Front suspension settings and upgrades

[Clayton]

Following on from http://www.gt40s.com/forum/racetrack/19561-ross-racing-weekend-4.html thread, I’ll start by saying my RF isn’t on the road yet. So the changes I’ve made are not proven yet.
I would like to hear from owners that have made changes / upgrades to their front suspension, Ross, Tim, Chris, hint hint : )

My modes so far:
Reduced bump steer to 0.011” over 4” of travel
Increased Ackerman (moved rack rearwards by ~2”)
Replaced lower inner pivot bushes with press in spherical ball joints
Raised rack ~2.5” (to clear my feet) by fitting the tie rod ends on top of the arm
Changed rack and its length (for bump steer, used TE/TF Cortina)
Rolled rack to get pinion higher (again for foot room)
Fitted higher angle universal joints from std

Regards

Clayton

 

[Clayton]

Any info would be great.

 

[ChrisL]

I too was hoping that there would be more people chiming in, but to avoid making this post a total orphan I'll post my limited contribution.

As I see it, the front end does not seem to be a problem. That's not to say that there is no benefit in performing some sort of advanced analysis. I've noticed though that you’ve detected some bump steer at the front, but that doesn’t seem to translate to real bump steer on the road. My current setup allows me to drive the car over bumps while holding the steering wheel lightly with one hand (or even no hands) and make no real corrections.

From a balance perspective on the track, there is oodles of grip at the front but less so at the rear, so purely from an effort/benefit assessment there is far more to be gained from improving the rear-end first. (The next biggest gain would be made from improving braking thermal efficiency). My last track outing (at Winton) showed the car to have very reasonable manners in the morning cool, but as the day warmed (very warm) and the track got more slippery, the rear fell away far more quickly than the front, so again, the front holds no concerns for me… if anything at this stage I would be attempting to reduce grip at the front to find balance if I were not looking to improve grip at the rear instead.

Incidentally Clayton, if I’m not asking too much, can you explain how you concluded that less Ackerman was required?

 

[Ricky]

Hi Chris,
Interesting reading how your car is handling. If it is OK can you tell me what your setup figures are, front and rear and what tyres you are running.

I have found from doing sprint events here in WA that I am getting quite a bit of front end push. I am running the car pretty hard albeit on sumitomo htrz11 street tyres running around Barbagallo in 59.5sec laps (about 2 sec of R spec tyred Porsche GT3's)

I am running
(Rear) 3deg castor, -1 deg camber, 3mm total toe in & 450# springs, no ARB.
(Front) 6deg castor, -1.5 deg camber and 1mm toe in, 400# springs @ 26mm ARB.

Front tyres are still scrubbing too much on outer shoulders so am fitting Jim Cowdens lower wishbones at the front to increase camber to -3+ deg. so the tyre is better used.

I have used the analagy that if I can get the balance pretty right on street tyres, then when I change to R specs the balance should stay but grip levels incease considerably.

Maybe Ross can chime in with his setup if it's not too much of a secret.

I am not after sheep stations, but want to get the satisfaction of getting personal pleasure of better lap times.

 

[Jim Cowden]

This is such a coincidence.
I haven’t looked at my car in weeks because of things.
But today I decided to check the front bump steer and as Chris has stated I don’t think it is to far off.
I don’t have my figures on me but it was about .016 there about on bump and droop.
That is .016 toe in on droop.
.016 toe out on bump.
2” up 2” down.
Some spacers at the outer rose joint (tie rod end) will get it closer.

I don’t have the wheel alignment fully set up yet but one thing I did notice is not a lot of camber gain through the travel.
I would say about ½ - ¾ deg.
I would have expected a little more even though you would not expect to much role.

Does anyone have any thoughts on expected gain .

Jim

 

[Ricky]

Oops, that should have read 69.5 sec laps and Aiming at -3 deg front camber or more.

The car is turning in really well and is carrying good corner speed but on long corners (greater than 110 degree) the understeer starts as I am powering on. If I stab the throttle, the back end will kick out into very rapid oversteer which is very difficult to catch. Oh, and yes I have spun it a few times experimenting with driving styles.

I'd be interested in comments from other people that have tracked their GT40 and what handling experiences thay have had.

 

[Clayton]

Hi Chris

Good to hear from you. Regarding the Ackerman, I have increased it from std by moving the rack rearward. As my car will be mainly road driven I thought the closer I get to true Ackerman ( Ifs that’s right terminology ) the better it would go around tight corners without scrubbing the tyres.
Carroll Smith has also stated in his books that Ackerman has helped with turn in on his later cars, so it cant be that bad : )
Does that help ??

What brake pads are you running ?? Try a set of Ferodo DS2500’s for street / track use, they are great. Don’t require warm up and work brilliant all the way to hot. Or if you want to change your pads at the track, try the DS3000’s, the hotter they get the better they work.

