comfrotable position is. this set up lets me into the drops with a 40degree bend at the waist and about 55-65 degree bend on the hoods-flats-tops. i feel that a relaxed seat tube angle is prefered as i already prefer my saddle to be quite far behind the bb (a long femur i believe). this saddle positioning is probably a big part of my desire for a short TT. would a super relaxed seat tube, make sense here? or would it trow handling off too much? is a 70degree seat tube rediculous? it's tough to get my brooks far enough back in the seatpost (a cheap setback post).
i am actually quite proportional for a tall guy. 34-35 inch inseam 36-37 inch sleeve (based on dress shirt size) and a longish torso. I like the idea of longer chainstays, as my 62cm LHT offers a very stable (loaded) but sluggish ride (unloaded). the geomety of my 60cm crosscheck feels nice but this is with a 50mm stem about 1 inch below saddle height and a flat bar. riding on the lower section of the barends feels just right.
thanks again

AnthonyG

A 70º seat tube angle sounds perfectly reasonable and you could say that its even NORMAL for someone with a proportionaly long femur. I'm in a simmilar boat to you in that I ride with a 69º seat tube angle and I have a VERY short top tube, especialy when you consider that the nose of my saddle is 73 mm behind the BB. I am however on a very small bike with 650c wheels but the proportions are somewhat simmilar.

A bike built like that would handle fine although I don't have an issue with sitting too far back over the rear wheel which could be an issue for you.

Here's my custom framed bike,



Regards, Anthony

Mariner Fan

Wow! This discussion is an eye opener for me. All my bikes have the saddles slammed completely back and I have seat posts with as much setback as possible. I'm 6'3" and have never been able to center my saddle on a seatpost. And yes, I have been professionally fitted. Looks like I'm a good candidate for a custom frame?

MichaelW

It helps to use some reference point on the bike and I use the bottom bracket.
Many tall riders use cranks of M length. To get a good position (some varient of K.O.P.S) they have to move the saddle back or get a really slack seat-tube angle.
If you select a proportional L crank you foot will be further forward from the BB at 3:00 so your saddle will be equally forward (ie a normal distance). Your weight will no be so far over the rear hub but more balanced.
This will allow you to use a longer stem for the same reach, which for a big rider is usually >120mm .

By selecting proportional cranks and designing the frame around them you solve all the problems of bodged geometry and unbalanced weight that most big frames create.

Note how it is really difficult to judge the size of AnthonyG's bike, it is tiny but perfectly proportioned, built around proportional very short cranks.

NoReg

Just for fun you might want to read Keith Bontragers' piece on why KOPS is not correct (hasn't changed my angles but it makes interesting reading).

https://www.sheldonbrown.com/kops.html