Rear Roll Resistance Never Needed

[Ed Womer]

Like someone mentioned you absolutely must align the car with you in it or a simular amount of weight in the car and possibly in the same distribution. Since I do all of the work on my car I have 20lb peices of lead I position in the car to do the alignment.

As for understeer, oversteer you should be able to change from one to another just by adjusting the toe at the front and rear. With my standard alignment my car will have some oversteer which I prefer but if it is more than I want I just toe in the rear in small amounts until it is more comfortable. Now as Brian H says add more front camber it should help with the understeer but it is basically a lot of work. With the standard 1 1/2 deg offset bushings and using one shim on 1 side and 7 on the other, 1 inside on top and outside on bottom I have 2 + deg on the right and 2 on the left. The other thing with the front is you absolutely must have it move freely with no binding, many new vee people will have this problem.

At the runoffs this year I started to have what seemed like snap oversteer after turn in which wasn't normal and I had replaced my limiter rubber bushing since the old one was getting hard and starting to tear before I left and the new one was pretty soft and it finally jumped over the washer that it rode against. So my crew guy got some large fender washers and I put them on the outside of the rubber and that stopped it from trying to get over the stops and the handling became perfect by just doing that. So it must of been going too positive and allowing the rear to lose to much grip.

So playing with alignment is something you should do until the car feels OK to you and then you can make adjustments to it to change the feel.

Ed

[jpetillo]

Brian, sorry, I want to get back to this instead of my harried answers from last night before dinner - low sugar.

So, if we restrict our discussion to weight transfer only.... springs and sway bars have no effect on weight transfer ONCE we reach a steady state, mid turn condition?

No. Agreeing that in the front the springs hold the car up and affect its roll and roll bars only affect roll, let's only consider the part of the spring's job that affects roll. In mid corner, both the springs and roll bar limit the amount of roll. Limiting that roll causes weight transfer. Since we only allow roll to go a few degrees, CG isn't affected significantly, so the static (mid-turn) weight transfer is not affected much by different springs & bars.

Now to model the dynamic part of this weight transfer situation, getting to and leaving the middle of the turn.

I'm going use the mental example of the weight transfer being represented by a liquid filling two fixed volume containers, one at the front and one at the rear. As the car enters the turn, liquid flows into these containers at different rates based on the spring, sway bar and shock(?) combination. No matter what the combination the containers always end up filling front and rear fluid container to their same limits. Can one container fill-up before the other? Or if they must finish up at the same time, if one end starts slow it must end faster relative to the other.
Brian

Yes, No. I have to think about this more to see if this makes sense to use only as an analogy or as a model. Either way, like damper / spring combinations, a soft spring will allow more movement, and a strong damper will change the rate of that movement. A specific spring rate and damping rate combination will determine the settling time, the spring will determine how much it moves. So, one container can fill before the other (settling time). That's the way I look at it - interesting concept. John

[hardingfv32-1]

John

The reason I need this liquid model is that I can not visualize the relationship of springs, bars and shocks controlling roll over TIME and the fact that weight transfer is controlled by CORNERING FORCE. There is not time variable in the weight transfer formula.

Brian

[hardingfv32-1]

Ed

I completely agree with you that front camber is a hassle to change, but if more people thought it was the correct way to tune a FV them maybe there would be more than one choice of offset angle for the bushings competitors use. I also use toe changes for a rapid tuning change between sessions, but if you assume there is an optimum toe setting for minimal drag then the toe needs to be restored at some point and the camber modified the get the net effect you are after.

In the case of your drop issue, I am going to state it is a classic FV example of the droop setting not having ANY effect at all until it gets to a point where it prevents the rear suspension from jacking to the optimum camber level. Why do we need it if it can only do harm? Is the FV community afraid that the car will jack too much under NORMAL cornering conditions? How is that possible if too little camber is just as bad too much? If the cornering force is lower as we go back down the camber curve, what force is going to continue raising the rear of the car?

Brian

[Mystique Racing]

In general there is no better handling car than mine (not saying the best) west of the Rockies. I do not have a droop limiter. The shock is used to keep the camber from going to positive camber as a safety precaution. If you want, you can say the droop is set at 0 deg. I use a normal rocker type zero roll rear suspension.

OK, where is this self proclaimed "best handling car " You cant be serious...... BTW, you are saying it is the best.

When was the last time you won a regional in SF region? I'm not counting nationals that have 2 cars racing in your class.

Please bring out the best handling car next year so we can see how it does against all of us slackers. Sears Point or Laguna would be best.

[hardingfv32-1]

The context of my statement is not boasting. I was careful to state that it was not the best. We had the pole at the last NP Nat of 2010 at PIR in July. This was the first race weekend for a completely new car.

