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Old 07-23-2002, 04:06 PM   #1
keystone
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Lightbulb Important tire sizing information--I learned the hard way...

This information may only apply to the "Michelin Pilot Sport" tire, but in any case you should read this. Tire sizing is a very important thing when it comes to fast cars, fast turns, and reliability/predictability. I recently had a serious accident in my WRX, it was sudden and unpredictable. If you read current reviews of the "Michelin Pilot Sport" you will find most people find that they produce a slight over-steer when pushed to their limits. Now this over-steer, is not unpredictable, but just an aspect of that particular tire. The main problem with these tires only really appear if you miss-size or oversize. For instance I was running on 17x7 wheels with 235-45-17 pilots. I also had the SPT suspension... Now I never had any problems with reliability in or out of turns for 5 to 6 thousand miles. I noticed something odd, but didn't really think much of it, this was a few weeks before my accident. What I saw was discoloration/oxidation of my sidewall, these marks went well up my side wall (about 20-30%). I just thought it was normal tire wear, and like I said didn't think much of it. Another thing that caught me off guard was how my car sat on the tires. I saw a noticeable increase in sidewall flex. I thought it was nothing, I mean I was like ohh well, I was planning on getting new tires in the next couple weeks anyways... Well about a week before my accident I installed strut-tower bars (cusco front, cusco carbon rear). First I would like to say how much strut-bars help handling, they are great! With the strut bars installed my car sat completely flat into and out of turns, for the most part. Now back to the whole tire deal. Now that predictable over-steer I was talking about before, well I entered a turn, a turn I have done many times before (without the strut-bars), the tires gave a little around the turn, but nothing unusual. But as I left the turn my car started to over-steer, no big deal just give it some gas, straiten it out... Thats when my tire rolled (side-wall temporarily collapsed), my steering wheel dipped to the right a bit, and i felt the car dip as well. Immediately after I spun out...thats that... I can not blame the car for what happened, if I would have taken the turn slower everything would have been fine. I will say that my oversized tires with already weakened sidewalls, made this incident completely unpredictable. This is definitely something I will never forget, and I would suggest that you take GREAT care in selecting a tire, and size it accordingly to your wheel specs. Also if something looks odd, as in weird discoloration or wear, don't push it off. As far as my car is concerned, the body shop already deemed it a total, and I'm just waiting for the insurance. I'll be back driving again...
Drive safe,
-Dan

ps- for the record I am not saying anything bad about the pilot tire...
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Old 07-23-2002, 04:12 PM   #2
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Had you checked the pressure in your tires recently?
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Old 07-23-2002, 04:14 PM   #3
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actually during the summer I checked it almost every day...
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Old 07-23-2002, 04:21 PM   #4
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(1) How does a specific model of tire create an oversteer situation? Assuming you used the same size and brand of tires at both ends of the car, the balance of the car will not be affected. Oversteer occurs when the rear tires lose grip before the front tires. If you were using the same tires front and rear, the rear tires would not be any more prone to lose grip first whether you had Pilot Sports or RE92s or S-03PPs or whatever on the car.

(2) What kind of pressures were you running? When you noticed the sidewalls were discolored (a clear indicator that you are over-driving the tires and causing them to roll over onto the sidewalls) what did you do? Did you increase the tire pressures at all?

(3) Are you talking about strut tower bars (braces), or sway bars? Strut bars have essentially zero effect on the cornering attitude of the car, so the car wouldn't corner any flatter after installing strut bars.

(4) If you really meant to say "sway bars", then my guess is your crash was not caused by soft tire sidewalls, but was instead caused by the driver not being familiar with the handling characteristics of the car with the new sway bars installed.

