Did I purchase the wrong size tires???
03-14-12, 01:37 PM
#1
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Did I purchase the wrong size tires???
I purchased some new Vossen rims 20X9 fronts and 20X10.5 rears for my RWD IS350. The tires I purchased were 235/30/20 fronts and 275/30/20 rear. I just called a place to get them installed and he told me I purchased the wrong size tires. He said I should have gone with 225/35/20 fronts and keep the same rears or keep the fronts (235/30/20) and go with a 275/25/20 rear. He says if I keep the current tires the car has two different wheel speeds on the front and rear and can cause damage to the vehicle (transmission) due to different sensor readings. Can anyone confirm this? PLEASE HELP!
Last edited by WhatYaGot; 03-14-12 at 04:59 PM.
03-14-12, 01:51 PM
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Seems a little bogus that a little bit more of sideall would cause transmission problems but then again im no tire specialist. I would say however that sometimes certain individuals go by the book too much. for example i had a person at bridgestone tell me that i could only run V rated tires. I still got my W rated tires.
03-14-12, 01:58 PM
#4
It really shouldn't matter since you have RWD. Sure the speedo will be off by a +/- amount depending on the difference in overall diameter of your new set up vs. stock, but i've never heard of this doing harm to the transmission. If you have AWD however, you're safer making sure you keep the overall diameter the same front and back. But that doesn't stop people from running different sizes on AWD either 
03-14-12, 05:17 PM
#7
^
Jeff you can probably correct me on this.
There is some truth if one get incorrect tire size to the extreme. It would throw off the speed sensors and the shift points of when the car would shift gears which harm the transmission as it would be shifting at now incorrect speeds as opposed to correct speeds with the correct tire size.
Jeff you can probably correct me on this.
There is some truth if one get incorrect tire size to the extreme. It would throw off the speed sensors and the shift points of when the car would shift gears which harm the transmission as it would be shifting at now incorrect speeds as opposed to correct speeds with the correct tire size.
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03-15-12, 05:47 AM
#12
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AS long as its RWD there is no issue. If your AWD then you want the diameter of the front and rear tires to be the same to keep the Transfer case happy. The transmission has nothing to do with it. I would say your tire guy doesn't know what he's talking about.
03-15-12, 08:17 AM
#13
Okay let's break this down:
Stock Front: 225/40R18
Diameter: 25.1 in.
Stock Rear: 255/40R18
Diameter: 26.0 in.
New Front: 235/30R20
Diameter: 25.6 in.
New Rear: 275/30R20
Diameter: 26.5 in.
Difference between Stock Front and New Front: New is 1.9% larger
Difference between Stock Rear and New Rear: New is 1.8% larger
Difference between Stock Front and Stock Rear: Rear is 3.8% larger
Difference between New Front and New Rear: Rear is 3.7% larger
So no, these are not a problem, in fact they are closer in diameter between the front and the rear than the stock tires were on the RWD model. They will not damage or ruin anything unless you get rubbing from them being taller than stock, but that's just because of their height.
Most cars run the same diameter front and rear, including the AWD models, so for most cases he would be correct, but for a RWD the shop is definitely incorrect.
As for damaging the vehicle, that seems almost impossible, the vehicle speed signal to the ECU/Transmission comes from the rear wheels only, so it honestly doesn't care what the front wheels are doing, it will shift at the same "speed" as it always has. What can happen if you have sizes that are too different is the ABS/VSC may not react properly to differing wheel speeds in situations with skid, etc., though I've found that the 2IS ECU is quite adaptable and in most cases it probably would work just fine as well. The RWD IS250 has a wide variety of stock tire sizes and the ABS/VSC computers are always the same between them. This ranges from having the same sized tires all around (205/55R16) to the staggered diameters listed above. I run 205/50R17's all around on my RWD for the winter, and my VSC still works just dandy.
So are they the wrong size? They're a bit tall, but the difference between front and rear sizes? It is correct. Will anything get damaged? Not because of the size difference between them. Was the shop right? No they were not.
Jeff
Stock Front: 225/40R18
Diameter: 25.1 in.
Stock Rear: 255/40R18
Diameter: 26.0 in.
New Front: 235/30R20
Diameter: 25.6 in.
New Rear: 275/30R20
Diameter: 26.5 in.
Difference between Stock Front and New Front: New is 1.9% larger
Difference between Stock Rear and New Rear: New is 1.8% larger
Difference between Stock Front and Stock Rear: Rear is 3.8% larger
Difference between New Front and New Rear: Rear is 3.7% larger
So no, these are not a problem, in fact they are closer in diameter between the front and the rear than the stock tires were on the RWD model. They will not damage or ruin anything unless you get rubbing from them being taller than stock, but that's just because of their height.
Most cars run the same diameter front and rear, including the AWD models, so for most cases he would be correct, but for a RWD the shop is definitely incorrect.
As for damaging the vehicle, that seems almost impossible, the vehicle speed signal to the ECU/Transmission comes from the rear wheels only, so it honestly doesn't care what the front wheels are doing, it will shift at the same "speed" as it always has. What can happen if you have sizes that are too different is the ABS/VSC may not react properly to differing wheel speeds in situations with skid, etc., though I've found that the 2IS ECU is quite adaptable and in most cases it probably would work just fine as well. The RWD IS250 has a wide variety of stock tire sizes and the ABS/VSC computers are always the same between them. This ranges from having the same sized tires all around (205/55R16) to the staggered diameters listed above. I run 205/50R17's all around on my RWD for the winter, and my VSC still works just dandy.
So are they the wrong size? They're a bit tall, but the difference between front and rear sizes? It is correct. Will anything get damaged? Not because of the size difference between them. Was the shop right? No they were not.
Jeff
03-15-12, 08:36 AM
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are you AWD??? thats the main question. if you are you might potentially break or malfunciton either your transfercase or the differential might kick hard and other weird things may happen. If you are just rwd it should not matter the tire/wheel difference from the front and back since your front tires are just rolling in neutral.
