ARB mods & suspension

[e21-Mark]

I want to stiffen up my track car and plan to double up on the front ARB while replacing the rear with an adjustable one. I have taken the rear springs up to 275lbs and the fronts are going to be somewhere between 550 and 650lbs. What spring rates are other people running on track? I also want to bring the ride height back down an inch or so, but not so low as to adversely effect the suspension geometry. I took the ride height up because of occasional road use but I don't intend on taking it on road next year. When I clamp the 2nd ARB to the original would I need to fit some kind of bush between them?

I have also fitted 15 x 7J alloys with 195/50 cut slicks but, partly because of wanting to mimic the old county race cars, I am wondering if it might be good to drop back down to 13's? There was a track prepped Viva at Brands, that ran 13's and balloon Avon slicks, and I really like the period look they give. Would running 13's have an adverse effect on handling?

I cannot easily / cheaply get more power from the M42 so want to concentrate on getting the car handling as best I can and improving my driving. There is still a bit of weight to be lost from the car too. I am also planning on losing weight myself. I can't see the point of working to improve the car yet still expecting it to drag my lard arse around. My personal goal is to put in a sub 1 minute lap @ Brands Indy circuit.

I have also decided not to fit the Stack digital dash but have opted for a period look instead, with a single large Stack tacho. I am also fitting oil pressure and water temp' gauges and a shift light. I am also looking for a more comfortable race seat.

[PeteK]

I put a second arb front and rear on the 323i and it made a bit of difference. There are a few things to watch out for. You can't just bolt on a second front as it will interfere with the tyres. I made up some brackets out of steel flat bar just to see if it worked. The next step was machined brackets, but I moved countries before we could get that far.

In the picture, you can see the brackets are not right out at the ends. We were adjusting them to see what would happen. It did make the car pretty tunable. I assume you have an LSD? If not, any stiffer rear arb will just spin the inside wheel.


IMHO 550lbs would be way too stiff. I know guys with full race prepped e12 535i's who don't run that. My track day 520i (1250 kg with me in it) only has 275 front and handles beautifully. 13s would make the car softer again.

Make yourself a set of coil overs for the rears with some bilsteins. Then you can have best of both worlds. Here's mine but made with Konis.

[Jeroen]

What about this kit?

http://store.vacmotorsports.com/suspens ... -p262.aspx

[e21-Mark]

I already run Gaz Gold coilovers all round with 275lb rears but there is definately scope to go harder on the front. I know many of the e30 race cars exceed 500lb on the fronts too.

The TWR County race series was run with identical spec 323i's and this included double front ARB's. I couldn't run a second ARB that's as low as yours so would have to machine mounts that clamp the 2 bars much tighter together. I plan to try and find out exactly how TWR did it but that may well not be possible. The TWR cars also retained 13'' rims.

BMW 323i - County Car Specification

* 2.3 litre engine balanced throughout
* Gas flowed cylinder head polished and raised compression to 9.8:1
* Brake tested to deliver 170bhp
* Heavy duty clutch
* Front struts specially rebuilt to TWR Racing settings, with stiffer springs and adjustable abutments.
* Competition rear dampers have adjustable bump and rebound settings with stiffer springs.
* Adjustable front anti roll bar of 24mm fitted in addition to standard one.
* Rear one of 19mm also fitted.
* Limited Slip Differential fitted with reinforced rear crossmember mountings.
* Racing brake pads front and rear have been specially made with additional ventilation to the discs.
* Mahle wheels 6Jx13 are fitted with Dunlop racing tyres.
* Body stripped of all interior trim, fitted with FIA roll cage front and rear, competition high back driving seat, BMW Motorsport steering wheel, four point racing harness, 2.5 kilo FE1301 plubed in extinguishing system, battery cut off switch and reinforced fuel tank.
* Specially made fibreglass bonnet and boot lids fitted. The boot lid carries a rear wing and there is a special racing air dam at the front.
* A special free flow exhaust system is fitted complying with the 1980 RAC noise regulations.

[TopCat]

For Camaro Racing car(Butch):
we swear by ProTech Shockabsorbers
http://www.protechshocks.co.uk/

even better than the ProDrive reset Bilsteins that we used to run- they will build you a custom set to your order

I do think that many try to overharden their race car suspensions- I would be inclined to soften the rear, to help with power delivery and harden via the adjust in the shox esp bump.

sounds like you have harder spring settings than Butch!

[Duracel79]

Mark,

When I bought my car it came with 425lb fronts and 400lb rear springs. never had problem with traction at the rear even with the 2.7 in there.

I have now upgraded the front springs to 600lb to try and stop the car standing on its nose under heavybraking making the rear very light. The springs seemed to have helped with this and has had no adverse effect on the handling otherwise.

Key to traction at the rear is to set up with as little rear camber as possible (I'm aiming for 1.5 to 2° neg with the new rear axle), keeping a wide tyre footprint. For the front its getting the camber and toe-in set for how you want the turn-in to feel (I run about 3.5°neg camber and a touch of toe out). Also as much caster as possible is usually best.

I've mostly run on 13" tyres and currently with Toyo R888 in 225/45/13. Also didn't really notice much difference to running some old 195/50/15's R888's.

As for adding roll bars, well you either want stiffer springs or stiffer roll bars. NOT BOTH. I run with the std bars all round but with quite a stiff front end now.

Hope that helps

Ben

[e21-Mark]

To be honest I cannot criticise Gaz as both their product and their after sales service has been excellent. When I did have a problem, with the lower spring perch fouling the tyre wall on the rear, they immediately worked to solve the problem. Obviously this was all without cost to me. In fact, they even supplied me new springs FOC to compensate for the tyre that blew.

I've spoken to a lot of the guys who build and/or run e30's in the Production Championship ( http://www.pbmwc.co.uk/ ) including the front running cars and general consensus seems to be erring on the side of much stiffer fronts than the 275lb rears. Obviously an e30 isn't an e21 but it's about the closest guide I can find with recent input. I do know my ex Khumo car was pretty stiffly sprung too though. When you look at the lap times for the Brands indy circuit, a quick lap was around 58.2 - 58.7. I'll be happy if I can get a one minute lap in.

Cheers Ben. I'm going to do one thing at a time so it'll be the simplest thing first. i.e springs. I do want to mess about with ARB's eventually but I'm also mindful that with Autumn & Winter coming, I will want to keep some roll to aid with traction in the wet. It'll be good to try a selection of springs and see what happens. I've got a Q-startz GPS data logger which is cheap but provides some pretty accurate data for comparison.

[e21-Mark]

Mark,

When I bought my car it came with 425lb fronts and 400lb rear springs. never had problem with traction at the rear even with the 2.7 in there.

I have now upgraded the front springs to 600lb to try and stop the car standing on its nose under heavybraking making the rear very light. The springs seemed to have helped with this and has had no adverse effect on the handling otherwise.

Key to traction at the rear is to set up with as little rear camber as possible (I'm aiming for 1.5 to 2° neg with the new rear axle), keeping a wide tyre footprint. For the front its getting the camber and toe-in set for how you want the turn-in to feel (I run about 3.5°neg camber and a touch of toe out). Also as much caster as possible is usually best.

I've mostly run on 13" tyres and currently with Toyo R888 in 225/45/13. Also didn't really notice much difference to running some old 195/50/15's R888's.

As for adding roll bars, well you either want stiffer springs or stiffer roll bars. NOT BOTH. I run with the std bars all round but with quite a stiff front end now.

Hope that helps

Ben

Bumped for Topcat.

[TopCat]

thanks!