Max Front Spring Rate With Standard T/b

[Rich_p 23]

What is the max advisable spring rate to use with standard torsion bars and anti roll bars?

 

Comfort is not an issue at all as the car is not a daily driver, will be used for airfield sprints and similar.

 

Will be either coilovers if I can find a cheap set or normal fixed platform adjustable dampers and I'll get some springs made up to fit.

[welshpug 1,657]

depends how much you want it to understeer!

 

read many a time that on RWD, you stiffen up the front, and FWD you stiffen up the rear (more than the opposite end that is)

[Rich_p 23]

Ok, max advisable spring rate that leaves the car fairly well balanced still

[Dan Ingram 1]

What dampers are you using on the front?

[Rich_p 23]

Not sure as yet, most likely to be Koni or bilstein, depending on what comes up.

[large 33]

I run about a 180lbs spring(i think) no problem with bilstein

[SPGTi 2]

I run 185lbs springs on my road rally car and this is firm enough.

The PTS Rally car build manual I think recomends 185lbs front with 20mm torsion bars for forest and 225lbs with 23mm torsion bars for tarmac. There are also a forest and tarmac Bilstein insert which have different bump / rebound values.

 

Steve

[j_turnell 137 3 Cars]

Would also depend on what ARB's your using, could prob get away with being a bit stiffer up the front if you had a thicker rear ARB.

[mmt 15]

Hi

 

I´ve seen rates up to 350 lb for racing only.

 

Can anyone confirm that kind of rates?

 

I´m considering 330 Lb for my track 205.

 

/Martin

[petert 586]

I've got 350lb front springs with 23mm TB's and 25.4mm rear ARB. Works well for me. I used to have 225lb springs but they were a bit too soft for my liking.

 

You definitely need to upgrade the rear first however.

[AdamP 0]

I would say 225s with standard torsion bars. If its stripped out then the rear will be light and oversteery anyway so you want to bring in a bit more understeer and wider tyres to counteract that.

 

When I get round to converting to coilovers i'll be putting 225s on.

[Rippthrough 98]

It'll also depend to a slight amount on what dampers you are running, you'll get away with a bit more front spring rate if the rear dampers are decent quality high-pressure monotubes.

[mmt 15]

I run Bilstein race dampers in front and Gaz adjustable rear dampers.

 

Adjustable toe/caster/camper front and rear.

 

15" Yokohama/Advan slicks.

 

 

I think i´m gooing with some 336Lb springs front.

 

/Martin

[Sandy 191]

I wouldn't use any more than 175lb/inch on the front with standard bars, even stripped out. It's asking for understeery nodding dog syndrome.

[niklas 1]

Otoh, running too soft will cause more body roll thus reducing grip!

[welshpug 1,657]

I think losing grip from body roll is better than losing grip because of too hard a spring (rough/uneven surfaces, I.E British roads )

[Rippthrough 98]

I think losing grip from body roll is better than losing grip because of too hard a spring (rough/uneven surfaces, I.E British roads )

 

Even on track, the top teams aren't running rock hard springs....

[niklas 1]

I think losing grip from body roll is better than losing grip because of too hard a spring (rough/uneven surfaces, I.E British roads )

 

Either sucks!

But obviously I'm talking from a track point of view. Why anyone would want/need race spec suspension for driving to work is beyond me.

 

And of course it's all a matter of balance (yea very funny....)

Basically make the rear end as stiff (roll and pitch balanced accordingly) as you can afford, then make the front as stiff as it needs to be to make the best laptimes. Often on our type of cars it needs to be stiffer in the front than what you calculate in your favourite chassis setup excel sheet! Just because excessive roll and lack of camber tends to be a bigger problem than front-rear balance.

Driving style is a major influence to the setup too. Some drivers are faster with massive oversteer, some are faster with massive understeer etc...

 

EDIT: My point is just that the single most important factor to cornering on the 205 is the grip of the outer front wheel as it alone takes very much of the cornering forces, so improving the grip of that wheel will enable you to go faster in the corner!

Edited March 9, 2008 by niklas

[Sandy 191]

The grip should come from getting the overall front and rear geometry* right and the springing should be soft enough to allow it to work. Getting rear end grip is relatively easy, the front needs greater attention. If the geometry is correctly thought out, roll won't be a problem, it'll be part of the system. Using springing to defeat roll induced by incorrect geometry is a popular bodge.

 

*By geometry I mean roll centres and changes thereof as well as camber/castor etc.

[niklas 1]

The grip should come from getting the overall front and rear geometry* right and the springing should be soft enough to allow it to work. Getting rear end grip is relatively easy, the front needs greater attention. If the geometry is correctly thought out, roll won't be a problem, it'll be part of the system. Using springing to defeat roll induced by incorrect geometry is a popular bodge.

 

*By geometry I mean roll centres and changes thereof as well as camber/castor etc.

 

Sometimes the only available bodge.

The 205 GTI is pretty flawed for racing. The camber gain is pretty tiny, the neg camber can only be adjusted to ca 2.5 degrees without custom bottom arms or other custom changes. (Custom changes means expensive custom racing classes)

2.5 degrees covers the deflection of the tyre and something like 1-1.5 degree of body roll. From that on the grip on the most important tyre is starting to decrease...

The balance of the car is very important, but without getting all of the grip from the tyre it makes for a good fun driving the car but it ends there!

[Rippthrough 98]

Most series' don't mind you adjusting the geometry of the lower wishbone provided you only alter it to fit offset bolts, which is fairly easy to do, then lift the pivot as far as you can vertically.

[Sandy 191]

Opinions differ obviously, but I would say that's too much camber, what you gain in lateral grip, you'll lose in traction, or the lack of.

[petert 586]

One of the nicest setups I've had has been standard front GTi springs reset 30mm lower and 21mm torsion bars (and of course a full cage). For me this emphasised how important it was not to have the front too stiff. I've since gone way beyond that, as I said in earlier in the thread. But the car is now a full race car and 23mm is a BIG step up from 21mm. It stills rides well however, as the damping matches the springs, but you wouldn't drive it around town.

[niklas 1]

I guess I need to clarify that from my perspective I'm talking about a pure racing setup running on semi-cut slicks (aka r-tyres). That type of tyre is very common over here but I'm not sure which type is commonly used in the UK.

Road tyres obviously don't require that amount of neg camber and doesn't produce as much roll, while slicks typically require 5-6 degrees neg camber to use them right.

 

For just road fun and the occasional track day, a more road-oriented setup will give much more fun!

 

But when you go beyond that and just need to go faster, the next step is to locate where the grip is lacking. And this is normally the outer front wheel which takes something like 65% of the load during cornering and probably even more when accelerating out of the corner.

So that is my reasoning for a very stiff front setup, increasing the grip of that wheel as much as possible. It doesn't mean I ignore the rear axle but there are physical limits to what can be done without altering the suspension completely.

 

But I think it's the same as with engine tuning, there are many different ways to reach the same result!

[brianthemagical 1]

tyre gets most grip when tread is flat on the road surface, ideally, the wheel is perpendicular to the road surface. lateral grip is shared between the front and rear wheels depending on the weoght distribution and weight transfere, nothing else, i'e more lateral grip on the rear during accleration. pretty much irelavent what tyres are used. the static neg camber is only really there to counteract flexy type stuff and any posotive camber gaied during roll or compression, like on Mac struts.