I always thought the purpose of the spokes was to keep the rim from deforming. In other words, the spokes are tensioned enough so that the rim effectively becomes a very light solid disk.
But I recently saw a wonderful video by Brian MacKenzie of a high speed Coker downhill run.
At the bottom the Coker hits a log and takoes the rim left, then right. But it looks like the rim pops back to normal. Is that possible? Or once a rim is tacoed is it ruined forever? Would a stock Coker rim do this, or was this the new airfoil rim? If I did that with my new Bedford Coker (non-Airfoil) would I be looking to buy a new rim?
DonO
PS How do I put a URL into a word, like “here” in a post?
I am not a coker rider and i don’t know many things about coker rims but doing trials with my freestyle uni i experienced some twisted rim problems.
Seeing this video i would say that the rim is ruined. It seems to pop back to normal because the wheel keeps on turning and the damaged part goes in rear. And when it arrives at the frame, it just doesn’t fit, the wheel is stopped and the rider falls.
I believe this rim was saved, if you look as the uni falls to the ground the wheel is straight again. This is a pretty rare occurence, i certainly wouldn’t rely on this happening, but it is certainly possible. The fact that it was almost certainly an airfoil rim probably had alot to do with it, i think with a steel rim this would be verging on impossible. If you can search and find the thread that that film was originall yposted in it might give you more ideas.
P.S i’ve been wondering how to place links on words for ages, still no idea.
The easiest way, on the new forum, is to type your post and then highlight the word/s you want to use for the link. Click the 'Globe ‘n Chain’ Icon (‘Insert Link’ when you hold your mousepointer over it) and enter the URL into the prompt window that jumps up.
All other things being equal, the bigger a wheel is, the more it is subject to tacoing. The stock Coker rim is not the highest quality piece of rim out there, but has shown a remarkable ability to take abuse and “bounce back”. The rim is not going to be perfect afterward, but the stock Coker rims were never that perfect to begin with.
In other words stock Coker rims seem to be able to survive a lot more deforming than pretty much any smaller rims. I’m guessing this is mostly due to their size more than anything else.
If you search around the forums, you can find many other stories of Cokers tacoing and popping back.
Even if the rim were a solid disk, it is still easily deformable given the forces that the rim experiences. A solid disk is difficult to deform with radial forces (forces directed along the surface of the disk, towards the hub), which is why the wheel doesn’t taco when you sit in your saddle and pedal down the street.
A solid disk does not handle axial forces well (forces perpendicular to the surface of the disk). When a rider makes a hard landing on a wheel that is off-tilt, he/she applies some forces in the axial direction, which can deform the rim quite easily, no matter if the wheel is solid or spoked.
To illustrate this point, you can do a simple experiment. Pretend you’re the hub and your arms are spokes. Hold your arms straight out from your body and press one hand against a wall, perpendicular to the wall. Have a friend push on the other hand, towards the wall. You’ll find that you can easily withstand the force. Now have the friend push on your hand, parallel to the wall. You should find that it is much more difficult to withstand the force.
The main purpose of the spokes is to hold the axle in place, which in turn holds the rider up (most of the time )
thats actually happened to me as well, my coker has popped out of shape. I really think I ought to get a new rim, but for the time being I have no money, and it still works for just riding down the street and the occasional curb dropoff.
Spoked wheels aren’t actually as solid as you may think. The spokes themselves act as springs which compress and extend as the wheel rotates. If they didn’t do this the ride would be extremely harsh.
It is possible to un-taco wheels that seem beyond repair. Sometimes this involves holding the wheel above your head and whacking it with almighty force on the ground to bend the rim back to where it should be. As John Foss pointed out bigger wheels are more inclined to bend out of shape than smaller wheels. A 36" uni with a wide hub such as the UDC 36" unicycle is less likely to taco than a 36" uni with a standard width hub.
Glad you like the video, I’m glad i was able to capture it like I did! (and finally see what that crazy feeling looks like!)
The wheel had already sprung ‘back to good’ by the time it hit the ground. Had I landed with my weight on it I’m sure it would have completely buckled.
However, I was not only able to ride out of the woods on that thing, but also able to go several more rides (i tensioned it very slightyl after this ‘incedent’)
I rode a very rocky technical 13km lap at the 24hr race with this, but that lap was what made me realize I need an airfoil, as it was pretty wobbly by the time I was done.
That rim is still intact. You can see the very Log bridge Too Far rim right here
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