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Old 04-26-2005, 08:33 PM   #1
BajaT05
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Default Did some reading about AWD and changing tire sizes.

Well I read that in an AWD car you cannot change the rims size and specially do not change the diameter of the actual wheel (tire and rim) since it could affect the AWD system.
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Old 04-26-2005, 08:59 PM   #2
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I don't think its so much changing tire or rim size as mixing different sizes that causes problems. I am running non stock rims with 225/55-17 tires with no problems. I know if your running the donut spare you have to put the baja in FWD mode with the fuse so the center diff doesen't toast.

Bob
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Old 04-26-2005, 09:04 PM   #3
BajaT05
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Well that was just what I read and I wanted to share.... I know that different tires is NO-NO, all tires must be the same, but then I read this that the system may suffer if different tire diameter are used. The rims arent that bad but one must keep the overal diameter the same.
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Old 04-26-2005, 10:11 PM   #4
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And if you have a flat tire in the rear, Its a pretty good idea to take a full size front wheel, put it on the rear, then put the spare on front. It keeps the rear limited slip dff. happy.
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Old 04-26-2005, 11:04 PM   #5
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I know the Volvo 1998-2000 AWD systems are very sensitive to tires and tire pressure. Tires with significant tread depth difference can cause undo stress on the angle gear. When Volvo switched to the Haldex AWD system the sensitivity lessened as well as some of the AWD issues of the previous generation system.

As long as the diameter is equal at all four corners and unless you alter the angle of the driveline components, i don't see how you could damage the AWD system, whether that is with 15, 16, 17 or 18" wheels. Manufacturers offer wheel upgrade options and they do not alter the AWD systems to compensate.
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Old 04-28-2005, 08:07 AM   #6
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i have had a few 4WD and this is my first AWD but i have never heard that tire size is bad for the diff. I do know if you put bigger tires it makes the engine work harder to turn the tire which can cause the engine to not last as long as if you were running stock rim and tire size and i know if you put to big of a rim on your auto it can cause the brakes to over heat and worp the rotor.
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Old 04-28-2005, 09:22 AM   #7
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Quote:
Originally Posted by BajaT05
Well I read that in an AWD car you cannot change the rims size and specially do not change the diameter of the actual wheel (tire and rim) since it could affect the AWD system.
As others have said... you don't want to mix diameters on the same car (ie: borrow a tire from someone that is not the same diameter).

Ideally, you'd want the same diameter as the stock wheels for your replacements. Example: WRX Stock tire is 205/55-16. A 225/45-17 wheel/tire combo is the same diameter (as close to stock as you'd get in any plus size) as the stock wheel/tire combo.

It's also good practice (that someone said) that if you blow a rear tire, take one off the front and put it on the rear.

As long as all 4 tires/wheels are the same there'd be no issues. At all.
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Old 04-28-2005, 05:57 PM   #8
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You can run 27" rimz yo as long as you run four o them! W3rD
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Old 05-04-2005, 04:03 PM   #9
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Having mixed diameter tires/wheels is very bad news for the AWD system. But if you change the diameter of ALL FOUR at the same time, you will not harm anything. Your speedometer reading will be off, but that's about it.

If you need to run with a spare and you have an Automatic transmission, make sure you install a fuse into the FWD fuse holder in the engine compartment. This will make your Baja front wheel drive until you can get the tire fixed. This is all outlined in your Baja's owner's manual.
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Old 05-04-2005, 04:22 PM   #10
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As long as all 4 are the same diameter it doesnt matter how big they are. You could run tractor tires on the mofo if you want. All the driveline will see is slower moving wheels.
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Old 05-11-2005, 08:23 PM   #11
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The ABS tone generators will be off with a differant size tire diameter (all 4 of course) May mess up the TCU as well and shift wierd in an auto. Gas mileage will most likely drop. Why spend money to screw it up? Do that stuff with grandpa's 55 Chevy.
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Old 05-12-2005, 08:22 AM   #12
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Quote:
Originally Posted by baja03
i have had a few 4WD and this is my first AWD but i have never heard that tire size is bad for the diff.
Since these vehicles have LSD's different size tires will cause the clutches to slip, creating heat and wearing out the diff clutches after a while, no more LSD . The 4WD vehicles you had previously probably had open diff's and it wouldn't matter. If you had a system with part-time 4WD that locked the diffs., you may recall that that was for 'offroad use only' use on tarmac would cause the system to bind because the tires couldn't slip the way they would on dirt/gravel...
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Old 05-12-2005, 08:41 AM   #13
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Quote:
Originally Posted by wagman01
Having mixed diameter tires/wheels is very bad news for the AWD system. But if you change the diameter of ALL FOUR at the same time, you will not harm anything. Your speedometer reading will be off, but that's about it.

If you need to run with a spare and you have an Automatic transmission, make sure you install a fuse into the FWD fuse holder in the engine compartment. This will make your Baja front wheel drive until you can get the tire fixed. This is all outlined in your Baja's owner's manual.
Not in my Baja Automatic. Nor in the new Legacys either. There's no fuse to pull to disable the AWD.

I can't pinpoint when they got rid of that 'feature'.

--kC
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Old 05-12-2005, 01:17 PM   #14
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You dont PULL a fuse you INSTALL a fuse to disable the AWD. It only works for non-turbo automatic subaru models. Will not work on 5MT or 4EAT-T. We never got rid of the AWD-disable feature.
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Old 05-12-2005, 05:29 PM   #15
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Quote:
Originally Posted by RacingBlue
The ABS tone generators will be off with a differant size tire diameter (all 4 of course) May mess up the TCU as well and shift wierd in an auto. Gas mileage will most likely drop. Why spend money to screw it up? Do that stuff with grandpa's 55 Chevy.
i dont understand-- i cant change the tire size at all, even when all 4 of the tires are kept the same o.d.?
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Old 05-12-2005, 06:59 PM   #16
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You INSTALL the fuse to disable the Auto AWD for testing etc.

Changing the tire diameter much (circumferance) changes the tone generated by the tone sensors thus sending an error signal to the ABS system. A larger dia. would tell the ABS you are going a differant speed than you actually are. Ditto the TCU (Trans Control Unit) in an auto. If the O.D. is same as the OE tire your fine.These cars are not like Uncle Jake's Fordson tractor. Factory tolorance in circumferance for worn tires is 1/4 inch. Any more you will tend to screw up the center diff or limited slip if yours is equipped with one. In other words you should not install a new tire with a set of three that are 3/4 worn out.
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