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This confuses me. The point of a differential is to make it so the wheels don't slip when one needs to be turning faster than the other, such as during turns.

So if the rear wheels are directly connected by a solid axle, doesn't that force them to turn together? How is turning handled?

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3 Answers 3

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FWD cars dont have a rear axle, the wheels are mounted independently, there may be some situations where there is a tube there, but it will not have an axle shaft.

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To expand on this, @Aerovistae, you may be getting confused after seeing cars with things like Twist Beam Suspension which can look like a solid axle from behind. –  Dan Feb 1 '13 at 10:11
I wouldn't go so far as to say FWD cars don't have a rear axle. They could certainly have a rear axle--but the rear wheels would ride on independent bearings, so you're right about the key point. From wikipedia: "An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle." –  mac Feb 1 '13 at 15:21
@mac "Stub Axle" tends to be the phrase, there. –  Dan Feb 1 '13 at 15:27

The wheels just ride independently on bearings, they aren't connected by an axle like in a RWD vehicle.

I think you misunderstand the true purpose of a differential. A ring and pinion is necessary to take the rotation of the driveshaft and change it's rotational axis. That is, the driveshaft is spinning about an axis from front to back of the vehicle and something needs to convert this rotational force perpendicularly to turn wheels.

True that differentials (non-spools) allow one wheel to "slip" but that is a design to handle that scenario rather than the true intent of the differential.

I hope this makes sense.

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I actually disagree a little with this - a differential is there to allow the wheels to turn at different speeds and there are plenty of examples of vehicles with a 'solid' drive axle. –  Dan Feb 1 '13 at 13:57
I'm with @Dan. There are plenty of mechanisms that "change the rotational axis" without allowing a rotational speed differential (notice the similar terminology--no coincidence) between the two output shafts. The purpose of an automotive differential is to allow such a speed differential. –  mac Feb 1 '13 at 15:18

On FWD cars the rear wheels do not transmit the power, they are free to rotate freely

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