DamonB

If any test shows "that in order to get max tire grip, you want to allow the car to roll over onto the outside tires and increase the tire to ground contact force" as he said in his post that test is completely wrong. Read any book about suspensions.

Sorry, they do contradict. I should have said stiffer bars create greater load transfer, not greater weight transfer. Let me see if I can explain this without screwing up. There are two things going on here: weight and load. Weight shifts around because the CG of the chassis is heaving around. This shifts weight around the different tires. The swaybar on the other hand is merely a spring. There's nothing it can do to physically move the CG or weight around on the car, it can however change the load the tire sees by making its spring rate stiffer. Since the spring rate goes up that tire must now handle a greater load than it would with a lesser rate.

It does seem confusing but consider a car resting on scales. We can't change the weight of the car or the weight distribution of the car by monkeying with the springs. You can't actually move weight in the chassis without unbolting it and putting it somewhere else. Changing the spring perches isn't moving any weight around the car at all, it's merely balancing the loads on the tires. It seems contradictory because you look at the corner scales and see the numbers change but you have to look at the car as an entity. If springs really had an effect on weight putting softer springs on a car would make it weigh less! They of course don't do that, but they do decrease the loads on the tires.

The same is true of downforce. If we could put scales under the tires as the car traveled we'd see the scales read higher and higher weights as speed increased due to downforce on the car. In truth the car is not any heavier, it is merely exerting greater load on the tires. If you merely looked at the number on the scales you'd insist the car was heavier just because it was going fast, but in fact it weighs just the same it did standing still!

dubulup

this is the way I always viewed it...

thanks for clearing up the weight/load term. If you read axr6's comments with load in instead of weight...they agree with your statements.

Do you know if the R1/2 front sway bar is identical to the base? If so, happen to know the diameter? that way I won't have to wait until my car is out of paint to measure and order some bushings.

DamonB

IIRC correctly all the front bars are the same. Rear bars varied among model years but not trim levels. I believe for a given year the rear bars are the same regardless of base, touring, R1, R2 etc but there were different rear bar rates between the 93, 94 and 95 years. The 93 had the stiffest rear bar. The 94 and 95 have softer rear bars but I'm not sure if they were the same.

Double check all of that. The only thing off the top of my head I'm 100% certain of is that the 93's had the stiffest rear bars.

axr6

I believe that to be true as you put it, particularly when you introduce CG into the picture. The ideal grip is the one divided amongst four equally loaded flat tire patches. Yet, as shown by the change of a rear bar on the FD (or any car) by increasing the rear roll stiffness we are also reducing the sum of rear tire grip, even though the apparent loading of the tires, side-to-side, appear to be more equal. From all I've learned I still tend to agree with edmcguirk, below, when it comes to dynamic weight and load transfers. I believe that he is referring to softer suspension as softer springs AND bars. (correct me if I am wrong in my assumption)

Actually the ideal weight distribution for race cars (to me) is more biased towards the rear, to provide better accleration traction by placing weight on the accelerated wheels, as well as providing less dive under braking, again for having a rear weight bias.


Those two statements appear to contradict each other. With less roll stiffness the weight and the CG will be heaving around during cornering shifting weight onto the outside tires. I'd have very little doubt in my mind that a softly suspended car, if run on a set of weight scales, heaving its body and CG over the outside wheels, would show a marked increase in tire-to-pavement contact pressures on the outside tires.

Yes, I have been suggested such many times during my racing years. I have no problem with the concept. Yet, having said that what would be your fix for this understeer scenario if not an increase in the rear bar stiffness? Assuming that the front bar is the correct size and reducing it is really not a good option as you'd get more roll. Is there anyone out there succesfully racing and FD with the stock rear bar? I'd find that difficult to imagine.

Actually you are, at least partially, correct on this one. I was thinking back my racing years watching all those stock classes and seeing some of those sedans with huge body rolls with one tire dangling off the ground. Some of those cars have so much spring/shock travel that they lean over alarmingly while do not seem to go down on their bumpstops before lifting off their inside tires. Remember the Citroen CV? I have seen some GT spec cars lifting inside tires but, when equipped with very stiff bars. I always believed that to be a chassis problem, allowing diagonal flex.

I did say, myself, that it was all about balance. I simply cautioned not to arbitrarily stiffen up shocks to do someting that they were not designed for (the primary function of a shock is not for tuning out moderate to heavy understeer) and something that could bite one under certain conditions.

