Need some input from Geometry wizards- Mtbr.com

# Thread: Need some input from Geometry wizards

1. ## Need some input from Geometry wizards

I finally have dialed in my perfect gear ratio 1.94:1 (using 33t chainring and 17t freewheel), but there is one problem. When I am climbing loose rock spots in the trails I ride the back end slips a little more than I would like. The normal answer would be to use a 16t freewheel so that there is less torque (this may be wrong).

The question I have is, if I had a frame with a longer top tube and used a shorter stem to have the same effective top tube length would more weight be shifted back to the rear wheel when I stand to climb? Or would I have the same problem?

Dave

2. Have you tried just leaning back a little more. Or have you tried a different rear tire?

3. Leaning back does work, that was the principal for the question. The problem is that it is less comfortable for extended climbs. As for the tire (Paneracer fire), it hooks up so good on everything else I dare not change it, but I have tried several other tires in the past.

4. You'd have a heavier bicycle but the weight on the rear is almost the same.
On the plus side you could counter-pull the bars harder since you'd be less likely to wheelie.

5. Originally Posted by The Tree
I finally have dialed in my perfect gear ratio 1.94:1 (using 33t chainring and 17t freewheel), but there is one problem. When I am climbing loose rock spots in the trails I ride the back end slips a little more than I would like. The normal answer would be to use a 16t freewheel so that there is less torque (this may be wrong).

The question I have is, if I had a frame with a longer top tube and used a shorter stem to have the same effective top tube length would more weight be shifted back to the rear wheel when I stand to climb? Or would I have the same problem?

Dave
The TT length/stem length thing is moot.

You don't say whether your slipping problem is while you're standing or sitting, but in either case you'd be better served by shorter chainstays. These will bring the rear wheel closer to the cranks (where your weight is while standing) and closer to the seat (where your weight is while sitting). Additional weight on the rear tire will help improve traction.

Yes, a taller gear will help you spin less, so long as you are strong enough to push it. I like to combine a taller gear with a longer crank. Torque is increased but so is the ability to effectively meter that torque due to the longer lever/crank.

--Sparty

6. ## Agree completely w/ Sparty.

He's said all the big important points on this question.

7. Originally Posted by Sparticus
The TT length/stem length thing is moot.

You don't say whether your slipping problem is while you're standing or sitting, but in either case you'd be better served by shorter chainstays. These will bring the rear wheel closer to the cranks (where your weight is while standing) and closer to the seat (where your weight is while sitting). Additional weight on the rear tire will help improve traction.

Yes, a taller gear will help you spin less, so long as you are strong enough to push it. I like to combine a taller gear with a longer crank. Torque is increased but so is the ability to effectively meter that torque due to the longer lever/crank.

--Sparty
Seat tube angle is a factor, too. Given the same tt/stem length and chainstay length, a laxer ST angle will put more weight over the rear while seated and farther forward when you stand.

8. ## Thank You

Thanks for all the input. It really shows how complex subtle changes in geometry can change a bikes handling.

Dave

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