Understeer...

[rallyeash 155]

Hi guys, im after abit of advise on my 205 rallye track car on the handling front. i feel like im getting to much understeer with my current setup, front seems to want to just push on when any slight power gets added. for the setup im running i think it should be much tighter...

 

 

suspension setup is

 

Front

 

205 gti subframe

205 gti arb

Gaz GHA coilovers

300lb springs

eccentric top mounts, set as far back and in as possible

Hispec ulralite calipers on 266mm discs (not suspension related but still unsprung weight)

Quiafe Atb diff

 

Rear

 

205 1.9 disc beam,

23mm Torsion bars

Gaz rear dampers

24mm ARB

 

rear beam was built by anthony approx 2k ago and about 200 miles ago was checked over and the 23mm tb's added.

 

Wheels, S2 rallye steel wheels, 185 60 R14 toyo R888's, although will be dropping down a size to 185 55 R14 Yoko A048's which should have less sidewall flex and stop the rubbing on the rear arches when ive a passenger

 

colin satchell cage, full weld in job which goes through to the front struts, across from the front of the cage to the RH suspension turret then a built in strut brace between the turrets

 

running an iron block Xu10 engine

 

 

all suggestions welcome.

[welshpug 1,655]

try less power

 

maybe a proper diff, what's the ride height like front to back? i.e rake to the sills?

[rallyeash 155]

 

for example earlier, on the way home from fitting my 24mm arb back in i came around a medium sized round about, second gear, not really on the power much and just feels like there isnt enough front end grip. even on a trackday at combe a few weeks ago i couldnt hold my lines as tight when following a few cars and was going the same speed

 

 

 

the rear is a touch higher than the front, although i couldnt tell you exactly how much lower it is than standard, (gti gear on a rallye, iron block etc etc so quite a few factors in there)

 

i could measure the distance from the floor to the sills front and rear though?

 

maybe a plate diff is somthing to think about, although i can't afford to buy a new one as yet. a mate with a 205 gti6 just had one fitted and i must say its impressive

Edited May 2, 2011 by rallyeash

[Anthony 1,002]

How are the front tyres wearing?

 

The only thing that jumps out is that the combination of 309 wishbones and the eccentric mounts as you've got them set will be giving you quite alot of negative camber - not a huge amount and less than full on dedicated race cars would likely run, but certainly a fair bit more than the vast majority of 205 track cars will be running.

 

A plate diff will potentially help, but in this instance I'd suggest that it will be merely masking an underlying cause if you're struggling that badly.

[rallyeash 155]

front tyres are wearing fine, although as they don't do that many road miles the wear comes from the track so hard to tell i guess.

 

forgot to mention its on 309 arms and shafts on the front.

 

you can tell that there is a bit of camber on the front wheels but nothing that really makes it stand out. certainly nothing like the BTCC cars wer running at thruxton yesterday!

 

think it could be worth rotating the mount around abit to achieve abit less camber, but still leave them at the back to get abit of caster though?

Edited May 2, 2011 by rallyeash

[Cameron 16]

What tyre pressures were you running, and what are your damper settings?

 

There's nothing that screams out from your setup, what wishbone bushes are you running?

[Anthony 1,002]

If you've got some time to try it then there's certainly no harm in doing so - worst case is that you'll lose an hour and have achieved nothing, but certainly my gut feeling is that too much negative camber certainly won't be helping (remembering that in effect caster adds negative camber as you turn the wheel) and winding some off would be a good starting point. Try full caster, no camber as a starting point and go from there.

 

Ideally you need to reset the tracking everytime you adjust the eccentric mounts, but if it looks reasonable then it'll probably be OK for testing purposes.

 

Other thing you can try is removing one of the ARB droplinks (only one!) and see how much that helps - I don't think you're running enough front spring rate to have no front ARB long-term, but it would be interesting to see if you notice a dramatic improvement when the ARB isn't trying to lift the inside wheel all the time.

 

Ultimately though, with 200hp odd at the wheels you're going to have more power than you have grip and hence will need to exercise some restraint on the loud pedal.

