I hope that Mazda does NOT use a Torsen differential in the RX-8.

I would like a speed sensitive differential, something like the GeroDisc, or the BMW M variable differential lock.

Why?

yes MikeW, you seem like an estute fellow, and i'm not quite so... please enlighten us... :confused:

Being the owner of a turbo Miata with a Torsen, I think I know what Mike's concerns are, but I would like to hear why he wants this before I start opening my yapper.

And if his concerns are what I think they are, it wouldn't be a high priority for me, personally.

---jps

A torque sensitive differential is good for going straight when you are level (side to side weight) basically drag racing. They excel where an open differential basically sucks ass (without a brake actuated traction control system). A locked differential "spool" is probably the best for drag racing.

Since life is more than going fast and straight, a traction aiding differential is needed. A torque sensitive differential isn't good for extended differentiation (too much heat, requires a good cooling strategy). A viscous coupling clutch is a good solution, but doesn't have great compatability with ABS. So a linear speed sensistive differential is what I want. The GeroDisc looks good, but the BMW M differential has some 'history' with the silicon fluid, so the diff. can have initial torque biasing abilities.

But the reason I personally don't like torque sensitive diff. is that when cornering more torque goes to the inner wheel. When pushed to extremes, having more torque sent to the unloaded wheel means that will skid (break traction) far easier than an open differential, and skid the inner tire along biasing a little more torque than a open diff. But not under extremes, the outer wheel will have less torque applied to it. This will allow for smaller slip angles and possibly better cornering, but isn't the fun of rear wheel drive controlling the rear slip angle, hence oversteer.

Since life is more than going fast and straight
Tell that to guys like Kenny Bernstein, John Force and Warren Johnson.

Interesting. I don't know a whole lot about differentials, so I'll try to track down some information. I'm most interested in whatever will help most on the autoX course and still be reasonably priced.

If you know of any good links, please post them!

Originally posted by Rich
If you know of any good links, please post them!

Please! I posted one a while back in a thread on what kind of "special" differential the RX-8 was going to have, but I can't find it now, and it didn't have anything on hte linear differential Mike mentioned. On the other hand, I find it hard to believe that *any* part used on the m-series BMW is affordable. :)

patrickb, i was involved in that earlier dicussion about limslipdif's.
i think mikes question is similar to mine. we both want to know- what kind of dif will be in the rx8? you may have answered that at the time but i don't remember.
by the way i think this is your link
http://www.canadiandriver.com/articles/jk/at_010410.htm

Originally posted by MikeW
...But the reason I personally don't like torque sensitive diff. is that when cornering more torque goes to the inner wheel. When pushed to extremes, having more torque sent to the unloaded wheel means that will skid (break traction) far easier than an open differential, and skid the inner tire along biasing a little more torque than a open diff. But not under extremes, the outer wheel will have less torque applied to it. This will allow for smaller slip angles and possibly better cornering, but isn't the fun of rear wheel drive controlling the rear slip angle, hence oversteer. That's pretty much what I thought you were thinkin' (I know, everybody is thinking "yeah, right").

I haven't been as impressed with the Torsen as I thought I'd be. I didn't think that it would magically stick the rear end, but I can't say that it has really made that much of a difference, even before the turbo went on. And the inside wheel "barks" occasionally in tight city corners under moderate throttle, and moreso now that the turbo is in. I've had almost two years to "get used" to the way it works, and if I'd have my "druthers", I'd rather go back to an open diff.

But the difference is so minor, that it is definitely not going to cause me concern either way.

---jps