OldSStroker, I read this 3 or 4 times before I got it, you really lost me with the RRO/S RRU/S stuff till I sat down in front if it with some food to get the brain working…

lowering the car lowers the CG height, and raises the relative rear roll center as determined by the panhard rod.

WRT to RRO/S vs RRU/S, I always prefer RRU/S it makes the car much more drivable the faster you get and the more HP you’re running. The only time I’d consider O/S is if the car was a slalom only car (which the way some autox guys are, maybe that’s what you need sometimes), but this would never be in a car like an f-body. In the handling world F-bodies are heavy, heavily overpowered cars, and you pretty much need to do anything that you can to keep the back end, well, behind you.

If the course is really that tight, I’d rather mess with the front in the form of changing rates or toe out. On most cars this is easier to adjust. On an optimized setup you could make the panhard rod location adjustable so you can adjust your rear roll center to help.

If you really wanted to play with this, if you have access to a play station/PS2 and GT2 or 3, they really do a great job at simulating this, especially GT3 (but you can’t really play with it there while racing someone else unless you use BT2 ). Pick a high powered rear drive car and tinker with the suspension settings, and you’ll find that anything that you do to keep the back end behind you lets the driver go faster. Real world, f-bodies are the same. It’s much too easy to get the back too stiff (loose) on them then the other way around. The only time they seem to understeer is when they’re dead stock.

Very little, but nothing that you’ll really be able to feel.

Again, I’d much rather attack this with a better turn in then mess with the rear suspension. Maybe I see the rear suspension in too much of a black/white light, but I’m comfortable there. The easiest way to make an f-body a scary handler is to mess with the rear suspension. With the front alignment completely off it’s nowhere near as bad as a slightly tweaked rear suspension. From my experience, the easiest way to get an f-body rear suspension right is don’t touch it, just get the right shocks. If you want/need to go further, then stiffen the hard parts so they locate things better (and in most cases soften the bushings).

whether you’ve got RR U/S or O/S at that point depends on the LCA geometry you started with and your total antisquat. From my experience, with over about 70% AS in an f-body, you will usually get the rear of the body LIFTING under acceleration. If the rest of the rear suspension is setup as above, that means you’ll get RRO/S, which will mean that you won’t be able to go as fast out as you would otherwise, which will hurt your times greatly. (proof reading this I started wondering if I contradicted myself here but I didn’t, the tire will O/S, what the car does depends on the slip angle of the tire)

This would not be an issue on a road course because you’ll be at a higher speed and will not be able to generate the torque to get that lifting with most engines.

Either way, at this point I’d rather have RRU/S (for that matter, I think that everyone would), and be able to use the torque of the car to control O/S.

This is why for autox on an f-body I prefer massive spring rates and soft sway bars (with rubber end links. You get the advantage of controlling roll AND dive/squat, and then you can focus more on geometry as it effects steering attitude.

I’ve found that what works for AX usually works well for the street, you might want a little more rear stiffness if you do a lot of highspeed/highway stuff. My ’83 TA with it’s 890lb front springs was as gentle as a lot of stockers on the street.

I think that this is where 90% of f-body owners get themselves all screwed up. More AS is not always good for drag racing. At 1” lower then stock ride height, lowering the rear LCA pivot to the middle hole on most relocating brackets is enough that most cars will hit so hard that they’ll squash the sidewall and BOUNCE loosing traction about 10’ out if you know how to hit the tires hard. I have this on video somewhere, where I was able to hook so hard off the line on radials that we were debating if the front was pulling off the ground, but then about 10’ out it would turn into a smoke show.

FWIW, In my ’97 WS6, I was able to slip the clutch out and HOOK at between 4200-5200rpm on radials with low 1.7 60’s with stock suspension geometry, why do I need more AS?

you’re right, and even more then that, suspensions are not as cut and dry as engines. An engine either makes the power or it doesn’t. A suspension that works PERFECTLY but does not inspire trust in the driver is worthless, but a good suspension that the driver is comfortable with is a winner.