The point of the statement is that we have a very fast car that does NOT use droop control. For all of you droop lovers out there, your challenge is how to explain how that is possible.

Give it your best shot!

Scott, if you want to provide a set of new spec tires for me I will be happy to come, otherwise you won't being see us anytime soon.

Brian

[Mystique Racing]

I do not have a droop limiter. The shock is used to keep the camber from going to positive camber as a safety precaution. If you want, you can say the droop is set at 0 deg. I use a normal rocker type zero roll rear suspension.

Oh, one other thing. Using the shock to stop the travel of the suspension is a droop limiter.

[hardingfv32-1]

So you are implying that since it is set at 0 deg, that I get maximum cornering performance from my rear suspension at 0 deg total rear camber while jacked up against the droop limiter? After all we did set pole with this setup, so it must be doing something right.

Brian

[Mystique Racing]

I am not implying anything other then using the shock to limit the travel of the suspension is a droop limiter. That is no different then 100 percent of the other FV's out there. Use the shock, or use a cable, or use a rod to limit the travel, its all the same to me.

No one ever said that you are not a smart guy with a lot of creative ideas, but put it on the pole at the run offs and I will be impressed. Then you can truly call it the "best handling car" east and west of the Rockies.

[hardingfv32-1]

"No one ever said that you are not a smart guy with a lot of creative ideas"

As a smart guy I say there is no reason for droop control other than the safety of never letting the rear camber go positive. Droop control has NO cornering performance benefits!

Prove a statement otherwise. I can learn something if proven wrong.

Brian

[Mystique Racing]

The only thing that I will say is that droop at the rear, with a zero roll suspension, is completely different then droop at the front.

I happen to use it in both locations and feel it is advantageous. Of course I also run a sway bar in the rear for roll resistance. Which I know you say is "never" needed.

Never is a strong word. Your results may be different.

[hardingfv32-1]

You really strained the brain to get that statement out.

You have no idea what you are trying to accomplish with your rear droop setting?

Brian

[Mystique Racing]

No, I just happen to have my own theory's that I don't really want to share with everyone.

I have already been told that I don't know what I am doing because I run a rear sway bar.

I'm just a regular guy...... not really smart like you.

[CitationFV21]

..........................................

As a smart guy I say there is no reason for droop control other than the safety of never letting the rear camber go positive. Droop control has NO cornering performance benefits!

Prove a statement otherwise. I can learn something if proven wrong.

Brian

Brian,

As a general statement, I would agree with you. I had a local photographer take pictures of the rear of my car in the middle of a turn, and looking at the camber I am no where near the droop stop. However; I would never race without one as one trip off the track, or contact with another car could put the car in a position of disaster.

Now as I stated in a previous post, I don't like to be near the stop if I can help it. The times I set the droop wrong the car was almost undriveable with oversteer. So the questions is, if you could use a controlled stop (tapered bumpstop, spring, etc) you might be able to use this to balance the car. My feeling is it is not worth it as the cause would probably be from reducing the load on the inside tire, and again "I hate to decrease one end to balance the other."

ChrisZ

[hardingfv32-1]

Yes, you are correct. Although this has nothing to do with weight transfer. It is about the camber curve. In your example you are setting the droop to prevent the rear suspension from reaching optimum mid turn camber, but why degrade the rear while we can ALWAYS improve the front instead. Which gets us back to the original premise of this thread.

Brian

[jpetillo]

John
The reason I need this liquid model is that I can not visualize the relationship of springs, bars and shocks controlling roll over TIME and the fact that weight transfer is controlled by CORNERING FORCE. There is not time variable in the weight transfer formula.
Brian

Yes, there is no time variable in the weight transfer formula. That is an indication of how limited in utility the weight formula is. It's not clear we spend any significant amount of time operating in regimes where the weight formula applies. However, characterizing what happens between turn in and mid corner is very difficult. If we want to come up with something that may be helpful, we need to keep the question/problem simple or else it's too hard to do. Even if the model is valid for some very limited set of circumstances, it would still be useful to help figure out what to try on the car. Perhaps the liquid model can help visualize it. John

[cendiv37]

Having run a potentiometer on my rear shock for the last few years, I can state with some confidence that MY car corners ON the droop limiter in every corner at RA except turn 5. In every other corner, the shock (my droop limiter) is at full extension by about mid-corner in all other corners. I happen to set my shock/droop limiter at about 2 degrees total negative. I suspect I should try to run with a lower droop setting and I plan to do so.

Since my static setting is more than the droop limiter, something is "lifting" the rear of the car at mid-corner even though I'm at full throttle (which would seem to make it squat, not lift). Seems like pretty good evidence of swing axle jacking to me...