DamonB

Weight transfer is completely independent of roll stiffness. The equation for Lateral Weight Transfer is:

Weight transfer= G*CG height/track width

Where
G = cornering G
CG = center of gravity

Note that no where in that equation is there anything about springs, bars, shocks, suspension travel etc. They have no effect on the amount of weight transfer.

So far all we know is what the original poster said: "Ok, so I just got adjustable shocks.

If I want to decrease understeer, should I make the rear stiffer than the front, or the front stiffer than the rear?"

Without knowing more about the setup other than he has adjustable shocks and when exactly in the corner the car is pushing no well informed advice can be offered. However no race engineer's first decision is going to be to attack the end that is working rather than the one that isn't. If I walked up him that day and tried to fix it? Absolute first thing I'd want to know is tire pressure and temp.

Depends on what you call successful and what you consider the correct size. I know of many fast FD's with stock rear bars and larger front bars that have no understeer problems whatsoever (mine included).

If an inside tire lifts it will first happen at the end of the car with the most lateral load transfer, that means the end with the more roll resistance. On the vast majority of cars the non-driven end is setup with less lateral load transfer than the driven end so that the drive wheels can put power down as well as possible. If you can't put power down you can't accelerate. That means front wheel drive cars tend to pickup the inside rear tire (especially under braking) and rear wheel drive cars tend to pickup the inside front (especially under acceleration). 90% of the time when a tire lifts in a corner it's not because the suspension has run out of droop and pulls the tire from the ground, it's because the bar is stiff enough and the grip on the outside tire great enough that the bar overwhelms the spring on the inner tire and pull that tire up from droop.

2CV's are strange beasts in that their front and rear suspensions are interconnected. Even though they are raced overseas I've never heard anyone use "2CV" and "handling" in the same sentence They either make it around the corner or they don't

Anyone running shocks with multiple adjustments disagrees with you. The entire point of developing 2, 3 and 4 way shocks was to isolate slow speed adjustments (chassis management) from high speed adjustments (surface irregularities). Shock adjustments are exactly for tuning such things as understeer.

jgrewe

iTrader: (1)

DamonB says "Without knowing more about the setup other than he has adjustable shocks and when exactly in the corner the car is pushing no well informed advice can be offered."

I can't believe it took this long to get to this statement. While there has been a ton of great info thrown around this is the first thing we need to know to realy help.
General statements here, and it will depend on if you can change rebound independent of compression.

If it is pushing when you first turn in soften the compression in front or stiffen rebound in rear.

If it pushing as you exit soften rebound in front, stiffen compression in rear.

If its pushing in the middle its not your shocks that are the problem.

Don't add so much rebound that you smash the chassis on to the bumpstops after a few laps.

The ability to adjust things independently is why people spend $5-10K on shocks.

edmcguirk

You purposely restricted your question to adjusting shocks to decrease understeer and I understand that if there is only one device that is easily adjustable then that is the one you want to adjust (when you have a hammer everything looks like a nail) but there is often another thing that is easily adjustable - the nut behind the wheel.

When I increased the boost on my autocross car by 30 HP, suddenly I had an understeering problem. It turned out that my increased speeds were causing me to go just a little bit too deep into every corner. I had to use the brakes too much and the front end washed out.

I entered the corners a little less aggressively and suddenly the oversteer that I knew my car was capable of was there in abundance.

Step back and examine your driving style. Adjustable shocks on an otherwise stock car can change the flavor of your handeling a bit but the driving style can have a major difference.

ed

axr6

DamonB -

I have read and learned a lot from your posts in the archives since I'd joined this club only a few months back and I do have a lot of respect for your knowledge.

I think that we have some differences of opinion regarding proper car setup. That is fine, as there are more than one ways to skin a cat. I assume that you are a successful racer and an engineer as well.

I have had my share of racing success, winning a title in autocrossing going back to 1984 and racing in NASA Pro7, SCCA GT, FM and FS classes, winning probably close to 50 SCCA road race events, including 3 Regional titles and one West Coast Road Racing Champ title. During that process I built much of my race cars and set up the suspension, did my alignments, etc…, as well. I must admit that I ran on a shoestring budget, financing my racing through the pay of an Electrical Engineer, so I never had the experience to use some of those very expensive Penske style shocks that you seem to be referring to.

