I know. Strange title.

This seems somewhat normal to me but also not normal.

When I get on it hard in 1st gear, the rear tires will break loose and the rear end wants to go right. On a road this somewhat makes sense as roads are crowned.

On a flat dragstrip it doesnt make so much sense to me.

Also, what really doesn't make sense is that I don't have a LSD. I have driven a jeep with a locker in the rear (just like a pickup with a LSD on ice) on slick stuff and by nature wen one tire spins, both do. This means both rear tires are "floating" and move around. But with an open diff, typically the tire that first breaks loose just continues to spin more and the other tire doesnt spin. This means that tire should be firmaly planted to go straight ahead and I would think that would keep the rear end straight. Again, if you drive a pickup on snow with an open diff, it will spin one tire lot, make no forward motion, but go straight ahead.

So, WTF is really going here? Am I actually getting both tires to spin with an open diff? The only way i understand for the rear to want to do that is to spin both tires.

Maybe I am over thinking and putting dots together that dont go together.

-Dana

 

My first 86 turbo did that which I owned from 93 to 95. Don't know if it was an LSD though.

Jason

 

Hmm...sounds like LSD to me cause that's what mine TS does. You can jack the car up so both wheels off of the ground, car off ofcourse, then spin one side by hand and the other should spin also.

 

mine does that with initial wheel spin but starts to even out. I have an LSD

 

lol - Dana your over thinking it...
Its simply a function of static friction (non-spinning tire) vs kinetic friction (spinning tire). At some point the work done by each is equal, which causes both tires to spin.

 

I have LSD and mine does the same. Break the tires loose in reverse. See if it goes to the left. Keep spare half shafts on hand in case of joint breakage.

 

There have been quite a few people saying that they spin both tires in a straight line without LSD... it's coming out of corners that the LSD is especially noticeable. I've autocrossed a few non-LSD cars and it was very difficult to get the power down out of corners.

If the car really ALWAYS goes right, then it could be because the engine spins clockwise looking at the rear of the car... thus attempting to lift the passengar side of the car (and compress the driver side). This would tend to make the car have slightly more traction on the driver side and slightly less on the passengar side....causing the car to steer towards the passengar side.

That's how it plays out in my head anyway.

 

Simple physics...torque and the "Right hand rule". As the tires spin forward, they create a torque with a force towards the left of the car, forcing the rear of the car to slide to the right, as the force is counteracted by friction of the tires against the ground. The way it was explained in my physics classes was if you roll your fingers on your right hand in the direction of the spinning force, your thumb will point in the direction of the torque. This indicated the torque force is to the left of the car, making the rear end kick out to the right from the force of torque.

 

The right hand rule is used for determining sign convention of moments. It is also used for determining the direction of a magnetic field resulting from the current around a coil.

If the back end is sliding to the right under acceleration, the right tire is providing more frictional force than the left one, which results in a counterclockwise moment (viewed from the top of the car) about the car's COG.

As for why the right tire is providing more grip... it probably has more weight on it. The torque from the motor (acting as opposing forces through the motor mounts) will twist the whole frame clockwise (viewed from rear), thereby putting more load on the passenger side tires. Since frictional force = coeff. of friction x vertical load, you can see why the tire with more load will produce potentially more grip. There is a point of diminishing returns here though, as the coefficient of friction changes with load. Generally you have a higher coeffiicents the lower the load... Tires are not an exact science!

And like Rogue said, once you start spinning a tire there is no longer static friction (generally speaking) but rather kinetic, which is a lower coefficient. It is a little more complicated than this with tires of course because you need some slip to generate the maximum force (slip ratio, ~0.1-0.3).

I hope I didn't just kill the thread with this boring explanation!

 

Can't you correct this by preloading the rear sway bar?

 

Toe

 

Put more rubber back there...