Quote:
Originally Posted by Gforce
No problem. My main point was to reassure the poster who seemed concerned about the use of the space saver spare. (The Chris Harris video of using four on that Mercedes had me practically in stitches. Now he's quite the wheelman).
If you have a clutch type LSD then you need to be concerned about wear from different sized drive wheel/tires. Not with a Torsen though.
Anyone using a space saver also needs to be aware that the traction characteristics of those tires are markedly different from any regular tire. The speed limit for those tires is 50 mph /80 km/hr for good reason. The wheel speed inputs will likely be off and that may affect a lot of driver aids some drivers rely on. Hence the warning in the owner's manual.
That shuddering you experience from the Torsen in the BRZ results from the high bias ratio. At low speeds in tight corners the Torsen reaches the limits of its capability to differentiate and you feel the slower moving tire being actually over speeded just like a four wheel drive with locking hubs. Only it's a rear tire that is getting pushed faster than the car is travelling. In effect forcing the tire to "slip."
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Ok, I'm sold. ...more or less. I don't sweat a donut on an open diff because involutes. I also see your point regarding service life and the difference in contribution to heat dissipation.
I'll change my tune with appreciation for some good honest schooling and maybe even sketch some free body diagrams to convince myself. I may come back here with more questions.
Your point I emboldened is probably the most important observation for the casual reader.
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Kronos, nevermind the fluid change but do heed the owner's manual's guidance in the future. It may not be tragic to drive in a constant turn but it certainly isn't doing anything to extend the life of the diff.