quote:

Originally posted by PSUAlum06:
the other issue I've heard of with student designed or fabricated wheels is out of spec rim flanges. You don't have to be too far outside of the ETRTO or TR&A guidelines to be at the point where it either takes 90 psi to get your tires to seat or your tires just don't stay attached to the wheel.

Or you can get Kodiaks and they'll take 120psi to seat....fun time to be had by all concerned....

Joannum(sp?)Graz also sport the identical Carbon wheels that TU Graz uses, which leads to to wonder if such items are available commercially...I had a poke around with TU Fast Munich's carbon wheel in 2006, they are ridiculously light and seems very well made. IMO if your team is on a diet and everything else was as light as you can get it this will be worth investigating since each carbon wheel weighs 1-2lb, where as a conventional 13 inch CNC 3 piece will be in 7-8lb minimum commercially, so in effect 1 CNC wheel = 4 carbon ones...

I heard directly from team members of cf-rim-teams that they switched back to aluminium as the lack of stiffness totally destroyed their setups including teams running cf-rims at FSG.

quote:

Originally posted by murpia:

quote:

Originally posted by J.R.:
Darmstadt,

Did you have any problem with loss of tyre pressure due to the way you mounted the valve? Carol Smith warns against mounting the valve pointing directly to the center of the wheel, stating that the centripetal force will open the valve during operation, and I was wondering how this actually plays out a FS velocities?

This is one of the reasons to always fit a valve cap. The good ones are o-ring sealed.

Regards, Ian

We never had any problems with the valve, but with the loss of tire pressure, yes.
But that was a housemade problem because we use a sandwich bed to increase stiffness with very thin layers. But we solved it, (hours of work that ended in the night before Saturday at FSG). It wouldn't have been that big to drive with the pressure loss, it was only 0.1 bars/h.

Concerning the flanges we have a special solution. Our tire "jumps" at sometimes 5-6 bars ans would easily destroy the flanges. Thats why we bolt the rim during tire mounting with an ultra-stiff 10mm thick cfrp corset to bear those huge "jump-forces". Then we remove it again.

As I said, lateral stiffness is the key to a good cfrp-rim. You can design a light rim with a good durability but the hard thing is to increase stiffness.
This needs extensive prototype testing. We developed a prototype, tested it on the Fraunhofer Institute concerning stiffness and durability (and to verify the anisotropic ansys model) and then optimized the lay up for the next protoype.
You could also indentify the critical areas and overdimension them. With this method you can still manage very light rims with ~2kg.

Look at Stuttgart, they managed incredible times with their cfrp-rim. Our car was also able to clock the fastest time in autoX on the cfrp rims (except one cone )

One thing I am curious about is how you mount and dismount tyres from carbon fibre rims. At the moment we have our own tyre machine and use 3 piece aluminium wheels. When we mount the wheel on the machine the four feet that slide out radially to lock the wheel in place damage the wheels. The face of the feet that grips the inside of the wheel have a very course pointed knurl type of pattern. The only real thing I can think of for CF wheel would be to mount rubber to the feet or something similar.

Cheers

Olly

We do it like you said. We mount plastic covers to the feet. You need to use a maschine which is in very good condition. Somtimes on older maschines the arm scratchs the rim. That would be a problem for the carbon wheel.

quote:

Originally posted by smb96:
Sometimes on older machines the arm scratches the rim. That would be a problem for the carbon wheel.

That sounds like a problem for any material, not just carbon...

Either tyre fitting damage is accounted for in the safety factors of the rim design, or it isn't. If it is, it adds weight, whatever the material involved.

Regards, Ian

quote:

Originally posted by murpia:

quote:

Originally posted by smb96:
Sometimes on older machines the arm scratches the rim. That would be a problem for the carbon wheel.

That sounds like a problem for any material, not just carbon...

Either tyre fitting damage is accounted for in the safety factors of the rim design, or it isn't. If it is, it adds weight, whatever the material involved.

Regards, Ian

I'm no expert with carbon, but after working with the Darmstadt team I got the impression that carbon is a whole lot more sensitive to scratches than Aluminum.... We had new tyres mounted yesterday by a sponsor, and they managed to damage our Kiezers, so I can't imaging having anyone other than the team mount tyres on the carbon rims.

If you want to realize very thin rim flanges the main problem beneath scratching the rim is bending due to the mounting arm. Consider that in a design. We measured these forces with strain gauges, they can become quite high depending on the mounting machine you use.

These machines you talk of, are they pneumatic?

If so, most, if not all are regulated by a regulator. Reduce the regulating pressure enough that the clamps only begin to work - this will reduce clamping force.

Clamp your wheel.

Then increase the pressure to perform the tyre mounting.

Fred