Question for Alex re:Bilstein/Eibach coilovers

[Andy]

I notice that you have Bilstein/Eibach coilovers on your rear suspension. Is this because you want to limit the squat under excelleration.

I am thinking of having the same, but also thinking about uprating the torsion bars (instead or as well). Would you recommend the coil overs?

I have been told that large low profile tyres may create problems getting traction off the line during hard launchs, have you any knowledge of this?

Is your bug gor IRS rear?

[Alex]

Hi,

I can not answer a few of your questions because my car is still in the project stage. The main reason for me to go to coilover was for the height adjustability in the back. I was told that they were mainly developed for the Käfer Cup series in Germany.

Once using coilovers you do not need the torsion bars. I do not not know yet how they are while driving but I was told that it is the way to go. I will have to let you know in a year or so on this one.

I believe you want some of that squat in the back when you launch hard to get more weight and therefor better traction. But that would be more for drag racing I guess. That would be the same reason on not using low profile tires....the tire can not work as much and therefor start spinning quicker off the line.
Again.....this are just my thoughts.....I could be totally wrong.

My pan is IRS.......converted a swing axle pan to IRS because I could not find an IRS pan at that time.

Hope that helps a bit,
Alex

[Andy]

thanks for the reply Alex.

I am at present having a big engine built, and I will be using it on the drag strip occasionally, although it will be a street car.

The person building the engine has said that there may be a problem with using the low profile tyres 215 * 45, for the same reason that you mentioned. But he also spoke about upgrading the torsion bars or using coil overs to limit the squat when launching.

I will need to ask him again about this. I would love to be in contact with someone who drags their GL.

By the way, very impressed with the spec of your project, that will be some car. Will you be taking it up the strip occasionally?

[Alex]

I hope to get some track time with it.
You should talk to a drag racer and their suspension setup.
You might have to find an inbetween setup for your car if it is mainly for the strip but still street driven. I do not believe that you want to eliminate most of the squat because of traction during the launch. that is why low profile tires are no good either. You have to put too much air in them and the tire will not work for you.

There was once a very good article in a German car mag....AutoMotor&Sport and they said that the best performance combo is 17 inch rims with 45 series tires I believe for the same reasons......the tire will work giving you some extra traction.
I believe that a lower profile tire will make it very hard to know when you reach the limit.

I remember my old 1776 bug 10 years ago with 195/60/15 and you could feel while cornering when the tire was working really hard. With my New Beetle I could feel the fronts starting to rub on the asphalt with 225/45/17 but it was less of a notice than what I remember from my old bug. It is a though comparison but it gave me a good indication on what is happening to the car.

Again....this is just my personal experience and I am by far not a racer or have any knowledge about track racing. The best person to ask about track setups and tires would be Jak Rizzo. I hope that he finds his way to this board. Also Sandeep can help you......since he is (was) a kart racer and had the chance to drive some very nice and fast cars on the track.
I have to wait to get my car done to see what it will actually do while driving hard and I hope not to end up in the gravel. For suspension setups for the strip check the STF (Shoptalk) or the CLF (Cal-look.com).

Alex

[bren]

Originally posted by Andy
The person building the engine has said that there may be a problem with using the low profile tyres 215 * 45, for the same reason that you mentioned. But he also spoke about upgrading the torsion bars or using coil overs to limit the squat when launching.

who the hell told you that??? for ultimate grip during a hard launch you need to transfer the weight to the back of the car.. the best way to transfer weight is to allow the rear end to squat and the front end to lift.. thats why succesful drag bug use stock size torsion bars and 90/10 shocks up front.. if you make the rear stiff you prevent it from squatting.. thios means no weight transfer, which in turn means reduced grip. your guy sounds like hes got his advice mixed up.

setting up a car for drag starts severely reduces its roadholding capability though.. i would not recommend the above if you intend to go round corners fast... stiff is the way to go for that. my bug hangs onto roundabouts like you wouldnt believe, but at santapod my 60ft times were laughable! i span the tyres on a freshly prepped trackall the way up to 5k rpm in 2nd gear! ...not enough weight transfer!

[Andy]

Thats exactly what I have read, I take it you got this from the cal-look site. But they are not talking about low profiles, although the weight transfer makes sense no matter what your profile.

I got hardly any spin at all at Santa Pod, only a touch after launching, but the car is a lot heavier than yours and did have almost 5 stone of speakers in the back.

I will probably leave it as it is, and see how it goes.

[bren]

no, not from cal look site.. you mean... they have a section on handling???!!! surely not!! ;) aahh!! no, you mean they have a section on launching!! hehe.. you nearly had me shocked there for a minute!! :D

[DORIGTT]

Hey Bren,

Don't go bad-mouthing Cal-look cars! They'll out handle you any day of the week in torrential down-pours (narrow contact patch) or in snow and ice (if they're studded).:p

[bren]

135 section tyres performing well in the wet?? thats a contentious issue in itself!

[DORIGTT]

Yes I know, I know. It was a gesture to defend the honor of all the Cal-lookers (which I used to be seriously into) who we all know wouldn't be caught dead lurking here.

[bren]

Originally posted by DORIGTT
Cal-lookers who we all know wouldn't be caught dead lurking here.


