Your thoughts on roll oversteer please

[John Bonnett]

With my special still in the planning stage, I have a blank sheet of paper and would appreciate your advice.

The Austin Seven in common with the Austin Healey Sprite share quater elliptic rear springs and inherent roll oversteer. This I believe is a result of one spring lengthening and the other shortening as the car rolls through a corner. I think this could be eliminated by either an A frame Rose jointed off the chassis cross member close to the torque tube mounting or parallel radius arms. 

I'm sure this problem has been tackled although I cannot find any information.

Thank you

John

[Ian Williams]

I guess if you are contemplating serious competition John there may be a small gain to be had, but in all fairness it is hardly worth the trouble, most of us have few issues with flat springs and reasonably tight dampers. A well set up Austin seven special is extremely nimble on the track and will out handle most other vintage cars that you are be likely to come up against. Some of our other competition minded members may have other views, but thats my two penneth.

[Mike Costigan]

'Your thoughts on roll oversteer' - Exciting, isn't it 

[Alan]

I agree with Ian. I ran flat springs all round for many years and never had handling problems. The subject of roll steer is complex and it’s as much to do with weight transfer and roll centre position as it is with spring camber. You could start by looking at what Austin’s did with the rear of the SV racer, but I’d advise reading. I don’t mean the internet, it’s too difficult to sift out the bullshit. I’d advise anything by Allan Staniforth, or RAce Car Dynamics by William and Douglas Milliken.

[John Bonnett]

I agree with Ian. I ran flat springs all round for many years and never had handling problems. The subject of roll steer is complex and it’s as much to do with weight transfer and roll centre position as it is with spring camber. You could start by looking at what Austin’s did with the rear of the SV racer, but I’d advise reading. I don’t mean the internet, it’s too difficult to sift out the bullshit. I’d advise anything by Allan Staniforth, or RAce Car Dynamics by William and Douglas Milliken.

A bit of oversteer is no bad thing in a race car but it is how it is delivered that's crucial. If it starts with understeer moving seamlessly into roll oversteer like a factory MGB V8 that really is evil. The key may lie in the flattened springs and a car with a low cg. In the interests of lightness the A frame might be ruled out but there is the option of rose jointed links from the spring mount to the axle one on each side. This mod would add little weight and keep the axle positively located fore and aft though not from side to side.

If the car has flattened springs, does the front mount of the torque tube need raising to maintain its angle?

John

[Alan]

Agreed, you really want oversteer, blending into progressive understeer, and there are ways to do that. However you need to mess around with roll centre heights to get there.
If you lower the springs, you need somehow to stop the axle oil migrating into the torque tube. You could raise the mounting point, but I put a seal behind the pinion bearing.

[Malcolm Parker]

I would suggest that you get hold of a copy of 'Austin Seven Specials' by L M (Bill) Williams as a start.  Good, sound advice.   I think it is easy to get carried away with how the Austin 7 suspension and handling could be improved.  Some people use different tubular front axles, fancy radius arms, Panhard rods, etc.  Look good but add extra weight.  Many very good competition Austin 7's run on very standard suspension.  Flattened springs and better shock absorbers (double front S/A's are readily available from the specialist suppliers) work wonders.  If using a flat or negative camber front spring, the radius arm mounts on the end of the axle will need to be lowered so the arms have clearance under the chassis rails.  The factory used special front forgings on the sports models.  Alternatively a set of drop links can be used, all described in the Bill Williams book.
For a road going special, rear springs that are almost flat under load and a slightly cambered front spring, with double S/A, should give you reasonable handling.   A lot depends on what you are going to use the car for.  I live in rural North Yorkshire and find that slightly cambered springs are better on the country roads than flat ones.   I think the relationship between front and rear is important.  My thoughts are that the rear end needs to be a bit lower than the front with the car unladen.  Something to do with roll centres but there are people on the Forum far better qualified to comment than me!
Saloon Austin 7's are more prone to roll oversteer!

[Steve Jones]

Well I agree with Ian and Alan as well; all three of us long term competitors in Sevens. I also agree with Malcolm, unsurprisingly! I've found pretty reasonable handling with flat rear springs, tight (very) rear dampers, a very stiff front end and, importantly in my experience, high tyre pressures.

You don't say what you intend do do with your car. If it's to be used for competition, the more you modify it down the route your discussing, the less the number of events you'll be able to enter as it will come progressively less eligible for events where Sevens usually compete. If it's modern cars you're looking at taking on, perhaps better buying the proverbial Caterham! There again, you might simply be looking to show those moderns how good Sevens actually are and if so, fair play.

Steve

[John Bonnett]

Thanks Gents for your considered replies and your patience.  I'm just asking the questions as a newcomer to Austin Seven Specials and don't want to waste time by producing something that doesn't work or will not be accepted. Over the very many years of racing I'm sure just about every possibility and every path trodden, to give a car the edge has been tried and I would like, if possible, to tap in to the knowledge base and avoid trying to reinvent the wheel.

I do have the Bill Williams book and also the excellent "Would suit Enthusiast" by Stuart Ulph.

My intention is to build a car suitable to compete in the Bert Hadley Championship, based on the Bill Williams Cambridge body which is very pretty and offers plenty of double curvature to get my teeth into.

[Ian Williams]

In that case perhaps Stuart you could be persuaded to comment on the suspension set up and handling of your cars??

I am very much in agreement with Steve regarding tight dampers, stiff front end and tyre pressures.