GaryCat

and what benefit it's removal has?

G

skiddus_markus

http://www.drivingtechniques.co.uk/S...u=63&PageID=56

The site seems to be down at the moment so I couldn't copy&paste it.

Neanderthal

iTrader: (6)

I think there's quite a few threads on here about it. I spent Sunday evening reading through them all and have consequently just booked my car in to Power Station to have it done early next month

Basically, it reduces understeer, makes the car turn in quicker, brakes in a more sure footed way and best of all it makes the car feel a lot more netural through the corners.

Matt

darkblueturbo

i got the TSL geometry the other week (basically the same thing I believe) and it's AWESOME!

DO IT!

wildrider

Hi all,

Bump steer is basically the effect of the suspension moving over bumps which inturn alters the effected wheels track,(movement input into the steer)which pulls the car around on the road meaning you need to be putting in small correction all the time. The car figits more the bumper it gets and can dart about under braking. Good geometry setup can dial most of this out leaving just a hint but i like that. Hope that helps.


Cheers

mutant_matt

Not true I'm afraid, Bump Steer cannot be changed with Geometry alone - you need to shim the steering rack. It also depends on which model you have as the MY 01/02/03 have either very little or none at all whereas the old shape cars (pre MY01) do have it.

There has been reams written on here about it so search will bring up loads of hits but simply put, when the suspension compresses, if you have Bump Steer, the front wheels will toe out and induce some understeer (which gets steadily worse the more the suspension is loaded up). This is obviously a bad thing if you want the front end to go exactly where you tell it to when cornering.

Matt

darkblueturbo

mutant_matt - cheers for that, learn something new every day.

But I can say the geometry does drastically reduce this from standard... but it's not totally gone when you hit the harsher bumps on the crappier roads.

mutant_matt

The only way to counteract the dialled in Bump Steer with geometry is to add more static toe in, so that when the wheels splay out when the suspension loads up, the overall toe is still "in". The downside of this is you have to run more toe than is ideal when you are running in a straight line and also, increased tyre wear on the inside edges.

It's a compromised solution IMHO!

Matt

darkblueturbo

fair enough.

I'm more than happy to put up with a bit less straight line stability (haven't noticed it TBH) for better turn in.

But as you say, it hasn't really got rid of bump steer, but it has reduced natural oversteer and the biggest benefit of the geometry was there is no horrible fighting of the wheel under heavy braking. For that alone it's worth it..

I'll investigate bump steer in the future.
Thanks matt.

Dan

mutant_matt

You mean Understeer right? (where the front runs wider on a corner than the rear) (Oversteer is where the rear wants to run wider than the front)

Matt

Chelspeed

Or to put it another way - understeer is where you see what you're about to hit, oversteer is where you don't.

wildrider

VERY GOOD!

darkblueturbo

DOH! yes I did mean natural understeer, not oversteer. Muppet...


and it's true, you can't see what you hit on oversteer. Like it!

Dave T-S

Matt
The rack arms are roughly parallel to the rack/ground static (on a STi MY02, anyway), and the rack is mounted in *front* of the wheel centre, so you will get toe *in* not out on the outside wheel under compression whilst cornering

mutant_matt

Matt

Dave T-S

Pah! You expect me to read the whole thread/post?!

mutant_matt

Leslie

Matt's description of bumpsteer was correct-the front wheels do toe out when the suspension is compressed and when entering a corner the outside front wheel will toe out as the suspension compresses when the chassis rolls. This will induce understeer and can be quite marked.

The toe out was demonstrated to me at Powerstation and was 41 minutes when the suspension was compressed. When the rack was shimmed correctly the bumpsteer was reduced to 1 minute! with the rest of the suspension alignment and the fitment of whiteline solid anti roll bar links the car's handling was transformed absolutely. The front tyres now wear totally flat instead of wearing out the inside shoulders.

Setting extra toe-in would not do anything to cure the problem since the toe-out would still be present as the suspension compresses. The rolling resistance of the car would increase and the tyres would wear unduly rapidly.

My car is an STI 1.

Les