Thoughts on no bar/one bar autocross set up?

[mwood]

I recently bought an RF88 Van Diemen that I will be autocrossing. ETA for the transporter arrival is in the 12/21-22 time frame, so I don't have the car here to look at as I ask questions.

The car currently has no sway bars/anti roll bars/stabilizer bars (that should cover everyone's preferred terminology) installed, which leads to the topic of my post.

Has anyone experimented with a no bar set up for solo? How about just an adjustable rear bar? Any ideas on where one would start with spring rates if going down either path (given I don't even know the motion ratios of the RF88, maybe I should be asking for wheel rate)?

Just starting to think through what's in front of me. Set up is not my strong point, by a long shot. I am going to post on the general FF board for ideas on where to source the necessary hardware (particularly the front bar stuff, like the bearing blocks that bolt to the upper frame tubes and the torsion bar), but if anyone has thoughts on those items, I'm needing help!

Thanks-Mike

[Barry Ott]

A "no bar" set-up is something I'm curious about too. I've read in a couple other forums that say "sway bars reduce grip", but it's not intuitive to me why. I also know of a few cars (full body cars, street prepared and prepard AX cars) that have been very successful with huge sway bars. So I think this is a great question and I'm hoping some of the true suspension guru's can enlighten us. I saw Neil's response in your other thread, maybe that will get some discussion going there? Sorry, I wish I could contribute to an answer for you, but hopefully keeping this thread current will get some attention from someone who can :-)

[mwood]

Thanks, Barry.

Bar vs spring is one of those set up questions which never ends. I've just recently seen a good number of cars going to the no bar set up with good success. But, at the same time I've seen friends like Mike Maier going the opposite direction, after tons of industry level research and prototyping new stuff for Maier Racing...I just end up confused.

The one wheel vs two wheel piece I get intuitively, but when Neil says no bars ultimately allowed too much roll/camber gain, I don't get how that is just no bar related, if he had sufficient coil spring rate?

The ability to adjust f/r roll stiffness seems like a "good thing", seeing as we run on pretty different surfaces throughout the year. I'm planning on getting all the stuff I need to install the factory VD bar set up, just because, and start there, but may experiment a bit next year when I have access to a skid pad.

[RussMcB]

Mike,

You must be excited, waiting for it to arrive. Cool to think about a new race car showing up at your house.

I haven't autocrossed in years and don't know your level of experience or competition, so feel free to discard these thoughts. :-).

When is the first autocross? My recommendation is to get the car, make sure it's in good shape and ready to go, make "autocross" changes (i.e., gearing), then race it and see where it is before deciding about ARB's.

I agree that ARB's provide tuning options, but there are lots of variables and options.

Good luck, have fun. Sounds like it will be a hoot.

[mwood]

Thanks, Russ. I started on road course (motorcycles and vintage Vees) and then later went to autocross. I've autocrossed at a National level since I started in 2005, mostly in stock class cars, but lately in "Street Touring" (limited prep on street tires). No expert on set up, but a competitive enough person that I want the car "right" asap!

The car I'm getting is 90% of the way to an autocrosser, with the gearing and other first steps done. The dampers (Koni 28 series DA) were built by Stimola a couple of years ago with autocross valving. But, the car doesn't have the factory bar set up installed. My plan is to do an alignment/corner weight before I run the car, but am not sure where the car is in terms of wheel rate and what would be best to do to get it in the ballpark before I spend my time doing the alignment work. The more I think about it, the more I'm of a mind to find/make the needed parts and baseline the car with the VD factory set up. Make sense?

[Don Elzinga]

If the car was handling well for the previous owner, I'd take it out and see what it does before you make any big changes. Somebody told me once that the factory setup sheets on the English cars are based on running non-cantilever rear tires, and that setup will push like crazy with the tires we run over here. Never found an original setup chart for the '84 Reynard, so I can't say I've tried it myself. I run very little bar, because that's what seems to work on my car.

Don

[mwood]

Thanks, Don. That is interesting information about the English cars not being set up for cantilever slicks.

The car hasn't been run much since Ed put it back together. I'm planning on putting it on my friend's scales and check corner weighting and aligninment. Since I now know I have most of what I need to get the original ARB's on the car, I think I'll start with them both on the car. Do full soft bars and do the basic shock tune, first, then see where I'm at. If the car had been run a bunch and dialed in, I'd just go have fun, but based on my talks with the PO, it needs to be baselined.

[Neil_Roberts]

A "no bar" set-up is something I'm curious about too. I've read in a couple other forums that say "sway bars reduce grip", but it's not intuitive to me why.

