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ActionDan

Car too firm/skittish/struggling for grip.

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S13, but that shouldn't matter.

 

See video and not that in the long left hander at 0:41 and 1:43 how the nose of the car seems to want dart around a bit. All throughout the video you can see how skittish the car is. Last time I drove here it was much more progressive, I've added swaybars since then and I'm guessing the whole setup is too firm now.

And this is before the bars went in and starting from turn 1.

Here's what's in it/the alignment, let me know what you think. I did the alignment with a stringline, took 6hrs going up and down allowing the car to be settled again then re-measuring. I had no success with local shops.

 

So after A LOT of stuffing around it now has the following and "looks" a lot better.

 

Front - Camber/Toe (can't tell you what castor is, arms are stock). Considered maybe less camber might give me a better contact patch if the car is now not leaning over as much with the swaybars.

Driver: -2.75/1mm toe out

Pass: -2.75/1mm toe out

 

Rear- Camber/Toe

Driver: - 1.3/1mm toe in

Pass: -1.3/1mm toe in

 

Car has BC BR Coilovers with 8kg Front and 6kg rear springs - maybe these are too firm?

Whiteline 27mm front swaybar (adjustable and on max soft)

R32 GT-R rear swaybar (25mm hollow)

New end links both ends.

 

Federal RS-Rs 235 all round, was running about 29-30psi hot on that day. Maybe I'm just at the limit of what these tyres can do?

I'm yet to get under it and have a look at how the tyres wore, but the car was a late more skatey than usual, not sure if that's because the swaybars are allowing me to go faster or because something is wrong.

 

Yes I realise I am also a shit driver and smoother inputs will help :)

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Can't compare, the pre-swaybar time was starting at turn one as we were not using the full track, we stopped at the switch back coming on to the straight. I believe it was 55secs or so from a standing start, the full flying lap was 59secs but included the main straight and an extra braking zone.

Edited by ActionDan

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I don't race grip so there will be others here far more qualified than me to comment, but 8/6 sounds far too stiff for a stock S13 chassis chasing grip. I would have expected something more like 6/4. My MCA blues are 6/4.5 and I don't think I would want anything stiffer on smooth sweepers (I like to explore the limits of grip when bends are dry, empty and free of debris).

 

With uprated swaybars front, rear, and poly bushes for the end links, I'm not really surprised that it was skating all over the place. Have you tried changing the GTR rear anti-roll bar back to stock and see how it goes? Given how stiff your rear springs are I don't know that you necessarily need to be lifting the inside wheel even more in turns, since the outer spring won't be compressing that much to start with, and you were oversteering a lot.

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That was the first outing with those bars and I knew there'd be soem more changes needed but needed a benchmark.

 

Next day is at Winton for which I have times so I'll have something to compare to there.

 

Re your comment about lifting the wheel, maybe I've got it wrong but I thought the whole point of roll bars was to transfer load from the outside wheel to the inner, planting it more firmly.

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Camber doesn't give you grip with body roll, it gives you grip when the wheels are turned - in a "normal" car, when you turn the wheels full lock, the outside wheel develops positive camber. Adding static negative camber means when you do go towards lock, the outside wheel will be on more of the tire. Haven't had any experience with semi's, but I've always seen comments about not having enough camber trashing semi's. If you're able to do a hot lap, and had something like an infrared thermometer, you'd be able to see if the inside/middle/outside of the tyres are getting hot/cold compared to each other. If you're not loading up the whole tire, you're not getting the most out of them.

 

re: alignment. I would try more camber. More castor is betterer, does drastically change steering feel. I can't remember how much I'm running, but its 'not enough'. I'm limited by stupid wheels vs. windscreen washer bottle.

 

re: spring rate. 8/6kg is just what people do, its the scene standard for a drift/sports car. A lot of the 90's jap "lowering springs" were around the 2-4kg mark or even the tein super streets were at 5/4kg, and probably much more suited to grip. Nismo S-tune springs are 5.2kg front, 3.7kg rear, and still pretty comfortable to drive with. Mate has done a lot of days at wakefield in 230-250kw cars, the quickest time he did was on 5/4kg springs.

