CSG and RCE tag-team suspension Q&A thread! Ask us anything!

[7thgear]

they spring up every day, i swear

http://www.ft86club.com/forums/showthread.php?t=46660

time to make a catch-all demotivational meme or something

[mike156]

Is droop travel overrated?

For a long time, I had the opinion that a tire in the air meant you were losing grip. My world was rocked though when I was told to think more about what is going on when that tire comes off the ground. The weight cantilevers across the car, thus picking up the front inside tire means it's also trying to lift weight off the rear outside tire.

Obviously mass doesn't disappear so the front outside and rear inside tires have to pick up this weight difference. More weight to the front outside isn't desirable, but keeping weight on the rear inside is going to help the diff out on corner exit. Will lifting the front inside tire potentially help the corner exit under power?

On the other side of this, would lifting the rear inside tire on corner entry help balance out the front by removing weight from the front outside tire?

This only works if the tire physically comes off the ground though so you can turn that corners unsprung weight into sprung weight for the other 3 corners. Ideally, you'd want just enough lift to get it barely of the ground. Tons of droop travel would prevent this from ever happening.

Any thoughts on this?

[MyRx]

Originally Posted by 7thgear

erm..

compensante is the wrong word

LCA's etc (which really just means bushing upgrades) improve response (due to being stiffer) and reduce alignment deflection (again, due to being stiffer)

for argumetns sake, an overgeneralization is that these don't make the car faster, they just make it easier for you to drive at the limit, make your driving experience crisp, and improve predictability


you can't compensate for this with "coilovers", which serve a completly different function.

Thanks. I have bushings sitting on the shelf, perhaps with this improved alignment, they will actually help rather than hinder. And move on from there.

[Racecomp Engineering]

Originally Posted by MyRx

Can higher priced coilovers compensate the lack of other equipment ie LCAs, camber kits, etc? Same coilovers, can they be manipulated to 'dial in' rear differences from OEM configurations? I ask b/c I recently got a 'sit-in-car-alignment' with a forum member's rec settings. Afterwards, car has never felt better - 100% improvement over stock. When I returned to the shop, the findings were reviewed, .5 degree diff in rear cambers were apparent, diff springs height/rest. Suggestions were reviewed. Now I ask, saving $ where I can, high priced COs or bits n pieces to achieve a good balance?

I'm not sure about the question. Are you asking specifically about alignments or in a broader sense?

- Andy

[Dimman]

Originally Posted by mike156

Is droop travel overrated?

For a long time, I had the opinion that a tire in the air meant you were losing grip. My world was rocked though when I was told to think more about what is going on when that tire comes off the ground. The weight cantilevers across the car, thus picking up the front inside tire means it's also trying to lift weight off the rear outside tire.

Obviously mass doesn't disappear so the front outside and rear inside tires have to pick up this weight difference. More weight to the front outside isn't desirable, but keeping weight on the rear inside is going to help the diff out on corner exit. Will lifting the front inside tire potentially help the corner exit under power?

On the other side of this, would lifting the rear inside tire on corner entry help balance out the front by removing weight from the front outside tire?

This only works if the tire physically comes off the ground though so you can turn that corners unsprung weight into sprung weight for the other 3 corners. Ideally, you'd want just enough lift to get it barely of the ground. Tons of droop travel would prevent this from ever happening.

Any thoughts on this?

Can break the Torsen that way.

Another problem is tire grip:load isn't linear, so you may be sacrificing more grip than is necessary.

[MyRx]

Originally Posted by Racecomp Engineering

I'm not sure about the question. Are you asking specifically about alignments or in a broader sense?

- Andy

Lesser priced coilovers VS higher priced ones. The alignment is not an issue, found the knowledgeable shop to do that. The differences they found and what they suggest I may look for, is now the realm. 3 days of spirited drives after and a new set of tires sooner than later, I'm looking at either coilovers or build the grip with arms, camber kits, etc...

[chanwon88]

Can you recommend camber arms? My rear camber is at -3.7 and -2.9 from lowering on ST coilovers. Car is a daily and need less camber so my tires won't die on me so quickly. Shop recommended GT specs, but they are so damn expensive. I'd like to be at something like -1.5 to -2.0 for the rear. Thanks in advance.

[Calum]

Originally Posted by 7thgear

they spring up every day, i swear

http://www.ft86club.com/forums/showthread.php?t=46660

time to make a catch-all demotivational meme or something

http://www.reddit.com/r/Stance/

Enjoy...

[solidONE]

Originally Posted by mike156

Is droop travel overrated?