I know of a number of Vee drivers with conventional external droop limiters (not using the shock as the droop limiter) that set their conventional droop limiters at about zero degrees total. Mr. Harding appears to also prefer to set his droop limiter/shock to zero degrees total camber.

In thinking about droop limiter settings, consider any overtravel beyond your droop limiter "setting" that could be caused by a soft limiter cushion. A shock is a pretty hard limit stop so there is little overtravel beyond the setting made in a static condition. Not so with a soft cushion.

If I ran 0 degrees droop would I still corner "on the limiter"? I don't have any data to say yes or no. But I will speculate that I would still be on the limiter by mid corner more often than not.

Here's a challenge Brian. If you believe so strongly that you don't need a rear droop limiter, set up your car with the shock length adjusted to allow about 10 degrees of total positive camber, add NO other method of droop limiter, take it for a spin and report back with your results.

Bruce

PS: Think about the effect of roll center height on weight transfer, and the cause and consequences of jacking on a swing axle suspension.
For more background you could also read "Unsafe at any speed".

[smsazzy]

I agree with Bruce. EVERY person i have spoken with that runs a shock potentiometer has told me the same thing. Nearly every turn results in droop limiter engagement. I have not personally run one, but I plan to with the next car.

[tiagosantos]

so how do you adjust (or check what it's set to, even..) the droop limiter? Is jacking up (with an actual jack!) the frame and measuring the resulting camber the correct way?

[problemchild]

I agree with Bruce and Scott and Stephen. The droop limiter is doing the work in the corners.

Using the internal droop limiting properties of the shock is not running without a droop limiter. Of course, for those not aware, Harding is not trying to help anybody but trying to "mess with everybody". Rather than running with a zero droop setting, if he put on a limiter at 3-4 degrees Neg .... and cranked in some rear rebound ..... his car would push like a pig that no amount of cheater cockpit-adjustable front camber adjustment will tune out. By running with a zero-rear droop setting he is already subtracting from rear grip to balance the car ..... which I am sure he is well aware of.

For those that believe FVs are naturally balanced and need more rear grip .... no rear roll resistance would be required.

For those that struggle to reduce understeer in their FV and believe their front grip is already optimized, rear roll resistance is one of many tools that can be used for tuning and improving overall cornering ability.

Tiago. Jack it up under the tranny. When the wheels come off the ground, measure the camber. That is you droop setting .... usually referred to as a total of both sides.

[smsazzy]

so how do you adjust (or check what it's set to, even..) the droop limiter? Is jacking up (with an actual jack!) the frame and measuring the resulting camber the correct way?

Correct. Jack the back up so the rear wheel are off the ground. TYhen check the camber.

1.5 degrees is a good starting point for most cars. Check with your car builder for a starting point specific to your car.

[CitationFV21]

A picture is worth a 1000 words.

What do you think:

http://pages.cthome.net/czracing/FV/ChrisLR1.jpg

http://pages.cthome.net/czracing/FV/ChrisNH1.jpg

ChrisZ

[problemchild]

Looks like the rear is jacked up. Certainly not squatting.

Sorry .... only 9 words but not understanding your point Chris. If you put a sensor on the rear, the rear is cycling constantly but spends virtually all its time closer to the droop setting than the static camber setting. The exception is the exit of slow corners where the dreaded low-speed power-on push appears. I doubt this ever happens at Lime Rock. The exits of the Carousel and Keyhole at M-O are classic examples. The last corner at Nelson Ledges would be another.

[CitationFV21]

Looks like the rear is jacked up. Certainly not squatting...

I wish I had some data on the car. In the LR picture the fronts are certainly cornering as the roll over in the front tire shows. You can see the steering input as my hand is at 12 o'clock. And the camber on the outside tire is definitely negative.

From the rear shot there is jacking but also roll. Could it be that a lot of roll offsets some of the camber change? I think there is a lot going on than the traditional swing axle jacking.

PS: Think about the effect of roll center height on weight transfer, and the cause and consequences of jacking on a swing axle suspension.
For more background you could also read "Unsafe at any speed".

Thinking about it there is a difference between the Corvair and the VW. The Corvair (and Triumph Spitfire) had external universals. The VW has internal pivot points. Not a big difference but in this case VW (Dr Porsche) might have gotten it right - size does matter. And come to think about it, I have owned Corvairs, a Triumph Herald and now a FV - I must really like these cars......

ChrisZ

[problemchild]

Chris,
Remember that if the back end is jacking and chassis rolling, there are camber curves involved and the wheels will have different camber values than the droop setting. The inner end of the outside axle tube is dropping relative to the center of the diff and may give a different camber value than you are expecting.