suspension wili etc - understeer, then oversteer

[Top Gear TVR]

All,

many of us have shared our set up but i am not sure i can draw any conclusions?

No matter how i play i am always happy with the rear but find the front end a bit over keen to understeer, requiring a good 'chuck in' when driving with some passion on a bend, especially where a sharp 'turn in' is needed.

I have 400lb spring up front, 375lb rear. I am wondering whether some progressive springs are needed?

what is the BEST answer?

also, can you comment on tyre pressure, i feel this too may be a factor?

[Stone Cold]

oo,eer ,missus - suspension wili!!

"no matter how I play I am always happy with the rear"

I think you have posted on the wrong forum

[m3jappa]

Stone Cold said:

oo,eer ,missus - suspension wili!!

"no matter how I play I am always happy with the rear"

I think you have posted on the wrong forum

Anyway, try some more negative camber up front or a bit less on the rear, would be my first thing to initially reduce understeer.

[Barkychoc]

Try changing your driving style, slower into the bend, constant light throttle through the bend then accelerate progressively as you exit, no hoofing it till you have straightened up or you may end up looking where you just came from!

[Barkychoc]

How old are your tyres ?

[Top Gear TVR]

Hmm, alignment to be checked I think, what tyre pressures are you all running?

[Top Gear TVR]

Tyres are all the same and mediocre at best but with 4 the same I have pushed that aside as not the issue. I am convinced its a setup thing. I might try lowering front pressures a bit, then look at camber?

[techbotics]

I know what you mean the front doesn't inspire confidence to push on in bends. I was also thinking my front springs may be too hard. I would be interested in progressive or double springs for my gaz gp's but wonder if the ultimate for these cars has to be to go wide track like the v8. Not sure I like the idea of spacers and v8 wishbones etc are pretty rare.

good luck report back please..

damian s3

[techbotics]

thinking aloud but would putting 8" wide wheels on have the same effect as widening the track with regard to handling..?

[Top Gear TVR]

Not in my experience. I might talk to some racing peeps I think

[Top Gear TVR]

Now here we have some sense.


Front spring rate increase:
More under steer; increase in proportional weight transfer to the front when rear wheel rate is not increased; reduces front traction when rear rate is not changed.
Usable adjustment: 150-600 lbs/in
Symptoms of too much adjustment: terminal under steer; front of car hops in corners; excessive wheel spin on inside front tire on FF cars.

Front spring rate decrease:
Less under steer; decreases proportional weight transfer to the front when rear wheel rate is not increased; increases front traction when rear rate is not changed.
Usable adjustment: 150-600 lbs/in
Symptoms of to much adjustment: Too much over steer; over steer then under steer if spring is so soft that the car bottoms out on lean, car bottoms out excessively with a jolting ride.

Rear spring rate increase:
More over steer; increase in proportional weight transfer to the rear when front wheel rate is not increased; increases rear traction when front rate is not changed.
Usable range: 100-600 lbs/in
Symptoms of too much adjustment: too much over steer; sidestep hop in corners; twitchy; pretty scary.

Rear spring rate decrease:
Less over steer: decreases proportional weight transfer to the rear when front wheel rate is not changed; increases rear traction when front rate is not changed
Usable range: 100-600 lbs/in
Symptoms of too much adjustment: car under steers; if way to soft car under steers then over steers as car bottoms out on lean; car bottoms out excessively with a jolting ride.

Front anti-roll bar stiffer: more under steer
Usable range: none to 1.25 inches in diameter
Symptoms of to much adjustment: terminal under steer; lifts inside front tire off the ground witch can cause massive wheel spin on FF cars; also not good for most effective tire usage as inside tire is now doing nothing.

Front anti-roll bar softer: less under steer
Usable range: none to 1.25 inches in diameter
Symptoms of to much adjustment: overstate scary; more like fun

Rear anti-roll bar stiffer: more over steer
Usable range: none to 1 inch in diameter
Symptoms of too much adjustment: Big-time over steer. Can cause inside rear tire to lift off the ground.

Rear anti-roll bar softer: less over steer
Usable range: none to 1 inch in diameter
Symptoms of to much adjustment: under steer; slow and boring

Front tire pressure higher: less under steer by reducing slip angels on most tires
Usable adjustment: up to 55psi hot
Symptoms of too much adjustment: no traction- tire crowned so more under steer; adds wheel spin in FF cars; jarring ride; center of tire wears out

Front tire pressure lower: more under steer by increasing slip angles on most tires
Usable adjustment: not less then 20psi
Symptoms of too much adjustment: edges of tire wear quickly because tire is folding over; feels mushy; tires chunk because low pressure means heat build up.

