Gtr Suspension Advise

[Risking]

Ill start with the general set-up of the vehicle.

Its an R32 GTR.

Ohlins dampners with 6kg front and 4.5kg rear springs

ARC adjustable sway bars.

Adjustable rear camber arms

Adjustable front castor rods

Roll center adjusters (lower control arm)

Usual strut bracing

Comprehensive Half cage(front section currently not finished)

245 A048's hot temp of 32psi

Currently using 7degrees castor

total 2mm toe out on the front

2deg neg camber front

Rear camber 1deg neg

rear toe total 1mm toe in

Sway bars were set to medium rear, soft front.

Ride height is set correctly

New engine is making more power but otherwise the same.

Now this all used to work really well with the old engine. However now with the new engine im finding a massive ammount of power oversteer. The attessa is working perfectly and the transfer case is not that old.

Perfect example is coming onto oran parks main straight I used to come into the final turn and be able to brush past the wall with confidence.

Now however the rear ends so taily im having to use up alot more circuit than I like too.

I tried all types of sway bar combinations over the weekend however everything seemed to give me the same result. Tire temps are even all the way accross the surface and was checked using an infa red sensor (I cant remember the temp but its written down in my log from the day)

It does suffer from some mid corner understeer as well but thats always been there and ive come to accept it.

Am I missing something with the setting up of what I have?

Could the use of the half cage and not having the front section fitted yet be contributing to the problem?

Can anyone suggest possible changes to what im using?

Im sure ive missed some info but if people have useful input or need extra info any help is appreciated.

Thanks In advance Brad.

Edited February 4, 2008 by Risking

[sh@un]

"advice"

(sorry, i've seen too many threads with the wrong use of advice/advise in the title lately)

[Duncan]

brad I know its kind of obvious....but I've always had too much power oversteer in a 32 without attessa controller.....or turn in later and come out straighter. Your suspension and alignment seem reasonable - nothing obvious wrong.

[Risking]

sorry I forgot to mention I have a basic controller in the car.

I have it currently at 30/70 split which worked great previously.

I have always entered turn 1 very late and had a good run to turn 2 on south circuit. but even now it tends to power oversteer between 1 and 2.

to the point I could almost hold a steady slide before backing off and "setting" the car into turn 2.

The car is awesome everywhere else and the times reflect that but there is so much more to be had. through the flip flop its a case of nail it in 3rd and steer right through the turn, no sweat. same as turn 2 and 3 really. carry as much speed as I dare and let the car do the rest. I had 1600's pulling away coming onto the main straight as I was oversteering then by pit lane entry I had realed them back in. Was mighty annoying when I knew the car should be able to grip up better.

Edited February 4, 2008 by Risking

[Sydneykid]

As Duncan said, it doesn't look too far out in any one area, there are however couple of minor things that concern me;

1. You make no mention of HICAS removal, I assume it has been done?

2. You mention "Adjustable rear camber arms" but don't mention adjustable rear traction arms. If you haven't adjusted the traction arms to the same degree as the camber arms, then you have introduced a fair bit of bump steer. You need to adjust that out.

3. I would suggest that you try more than 1mm toe in on the rear, we rarely run less than 2mm each side.

4. What do you mean when you say "Ride height is set correctly"? I am sure that you are aware we stick to around 355 mm front and 345 mm rear, then adjust the rear ride height in 2 mm increments to achieve the desired weight transfer.

5. In conjunction with #4 above, I am always concerned when I see "Roll center adjusters" mentioned, exactly where do you have the roll centres adjusted to? Around 150 mm front and 250 mm rear is a good starting point.

6. As you have surmised, the half cage will result in higher effective rear spring rates (at the tyres) as the chassis flex won't be soaking up some of the spring rate.

7. I am surprised at the low level of negative camber, front and rear, that appears to give even tyre temperatures. We never run less than 2.5 degrees on the front and 1.5 degrees on the rear. At Oran Park it's closer to 3.5 degrees on the front right and 3.0 degrees on the front left with 2 degrees on the right rear and 1.75 on the left rear. Plus I am not a big fan of infrared pyrometers as they only measure the skin temperature, whereas a probe gets into the tread where the action truly is. OP is also not that great for tyre temps, due to its long run into the pit lane, too much time for the temps to even out across the tread. Where you pit up also has an effect, on practise days we try and get as far up as we can to shorten the run. My guess is that with only 1 degree of negative on the rear you are getting up on the outside of the tyre in the longer corners and that is reducing your rear traction enabling contact patch.

