Will I damage the diff.???

[ej22t]

Hi all, hows going.

Just have an questions before going to winter rally this weekend!
Since I have a set of winter tire in 215-60-15(I know its irreguler size but I got it free from a friend of mine so I just use it for winter)
Since its an overnight rally so I would ike to bring 2 summer tire for spare. The summer tire size is 205-55-15.
What if I put 2 205-55-15 in front (in case of run flat) will I damage the center diff? or should I put at the back?
Thanks for reply!

Ben

[rallysam]

It doesn't matter whether you put them front or back - either way they will be turning at a different speed than the other set. I don't know for a fact what would happen, but I wouldn't do it... unless it's a junkyard beater you are running into the ground and you really don't care.

Subaru's spec is absurd - they say the circumferences must be identical to within 1/4". I don't know if I really believe that is necessary, but I wouldn't go WAY over it. If I do my math right, your tires circumferences would be different by 2-3" or so.

[BAC5.2]

It'll fuck up the diff.

Like Sam said, the Subaru Factory difference limit is some outrageously narrow variance

[NuwanD]

Hey Ben, how are you?

You may be asking since everyone's been talking about it lately because I had a flat at the last winter rally. Happened right before the drivers meeting. Anyways I ran 1 195/65/15 in the rear in place of the 205/55/16... by A4 there was a smell whenever we stopped at checkpoints, by A7 we could smell the burning diff fluid. I don't think it's the overall size so much as the traction difference between the varying tires, last rally was very slippy and i'm sure I was spinning that spare non-stop for the 3 hours before retiring.

[rallysam]

Hey Ben, how are you?

You may be asking since everyone's been talking about it lately because I had a flat at the last winter rally. Happened right before the drivers meeting. Anyways I ran 1 195/65/15 in the rear in place of the 205/55/16... by A4 there was a smell whenever we stopped at checkpoints, by A7 we could smell the burning diff fluid. I don't think it's the overall size so much as the traction difference between the varying tires, last rally was very slippy and i'm sure I was spinning that spare non-stop for the 3 hours before retiring.

Also note that those tires are better matched than the original poster's situation. If I do my math right:

Original poster's situation has a circumference discrepancy of 4"
You have a circumference discrepancy of 0.3"

[scuzzy]

205/55/16 = 78.2
195/55/15 = 78.5

215/60/15 = 79.2
205/55/15 = 75.1

So yes, you did your math right.

In either case, you'll smoke the differential in very short order Somewhere around 10 miles for the 0.3" difference, somewhere less than one to two miles for the 4" difference.

that's not to say that if you only go half a mile you'll be OK, going any distance like that is very bad for the differential.


This is why it's also important to check the air pressure in your tires on a regular basis. a low tire can give you that 0.3" difference.

Hey Ben, how are you?

You may be asking since everyone's been talking about it lately because I had a flat at the last winter rally. Happened right before the drivers meeting. Anyways I ran 1 195/65/15 in the rear in place of the 205/55/16... by A4 there was a smell whenever we stopped at checkpoints, by A7 we could smell the burning diff fluid. I don't think it's the overall size so much as the traction difference between the varying tires, last rally was very slippy and i'm sure I was spinning that spare non-stop for the 3 hours before retiring.

Also note that those tires are better matched than the original poster's situation. If I do my math right:

Original poster's situation has a circumference discrepancy of 4"
You have a circumference discrepancy of 0.3"