The advice I had given to the poster was reflecting my experience and my successes. I would begin setting up a race car with the initial establishing of a basic balance front to back, selecting the best combinations of spring rates, ride heights and sway bar rates. I did a fair amount of track component testing but, nowhere near enough (budget) to feel confident for having the “best” possible setup. (Is there such a thing?) It probably would have been a waste of my money to even purchase those multi adjustable shocks as, witnessing some better financed National or Pro teams, they had spent way more time and money on testing shocks only than my total testing expenses for the whole car. So, I would just ask some experts on shocks to advise me on my selection (reasonably priced) as to their suitability to my spring rates.

Once a basic desired handling was established with the above tools, I simply used tire pressures and the shocks to fine tune that handling to the track conditions.

Having sad that to introduce myself, now I agree with you and other posters here that we've gone too far in advising the original poster. He told us he had adjustable shocks and asked us what to do with it to reduce understeer. Now, we're at the point of suggesting entirely race specific issues such as tire temperatures and multi stage shocks tuning ,which in itself is a small science. In all likeliness these issues are entirely not relevant to the original question but, would make a great educational discussion for racers only.

I also used to race my 1993 R1 FD rather successfully back in 94 and 95. I quit racing street cars on road race tracks when I put it into the barrier in Turn 7 at Sears Point. One could argue that it was because I used a much stiffer than standard rear sway bar for it, for the car did spin on exiting the hairpin under power. Yet, in my tested experience the adjustable rear bar gave me considerably better balance and reduced lap times. It was a matter of a minor mistake in a very neutral handling car when I was unwilling to give up a fraction of a second to back off at the fist signs of a loose rear end, for not wanting to miss what was shaping up to be the fastest lap of the race, over some very respectable competition.

My second, recently purchased FD, a 1993 touring version, also came to me with stock suspension. After replacing the springs with rates of 430-325 F-R, I had, once again, found way too much understeer to my liking. So, I put on a much higher rate rear bar and for the street driving that I intend to do, this is close enough for me. The car is a joy to whip around medium to fast corners. I would love to go back to tubular bars with aluminum arms to save weight and give me more range but, it is not worth the cost for the present use. I will put on a set of Illuminas to give me some adjustability and, hope to find a setting that will keep that car glued to these horribly bumpy CA mountain roads. No more racing in my future, simply pleasure driving.

I am sure, you also recognize that different people select different solutions to make their cars handle well. My suggestions reflect my knowledge and the solutions that appeared to work for me over the years. The great thing (and also the great confusion) with a forum like this, that a poster can receive contradicting advices to his/her questions and just have to walk the line and do the homework with all that info to make the best possible decisions that fit a particular car setup, driving style, budget.. etc. I’ve been there and, I suspect, you have too.

Best Regards

Albert

DamonB

^ Albert I don't doubt at all that you're fast and it sounds like you certainly have more driving and building experience than I do. The problem we all run into however is in using words to describe something animate like driving or setting up a car. When that happens we must be certain that our language is correct or our the facts we present end up being wrong. I have no ill wishes at all toward you.

I'll be the first to agree with you that in amateur racing you don't need money to be fast (or have fun!), but it always helps If the guy with more money still can't drive what he's got then his money won't help him. My car is a consistent underdog against the competition and that always leaves me with a convenient excuse. I hate that. At the same time it's an absolute joy to get behind the wheel of the FD and drive or compete, even if my competitors are beating me. I considered buying a different car to try and prove to myself how I really rate among established top drivers but it came down to me deciding my ego shouldn't be out spending money. If I had a lot more money I'd do it though

Jack

iTrader: (2)

Totally correct...

ShadowX

Dont' forget camber, too. Oh, and corner weights, physical weight distribution...

Rhode_Dog

Mmmmm brain food thread.

Richter12x2

iTrader: (1)

This may not be 100% technically accurate, but this is the way I reconcile the physics of it all in my head. The more flex you have in a setup, the more it will absorb the cornering action.

Like these extreme situations, with no sway bar in the rear, the strut towers and wheels will flex independently depending on the force applied to them, absorbing the tendency of the rear end to come around. The struts will compress individually to the best height to absorb the momentum, and the body will roll (because the outside strut will compress more, and the inside one will actually want to climb). Between the 'damping' force of the struts (or dampers, if you prefer), the springs compressing, and the sidewall compressing and tread of the tire in friction with the road, the car will fight the cornering forces. So relatively speaking, the softer end of the car will hold the road better. If your whole car is too soft, cornering will feel mushy and unresponsive, the car will tend to understeer, and body roll will be very uncomfortable.