...or turning corners at speed! ;) :p :silly:

[vujade]

i ran 135 tires many years ago & I believe they are the cause of my ghia being totalled. there is not enough contact patch for them to be used on the street. they did not provide me with grip to the road and they just broke loose under severe braking. I blame this all on magazines. they are at fault for not informing younger kids that these should only be used on a drag strip on not on the street.

[MattKab]

Alex, I have a heavy sound system behind the seat in my Bug, It's a Karmann '03 so it's heavier to start with. Would the larger diameter T3 or 944 rear torsion bars be more suited? I'm building a heavy, T1 cooled T4 and I'm worried about the spring rate being low. Would the 944 torsion bars be too stiff? it could turned down if it is I suppose. What are your views?

:coffee:
I have strong opinions about stupid 135/145 tyres used on the roads, I've used 145 firestones on empi8's 8 or 9 years ago and they were leathal for a younger, more careless driver. I never stuffed my Bug, and changing over to 195/50 made the handling and braking safer than before. (~70bhp).

IMHO 'skinny' tyres make any Bug look 'feeble'.

Bren, I think your lack of traction on the strip is more to do with your control and low profiles than weight transfer. You still get weight transfer with no suspension, inertia and aerodynamics. A wheel/tyre with almost zero pneumatic trail will never 'hook-up' like a taller, more compliant tyre would. You don't get low profile slick tyres do you? tyres are heavier than wheels.

The angular acceleration of the tyre footprint relative to the wheel is critical in drag launches. Underdamping the response of the wheel/tyre during a launch increases traction. The 'Snatch' effect (?) coined. ;)

Weight transfer only occurs once your moving, save the wheel spinning for front wheel drive cars.

Mattx

[Alex]

Hi MattKab,

I think that I am the wrong person to ask the question about the torsion bar switch. I have heard that it has been done but I do not know how they drive or if they would be too stiff.
Maybe someone else will have a good answer for you.

Alex

[Andy]

Hi MattKab

I have been asking questions regarding rear suspension, and spoke to a few people with knowledge. Hopefully some of it now makes sense.

If you add Avo Adjustable Coil Overs this should help the torsion bars out to take some of the load. They are fully adjustable, so you can adjust them to suit your needs, www.vwspeedshop.co.uk sell them, give Paul a ring.

Low Profiles do spin more than higher profiles, I think this is also due to the fact that the higher profiles twist and absorb some of the power allowing hookup, as you say the "snatch" effect. Probably going to get a set of 15 inch Ercos with street legal slicks with I will use for the strip, and keep the Cups and low profiles for street use.

[bren]

Originally posted by MattKab
You don't get low profile slick tyres do you?

err... yes! what do the touring cars use?

thinking about it more, i think another part of my problem was the amount of negative camber i run at the rear.. doesnt help on straight line launches as the outside inch or so of the tread doesnt touch the ground when the rear end squats.... my front end doesnt lift at all either..

[MattKab]

Thanks guys, I still have some reservations about compound spring suspension. The coil-overs alone and the torsion bars removed would do the trick, if the springs could be made to order, with the appropriate springrate. I might just try the 944 torsion bars and see for myself. Another thing on the list to try! :D Of course I'll share the results. I can't find any technical data on 944's- axle weights, weight transfer, that sort of stuff. Any ideas?

Bren, have you considered an IRS set-up for you Bug?

'Touring cars don't drag race! my point was about hooking up. Drag cars don't do bends. Touring cars take care not to wheel spin to the back of the pack (from the startline).

Back to drag launching Bugs- a ~23" cast/spun Ally wheel with a lowpro slick would accelerate easier than a 15" wheel with squarer section slick- far less inertia to overcome. And a massive saving in weight. It doesn't happen! The sub 6sec drag cars drivewheels are nearly all rubber! Less likely to 'snatch' due to the massive potential energy they have to store. This stored energy comes from the losses in the dynamic response of the tyre. The difference in the relative accelerations between axle and tyre footprint aids traction from static. Underdamping. That's why you don't get lowpro slicks at the 'pod.

This is based on my understanding only, please correct me if i'm wrong. Too much control and response theory work to keep it to myself ;)

Andy, I looked out for you/your Bug at 'Action! 'you there?

[bren]

Originally posted by MattKab
Bren, have you considered an IRS set-up for you Bug?

yup! but it wont happen until i tear my car apart for a rebuild.. ie: its a long way off! im perfectly happy with the handling of the swingaxle rear end anyway, ive spent a long time getting it to work well on the street so im not gonna undo it all for a while yet..

'Touring cars don't drag race! my point was about hooking up. Drag cars don't do bends.

exactly! its all about compromise! you choose setup and parts for your car depending on its main use. my car was built for the street, particularly setup for cornering, hence its poor launches at the 'pod.. no big deal for me, i would rather have a car that handles well on the street than one that handles like a dog but is able to launch hard.. after all, the roads in this country cannot be described as straight! ...and as my car does 6000miles a year on the roads, and only about 2 miles a year on the dragstrip you can see why my car is setup like it is! decent drag cars cant take corners.. its the flipside of the coin.. they see little or no road use, so they dont care that they cant corner.. dragstrips dont have corners after all! ;)