Understeer...

[rallyeash 155]

standard rallye steering rack Mark. quick rack or a Xsara rack worth changing too?

 

standard throttle pedal arrangment still,(for a gti)

 

my personal feeling its down to, Spring rate, tracking setups, damper adjustment, top mount adjustment, running 185 width tyres, little things like that which add up.

 

i mean the understeer isnt horrendous, just i think the car could be improved alot more than its current setup without to much expense.

[Cameron 16]

But you're running throttle bodies, so it could be that the cam is a different size to the standard one and you aren't getting much pedal travel.

 

Could well be a combination of heavy engine, soft springs, thin tyres etc.. What compound are your 888's?

[swordfish210 20]

standard rallye steering rack Mark. quick rack or a Xsara rack worth changing too?

 

 

 

It won't solve your current problem but it would be a worthwhile upgrade considering the spec of the rest of the car.

[Henry 1.9GTi 36]

I did mention front camber cam, and yes I agree that it is very benificial to stop the roll to provide the correct camber. The front, depending on your wishbone angle when static should have some limited camber compensation unlike the rear and the right camber can add ~10% grip. From the pic it looks like the contact patch is good but perhaps need a little more to deal with the tyre plunge, its amazing how much a tyre moves on the rim! check out some of the aussie v8 super car undercar vids on youtube.

 

Also if its when applying the power if you are on the limit and try and accelerate it will most definately understeer. google a traction elipse

 

If you think about rear wheel drive sports cars with more weight at the rear they have much larger tyres at the rear to increase the cornering stiffness and reduce the slip angle. May be worth trying (on the front). Definately try one thing at a time and see how you get on. Easiest way to test on a track day would be to take the set of wheels and tyres with you. And also try softening the front by disconnecting the arb. Cheapest way to go about it, and least time consuming considering you want to enjoy the track day!

 

Another cheap option try running very soft rear tyres in terms of pressure and pumping the fronts up a bit. This will again reduce the cornering stiffness at the rear and increase at the front hopefully adjusting the slip angle to be bigger at the rear than the front.

 

good luck, I am in a similar situation so keep us posted

[rallyeash 155]

theres plenty of travel on the pedal, pretty much the same as my mates 205 gti6 on standard inlet.

 

im not running the standard gti6 engine mount so theres quite a few kg saved there, im running a tiny denso alternator, another few kg saved, race battery in the boot so i don't think the engine would be any heavier than a complete mi16 engine. blocks only 18.5kg heavier from memory to start with.

 

R888's are medium compound, the tyres get hot enough i shouldn't worry about that

[Henry 1.9GTi 36]

heres an indication of how there is no camber compensation at the rear. Any body roll is transfered to the tyre. You can also see a bit of tyre plunge. Still understeers though lol

 

[swordfish210 20]

 

 

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.

 

Thats what i found when i disconnected my front ARB, too much roll was unloading the inside tyre and the turn in was virtually non existent. When we reconnected the ARB's on the 306 racecar i was working on the car went much quicker (some 2 seconds around Combe) and the driver was much more positive about it, that was with 400lb springs on the front and later 500lbs

[kyepan 291]

judging by my own experiences... on a similar set up with a similar problem, which got solved i might add.

 

Raise the front 20-30mm and add a touch of toe in 0.5-1 degree total, then re-test.

 

raising the front will help wishbone angles, which currently under the compression of cornering are probably inducing more positive camber than negative..

 

the toe in will probably be neutralised as the suspension compresses due to the natural bump steer curve of the suspension geometry.

 

once again, raising the front will move it more towards the stable end of the bump steer curve.

 

 

then.. and only then start softening the front and or buying expensive differentials, i learned this the hard way..

 

ps tyre pressures may also help.

 

cheers

 

j

[rallyeash 155]

didnt you find the rear to low though with raising the front 20-30mm?

 

look like its going to take off!

 

i can see where your coming from with bringing the ride height up though, what was the sill height from the floor?

Edited May 4, 2011 by rallyeash

[Flozman 4]

you need to be able to shift weight onto the front, you cant really do that with the sump dragging 300lb springs???

[Henry 1.9GTi 36]

what do you mean Flozman?

[rallyeash 155]

just about to post the same thing

[Flozman 4]

Well everything seems to be geared towards eliminating movement, ARB, dampers, springs, strut bars. But it just makes weight transition too sudden, why not give yourself a bit more movement so you can adjust the throttle, brakes and steering according to the situation. After all thats how the thing was designed.

Edited May 4, 2011 by Flozman

[Henry 1.9GTi 36]

I think the main reason is becuase this specific car is for the track only, or so I gather.

 

Reducing response time and roll will improve drive feel alot as well.

