Cornering Analysis

[AdamP 0]

This photo taken at gurston gives a very good image of how the car responds to hard cornering.

 

http://www.zipp.co.uk/gallery/Gurston-Down...204184.jpg.html

 

In that photo it's running GTi-6 dampers, spax springs, 309GTi wishbones and the standard GTi ARB at the front; spax dampers, GTi TBs and a 24mm ARB at the rear. All on Grp N / Poly bushes.

 

Looking at this picture I would say stiffer front springs is the way to go, as the inside rear is unloaded long before the front reaches full roll? This should increase front end grip as the contract patch of the tyre is kept flatter on the tarmac? And increase the traction of the inside front out of the corner as less weight is transferred across to the outside front?

 

If this is true, does anyone know what rate the Spax -40mm springs are?

 

Cheers, Adam

[Batfink 201]

Spax springs are most likely around 115-130lb.

I'd say stiffer dampers would help too...

Edited May 20, 2010 by Batfink

[oz. 2]

309 front ARB? Might help with the roll but the suspension would still sag.

[AdamP 0]

Spax springs are most likely around 115-130lb.

I'd say stiffer dampers would help too...

 

Well i should have mentioned I've just bought a pair of spax adjustables off ebay as the GTI6 ones are leaking pretty badly now.

 

What sort of spring rate should I be looking at? Around 160lb possibly? Considering it's completely stripped and running a TU3S ali-block engine and therefore a fair bit lighter than a GTi at the front end.

[AdamP 0]

309 front ARB? Might help with the roll but the suspension would still sag.

 

I want to avoid a stiffer front ARB where possible as it reduces traction of the inside front out of the corners, which is pretty important on low speed corners at hillclimbs.

[Batfink 201]

I sell 155lb springs as a nice medium between road and track. Personally I would be saving for and fitting at least 280lb springs with coilovers....

The problem will be as you stiffen up using a standard type spring the car will not compress the springs. You can go too short in the quest for a lowish ride height and as the suspension fully extends the spring will unseat...

[Cameron 16]

Looking at this picture I would say stiffer front springs is the way to go, as the inside rear is unloaded long before the front reaches full roll? This should increase front end grip as the contract patch of the tyre is kept flatter on the tarmac? And increase the traction of the inside front out of the corner as less weight is transferred across to the outside front?

 

That's half right, half wrong.. You'll actually be increasing front weight transfer by fitting stiffer springs, and losing some front end grip. BUT you'll benefit overall as the grip increase brought about by reducing the body roll angle, and therefore the positive camber on the outside wheel, will outweigh the small reduction in grip caused by increased load transfer.

 

Also with stiffer front springs you should see a small reduction in rear load transfer, which may help reduce your tripoding.

[AdamP 0]

I sell 155lb springs as a nice medium between road and track. Personally I would be saving for and fitting at least 280lb springs with coilovers....

The problem will be as you stiffen up using a standard type spring the car will not compress the springs. You can go too short in the quest for a lowish ride height and as the suspension fully extends the spring will unseat...

 

I'm a student on a budget of essentially nothing. I can't do 'saving' as im not earning

 

I don't want to go really stiff on the front as a) the car is used for a variety of disciplines over various surfaces (trackdays through to the odd 12-car), and I cant afford the TBs to match.

 

My two options are:

 

1) Try and find some off-the-shelf springs that are stiffer.

 

2) Convert the dampers to 2.25" adjustable platforms.

 

I've read (in a post by Sandy IIRC) that the Eibach E20-70-001-01-20 springs (106 sportline springs) are progressive from around 100lb to 160lb and work well on the TU engined 205s.

[Miles 331 1 Cars]

Get a Diff in it, Doesn;t matter too much about the rear wheel being in the air, What tyre's are you running and what Camber have you got on the front, Ignore the so call -1 which the 309 give's, they rarely do unless your lucky.

Need to be more on the Kerb thou

[AdamP 0]

What tyre's are you running and what Camber have you got on the front, Ignore the so call -1 which the 309 give's, they rarely do unless your lucky.

