I have observed that when a 4-wheeled vehicle takes a turn, one of it rear tire moves with more speed as compared to the other. For example A car is taking right turn, its right rear tire will be slower as compared to left rear tire.

How is that done?
Without this system, the vehicle wont take a turn and collapse.

  • 10
    $\begingroup$ I'll leave two of my favorite videos here. The first is a perfect answer to your question. The second is the amazing Richard Feynman talking about this exact question but in the case of trains. $\endgroup$
    – Wasabi
    Oct 7 '18 at 15:05
  • $\begingroup$ @Wasabi excellent stuff, thx. $\endgroup$
    – Phil Sweet
    Oct 7 '18 at 16:00

It depends.

The driven wheels need to be connected by a differential whcih allows power to be transferred to both wheels but still allowing them to turn at different speeds.

It's not that easy to comprehends exactly how this works mechanically without having a physical model to play with but it does work , at least within certain limits.

The problem with a gear based differential is that if one wheel loses traction the opposite wheel doesn't get any power either whcih is a big issue on slippery surfaces like snow, ice, mud or gravel.

A simple fix is to lock the diff which improves traction but means that the wheels need to slip on cornering on slipper surfaces this may be acceptable but is a problem on dry pavement.

Many 4x4 vehicles have the ability to lock and unlock their differentials according to the conditions.

A more sophisticated solution is a limited slip differential whcih allows the drive wheels to rotate at different speeds but ensures that both get at least some torque in all conditions.

There are various ways to implement LSDs but some sort of viscous coupling (a bit like the torque converter in an automatic gearbox) is common).

These are often used in conditions where vehicle performance is traction limited ie some wheel slip is frequent but not consistent eg in rallying and racing.

Modern systems allow the degree of slip to be controlled either by directly by the driver or by a computer with reference to some pre-set parameters. Indeed diff settings are one of the important driver-controlled parameters in a modern F1 car.

In a 'loose' setting any loss of traction on a driven wheel will reduce overall torque so you want ta tight diff for exiting a low speed corner conversely a tight diff will tend to push the car in more of a straight line and induce under-steer (at least in general).

This is further complicated by that fact that cornering at any speed tends to induce roll which unloads the inside wheel to the inside driven wheel will tend to lose traction before the outside one.

It isn't impossible to turn without a differential most go-karts don't have diffs and they are more essential on fwd than rwd cars. A fws car with a simple Limited Slip Diff tends to have fairly epic torque steer. But in rwd you can use engine torque to deliberately slide the rear and break traction to assist turn-in so the tyres provide the slip rather than the transmission.

This is very obvious in 'drift' racing, whcih tends to use locked or relatively tight LSD.

  • 2
    $\begingroup$ Regarding how "it's not that easy to comprehends exactly how [a differential] works mechanically", I suggest you check out the video I linked to in the OP. I find it astoundingly clear, probably the most educational video I've ever seen. $\endgroup$
    – Wasabi
    Oct 7 '18 at 15:20
  • 2
    $\begingroup$ Ah yes that is indeed an excellent explanation....good find. $\endgroup$ Oct 7 '18 at 15:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.