dand86951

A big reason to delete the torsion bars is to be able to get the rear end down along with the higher spring rates for a better balanced car.

ehall

The other big reason is to be able to make significant suspension changes quickly. It significantly enhances adjustability as well as track options.

333pg333

Yes, Elliot is right. Now it's going to be much easier to tune the car for different tracks. All both of them...

Having driven it a little more I have to say that it feels a lot more responsive to turning. We'll have to check all the geometry again of course but if this doesn't lead to any mid corner to exit oversteer I'm thinking I like this quite a lot.

The old setup was 25.5mm T bars + 285lb springs. This equated to 708lb/in (not at wheel). The new springs are pretty much bang on 200lb stiffer, we have the same ride height, but there is definitely more rear camber. Any guesses?

ehall

The rear camber is probably helpful. I haven't done the math, but the new springs should be creating a softer rear rate?, just from Eyeballing the number. That should be reducing oversteer.
I could be wrong, as I hate doing equations.

blade7

So you can bin the torsion bars, fit stiffer springs to regain the combined spring rate and no change to the KW's damping ? and no other issues ?.

333pg333

No, that's the weird thing. The new rear rates are stiffer than the old ones. The old ones were 296 at the wheel and this is now 386. Front was 519, now 615. So I don't get why we're seeing more rear neg?

Yes. The shocks can handle quite a big jump in spring rates. This is on their race version so I'm not sure about the V3 version, but I have heard of guys doing an upgrade in spring on those as well.

ehall

The car is rotating better, with the stiffer rear end.

333pg333

Well yes it is, but we did the calcs and the balance should be essentially the same % ratio as before (front to rear) all else being equal...so not sure why. I feel like this new rear neg must be helping to bring the rear around with the front more, just can't figure out where this new rear neg came from? Whatever it is, I like it but the test will be on the track. Could result in 720o rotation which is not so desirable.

blade7

Thanks

Techno Duck

Regarding the V3's and valving for no torsion bar, i talked to KW North America a few months back and they said the rear shocks should be revalved if you up the spring rate anymore than 100lbs. They said it would be about $100 and turnaround was 2 weeks if i remember right. If i did the math right, you would need something in the area of a 700lb rear spring to give you the same effective rear wheel rate as running the stock torsion bar and KW V3 spring (aprox 300lbs wheel rate).

An interesting point that was brought up when i was looking into this, the shock valving might be okay as it is valved for both the torsion bar and coil spring. But what confuses me is the the actual spring rate the shock is seeing may be different due to the geometry of the suspension.. trailing arms are uber confusing .

333pg333

I'll have to check with my suspension guru on that Jon, but I'm inclined to believe you. I always wondered on the differences of rates to the wheel of T Bars and coils. You sort of have to assume it's different.

Oddjob

What did you pull apart when you yanked the t-bars? You had to unbolt the trailing arms from the spring plates, right? So the car needs to be realigned, no?

How does 25.5 (175 lb/in)+ 285 = 708?

333pg333

Jim, the 708 is equivalent coilover. For the explanation read below:

Here's an excerpt from an email between Karl and me when I was questioning him about my original incoming KWs. I've posted this many times before so apologies to the others who've read it.

"I have not spoken with Bob, and actually don't know who he is. But believe me, my numbers correct (or close to it - see the following explanation).
The info on Paragons site is stuff they got from me a few years ago. In any case, the 47% is a number that I have calculated By taking measurements. I am now pulling out one of Porsches own Motorsport sheets that shows all the rates of their Turbo and "Cup" cars back when they ran competitively.
Porsche lists the 25.5 mm bar as 31 N/mm which is 177 lbs/in. They also then give the variable rate coilover helper spring rates at 34-65 N/mm which is 194 lb/in - 371 lb/in. They then give the total Rate at the wheel(T-bar plus coilover) as 45.4 - 58.5. Back out the rate at the wheel due to torsion bar which they list as 31 and you have 14.4 - 27.5 at the wheel due to the coil over. So take your pick, 14.4 / 34 is approx 42% or 27.5/65 is 42%.

Bob is right about them being inboard but his numbers are off. Actually
they are correct I think in that the motion ratio is about 65%. But when
calculating wheel rates from spring rates it is the motion ratio squared that is uses. So 0.65 ^2 is , guess what,... 42.25% which is the number that Porsches own sheet claims as I outlined above. So your torsion bar is
177 at the wheel, and your helper spring rate is a 285 which is 119.7 lb/in at the wheel. So working backwards 177 plus 119.7 is 296.7 pounds per inch at the wheel. Divide this by .42 and that is you equivalent coilover, or
706 lb/in coilover (initially I had 661 lb/in which is attributable to my measurement error - I had 47% and Porsche lists it at 42%).

So it may be a bit stiffer in the rear than I might run but with the ability to tune sway bars etc... you should be Fine. Your setup is actually much stiffer in the front than the Porsche cup setup which ran progressive front springs (200 - 371 lb/in) with the rear setup I described above which is not that far from what you have( yours is 296 at the wheel and theirs was 259 -
334 lbs/in at the wheel).

Hope this make sense, but believe me, what is above is 100% correct. I can fax you the Porsche motorsport sheet if you think it will help."

Oddjob

Oh, ok - you are saying that your existing 285 lb/in linear spring and 177 lb/in t-bar combined are equivalent to a coilover w/ a 706 lb/in spring rate w/o a t-bar. Both setups would have an equal effective wheel rate of 296 lb/in.

Using your effective rates above 519/296 = 1.75 front/rear effective ratio, 615/386 = 1.59. So assuming all else equal, the car should have more tendancy to rotate (ratio is more torwards oversteer).

Did you figure out why the alignment changed yet? Had to of moved the trailing arm on the spring plate.

There is some difference when running combined t-bars w/ helper springs vs. straight t-bars, vs straight springs. Some depends on how the t-bars are indexed when used with helpers. As once the t-bar passes the neutral index point, its spring rate becomes subtractive to the helper instead of additive. Inside wheel in a corner, as the car body is lifting off the suspension, the coil spring is pushing upward and the torsion bar will be trying to pull the trailing arm back to neutral (if the t-bars are indexed neutral at ride height).

ehall

FWIW, everything I learned about suspension I learned from him^^^

I'm happy to see that my first thought was correct. You have a bit more oversteer as a result of your actual f to r sring rate change. The numers for T-bar + spring vcs just spring can get fairly compliucated as they apply to the "effective rates".