The fact is that I feel that a lot of this discussion is academic WRT to an f-body and autoX, since 99% of f-bodys in a neutral/coast/decal attitude are almost always oversteering anyway, I don’t really feel there is a place to purposely dial in more oversteer. My ’83 TA was a work of art in this way. After years of tinkering I finally got it to the point that it would act neutral under 99% of situations and then only O/S or U/S if I ‘told’ it to. It’s too bad my neighbor plowed into it 3 times while it was parked in front of the house…

What’s stopping him? You can sign up for multiple heats, bring both…

Heh, you think that I’d pass up a chance to open my big mouth…

 

Very True! I just verified this exact problem 2 weeks ago with video. My car is at stock ride height and my LCA's were in the bottom hole. The tire was being hit so hard it almost left the track when it rebounded. Mine was taking about 4 or 5 of these cycles before things settled down. Last week I moved up one hole and I was in dead hook bog mode until I added tons of air. Like night & day.

Steve

 

Mark (WS6 TA),

Thanks for the input.

As far as PS2, Bret uses that extensively for just the reasons you suggest.

quote:
you’re right, and even more then that, suspensions are not as cut and dry as engines. An engine either makes the power or it doesn’t. A suspension that works PERFECTLY but does not inspire trust in the driver is worthless, but a good suspension that the driver is comfortable with is a winner.

Well, here we diverge a little. How much power is the point in any close competition. Cup guys talk of 2-3 hp being an advantage on a restrictor plate engine. Geting (or even measuring!) that is not cut and dry.

I tend to subscribe to the philosophy that says there is an optimum setup which allows the car to achieve max performance, and it's up to the driver to adapt him/herself to get that max performance. "Comfortable" isn't necessarily fastest. It's hard for me to believe that the same car set up loose for one driver and tight for the other is in it's optimum (physically fastest) mode.

IMO, the very best drivers are able to adapt to the car instead of adapting the car to them. Mark Donahue and Michael Schumacher come to mind as that type of driver.

My highly opinionated $.02

 

Funny this is the first thing that poped out at me here too. Learning to drive with a fast but uncomfortable car takes some time.

This is a interesting read from both parts, because WS6 TA has done this and I talk wiht the Old guy alot about random things like this. We got thinking about the max anti squat where it's still driveable RROS setup and it's interesting to me. Big springs and bars on the rear with a compatible setup on the front would be interesting. Limiting the roll somewhat would help the driver feel for sure here, but the more forward bite coming out of the corners would be fast. As long as the rear was pretty stiff this could be pretty controlable if it doens't go to far. One thing I found that I like is a car that is twitchy and very agile in autocross. Two things that I have found in autocross that you have to learn are: 1. drive extremely agressive, pushing to hard is the first step. 2. learn where slow is fast, control the agression and use it to your advantage. I had a race in the GTI one day on a very wet course. I won the class of 13 and PAX with almost bald tires in the rain by using this theory above. Then I went out with my buddy to show him overdriving with alot of oversteer but controled in the fun runs. After we got kicked of we looked at the time, which was the 2nd fastest time of the day at about .3-.4 behind my best during the race. Overdriving can be very fun, but sometimes slow.
The point being that I had max counter steer in the car doing this but it was fun. I'd always rather have the wheel straight and the car turning than the wheel turned and the car going straight. As WS6 said it's the slip angle that counts. Luckily on a street tire that peak on the slip angle curve is very big and wide so a little more slip can be very driveable and fast due to proper rotation. Driving a car fast in oversteer is never really taught, and engineers seem to hate it in the supsension design, but a good driver will put the car there and make it fast. I think Childress picks his drivers that way i.e. Tim Richmond, Jeff Gordon, Jimmy Johnson, all of those guys hang it out there on the edge and are still fast.

