Ron Simonds' Coilover Suspension - Thoughts?

[gtv6sv]

Hey guys,

Have people here used Ron's coilover suspension? What's people's take on it for a fast road car?
I've only read good things about it overseas but would be good to get people's opinion here.

Thanks guys!

[gtv6sv]

Here's the link if you want to check it out!

http://www.rsrshop.com/

[Duk]

I've not got any direct experience with the RSR set up, but when you learn some stuff about suspension the RSR stuff looks like a very big compromise that puts a lot of stress into the chassis.
The combined front spring rate alone is very high and in a relatively light car like a GTV or even the slightly heavier GTV6 would push the front suspension's natural frequency well over the 2Hz (probably over 2.2Hz). That sort of natural frequency (suspension stiffness) is the domain of dedicated track cars, running on atleast semi-slicks and more importantly, with a reinforced chassis.

The 30mm front anti-roll bar is 244% stiffer than the 75's 24mm bar.
And is 346% stiffer than the 22mm front bar.
Huge anti-roll bars on independant suspension reduces the independance of the suspension.

The rear spring rates are just as mad in the natural frequency that they give the car and the rear ant-roll bar is even more massive in its percentage gain. 350% stiffer than a 19mm bar.

Now all of this is just my opinion, but the RSR stuff never addresses the Alfa TA chassis biggest issue of poor front suspension geometry and tries to brute force the chassis into submission. All of that brute force gets fed into what is not only an old chassis that has more than likely been battered by use, but a chassis that was not particularly rigid when they were first built.
Jim K on GTV6.com once made some rather interesting observations about how effective a simple bolt in roll cage was for the feel and lap time of his 75 road car.

[gtv6sv]

You have quite the wealth of mathematical knowledge there Duke!
Definitely makes sense though. Even if thought the 30mm bars were quite large, especially without reinforcing the chassis.

Roll bars aside, I've heard that the coilover suspension can be a better ride than bigger torsion bars (say 28mm) with Koni Shocks whilst also providing better handling providing adjustments in the dampers are correct for the road.
I haven't got experience with this so I'm not going what I said is correct, just what I've heard/read.

Reason I ask is that I'm in 2 thoughts with my suspension:

1. Go through Performatek and get the 27mm torsion bars, and the recommended other bits to go with it (ie Koni yellows all round, castor ball joint conversion, SZ de dion bush conversion, slightly bigger sway bars front and rear, reinforcement plates where the front sway bars mount, lowered Springs at rear and upgraded watts linkage if required)

Or 2. Go through either RSR or Intrax and go down the coilover method (Intrax recommended me to go down the path of just coilover front and rear with dampers pre-adjusted from their factory without adding bigger roll bars or upgraded watts linkages as they are confident their system will eliminate a lot of roll and that this is meant to be a fast road car).

Again the whole world of upgrading suspension is still relatively new to me so anyone's recommendation of what they have done is more than welcome!

I do plan on installing a half cage in the car so hopefully that can help with the rigity of the body.

[gtv6sv]

Here's the link for a company called alfa 9 supply, also supply the intrax suspension:

http://www.alfa9supply.com/transaxle-alfa-parts/

Read up on the ARC (anti roll control) system, seems like a quite advanced system!

I've been recommended the IK2-V2 system in conjuction with the ARC system, for a road car they say to remove my roll bars all together!

[Duk]

Roll bars aside, I've heard that the coilover suspension can be a better ride than bigger torsion bars (say 28mm) with Koni Shocks whilst also providing better handling providing adjustments in the dampers are correct for the road.
I haven't got experience with this so I'm not going what I said is correct, just what I've heard/read.

Reason I ask is that I'm in 2 thoughts with my suspension:

1. Go through Performatek and get the 27mm torsion bars, and the recommended other bits to go with it (ie Koni yellows all round, castor ball joint conversion, SZ de dion bush conversion, slightly bigger sway bars front and rear, reinforcement plates where the front sway bars mount, lowered Springs at rear and upgraded watts linkage if required)

Or 2. Go through either RSR or Intrax and go down the coilover method (Intrax recommended me to go down the path of just coilover front and rear with dampers pre-adjusted from their factory without adding bigger roll bars or upgraded watts linkages as they are confident their system will eliminate a lot of roll and that this is meant to be a fast road car).

Just for comparison sake and this is calculated for the short torsion bars, but an RSR front spring is 600lb/in. With a 22.8mm TB (standard 75 TB, 'cause that's what I should be working on.............  ) and that spring, the combined overal spring rate would be comparable a torsion bar about 31.2mm in diameter.

