Damper Settings - Recommendations For A Circuit Car

[SweetBadger 94]

Hi All,

 

I'm after some recommendations as a starting point for my Gaz Gold damper settings as I don't really have a clue - last race we set them at mid way both front and rear.

 

Any recommendations for a starting point to work from?

 

Also any recommendations on tyre pressures would be welcome (Yoko A048 medium compound tyres for dry, Michelin Pilot Sport 3s wet)

 

 

My current suspension setup is as follows:

Tyres:

yoko A048s (were set to 24psi all round last race)

Front:

309 bottom arms, plus 10mm hub centric spacers
Gaz gold struts with 350lb springs
Gaz eccentric top mounts set for max camber & caster

Rear:

205 beam with 23mm tbs and a 27mm arb
Solid beam mounts
Gaz gold dampers

Ride height has just been set so that the front suspension arms are parallel with the ground, and the rear set to match (rear was way too low before). Pic below:



Also have a 3j LSD set up by miles for a circuit car with power steering (vts mk 1 steering rack)

[calvinhorse 870]

From past experience I'd say set the dampers to full hard + maybe turn them down one or two clicks

 

If you have adjustable top mounts on the front set them to get half way between max camber and max caster, you will probably want to go full camber once you get used to it.

 

26 psi front and 25 psi rear should see you at 30psi after a few laps but that's a preference thing but a good starting point

Edited May 14, 2015 by calvinhorse

[welshpug 1,657]

dont forget to check toe settings if you alter camber

[SweetBadger 94]

Sorry should have made clear that the eccentric top mounts are half way between max camber and max caster as they're the ones you rotate (don't have individual caster/camber adjustment), so I won't need to adjust these further just yet.

 

Cheers for the tips, that's quite a lot firmer than we had them set last race!

[Tom Fenton 1,542]

In my experience castor is equally as important as camber. On my own car I have castor set to max on the top mounts and then achieve the desired camber from rose jointed lower arms.

 

I would also suggest some Bridgecraft neg camber rear arms to match the rear to the front.

[petert 588]

I'd start the tyres at 24-25 front and 28-29 rear, aiming to finish at 33 max all round. Don't let them hit 34. Only stringent record keeping and vigilant checking of pressures at the end of each race will get it right for your set up.

 

Rear needs to be 20mm higher than the front.

 

Max caster and 3 deg camber, 6mm toe out.

 

Start dampers at mid way. Increase 4 clicks at a time. Only you will know what happening. Don't let an artificially hard rear influence a poor setup on the front however.

Edited May 14, 2015 by petert

[allanallen 528 2 Cars]

Sorry I never replied to your pm!

 

33psi seems excessive peter? 30 hot is what I'd be aiming for.

 

What's your diff set at and what toe are you running?

 

I personally think the front spring rate is a little to high and you won't have enough camber on for the tyres.

As Tom says castor is very important and is difficult to get on 205s. Easiest way is to set your eccentrics to max castor and then get your camber with adjustable wishbones and/or machining your hubs.

Camber wise a good starting point I'd be looking at is -3 all round or at least at the front.

[welshpug 1,657]

we always went lower on the back than front on the rally car pressures on the ao48.

[Tom Fenton 1,542]

Just to add. To agree with what Al says, I don't think you will have anywhere near enough camber at the front. One of my road cars has the same setup, e.g. 309 arms and eccentric top mounts, from memory when I measured it there was something like 1.2 deg negative camber, which is adequate for road use but not enough on the track.

 

But finally, as Peter says, only you can decide what you are comfortable with and what works for you, every car and driver is different.

[SweetBadger 94]

Thanks guys, all good information.

 

Peter - regarding running the rear 20mm higher than the front, where are you taking the measurements from e.g. from the arch to the centre of the wheel? Or is there a point on the car that you can measure front-back rake with a level? Reason I ask is that I thought that there was already some rake as standard; so when the wheels look at the same level in the arches the rear roll centre is actually higher?

 

Tom, to sort the camber I have a couple of 306 hubs that will be destined for Bridgecraft to be machined for -ve camber, but that'll have to wait till funds recover a bit. I want to get a couple more races under our belt so I'm confident that any issues are ironed out on the car as it is before continuing ploughing money into it!

 

Al - no worries, will be in touch about machining the hubs and possibly rear trailing arms. I don't know the settings on the diff I'm afraid, I just asked Miles to set it up for a circuit car with power steering - hopefully he'll see this post and post up the settings. Toe settings are parallel at the mo.

 

Short term the front spring rate is easy enough to change - what would you recommend? 315? If it feels understeery this race I'll probably look into that.

[Tom Fenton 1,542]

Just be aware driveshaft wise that machined hubs will affect the length (again).

[petert 588]

20mm, as measured from the horizontal sill line, with a tape/ruler to the ground.