Hi Ricky

Sounds like you’re getting a handle on the settings, it won’t be too long before you’re ahead of those GT3’s

Hi Jim

I never did check the bump steer on the std front end (didn’t have an original rack to check) just whacked in the TE/TF Cortina one where I thought it looked good and had 5/8” bump steer from the start : (
If the front end had more camber gain, could you than run less static camber ??
How much camber gain should you have ?? Buggered if I know !!

Clayton

 

[Ross Nicol]

Hi Guys
Rick I reckon your doing the right thing by increasing negative camber. I have taken tyre temps for a while, but you don't even need to bother when you look at how the tyres are wearing/scrubbing across the tread. If your scrubbing the outside edge the loaded tyres in the corners are not flat on the track and hence not giving you maximum grip. I have just increased neg camber on all 4 corners of my car to get even wear across the tread. That has been the single most improvement in the car's handling in 3 years. I'm at 2.5 degrees now and I can still see I probably could put on another 1/2 a degree. Incidentally I've got Sumitomo road tyres on a set of wheels and I did a 1min 25sec lap at Sandown but I reckon I could lower that time on those tyres now with the new new set up. I've been having trouble with the long sweepers at Phillip Island so I know the car will be much improved there now. If you get the negative camber right and chuck on a grippier set of tyres you will be very surprised. I'm sure the understeer will disappear and your confidence will skyrocket as has mine. To get more neg camber on the front I cut back the top wishbone arms (inner). I lengthened the lower wishbone at the rear but you have to be careful how far you go as the lower trailing arm is nearly fouling the chassis.
Clayton when I first read of the changes you made my first reaction was that's a lot to do without driving the car. I realize you are moving things for feet clearance but I like to change things one at a time and prove the change was worthwhile by driving the car. I believe the others have a similar opinion to me ( i've never noticed any front bump steer) however that's not to say it's not there and that some drivers may be more sensitive to it than others. Hope this is helpful.
Ross

 

[Ron Earp]

To get more neg camber on the front I cut back the top wishbone arms (inner). I lengthened the lower wishbone at the rear but you have to be careful how far you go as the lower trailing arm is nearly fouling the chassis.

Hey Ross,

It has been a long while since I've looked at the front suspension on an RF, but couldn't you bolt the upper ball joint to a plate with slots so that it could be pulled in and increase negative camber?

All cars need development, no matter what make or model, and it is good you fellows are dicsussing it openly. Nothing is worse than someone saying "you have to watch out for XYZ" and never tell you anything about XYZ, or how to watch out for it. That happens on the forum from time to time and is discouraging from the standpoint of forming a helpful community.

Best,
Ron

 

[ChrisL]

Rick,
I’m not surprised to hear that you have different handling characteristics having discovered for myself that the car is very responsive to variations in setup. If you read the thread on rear-end geometry (as directed in Clayton’s original post) you’ll find that the consensus there is that the RF40 is very tail-happy, to which I have vigorously disagreed, so I’m glad to hear that someone else here has found this not to be the case.

I did make a passing comment though in my last post that the rear end fell away more quickly than the front as the track got warmer. Just to expand on this… With no changes to the settings, the car’s balance changed considerably through the day purely as a result of changing track conditions (everyone on that day was commenting on how slippery the track had become as a result of the track getting warmer). In the cool of the morning I was countering the over-steer by powering through the corner. In the heat of the afternoon, more power would only result in more over-steer… quite different. This bothers me a little because I have been trying to make comparisons between a settup at one track and a different settup at another. Now I’m starting to wonder how much can be attributed to the track conditions.

Anyway, I’ve rambled a bit here but to get back to your original request, I don’t have any setup figures as such because I’m still going down the path of making wholesale changes before each meeting and just keeping notes on what I’ve done… the intention being that I will take a full set of proper measurements once I am reasonably happy with what I have.

I can tell you this much though…

On the front suspension, I have cranked up as much –ve camber as I can get (which is not all that much really) and gave it 1mm toe-in (as measured at the rim of a 17in wheel). Shocks are set to 3 clicks from max stiffness. I’ve made no attempt to alter the castor at the front, but maybe I had a lot to start with. If I do, then that would result in more –ve camber on turn-in and explain why I have good grip and the scrub pattern on the front tyres seems to be even across the entire tread.

The rear is the area that I’ve spent most time on. I’ve mentioned this before so I won’t go into a lot of detail other than to say that I have set it to 0 toe at full bump (which results in 0.7deg toe-in at rest) and 0 camber at rest. Rear castor is set to as much as I can get with the standard suspension. Shocks are set to 7 clicks from max stiffness.