Need to be more on the Kerb thou

 

LSD is WAAAYYY out of my price range

 

185/60 R13 Yoko 48Rs at the moment. No idea on the camber, have never had it checked. The 309 bones have definitely added a fair amount of camber, this is hard cornering before they were fitted:

 

 

And that's my dad driving in that one, i'm a bit more aggressive on the curbs

[Cameron 16]

What bushes are you running front and rear?

[AdamP 0]

What bushes are you running front and rear?

 

Polybushed front wishbones, BBM grp N top mount rubbers and (solid) beam mounts.

[Cameron 16]

Wow, it just looks like you're getting some epic flex somewhere.. I guess it's down to the soft springs then.

[TT205 42]

IMHO

 

Looking at your picture I think your problem is actually created by your 24mm rear ARB as your suspension isn't particularly trick

 

But is it actually a problem? - there's nothing wrong with an ARB that size so long as the rest of your suspension matches it

 

Basically if you are going to run a 24mm rear ARB then you really need bigger torsion bars, 175+ (if not 250 ish) front springs and tarmac spec rear dampers to get the best out of it. That way the hight of your 'tripoding' will be far less

 

But .... lets be realistic

 

If you can't afford the upgrades - this level of 'tripoding' will reduce understeer significantly and you will corner faster - but do at least fit solid rear beam mounts if you don't already have them

 

Do bear in mind that essentially you are running slicks on a standard car! With no other mods, I think a bigger than standard rear ARB is the biggest (and cheapest) bang for buck modification and you already have this

 

Personally I would leave the front ARB alone, given some bank balance - Yes an LSD would be great but to go further, you need (in no specific order) bigger torsion bars (maybe 21's given how light your car is) coilovers with eccentric top mounts and tarmac billies - get saving

 

Dave

Edited May 20, 2010 by TT205

[AdamP 0]

I'm by no means suggesting that the tripoding is detrimental. The rear ARB has been the single biggest factor in reducing understeer and improving turn in, and the times on the hills have proven this. The addition of the 309 wishbones, 19mm tbs, GTi front ARB (smaller than the XS one) and 24mm rear ARB took my time at Prescott down from 58.6 secs to 55.3 secs. I spent the first season chasing the weak link around the suspension which has led to the setup i have now. Im just trying to figure out whether it can be improved at minimal cost. I can't justify spending any real time or money on it as my Locost will be the main competition car from now on and if I have money it will be spent on that.

[AdamP 0]

Wow, it just looks like you're getting some epic flex somewhere.. I guess it's down to the soft springs then.

 

If you're looking at the Oulton Park pic, it didnt have any of those there! It was still running rubber bushes all round and the XS subframe. It was giving me some very unpredictable grip changes.

 

The Gurston pic is how it is now

 

Thinking of flex, would I gain anything from an upper strut brace?

[Miles 331 1 Cars]

Providing you use a good brace, them maybe a little, most which have bends in or oversize holes to go over the studs are all pretty much useless

You want a nice straight tube is possible with drop plates to mount on the edge of the strut tower's

 

What time did you do at Gurston?

Edited May 20, 2010 by Miles

[AdamP 0]

Providing you use a good brace, them maybe a little, most which have bends in or oversize holes to go over the studs are all pretty much useless

You want a nice straight tube is possible with drop plates to mount on the edge of the strut tower's

 

What time did you do at Gurston?

 

The problem is the carb sits directly between the strut tops. Will have to have another look.

 

In 2008 I did a 44.5, which was when it was still running the XS subframe, tbs and arb. In 2009 I span on the first practice, and did a cautious low 43 second run on the 2nd, then it bucketed it down before the competitive runs Could have got into the low 42s if it had stayed dry I reckon.

[DaveW 6]

Should be ok if you got a k&n filter on the carb?

[crf450 0 1 Cars]

That's half right, half wrong.. You'll actually be increasing front weight transfer by fitting stiffer springs, and losing some front end grip. BUT you'll benefit overall as the grip increase brought about by reducing the body roll angle, and therefore the positive camber on the outside wheel, will outweigh the small reduction in grip caused by increased load transfer.

