snap aversteer

[budgie]

What are the causes of 'snap oversteer'.I have been caught out twice recently.

Its not just damp roads and a heavy right foot,last time was just a tickle on the throttle and woops!!

I think I have read something about the toe in(or out ) of the rear wheels being critical to this.

 

 

[Alex Wong1697456877]

Possible cures

 

dec rear ride height/ inc front ride height

check tyre pressures

softer or remove rear ARB

Softer rear springs

Stiffer front ARB

Stiffer front springs

 

I'd look at tyres, and ride height to start, then look at ARB's and springs. Not that I'm an expert but I think that's how I'd approach it.

[Alex Wong1697456877]

I don't think there is an easy way to alter rear toe and the fixed factory setting (parallell?) works well enough on so many cars that I'd leave that alone.

[Graham Perry]

A few less clicks on the rear dampers might help, if they are wound up a bit ?

[Chelspeed]

There might well have been some dodgy de dion tubes around in the past. It doesn't take much "production tolerance" on welding the ends onto the tube or post welding distortion if it's not welded properly to cause significant rear toe numbers. Mine was certainly different left to right.

 

Or a small nudge of a curb or whatever can distort rear track the same as it can front.

 

So by all means check the rear toe if it's behaving oddly.

 

You can adjust toe very simply by adding shims between the ear and the de dion tube (and likewise camber by shimming the bearing carrier from the ear). Some people poo poo this and claim it's dangerous but Freestyle were thinking about doing a kit to deliberately change the geometry to something else by shimming also the R400 race regs says in 5.8.1 that you can shim to adjust toe or camber. If people of this caliber say it's OK then it's OK by me.

 

I think the answer is to use a full shim with holes for the bolts rather than just a washer or small shim in one corner which could distort the ear and introduce new stresses.

[Hippy Crippy]

I'm in the middle of building a brand new 1.4K classic. Back in October last year Caterham telephoned me about snap oversteer asking me to check the size of the dedion tube to A frame bush. Apparently it can be manufactured too long causing snap oversteer in extreme circumstances possibly track use. You might want to think about contacting Caterham direct for their advice.

[budgie]

Actully it's a Striker -so might not bother contacting Caterham.

[Chelspeed]

Best not.

 

So what sort of back suspension do you have on a striker? Almost certainly not a de dion. Is it live axle and 4 link? Is it double wishbone independent?

[Paul Ranson]

A Striker should have a live axle located by two fore-aft Watts linkages and a Panhard rod.

 

It's not a very aesthetically pleasing system, twisting up a live axle. There's something similar on the back of an Alfa Sud, but of course with a designed to twist undriven arrangement rather than an Escort job.

 

I think all Sevens of whatever ilk can be a little unruly on winter roads. Quicker reflexes and a fast rack is the best answer.

 

Paul