 

34psi is the absolute limit for 48's, 29psi for 50's. Keep records so you can ensure they all end of the same at the end of a run.

 

Parallel toe will definitely hurt turn in. Believe me when I say +6mm toe out is the go.

 

When you machine the rear arms, set up to achieve zero toe and -3 camber.

Edited May 15, 2015 by petert

[SweetBadger 94]

Well at Brands at the weekend the car felt way more balanced with the ride height sorted and the tyre pressures set at 25.5 front, 27.5 rear.

 

Again if anything a little more prone to under-steer than over-steer, I found that lifting off to try and tighten the line in a corner resulted in more understeer and the front of the car washing out, so I was braking to the apex to bring the front of the car in (worked quite well actually).

 

We were putting in some decent times too with our fastest lap at 57.2 secs - had we not buggered up the swap over and had another driveshaft failure we'd have been on for a respectable position...

 

The solid rear beam mounts really helped with the rear stability of the car in high speed cornering and when changing direction - highly recommended mod for anyone doing a lot of track driving.

 

I think we both felt that the car needed to be stiffer - it was on three wheels a lot of the time. So in addition to the -ve camber hubs I'm going to give some 25mm torsion bars a go, and slightly stiffer springs up front for the next race.

[Henry 1.9GTi 36]

Nice one. Decent time. I still havn't got an Indy dry laptime and couldnt make the 16th

 

I have not used the AO48s before but with other tyres on a warm day I have to start the fronts as low as 16psi on front left to get to 30psi hot. Its also what I aim for roughly speaking, wont go into details! I usually run the RHS tyres 2psi higher to bring them into line. Its worth check your pressures during the pitstop and bleeding down to 30. I have run a tyre from ~25-30 cold as forgot to check it and it indeed lost a shed load of grip as it got hot so worth getting it right. The pressures you mention above are about what I ran in the pouring rain at brands to get to 30psi 'hot' so id recomend rethinking. You could also try very low rear pressures to dial out some mid corner understeer, but with the weight on said rear tyre it doesnt have much affect in terms of tyre plunge and slip angle.

 

As for damper settings general principal is to go full soft front and full hard rear to see if you can dial out some of your turn in understeer and tune back from there. I havn't had good experience with GAZ though on my 205

 

Racings is addictive isn't it?

 

edit: just seen your race number. That was my number when I first entered Trackday Trophy

Edited May 19, 2015 by Henry 1.9GTi

[SweetBadger 94]

Have just seen the video you posted of Brands in the wet - crikey that looked tricky! We've been lucky with the weather so far, hopefully that continues!

 

Unfortunately with the tyre popping in qualifying and then my team mate pitting earlier than planned meant we didn't get chance to check tyre pressures. The car seemed to have much less grip when the tyres were cold than at Cadwell where we ran them at a lower pressure, but I didn't notice them losing grip once up to temp.

 

My team mate felt that the tyres gave more grip when we ran them at around 24psi, so I'll go with your advice and try them a bit lower next race (hopefully Silverstone)

 

Racing is definitely addictive, can't wait till the next race (just need to get the car fixed first - it's also bloody expensive). We're still getting the car sorted handling and drivetrain wise so it's been a bloody expensive start, but hopefully when that all settles down we'll get some races in without any major repair bills in-between!

 

Are you planning on making any of the Team Trophy races this season? Silverstone GP on 14th June and Brands GP on 15th Aug are open to both Track Day Trophy and Team Trophy so you could be racing against your old race number!

[Henry 1.9GTi 36]

Hoping to do Brands GP as I love the track. But havn't booked as I will have to fork out for registration fee and dyno just for one race so still contemplating. Shaking down at brands in a couple weeks so will make a decision after that I guess.

Silverstone GP is a no go for me as car will only do 120mph. Its really high speed and other cars just have so much cleaner aero you can expect class C cars to be a pain down the straights. I assume your class B?

 

I completely understand what your going through. I started racing in 2012 and the car has been through so many iterations and just generally sorting stuff out. I don't think I have done a race where I haven't changed something in between, but that's what it's all about!

 

There is also so much to think about on the day that stuff as important as tyre pressures can get overlooked. I think I have had 2 good pitstops in terms of time out of 6 or 7 The more you do the more you get comfortable with all the procedures and where to be at what time etc.. you then start to find you have time to think about other stuff thats gonna make you quicker rather than just being where your supposed to be.

[SweetBadger 94]

Ahh right, yes 120 mph is going to be quite limiting at Silverstone! The series registration and dyno test is a lot for 1 race, but I guess you could fit in another race to make it worth while ?

 

We're actually class C - Weight is 960kgs, and as power is the outright power at the hubs, and we have a Gti6 gearbox we can power test it in 5th gear instead of 4th - so we sneak in under the class C limit.

