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"Stiffness" in wheels - power efficient, or just harsh ride?(9 posts)

"Stiffness" in wheels - power efficient, or just harsh ride?Fez
Oct 7, 2003 9:38 AM
This recent message had me wondering:

Spiderman "5500 new fork and handling problems/ help" 10/7/03 9:46am

In addition, I think I read a post from Doug or someone who stated something to the effect that various wheels ride differently, but had little effect on stiffness as it relates to power transfer.

My own experience tells me that Mavic Ksyriums ride a little rougher than an Open Pro/DA combination. This is after putting them on the same bike, with the same tires.

Many others comment that the Ksyrium is a stiff riding wheel. So is a wheel like the Mavic Ksyrium a power efficient wheel, or is it just a rougher riding wheelset? Or both?
re: "Stiffness" in wheels - power efficient, or just harsh ride?gtx
Oct 7, 2003 9:50 AM
Wheels don't flex in the vetical plane so I can't see how anyone could claim one set of wheels is more comfortable or rough riding than another set--it really is all in the tires/tire pressure. You will find differences in lateral stiffness, though.
I have heard this POV before, butFez
Oct 7, 2003 10:00 AM
I have heard your statement before. I believe that is also what Doug or someone else stated a while back.

However, I really do feel a rougher ride with Ksyriums than I do with Open Pros. I have ridden more than one set of each, and the tires and pressures have always been the same. Many others have commented how Ks ride "stiffer" than most other wheels.

So what other factors can be at play here? Would it be the spoke pattern and tension? And again, does it contribute to efficiency, or just a harsh ride?
re: "Stiffness" in wheels - power efficient, or just harsh ride?My Dog Wally
Oct 7, 2003 9:51 AM
The Ksyrium is both an efficient wheel and a stiff one. Those two qualities generally go together. It's also a pretty light wheel. When I got mine, I noticed their stiffness right away. It took me about five rides to really appreciate what they can do.
both--and likely handles better (nm)ColnagoFE
Oct 7, 2003 9:52 AM
Stiffness and rim shapesFredrico
Oct 7, 2003 10:53 AM
The shape of the rim can affect stiffness very much.

Open Pro's are box section rims, right? They'll absorb shock a bit better than Ksyriums.

Weinmann "concave" rims and other wider box section rims can be amazingly stiff sideways, but "compliant" in the vertical plane, and therefore very comfortable. Narrow, deep section, V shaped aero rims like the Ksyriums are always harsh riding. Not only are they stiffer in the vertical plane, but the spokes are shorter and can absorb less shock.

That's why box section rims are still ubiquitous on touring rigs and in stage races.
Nope OPs and Ks are roughly the same shape rim (nm)MShaw
Oct 7, 2003 2:14 PM
re: "Stiffness" in wheels - power efficient, or just hHeron Todd
Oct 8, 2003 7:55 AM
First, I am unaware of any study which shows that wheel stiffness (lateral or vertical) will affect either ride quality or power transfer. The amount of vertical deflection found in any wheel is very small compared to the deflection of a high pressure tire, fork, stem, handlebars, seatpost, and saddle. Additionally, a study by Francois Grignon () showed that aerowheels that were often perceived as stiff or harsh riding were actually relatively compliant vertically. The least stiff wheel tested was a Specialized trispoke. The stiffest was a Mavic GL330 laced 36H. An engineer at Specialized confirmed for me the stiffness issue this past August.

Second, while I have seen no data regarding the vertical stiffness of the Ksyrium wheels, I have seen data regarding the lateral stiffness. Damon Rinard's measurements () show that the Kysrium's are relatively flexible laterally. Wheel laced with more spokes to conventional rims typically are measured to be stiffer laterally.

Generally, I think that you want your wheel to be as stiff as possible. This typically indicates a stronger wheel and one that won't cause handling problems under a heavy load.

Todd Kuzma
Heron Bicycles
LaSalle, IL 815-223-1776
Oct 9, 2003 1:12 PM
I agree with the first poster - that wheels *DO* make a noticeable difference to ride quality. If this can't be shown to be true via deflection testing (or more likely, hasn't been shown to be true in the quoted studies...), it is nonetheless obvious via the seat of the pants.

This can be demonstrated graphically by substituting different wheels on the same bike, using identical tyres and inflation pressures. Spokes as well as rims make a difference.

For a hard ride use a deep alu rim (ie Velocity Deep V) and plain 14g spokes. Conversely, a low-profile box rim like an M13L or Mavic G40, etc with DT Revolutions, CX-Rays etc will make a noticeable difference.

As for the allegation that wheels make *no difference* to ride quality, and that everything depends on tyre pressure, IMHO this is complete and utter crap!!! I suppose the writer thinks old Cannondales with 1 1/4" forks had a comfy ride too...

I think the wheel needs to have enough spoke tension to stay true, but that elastic spokes make for a more comfortable and reliable wheel. Straight gauge spokes are also more likely to result in cracked rims from over-tensioning.

Durability under load is best achieved by using more, lighter gauge spokes *NOT* a deeper rim with PG spokes. Wheel dish is the biggest problem with rear wheels, best dealt with by using hubs and rims requiring less dish, and by using differential spoke gauges between the right and left sides to prevent the left spokes becoming too loose or the right spokes needing to be tight enough to crack the rim at the eyelets. Bigger tyres help too, as do stiff racks, long chainstays and anti-sway bag mounting, all of which mean less force applied to the poor abused wheels.

Strength and stiffness are *not* the same thing - a deep section aero wheel can be very stiff indeed, but will not withstand much load carrying. The annual reversion of pro teams to "traditional" box section rims for Paris-Roubaix and other cobbled classics is further demonstration of this...