Rough pavement moves the optimum setup toward suspension that is actually independent, as in no bars. On a smooth track, the optimum is springs + bars because most cars benefit from more roll stiffness than they can stand in ride.

Tangent alert: Because of a huge difference in corner speed and top speed, and significant ground effect downforce, Indycars and Champcars on street circuits need more ride stiffness than they can stand in roll. That's the origin of 3rd springs.

I saw Neil's response in your other thread, maybe that will get some discussion going there?

I ran out of development time before definitively determining which was better for the venues that I autocrossed on, bars or no. One of my limitations was that I didn't have springs that were stiff enough to fully counteract the roll stiffness loss from disconnecting the bars.

This time around, I plan to run bars because they will both be cockpit adjustable, so I will have very easy adjustability of both cornering balance and roll stiffness.

[Jim Garry]

Just my opinion based on a couple of decades with solo experience in FFs ...

When I tried stiff springs the car's grip was mediocre. Soft springs appear to be required in solo although I know at least one leading car manufacturer who contests that. So IMO, softer springs yielded more grip ... for me.

Given the soft springs, the car needed ARBs (mine were pretty stiff) in order to allow for appropriate transitional characteristics so critical in Solo competition.

Those good characteristics appear to have been attained by others through the use of droop limiting but that is a technique that I've never tried.

[Jim Garry]

In addition, as Neal pointed out, using at least one ARB allows for adjustability.

[Dick R.]

What I did (when I was still active and competitive ) was stay with the "original" relatively soft bars as I went stiffer with springs. This effectively made the bars even softer relative to total wheel rates. For tuning I used the rear bar.

We will see what happens when I try to scrape the rust off the driver in 2012.

Dick
85 VD

[Neil_Roberts]

We will see what happens when I try to scrape the rust off the driver in 2012.

This topic deserves its own thread, so I will go start one.

[mwood]

Just my opinion based on a couple of decades with solo experience in FFs ...

When I tried stiff springs the car's grip was mediocre. Soft springs appear to be required in solo although I know at least one leading car manufacturer who contests that. So IMO, softer springs yielded more grip ... for me.

Given the soft springs, the car needed ARBs (mine were pretty stiff) in order to allow for appropriate transitional characteristics so critical in Solo competition.

Those good characteristics appear to have been attained by others through the use of droop limiting but that is a technique that I've never tried.

Jim, when you say "soft springs", what kind of spring rate and wheel rate are you talking?

[Jim Garry]

Spring rates are not relevant for discussion because of the difference in motion ratios from car to car. But wheel rates for solo, IMHO, should not be greater than the weight on each wheel. That is, 1:1. That's max. Less might work even better. Down to (throwing out a number) maybe 0.75:1 ... i.e. 230 lbs of corner weight at one front wheel would be either 230 lb/in wheel rate down to about 170ish.

YMMV.

[RobLav]

The motion ratios are not so good on an RF88 (about .5-.6?). So you end up having to run some fairly stiff springs. My experience with an RF93 is to dump the RARB but keep the FARB. But that is in road racing.

[mwizard]

The motion ratios are not so good on an RF88 (about .5-.6?). So you end up having to run some fairly stiff springs. My experience with an RF93 is to dump the RARB but keep the FARB. But that is in road racing.

I have my RARB set to near 0, but I value the flexibility to be able to adjust it, for autocross.
Mark

[mwood]

I haven't done any measuring of the MR on the front of the RF88, but the rear is .75 (if I did my math correctly, 4:3 ratio on UCA/rocker, equals 1" wheel travel = .75" at the spring) and I think the front is approximately in that ball park. So, I currently have 500# front springs, putting me around 280# front wheel rate, I believe. I also haven't corner weighed the car, yet, but it seems I may be about 15-20% above the targeted wheel rate you described, at least in the front?

edit: didn't see the post from Rob about RF88 motion ratios..if the front is in the .6 range, my 500# spring should be just about right (180# wheel rate) with a front ARB.

[Buc01]

Not sue how to reach him anymore, but Tommy Saunders (from Texas) won an Autocross national championship in a 198 VD FF which I used to run in road racing (won a COMMA championship at Hallett in 1992).

Would be worth tracking him down to see if he had any setup info he would share.

Hopefully some of the Autocross guys here on the forum may know how to contact him.

Aaron

[mwood]

I have a number of friends from national Solo in TX. While I don't know Tommy, myself, I'm sure one them will. Thanks for the idea, I'll send out some emails.

[RobLav]

Easiest way I've found to approximate motion ratio is to raise the car up, raise and position the wheel at the set ride height, measure the shock length, raise the wheel exactly one inch, then re-measure the shock length. And do the same for droop.