My Thoughts on the Matter

[Dudley]

OK, here is something I have been thinking for some time about rear tire wear on our Spyders. I will use easy rounded numbers for mathamatical symplicity. Let's say that the total weight of the Spyder with rider is 900 pounds. So, because the engine if front of center, let's assume that the front axles weight is 600 pounds, leaving 300 pounds for the rear. So, the total weight resistance to ground is 600 front, 300 rear. When you throttle the Spyder, a rear tire with 300 pounds resistance to ground is trying to move a front end with 600 pounds resistance. The one rear tire has to do all the work to move the Spyder. I wish I had a high speed camera to mount off the rear fender to see what happens when a hard throttle is applied. I believe the center of the tire will bulge outward somewhat because the rear is so much lighter. This would cause the mysterious "wear in the center" question we have. Not all tires are wearing the same, as in no two riders ride the same.
Now, if anyone has a scale that can weigh their Spyder with them on it; total weight, rear axle weight and front axle weight, then we can have actual weight differences per axle instead of theoretical. Maybe together we can come up to a better understanding of what is happening.

[ataDude]

Here's my $0.02 worth... a simplified and general statement that applies to all rear-wheel-drive vehicles:

One main thing causes tires (both front and rear) to wear: scrubbing. Only scrubbing removes rubber.

Front tires are subject to two main forces: (1) lateral turn and (2) normal braking forces... both of which can cause rubber removal... even if you don't notice it immediately or in the short term.

Back tires are not only subject to the (1) lateral turn forces <more because the tire doesn't turn and follow... it's dragged around the turn> and (2) normal braking forces mentioned above, but two more: (3) acceleration and (4) engine braking... if you do that. Both of these cause additional scrubbing on the rear tire... again, whether you notice it or not... and, IMHO, much more than you may think.

In my case, with occasional heavy acceleration... combined with engine braking used in the twisties... I fully understand why I get what I get. I had the same "problem" with my Corvettes.

I forgot to add... google any m/c forum and you'll see the same topic... rear vs. front wear. You'll see it particularly in the sport bike forums... where extremes are the norm.

There are, indeed, other factors such as weight, loading, tire pressure, frame geometry, road surface, tire compounds, etc... but scrubbing is the root cause... the others are contributors to scrubbing of the tire.

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[bjt]

...
Back tires are not only subject to the (1) lateral turn forces <more because the tire doesn't turn and follow... it's dragged around the turn> and (2) normal braking forces mentioned above, but two more: (3) acceleration and (4) engine braking... if you do that. Both of these cause additional scuffing on the rear tire... again, whether you notice it or not... and, IMHO, much more than you may think...

I was going to bring this up a few different times but I was still trying to decide for myself how much of a factor that "dragging around the turn" could play in the extra wear. Its probably amplified over other vehicles like cars or trucks as the Spyder's wheelbase can be much shorter and / or because it only has one rear tire, centered on the vehicle.

[ataDude]

I was going to bring this up a few different times but I was still trying to decide for myself how much of a factor that "dragging around the turn" could play in the extra wear. Its probably amplified over other vehicles like cars or trucks as the Spyder's wheelbase can be much shorter and / or because it only has one rear tire, centered on the vehicle.

That's my story and I'm stickin' to it. Killjoy.

Actually, even on my two wheelers, I always used more rear tires than the front... typically on a 2-to-1 ratio. Seems like, for me on the Spyder, it's more like a 4-to-1 ratio.

And, I agree with the wheelbase thingy... the shorter the wheelbase, the more the drag... particularly with our big ole fat tire back there.
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[Firefly]

Multiple factors causing the rear to wear sooner - but just like a car , the drive wheels will wear sooner. Front wheel drive will wear the fronts at a faster rate. Any bike I've ever had wore the tires pretty much 2 rear for every 1 front.

In order to get more even wear, instead of just in the center, I'm going to run lower pressure and see if it helps.

[tweeder]

center wear = overinflation

[NancysToy]

center wear = overinflation

Usually...or too narrow rim width.
-Scotty

[Joey]

Not sure how the following info will relate, since it is based off of normal motorcycle tires, but good info none the less.

http://www.rattlebars.com/valkfaq/tirewear/

[Joey]

One other thought, I know this may also be unrelated, but it might be.

Years ago I read on one of the Land Rover forums about tire pressure. The argument was that on a LR front pressure was to be 28 psi and rear was 34 psi IIRC.

Any ways what the thoughts were is if you take caulk and basically draw a thick line across the tire at the recommend tire pressure. Then with normal riding weight on the bike (i.e. the rider with gear and if needed passenger and gear) then drive in a straight line for 50 feet.

Stop and look to see if the caulk has worn off. Worn in the center over inflated, worn on the sides under inflated, worn even tire pressure good.

Since this is a relatively flat surface tire this should in theory work on the spider as well.

[NancysToy]

I hope you mean chalk, and not caulk. Messy stuff that caulking compund.
-Scotty

[Joey]

yes Chalk, sorry long day.

[Dudley]

I hope you mean chalk, and not caulk. Messy stuff that caulking compund.
-Scotty

Scotty, you're sharp! I hadn't caught that one.

[ataDude]

Not sure how the following info will relate, since it is based off of normal motorcycle tires, but good info none the less.

http://www.rattlebars.com/valkfaq/tirewear/

Ah, good ole Chet at rattlebars.com One of my heroes from the early Valkyrie days... and VTX1800... and Goldwing... and.....

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[tweeder]

Usually...or too narrow rim width.
-Scotty

Yeah that too

[tweeder]

One other thought, I know this may also be unrelated, but it might be.

Years ago I read on one of the Land Rover forums about tire pressure. The argument was that on a LR front pressure was to be 28 psi and rear was 34 psi IIRC.

Any ways what the thoughts were is if you take caulk and basically draw a thick line across the tire at the recommend tire pressure. Then with normal riding weight on the bike (i.e. the rider with gear and if needed passenger and gear) then drive in a straight line for 50 feet.

Stop and look to see if the caulk has worn off. Worn in the center over inflated, worn on the sides under inflated, worn even tire pressure good.
Since this is a relatively flat surface tire this should in theory work on the spider as well.

I usually have more air in the front as theres more weight there

[NancysToy]

I usually have more air in the front as theres more weight there

But it is spread over two tires.
-Scotty