8. The mid corner understeer is also systemic of insufficient front camber.

Personally I prefer to get the handling optimised, then use the ATTESA controller to balance the acceleration forces. Rather then trying to use changes in drive split to overcome what is truly a handing imbalance.

Cheers

Gary

[Risking]

Many thanks for the input gary.

Yes the HICAS has been completely removed as you mentioned

Rear traction arms have not been fitted to the car yet as ive never really had a need for them (or thought I did)

In saying that I asume you bring the hub back (or close to) factory geometry after the camber changes??

I shall try your recommendation with the toe settings for the rear. It has been on my mind since sunday that it would be something to try perhaps.

Yes the ride height is exactly that. I used to find it felt better 10mm lower on the rear but thats been raised back up now to get a base line again.

I think from memory the roll centers are at 150 or close to it and the rears are less than 250mm, ill have to check through the cars logs to see what they were set to as I have a terrible memory. If its less ill set them to that base to begin with.

I see your point about the infared sensors. Which probes do you/would you recomend using??

After reading your suggestions im inclined to agree about the temps more than likely filtering through the tread before my measurments (approx 1-2 mins after leaving the circuit)

Ive never run more than 2 deg front camber, I used to find it worked for the way I drove the car and its truely does feel excellent around the majority of the circuit. However I will be trying your suggestion and see how it goes in regards to the camber im running.

Its going to wakefield late febuary but ill be trying to get back to oran park in the mean time to try all of the suggested first. I really just need the oversteer gone and it will be a pleasure to race again.

Edited February 4, 2008 by Risking

[Sydneykid]

Rear traction arms have not been fitted to the car yet as ive never really had a need for them (or thought I did)

In saying that I asume you bring the hub back (or close to) factory geometry after the camber changes??

There are rear traction rods standard, you can't drive the car without them. So I assume that means you are using aftermarket adjustable upper control arms and the standard traction arms. That is very bad for bump steer, you end up with the traction rod fighting the steeering arm.

Secondly, have you left the standard rubber bushes in the upright and the standard traction rod? That means lots of moving around as the rubber is, what, 17 years old? It's one of the problems with aftermarket arms, people stick them in and think they fix all the problems, when the truth is they create more than they fix. If you haven't already done it, I strongly recommend that you replace every single rubber bush in the suspension with polyurethane.

I shall try your recommendation with the toe settings for the rear. It has been on my mind since sunday that it would be something to try perhaps.

It's a starting point, from which you can adjust. It is the most common setting we use but not the ONLY setting we use.

Yes the ride height is exactly that. I used to find it felt better 10mm lower on the rear but thats been raised back up now to get a base line again.

Once again it's a starting point, from which you can adjust. It is the most common setting we use but not the ONLY setting we use.

I think from memory the roll centers are at 150 or close to it and the rears are less than 250mm, ill have to check through the cars logs to see what they were set to as I have a terrible memory. If its less ill set them to that base to begin with.

That's very important, you should be able to feel very small changes in roll centre.

I see your point about the infared sensors. Which probes do you/would you recomend using?? After reading your suggestions im inclined to agree about the temps more than likely filtering through the tread before my measurments (approx 1-2 mins after leaving the circuit)

1 or 2 MINUTES, anything longer than 10 seconds is too long to get meaningful temperature differentials. I also hope you aren't doing a cool down lap before you pit for checking? A flat out lap, get it into the pits as fast as possible, get the probe into the front RHS tyre (at OP) as soon as the wheel is stationery. Then do the rear RHS tyre, then the front LHS and lastly the rear LHS. All 4 tyres need to be checked before you can get your seatbelt undone and your helmet off.

We use Longacre pyrometers, $70 US from www.racerpartswholesale.com

Ive never run more than 2 deg front camber, I used to find it worked for the way I drove the car and its truely does feel excellent around the majority of the circuit. However I will be trying your suggestion and see how it goes in regards to the camber im running.

As with all circuits, OP has critical corners, corners that effect your speed long after the corner itself is finished. At OP that's the left hander coming onto the straight, the right hander up to the bridge, and the left hander after the esses (us old guys call it Suttons). Set the car up for those 3 corners and the lap times will tumble.

