Similar bikes, different handling

[rpm]

I have two custom ti bikes that handle very differently, and I'm curious as to why. The contact points (seat height, reach, saddle to bar drop, setback) and wheelbase are identical on both bikes.

Bike A: 10 yrs old, STA = 73, HTA = 74, Fork rake = 40, Trail = 56, BB Drop = 7, Front center = 58, Chain stay = 41, Regal seat all the way back on post with 25 mm setback.

Bike B: 3 yrs old, STA = 73.5, HTA = 73, Fork rake = 43, Trail = 59, BB Drop = 7.5, Front center = 57.5, Chain stay = 41.5, Regal seat all the way back on post with 35 mm setback.

Bike A has smaller diameter tubes. I recently replaced its old Kinesis threaded fork with a new Wound-Up. This bike now corners with laser-like precision. When I test it on my favorite tight downhill curve, I can take the corner at speed and it holds my line. The one handling issue I've had with it is a hint of speed wobble on a long straight downhill bridge with serrated pavement. (I haven't tested it there since the fork change).

Bike B has larger diameter tubes, especially the top tube, and a Reynolds Ouzo pro fork. It's prettier and smoother than Bike A. It's rock steady on my downhill bridge test, but it's vague in the corners. On my test curve, it sometimes drifts out, which means I have to slow down to keep from going in front of cars.

What do you think might be going on with these two bikes? In a perfect world, I'd have one bike that was smooth and stable, but also cornered with precision.

[1centaur]

Before I got to your description of handling, that's what I guessed it would be. Bike B looks designed the way I like them - a smooth handling century bike more than a nimble racer. It would be good to say how much time you spend on A vs. B, since perhaps your handling expectations are honed from a lot of time on A (like a kid who plays video games and speeds up his reactions to everything around him), and also how tight that curve is (and how fast you are going) that makes B seem sluggish going around it.

As for the wobble, look in the Calfee part of bikefanclub.com for Craig Calfee's take on wobble. Some kind of alignment issue might also be part of it.

[rpm]

1Centaur--

Thanks for the feedback. I spent 7 years on A and bought B for a trip to the Alps, where I figured A might be a bit sketchy. I've ridden B quite a bit more since then. I've just been nagged by a little disappointment in B because I read people's raves about bikes that they say have it all--comfort, stability, and snappy handling. It also surprises me that such small measurement differences have such big effects. I'll check the calfee site on speed wobble. Maybe the problem will have gone away with the new fork.

[Ken Robb]

if you have different wheels and/or tires that could be the reason for the difference.

[Dave]

New forks are often purchased without considering a possible difference in length. If the length difference is significant, the HTA will change and so will the trail, even with the same fork offset. Trail = R/tanH - offset/sinH. A difference in H (the HTA) might be corrected by deliberately selecting a different offset to correct the change in trail. What I'm saying is that the trail may no longer be 56mm with the new fork. FWIW, I get a 55mm trail with a 336mm radius tire.

At 365mm, the wound-up is one of the shorter models around.

http://www.advancedcomposites.com/woundup.htm

[christian]

On my test curve, it sometimes drifts out, which means I have to slow down to keep from going in front of cars.

What do you mean by drifts out?

[rpm]

Dave--
Having learned about different fork lengths from this forum, I checked before I switched, and both the Wound-Up and the Kinesis are 365 mm.

[rpm]

Christian--

On a sharp downhill right hand curve, I start reasonably close to the curb, but in mid-turn on Bike A I've often gone farther out to my left where cars are passing. On Bike B I'm usually the same distance from the curb throughout the turn.

[1centaur]

"On Bike B I'm usually the same distance from the curb throughout the turn."

I think you switched A and B - that could drive us insane!

Assuming I am correct, the next question is whether you are steering B (the slower handling bike) by muscle memory/feel that perhaps was locked in on A, or you are changing your technique and really trying to stop B from turning slower but it seems like you can't. The obvious question is whether the bike does not corner with precision or you don't corner on B with precision given the bike's more stable handling characteristics. My instinct is that this is the issue - spend enough time taking that turn on B and your technique will adapt and it will seem natural - then go back to A and it will seem nervous because you over correct it.

I do think the trail difference, aided maybe a little by the CS length and the drop, is enough to notice a clear difference vs. A, since I have bikes with those kinds of differences, but I can't comment on the difficulty of adjustment because I don't ride down mountains - my technique adjustments are easy.

There are those here with a more acute sense of "correct" balance on a bike who may make more of the front center and your likely weight positioning than I do. If so, your perfect bike may come from taking the weight balance on A, which seems like the right balance for you, and translating it to some of B's aspects, but that's more subtlety than I have.

[rpm]

Ouch, yes I did switch A and B. It's bike A, the quick one that corners consistently.

[wanderingwheel]

I'm going to agree with 1centaur on this. I have found that my Colnago racing bike, with its generous trail -- 65mm or something -- not only needs a much firmer hand to get around corners, but it also needs a lot of weight on the front wheel. My touring bike with a more usual 56mm of trail is not affected as much as the Colnago from poor cornering technique. When I hit the corners well, the Colnago can keep up with anything. In fact, I caught a group of motorcycles while descending Mt. Palomar a few weeks ago. Now, my touring bike almost feels too nervous; I can corner at will while still sitting up on the tops.

[Dr. Doofus]

you think a bunch of internet yabboes will have the answer?


a frame builder or designer can tell you, and they won't tell you on an internet board


geesh...almost sounding like the drunk now...this is getting ugly....

[jerk]

you think a bunch of internet yabboes will have the answer?


a frame builder or designer can tell you, and they won't tell you on an internet board


geesh...almost sounding like the drunk now...this is getting ugly....


the jerk isn't a frame builder and he's not talking either.....

jerk