Obviously, a single solid axle connected straight through the wheels would bend if the wheels to which is was connected were to rotate right or left with respect to a vertical line (i.e. be steered). I’ve watched an explanatory video on the rack and pinion mechanism and how power steering augments this, but it didn’t show a mechanism by which the steerable wheels could also themselves be provided power. How can an engine provide power to wheels which are not perpendicular to that engine or the axle?

  • $\begingroup$ How does drive get to the rear wheels? what about the different distances that each rear wheel has to travel going around a bend? what happens when the rear axle moves up or down relative to the gearbox/ $\endgroup$
    – Solar Mike
    Commented Jun 7, 2022 at 17:33
  • $\begingroup$ Have a look under a front-wheel drive car. In Europe the huge majority of cars are front-wheel drive. Look for the drive shafts. $\endgroup$
    – Transistor
    Commented Jun 7, 2022 at 20:11
  • 1
    $\begingroup$ front wheels have a solid axle straight through the wheels only in children's toys $\endgroup$
    – jsotola
    Commented Jun 7, 2022 at 23:53
  • 1
    $\begingroup$ We've had front-wheel drive vehicles for over 60 years. Why are you asking this? $\endgroup$ Commented Jun 8, 2022 at 12:15
  • $\begingroup$ @CarlWitthoft because I am not well-versed in engineering, and could not conceptualize variable-angle rotation transfer from a starting point of no knowledge. $\endgroup$ Commented Jun 8, 2022 at 14:52

1 Answer 1


You could also include front-wheel drive in your question. It would be enlightening for you to look at what radio control rock crawlers do. It has much of the excess of a full-sized car stripped away.

But they are all basically variations of the universal joint. The variations come in different names with different tradeoffs: actual universal joints, dogbone joints, CVDs shafts, etc.

enter image description here Universal Joint: https://www.rpphobby.com/product_p/irc00220.htm

enter image description here Dogbone: https://www.rccaraction.com/drivetrains-driveshafts/

enter image description here CVD Shaft: https://www.rccaraction.com/drivetrains-driveshafts/

Something like a universal joint will have speed oscillations as the angle moves away from zero such that for a constant speed input, the output will slow down in certain parts of the rotation and speed up in others to catch up.

enter image description here https://www.pinterest.ca/pin/827958712741134409/

Most full-sized vehicles would use a CVD joint though because CVD stands for constant-velocity drive.

enter image description here https://www.kmpdrivetrain.com/driveshafts/blog-tripod-vs-rzeppa-joint/

And there's more than one way to build a CVD: enter image description here https://www.kmpdrivetrain.com/driveshafts/blog-tripod-vs-rzeppa-joint/

A second hiccup you might not have thought of is that the wheels ride on suspension arms so their distance from the differential might vary. Notice the telescopic shaft on some models while other models have a dogbone which can slide back and forth. Apparently this sliding or telescopic action is also necessary for the constant velocity aspect.

Also note that similar mechanisms are needed to transfer engine torque between the front and rear wheels since they are on suspension and thus will vary in height between each other and the engine.


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