Rear tire pressure higher: less over steer by reducing slip angles on most tires
Usable range: up to 45psi hot
Symptoms of too much adjustment: no traction—tire is crowned so more over steer; bad wheel spin on FR cars; jarring ride; center of tire wears out.

Rear tire pressure lower: more over steer by incresing slip angles on most tires.
Usable range: not less then 20psi
Symptoms of too much adjustment: edges of tire wear quickly because tire is folding over; feels mushy; tires chunk because low pressure means heat build up

More negative camber front: less under steer because of better lateral traction as tread is flatter on the ground under side load.
Usable range: up to 3.5 degrees negative
Symptoms of too much adjustment: poor braking; car is road crown sensitive; twitchy; front tires wear on inside edge

More negative camber rear: less over steer because of better lateral traction as tread is flatter on the ground under side load. More rear grip
Usable range: up to 2.5 degrees negative
Symptoms of too much adjustment: more over steer; car feels twitchy in back; tires wear out on inside edge; less breakaway warning when limit is exceeded.

Ride height to low (typical beginner mistake): car is twitchy with unpredictable dynamics. Bump steer make you life miserable.
Usable range: usually 1.5-2.0 inches lower then stock unless car has been modified to go lower.
Symptoms of too much adjustment: everything that could possibly go wrong: sudden over/under steer; twitchy due to bump steer; very harsh ride; premature tire wear.

Toe in – front: car is stable going straight. Turn in is average
Usable range: 0-1/8th inch
Symptoms of too much adjustment: car has slow twitchiness under braking; feels odd; kills outside edge of tires

Toe out – front: Car turns in well; works pretty well on FF car as they tend to toe-in under load.
Usable range: 0-1/4 inch
Symptoms of too much adjustment: Car is really twitchy under braking; car wanders on straight road; kills inside edge of tire

Toe in – rear: car is less likely to over steer when the throttle is lifted
Usable range: 0-1/8th inch
Symptoms of too much adjustment: weird, slow, rocking movement in back; feels slow but still unstable; wears outside edge of tires.

Toe out – rear: Helps car rotate useful in low speed and slalom courses; very common on FF pro rally cars.
Usable range: 0-1/8th inch
Symptoms of too much adjustment: not to good for street driving; causes lift throttle over steer; makes violent side to side rocking motions in the rear; tie wears on inside more.

Positive front caster: helps stability; suspension will get more negative camber when turning; reducing positive caster reduces steering effort. (Negative caster is not usable)
Usable range: 4-9 degrees positive
Symptoms of too much adjustment: can increase under steer especially in cars with wide low-profile tires. Can increase steering effort.

Single adjustable shock stiffer: Better turn in; better transient response; causes slower onset of over/under steer by slowing weight transfer depending on what end of the car is adjusted.
Symptoms of too much adjustment: suspension becomes unresponsive; ride gets harsh; car skips over bumps, loosing traction; Causes a big delay in weight transfer resulting in strange handling like under steer then late corner stage over steer.

Single adjustable shock softer: slower transient response; quicker onset of over/under steer
Symptoms of too much adjustment: car oscillates due to under dampened spring motion, like a boat. Car gets twitchy in turns. Feels unstable.




Have fun tuning your suspention. Use Toe and Camber to your advantage! Even Tire pressure helps.

[v8s4me]

I have two 5mm spacers if you want to give them a try.

[glenrobbo]

Steve,
That's really good information, thanks for that.

Can somebody add that to the Suspension Wiki so it can be preserved for all to refer to easily?
Or just add a Phillpot-style hyperlink to this thread?

[Longers]

Hi Steve

Although this is a technical topic and, as most of you already know, I don't do technical seeing as you have asked twice and not had answer yet I feel confident in saying my tyres are at 24psi all round

[glenrobbo]

24 psi all round for me too - seemed to work well enough for a complete novice at Spa.

[Top Gear TVR]

Adrian@ said:

Now here we have some sense.

A cut and paste from where, and it's relevance to a TVR trailing arm suspension set up...back to tyre pressures.
Adrian@

its a paste from another rwd forum - and matches my experience of my S (other than the occasional FF reference obviously!)

Have you got other ideas re my IP? all ideas welcome.

[Maffe]

I have 1.55-1.6 Bar, I don´t do psi

Edited by Maffe on Thursday 9th May 09:27

[spitfire4v8]

is it just turn in that is frustrating you? what's it like through the rest of the corner? you could always just drive slower

[Top Gear TVR]

i dont think its possible to drive an S slower.........its that addictive noise thing