Tweaking my Lemond's geometry to fit better?
 

My first posting on the framebuilders forum.

I am planning to have a bike built with S&S couplings for some planned trips to Europe after I retire.

Originally, I had thought that I would just have the couplings retro-fitted to my Lemond Sarthe (classic steel frame, TT OX) but I'm beginning to lean toward having a new frame built (probably by Naked) with the couplings included and the geometry tweaked a little so the bike fits me a little bit better.

My 51 cm Lemond has a TT that is a bit long for me (it's 532 mm) and also I want to reduce the handlebar drop (from 5.8 mm to about 4.0 mm). I have compensated for the TT length by using an 80 mm 17d stem but I would prefer to be using a 90 mm 10d stem. I expect that the handle bar drop will be more of an issue as I age (I'm in my mid 50's).

I don't know if it is feasible to consider having a “new front end" built for the Lemond to be joined to the rest of the frame with S&S couplers. The "new" front would have a 10 mm shorter TT, a longer HT with ~10 - 15 mm more than usual sticking up above the TT, and maybe reduce the HT angle by about .25 degrees to 72.25? The stand over is already at the maximum for me (SO is 770 mm, my inseam is 790 mm).

Am I completely wasting my time thinking about having a new front end built for the Lemond and I should just concentrate on designing a frame that fits me better?

To decrease the handlebar drop without using a big stack of spacers on the steerer tube, I am thinking of having the head tube constructed so it sticks up by ~ 10 - 15 mm more than normal and making up the difference with maybe another 3 - 5 mm spacer on the stack (remember the top tube can't be raised). Is this a reasonable plan?

Is shortening the top tube (compared to the current geometry of my Lemond) best done by relaxing the head tube angle? Will a 0.25 to 0.5 degree change to about 72d change the handling characteristics significantly from what I am used to? What would also changing the fork rake from 45 mm to say 40 mm do to the handling?

I am assuming that by deviating from a "standard geometry" that this precludes a frame built with lugs and I'm limited to Tig or fillet brazed construction?

Thanks for any suggestions in advance.

You'd be lucky to find someone who wants to cut an existing front end off a bike and add a new one, and if they do they might want to charge a lot because it's a PITA, so you might want to look at a new frame.

S&S Couplers have got pretty expensive in recent years so hopefully you'll find someone who has stock and will charge you at the old price.

The geometry questions you've asked would take a long time to go into detail about. I'd suggest you'd probably get better and quicker information if you had a small list of questions and fired them off to a selection of builders.

Phone is best as you'll also get a feel for the person who will be designing and/or building your frame.

Thanks for the input.

I have started working through some of the geometry problems using BikeCAD and I can see that there is lots of fun ahead in designing your own bike.

I know someone who does bike fitting; I think the next step for me is to get my position on my current bike perfectly dialed in and then use it as a starting point in BikeCAD.

Good work!

Great to see you're using your physiology as a base, then the frames' geometry becomes a result of fit, plus handling (steering + CG wheelbase), which is the way it should be IMHO.

We like it when we get customers who have had a fiddle and done a little homework themselves. :thumb:

Thylacine is right.
I'd just like to add that what you have outlined so far is easliy obtainable with lugs and there are several newer lug designs that incorporate the headtube extension you want.