 

re: spring rate vs. swaybars - I think most guys go for coilovers first because you need coilovers bro, and go for swaybars later because they're expensive and don't let you slam your car. iirc, stiffer spring rates (with respect to lap times) are really only useful when downforce is involved - stops the car getting too low when you start getting big amounts of kg of downforce. Swaybars however help all of the time.

 

re: swaybar combo. I'm running swaybar adjustible front and rear. When I had just the front installed, it made the rear end feel sketchy as f**k. Front alone on softest setting improved feeling and turn in, but overall the car was worse because it was so drastically different to the rear end. When I finally put the rear sway bar in, the entire car feels more balanced. Mid corner stability is incredible compared to stock/stock and upgraded front/stock rear.

 

disclaimer: I've had no sleep and never done a timed lap in my life.

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Appreciate it.

 

I'm awaiting BC coming back to me with parts on lower rate springs.

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Yeah it was a pretty abridged comment I made.

 

As I understand it to be (motorsport gurus please correct me) the whole 'load transfer' goal of anti-roll bars is achieved by flattening out the car's position when in a turn, through lifting the [unloaded] inside wheel and subsequently lowering the chassis on that corner relative to the ground. With the chassis sitting lower at that point than it otherwise would, it has more weight bearing on it, meaning the [weight] load has effecitvely been shifted.

 

The the issue with anti-roll bar sizing/stiffness is that running a stiffer bar will result in a more dramatic lift for any given outer wheel lean, so the stiffness of the anti-roll bars used must be suited to the suspension. Since you're running pretty stiff springs, it stands to reason that the car won't be squatting a huge amount on the outside wheel in turns, so I would think that you wouldn't need to shift that load to the inside wheel as hard as you might with springs that compress a lot more.

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I get you, cheers.

 

I've been doing some more reading and considering 5kg fronts instead of 6.

 

There's a local motorsport guy I might engage to set the car up as best he can.

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Another thought... did you try just taking a few psi out of the rear tyres when it was oversteering?

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No, there was limited time to adjust things.

 

Next round is at Winton with proper garages and time between sessions to check and adjust things.

 

I was running 29-30psi hot all round and as you can see from the footage it was also understeering.

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Fished this article out of my bookmarks, since it might be of interest to you Dan. Although a lot of the specfics are for the FD RX7, the chassis of which is far superior to an S13, it's a good no-nonsense read with decent advice.

 

http://www.rx7club.c...s-setup-723617/

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Fished this article out of my bookmarks, since it might be of interest to you Dan. Although a lot of the specfics are for the FD RX7, the chassis of which is far superior to an S13, it's a good no-nonsense read with decent advice.

 

http://www.rx7club.c...s-setup-723617/

 

Awesome link thanks

Edited by Skepticism

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Always fun learning about chassis dynamics and seeing/feeling the effects of a change, then planning how to work around it.

 

I had an alignment done by a guru. Running AD08r's and ended up with the following;

S15.

warm tyre pressure 32psi.

FRONT: -2.9 camber, 1mm toe in, ~6deg castor

REAR: -2.7 camber, 2mm toe in*

No rear toe arms. Guru was targeting 1.5mm in.

 

The car drives beautifully on the street and track. Straight line grip was noticeably down when the tyres are cold, but the mid corner speeds were up, which is exactly what I wanted.

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With what spring rates and swaybars though?

 

S15 geometry is also superior to S13 as I understand it, particularly around roll centre due to subframe.

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Spoke to BC who suggested I speak with Paul at option1, he recommended returning to the stock front swaybar and testing that, leaving spring rates alone. Then swapping that around and putting the stock rear back in but leaving the front.

 

That's a fir bit of f**king around at a paid track day but it's not impossible.

 

I might take both bars, go and run a session with it as it is, and see how those times compare to previous Winton times then look to swap a bar out and test again.

 

Federal said my hot tyre pressures are fine.

 

​Paul also said my alignment settings were on the money.

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Changing spring rates - the coilovers *should* be valved to suit 8/6kg springs. Not sure how sensitive the BC's will be, but ben ellis said with HSD's you should have the dampers revalved if changing springs by more than 2kg.

