Question about AWD

[Dominic Richens]

i read this in the manual for my legacy too. but i have a manual
transmission. what do i do if i have to use the stupid little spare?

<conjecture>
I'm guessing the AT have speed sensors on all wheels and adjust the transfer
clutch pack accordingly. Therefore if one wheel is always turning faster it
may drag the clutch to try to compensate, thus burning it out.

As for MT, there are no wheel speed sensors and the front or rear
differential balance out the difference in speed such that the two drive
axels are still turning at the same speed.
</conjecture>

Yes, I know the doughnut is the same diameter, but being skinnier I'm sure
it deforms more, beyond the 1/4" circumference allowed for.

 

[tonyrama]

sure
it deforms more, beyond the 1/4" circumference allowed for.

Yeah, but if it deforms that much it's underinflated, isn't it?
Tonyrama

 

[null_pointer]

Yes, I know the doughnut is the same diameter, but being skinnier I'm sure

it deforms more, beyond the 1/4" circumference allowed for.

This might not be the case as these tires are supposed to have around
60 psi in them. But since they are often neglected to the point where
they may actually have much less, your point stands.

 

[Bruce Hoult]

<conjecture>
I'm guessing the AT have speed sensors on all wheels and adjust the transfer
clutch pack accordingly. Therefore if one wheel is always turning faster it
may drag the clutch to try to compensate, thus burning it out.

As for MT, there are no wheel speed sensors

There are if you have ABS.

-- Bruce

 

[Dominic Richens]

There are if you have ABS.

(*sigh*)

 

[Nicolas Dore]

Mike Deskevich wrote :


I was told, though I haven't checked, that the spare is
the same diameter as a regular wheel, it's only smaller
width-wise. So it shouldn't cause any problems.

Hello!

Just checked and it seems the spare on my Legacy is a 135/70-16 tire,
which roughly gives it a 5% circumference difference from the stock
205/60-15 (used this tool to check:
http://pw1.netcom.com/~sgalaba/tiresize.htm ).

That is way above the factory specificed maximum difference (not
commenting on whether that spec makes sense or not, that's a separate
discussion... ). Hence the need to use FWD mode.

Nicolas

 

[marc]

Partially correct,\

Auto uses hydraulic fluid shift, 40/60..

MT uses ltd slip viscous coupling 0/100

no damage to MT though 4EAT will be damaged.

Marc