Can you tell me what size tyres you are using Rick? This might be the biggest difference. I’m using…

Falken FK 451 (road tyres)
Front 225/45 R17
Rear 275/40 R17

NB. I expect that the settings to be quite different for stickier tyres but I too am looking for a stable starting point before changing to stickies.

Also NB. I'm running an LSD which will also make some difference.

Clayton,
I’m using Race Brakes RB74 brake pads which are a vast improvement on the standard pads. Can anyone tell me how they would compare against the Ferodo DS2500’s? Incidentally, I was competing against a 1700kg Corvette with identical brake calipers to mine (I'm running C4 Corvette calipers) and his brakes were not cooking nearly as quickly as mine. I think brake cooling is next on the agenda.

 

[Ross Nicol]

Hi Ron
I agree totally with your sentiments and group information into at least 2 categories 1/safety and 2/ Performance. I like to share my info on this forum because I've benefitted from being a member in many ways, friendship,information, parts sourcing etc etc.... There are a lot of entertaining characters who contribute to the site too it's a wonderful thing,what did we do before computers and the Internet?
I had just woken up after a sleep on the couch (it's an age thing), when I
posted on this thread so when I said I shortened the front upper wishbones I should have included that it was to allow the rose joints to screw further in and thus allow more negative camber to be set. Similar thing at the rear to lengthen the lower wishbone/control arm I just screwed out the outer Rose joints. I'm beginning to think a rose joint on the inner end would be better than the sperical bearing I have now as camber and toe changes would require far less disassembly/reassembly which is very time consuming.
Rick when you say you get understeer in a corner when you apply power, I know what you mean and it may mean you have turned too tight a radius and are apexing too early. Anyway I wouldn't immediately blame the car setup beacause the driver can certainly promote this. I would suggest Chris and yourself get onto better tyres as soon as possible because you'll have to go through a new learning curve when you do.Better to do it now because setup changes will be more noticable and corner speed will be faster due to better tyre grip alone. That turn in understeer will probably be gone.
As for the stab the throttle oversteer I find it hard to believe you would be in a low enough gear to have this in a sweeping corner unless you've unsettled the car and the lateral G forces have overcome your grip. This should be much better with good tyres and camber changes too.
I was using Ferodo DS2500 brake pads and The car got too fast and cooked them even with cooling ducts. I'm now using DS3000 on the rear and have a set for the front when new rotors go in over christmas I hope.
Ross

 

[Ross Nicol]

I forgot to mention that body roll will negate negative camber in a corner. If you look at those latest pics of my car you will see i've got hardly any as compared to earlier photos. This is a great way to check. Get a friend to take photos of you driving on the track in a tight corner and you can identify how much body roll you have. Drive as hard as you can when the photos are being taken though.
Ross

 

[Ricky]

Firstly, I am really impressed with how open everyone is with the information and am sure that there will be many beneficiaries of our ramblings.

Hopefully i can cover all the inputs in the following....

Ross,
You apear to be the "man" and "shining light" in terms of exposure to setup on an RF so Kudos for sharing your info.

Neg camber on the front is obviously the next big step. By installing Jims lower control arm I will be able to increase the front track and then re-set camber at the desired amount via the upper control arm. I am pretty comfortable with that.

The Sumitomo tyres have been surprisingly good for a real "street" tyre but when they go off their as slippery as a dog on wet lino. - but balance stays similar, although the front will push harder due to increasing trye degradation. I will be replacing these with Toyo R888's which have been getting really good reports from those I have spoken to here in the west. I am really looking forward to experiencing the new grip levels when these are fitted.

My rear end is completely rose jointed and allows infinate adjustment, as it should, but also without any binding like the old bushes did. I will be replacing the lower trailing link connection where it attaches to the bottom of the upright to transversely relocate the link as it passes through the chassis.(which is limiting camber alteration due to the chassis clash)

Chris,
I am with you. I always note down the changes made and the result thereof. I have found similar to you that track conditions will vary the handling. Until R spec tyres are fitted (which are more stable due to less tread movement) I am trying to filter out the extremes of conditions to maintain a uniform evaluation point - as far as possible.

My shock settings were pretty high when I had standard RF supply springs. Now that everything is stiffened I typically use 5 from full soft on the rear and 6 from full soft on the front.

My tyre sizes are 225/45x17 (F) and 255/45x17 rear on 7" & 9" rims. I think the replacement R spec's on front will be the same but not sure about the rear at this stage.

I have the new 3.22 CW&P but am not running an LSD.

My brakes are wilwood 4 spot all round with Ferodo DS2500 pads which works well for my level of performance

 

[Ricky]

Ross,
Have been thinking more and more about how I am driving the car and if the understeer issue is driver error.
To some degree you are probably right. I have been taking a lot of notice of the fast guys and have invested in some 1 to 1 in car instruction from a few as well (the instruction is probably more valuable than making mods to the car in some cases) so I am reasonably ok with the lines being used. This is not to say it's not driver induced.

