Understeer

[Peter Mears]

 

Time to open a can of worms.

With the advantage of adjustable leda shocks has anyone got the general rules of curing understeer? Is it soften the front end or stiffen the back? Or is there some other formula. Suggestions welcome.

The 7 is de dion on 14" wheels.

[Nick]

Not related to Leda shocks, as I have the standard Bilsteins on my 1.6K with 13" wheels, but I have recently had a rear anti roll bar fitted (set at stiffest of 4 options) and a red bushed front anti roll bar, which has greatly reduced understeer.

 

Nick

[Andrew Russell]

To 'cure' understeer there are a number of routes you can take and it really is a matter of personal preference and the use to which the car is being used.

1) Soften front end...shocker or a/r bar.

2) Stiffen rear end...shocker or a/r bar.

3) Raise the rear ride height.

4) Increase front tyre pressures.

 

From my own experience, it really is a matter of 'suck it and see'....it's what sevening is all about!

 

Andrew Russell

[Graham Perry]

I agree with the solutions Andrew has suggested except perhaps for the last one. On my car with front pressures of 16 psi I have to inflate the rear tyres harder to promote neutrality and then oversteer. I guess all cars are different ! I have rock hard race springs though and Spax dampers so that may well explain it. I find though that playing with the damper settings is usually sufficient to time out any handling inconsistencies.

[old captain slow]

Item 4) is free and works with my 16" wheels, but you have to work the car long enough and hard enough to get any heat into the big tyres.

[Anna Rexia]

Can't you turn the steering wheel more - much cheaper!

[Alex Wong1697456877]

or just put your right foot down. Power oversteer is an instant cure for understeer!

 

Seriously though, I thought increasing the front tyre pressures would promote understeer. Tyres are funny things though. When I put wider rear tyres on, it handled more neutrally. I still can't figure that one out, but my car understeers less with more rear grip. I think what it really is is that the increased rear grip gives enough confidence to use the throttle to balance out the understeer. It's a fantastic feeling when you get it right, and quite an alarming feeling when you over do it a bit (backwards at 80mph towards the tyres!) I think the tourque of the Vx engine makes the four wheel drift "window" bigger which is why I'm probably the only person in the world who thinks the Vx cars handle better than the K cars. I know I'm on my own out here though, although Powder Puff may back me up on this despite his K loyalty. (I won't lend you the car again if you don't! wink.gif.

 

 

 

Alex Wong

alex.wong@lotus7club.co.uk

www.alexwong.net

Home : 44-(0)121-440 6972

Fax : 44-(0)121-440 4601

[jean luca]

Have you checked your front wheel camber?

[Dave H]

Increasing the front tyre pressures will, up to a point, reduce the tyre wall flex which leads to understeer. Beyond that certain point, which you will have to find, the increased pressure will distort the tyre and reduce the grip, leading to ...understeer. Of course,playing with the rear pressures to increase/reduce the oversteer tendencies at the same time can lead to many happy hours of throwing the car round a set of bends again and again and again...

[Mike Bees]

A rather obvious but possibly overlooked point about tyre pressures: For a given situation there will be a tyre pressure that gives the optimum amount of grip from the tyre. Adding more pressure than this will reduce the grip, reducing the pressure from this will reduce grip.

 

Ergo you can't have a general rule which says "increasing the front tyre pressures will cause less/more understeer" because it depends (a) on where you're starting from and (b) on loads of other factors.

 

The best way to determine the tyre pressure for optimum grip (or more correctly to make optimum use of the tyre's width) is to use a pyrometer. Measure the temperature of the inside, centre and outside of the tyre. Plot them on a graph with temperature on the Y axis and position (inside, centre, outside) on the X axis. If the 3 points form a horizontal line then bingo you're heating the whole width of the tyre evenly. If they form a straight line but with the inside hotter than the outside or vice versa then the pressure is optimised but the camber and/or toe is causing a temperature gradient across the tyre. If they don't form a straight line then draw a straight line between the inside and outside temperature points - if the centre point is below this line then the middle of the tyre isn't doing enough work so more pressure required, if the centre point is above the line then the middle of the tyre is doing too much work hence less pressure is required.

 

The requirements will change from venue to venue and day to day (even hour to hour) at the same venue.

 

Mike

[John Richens]

Mike ,thanks for that, I must go and lie down in a darkened room....

[Nick]

Mike

 

That's great, thanks for that.

 

Nick

 

PS - I take it a pyrometer is more accurate than the palm of my hand... tongue.gif

[Slipper man]

Sounds like hard work to me. I like Anna's solution.

[Dave H]

From what Mike is saying it sounds like what is needed is a way of continually monitoring all 4 tyre temperatures and continually adjusting the pressures...

[Mike Bees]

There are valves which can have a maximum pressure preset on them, which ensure that as the tyre heats up the pressure doesn't go up as well. Handy 'cos you can set the cold pressure to what you want to run at and the pressure will remain constant as the tyres heat up.

 

[Anorak on]

 

They're not allowed for competition use though, Year 2000 Blue Book Section E 12.9.4

 

[Anorak off.]

 

Mike