11-23-2017, 03:01 PM | #1 |
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Torsen diff and rear tire size sensitivity
This morning I switched on my winter tires and headed to PA for Thanksgiving. While driving I kept thinking, "Hmmmm, somethings weird. It must be windy or something because I'm making a lot of steering corrections.
Then a few minutes later I realize that every time I stepped on the gas the car was turning slightly left. And when I let off it was turning right. At low speeds you didn't notice it but at 80 on a straight highway it is very noticeable, and actually incredibly annoying. I hypothesized that the right tire might have more tread, making it a little bigger, thus putting down more torque now that I have an LSD. I measured the tread depth with a quarter and couldn't see any difference. This left me scratching my head. What the hell else could it be? I got to my parents and took both wheels off. Sure enough the right tire was just a little taller than the left. But we're talking less than a quarter of an inch (maybe 1/8th?) measured using a level. Could this possibly make that much of a difference?? So I swapped the wheels and sure enough, the symptoms reversed. The car now pulls right when accelerating (at least I think it does.. it was a crappy test on curvy roads.. I'll know for sure tomorrow.) I think this is a problem that will go away on its own because the larger tire will wear faster. But I wonder if it's bad for the torsen gears to be working this much while it wears down? I might also put more air in the smaller tire, but not enough to make them completely equal. Either way... Torque vectoring diff FTW! |
11-23-2017, 04:16 PM | #2 |
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If the tread depth is the same, how is one tire taller than the other? Unless they’re different tires or sizes.
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11-23-2017, 04:20 PM | #3 |
Relic
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It'll behave that way on an open diff.
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11-23-2017, 04:57 PM | #4 |
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11-23-2017, 04:58 PM | #5 |
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11-23-2017, 07:00 PM | #6 |
Relic
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We explicitly noticed it on Mike’s 335 when he had one new and one half used tire in back, before he put an LSD on.
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11-23-2017, 08:13 PM | #7 |
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Interesting. Maybe the effect exists either way, and it's just multiplied with the LSD. I know I've run different depth tires in the rear (much more than this current difference) and I never noticed it.
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11-23-2017, 09:11 PM | #8 |
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I noticed this on a 991S that I test drove. Must have been the tires but turned me off that particular car (not the 991S in general). On throttle one direction, off throttle the other... Slightly. I figured it must have been tire related but could not see obvious signs.
This has been informative. |
11-23-2017, 09:15 PM | #9 |
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I'm mostly shocked at how extreme the effect was given the small wheel radius difference. Driving the car at 70+ was incredibly annoying. Constantly corrections needed. On and off the gas created a zig-zag effect.
With one tire at 34psi and the other at 38 the effect is still there but to a smaller degree. The larger wheel is putting down more torque so it will wear down... it's just a question of how long it takes. Last edited by rumatt; 11-23-2017 at 09:27 PM. |
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