 

Also with stiffer front springs you should see a small reduction in rear load transfer, which may help reduce your tripoding.

 

 

I reckon looking at pictures of what your cars doing in hard cornering is the best way you can analyse what your cars doing without going for full datalogging. After learning so much from pictures like this with my own car I plan on setting up four camera's set as low as possible filming the tyre contact patch, I reckon this will tell me even more.

 

Harder front springs reduce weight transfer which seems pretty obvious too me. If your running standish front ARB or no ARB (as a lot of people with front wheel drive cars do) you'll need very high spring rates to stop body roll leading to weight transfer.

In my opinion you want to be looking at at least 450lb springs if your running sticky motorsport tyres. I've ran up to 650lb on my 1000kg 306. I am planning on going down to 350lb springs but I'm will be running much more front ARB which means the opposite springs to the one that's taking the cornering forces will be having much more of an influence.

Cheers Martin

[welshpug 1,658]

21mm torsion bars aren't that expensive if you speak to Paul (205turbo) or Anthony

 

I'd have a word with Colin satchel if you can get hold of him, his suspension knowledge may be able to help you, he still holds a hillclimb record from 2004 in a car he built himself I've been told!

[Henry 1.9GTi 36]

stiffer front springs will increase weight transfer significantly. Body roll only adds a small amount of weight transfer and the main reason you dont want it is because of all the geometry changes it induces. As well as making the car feel harder to drive.

 

How does the balance of the car feel?

 

Looks like your getting some positive camber on the front and I suspect alot more on the rear. Add a s*it load of static camber and keep the same suspension and it will corner faster. Or stiffen it up back and front depending on balance and don't worry about the camber. Whats cheaper?

Edited May 27, 2010 by Henry 1.9GTi

[crf450 0 1 Cars]

stiffer front springs will increase weight transfer significantly. Body roll only adds a small amount of weight transfer and the main reason you dont want it is because of all the geometry changes it induces. As well as making the car feel harder to drive.

 

How does the balance of the car feel?

 

Looks like your getting some positive camber on the front and I suspect alot more on the rear. Add a s*it load of static camber and keep the same suspension and it will corner faster. Or stiffen it up back and front depending on balance and don't worry about the camber. Whats cheaper?

 

Please explain why stiffer springs will increase wieght transfer?

[Henry 1.9GTi 36]

Total load transfer for a given cornering force during steady state cornering will remain constant as long as you dont chuck your passenger out half way round the corner The CG location will change during roll slightly, affecting the load transfer. Track width may also change slightly during tyre deflection.

 

Stiffening one end will shift the available load transfer to that end of the vehicle.

 

Going stiff helps control geometry during suspension movement, primarily camber gain during excessive body roll. and any aero the car is running. The aero part not being relevant on 205s.

 

Vetical load on a tyre has diminishing returns with regards to lateral force generated. This is key to tuning the balance of the car.

 

This is just my understanding as is probably far from the truth and doesn't take into account many other factors.

[crf450 0 1 Cars]

Total load transfer for a given cornering force during steady state cornering will remain constant as long as you dont chuck your passenger out half way round the corner The CG location will change during roll slightly, affecting the load transfer. Track width may also change slightly during tyre deflection.

 

Stiffening one end will shift the available load transfer to that end of the vehicle.

 

Going stiff helps control geometry during suspension movement, primarily camber gain during excessive body roll. and any aero the car is running. The aero part not being relevant on 205s.

 

Vetical load on a tyre has diminishing returns with regards to lateral force generated. This is key to tuning the balance of the car.

 

This is just my understanding as is probably far from the truth and doesn't take into account many other factors.

 

That's sound like its come straight of some text book and I think your overcomplicating things.

The concept that weight will transfer more with softer springs as far as I can see isn't complicated.

Lets take a Citron 2cv which has notoriously soft suspension. When it goes round a corner you can see the thing almost tip over because the soft suspension is allowing the weight to transfer. If you welded the suspension solid you would not get any transfer at all .

Edited May 28, 2010 by crf450