[ylee coyote]

Mr torque steer is back with avengence
suggestions are welcomed how to reduce this

I am experiencing a lot of wander on full power take off's It is as if the front wheels are on ice ..
now
Thoughts are
preventing weight transfer to the rear wheels
ie higher spring rate on the rear
stopping side to side wander by upping the effective a/r bar thickness
front ? rear ?
both ?
I have tried winding the koni's up to the max but they just make the ride harsher

Car has been comprehensively polyied and has koni adjustables front and rear

any suggestions ?

 

[whitesaab]

I don't suffer from it in my car, well I probably would, but every time I do anything other than tickle the throttle from a standing start I get a strange whining noise from the back of the car.

It sounds like " what're you racing for?, it's really uncomfortable in the back, or ,do you really have to do that?"

Anyway, back to topic

I know nothing about torque steer, apart from one of the main causes being having drive shafts of different lengths, therefore masses causing the diff blah blah.. You already know all this.

Anyway, I realise that the 9000 has an intermediate shaft to keep the actual driveshafts themselves the same length , and that the shaft is supported on bearings ,but this surely must mean that the mass of the N/S driveshaft is a lot less that the O/S shaft + transfer shaft.

Now in my oversimplistic ( ie engineer not scientist) way of looking at things, wouldn't increasing the mass of the N/S shaft to equal the mass of the O/S shaft(s) give a better balance under hard acceleration?

You're now going to tell me that a LSD throws this theory out of the window no doubt.

 

[ylee coyote]

interesting...
Lsd will make a diff
but the difference in rotational inertia may indeed cause the right /left imbalance which cause this "float " from right to left and back again with a little bit of steering lock...
I think the viscous coupling is causing the swing back but not the origonal swing to...if you know what I mean
And it could be the difference in rotational inertia between the two sides causing the origonal imbalance and swing to...

Thats all well and good but how do I solve it ?

 

[1989agoodvintage]

You probably need to look at ways of stiffening and/or preventing shifting of the front frame. I'd imagine there are several ways to do this, but the upshot will be that your car's less crash-friendly (i.e. because the cabin is more likely to crumple).

 

[California Saab Tuner]

Torque steer shouldn't have much to do at all with how much power is going to each wheel. With properly designed suspension and properly off-set wheels one tire could bear all of the load without causing the wheel to jerk.

Generally torque steer is caused by an irregular change in the suspension geometry under load. On the Viggen the bushings flex, the subframe flexes, and the steering clamp is not mounted rigidly enough to stop even the normal steering load from allowing it to move. All these things together cause the geometry of the suspension to change significantly.

When the subrame is under accelleration load on the Viggen the rear control arm mounts move outward slightly. This does not cause torque steer as long as both wheels grip evenly. However when one wheel loses grip, the other suspension mount flexes more because it's pulling forward with more force. This causes that wheel to point slightly inward, which pulls on the steering tie rod ends and jerks the wheels in the opposite direction of the wheel that is gripping. Try it sometime.

Next the suspension bushings can do the same thing. They flex. It's ok under even power loads, but as soon as one flexes more than the other the same problem that was there with the subframe is now there with the bushings.

Even a properly designed suspension and steering system won't fix improperly offset wheels however. When the offset of the wheels is incorrect each wheel will produce a net torque about the hub axis ... this only puts strain on the steering componants during normal forward accelleration, but when there is uneven load on the front wheels one wheel will produce a net torque in one direction that is greater than the normally ballenced net torque of the other wheel. Thus causing the difference to be picked up by the steering componants, and your arms.

ylee you may consider taking a picture of the 9000's undercarriage sometime. I've never seen it, so I'm not sure if the subframe is a possible culprit. But check very carefully all bushings (including tie rod ends, which if worn can cause a similar effect), and look up your offset, measure it if nothing else seems to be wrong. If you cannot find anything wrong at all (and all the other usual suspects such as allignment have been taken care of) there may just be some amount of incorrectable flex in the frame of the 9000. But ... since I've never heard of that problem before it's likely just some worn out or miss-alligned parts someplace.

Dubbya~

 

[whitesaab]

Originally posted by Adrian W:
[qb]there may just be some amount of incorrectable flex in the frame of the 9000.  But ... since I've never heard of that problem before it's likely just some worn out or miss-alligned parts someplace.

Dubbya~ [/qb][/b]

Could this flex possibly be induced by the 370+ BHP & matching torque it's having to cope with?

Ylee - If it was mine I'd get some shaft anodes from a yacht chandlers and get them clamped onto the N/S shaft. Probably wouldn't stop the torque steer but it would stop the car from corroding

 

[ylee coyote]

Could this flex possibly be induced by the 370+ BHP & matching torque it's having to cope with?  [/b]

err...maybe

 On the Viggen the bushings flex, the subframe flexes, and the steering clamp is not mounted rigidly enough to stop even the normal steering load from allowing it to move. All these things together cause the geometry of the suspension to change significantly.[/b]

now the 9000 has a subframe and it is fairly common for the bolts to come loose after a while
I am fairly sure everything is tight down there but if it comes loose then I am fairly certain that it will be flexing in some way

Perhaps the wishbone bushes need to be braced (anchored together ) to stop them changing geometry under 400 ft/lbs of torque..

 

[California Saab Tuner]

now the 9000 has a subframe and it is fairly common for the bolts to come loose after a while
I am fairly sure everything is tight down there but if it comes loose then I am fairly certain that it will be flexing in some way

Perhaps the wishbone bushes need to be braced (anchored together ) to stop them changing geometry under 400 ft/lbs of torque.. --- ylee

I believe that's basically what the Abbott subrame brace does for the Viggen. An even better solution would be a cross brace between the subrame at both front and rear mounting points with an x-cross in the middle of that brace. It would be difficult to arrange, and you might be better just doing a cross between the two rear suspension bushings, and attaching the center of that brace to the firewall.

The reason I reccomend that over what Abbott has done is because the Abbott brace only prevents one suspension arm from moving out at a time. It doesn't prevent both sections of subframe from moving side to side, which with a limited slip could theoretically happen. By attaching the cross brace to another reference point on the chassis away from the suspension you reduce the amount of independant motion. It would considerably improve on the stock setup.

However there is no free lunch. Part of the reason the GM900 and 9-3 chassis was so weak in this fashion was to reduce the amount of small vibrations making their way from the road to the interior portion of the chassis. If you stiffen up anything in the suspension, you may notice more vibration. Just something to consider before investing in any kind of brace.

Dubbya~

 

[ylee coyote]

x bar is what was being considered
I will run it up the ramps tomorrow and see if I can figure out if something is possible
harshness ?
A little more will not hurt !!