[rijn]

I did a quick search on this topic (reviewed the first two pages..). How does stem length affect descent stability or agility? If stem length doesn't affect these areas what does affect it? I'm not up on the benefits or disadvantages of various tube angles/geometries.

Thanks.

 

[MisterC]

minimally.

steep angles make for quicker but twitchier handling.

road bikes have steep angles.

i doubt if you could tell the difference between any two.

 

[rijn]

I flipped my stem (100mm 7 degree) upside down on my new road bike (transferred the parts). It feels very twitchy on turns and a bit on descents compared to my old bike.

 

[wim]

I flipped my stem (100mm 7 degree) upside down on my new road bike (transferred the parts). It feels very twitchy on turns and a bit on descents compared to my old bike.

Common experience with a new bike, but it's got nothing to do with the stem. How a bike feels in terms of handling is primarily determined by front wheel trail, wheelbase and rider weight distribution.

Because you're still using steering inputs learned and automated on your old bike, the new bike seems twitchy. After you ride the new bike for a while, you'll have learned and automated the new, more subtle steering inputs needed for the new bike—and you'll probably enjoy that new responsiveness very much.

 

[rijn]

I have a couple of hundred miles on the new bike frameset. I'm trying to figure out if the perceived handling issues are characteristics of the new frameset, in my head or setup issue. The new wheelbase is 101.9 vs 988.9 inches and fork rake is 50 vs 45.

 

[C-40]

trail...

Steering trail is a function of the head tube angle and the fork offset (rake). You need both values to compare. More offset speeds up the steering by reducing trail and less HTA slows it down. The bike with the 50mm offset could have the same trail, if the HTA is less (more slack).

 

[rijn]

Old:
HA 73
Rake: 45

New:
HA: 72.5
Rake: 50

 

[C-40]

info...

The old bike had a trail of 55.7mm and the new one is 53.5mm, so the new bike will have quicker steering.

Trail = R/tanH - (rake/sinH)

I used a common 336mm radius for the tire. Larger tires increase the trail and slow the steering.

 

[rijn]

C-40 thanks for the help. If there a good website or book that explains the pluses and negatives of road bike geometries? I have 700x20 wheels/tires.