Tire wear question. Please help

[Matt Kull]

I am wondering what is the condition that is causing the inside of my rear tires to wear. The insides seem to be wearing MUCH faster than the outsides.

There are 3 big left hand turns that I am assuming are the root of why my outside (right side) tires just generaly wear faster then the left side. However what I am seeing is that is that the inside of the right tire is very worn compaired to the outside.

Is there something in the setup that is causing this?

I would think that since karts have a solid rear axel that the rears would wear even or maybe even the outside edge wearing a bit faster due to the side bite from the inside tire lifting in the turns?

Can anyone please explain this to me, or even if there is some way to correct it?

I also have a hop in the turns that I can't get rid of no matter how soft I make the kart. any ideas?

The track is a .5mi sprint track 9 turns]

The kart is a Tony extream and I am running firestone 6" yff (same as yfb's in 5")

Thanks,

matt

[Scott Siegel]

The inside of the rears will always wear more. The reason for this is the fact that the rear axle is actually quite soft. As the kart is stressed in a corner, the axle flexes, like a smile and plants the inside of the rear tire. If you think the wear is excessive you might need a stiffer rear axle or longer hubs, which SORT OF work like a stiffer axle. As for the hop, try this:
http://www.thekartingwebsite.com/ubb/Forum8/HTML/000055.html

As always, your best help will probably be people that run with you at your track.


Scott
<><
Siegel Racing

[John Denman]

One reason the insides wear (you run a high grip track) is due to the tire flex. The tread surface rolls inwards and the inner sidewall in compression expands the tread diameter, while the outer sidewall in tension contracts the tread diameter. The axle does flex a little, but not nearly as much as the tire. Tire pressure helps a littel, but not a lot. I run 12F/15R cold on 5" (YGB) which most people say is too high.

I also run a Tony Extreme, and run with the rear bar at full stiff.

Seat position is very crucial. Fore & aft, I run about 40% front 60% rear weight.

Seat angle is important. If you are hopping, you may want to recline the seat a little by tilting it, usually by shimming the front mount up.

Lower the rear of the chassis by loosening the bearings and raising the axle (lowering chassis).

As far as rear tread widths, in some cases widening gets more bite or less bite. There are two factors at work; bending moment of the axle, and roll center. Moving the roll center moment arm out usually reduces bite, but it also depends on axle strength. A softer axle will bend more under the cantilever loads when it goes wider and gives more bite(read hopping). A stiffer axle does not bend as much and will bite less when moved out.

Front tread width is usually just the opposite. Front tread width has more factors involved; bending moments, roll center, scrub radius, castor and transfer stability (virtual swing axle length equivalent for suspended cars) among them. On your kart moving the front out is less front bite.

I would start with seat position, fore & aft to get weight around 42/58, then tilt it so the front is about 1.5-2" above the tabs. The seat bottom will be flush with the bottom rail. This should get you to 40/60.

Stiffen rear bar.

If you add weight (you run heavy right?) lower the weight.

Shortening the steering shaft an inch will lower your arms slightly and drop the center of gravity, but I would do this as a last resort to chip away at the hopping.

Lower the rear chassis. If it still hops, ask Collin Lynn about checking the axle.

Most important, is if you are running the backwards race, be sure the tires are stacked on the other side of the flagstand!

I won't be there this weekend.