Toe/wheel overlap

[hypnos]

I'm in the process of ordering another frame and just emailed a question to the builder. Perhaps this question would be worth posting here.

My current frame geometry results in some toe/wheel overlap. What changes in geometry would eliminate the overlap, if this is possible? How would the changes affect handling?

Jeff (hates riding in the basement)

[Smiley]

Shorter top tube OR a more relaxed seat tube angle are two of the biggest culprits. Some solutions : Go with a longer rake fork and steepen the head angle to maintain trail . Use a longer TT at the expense of short reach handle bars. Use a steeper seat angle and go with an off-set seat post. Better yet do all the above together .
Also overlooked is doing the above and using 650 wheels. Toe over lap can also be minizize if you used a more BOXED tip shoe like Carnacs versus Sidi . I think I have all my bases covered and some toe overlap is not too bad like 1.5 cm or lower , greater than this for a custom frame is , well lets leave it at that.

[Kevin]

Because I have long legs and a short torso I have a relaxed STA and the short TT on my Ottrott ST. As a result, my overlap is about 1 cm. I have no ride issues with this amount of overlap. The bike handles great. So I think tha Smiley is probably right, anything up to 1.5cm is probably ok.

Kevin

[dbrk]

In most cases, unless the bike has a really short top tube or someone has...uh...pretty long feet, TCO can be avoided with a steel fork. It's the limited rake options on most carbon forks that force TCO on riders who would otherwise easily avoid it by changing the fork rake. On French audax bikes TCO is strictly prohibited because when you ride that far and are on the bike a long time, you don't want to risk tapping your foot on the darn wheel. Personally, I can't stand it, not any of it, no how. The good news is that it rarely confronts me as an option. Again, a steel fork can avoid this. When you look at the "Hello Kitty Special 650C" bike that Dave Kirk built for my tinytiny wife Aimee, I specifically asked Dave to avoid TCO. One of the upshots of this was the beautiful rake that the fork took on.

It more than likely, hypnos, that you are dealing with a carbon fork and it's those few rakes that cause the issue.

dbrk

[BigMac]

I believe Captain has mistakenly confused trail calculation in his above post. For a given frame using 700C wheels, installing a longer rake fork would require a slacker HT angle, not a steeper one. In case of Serotta's which are typically built around 43mm fork rake and 73* HT resulting in approx 59mm trail, moving to a 50mm rake fork would require an approx 71.8*HT angle to maintain similar trail.

I would also suggest you never adjust ST angle as a means to eliminate TCO. Proper ST angle for me is the most fundamental fitting element. Get this right, no matter what the frame size and adjust elsewhere as needed. I also prefer traditional seatposts with setback for aesthetic and functional purposes. They better suit my admittedly conservative eye and I personally believe the help mitigate road buzz to my posterior.

Once ST angle is determined based on your individual static femur length, hip flexor strength and range of motion, you can adjust TT length and front end geometry to eliminate TCO. If you choose cf fork designs, there are fewer options available for front end adjustments, custom mandrel bent steel fork blades of course offer far more options. Smaller frames also perform better with longer trail geometry than large frames that can tend to feel slow and distant with long trail setups. A 71.5*HT with 5cm fork rake would be a fine riding and stable bike in <54cm frame size. The result would be a reduction in TCO of over 10mm versus a stock 73*/4.3cm setup. Some adjustments in lengthened TT would help as well, although I would personally never spec a frame with less than 10cm stem, the steering gets too sketchy for my tastes.

If this still results in excessive TCO, you should consider a 650C wheelset. This is typically not required in frame sizes over 50cm and really rarely on a frame over 52cm size. Give Kelly a call directly, I'm sure he can draft your frame with minimal or zero TCO.

Ride on!

[Smiley]

My mistake Mr Mac , I think most clients have a hard time understanding what " excessive " toe overlap means. I drew the line with a guy that had 3.5 cm and refused to design a 700 wheel bike for him, we ended up with a 650 wheel bike that he absolutely loves ( toe overlap ended up at 1.5-1.7 cm if my memory served me right ). This guy just had BIG feet and his cleat placement was such that he had the toe overlap in a major way. Steel forks are a excellent solution and MarvL has an Hor's with a custom steel fork with a 55 mm rake fork cause he ha a short TT and a relaxed seat angle ( 73 degree's ) and this is on a small bike with a 8 cm stem. I like you would never go shorter than 10 cm for a BIG bike and certainly no shorter than 8 cm for a small frame for stem lengths, messes with front end handling too much. Anyhow its importand to check CLEAT placement over the ball of the foot to start with as the KOP even if set correctly will be way off if the cleats are set wrong to start with. I always ask this question first. This sometmes or for me is always a trial and error thing till it feels right after its been tweaked on the road.

[dbrk]

This aversion to short stems should only refer to bicycles with "competition" geometries. When you get in the world of great audax bikes, like Singer and Herse that use what I call a French fit, these were _routinely_ spec'd with 9cm stems, even 8s on occasion. Rarely would you see a stem longer then 11cm, the occasional 12.

Stem length is a feature of the bike design's larger purpose. There is no "wouldn't ride a 9cm" in my confused little world.

dbrk

[hypnos]

Thanks for everyone's thoughts on this subject. The frame/fork in question will be steel. Will see what ideas the builder has when I speek with him later today.

Jeff

[Marron]

I am interested in the issue of short stems because my personal experience is that they quicken the steering of a bike. I had a custom Marinoni built for me a year ago and the end result required a 120 stem, about 1 to 2 cm shorter than I have been accustomed to. The resulting bike was actually quite pleasant but the steering seemed way too responsive for the purpose. My various Merckx and Rambouillet all have longish stems, 130-140, and the steering action always seems very steady to me. Comments?