[welshpug 1,655]

you'd need to raise the back too...

 

that does look VERY low to me, its hard to compare a gti shell to base model!

[swordfish210 20]

Ash, do you want to bring the car over to mine one evening, i still have Ed's tracking gauges so we could sort the rack out and have a look over the rest of the car to rule out anything obvious.

[Flozman 4]

I think the main reason is becuase this specific car is for the track only, or so I gather.

 

Reducing response time and roll will improve drive feel alot as well.

 

Yeah I understand Mate its always a comprimise but if there is no "give" in the suspension, then the front tyres will give up before you can turn in. If the springs were a little softer you could let them compress the weight while the tyres do the steering.

[Cameron 16]

I think you've got this confused.. If you make the suspension soft and compliant you dull turn in as it allows the body to roll and lumber around, and soft bushings will allow your geometry to change unfavourably; if you stiffen things up then you have the opposite. Ride frequency (the frequency that the body will "bounce" on the suspension) and cornering responsiveness go hand-in-hand, hence why an F1 car (very high ride freq) corners like a housefly and a big American car (very low ride freq) is more like an oil tanker.

Edited May 4, 2011 by Cameron

[Henry 1.9GTi 36]

Sotening the suspension all around by the same amount wont affect the load on the tyres, well the weight transfer, contact patch load variation is another topic. You can only adjust the weight transfer front to rear, not the total by adjusting springs and arbs. The only way to redcue total weight transfer is to lower the CoG increase the track, go slower and increase corner radius. So even if the car rolls all over the place, the loading on the tryes will be the same as if it didnt assuming the front to rear stiffness balance is the same for both setups.

[Cameron 16]

Wasn't talking about contact patch load or weight transfer though, I was talking about steering responsiveness.

[rallyeash 155]

im starting to get

 

 

firstly i will be

 

centralising the rack

setting the tracking up

Harden the rear dampers a couple of clicks

soften the front a couple of clicks,

 

should help abit i recon

 

thanks for the offer Mark, ive got hold of the Laser gauges from Matty so going to give it a bash over the weekend, probably saturday morning. will give you a shout though if im not really getting anywhere with it.

[stu8v 68 1 Cars]

I think you've got this confused.. If you make the suspension soft and compliant you dull turn in as it allows the body to roll and lumber around, and soft bushings will allow your geometry to change unfavourably; if you stiffen things up then you have the opposite. Ride frequency (the frequency that the body will "bounce" on the suspension) and cornering responsiveness go hand-in-hand, hence why an F1 car (very high ride freq) corners like a housefly and a big American car (very low ride freq) is more like an oil tanker.

 

Not strictly true, you can run bigger anti roll bars with a softer setup and still retain the sharpness. As proven by my old impreza.

 

I do agree its a balancing act though to gain the optimal setup.

 

Personally I would set it up with a sensible ride height front and rear (ie PTS Tarmac spec), use PTS spec front spring rates that work with the sizes of roll bar and torsion bars you have and then go from there changing one thing at a time to fine tune what you have.

 

I you cant be bothered, talk to someone who races they will no doubt tell you there base setup and that will get you started.

 

All IMHO

[Henry 1.9GTi 36]

sorry cameron was just trying to respond to Flozman.

 

Good starting point rallyeash. Also try low rear tyre pressure and higher front. Quick and easy changes.

[kyepan 291]

im starting to get

 

 

firstly i will be

 

centralising the rack

setting the tracking up

Harden the rear dampers a couple of clicks

soften the front a couple of clicks,

 

should help abit i recon

 

thanks for the offer Mark, ive got hold of the Laser gauges from Matty so going to give it a bash over the weekend, probably saturday morning. will give you a shout though if im not really getting anywhere with it.

 

i'll say it again.. in case you didn't hear the first time.

 

raise the front.

 

sorry if that sounded a bit bossy.. but it really is what you should do first.

 

it takes 10 mins to jack the front, undo the grub screw and use the gaz tool to spin the shock adjuster up.. you could even raise it 10mm, test it, come back, raise it another 10mm.. test etc, and really back to back test.

 

Don't worry about any of the other stuff or the back being low for the time being, get the wishbone angles correct, and the -ve camber being used properly, then try it out.

 

bearing in mind you have a nearly identical set up to me... and I also suggest you read the "how not to modify your suspension" thread that is pinned to the top of the suspension forum, if you have not already.

 

hope you get it sorted.

 

J

[rallyeash 155]

rite o boss!

 

only thing is ive driven cars which have been lower on the back than the front by abit and the back feels likes its on ice! yes i see your point about the angles etc but the car isnt that low on the front end anyway.

 

also shouldnt there be a 10% rake front to rear?

 

Ash