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Put single new tire in front open diff or rear weak LSD (~60lb breakaway) (self.mechanicadvice)

submitted 4 months ago* (last edited 4 months ago) by venusaur to c/mechanicadvice

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2001 Infiniti QX4 Automatic 4WD with RWD bias (4WD only kicks in when rear slips)

Had to replace one tire. Should new tire be on front with open diff or rear with LSD rated around 60lb breakaway torque?

The rest of the tires have about 60% tread left. Less than 15k miles on them.

I’m thinking front but want to make sure it won’t cause pulling to one side or mess something up.

Thanks!

EDIT: I know I should do pairs. Wondering if anybody had an opinion if I just kept the one.

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[–] venusaur 1 points 4 months ago (1 children)

Yeah I get that. Thanks for the advice. Could you tell me what’s best if u just kept one?

[–] [email protected] 1 points 4 months ago* (last edited 4 months ago) (1 children)

Since it sounds like front engages less (being an open diff, I guess they use the brakes to bias torque between sides), I'd go there.

In my opinion, the concern over tire replacement is overblown, especially with systems like Audi uses. Subaru uses a full-time system, that would be more concerning, but even there I'm not so sure any more.

I'm sure your LSD is some kind of hydrostatic, that was Audi's claim to fame from the start. Hydroststics don't care one whit about different wheel speeds.

Even a Quaife (torque-biasing using gears) wouldn't really care all that much, and it would effectively be engaging all the time... Which they kind of are anyway.

Clutch-based LSDs (old style, just springs and plates) would be a concern because it would cause more wear there, but you don't see those on road cars. Modern clutch-based diffs like Bendix supplies to Honda (and other companies) wouldn't care, since each rear wheel is independently (wet) clutched, and the clutches are electro-hydraulically controlled. It would simply compensate for slip, like it's already doing all the time anyway.

[–] venusaur 1 points 4 months ago* (last edited 4 months ago) (1 children)

Thanks for the opinion! Yeah it’s an old car that doesn’t bias left and right. Just front and back so if the right front slips all the power in the front goes there. No ABS LSD.

The LSD is old clutch type so that’s what I was worried about. Wearing out the plates/discs.

I’ll move the tire to the front. Thanks!

[–] [email protected] 0 points 4 months ago (1 children)

Wait, Audi used a clutch type LSD, ever? Wow, that's nuts - I had no idea. . They broke ground bringing out hydrostatic diffs for the WRC B series in the 80's - they were the first to pull off 4WD/AWD in racing back then, and kicked ass because of it.

[–] venusaur 1 points 4 months ago

Hm maybe you misread. I have an Infiniti QX4, not Audi.