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Old 03-31-2012, 11:50 AM
Big time Big time is offline
Join Date: Feb 2011
Posts: 134
Transverse rear-mid engine counter torque to help or hinder wheelstand?

An engine tends to create countertorque on its engine mounts contrary to the direction it spins.

Top fuel dragsters are an extreme example of engine countertorque hindering vehicle performance.

So if you have a car with its rear-mid engine located transversely
Under acceleration engine countertorque will make the car either squat or dive.

Which one would be better?
One would say dive its better as it counters normal acceleration squat. But it also reduces rear wheel traction.

On the other hand while squat increases rear wheel traction it tends to lift front wheels thus reducing steering control.

Which one is better overall?
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Old 04-01-2012, 12:59 AM
MilesR MilesR is offline
Join Date: Jun 2010
Posts: 82
Increasing the force of the rear wheels on the road will increase the available grip, allowing higher acceleration. This may occur due to the transfer of weight during acceleration, or due to a reaction from the suspension itself, depending upon design. If it occurs due to weight transfer, it will increase the potential acceleration while producing squat. It would also suggest that the car has a high centre of gravity, which is bad for braking, and cornering. If it is due to a suspension reaction, it may cause the rear ride height to increase, creating dive, yet still increasing grip. This would also have a drawback; it would be unpredictable, with the grip appearing or disappearing as the suspension reaches the limits of its travel, or as the suspension response varies with the situation. Again, it may not be ideal under braking, and may create tricky cornering characteristics.

There is a problem with the engine torque idea, though. The torque of the engine will probably not produce any usable effect. The only way that engine torque causes an alteration in the attitude of a car body is by inertia. The shaking and twisting of a car with a huge engine comes from variations in the speed of that engine. As the rotating speed of the engine internals increases, there is a reaction force on the engine itself, and therefore the rest of the car. If the engine speed changes relatively slowly, as it normally does during acceleration, this effect will not be noticeable.

Also, while the engine can exert a force/torque on its mounts while propelling the car, the torque will be internally resisted. Consider a longitudinal engine, and a solid rear axle, for the sake of demonstration. The engine may exert a clockwise torque on its engine mounts. The output, anticlockwise torque is transmitted via the propeller shaft to the axle. The axle then transfers the anticlockwise torque to the suspension, which transfers it to the chassis, which transfers it back to the engine mounts. The clockwise counter-torque of the engine on its mounts is compensated for exactly by the torque of the propeller shaft on the chassis. If it were not, the residual torque would result in something rotating. I am imagining the rear axle spinning like a propeller. An engine that is too powerful, or has too much torque, could theoretically twist the chassis enough to wrap it around the propeller shaft.

This does make the rear axle twist, which can be avoided by using an independent rear suspension, which has the differential bolted directly to the chassis. AMG went one better, using a torque tube around the propeller shaft, which runs between the engine and the transaxle. The output torque is transmitted directly to the rear transaxle via the propeller shaft, while the counter-torque is transmitted back to the engine via the torque tube. In this arrangement, the chassis does not have to resist the engine torque, and the engine would not create a torque on its mounts under acceleration.

In the case of a transverse engine, the engine would still not create a permanent overall torque on the car, and would therefore not cause a squat or dive response. The traction of the wheels on the road would create a torque on the driving wheels, tending to lift the nose of the car, but that is the same for all drive configurations, and is the source of squat under acceleration. The tyres are the only place where the engine torque interacts with the rest of the world, and are therefore the only source of a net torque on the car as a whole.

Last edited by MilesR; 04-01-2012 at 01:03 AM.
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Old 04-10-2012, 01:46 AM
kylawills kylawills is offline
Join Date: Apr 2011
Posts: 60
Nice info.MilesR
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Old 04-10-2012, 11:20 PM
MilesR MilesR is offline
Join Date: Jun 2010
Posts: 82
Glad to be of service. I aim to please.
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