Date: Thu, 25 May 2000 00:23:38 +0200 From: "Pros Mortier" <prosmortiernopsamgatez.be> Subject: Re: Viggen is stupid.
If I may be so bold to jump into this thread... Everett M. Greene <mojavegnopsamsp.com> schreef in berichtnieuws 20000524.7A34FD8.9785nopsamveg.iwvisp.com... > Winston <winstonnopsamail.com> writes: > > Viktor Haag <vhaagnopsamnet> wrote: > > > > > Could someone please explain what is meant by 'torque steer'? <snip> > > Torque steer is the unpleasant phenomenon which occurs when the > > driveshafts which run between the transmission and the front wheels are > > of different lengths, causing more torque to reach one wheel than the > > other (torque=forcexlength). So when you mash the accelerator, more > > torque reaches one wheel than the other, causing the steering wheel to > > twist to one side. To my humble opinion it is not the difference in driveshaft lenght that causes this, but the differential. The problem with an FWD setup is, (especially high powered ones) the driven and steered wheels are one and the same, when power is applied, the weels want to set themselves in the straight-on position. This is why the hi-power FWD's are by necessity equipped with servo steering. Without powersteering the car would become practically unsteerable when power is applied to the wheels. It would simply go straight forward. > > However, as someone pointed out, the Viggen supposedly has equal length > > half-shafts in its front drive train. Therefore, torque steer is > > impossible-- the same amount of torque will be reaching each wheel. The > > sensation of torque steer could be caused by so much power reaching the > > front wheels that each tire alternately breaks looks, causing that an > > odd sensation people have been taking for torque steer. > > Engine torque will cause the vehicle to attempt to rotate > about the longitudinal axis as well (unless you have a > cross-mounted engine). If you stomp on the power hard > enough, suspension geometry, wheel slippage, etc. will > cause a steering effect. Again to my humble opinion, this is not related to engine mounts etc. This is simply the weight of the car being transferred between the different axles, and the torque between the two wheels of the driven axle (due to the differential). Let's assume when the car is standing still, the load is divided 50/50 front and rear. When the car accelerates, the load moves towards the rear axle taking load off the driven wheels, reducing grip, causing wheelspin. When braking the opposite happens, load is moved forward. This is why the braking capacity of the rear wheels is only +/-20% where the front take +/- 80%. (ever wondered why the rear disks are always smaller in size compared to the front disks?) This is also why a Rear-wheel driven car has more traction; when accelerating, the driven wheels are loaded more, getting more grip. Ever wondered why racing drivers use left foot braking techniques? They keep engine torque applied while with their left foot applying the brakes. It serves only 2 purposes: 1) avoiding axle load shifts and 2) making an artificial limited-slip differential between all four wheels. (the brake pads innterconnect the four wheels through friction via the chassis) Result: the car acts more stable. > > The problems in delivering 230 horsepower to the front wheels of an FWD > > car are not unique to the Viggen... it is a problem inherent in this > > driveline setup. Yes. This is why I always lose when racing against BMW's in the rain... I'm still standing at the traffic lights up to 3rd gear, and the BMW is long gone by the time I get some traction... -- Pros "Everything that doesn't kill me, makes me stronger." - Nietsche __________________________________________________