Why does a limited slip cause the rear to go sideways?

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Truckedup
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Why does a limited slip cause the rear to go sideways?

Post by Truckedup » Sat Dec 23, 2017 7:05 am

What causes a rear drive vehicle with a limited slip or locked axle step sideways when spinning the rear tires on snow ? Or the same when locking the rear tires only when braking? Thanks
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Re: Why does a limited slip cause the rear to go sideways?

Post by joe 90 » Sat Dec 23, 2017 7:26 am

Too easy.

Because it's spinning both wheels, not just 1.

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Re: Why does a limited slip cause the rear to go sideways?

Post by Truckedup » Sat Dec 23, 2017 9:06 am

joe 90 wrote:
Sat Dec 23, 2017 7:26 am
Too easy.

Because it's spinning both wheels, not just 1.
Yes, but what's the mechanics? Is it due to weight transfer? Or that a rear skidding tire has less friction than a rolling tire so tries to pass the front?
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Re: Why does a limited slip cause the rear to go sideways?

Post by Dan Timberlake » Sat Dec 23, 2017 11:17 am

I'd say it is because a wildly spinning tire has about the same ( very low ) friction in all directions. Any small lateral force, like if the road has any crown, my hoodlum buds push sideways on the rear quarter, or the front tires have initiated any vehicle turning, out she goes.

Contrariwise, if the peg leg diff left one tire not spinning, that tire has a modicum of lateral traction so it can hold the rear in line. The mechanism of snow and ice friction apparently remains in debate, but as near as I can tell, a spinning tire smooths and melts the snow/ice interface and makes things extra slippery.

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Re: Why does a limited slip cause the rear to go sideways?

Post by PackardV8 » Sat Dec 23, 2017 1:19 pm

Agree with the above. Because limited slip often makes the driver braver/stupider with the throttle, when wheelspin does occur, it's usually more dramatic. Same-same up here in the frozen north where most vehicles are 4X4; the numbnuts are able to be going faster when the accident occurs or stuck farther/deeper when they learn there's no such tire as "all season."
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Re: Why does a limited slip cause the rear to go sideways?

Post by turbo2256b » Sat Dec 23, 2017 1:30 pm

some has to do with one wheel starts spinning then the other locks up. For quite a few years drove a 69 Mustang through quite a few winters. It had a spool and a Franklin quick change rear. It also had 275 50 front tires and 295 50 15 original tread design tires on it. Car would mill through snow better than a lot of 4 wheel drives. Wasnt much issue with side slippage. In fact it was more fun to drive in the snow than dry pavement.
Like driving a drift car.

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Re: Why does a limited slip cause the rear to go sideways?

Post by Truckedup » Sat Dec 23, 2017 5:01 pm

Do you guys ever drive in snow :D , the tires don't have to be wildly spinning to make the ass end come around...Unloaded PU truck with Posi can step sideways with the slightest throttle...
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Re: Why does a limited slip cause the rear to go sideways?

Post by PackardV8 » Sat Dec 23, 2017 8:07 pm

Truckedup wrote:
Sat Dec 23, 2017 5:01 pm
Do you guys ever drive in snow :D , the tires don't have to be wildly spinning to make the ass end come around...Unloaded PU truck with Posi can step sideways with the slightest throttle...
Only going on fifty-five years now. The first 1/4 turn which breaks traction on both drive wheels is almost the same as wildly spinning. If the drive tires aren't moving at the same speed as the vehicle over the road, it's over traction-wise. To make it more fun, just drive a 2WD diesel; all that low end torque, all that weight on the front, plus a drive-by-wire throttle, makes for the worst winter vehicle ever.
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Re: Why does a limited slip cause the rear to go sideways?

Post by piston guy » Wed Dec 27, 2017 6:26 pm

The rear end usually goes left ( making the car "turn " right.. That is because the right side tire counteracts to pinion rotation and tries to "lift" it. That is why the right rear spins in a peg leg. So add a posi , load the left and unload the right and it causes the left tire to load and "drive " harder than the lesser ( torque) loaded right. This is often why you see a drag car ( with leaf springs) jacked up a bit higher on the right rear. The body roll that lifts the left front is transferred harder to the right rear and lessening torque steer. That is without any concern about the housing being parallel to the front wheels OR unequal tire sizes on the rear.

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Re: Why does a limited slip cause the rear to go sideways?

Post by j-c-c » Wed Dec 27, 2017 8:53 pm

Truckedup wrote:
Sat Dec 23, 2017 9:06 am
joe 90 wrote:
Sat Dec 23, 2017 7:26 am
Too easy.

Because it's spinning both wheels, not just 1.
Yes, but what's the mechanics? Is it due to weight transfer? Or that a rear skidding tire has less friction than a rolling tire so tries to pass the front?
In my younger days, doing a very slow speed burnout with a LSD, allowed any of my nearby buddies, to gently push on the rear fender and make the car point a new direction with an amazingly small amount of effort.

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Re: Why does a limited slip cause the rear to go sideways?

Post by turbo2256b » Thu Dec 28, 2017 11:08 am

My 69 Shelby Mustang had a Detroit Locker from the factory. You could lock it up before staging at the tree. It would run really straight off he line.
4th gear would get a bit crazy as the car would burn the tires down the track like an old school rail.
It was realy set up like a trans am racer. I could steer the car at times just using the locker rear and just a tweak of the steering wheel and throttle

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Re: Why does a limited slip cause the rear to go sideways?

Post by pdq67 » Mon Jan 01, 2018 9:37 pm

I was on Hwy 270 going around St. Louis to the north one morning in a light rain.

Traffic was running like 60 to 70 mph both ways as usual.

Anyway, I glanced over and saw a big white 6-wheeler box-van doing a couple of donuts in traffic at speed going the opposite direction!

Nothing happened, the driver got her straightened out and everything was fine! BUT the traffic around him parted ways AND slowed way down for a bit!! He, He!!

I went on down the road and was glad it was him instead of me!

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Re: Why does a limited slip cause the rear to go sideways?

Post by CharlieB53 » Thu Apr 05, 2018 10:34 am

All roads are built with a little bit of 'crown' so the rain water will run off to the sides.

Break traction, whether it be spinning the rear wheels, hydroplaning tires on water or ice and snow and those wheels instantly want to slide DOWN HILL.

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Re: Why does a limited slip cause the rear to go sideways?

Post by lefty o » Tue Apr 10, 2018 1:30 pm

rotational torque.

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Re: Why does a limited slip cause the rear to go sideways?

Post by MadBill » Wed Apr 18, 2018 10:15 pm

piston guy wrote:
Wed Dec 27, 2017 6:26 pm
The rear end usually goes left ( making the car "turn " right.. That is because the right side tire counteracts to pinion rotation and tries to "lift" it. That is why the right rear spins in a peg leg. So add a posi , load the left and unload the right and it causes the left tire to load and "drive " harder than the lesser ( torque) loaded right. This is often why you see a drag car ( with leaf springs) jacked up a bit higher on the right rear. The body roll that lifts the left front is transferred harder to the right rear and lessening torque steer. That is without any concern about the housing being parallel to the front wheels OR unequal tire sizes on the rear.
This is true for high traction conditions but when the grip is low there isn't enough torque in play to significantly unload the RR, so road crown predominates. Try spinning the tires on a flat and really slippery surface and the vehicle won't consistently steer either direction.
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