For a long time, I had the opinion that a tire in the air meant you were losing grip. My world was rocked though when I was told to think more about what is going on when that tire comes off the ground. The weight cantilevers across the car, thus picking up the front inside tire means it's also trying to lift weight off the rear outside tire.

Obviously mass doesn't disappear so the front outside and rear inside tires have to pick up this weight difference. More weight to the front outside isn't desirable, but keeping weight on the rear inside is going to help the diff out on corner exit. Will lifting the front inside tire potentially help the corner exit under power?

On the other side of this, would lifting the rear inside tire on corner entry help balance out the front by removing weight from the front outside tire?

This only works if the tire physically comes off the ground though so you can turn that corners unsprung weight into sprung weight for the other 3 corners. Ideally, you'd want just enough lift to get it barely of the ground. Tons of droop travel would prevent this from ever happening.

Any thoughts on this?

Interesting question. I don't think it's ever a good thing to have a wheel lift in the air, particularly one of the driving wheels. Though having a non-driving wheel lift during cornering I've seen some very hard cornering FWD cars do. Like a dog taking a leak. While lifting a rear inside wheel on a FWD car may help it's front driving wheel gain traction and for the rear end to rotate (a good thing for the most part on a FWD car), this same action rotated 180* on a RWD car may make it push hard into a corner when you don't have both the wheels guiding it's path around a corner (not a good thing).

I'm sure there is a lot more going on than what I described above, such as having the rear wheels slip with throttle to help the RWD car rotate, but that's what I think about that from my limited understanding of the physics going on.

[ZDan]

Originally Posted by mike156

For a long time, I had the opinion that a tire in the air meant you were losing grip. My world was rocked though when I was told to think more about what is going on when that tire comes off the ground. The weight cantilevers across the car, thus picking up the front inside tire means it's also trying to lift weight off the rear outside tire.

No, that's not what happens at all. You're thinking of what happens when you adjust individual ride heights: taking weight off the right front also takes weight off the opposite leftside rear.
That's not what happens when you are cornering hard enough to pick up the inside front tire. At that point you will begin to add load to the outside rear and unload the inside rear at a greater rate, as you've gone from having significant roll stiffness up front to having NO roll stiffness up front. So now ALL your incremental roll stiffness is at the rear.

Obviously mass doesn't disappear so the front outside and rear inside tires have to pick up this weight difference. More weight to the front outside isn't desirable, but keeping weight on the rear inside is going to help the diff out on corner exit. Will lifting the front inside tire potentially help the corner exit under power?

Lifting a wheel is a consequence of having roll stiffness biased to one end of the car, highish center of gravity, high grip, and a combination of cornering and braking (fwd) or cornering and accelerating (rwd).
Ideally, you'd like to keep the load even on all four tires, as this maximizes total grip due to the nonlinear relationship between grip and load (add 75% to the load on a tire and you'll get something less than 75% more grip).

Picking up a tire will cost you overall grip, but it's not like turning off a light switch. Most likely you won't even notice (I never did notice it in the 240Z, and it would always pick up the outside front exiting some corners).

On the other side of this, would lifting the rear inside tire on corner entry help balance out the front by removing weight from the front outside tire?

Again, you have it backwards. Lifting the inside rear will *increase* the rate at which the outside front is loaded and the inside front is unloaded.
Think of it like this: if you use a jack to lift up the left rear corner of the car, what happens to the load at the opposite corner?

This only works if the tire physically comes off the ground though so you can turn that corners unsprung weight into sprung weight for the other 3 corners. Ideally, you'd want just enough lift to get it barely of the ground. Tons of droop travel would prevent this from ever happening.

It can still lift off the ground if there's a sway bar at that end of the car. The sway bar will prevent the outside wheel from drooping much.

But anyway, there's an overall grip disadvantage to lifting tires, but given the nature of some cars the optimal setup might cause this to happen, as other things than "total lateral grip" also have importance, like the ability to put all the power down on corner exit.

But again, lifting a tire isn't even noticeable from the driver's seat. As load on the tire goes down from 100 lb., 50 lb., 0 lb. nothing abrupt happens when it is totally unloaded and begins to come off the ground.

[Dimman]

Has anyone here ever got a hold of a tire's efficiency diagrams? Or know how to generate on experimentally?

[mike156]

Zdan, I would disagree with your assessment on where the weight goes. Your "jack the car up" outlook is flawed in that you are pyhsically lifting weight on the back of the car. Yes, in that case, it's trying to push the opposing corner into the ground. This is dynamics though, not a jack. Gravity is still trying to pull that corner down and inertia is the only thing keeping it up there. Lifting the wheel, you move the sprung mass center of the gravity towards the corner of the car that's in the air which means it is further from the opposing corner.