Whereas if you took the struts and springs off the rear completely and bolted everything together solidly, connected both struts with a swaybar, and put so much air in the tires that the sidewall wouldn't compress at all, then whenever you corner, the only thing fighting the cornering forces is the tread of the tire on the road. And most likely, if you have enough pressure in there to keep the sidewall from compressing, then your contact patch is only going to be on the center of your tire's tread anyway. Now when you corner, there's almost nothing fighting the cornering action. So now, relatively speaking, the stiffer end will break free of the road first. If your whole car is too hard, you'll turn fast and have no grip, so you'll most likely end up spinning down the track if you ever get going, and initially won't be able to keep the car pointed in the right direction.

Obviously, these are extremes for illustration purposes, and the right answer is somewhere in the middle. FWD cars will inherently understeer because of the nature of the drivetrain, and RWD and Midengine cars will inherently oversteer for the same reason. AWD cars will do either or both depending on the gearing and power/torque relationship between the differentials, and on some cars it's easily tunable, which is great, except it also adds 300-600 lbs depending on the setup.

Ideally you want the back end to break free first, but at a manageable rate so you don't go wildly out of control when it leaves on you. Which means stiffer than the front.

So to decrease understeer/increase oversteer, alter any of the things that affect stiffness, you'll obviously want softer/less in the front and stiffer/more in the back, so - (this assumes the car is otherwise setup correctly)

less tire pressure in the front, more in the back making the sidewall more or less compressible (Carroll Smith had a term for this, like dynamic stiffness or something in Drive to Win)

stiffer springs in the back or softer in the front

more(stiffer) bar in the back, less(softer) bar in the front

more damping on the struts in the back, less in the front

- With that said, experimentation (safely!) is key, because stiffening the rear of your car using tire pressures is going to feel different than stiffening the rear of your using sway bar, which is going to feel different than higher rate springs. Also keep other things in mind, like body roll which is a whole car thing. If the car leans a lot when you go into a turn, you need bigger bars or stiffer springs or both in the front AND back, and THEN adjust the ratios between them for more or less steering.

More maneuverability makes for better times, to the extent you can keep up. Like fighter jets for example. They're set up so dynamically unstable that the computer has to make thousands of tiny corrections every minute to keep it from spinning out of control. The pilot just suggests to the computer which way he wants the plane to go and the computer does it. If you set your car up to be dynamically unstable to that degree, it will turn great, but it won't help if you can't keep up with it.

Also, I second Damon's post about don't mess up the good end of the car trying to fix the bad end. If your body roll is taken care of, and the only problem is that the car pushes when steering, soften the front of the car. If you find then that you've induced body roll again, then solve THAT problem by stiffening the whole car.

I know this is an old thread, but I hope this helps someone!

edmcguirk

You have the "how" right but you have the "why" wrong. Phrases like "The struts will compress individually to the best height to absorb the momentum" and "the car will fight the cornering forces" don't actually mean anything even though they sound good.

I don't think I would say that you are wrong but your descriptions don't describe the phisical world in a way that could be extrapolated into other facets of driving and traction. If you have the basics down correct but you try to extrapolate your reasoning into weight distributions or driving styles you might come up with completely wrong answers.

You sound like you have the intuitive underlying reasoning correct but your descriptions of those reasons are not factually correct. (at least it is better than the other guys who are wrong and their explanations are the opposite of reality)

ed

Richter12x2

iTrader: (1)

That's right, I never actually finished my thought on the part about the struts compressing individually. :P I had intended to move into how the sway bar helps the body stay flatter on cornering by forcing both struts to move together (to a degree) instead of allowing them to operate fully independently. (Where one may compress and the other extend.) :P

But yeah, like I said in my disclaimer, this probably isn't 100% accurate, but it's how I make sense of it in my mind. To be fair, the guy I learned all this from didn't know a damn thing (I'm self taught)

Tune to Win is probably a better source of information than I could ever be, but I haven't made it to that one yet. Although I read Prepare to Win and it wasn't a great deal of help, unless I someday decide to construct my own race car. :P

SCCA RX7 RACER

At what phase of the cornering do you have the under steer problem? Is it entry, middle, exit? Is it on a slow corners or high speed corner what rate of speed are you traveling? What type of car and weight is it? What type of tire compound and pressures do you operate? Is your steering input slow, moderate or fast? I can not see any one providing any information except general bits to try and help. Provide more information then people can help. Also if you can maybe refer to a race track and a particular corner could help.

Run Hard and Race Safe.