[race_prep] Guernsey Hillclimb 205 Build

[wardy18 33 1 Cars]

Gaz are workin well, beaten my pb by 0.07s in the 2nd run of the day

 

The rear is tending to slide out a bit more than before, not sure if the rears too stiff whilst sat on the bump stop or if it's because I have them on full hard setting??

[welshpug 1,661]

better to slide than snap IMO

[wardy18 33 1 Cars]

I've softened the suspension by a quarter all round and also marked my tyre walls to read how much roll im getting.

 

It's a left hand straight into a long right hand after a fast straight that it's sliding out so when it kicks out a little round the left on de-acceleration I'm tryin to turn it into the right and it burries and scrubs speed off badly!!

[wardy18 33 1 Cars]

Mission now to understand geometry set up of a fwd car with McPherson strut, after 2 hours worth of reading so far holy sh!te there's a lot involved eh!!

 

1st thing to sort is either lower the front more if Its possible to get shorter 300lb springs or raise the rear because the new Gaz susp has raised the front slightly and so the rear is lower than the front which is a big no no for weight transfer!! But before buying any new springs for the front I will measure my corner weights and un-sprung weight to find if 300lb is the optimal spring!!

 

Mission on

[stu8v 68 1 Cars]

Maybe its already too low and thus causing more roll.

[Cameron 16]

Don't run your dampers too stiff, they'll "pack down" over undulations and you'll find you have less grip. I would start off by testing them from full hard to full soft, maybe at 4 points, to see which one feels best then fine-tune from there.

 

You run slicks don't you? It could well be that 300lb is too soft, and that's why you're getting roll.. would be interesting to know what your full spring & ARB setup is front & rear.

[wardy18 33 1 Cars]

Gaz rears have 43 clicks of adjustment and fronts have 20.

 

I started off fully hard on both then softened as day went on but found had more understeer however was adjusting pressures at the same time.

 

Reading up to tonight I think I have been a bit backwards with pressures, skip brown would recommend starting with FR 28psi and RR 24psi, I ran 26 max throughout the day and always the rears 1 or 2 psi more than the front, Avon reccommended no lower than 26psi and so this may add to my tyre roll issues, just seems odd to go more than 26psi but I'm willing to try anything.

 

Set up

 

Front - 300lb springs, ARB as standard diameter (i think) with adjustable drop links, 8.7" Avon crossply slicks on 9" rims

 

Rear - 21mm ARB, 8" Avon crossply on 8" rims

Edited August 12, 2012 by wardy18

[EdCherry 34 1 Cars]

Theres so many variables and so little information heres its impossible to give you a definitive direction to work in.

 

Starting from full hard is the wrong way in the first place.

[Cameron 16]

That would make sense, more rear grip = more noticeable understeer; so you're heading in the right direction, you just need to do something to improve grip at the front.

 

What static geometry are you running - i.e. camber / caster / toe front & rear?

 

If you're still on standard torsion bars you may want to remedy that asap! I would suggest at least 23mm TB's, or 24mm and increasing the front rate a little, this isn't a road car so you don't need to worry about ride comfort, you need to be more concerned with improving response and keeping good geometry i.e. not rolling around like a boat. Cross-ply slicks are very sensitive to changes in camber, so I would be aiming to keep body roll to an absolute minimum! It's expensive to buy new bars, but something you need to do unfortunately.. I would stick 24mm bars on and fit 350lb springs up front as a minimum, and it may be worth you investing in a 23mm rear ARB for when you need to tune the balance.

[wardy18 33 1 Cars]

I know, the amount the things you can change is ridiculous and not understanding them all means im pissing in the wind when making adjustments so im out to understand it better, will look into buying some Geometry books as i know there are hundreds out there.

 

1) Whats the best way to measure the front and rear ride heights so to be able to adjust them, i was told once by Nick at Shenpar the best way is to measure the sill at the points front and back where you jack the car up, the back should be slightly higher than the front using these measuring points??