Either way, it's a theory that works well for lots of chassis out there, including FWD, RWD and AWD. It's likely more biased towards the autoX guys though that take this approach.

[solidONE]

Originally Posted by mike156

Zdan, I would disagree with your assessment on where the weight goes. Your "jack the car up" outlook is flawed in that you are pyhsically lifting weight on the back of the car. Yes, in that case, it's trying to push the opposing corner into the ground. This is dynamics though, not a jack. Gravity is still trying to pull that corner down and inertia is the only thing keeping it up there. Lifting the wheel, you move the sprung mass center of the gravity towards the corner of the car that's in the air which means it is further from the opposing corner.

Either way, it's a theory that works well for lots of chassis out there, including FWD, RWD and AWD. It's likely more biased towards the autoX guys though that take this approach.

This may work for certain types of turns, and only for a very short duration. Kind of like how drifting around a tight hairpin might be the faster way around than maintaining grip on all fours. This will also depend on the available grip you have with your tires.

Say you are running a mix of hardened used tires you got from 'jose's tires' down the street while running massive sway bars that does not allow any independent droop while cornering. You will more likely spin out trying to lift that inside tire while throwing it around a bend.

Also, if you are at a track that favors more long high speed turns and have zero amount of low speed tight turns, aside from being a very boring track, your car that's set up to lift a tire probably will not go as fast as it is capable of while using a different suspension setup. Though you are right about auto-x setups like this. It might work very well.

[ZDan]

Originally Posted by mike156

Zdan, I would disagree with your assessment on where the weight goes.

Well then, you're going to have to think about it some more!

Your "jack the car up" outlook is flawed in that you are pyhsically lifting weight on the back of the car. Yes, in that case, it's trying to push the opposing corner into the ground. This is dynamics though, not a jack.

Just trying to make it easy for you to grok, but it's easy enough to demonstrate (see below).

Gravity is still trying to pull that corner down and inertia is the only thing keeping it up there. Lifting the wheel, you move the sprung mass center of the gravity towards the corner of the car that's in the air which means it is further from the opposing corner.

No center of gravity is "moving", period. And nothing is happening instantaneously when that corner comes off the ground. And cornering harder isn't putting additional load onto the *inside* rear, but rather to the outside rear.
Here's what happens, with a theoretical 50/50 rwd car weighing 3000 lb. (statically 750 lb each wheel), with 2/3 of its roll stiffness up front, 60" track, 20" c.g. height:
1g right cornering
lateral load transfer = 1g*3000*20"/60" = 1000 lb (2/3 front roll stiffness => 667F/333R)
Load distribution
LF 750+667 = 1417, RF = 750-667 = 83
LR 750+333 = 1083, RR 750-333 = 417

front/rear = 1500/1500 (pure cornering, front/rear weight balance doesn't change)
left-right = 2500/500 (purely a function of cornering g's, c.g. height, and track width)

Only 83 lb. load on the inside front. Corner much harder than this and the inside front will begin to lift off, and the load does NOT go to the INside rear.

At 1.125g, load transfer = 1.125*3000*20/60 = 1125 (750/375)
LF = 1500, RF = 0
LR = 1125, RR = 375

front/rear = 1500/1500
left/right = 1625/375

Increase cornering beyond this, and *all* additional load from cornering g's goes to the outside rear as the inside rear continues to unload. Load on the outside front remains at 1500 lb., since we're still in pure cornering, and there's no front roll stiffness with the inside front off the ground. So incremental roll stiffness is all from the rear, the front is limited to 750 lb. of the lateral load transfer.

1.2g load transfer = 1.2*3000*20/60 = 1200 lb. (750/450)
LF = 1500, RF = 0
LR = 1200, LF = 300

front/rear = 1500/1500
left/right = 2700/300

With forces balanced, increasing cornering g's with the inside front in the air adds load to the OUTSIDE rear, it *does not* magically tranfer more load to the inside rear. This is the law...

Either way, it's a theory that works well for lots of chassis out there, including FWD, RWD and AWD. It's likely more biased towards the autoX guys though that take this approach.

It's not a "theory that works", it's simply what happens given enough grip with a "normal" car (highish c.g. and narrowish trackwidth). Corner hard enough, you're going to pick up an inside wheel. Continue to increase cornering g's and you'll eventually pick up the other inside wheel as well (have to find pics of my buddy's Omni GLH-S with both inside wheels off the ground).

If you could lower the c.g. or add track width to keep all four on the ground, overall grip would improve.