Its going to wakefield late febuary but ill be trying to get back to oran park in the mean time to try all of the suggested first. I really just need the oversteer gone and it will be a pleasure to race again.

I don't think you will find as much of an oversteer problem at Wakefield, the 3 critical corners there are all more likely an understeer issue. Remember that WP is a clockwise circuit so the set up stagger is the reverse of OP.

Cheers

Gary

[Risking]

Thanks Gary.

Your correct im using the original traction arms but sorted out new ones today.

The bushes were all replaced just after I got the car 18months ago. They are still in good nick so ill be sticking with them.

No I was not doing a cool down lap before pitting however I was out there by myself so my estimated time before checking tires unfortunatly had to include getting out of the car, going to tool box etc etc.

I realised this is less than perfect but figured better then nothing untill you mentioned the temps evening out over the surface after sitting.

Im investing in a probe as you suggested.

I realise the settings you have recommended are a begining only as I have also done plenty of trial and error to get the car the way I liked it on various circuits, but now it has signifcantly more power im disapointed in the chassis and having to start again basicly.

Im hessitant to set the car up how I used to for the wakefield circuit as im almost certain it simply wont work.

Steep learning curve I guess.

Also in your oppinion is it worth getting a dynamic allignment done if I can find someone capable of doing it??

Do you have any techniques regarding bump steering measuring??

Im only familiar with blocking up the chassis to ride height, removing the spring and setting the control arm at the same angle as it was when the vehicle was on the ground, seting up a dial guage on a plate I have made up that bolts to the hub and measuring the toe differance through the suspensions travel.

Its kinda hard to explain but its worked for me in the past but im certain there is a better way.

I do my own alligments at the local bobjane, so sometimes ive had to try and be a bit ingenuis with equipement obviously.

Edited February 5, 2008 by Risking

[Sydneykid]

Thanks Gary.

Your correct im using the original traction arms but sorted out new ones today.

The bushes were all replaced just after I got the car 18months ago. They are still in good nick so ill be sticking with them.

No I was not doing a cool down lap before pitting however I was out there by myself so my estimated time before checking tires unfortunatly had to include getting out of the car, going to tool box etc etc.

I realised this is less than perfect but figured better then nothing untill you mentioned the temps evening out over the surface after sitting.

Im investing in a probe as you suggested.

I realise the settings you have recommended are a begining only as I have also done plenty of trial and error to get the car the way I liked it on various circuits, but now it has signifcantly more power im disapointed in the chassis and having to start again basicly.

Im hessitant to set the car up how I used to for the wakefield circuit as im almost certain it simply wont work.

Steep learning curve I guess.

Also in your oppinion is it worth getting a dynamic allignment done if I can find someone capable of doing it??

Most definitely worth it, for example John's Zed was 1.5 seconds a lap faster at Philip Island after we fixed the bump steer and set up the camber change angles. It still needs some work on the Ackerman and roll centres, another 0.5 second in that perhaps. The problem with that sort of work is that you need a quality/experienced engineer to do it, they are always extemely busy and, more importantly, they don't come cheap. Some guys have a problem with the reality that they don't get one physical thing that looks any different, put the car on the ground and it looks exactly the same. No new, shiny stuff, no fancy Jap parts with brand names all over them. Just a few angles changed here and there, that you can't even see.

This almost leads directly into track testing, you simply can't do it on your own, it's a waist of time and money, once you learn the circuit. We have a 6 person crew whenever we go testing, one driver, one engineer and one guy per wheel to do tyre pressures, tyre temps, brake temps, shock and bar adjustments and spring swaps if necessary. Even then we can easily spend a whole day flat out and not get through the full program of settings that we wanted to try.

Cheers

Gary

[Sydneykid]

Do you have any techniques regarding bump steering measuring??

Im only familiar with blocking up the chassis to ride height, removing the spring and setting the control arm at the same angle as it was when the vehicle was on the ground, seting up a dial guage on a plate I have made up that bolts to the hub and measuring the toe differance through the suspensions travel.

Its kinda hard to explain but its worked for me in the past but im certain there is a better way.

I do my own alligments at the local bobjane, so sometimes ive had to try and be a bit ingenuis with equipement obviously.