There are two particular corners where the problem is greatest.

The first is a long 170 deg right (Cat corner) at the end of a 180ish km/h (for me) straight which has a real late entry, I then place myself about mid track 1/2 way round, then apex about 3/4 the way around. I am very concious of staying wide and not turning in too soon on this corner.

The other is a 160 deg uphill corner (Shell) with similar positioning and apex points. This corner sucks you in to putting down lots of power and is after a series of high speed, 4th gear, esses.

In both cases turn in is sharp and direct. The push starts from about mid corner during the transition from trail braking to throttle and increases as throttle is being squeezed on.

I have tried a big stab on the throttle a couple of times (to see what will happen) and resulted in immediate oversteer which was not unexpected, but, quite sudden. Needless to say I have not been tempted to try that very often.

I have the final sprint for the year next weekend and will do some more evaluation of my technique and will endeavor to get more camber in the front end by then with luck. If I can't get the work done to the front I will try for a few tuning days early next year.

Two photo's are attached showing the limit of body roll. One from a hill climb right on the apex and another just after the apex on the circuit.

Appreciate your inputs.

 

[Ross Nicol]

Rick
These corners are really fast sweeping bends. My guess is the g forces have overcome your tyre grip and the car is not balanced so the front has let go before the rear. By applying power you have provoked oversteer because the rears have run out of grip too and the sudden driving force from you stabbing the throttle, tips the rears over the edge. More camber, balanced suspension and softer tyres will improve your corner speed and stability out of sight. With the balance right the G forces should make the car drift wide away from the apex in a controlled 4 wheel drift. This is assuming you stay on the throttle through the bend. Of course the trick is to know when you've reached the maximum speed your tyre grip will allow. As the books say many drivers are intimidated by these fast flowing corners.
Good luck at the sprint next week.
Ross

 

[Ricky]

Thanks for your input Ross. Roll on next weekend and see how we go.

 

[Clayton]

Hi Ross

Yeah the list of mods look quite long but the only change to the geometry was to increase Ackerman, the rest of the settings should be the same as std RF. Hopefully this change will work for me, will have to wait and see.

Hi Chris

If your brakes are getting that hot, I would try a set of DS3000’s first. You will be impressed, I’ll even put money on it : )
I have tried ‘Hawk blues’, ‘EBC yellows’ and ‘DS3000’s’ ( not on a GT40 though ) and the 3000’s are heads and shoulders above the rest in my opinion.

Do you check your tyre pressures after each run ??
I have found that if the rears gain 1-2 psi over optimum it becomes taily.
Again that’s what I’ve found anyway.

Clayton

 

[Jim Cowden]

Quote from Clayton
I never did check the bump steer on the std front end (didn’t have an original rack to check) just whacked in the TE/TF Cortina one where I thought it looked good and had 5/8” bump steer from the start : (
If the front end had more camber gain, could you than run less static camber ??
How much camber gain should you have ?? Buggered if I know !!

Clayton
Yes you can run less camber if you have camber gain.
I might be wrong but I would think if you had less static camber (good tyre wear) but on turn in the gain was to within what was needed it would have to help.
I admit that caster will also give the same effect but then you start falling into heavy steering ect (its that compremise thing again).
How much I suppose it would come down to body roll which I suppose thats were it gets complicated as it would be effected by individual set ups.
The other thing with camber gain you would get the inside front wheel moving in at the top, with caster doing the job you would get the inside tyre moving out at the top , either way you have tyre on the road but I dont know if one is better than the other.

One thing I havnt checked is the caster on the front so depending on the amount there if I pulled more at its current setting it may get rid of the small amount of bump steer as it will raise the steering arm (but I will have to see).
It all preliminary at the moment.
Jim

 

[Ross Nicol]

Clayton
Yes you can run less camber if you have camber gain.
I might be wrong but I would think if you had less static camber (good tyre wear) but on turn in the gain was to within what was needed it would have to help.

Jim That sounds pretty right to me and would be good for road cars that do track duty to be able to run less static camber. Having a lot of static camber doesn't worry me as I don't drive the 40 on the road much at all now.
Ross

 

[Jim Cowden]

Ross
I agree with you on that.
One other thing I was thinking it maybe of an advantage under brakes having less static providing it doesnt have to much dive.

It would come back to the combination of everything.
It sounds like your combo is starting to work for you.

Ricky(dont shot me)
Im not shore about playing with the tyres you have then going to a better tyre.
I have talked to a freind at length about my car and he has said that different tyres react to different suspension settings.
What works for one wont always be the best for another which makes sense
with wall flex , grip factor ect ect.
I would hate to see you spend so much time and it all changes with different tyres.

Jim