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Educate me: Tires


mmrmnhrm

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Over on the hippie boards, this message came through a little while ago:

 

Back in June i got a flat on my new car and I thought I would save a few dollars by replacing the one tire with a similar tire that was the same size but differnet tread pattern. Shortly after this change my car started running badly. High RPM's at 55 mph. To be exact it would stick around 3800 RPM's and not break until the car went under 50 mph. I took it to the dealer and they finaly admitted that there was a problem, but they didn't kniw how to fix it. They gave the car back to me and said they would get back to me when they had a fix.

 

Not satisfied with this I went through the process and filed a lemon law with txdot and demanded that my car be fixed within 30 days or replaced. On or near the thirtieth day I recieved a call from Honda asking if I would meet with the regional manager so that he could drive my car. Upon showing up, he looked at my car and had the service people to replace the one tire with one of the original tire. Wham! No more problem. My frusteration was that I had to file a lemon law case in order to get my car fixed.

I'm left wondering... can a mismatched tread really do that? I'd certainly be willing to accept that if the two tires weren't balanced, that this sort of thing would happen, but *assuming* they were (which they probably weren't, given that the shop gave a mismatched tire to begin with), could the tread alone cause that, or was something else going on?

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In a word, no. However, the aspect ratio of the tire can be different while the tread width is the same; causing differences in overall tire height. A wheel speed sensor may see this as a difference in speed, and adjust throttle, brake pressure, or whatever else the stability control system has at its disposal to correct it... resulting in a problem like the one described.
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if it was the same exact size ie. you took off a 185 70 14 and replaced it with a 185 70 14 there should have been no problem...

 

however if the tire on the other side had considerable wear it could throw off a speed sensor or stability computer....

 

tires should always be replaced in a minimum of pairs to ensure these types of problems do not occur...

 

if the dealer only replaced one tire and the problem vanished they probably also fixed something else and neglected to tell you about it....

 

hth

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Not sure how accurate tire sizes are for normal passenger cars, but for trucks a 31" tall tire often measures up to 3 inches smaller depending on the manufactors. Could have been a different brand of tire and therefore a different true height. That could be enough to cause a speed difference between the two tires, but not sure how much of a difference would be required before the transaxle would slip or the sensors would get all weird.

 

Evan

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Thanks for the comments, gang! Only one person over there made the size-difference observation. Our HCH's don't have traction control of any sort, though we do have ABS, so apart from the basic speedometer, what good do wheel speed sensors do? If I ever have to use the doughnut, should I expect the same wierdness this guy had? And no, Sigman, I've still got all four of my OEM's, hopefully for another 30k ;)
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Well to continue the hijack, but also help us understand how it does relate. If you had 2 tires with say 1" difference in size and you floored the brake pedal you'd have more stopping power on the smaller tire so it would lockup faster than the other and your ABS system would attempt to balance it out. The result would be very fun especially on a slippery surface.

 

BTW the EBD is the computer that monitors and controls ABS they work together and any car with ABS has EBD its just that not all marketing guys have caught on and marketed it as an added feature. EBD could be a 2nd level of ABS computer as well. Maybe an extra sensitive one, but I'd be more willing to be its a marketing thing.

 

Evan

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