[oli-pug 6 2 Cars]

How does it behave when changing direction and on turn in?

 

If it's only happening under power, it's not really understeer as such, just the power overcoming the available grip. Cheapest things to try would be proper setup of the front geometry, tyre pressures and damping. Wider front tyres and a proper diff would help things along no doubt too.

[welshpug 1,655]

how low is it sat BTW?

[rallyeash 155]

cameron, on track i was running 22psi which seem'd about right once hot.

 

just running standard bushes across the front setup, always thought pug stuff was as good as poly bushes.

 

i removed one of the droplinks when my car was on the road once before and the front end felt very loose and not very safe at speed.

 

i'll give the top mounts abit of adjustment later and take it for a spin. see how i get on.

 

i measured from the bottom of the lip on the sills to the floor and the front is approx 145mm and the rear is 160mm.

 

it kind of feels like that the front end doesnt grip on turn in but just sort of pushes on, as said this isnt on full throttle so i don't think its really the power thats making it understeer.

 

im running 300 lb springs which seems to be the recommended, although with my car theres no heaters, matrix, no heavy RS engine mount etc etc. i could be completley wrong but could it be there isnt enough weight over the front end?

 

here is a pic of under the bonnet, theres alot less than your average 205 gti6 engine conversion

 

Edited May 2, 2011 by rallyeash

[rallyeash 155]

wider front tyres ive been looking into, its possible to get 225 50 R14 R888's which could help a fair bit but the sidewall height would be more than my 185 60 R14's

 

seems to change direction fairly well, if you were driving at 40 mph turning from left to right, (like warming tyres up) feels fairly good

[stu8v 68 1 Cars]

You tried slower in faster out?

[rallyeash 155]

well even at low speeds the front seems to "wash out" more than i'd like

 

ive just been out and measured the turns lock to lock, im getting just a touch over 2 turns right and about 1 and 3/4s left. i then had a look at the TRE's and there is more threads on one side than the other which indicates the rack isnt central.

 

think im going to get it up on stands, centralise the rack, adjust the mounts to remove abit of the camber and see how i get on.

[Cameron 16]

I'm not convinced you're running too much camber, radials can take up to 6 degrees of static camber without issue! The problems with running too much are more related to braking than cornering.

 

I'm not sure about ATB diffs, but I know with a plate diff that you get push-on if you're not on the throttle round a corner. I find with my plate diff that if I brake, then turn in, then apply the power on the exit like I used to with an open diff, I find that it pushes on quite noticeably when turning in and especially mid-corner. If I then trail-brake the turn-in is super sharp, then easing on the power early helps guide the front end round and pull it in to the apex.

 

Don't consider this an attack on your driving style (I've never seen you drive round a track) it's just a genuine set of questions to rule out whether or not it's something to do with your driving style. How long have you had the ATB fitted and how much track time have you had with it? What's your driving style like, and how do you react when you feel the front end push on - do you stay off the power and / or apply more lock, or do you ease on the power? How do you approach turning in to a corner?

 

Ps.. standard wishbone bushes will contribute a small amount to understeer as they allow a relatively large amount of flex in the suspension.

Edited May 2, 2011 by Cameron

[rallyeash 155]

thanks for the reply, i consider myself quite a smooth driver and im not aggressive with either pedal. i will put the power on fairly early although progresively depending on the corner, im not all or nothing on the pedals.

 

ive owned the diff since 2008 although the car was off the road for a year for its rebuild etc so done plenty of driving on the track with it.

 

with regards to the driving with the understeer, ill be progressive with the power and lock and balance between the two and apply more power once the corner starts to open up.

 

i just feel the front end doesn't have the grip it should have with the setup ive got.

[Miles 331 1 Cars]

First port of call is get the measurements sorted for the front, without this it's a guessing game but with the iron lump there it will make the front end more understeery.

For stiffer sidewalls get away from the 48 and 888's as they are come more from a road tyre background, I run Siliverstone's on mine and the sidewall's are more like what you would get from a Slick than anything else.