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Old 07-23-2002, 04:29 PM   #5
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Patrick,

I was thinking along the same lines as you, however he does mention, "(cusco front, cusco carbon rear)", which points more towards strut tower bars.. Anyway, doesn't 235/45 seem entirely wrong for a wrx on 7 inch wide rims?

jb
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Old 07-23-2002, 04:33 PM   #6
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Pat's right. Oversteer can not be caused by tires unless they are unevenly worn(rears more worn than fronts) or their pressures are uneven.
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Old 07-23-2002, 04:41 PM   #7
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as for your reply...

1) First you can goto tirerack.com an look at test results for the pilot sport, compared to the S03 etc... Any who many factors come into play with over-steer. I believe the pilots have more of an issue with it because of sidewall design. if you compare a pilot, and S03 side by side look at the side walls. first of all the pilot has a thinner sidewall, along with that, it is also a more tapered design. The tapered design is a good idea, but bad at the same time (in my opinion), it lets your tire sit flatter at higher pressures, more so than other tires. but the downside to this is its kinda like a rubberband, once the limits are reached it "snaps", flexes. Over-steer comes into play when your front is decelerating/accelerating faster than the rear. so lifting off gas out of a turn, or braking into or out of a turn, accelerating out of a turn...
2) Strut tower braces play a HUGE roll in cornering. after I upgraded my suspension i noticed a huge improvement in handing (obviously). but was still dipping a little in and out of turns, due to frame/body flex. the strut tower brace connects your strut tops in order to disperse energy to the bar instead of the frame/body of the car. Adding these gives less body roll, along with increasing frame rigidity.
3) no not sway bars.. did i even say sway bars...
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Old 07-23-2002, 04:41 PM   #8
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I just looked up Michelin's website.

The range of rims to be used with 235/45R17 is 7.5 to 9 in. That's the reason the tire rolled over.

-Ray
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Old 07-23-2002, 05:13 PM   #9
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.... operator error....

~v6
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Old 07-23-2002, 05:16 PM   #10
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yeah, 215 is a more appropriate tire size on that rim.

225 is pushing it but reasonable

235, is a no-no
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Old 07-23-2002, 05:19 PM   #11
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WHAT TIRE PRESSURES WERE YOU RUNNING?

Please.

Kevin
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Old 07-23-2002, 05:24 PM   #12
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235/45R17 is an absolute no-no on a 17x7 rim. Maybe a 235/65R17 or so but 235/45 should absolutely not be used on such a narrow rim. Ideally, it should have been 215/45R17 or at worst a 225/45R17....anything beyond that would be courting disaster.

Later...AH
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Old 07-23-2002, 05:42 PM   #13
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1. Pat Olsen's right.

2. y2k4door is also right.

Strut Bars DO NOT flatten out your car's handling. It's impossible for them to do that. They merely make the chassis more rigid. They don't touch any moving parts, so how could they make things move less?

Also, particular tires do not cause more or less oversteer. Oversteer is something characteristic of a particular car, not of the tires it wears.
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Old 07-23-2002, 06:16 PM   #14
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Default Did I read it right....

If I read his first post and it said when he felt the oversteer he got on the gas to straighten it out. Wouldn't this worsen the oversteer?? Also, I would agree on the wrong tire application diagnosis, seeing as Subaru's tend to have understeer at the limit designed into them. Strut bars should not have affected the handling of the car that much. The 02 WRX is pretty darn rigid already.
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Old 07-23-2002, 06:27 PM   #15
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Default Re: Did I read it right....

Quote:
Originally posted by Keith99RS
If I read his first post and it said when he felt the oversteer he got on the gas to straighten it out. Wouldn't this worsen the oversteer?? Also, I would agree on the wrong tire application diagnosis, seeing as Subaru's tend to have understeer at the limit designed into them. Strut bars should not have affected the handling of the car that much. The 02 WRX is pretty darn rigid already.
not on an AWD car. That much he was right about...when you oversteer in an AWD car, unless you have soooo much power the tires will all break loose, it'll straighten out the car.
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Old 07-23-2002, 06:47 PM   #16
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Default Re: Important tire sizing information--I learned the hard way...