 

On top of the other issues with the car, we have also had some odd dyno results - all the same dyno, test 1: 130hp, test 2 (after a new exhaust manifold and remap: 126hp, test 3 power tested at Cadwell after qualifying (one week after test 2), car made 153hp at the wheels in 5th (which would make us class B !) Made us look a bit suspect but it was obvious that nothing was done to the engine or map.

 

We had it re-tested before Brands to try and get a repeatable reading and it made 140hp consistently... so that's what we're going with at the mo. Sods law says next time we're tested it'll be back up at 153, car has never felt any different to me though...

 

Like you say on the day there's just so little time, you look at the schedule and think there's time to swap tyres, check pressures, adjust suspension, but before you know it its scrutineering, or the briefing, or qualifying etc...

Edited May 20, 2015 by SweetBadger

[Henry 1.9GTi 36]

I'm also around the 960kg mark. Bit under but depends on fuel over the line. Yes those dynos are rubbish for all their claims of accuracy. I have had 162 then 155 trackside and then 167 with nothing whatsoever changed on the engine or mapping. This is ~80kg weight between the figures, something I have argued with MSV. Apparently if you want a faster car go to Tracktive rather than TDi as their dyno reads lower and they were the ones that gave me 155.

 

Having a passenger on a trackday @ brands dropped 5mph down the pit straight back to back same day... but its all good fun isn't it? I'll be very interested to see what I get on the dyno this time round.

 

Funny you mentioned gearbox, I always wondered how they did the conversion and theres a gear ratio on my read out of 4.9 or something. But it has a 4.4FD so perhaps thats skewing things. My fifth is probably the same as yours?! but they test in 4th

[SweetBadger 94]

This year it's Advance Motorsport Engineering near Silverstone for the power test only, so at least the dyno used is the same each time (Dynapack hub dyno).

 

I don't think gear ratios are taken into account; rules are the run must a) not be in top gear and c ) be over a certain wheel speed, and then it's whatever is measured at the hubs.

 

On my dyno plot it's interesting to see how the drivetrain losses affect the power curve - it makes maximum power at the flywheel at about 7600 rpm, but due to drivetrain losses in fifth gear the power at the wheels is tailing off at just over 6000 rpm

Edited May 20, 2015 by SweetBadger

[Henry 1.9GTi 36]

ah I didn't realise they changed the dyno providers.

 

Yep mine is the same curve goes flat around 6250 and holds to 7500 max around 7000. But to be honest it was the same on the dynodynamics rolling road which measured mine at 190bhp flywheel when it was mapped at just over 7000.

[SweetBadger 94]

Bit of an update on this - changed to 25mm t/b on the rear, lowered slightly more, 3 degrees -ve camber (309 bottom arms with bridgecraft machined 306 hubs) and 400lb springs up front.

 

Tyre pressures 23psi front, 24psi rear.

 

4mm toe out (2mm each side)

 

What a difference! Tendency to under-steer was reduced, car was much more balanced and easier to steer on the throttle. Even had some over-steer coming out of a fast corner on the power!

 

The only places we really seemed to be struggling to find as much grip were in the slower long corners around Brooklands and Luffield.

 

Ran the car at a 1hr race at Silverstone yesterday, and we were up there with the quickest cars in our class until really bad fuel surge slowed us down :-( (even with a 1 l swirl pot). My quickest lap was 2:37:03.

[Henry 1.9GTi 36]

nice one. Glad you had a good race!

 

Looks like I'm bailing on brands, cant justify the cost of fees and dyno for one race. Shame as my best and favourite races have been there. Have a good one 1:46.1 was my fastest lap to date although have done some changes since

 

Might still see you in the paddock one day as the Tricolore Trophy sometimes runs on the same weekend as the TDT.

 

Cheers,

Henry.

[SweetBadger 94]

That's a shame, would be good to have another 205 on the grid but like you say it's a lot to shell out for one race! Will keep an eye out if we're at a race on the same weekend as the Tricolore Trophy.

[SweetBadger 94]

Another update - and another improvement in handling from tweaking the damper settings.

 

At Snetterton on Sunday it was looking like a very wet race so I softened the dampers off a little and swapped to wet tyres - the sun then came out, it looked like it would dry out and we only had time to change back to the A048s. Turned out we'd stumbled upon a decent dry setup!

 

Running the front dampers softer (4 clicks softer than the rear dampers), and slightly more pressure in the rear tyres (25 psi) reduced under-steer further, and made the car much more eager to turn in. 4 wheel drifting even featured on some corners

 

Despite the crap qualifying times we put in and my team mate having an off that left him about 2 miles off the track we came third in class, and I managed to set the fastest lap time in class (2:18.354).

[aldworth33 45 1 Cars]

I'm curious why people don't fill their tyres with pure nitrogen? You can take your wheels to the local Nissan dealers and they will normally do it