# RS Geometry Question



## garbec (Mar 3, 2006)

My question is specific to the 51cm RS Geometry. This particular size has a relatively slack 71 degrees HT angle and considerably more fork rake at 53mm. How will this affect the way the bike handles? Also, I was looking at one in my lbs and measured the wheel base which was 99.4cm which seems long for a frame of that size. 

I realize the long wheel base will make the bike very stable and smooth. But putting the combination of all these together will the bike feel sluggish as to it's handling or will the increased rake offset the slack head tube and longish wheel base?

Thanks.


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## PJ352 (Dec 5, 2007)

garbec said:


> My question is specific to the 51cm RS Geometry. This particular size has a relatively slack 71 degrees HT angle and considerably more fork rake at 53mm. How will this affect the way the bike handles? Also, I was looking at one in my lbs and measured the wheel base which was 99.4cm which seems long for a frame of that size.
> 
> I realize the long wheel base will make the bike very stable and smooth. But putting the combination of all these together will the bike feel sluggish as to it's handling or will the increased rake offset the slack head tube and longish wheel base?
> 
> Thanks.


To some extent you've answered your question. The fairly slack HT angle along with the rake of 53 mm results in a trail in the high 50's - about 59 mm's, which I would catagorize as predictable rather than sluggish, but that's subjective. 

You're right that the combination lengthens the wheelbase, but that's consistent with the market segment the bike is targeted for. If you check the Specialized Roubaix's geo, you'll find it's very close, with a HTA of 72, rake of 49 and resultant trail of 57 mm's, for a 52 cm frameset. Wheelbase is very close as well. Serotta used a similar approach back in the 90's, so Cervelo isn't treading unchartered territory. 

If you're coming from an R3 you might feel a slight difference in handling between the two, but whether or not it's sluggish will depend on your preferences, so I suggest test riding before commiting.


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## conejo_dan (Aug 9, 2010)

I have a 52cm 2010 Cervelo RS frameset. The slack HT 71 degree angle coupled with a 53mm rake in no way makes the bike handle sluggish. I just came off a Specialized Allez 54cm frameset and I think the handling is almost the same except maybe the RS is a little less stable on very slow uphill climbs; it tends to weave around a bit but is much stabler on downhills.

The benefit with the slacker HT angle is that there's no toe overlap. I thought the longer chainstays would influence the back of the bike handling but I don't sense anything unusual at all.

All time best handling geometry for me has got to be the Colnago c40... just a sweet balance between alert but super stable handling with a good measure of "tracking on rails" effect whereby the front wheel always feels like it naturally wants to center itself. Only thing is you have to steer with your body and not so much with your handlebars but that becomes intuitive after a while. Alas, the Colnago geometry doesn't fit my long femur, short torso body measurements too well =(.


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## dcl10 (Jul 2, 2010)

Contrary to popular belief wheelbase generally has very little to do with how a bike handles. It will decrease the turning radius, but at speed that is already limited by tire grip long before any differences can manifest themselves. Also in conjunction with certain other design features it can increase stability, but that is more a result of optimal weight distribution, and the effects can be dependent on fit. More important is the HT angle, fork rake, BB drop (which is pretty standard these days), as well as the front-center distance, which is not always proportional to the wheelbase. One thing to keep in mind is that you can always modify the handling characteristics by changing the fork. If you use a fork with a shorter axel-crown dimension you will effectively increase the HT angle, and would then be able to use a shorter rake to achieve a given trail, which would also reduce the overall wheelbase. That is if you do not wish to maintain the more stable handling characteristics with which the bike was originally designed, but by no means are you locked into a certain front end setup.


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