Handling for Audi Quattros
Handling for Audi Quattros
(OP)
Can anyone tell me how to improve the handling of an all-wheel drive Audi, particularly in regard to the fairly chronic understeer they suffer from. I would like to understand the physics of car handling a little better too, if someone can spare a little time to let me know how a stiffer rear sway bar affects the cars handling, and how lower springs, or softer springs etc affect it too. Thanks.
RE: Handling for Audi Quattros
Which year and platform Audi Quattro are you referring to? Understeer is a common handling characteristic and a safety feature of Audis which began their lives as front wheel drive vehicles. Their AWD systems have improved significantly since they first appeared in production in about 1980.
Many guardrails have modified the graceful lines of Audis in the wrong hands with weight and balance characteristics that favor oversteer. Driver technique and wheel alignment are critical and it's tough to beat the factory specs. Not every shop out there is qualified nor has the equipment to properly align Audi quattros. If you are sure that all your suspension components are functional and your alignment is exactly to spec, and I do mean exactly, go to this site do a little reading before you register. There's a few guys there who regularly race them and can get them to stick to the pavement a little better. Ride quality will suffer though. After you read a few thousand posts you'll find a few guys who are pretty good with them. As Evelrod often points out though, the real hot racing tricks are pretty tightly guarded secrets, so, don't expect to learn everything the first day.
http://www.audifans.com/mailman/listinfo/s-car-list
Chumley
RE: Handling for Audi Quattros
Hueyoz
RE: Handling for Audi Quattros
OK, sarcasm mode off. If you want to learn about interactions then the best book is Race Car Vehicle Dynamics by Milliken and Milliken, available from the SAE. That has a longish section on both primary and secondary interactions.
I haven't found much on the web that rises above the very basics for interactions.
The simplest thing you could do to reduce understeer would be to remove the front sta bar, or drop the front spring rates. But you would be unwise to do so without understanding the other likely effects - I suspect you'll find that the 'lazy guys' I mentioned before were very concerned by throttle off in turn characteristics, and the behaviour under braking, and mixed mu surfaces. They might also have decided that newer drivers in a turbo would spend a lot of time backing off, so a tendency to plough under most conditions might be built in.
You do realise that all practical 4 wheeled vehicles with rubber tyres understeer in steady state cornering at anything less than 8/10 don't you?
Cheers
Greg Locock
RE: Handling for Audi Quattros
I'm with Greg on this. The best engineering minds in the automotive industry have been continuously working on improving the handling of the Audi Quattros now for about 25 years. Those same minds somehow managed to finish 1,2,3 this year at Le Mans and basically thrash the competition in most of the professional level races that they are still allowed to compete in.
It's interesting that you think the Audi Quattro handling is "OK, but could be considerably better . . . without a lot of work." I'll be looking forward to reviewing your suggestions for improvement.
Chumley
RE: Handling for Audi Quattros
I've already added a larger rear sway bar which has improved the balance of the vehicle quite a lot. It still understeers quite a lot though, which is why I'd like to learn a bit more about suspension b4 I do much else. I suspect, from what I've read, that reduced front springs would make quite a difference, although I'd probably have to reduce the rear as well, given the meatier rear bar. Otherwise I might be going through the corner backwards!
Greg, if I reduce the spring rates all around, do u have any idea what that will do to the overall handling? I assume there is a good reason the springs are rated at whatever it is they are rated at now.
RE: Handling for Audi Quattros
SAE International is the "The Engineering Society For Advancing Mobility in Land Sea Air and Space" formerly know as the Society of Automotive Engineers. Thier internet locations is www.sae.org.
Best regards,
Matthew Ian Loew
RE: Handling for Audi Quattros
Since you've spent quite a lot of time and money making sure that all four wheels move independently, you can now spend some time and money stopping them from doing that by fitting an anti roll bar or two. Quite how you decide how much extra roll stiffness to add in, which may even allow you to go softer again on the road springs, is something that evelrod can describe with far more insight and experience than me.
On a road car in the first instance we use the relative roll stiffness of the two ends to change the way that each tyre weights up, which affects how much it saturates, which affects how much lateral force it generates, which affects the understeer of the car. We also need to keep an eye on the ride of the car which is strongly affected by the roll mode of the car, which can cause head toss. It is probably worth pointing out that in 'normal' driving (ie that which would not get you a ticking off, say 0.3 g) there is so little weight transfer that the handling is hardly affected by the a/r bar, in the sense I've discussed - the shocks probably have more impact.
I agree, the handling on a BMW is much nicer than the handling on the Quattro, I don't think a 4WD will achieve the crispness of a RWD, although it could and should have better objective performance.
Cheers
Greg Locock
RE: Handling for Audi Quattros
RE: Handling for Audi Quattros
2)The anti-roll bars change the way that the tyres across the car load up as you enter a corner. This affects the slip angles front to rear, and so affects the understeer. In an ideal world you would not use them, I think, since the whole point of an independent suspension is to maintain wheel contact as much as possible. Oddly enough on the active suspension cars they usually have antiroll, antipitch, and cross diagonal 'bars' in the software. I don't know how much of each they use. If you run no antiroll bars then the car will roll too much in corners, maybe even to the extent that the suspension tops or bottoms out. The enormous non linearity this would introduce would be very difficult to control. I'm not sure if a standard car would bottom out like this, but I guess it would (too lazy to work it out).
There is one proviso with antiroll bars - if the car does lean too much then the contact patch may cant relative to the road surface. In that case an antiroll bar may help traction by keeping the tyre flat to the road.
Cheers
Greg Locock
RE: Handling for Audi Quattros
The stiffer bar has more effect on the understeer problem (I had the 18mm bar fitted first) but there was no head toss problem when I had it on (at least I didn't notice such a problem).
Thanks for your input,
Craig
RE: Handling for Audi Quattros
We typically get worried about head-toss when we go from our usual setup to our sports setup, but they do very strange things to the road springs as well as fitting eneormous anti roll bars and low profile tyres, which may exacerbate the problem.
Cheers
Greg Locock