Quote:
Originally posted by keystone
.....but nothing unusual. But as I left the turn my car started to over-steer, no big deal just give it some gas, straiten it out... Thats when my tire rolled (side-wall temporarily collapsed), my steering wheel dipped to the right a bit, and i felt the car dip as well. Immediately after I spun out...thats that...

After your accident, did the tire and rim stay in place? because you said the side wall collapsed and in that case, wouldn't the tire came off the rim?
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Old 07-23-2002, 07:09 PM   #17
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Quote:
not on an AWD car. That much he was right about...when you oversteer in an AWD car, unless you have soooo much power the tires will all break loose, it'll straighten out the car.
Jgaurd is correct, but there is "point of no return" that people here seem to foget about when in this situation. They understand the "physics" and how to handle it, but don't get the timing right. So, they try some rally move to "power out of it", to only accelerate more towards the object they end up hitting.

I still can't believe this post. Did someone sell you the rim and tire package, or do you select all the sizes yourself? Either way, you YES, you keystone over drove your limits. Write Michelin a letter for me, so we can all see their responce on how they are at fault for designing a tire that produces oversteer. That would be pricesless..

Paul G. <-- someday, on a bulletin board far far away, someone will post how stupid they are for driving like a "bone head" and crashing their car, and then thank the lord above they didn't kill themselves or any innocent people while in the "bone head" moment.

Last edited by paultg; 07-23-2002 at 07:50 PM.
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Old 07-23-2002, 07:29 PM   #18
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I wonder who did the mounting and balancing of that tire on such a narrow rim....

This has absolutely nothing whatsoever to do with oversteer or strutbars or Michelin tires or whatever. The overwide tires did not seat well on the narrow rim and he overdrove the car with that setup. Period. Having a stiffer than stock suspension setup, worsened the situation by increasing the limits of the car beyond the capability of the weakened tires that were erroneously seated on rims that were way narrower than what the tires were designed for. No ifs or buts about it.

Later...AH
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Old 07-23-2002, 08:15 PM   #19
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I have the same strut tower bar setup, that I bought for a decent price. (well they weren't free but oh well). The front bar doesn't do anything for the car, imho, but it is nice and shiny. I thought the rear one actually stiffened up the rear a little bit. I think he has openly admitted to using the wrong size tires and just wanted to keep someone else from doing the same thing, no reason to berate him further over the subject.
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Old 07-24-2002, 07:34 AM   #20
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Ahhh yes, the American way, it can't be my fault, it must be something else, ahh yes, the tires are to blame.

Regardless of tire widths, tire pressures, etc. if you over drive your car for the conditions, you can do bad things. Most of all of the high performance tires don't give tons of warning before they break loose, it's the nature of the beast. If you don't like it, put on some RE-92s which will squeal like there is no tomorrow when reaching their limits.

So, you can blame the tires being too wide, or the tire pressures not being right, but simply put, you over drove the car for the conditions.
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Old 07-24-2002, 08:17 AM   #21
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Sorry about the accident.

235 on a 7 inch rim? I concur with the others who have expressed concern over that.
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Old 07-24-2002, 08:44 AM   #22
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Thumbs up

I give him props for fessing up and also cautioning all the others from doing what he did. Not many folks are man enough to do that !

Later...AH
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Old 07-24-2002, 09:44 AM   #23
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Yes, you learned the hard way but, thanks for sharing your experience and glad you're "ok"

Tires have specs for a reason .... maybe others will heed your advice


Luke
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Old 07-24-2002, 10:17 AM   #24
joe z
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slow down and get the right tries next time
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Old 07-24-2002, 12:57 PM   #25
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Quote:
Originally posted by paultg
...someday, on a bulletin board far far away, someone will post how stupid they are for driving like a "bone head" and crashing their car, and then thank the lord above they didn't kill themselves or any innocent people while in the "bone head" moment.
http://forums.nasioc.com/forums/show...threadid=41778



Tony
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