Full size spare cover

[venturaII]

I hate not having a full sized spare tire. The hassle of not being able to use it at the rear of the car, the speed and distance limitation, etc.

Does anyone know the part number of this trunk mat which makes room for a full sized spare? I'd like to see if my local US-based dealer can get their hands on one....and if not, any ideas where I could find one? Wasn't sure if this should go in cosmetic mods or here; I assumed this section would get more traffic...moderators, feel free to move if another section is better.

http://www.ft86club.com/forums/showp...35&postcount=6

[Clipdat]

[BRZyJ]

Originally Posted by venturaII

The hassle of not being able to use it at the rear of the car

Wait, wat?

[Clipdat]

If you get a flat, you don't want to put a spare donut tire on the drive wheels (the rears), only the fronts.

Originally Posted by BRZyJ

Wait, wat?

[churchx]

If one have full-size spare wheel it's also advisable to put it in front, as more then probable for it to have way different wear then those tires on car all the time.

[BRZyJ]

Originally Posted by Clipdat

If you get a flat, you don't want to put a spare donut tire on the drive wheels (the rears), only the fronts.

Originally Posted by churchx

If one have full-size spare wheel it's also advisable to put it in front, as more then probable for it to have way different wear then those tires on car all the time.

Ah. Never really gave it any thought but that makes sense.

[churchx]

BRZyJ: Rationale being - on cars with limited slip diff on drive axle (including ours) different diameter wheels/tires will mean LSD working all the time, even when driving in straight line, to compensate different rotational speeds. Result = overheat / heavy wear, possibly even killing diff in not that long distances. Thus both in manual for ours (and for other cars with LSD, eg. FWD ones, but of course, regarding front axle then) it's mentioned to put different wheel (such as space saver) on dead axle, and move wheel from it to drive axle, if punctured tire happens to be there.
Actually if wheel and tire is of same size for full size spare, difference might not be that big, thus i might be overthinking things too much. I don't happen to have clear data of how big difference is "too big", and "how long one can drive in emergencies", so maybe being too cautious, wishing for everything in car to last longer. But f i have time, if it's not emergency, i'd probably try to put as similar as possible tires on drive axle. Full size spare one can be of different wear, different make, maybe even of different size (eg. - stock primacy, when you changed rest to some wider other tires) or underinflated by years unused, due forgetting to check it's pressures too). Front ones most probably will be more similar ones to punctured one. And it almost doesn't matter to have different sized wheels on dead axle or on car with driven axle with open diff (open = little to no friction / less heat generated), so even different wheels/tires can be safely be used there for long distances/several days.

[venturaII]

More specifically, it's because of the Torsen-style diff we use. A clutch type LSD would be much more tolerant of a small variation in diameter for a short period of time, however the way a Torsen operates, any difference in rolling circumference would create a locked condition which really stresses the unit over any sort of extended distance, beyond what you'd see in just a corner, for example.

[churchx]

venturaII: same with clutch type diff. It works on different principle, but it will slip a bit => friction => heat, and here you get again overheat, degradation of oil, extra wear, failure. Think of driving for two hours with dragging brake. No time to cool off, just more and more heat buildup. Fluid long since boiled but you keep driving that way.
There is reason for diff cooling solutions to exist. Be those extra finned covers or even solutions with external rads. But constant dragging/heating for long time in my eyes seems even worse then race abuse.

[venturaII]

Originally Posted by churchx

venturaII: same with clutch type diff. It works on different principle, but it will slip a bit => friction => heat, and here you get again overheat, degradation of oil, extra wear, failure. Think of driving for two hours with dragging brake. No time to cool off, just more and more heat buildup. Fluid long since boiled but you keep driving that way.
There is reason for diff cooling solutions to exist. Be those extra finned covers or even solutions with external rads. But constant dragging/heating for long time in my eyes seems even worse then race abuse.

The difference is that the clutch LSD has slip designed into it, whereas the Torsen is pretty much either locked or not. Driving for an extended period of time with the clutch LSD would still be a bad idea, but you'd run less chance of breaking something than with the Torsen. Would you rather replace a clutch pack or buy entirely new Torsen? I mean, neither is ideal, but I'd much rather just service the clutch LSD early.

[BRZyJ]

Interesting. So unless you carry a jack stand around or want to assume the risk of potential damage, a space saver spare is next to useless in the event of a tire issue on a drive wheel.

[venturaII]

Actually, you can get both tires on one side off the ground using the front jack point, but I've never tried it with the factory scissor jack...just a hydraulic floor jack. And even if the scissor jack would work, it's not something I'd want to do under the best of conditions, let alone on the side of the road at 2am, in the middle of January...

[churchx]

venturaII: whatever operating principle, there are such things as operating parameters outside designed in capabilities. Brakes are also designed to slip. You can cook them/damage rotors/pads/etc. Clutch is designed to slip. You can burn it by dragging too much/too long/or asking to handle too much torque. How clutch type diff would be any different, if you subject to permanent heating up to temps/heat build up it's not designed for?

[venturaII]

Originally Posted by churchx

venturaII: whatever operating principle, there are such things as operating parameters outside designed in capabilities. Brakes are also designed to slip. You can cook them/damage rotors/pads/etc. Clutch is designed to slip. You can burn it by dragging too much/too long/or asking to handle too much torque. How clutch type diff would be any different, if you subject to permanent heating up to temps/heat build up it's not designed for?

For starters, how much slip do you think there will be in a clutch type LSD if there's only, say, 5% difference between rolling circumference? That small amount of slip is much easier to manage/tolerate than the accumulative effect of that same difference with a system that is effectively locked. The clutches are in an oil bath which adds a significant amount of thermal mass and cooling, and it's not like one side is spinning wildly while the other is stationary. Driving 10 miles on a clutch LSD with slightly mismatched tires would be like taking 20K miles off a system that would otherwise have gone 150K. And even if you burn up the clutches 100% (which you won't), you still have a functional open diff. A broken spur/worm gear in a Torsen takes 100% of the miles off it's life and leaves you on the side of the road (again).


Want proof of the durability of Eaton type diffs? Look at how many are still driving around the roads after 15, 20, 30 years, and are still functional.