Interesting to see this picture. Notice the car has an upside down lower balljoint (to dramatically raise the front roll centre height and make the camber curve characteristics much more effective), with what an aftermarket forged aluminium lower control, what looks like a 105 upright arm and a bent steering arm to correct for bump steer.

[105gta]

Duk, you're all over the math! just out of curiosity, what spring rate would that equal to for a coil over only set up? Any idea what 29mm torsion bars would be equivalent to?

[gtv6sv]

Definitely an interesting set up, looks quite serious!

I agree 105gta, your math work phenomenal!
I too would be interested to know the spring rate for a cool over only set up if you know?

[Duk]

A short 28.7mm torsion bar would be the increadably close to a 600lb/in spring mounted on the shock absorber.
Wheel rate would be 233lb/in.
Sorry for the imperial numbers, that's just what seam to work best for me.
The spring would be 107.37kg/cm.
The wheel rate would be 41.7kg/cm.

[105gta]

Thanks duk. I work in imperial most of the time myself. Do you happen to know what a 32mm torsion bar would equate to?

[Duk]

Standard (75) 22.8mm TB equal around 242lb/in.
27.3mm TB would be around 495lb/in.
28.7mm TB would be around 602lb/in.
30mm TB would be around 723lb/in.
32mm TB would be around 932lb/in.

Again, those are comparable for the short TBs.

[gtv6sv]

Great info on all the statistics  Duk, thanks for that!

I'll ask Ron on what he reckons of just having the coil overs and see what his response is and come back here.

I'm the meantime, Duk what do you recommend for suspension upgrades for a fast road car?

Anyone has experience of putting on the SZ De Dion bush onto a GTV/GTV6/75?

[105gta]

I have the dedion spherical bearing as well as rose jointed watts link, lowered roll Centre and 2' of neg camber. This was all done at once naturally so I can't say what had the most impact, I guess the roll Centre change but all together it sticks, and sticks good.  Can highly recommend it!

[105gta]

Gtv6sv, in response to your original questions, what are your goals/use for the car but just as important what else have you done to improve it? Or plan to do. For example wheel and tyre size have an impact on suspension setup.

[Duk]

I'm the meantime, Duk what do you recommend for suspension upgrades for a fast road car?

Front suspension geometry fix. Easiest is something like the Pace Engineering top balljoints, but you still need a bumpsteer solution after that. It's not that hard to sort out.

Torsion bars either 27.3mm and 28.7mm, but more than likely the 27.3mm. Or adding 250lb/in spring to the damper to get that. Or a 360lb/in spring to get you closer to the 28.7mm bars. But you can't get an off the shelf 360lb/in spring so either a 350 or a 375 spring........... Not much difference either way.

Rear springs are a bit harder because the motion ratio of the rear springs is much higher than any added front spring/damper motion ratio. A 175lb/in spring is probably a good start, but maybe a touch soft. A 200lb/in spring is getting up there (in natural frequency), tho.

Anti roll bars would be something like an adjustable 27mm front bar. And either modify the rear bar so it can be adjustable or just leave it standard. Being able to tweak the rear bar would be helpful if you went with 200lb rear springs and wanted to soften the rear bar a touch.

But dampers (shock absorbers......... ) is the biggest issue and 1 I only have opinions on and no real experience to back it up.
Dampers is where, from peoples comments on the ride quality, the Intrax/RSR set up sh!ts on everyone else!
And the ability for them to be able to have all of that (excessive) spring rates and still give a decent ride quality comes down to having digressive style dampers. That and the fact that the chassis is flexing a lot...............
But properly set up digressive dampers give the best results.
And here's where I end up standing alone (so to speak) in that most people just say use Koni's and have them revalved to suit, I say Koni's are a linear valve damper and will always be compromised in their ability to control the car and spring(s) and provide over all decent ride quality.
Bistein make digressive valve dampers (NOTE: I'm not talking about the off the shelf Bilstein dampers that you buy for the Alfa's, they are linear valve dampers), but I don't know enough about what ones to use or how to assemble a shim stack to say "For 'X' torsion bars in a V6 Thingy-bob, use Bilstein 6035s at the front and 5030s in the rear.................".

So geometry, with bumpsteer correction. Fairly easy, and in my opinion a must.
Spring rates for the lighter GTV6 (rather than the havier 75 3 ltre that all of my number crunching has been based on), I'd look at the 27.3mm TB (or standard bars with a 250lb/in additional coil spring) and 175lb/in rear springs.
27mm adjustable front antiroll bar and probably just a standard rear bar.
Dampers/shock absorbers..................... That's the hard part. Off the shelf Koni adjustables will work. Revalved ones will work better again, but I still believe that properly shimmed Bilstein digressive valve dampers would give the best end result.