That's the best way to check bump steer, works for both front and rear. Camber curves are tuned in much the same way, instead of a dial gauge you use a camber gauge. I am string and camber gauge guy, too many years spent at race tracks with no wheel alignment machines in sight.

Cheers

Gary

[Risking]

I have previously looked into a dynamic allignment to get a base but as you said the cost and difficulty of finding someone is the killer.

I can completly appreciate the work that goes into geometry and being in the trade understand your comment about people wanting shinny things or something to look different.

At the end of the day spending the time etc getting it right will make it so much better to drive so why not.

I was taught that technique a long time ago and its stuck with me. Im glad to hear its a good way of checking as im familiar with it. Ill be re-doing the allignment and setting up the traction arms during the week before going back to oran park (with help this time) on sunday.

Interesting about Johns car, 1.5 seconds is alot of time to knock off. Lap times dont lie though so its going to be interesting in the coming weeks.

Many thanks Gary,

Ive got a good grasp of where the car has been lacking now so with some time and effort it will be quicker than ever.

[Risking]

I had the car back out at wakefield today,

Basicly it was set-up as you suggested Gary with a little more camber on the front which made it feel alot better.

The car was running less power than its capable of (mearly to ensure I could get it home again as tow car was busy today)

with 1 bar it was lapping constantly in the 1:09's. I know it can go faster with more power but not today.

Ive solved the power oversteer issue, its virutally non existant now, however I now have sever understeer at turn 2 and 10. Today I was using RE55s instead of the usual A048's. They did feel good but the problem was consitant regardless of tire pressures.

Im leading towards using the sway bars to try and stiffen the rear slightly as im really happy with the allignment now.

Otherwise a few Braking issues (air in the system) have to be sorted but its a lot better to drive now.

Anyone looking for decent allignment specs definitly try those suggested earlier in this thread

[Risking]

Since this last post I ended up getting the car working really well with the A048's

however Im now trying 300 wide 18 inch michelin slicks.

Ive had the car out twice now with now 2nd hand tires and the times plumeted as id expect, however im not happy with the way it behaves mid corner now. It doesnt understeer or oversteer but rather bounces mid corner. It almost feels like the outside shock is too soft and the front of the car dives into the track.

Back on the Advans the problem is gone.

I want to get it right before using the new tires as im not worried about trial and error with the 2nd handies.

Really the only changes have been the fitment of the full cage (before swapping tires)

and the tires themselves. The rest is all still the same and all components are in perfect condition

Am I missing vital allignement changes to suit the slicks or the 18inch rim diamter (up from 17)

Im asuming that changes are vital to get the most from them, Ive got the setup for the R tires down pat now but the slicks in this width are a bit different.

Its going to east coast next week but thought id ask for suggestions prior to sending it over there.

[Sydneykid]

Since this last post I ended up getting the car working really well with the A048's

however Im now trying 300 wide 18 inch michelin slicks.

Ive had the car out twice now with now 2nd hand tires and the times plumeted as id expect, however im not happy with the way it behaves mid corner now. It doesnt understeer or oversteer but rather bounces mid corner. It almost feels like the outside shock is too soft and the front of the car dives into the track.

Back on the Advans the problem is gone.

I want to get it right before using the new tires as im not worried about trial and error with the 2nd handies.

Really the only changes have been the fitment of the full cage (before swapping tires)

and the tires themselves. The rest is all still the same and all components are in perfect condition

Am I missing vital allignement changes to suit the slicks or the 18inch rim diamter (up from 17)

Im asuming that changes are vital to get the most from them, Ive got the setup for the R tires down pat now but the slicks in this width are a bit different.

Its going to east coast next week but thought id ask for suggestions prior to sending it over there.

If you are still using them, the originally posted spring rates are way too low for slicks. The extra grip means additional G force and hence weight transfer which the 6/4.5 spring rates can't handle. You need to to look at around 10kg/mm in the front and then using the 6kg/mm's in the rear. You could try setting the swaybars on maximum, but I don't think that will be enough. Obviously you need to be sure that the shocks can control those sorts of spring rates.

Slicks require a very different set up, not just spring rates. Alignment settings, particulalry camber will be different so you need to work through the processes like we discussed above for the R type tyres.

Cheers

Gary