 

2) Has anyone experimented much with Caster adjustments? I have read for a FWD that between 3-5deg or even up to 7deg +ve caster. With more +ve Caster the turn in to a corner wont be as sharp but the mid corner and exit will be easier due to more self centering action and will be more stable at higher speeds. Plus, more caster adds more -ve Camber on the outside wheel through turning a corner and more +camber on the inside wheel which is ideal to counter act the roll and keep the tyres flat on the track.

 

So far my plan is for the next hillclimb in 2 weeks:

 

Raise rear ride height

Set suspension to Medium all round

Run fronts pressures higher, min 28psi

Run rear pressures lower, min 24psi

Keep front camber at -ve 1deg

Set front caster to +ve 5deg

 

Variables to test through the day:

 

Front suspension 4 clicks either way

Rear suspension 10 clicks either way

Pressures up to 2psi higher (so 30FR, 26RR)

Caster up to 7deg +ve

 

However before then i am going to attempt to measure the corner weights and un-sprung weights and also attempt to work out the wheel frequencies to ensure the 300lb front springs are adequate and the 21mm ARB at the rear is adequate.

 

 

Cameron - My current set up is 1deg -ve Camber, Caster no idea , Toe 1.5mm Toe out (dont need a lot as im rose jointed wishbones so nothing going to move much).

 

What are standard torsion bars, these 21mm i have i was under the impression these were turned down from standard size but i could be wrong?? Do you mean to change the front ARB too??

[welshpug 1,661]

Standard bars are 18.9mm, i'd imagine as cameron said that even 21 mm is too soft especially if you want it low for some strange reason.

 

21mm was tarmac rally bars for peugeot sport years ago at a lot higher than you are running, their specified ride height is around 25 mm lower than std.

[wardy18 33 1 Cars]

especially if you want it low for some strange reason.

 

I was always under the impression that the lower the centre of gravity the less the car will roll, for the front baring in mind that as long as the lower wishbones do not go pass horizontal and always remain inclined down towards the wheel and you have enough suspension travel then your at your limit, the rear then can be lowered to remain slightly higher or equal to the front???

 

Plus the Roll Centre on the rear of 205's with the beam is apparently at ground level and the front roll centre should always be at best lower than the rear but you cant get lower than ground level so getting this as low as possible on the front is optimal?

 

Is that not a correct understanding?

[Cameron 16]

Nope! The general rule is that rear roll centre should be higher than the front as it helps turn-in. Not much you can do about that with trailing arms though!

 

The reason you'd get more roll is that the roll centre height drops faster than the CG lowers, and it's the height difference between GC and RC that determines the amount of body roll you get. However, contrary to the old fashioned way of thinking (and a rather long thread on here) low RC is not such a bad thing! You just need to regain some roll stiffness by increasing your spring rates so that body movement is controlled and you don't end up bottoming out your suspension constantly.

 

Edit: What you do need to be worried about is bump steer when lowering, and that isn't such an easy fix. "Bump steer correction" kits are available but they move the outer track rod balljoint down, which isn't what you want to do when the steering arm (on the upright) is behind the wheel centre.. but moving the rack upwards can be difficult so you're not left with much choice.

Edited August 13, 2012 by Cameron

[wardy18 33 1 Cars]

the front roll centre should always be at best lower than the rear but you cant get lower than ground level so getting this as low as possible on the front is optimal?

 

 

Nope! The general rule is that rear roll centre should be higher than the front as it helps turn-in.

 

This is what i said just in a different way is it not??

[wardy18 33 1 Cars]

Edit: What you do need to be worried about is bump steer when lowering, and that isn't such an easy fix. "Bump steer correction" kits are available but they move the outer track rod balljoint down, which isn't what you want to do when the steering arm (on the upright) is behind the wheel centre.. but moving the rack upwards can be difficult so you're not left with much choice.

 

I have big arms and a strong grip :P but i have the bump steer kit fitted which lowers the track arm but about 2 to 3 inches to counter act bump steer and it works just fine, i have no issues with that plus running a diff like the Gripper i have makes for an aggressive ride at cruising speeds but when in full race mode you hardly even notice it!!

 

Definitely going to look into upgrading the rear TB's, do you recommend upgrading the front ARB too or just concentrate on the Spring rate? I dont just want to just throw money at a educated guess though, so i think working out the wheel frequency (cpm??) and then converting that to spring rate will give me the best choices!!

