VL spring rates for track car?

[VECom]

Hi,

I'm building a VL track car and wanted to know if anyone has any experience with front and read spring rates for an early commodore. If so what have you been using?

Car is RB25DET and will be running on semi slicks. Probably be using BC coil overs.

Thanks,
Greg

 

[harrop.senator]

Is there a lot of lift and camber changes on the local track to you?

Our two tracks are polar opposite , one is very tight and changes direction a fair few times.

The other is extremely fast and open.

At the tight track I've got the shocks set to almost full soft and 3/4 hard on the fast track.

I've always ran 10 kg front with Rb's and 8 kg rear if is coil over shock. No rear sway bar , stock front. I've found it easier to dial a car in without sway bars or only the front and stock.

Having non coil over I think you need around 2.5-3x the rear because of the leverage point.

My Datsun has 6 kgs in the front and 18 kgs in the rear but all my other Nissan's I run 2 kgs less in the rear then the front.

That's with s13's and r31's. Similar size , weight and the same engine in them as you.

Unsure on commodore set up as I've only drifted jacks hill in V6 commodores for a laugh. To do that I was running king's HD front , HDD ute towing springs rear and dual rear sway bars. Did alright.

 

[VECom]

Thanks for the info.

The two track in Tas are more lower speed corners.

R31 skyline prob similar weight, but you're right, rear sping in VL is not a coil over so distance from wheel will influence it. Could measure distance along trailng arm to work out ratio..

I have a 240Z track car that handles quite well. Prob about 200kg lighter than VL and run 330lb F (5.9 kg) and 280lb R (5Kg). Running RB25DET.

18kg springs in rear of a Datsun seems very heavy.

 

[Smitty]

Hi,

I'm building a VL track car and wanted to know if anyone has any experience with front and read spring rates for an early commodore. If so what have you been using?

Car is RB25DET and will be running on semi slicks. Probably be using BC coil overs.

Thanks,
Greg

ok.. you have provided most of the info needed.

firstly, set spring rates to suit your tyres
secondly stiffer/tighter/harder is NOT better.. any time! (talk to Larry or Jack Perkins if you disagree)
third.. do not set spring rates around sway bars (do the reverse)
Forthly.. don't do much with street type springs if you are serious . A proper coilover will outdo an SSL... anytime!
Fifth... set springs before getting shocks (and get shocks that can be revalved or are adjustable)
Six... how much does the car weigh? have you changed the weight distribution from factory? (battery in boot etc)
and
finally, make the final choice based on your actual suspension. What toe? what castor? what camber?
what akerman? CV jointed rear axle? spool?? and be prepared to change it .. if you move to slicks or if it rains

Final hint ... always aim for driveability, having to wrestle with the car means it ain't right! Mine is hands off at 200+
down the main straight at Sandown (if you want)

and
sorry, I am not giving you my settings .. my VK will weigh more/less and have different suspension set up to yours

 

[VECom]

Thanks. But info and photo does not help me ordering a set of coilovers that come with springs.

Yes same model race car will be slightly different in a number of areas, but weight of stripped car would only vary by a few %, and similar suspension design, so what others use in same car is a good starting point. Saves me buying more sets than I need to get to where I need to be.

 

[harrop.senator]

18kg springs in rear of a Datsun seems very heavy.

240z is coil over spring. I'm running baz's set up. He dropped my fronts to a 5 with the turbo l18 due to the fact I've got the K Mac front sway bar. I've got 240k struts and Volvo 4 pots with verada discs.

The 180b and 1600 rear spring is angled and further up the trailing arm. Creating a pivot point dramatically increases the spring load needed.

He reccomended (or did I think cam does all the Australian and mechanical stuff. Last time we spent hours on the phone he was south east Asia. Finding places to do entire custom harnesses 21st century fuse boxes ) 700 lbs for street with factory sway bar , 900 lbs street no sway bar and 1100 lbs track or if you drive it to the track and aren't a sook no rear sway bar.

Running tokico excel g's.

My 31 with interior was 1280.

The sil80 track car is 1150 no carpets , no aircon , dash , cage , stock passengers and fixed back drivers.

Still running 10's and 8's now we're on stock sway bars again. Were running 8's and 6's with 32 GTR rear sway bar and 27mm front. Were three wheeling on the tight track too often and didn't have as much control.

 

[VECom]

Thanks for all the detail, much appreciated. Yes recall the 1600 springs is someway up the arm.

So based on my calcs for length or rear arm and distance rear spring is from the axle I believe I only need to be 31% higher value for spring compared to what it would be if sitting on the axle

From my 240Z set up worked out equivalent in VL considering differing weights, weight distribution and rear spring not on axle. Came up with 7 kg F and 7.2 kg rear. Sounds a bit soft compared to what you you've been using.

R31 should be reasonably close to VL, especially for front. So might start with 8kg on front and 8kg also in rear or slightly above. As rear spring inboard from axle a bit the same value will effectively be less at the rear.

 

[harrop.senator]

Thanks for all the detail, much appreciated. Yes recall the 1600 springs is someway up the arm.

So based on my calcs for length or rear arm and distance rear spring is from the axle I believe I only need to be 31% higher value for spring compared to what it would be if sitting on the axle

From my 240Z set up worked out equivalent in VL considering differing weights, weight distribution and rear spring not on axle. Came up with 7 kg F and 7.2 kg rear. Sounds a bit soft compared to what you you've been using.

R31 should be reasonably close to VL, especially for front. So might start with 8kg on front and 8kg also in rear or slightly above. As rear spring inboard from axle a bit the same value will effectively be less at the rear.

Japanese cars always reccomended 2 kgs lower than the front . It may be why it's always been my starting point and I've dialled the shock in.

 

[Smitty]

Thanks. But info and photo does not help me ordering a set of coilovers that come with springs.

Yes same model race car will be slightly different in a number of areas, but weight of stripped car would only vary by a few %, and similar suspension design, so what others use in same car is a good starting point. Saves me buying more sets than I need to get to where I need to be.

you would be surprised...a cast iron V8 + full cage adds a lot of weight (where you really don't want it)
then have a modded fuel system, exhaust will mean your build will be different to mine

I went thru 5 different setups until I was comfy with mine (based on the 3 main tracks I run at)
... get an exercise book and write the details down as you experiment

 

[_R_J_K_]

Having non coil over I think you need around 2.5-3x the rear because of the leverage point.

calcs for length or rear arm and distance rear spring is from the axle

The term you're looking for is 'motion ratio'. Seems there's a few different ways to calculate it.

Would look at converting to front VR-VS (not VT+ though) knuckles and LCAs as it will allow you to run a coilover with a clevis instead of needing one of the old school VB-VP ones. An S13 front coilover then becomes almost a drop in which exponentially increases your access to different brands and options. This setup would also allow you to run longer LCAs if you wanted using VT+ control arms.

Japanese cars always reccomended 2 kgs lower than the front . It may be why it's always been my starting point and I've dialled the shock in.

I think it's a bit of a side effect from the age those cars were in their prime and what they were mainly used for, and that people and companies making cheap coilovers just kind of never wanted to try anything different or change, particularly if Japanese brands were using particular settings. Relatively good suspension was kind of out of reach for mere mortals. That and a majority of the people in that scene was also extremely stingy with money.

It's interesting now, at least in Australia, watching companies like MCA and Shockworks develop suspension for new car models and seeing the differences between their setups for the same application.