Some Suspension Set Up Info....

[Erko]

Gday Lads,

I have just been using a suspension design spreadsheet to have a look at different spring / sway bar configs and the effect they have on the front roll couple (FRC) which is a percentage of the weight transfered over the front wheels (divided by the total weight transfer).

In effect the lower the number, the more the car will oversteer. The higher the number the more the car will understeer.

I have used BA-F XR6T Sedan data as below

Weight 1780kg

Weight distribution (front / rear) 56%/44%

Stock sway bars (front rear) 24mm/19mm

Stock spring rates (front/rear) 450lb/250lb

above weights / distribution info is from my car when I had it corner weighted.

So stock FRC is 48.5% I have calculated below FRCs for commonly available upgrades.......

Sway bars only :

Front 27mm sway 52.8%

Front 30mm sway 57.8%

Front 27mm sway / rear 22mm sway 45.0%

Front 30mm sway / rear 22mm sway 50.0%

King Springs only (520lb/390lb) 44.5%

Tein Performance Coilovers only (670lb/436lb) 47.3%

With sway bars and King Springs (520lb/390lb)

Front 27mm sway 48.4%

Front 30mm sway 53.1%

Front 27mm sway / rear 22mm sway 42.2%

Front 30mm sway / rear 22mm sway 46.8%

With sway bars and Tein Performance coilovers (670lb/436lb)

Front 27mm sway 50.7%

Front 30mm sway 54.6%

Front 27mm sway / rear 22mm sway 44.8%

Front 30mm sway / rear 22mm sway 48.8%

So this gives you an idea of how changes in spring / sway bar will affect the front/rear balance. I have been playing different sway bar configs on my Tein equipped phoon....the above does line up with my experience, and I think I have almost settled on the 27mm front bar with stock rear bar, after trying 30mm only, 30mm +22mm and 27mm + 22mm. As I expected the numbers line up with what I was feeling, the Teins with 27mm front and 22mm rear were causing more oversteer than stock, not something I want to be dealing with at 180kmh+ on the circuit.

anyway, hope someone might get some use from this info.

Cheers

Rob

[R-SPEC]

Rob, with the stock RSpec suspension, would you suggest only the 27mm front sway and leaving the back sway stock for best overall results?

[senna_T]

Nice info there Rob, I was considering the 27/22mm F/R sway bars, if I am reading this correctly this is the most oversteer prone setup correct?

[Erko]

Jim, yes the 27mm front could work well. Certainly would feel more stable at high speeds.

Pat - yes you are reading it right. I just removed my 22mm rear bar because with my Teins was tending to shift too much weight off the inner rear wheel in tight turns and unload the wheel......not what you want with added power.

these numbers are not 100% spot on and there are variables however will serve as a guide.

Edited 13/05/08 08:02 AM by RACEFPV

[Dirty32]

Great thread Rob. Good for those that arent fantastically technically savvy to suspension etc.

Out of curiousity & without results infront of u - would there be a hell of a lot of difference for a ute?

Im hoping to get my ute lowered soon (been sayin it for ages) and was thinkin of throwin a sway bar on. Just not sure on what combo as yet... Also not sure if I wanna throw on some nolathane bushes but wondering whether it will be wasted on a ute?

[Erko]

Great thread Rob. Good for those that arent fantastically technically savvy to suspension etc.

Out of curiousity & without results infront of u - would there be a hell of a lot of difference for a ute?

Im hoping to get my ute lowered soon (been sayin it for ages) and was thinkin of throwin a sway bar on. Just not sure on what combo as yet... Also not sure if I wanna throw on some nolathane bushes but wondering whether it will be wasted on a ute?

thanks mate, thought I would "put in" so to speak.

to be honest I have no experience at all with leaf spring rear ends, and I am not sure of the size of your front sway bar....though I do hear some of the Ute guys like to increase front sway bar diameter - how does your car handle now? at the limit say above 60kmh what does it do on the throttle? off the throttle?

Re bushings, the front lower inner control arm bushings are a worthwhile upgrade on either a sedan or ute....and if your bushings are worn its certainly a good idea to do the rest of them. I like superpro stuff, its a pretty good performance/comfort compromise.

[Dirty32]

It handles Ok for a ute - havent driven any other utes to be honest so im not sure what to compare it to... I had a 32 GTR prior and the ute handles like a boat compared to that - had coil overs and bushes allround so not really a good comparison.

I highly doubt my bushes are worn - ute only has 15K on it. Just wanted to upgrade for the handling gains. Thinkin of getting lowered front springs, reset rear leafs and maybe a sway bar & bushes (unsure on the last 2). I suppose I just want to tighten it up a bit, not in an understeery kinda way but just to handle better in general.

Hence the question about the difference between results you have in this topic for a ute/sedan. All the same - thanks for the info.

[Full Monty]

I highly doubt my bushes are worn - ute only has 15K on it. Just wanted to upgrade for the handling gains. Thinkin of getting lowered front springs, reset rear leafs and maybe a sway bar & bushes (unsure on the last 2). I suppose I just want to tighten it up a bit, not in an understeery kinda way but just to handle better in general.

The Front Lower control arm bushing is worth replacing from new, absolute garbage, allowing massive deflection of the steering spindle under hard braking.

It is solely designed for low NVH levels, and is fluid filled for vibration / damping.

Increased steering feel and sensitivity , along with greater braking feel results from replacing it with a nolathane / equivalent.

Edited 13/05/08 10:39 AM by Full Monty

[zakxr8]

Hi Rob

Great read & thanks. Would you have any figures for XR8. I have TIEN with 27/22 on my XR8. On the track it felt OK but that may be because I don’t know any better. I have kept my original sways and may change the rear back, any input would be appreciated.

[ZAP]

I have Konis, King springs and 27/22mm ajustable swaybars.

I agree with Rob's view on the setup. My car is setup for drifting and is VERY prone to oversteer.

It makes it fun to drive at times, but you need to be on the ball in the wet.

I should ajust the bars to soften them up a bit.