I was browsing through some historic race cars on wikipedia and saw that the famous Porsche 935 Moby Dick has no differential at all. Why would this be used? Wouldn’t it seriously impair handling and tire wear?
In: Engineering
It had essentially a locked differential. This means that both drive tires are being driven at the same speed at all times.
Pros: Extra traction. An open differential such as on a modern passenger car really only drives one wheel effectively, since as soon as one wheel breaks traction you lose acceleration. A limited slip differential is a step up, in which there is a small speed difference allowed between the wheels, and a locked differential is maximum drive traction.
Cons: Reduced handling. A locked diff reduces how easy it is to make the car turn corners. It will cause the car to try to drive straight. This can be a problem, but the 935 had so much power that 1, it needed the extra traction on the back, and 2, the extra power meant that it would wildly oversteer in corners (oversteer is when the rear of the car breaks traction while cornering and slides out). The locked diff tamed that a little and allowed extra power down during cornering.
Since it was rear engined, it probably used a trans axle. That’s a transmission and differential in the same package.
I can’t tell you why that Porsche has no diff, but I know that many of the race cars that have no diff are missing it specifically in order to make drifting easier and more controllable. Sprint cars, for example, have no diff.
I can speculate on likely reasons why the Porsche might be missing a diff. I know that limited-slip differential technology was pretty lacking back then, and so perhaps a solid axle was a better choice, to negate tire spin on the inside wheel.
If a car with an ordinary diff sends a lot of power to the drivewheels, the tire with the least traction is likely to spin, and then the other wheel gets little to no power at all. A solid axle negates that problem; both wheels get the same amount of power, and in order to break loose, you need to break *both* wheels loose, which is much harder. Obviously limited-slip diffs do an even better job, and modern traction control systems are even better again, but older cars or cars in classes with limited tech or budget might still use a solid axle.
It looks like it was designed mainly to kick ass in endurance races, where other factors (like straight-line speed and not breaking down) matter more.
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