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what's the dif w/ long or short top tube?(7 posts)

what's the dif w/ long or short top tube?jbw
May 13, 2002 3:46 PM
so... i've decided i'm between 2 sizes. 58 top tube would be ideal, but i only can get a 57 or 59. i can adjust with the stem to get where i need, but what is the performance difference? how am i going to notice it once i get the bike dialed?
re: what's the dif w/ long or short top tube?weiwentg
May 13, 2002 3:55 PM
longer stem = slower steering. shorter stem = twitchier steering. I think. I also think this is why the pros in the TDF use long stems - they want stable handling in a long, long race.
someone correct me if I'm wrong.
yup!JohnG
May 13, 2002 5:38 PM
"Appropriate" TT length really depends on the relative leg/torso length of the rider. Long legs and short torso ===> short tt length. The converse is obviously true also.

FWIW: I recently set up a " too long" TT bike for a gal rider and had to put a 8cm stem on the bike so she could reach to levers comfortably.. Holy COW..... that dang bike went from being very stable (with an 11cm stem) to VERY-VERY squirrelly with the 8cm stem. Bad news.....!! Bottom line: A new frame with a shorter TT was ordered!

I suspect that any bike set up with a stem 10cm or longer will probably be reasonbly stable.... with the caveat that longer is generally better. Much shorter than 10cm and...... ???

Keep in mind TT length MUST (repeat MUST) be "qualified" by the seat tube angle!!! Do a little geometry to verify this for yourself.

JohnG
Back in The Dayshirt
May 13, 2002 10:49 PM
many of us went with smaller bikes because they were:

1. Lighter
2. Sprinted better

We ended up with longer stems to counter this geometry. I'm 5'11" and actually used to race on 54/54 bikes!

I'm also not sure that twitchiness is solely a by-product of stem length. I put a really long stem on a mtb to make it fit, and it became unbearably twitchy. I'm wondering if the relationship between the point where the bar goes through the stem and the hub has something to do with "twitchiness."
Eddy says 110McAndrus
May 14, 2002 4:00 AM
I read somewhere that Merckx said the 110 stem was perfect and that he'd design the rest of a frame around a 110 stem.
Back in The Daygreg n
May 15, 2002 6:21 AM
On a mt. bike, fork offset has an effect on "twitchiness" too. The standard offset of a suspension fork is 1.6. In the case of Bontragers, Keith spec'ed custom 1.25 crowns. Yes, it did make the bike more nimble, but in loose dirt or sand, a little too much steering could take the front wheel right out from under you.
not muchDougSloan
May 15, 2002 6:53 AM
I doubt you'll notice much difference. I have switched out 115 and 130 mm stems on my Colnago, and for the life of me I can't tell any difference in handling. (I like the shorter one for road racing and the longer one for aerobars for ultra events).

The smaller size will likely have a lower head tube height and stand over. If you want a very low position, the smaller might be better.

The smaller size might be slightly lighter.

Some people get all worked up over very small differences. 1 cm is only about 4 tenths of an inch. I doubt you'll ever notice.

If it were me, I'd always choose the smaller size and use a longer stem.

Doug