Diagonal spin test

why only center locking differential is not enough. Diagonal spin test.

These videos show a Subaru Forester (2.5 A/T) whose diagonally opposed wheels have lost traction. This is a typical off-road situation where most four-wheel drive vehicles fail.

The car does not have an optional rear Limited Slip Differential neither it has an electronic traction control system. One of these devices could have helped to move the car forward.

These videos show a Jeep Grand Cherokee whose diagonally opposed wheels have lost the ground contact. The front left wheel and the rear right wheels spin. This is a typical off-road situation where most of the four-wheel drive vehicles fail because they do not have a locking differential in either of the axles.

As a rule, neither electronic traction control systems nor limited slip differentials help here. This is because these traction devices cannot transfer enough torque to the wheels that are on the ground. A fully lockable differential installed in the rear axle is needed to get the car moving in these conditions.

A few vehicles with electronic traction control systems are known to be able to deal with diagonal spin. Suzuki Vitara II, Subaru XV, and 4th generation Subaru Forester (2013-) are some of them. Their traction control system is very aggressive and able to bring the spinning wheel to a full stop. Look at the following video (from 9m14s).

Start watching the following video from 1m07s.

Have you seen a better description of Why Only Center Locking Differential Is Not Enough. Diagonal Spin Test. in a paper magazine? Can you please scan it or take a photo and send it to ?

This is a Wiki, so feel free to correct any factual or grammatical error. Test here before posting.

There are 6 comments
October 03, 2015 - 07:00
March 11, 2015 - 17:09

"As a rule, neither electronic traction control systems nor limited slip differentials help here."

"Electronic traction control" is a confusing term in this context. Usually traction control refers to reducing engine output in case of spin, which is not very helpful here. "Brake-based diff anti-slip" or something might be better.

"Limited slip differentials" usually do work. Strong passive slip/speed-sensitive diffs (the Jeep is a special case), active clutch pack LSDs or passive torque sensitive LSDs with the brake trick are fully capable of providing enough anti-slip torque to move the vehicle forward.

Norman Silva
December 25, 2013 - 04:36

You need to update your videos. The 2014 Forester has traction control.

You also need to simplify your spam guard. The words are illegible and the sound is inaudible. Don't you want people to contact you?

September 24, 2012 - 09:23

I've heard Eaton locking diffs are very good--right up to the point where they explode.

November 27, 2009 - 07:58

Actually that Jeep has speed sensitive differentials front and rear.
The problem is that the front differential is 'tuned' too conservatively. The outlet port is too large, and the maximum pressure relief is too low. [and he isn't giving it enough gas! the power transfer is proportional to torque and speed difference. He has the speed difference but isn't applying very much torque at all]
Ideally you'd want torque sensitive differentials front & rear, so you can do the Hummer/HMMWV 'trick' (apply service brakes, apply throttle, slightly release brakes and the torsen differentials will make sure you get torque to the wheels with traction)
That is the route that Jeep went with in the Wrangler Rubicon models (and they can be mechanically locked too!)

As you show in the Jeep section, the next generation of Grand Cherokee removed those limitations. Clutch pack clamping pressure is now regulated electronically.

Reply to George
November 27, 2009 - 10:16

Thank you for contributing to this web site, George. This is very valuable information that you are sharing.

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