[Cameron 16]

The A048's have a proper carcass too, I think it's just the 888's that have road tyre sidewalls.

[edbar 6]

From driving my 205 round mallory in the wet it would understeer if you were off the power, but if you loaded the diff it stuck like S@£t to a blanket(trail braking also). I know they take a bit of a panning from people on here and as I havent had a plate diff I cant comment on the differances but once you suss out what works with the atb it still is alot better than an open diff.

[TT205 42]

Have you tried some slightly softer front springs?

 

Are you running gti or 309 front arb - if 309 -maybe swap for gti?

 

Can you soften the front damping?

 

Failing that trail/left foot brake?

 

Raise the rear a fraction?

[swordfish210 20]

 

 

Are you running gti or 309 front arb - if 309 -maybe swap for gti?

 

 

 

 

 

 

suspension setup is

 

Front

 

205 gti subframe

205 gti arb

 

[Henry 1.9GTi 36]

Can you identify when it understeers?

 

If you were to go around a roundabout and slowly go faster and faster untill the limit is reached will it under or over or stay neutral. Usually this will indicate a steady state problem which will be primarily due to the balance of weight transfer. 23mm bars have approximately a 220lbs/in wheel rate although im not sure on the arb. You may wish to change your balance, would recommend finding grip at the offending axel rather than loosing it at the rear. i.e go softer on the front.

 

If its a transient problem with turn in. First check all thats mentioned above regarding geometry. And then you can either soften the front damping or increase the rear to slow down or speed up the weight transfer respectively. This will help if in steady state the car is ok but wont turn in well.

 

Failing you can gain grip at the front by optimising the camber. aim for ~2 deg when at full lateral G i.e the car has rolled what its going to roll and has rolled the tyre as much as it will. (quite alot on a 205!) Move weight backwards in the car as best your can. Best way to do this is move the heavy lump that is the driver, well I am a heavy lump atleast, extend the steering/pedals and move the driver seat back.

 

I would suggest going by my own car setup where the rear roll stiffness is only marginal higher at the rear ( 250lbs springs, 21mm arb. 23mm TBs 25mm arb) that you may want to soften the front. If it lifts a rear wheel already then max weight transfer has occured and any additional weight transfer that is required in order to increase the G further will happen at the front not helping then you simply have to find grip at the front by movng weight back and sorting camber out. Bigger front tyres will have a higher cornering stiffness and will help reduce the front slip angle for a given normal load so thats worth a shot as well.

[Cameron 16]

The problem with going softer is you then suffer from more body roll, it's not as clear cut as saying softer suspension = less weight transfer = more grip, as you have to factor increased body roll and gaining positive camber that comes with it. Would you gain enough from a slight reduction in weight transfer to make up for a increase (i.e. towards positive) in camber? I'm not so sure..

 

I recently re-fitted my front ARB as it felt like the car was understeering slightly on neutral throttle the last time I went to Oulton, and when I looked at some of the photos from the day it was clear that the front was seeing a lot of roll! I went out last week and definitely felt like the front had more grip than before, which I put down to less roll and less of a tendency towards positive camber. Turn-in has also improved from last time.

[rallyeash 155]

Heres a picture of my car at quarry at castle combe, looks pretty flat mid corner. (please ignore the flappy bonnet, and lack of filter, these are being sorted atm) as far as i know it hasn't lifted an rear inside wheel on track.

im still learning about suspension setups, calculations weight transfer etc but i think im understanding it so far.

 

henry, its when the power is being progressively applied through corners on track the front end wants to run abit wide, never wants to oversteer atall.

 

ive got hold of the tracking gauges again so im going to set the rack straight and add a touch of toe out as this should help with turning in also?

 

[swordfish210 20]

What steering rack do you have as it looks like you're using a lot of lock there?

[Cameron 16]

How much throttle pedal travel do you have? Nothing looks too offensive from that photo, could it be something as simple as a throttle that is too aggressive? Seems pretty plausible, especially if you're making 200bhp at the wheels!