[welshpug 1,661]

Moving the rack up isnt that difficult if youre handy with bits of steel and a welder, getting it in the right place is time conduming though

[Cameron 16]

DERP! Sorry, I simply must stop masturbating!

[wardy18 33 1 Cars]

Whats the best way to measure Sprung Weight, is it Corner Weight less Un-Sprung weight??

 

If so, how best to measure Un-Sprung weight because i have read you can drop the top mount bolts off so the whole of the hub/suspension etc etc is sat on the scales but part of the suspension is Sprung Weight is it not?

Edited August 13, 2012 by wardy18

[Cameron 16]

The best way to measure is to take a corner off and put it on the scales - no doubts then!

 

Sprung mass = vehicle mass - unsprung mass.

 

Starting from a ride frequency is a bit of an odd way to go at it really, unless you know exactly what ride frequency you need, so I would just try to keep it as simple as you can! Your front spring rates are lower than the 350lb/in I was recommended to run with semi-slicks, and after a while I thought it would be better with slightly stiffer springs. If I were you I would run 350lb at the very least, matched to 24mm bars. You already have a 21mm rear ARB so maybe try that out first before thinking about any ARB changes.. if you find it understeers then maybe up it to a 23mm.

 

A tool that will help you no end with tyre pressures and geometry is a temp probe for your tyres. It may sound a bit excessive but tyre temps can tell you so much about whether you have the correct pressures and amount of camber, and really helps to take some of the guess work out! Take the temps across the surface (outer shoulder, middle & inner shoulder) and the hot / cold areas will tell you what parts of the tyre are working the hardest - you want temps to be even throughout.

[wardy18 33 1 Cars]

Thanks for the advice Cameron, a little confused though, I have 21mm torsion bars at the rear and no ARB?? Isn't a rear ARB an aftermarket attachment??

[welshpug 1,661]

No its 19 mm on a gti, 106 runs 24!!

[wardy18 33 1 Cars]

Here's some photos from Saturdays hillclimb, you can see from these pics the issues im having with the front end burying round fast corners:

 

Pic 1 - This is a short distance from the wall behind so if you thinking how di i get that angle so quickly off the wall its because the car is drifting sideways due to de-acceleration after a very close call to that wall behind. http://www.guernseymotorsport.com/gkmchillclimb11-08-2012-3

 

Pic 2 - Off the line, see the front lift and rear squat http://www.guernseymotorsport.com/gkmchillclimb11-08-2012-6

 

Pic 3 - Again the same corner entry as pic 1, see the roll of the front and rear outside wheels http://www.guernseymotorsport.com/gkmchillclimb11-08-2012-93

 

Pic 4 - Here's a good one, fast corner our of the long long right hander coming onto the bottom straight, you can see the understeer happening http://www.guernseymotorsport.com/gkmchillclimb11-08-2012-155

 

Pic 5 - Same corner as pic 4, serious rear wheel lift and front right burying http://www.guernseymotorsport.com/gkmchillclimb11-08-2012-166

 

Pic 6 - Round the last corner before the finish line, see the rear wheel roll, rim almost touching the ground, front wheel rubbing on arch due to reducing camber from 1.5deg to 1deg and so top of wheel out further than usual http://www.guernseymotorsport.com/gkmchillclimb11-08-2012-212

[Anthony 1,003]

Rear - 21mm ARB, 8" Avon crossply on 8" rims

and the 21mm ARB at the rear is adequate.

I for one am a little confused, as you've clearly stated you've a 21mm ARB there?

 

Which is it that you've got - 21mm torsion bars (the bars on the outside of the tube) or a 21mm ARB (the bar on the inside of the tube)? If you really have got no ARB on the back then at least refit the standard one as a sensible starting point!

[wardy18 33 1 Cars]

Sh!t sorry getting confused, I'll check and report back!!

[wardy18 33 1 Cars]

Ok apologies, it's standard ARB (size unsure but i know I've never changed it) but i fitted my 21mm torsion bars!!

 

What's standard sizes for both?