Generally it's right that a RRUS car is what would be fast for most guys. With soft springs it would be very close to impossible to drive on a RROS car, but with minimal RROS say 1-5 degs in the LCA and stiff springs it could be fun and fast if you trusted yourself.

One thing that got me on the max anit squat setup on the f-bodies. Since we have that 3 link w/ TQ arm it's pretty hard to get alot of antisquat. The parallel LCA setup is very small, but even a upward sloping mounting LCA with much more AS could with the right tuning work really well. The bounce thing is interesting, but it seems that some good shock/spring tuning could take care of that. Not to discount what you guys see, but I'd rather take more of one good thing and fix it's problems.

I think it's something to try, lord knows tuning all of these things would take some patentince but should be faster in the end. It's alot like Renaults 111deg F1 engine, it's been a bitch to work with but it's starting to pay off.

BTW I do like GT3, I can't wait for the online GT4. GT2 and Donahues old Camaro with a setup like that out of his book works extremely well. Who would have thought that a locke rear end would be so quick.

Bret

 

SABLT194- That’s really common, but I’d argue that unless you’re running a ‘slick type’ tire (in other words, not a street radial or nitto DR, BFG DR’s are somewhere in between), even the middle hole will have some problems for you.

If you want to see an extreme case of how this myth that ‘more antisquat will get you more traction, always’ check out a mustang running SSM ‘lift bars’ at the track. On a hard launch with soft tires I’ve seen them actually leave grooves in the track surface from where the RIM hit the track.

OldSStroker, I don’t think that we diverge on that at all. I agree with you that there is an ‘optimum’ setting as you put it or a ‘perfect’ setting as I put it, where the car will be the fastest. And the best driver will be best able to adjust his driving style to best take advantage of what they’re given. The problem is that it is difficult to maintain that level of precision, and that we are very capable of building machines that can react and do things faster then a human can react, in some cases that can exert greater forces then the human body can withstand. I guess that just like the best driver, the best builder/engineer understands the limitations of the driver and of real world conditions and can best compromise that perfect setup to work well with what he’s given.

Also, like I said before, we are arguing over 2-3hp in a lot of these threads. In the case of some races, that 2-3hp is the difference between making power and not making power. Our discussion is considering suspension changes on the same level. We’re debating the difference in RR O/U S by making changes roughly on the scale of 1” (or less) in the pivot point of an LCA. That is a change of .02” in the wheel location front to rear, which is a change of .000012 degrees in the tire angle on something with an f-body’s track width… Wait, is that math right? If it is, then that’s smaller then the change due to bushing deflection or even the play in a spherical link…

OK, I know that I haven’t had enough sleep in the last few days, but if those numbers are right, then what we’re discussing is a non issue (and leads me to wonder about some of the published circle/dirt track rear suspension tuning tips that I’ve read about). Hum… I’m sure I’m missing something here

 

Bret, you posted that while I was typing my reply…

Sounds like we’re almost exactly on the same page except one part, and it’s mostly that I’m not sure that I’m following what you’re getting at (and in another way I’m wondering if it’s something that I’ve figured out that I like in my cars accidentally/empirically). The RROS + stiff springs. For the life of me (and my sleep deprived little walnut of a brain) I can’t seem to figure out what the stiff springs does for the combination.

The reason that I’m really wondering is that while I described my favorite car as having fairly soft way bars and even using rubber end links on the rear bar, it also used very stiff springs, much in excess of what most use, 890 in the front, and something in the 200 range in the back (I really need to double check which ones I ended up leaving in there, I had a few that I was experimenting with in the 185-possibly as high as 250 and when I found what I liked I just left it there, and that was at least 5 years ago, I haven’t autoxed for at least 3 years).

How that setup would work on the dragstrip I have no idea. I’ve run it there, but the car really didn’t have the power to really tax the rear suspension.

BTW, what range are you talking about when you say ‘max AS?’