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Limeyboy
04-24-2006, 07:28 PM
is it an absolute necessity to replace all 4 tires when replacing one? If so, is there anywhere in the maintenance book, handbook or other documentation from Mitsubishi so I can prove this to my insurance co? they want to replace just the one damaged tire and leave the rest (with about 20% tread).

Im of the opinion this will break my car.

dohcvtec
04-24-2006, 08:29 PM
I think it is you want all 4 tires to be within like 5% of tread variance.

Limeyboy
04-24-2006, 08:36 PM
Exactly - however I need to get that in writing from somewhere, as I dont have an owners manual (assuming its in the manual)

egui42
04-24-2006, 10:13 PM
Go to the dealership. One new tire will mess the diff's up on an all wheel drive car.

vtluu
04-25-2006, 12:59 AM
One new tire will mess the diff's up on an all wheel drive car.
Uh, no. Unless the old tires are extremely worn--enough to make significant difference in overall tire diameter. Or the tires aren't exactly the same model and size.

The point of a diff is to allow drive wheels to turn at different rates. Overly mismatched tires will cause premature wear of the diff due to tires turning at different rates all the time. But if it were as sensitive as you seem to believe, the diffs would get messed up pretty quickly by other things that cause the wheels to turn at different rates. Like, oh, turning.

Limeyboy
04-25-2006, 06:03 PM
Hi Tam,
I would say the tread is 50% worn if not more on the current tyres..

vtluu
04-25-2006, 07:35 PM
Okay. Time for some high-school geometry.

Let's say for the sake of argument that the new tire comes with 8mm of tread, so 50% of that is 4mm. Say a new tire's diameter is 640mm (a bit over 25" which is about right). So one tire's diameter is 640mm and the other's is 632mm. That's roughly 1.2% difference but what we're more interested in is what this means in term of diff wear.

The circumference of the tire is directly proportional to the diameter, and the rolling rate (revs per mile) is inversely proportional, but for simplicity's sake let's just say 1.2% difference which is roughly correct. I.e. we want to find the turn radius for which the speed of two same-sized tires differs by 1.2%. That's a function of the track of the car (distance between the left and right wheels) and for the Evo, that's (stock) 59.6" or 1514 mm.

We want the ratio of the turning circumference of the outside vs. inside tire; the ratio cancels out 2*pi, and we're left with solving for ((x + 1514) / x) = 1.012. That gives us x = 1514 / 0.012 = 126167 mm = 126.2 metres.

So what this means is that the "wear" on the diff when driving a car straight where one tire has 4mm less tread than the other is equivalent to driving a car with equally-worn tires tires in a circle of 126.2-metre radius. Doing the conversion and circumference, basically that's driving your car in a circle about half a mile (0.493) long. Think that's going to do anything to your diff?

Limeyboy
04-25-2006, 09:02 PM
Sweet - so im not as worried now :) Thanks Tam!

Although they did try to palm me off by saying they would replace the alloy with a standard lancer wheel (not even a standard evo alloy) I laughed.

nyne
04-25-2006, 09:20 PM
will the standard lancer wheel even fit over the EVO brakes? lol

Limeyboy
04-26-2006, 09:57 PM
Just a follow up,

The damage is estimated at about $3000 (though I think we are still at a disagreement over the ABS). They managed to track down a replacement alloy. The insurance co has caved to replace all 4 tires thanks to (believe it or not) intervention by Capitol Mitsu. It wasnt actually the wear factor that did it, it was actually the fact the toyo proxes t1-s tires just arent made any more, and the insurance co couldnt just source the single tire. They are charging me 'betterment' on top of the deductable, so im ending up paying $700 for the repairs to the car, and a set of 4 new Yoko's on each corner. What the hey, I needed new rubber anyway.

Still would have preferred to not go through the whole affair, but as the saying goes, sh*t happens.

MitsuMan
04-27-2006, 10:58 PM
see I told you so :o