one tire with different tread depth than others, problem? - Subaru WRX Forum
 
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post #1 of 11 Old 01-13-2009, 01:36 AM Thread Starter
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one tire with different tread depth than others, problem?

Ok so I was on the way to work this morning and driving through a bunch of snow in Denver with my Blizzak Revo 1's. Some plastic piece came flying off a car and across the Highway with perfect timimg to be ran over by my car. I couldn't avoid it and shortly after I had an exploded tire.

So I had to get a replacement Blizzak. Problem was Bridgestone doesn't make the Revo 1's anymore so I had to replace it with a WS-60.

Now comes my question. I have about 7,000 miles on my Revo's and the tread remaining is about 8 to 9/32" and the new WS-60 tread depth is
11/32" So should I worry about my 2 rear tires having different tread depth because the newer tire will be spinning slightly slower than the older tire and maybe mess up the differential? Or is the 2 to 3/32" not enough of a difference to worry about? I guesstimated the difference in circumfrence between the three Revo's and the one WS-60 tire to be around 5 to 6 tenths of an inch (Diameter being .1875 inches shorter on the revo's). Let me know your thoughts.

Hopefully it won't make a difference. I will have to be cautious that having one different tire than the others may give me some interesting traction. But looking at the two types, they are pretty similar.



On a side note, after having to change my tire on the side of the highway in 6 plus inches of snow and slush I came to discover a few things that may be nice for others to know. One thing is that the jack that comes with the WRX in the trunk worked very well. I was doubtful at first but it worked better than some cheaper garage jacks that i have used in the past.

Another thing to note is that the tire iron that comes with the car is short. So if you use it on lugnuts that are tight than you could be in some trouble trying to loosen them. I would recommend getting a longer tire iron to store in the trunk for better leverage in case you have to change a tire.

Last edited by HUMANPIE; 01-13-2009 at 09:13 PM.
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post #2 of 11 Old 01-13-2009, 01:58 AM
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3/32 is not OK, 2/32 is reasonable. Your case is rather... borderline. I would say combine with it being a different tire, you should err on the side of it being NOT ok and look for a place that will shave the tire down some for you.

Generally 3/32 is the limit for tires of the same type. If they're not the same type, that can lead to other problems too. These two tires are close togeather though but it's still not ideal.

Oh, and put the WS-60 in the back.

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post #3 of 11 Old 01-13-2009, 02:11 PM
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Yeah, mosc is the tire guru. But, I've been lead to believe that mis-matching tire tread and types were a bad thing on subarus. But, I guess if it's shaved down some it wouldn't hurt as much. Just curious as to why it should be on the back. I'm thinking that'd screw with the rear diff. Isn't the front diff open on bugeyes? But, I guess mis-matching the front would screw with your steering.
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post #4 of 11 Old 01-13-2009, 02:20 PM
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Exactly, it's the steering. Also, we're not talking about a summer tire and a winter tire. The WS-60 and the REVO-1 are both very similarly intended bridgestone winter tires.

This is a borderline case. I think the answer is yes, it'll stress your diff and it's outside of the safety margin. That doesn't mean it's most cost effective to do anything more than shave it though.

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post #5 of 11 Old 01-13-2009, 06:07 PM Thread Starter
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Thanks for the help Mosc. I have called all the tire stores in my city and none of them shave tires anymore. I did however find a tire store in another city that can do it. $25 and the guy said I needed to drop it off cause he needs about half a day or a day to get to it and shave it. It is worth the hassle to me for peace of mind.

However I am not going to be able to get it to that store until i have put probably about 200-300 miles on it. Do you guys think this would be too much and I shouldn't drive it at all...i.e try to find someone to drive me and the tire to the store (it's a good distance away) or will I be "ok" to put the few hundred miles on it to take the tire in to get shaved?

Thanks again for your help.
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post #6 of 11 Old 01-13-2009, 06:13 PM
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Considering subaru says you can go 50 miles with the 23.4" doughnut in your trunk I think 200-300 miles with a 3/32 too tall tire is not a big deal. Lets do some math.

A 23.4" tire spins every PI*23.4" which is 1 rotation per 6.126 feet
A 24.8" tire (205/55/16 with 3/32 wear is about 24.8" tall) spins every PI*24.8" which is 1 rotation every 6.493 feet.

over 5280*50 feet, that means you've got 2433 extra revolutions on the shorter wheel. Assuming this is roughly subaru's tolerance, we can equate that amount of mismatch to your situation of 24.9" vs 24.8" and you're talking roughly 2500 miles to get that same revolution mismatch. I'd probably cut that in half because of the tire tread pattern difference and the rounding of my math here.

Basically I'm saying you can prob go about ~1200 miles and it should be about the same or less stress as going 50 miles on that short ass doughnut Subaru sold you in the trunk. Looks like our 200-300 mile estimate is in the safe zone.

I think this backs up the need to shave it in general though. We can see that 1200 miles is not really the life of a tire. If that number had been something like 25,000 miles, you may have not wanted to bother doing anything at all. Clearly though it does add up over the miles.

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post #7 of 11 Old 01-13-2009, 09:12 PM Thread Starter
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Thanks again Mosc. Your logic and math makes sense to me and that helped alot. I appreciate your time.
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post #8 of 11 Old 01-13-2009, 10:32 PM
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Mosc, you are WAY too good at this. But it was helpful to any and everyone who may encounter anyhing like this.

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post #9 of 11 Old 01-14-2009, 12:03 AM
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I like tires. It's just geometry. Much of the rest of the car is still voodoo but tires/wheels make sense to me.

HUMANPIE, I commend you for respecting the issues with AWD and tire differences and doing your homework to try and prevent problems. I hope everything works out for you.

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post #10 of 11 Old 04-01-2009, 08:52 PM
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Humanpie- I think that you might be my hero for the day. I am in Denver and having an impossible time finding someone who shaves tires. Could you tell me who you found?
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post #11 of 11 Old 04-15-2009, 04:40 AM Thread Starter
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The one place I found is in Boulder and it is called The Tire Source. Its $25 per tire and he will need the tire(s) for a few days to get to it. I don't remember the address but the phone # is 303-443-3021. Hope this helps.
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