Lateral rigidity of the rear wheel, question for wheelbuillders

[53-11]

My question is why don't you see more front to rear spoke ratios like 28/36 or 24/32?

It seems to me that the front wheel has more distance in between the flanges ( in addition to no dish) plus a much smaller load to carry, why are they being made with equal spoke or only 4 less spokes than the rear.

Furthermore, I can see the advantage of mixing spoke guages on the rear (thicker spokes drive side), but why change the lacing pattern? (3x vs 2x on non-drive side)

[christian]

Price. That's the only reason. It's cheaper for OEMs just to order a bunch or 32h hubs and 32h rims and lace those up, not having to worry about what rims are front rims and rear rims and so on.

I like to run 32/36 and 24/28 on my bikes.

- Christian

[flydhest]

Lots of wheels have asymmetric rears. I often build my wheels to use very light spokes on the non-drive side and stout ones on the drive side. The Eurus and other Campy G3 spoking wheels have things asymmetric, I think. Dave Thomas of SpeedDream wheels has a mismatch in the number of spokes he uses in the back for some wheels.

[zap]

Concerning more extreme front to rear spoke counts, this would work best with stiffer rims such as carbon offerings by zipp and especially nimble, maybe even Mavic's CXP 33 rims. The front wheel still needs to be stiff for that winning sprint.

Rear wheel design gets pretty tricky. I like the idea of having more spokes on the drive side and less on the non drive side. Mavic does something different with their isopulse design by using radial lacing on the drive side and cross pattern on the nondrive side. This is another attempt at evening out spoke tensions to improve durability. It must work otherwise those al spokes would break pretty quickly.

An arguement could also be made for a higher non drive hub flange like the original Mavic cassette hub and current AC rear hub. This helps increase n/d spoke tension a wee bit.

Best bet for rear wheels might be trispokes built by HED and Nimble.

[Ti Designs]

You can ask a dozen wheel builders what would be the perfect wheel and you'll get 13 answers. Everybody has their own version of the perfect wheel, everybody weighs different parameters differently. Rolf wheels (Bontrager wheels use the same design) use paired spokes. The concept is simple, if you were to build a light wheel with 18 spokes there would be a 20 degree open span between spokes, one spoke pulling left, the next spoke pulling right... The result is a wheel that waves side to side under the tension of it's own spokes, or a heavy wheel due to the need of a greater restoring constant of the rim. So, Rolf paired the spokes and that problem went away (along with a number of others). A new problem popped up, they aren't fault tolorent in the least - one broken spoke will bring the bike to a hault.

Cross patterns place the spoke at an angle off the hub which allows the hub to transmit torsional forces to the rim. It comes down to simple vector force calculation, with the COS(angle off the hub) as the force transmission. OK, it's not as simple as that, it's a balanced tension system... A 36 hole built x4 is pretty damn close to 90 degrees, the angle depends on the number of spokes, the cross pattern, the size of the hub flange, the diameter of the rim and the phase of the moon (just kidding about that last part). On the flip side, spokes can better take a radial load with less angle off the hub, which was the idea behind all those radial front wheels that showed up on everything a few years back. A radial wheel is not a balanced system, there is no left pulling and right pulling wind-up tensioned agains each other. It's simply spoke tension holding rim. If the rim moves or is damaged the whole structure of the wheel goes. Many companies built radial wheels for their production bikes AND STRESS TESTED THEM. Many individuals build radial wheels and don't have the test equipment to stress test them, and lots of them fall apart.

If you must ask about different spoke patterns on the two sides of the wheel, or the effect of fewer spokes on the whole system, it's not that hard to understand. The system is the summation of all of the tensions (let's just assume there are no compression forces here, it leads to too many flat tires). Hmmm, this is where a picture is worth 1000 words (without any spelling errors). I'll have to come up with a few diagrams for how it all works - give me a few days, I have some serious saddle time scheduled.