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S-works Stem question
I bought a 2005 S-works SJ a few months ago, large frame. I am 6'3" and weigh 235. I had been riding a 2003 Epic, XL frame and wanted a plusher ride to take to Moab and other places with big ledges and drops. I seem to be right at the border of L vs. XL frame. Obviously, there is a difference in the geometry of the two bikes. The Epic is more "stretched out" and when I rise from the saddle I feel very centered. On the S-works, when I stand I feel that my weight is more forward. A savvy friend suggested I change the stem of my S-works from 100 mm Thomsen, 0 degree rise to a 110 mm, 0 degree rise. I am confused as to how changing the length of the stem by 10 mm will alter my ride. Can anyone help me?
Well, I'll try, your friend has made an....
assumption. He is assuming that the geometry of the L Stumpy is the same as your XL Epic! This is NOT the case. If you look at the geometries of the two frames they are a bit different which is why they feel different. The measruements that make the most difference are listed below
Top Tube Length Epic: 638mm Stumpy: 612mm
Stem Length (Stock): Epic: 120mm Stumpy: 105mm
Wheel Base: Epic: 1128mm Stumpy: 1108
Okay, now here is a bit of a break down. Tope tube length is measured from the center of the seat tube straight across to the center of the head tube. Stem length is measured from the center of the stem clamp to the center of the bar clamp. and wheel base is measured from the center or one drop out to the other with a plumb line to the ground or floor. These are the measurements that matter most in this instance.
If you add the top tube and stem length measurements together the firgure you get is a rough "reach" calculation. To get a precise calculation you'd have to measure from the center of the seat to the center of the bar clamp and then calculate for handle bar rise and sweep as well. But for illustrative purposes this will do.
So, Total Reach, Epic: 758mm Stumpy: 717mm
You have a total of a 41mm differnce between the two. The wheel base comes into play hear too as it affects where the center of the cocpit is in realation to the frame. The lengthening of the stem will on the stumpy will stretch you out a tiny bike more, going to a 140mm stem will put the two within 1mm of each other and stretch you out an equal amount on the stumpy. BUT, it will NOT make the bikes feel the same! This is due to the overall shorter length of the frame. You will still feel even more weight foward on the Stumpy because as you stretch out more you are putting even more weight foward.
If you want to get rid of the weight forward feel when seated, then a set back seat post would be in order, and leave the stem as it is. This would move your weight more to the rear, stretch you out a little more, and compensate for the difference in centers between the two frame sizes, but only when seated. But to help with the weight forward feel when out of the saddle you will need to learn to adjust your body position over the center of the cocpit when standing. This is due to the shorter frame of the Stumpy and is something which you cannot change.
The bottom line is the longer stem is going to do nothing to chang the feel when out of the saddle, it will in fact increase the weight forward feel. It is the change in realtionship between your body and the XL frame and your body and the L frame that is the cause. It will have to be compensated for by your body position when out of the saddle. It cannot be compensated for by additional stem length. The only other way to change it would be to go with an XL frame. The TT lengths of the Epic and Stumpy in XL are identical and the "centers" of the two frames would be VERY close and would probably produce close to the same feel when out of the saddle.
Sorry for the long post, it's kind of tough to describe and explain. Much easier to show. Anyway, hope this helps.
Last edited by Squash; 11-23-2005 at 09:27 AM.
"I do whatever my Rice Cripsies tell me to!"
Die trying, not watching.
Thanks so much for the quick, detailed reply. You are very helfpul and your information confirms what I suspected. A longer stem seemed counter-intuitive given what I feel on the bike. I do have a set-back seat post (Thomsen) that came stock with the bike, but I have room to move the saddle rearward. I also notice that the more I ride the S-works, the more my body "adjusts" to the forward position - so now when I stand up, my butt starts to slide back to move my center of gravity astern. I love the plush ride of the S-works, and due to the circumstances of purchase, I am not able to get the XL frame now. I will ride it as my primary MTB and adapt to it. But it may make a great birthday present for my son (he's only 6' 1") when he trashes his current SJ frame. Thanks again.
Originally Posted by Squash