 

Also - you running a power brace? Probably changes steering feeling as much as the whiteline swaybar did.

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No power brace, if you mean the k frame style one?

 

BC also said the same thing, that 2kg would be the max you would want to change the spring due to valving. As above, Paul said leave the springs and play with bars. Whiteline don't offer any smaller bar for the front and the rear bar they offer is 20mm, which im assuming is solid? which would be close to the 25mm GT-R hollow anyway?

 

I just want to take it into a shop and have someone sort it...

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Wheel alignment looks fine. Stock sway bars would probably work better, cheaper and easier to change them than springs.

 

I'd probably go a bit higher with pressures on street tyes, semis/slicks are normally a bit stiffer construction and I usually aim for 31-32 hot.

 

Why did you change bars? Did you just want less body roll?

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Less roll and more grip was the objective. I assumed that the body roll it had was costing me some grip.

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I put it on stands last night after packing up all my gear from the track day.

 

Interestingly the outside edge of the tyres front and rear looks darker/more worn.

 

Which I thought would imply it needs more camber.

 

Talking to a buddy of mine with a very similarly setup car (but better and wider tyres) he runs -3.5 front and -2.5 rear with the same bars and spring rates (although Tien RS and no BCs).

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Two other things.

 

I'm being advised to get some adjustable castor arms and dial in more positive castor and was also asked to look at the angle of my LCAs, which are definitely not parallel upfront. Cross member side sits lower than wheel side which as I understand it is not good for Roll Centre,

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Needs more caster. Surprised you still run the stock ones. They suck at the best of time. Won't need to increase - camber if you increase the caster.

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I know it will gain some more camber with caster.

 

Ride height has been mentioned by a local suspension builder also, he was not happy the arms were not parallel at the least.

 

Also, how is that going to help the rear.

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I think it's just a matter of adding more front swaybar.

 

Less roll and more grip was the objective. I assumed that the body roll it had was costing me some grip.

 

Stiffer sways reduce body roll at the expense of grip. That's because they tend to unload the inside tyre. Bear in mind that softer bars will yield slightly more grip, at the expense of transient response e.g. changing direction in slaloms, or turn-in. So if you're fighting the car in slaloms then more swaybar is the go.

 

They're mainly used as a balancing tool as they can decrease the GRIP at the front or the rear as needed.

 

Front stiff, rear soft - car will understeer, as lateral grip is removed from the front

Front soft, rear stiff - car will oversteer, vice versa

 

Judging by the newer vid you're fighting oversteer everywhere. In the older vid the car looked pretty composed, stable and grippy. You could add more front swaybar - since its an adjustable Whiteline bar - or return the rear to stock. It depends whether you want less or more roll respectively.

 

 

Ride height has been mentioned by a local suspension builder also, he was not happy the arms were not parallel at the least.

 

This too, S chassis front suspension geometry can't really cope with slammed ride height. You get a lot of unwanted dynamic behaviour like bump steer which certainly can destabilise the car.

Edited by Skepticism

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Well we know it definitely needs "stuff" it's just a matter of what I can do easily between now and Winton.

 

I'm not opposed to buying caster arms and camber bolts, but would like to stick with the tyres for now. Think I'll take the stock bars with me to Winton and swap them out or at least disconnect one end to see what difference it makes.

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With what spring rates and swaybars though?

 

S15 geometry is also superior to S13 as I understand it, particularly around roll centre due to subframe.

 

BC BR 8kg/6kg

Whiteline non-adjustable

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Where do you live dan? I'm not familiar with the s13 but before you go replacing/ removing springs and sway bars I'd dial a little more camber and castor in the front first. N second drop ya spring rates to 6-4. I would keep your sway bars and go for an adjustable in the rear. Obviously ya coils aren't the greatest and the dampeners in then could be giving u greif. I had 8/6 cuscos in my 15 track car n they work well after playing with setup.

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Also as mentioned rsrs seem to work best at 31.5-32psi on my full weight s15 n a mates Evo. They are slippery if your pressures are low. Not sure how much lighter the 13 is but there an awersome tyre! Also what sizes are you running?

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