setup help...lifting wheel

[ckcadavona]

I went to a local autoX today and I was told I was lifting my rear tires during corner entry. What is the proper way of dealing with lifting my rear wheels. I get a little more oversteer than I'd like and my corner exit is not where I think it should be.

Attempts at helping the issue-
lower rear tire pressure
less rear rebound- 1/2 turn from soft (Koni)
slower entry speeds and different turn in

other options-
increase rear droop-How is this done?
remove rear sway bar (hicas)
change out 210K+ VLSD-Thinking about putting some heavier gear oil in it. Currently running OEM viscosity Mobil 1 gear oil.
more rear rebound-I thought this would not help with oversteer/corner exit.
larger front sway bar-Doesn't seem like it'd help the rear wheels from lifting
stiffer rear spring rates
stiffer front spring rates

44 front psi 37 rear psi (after 3-60sec runs)
450#front 350#rear springs
front struts full stiff/rear struts 1/2 turn from soft (Koni)

My full setup is in my STS blog.

[veilside180sx]

Looking at your blog I would say you have too much camber both front and rear for street tires. (something more like 3 degree's F/ 1.5-2 degree's R and 1/8" toe in rear)

Remove the rear bar to try and keep it a little more composed as well.

[ckcadavona]

Should I run higher spring rates to compensate if I remove the rear sway bar? I'll probably take it off and see how it feels first. You think more rebound would help?

[AceInHole]

Less rebound in back, more in front. Remove the rear bar. If you need to, bump the rear springrate up a bit to balance it all out.

[spool_sample]

You could also try adding helper/tender springs in the rear.

[ckcadavona]

Thanks guys...I'll pull the rear sway bar off and see how it works at this weekends autoX. The course is tighter and slower then last weekends course but we'll see.

[ckcadavona]

I took the bar off and I took a few measurements. From the fender to the center of the hub L16 R16 7/8. From top perch to bottom of strut was 22 3/4 on both sides. I wonder what caused the difference. I measured three times. The car has more body roll now but I'll see how it works this weekend. I might have to start swapping spring rates for every event.

[SoSideways]

Your alignment might have changed when the sway bar isn't there putting pressure on pushing on both sides of the suspension, plus the bushings in the arms/spindles are probably more relaxed now, so you'll get a little bit more variations between the 2 sides.

[Wiisass]

Is your rear spring loose when the car is in the air? If it is, make it not loose. That will help to keep load on the wheel until you get to the point of fully unloading the corner. You need to figure out why the wheel is lifting. I don't think removing the rear sway bar is the answer, especially when it's a HICAS bar, they're stiffer than stock but not that stiff at all. The only reason this would help would be if your springs weren't captive and the load on the outside wheel was lifting the inside wheel due to the sway bar load transfer.

What arms are you running in the back? And is this only happening during braking and cornering or under pure cornering as well?

[ckcadavona]

I assumed it was the sway bar load transfer that was causing the wheel to lift. That is why I removed the rear sway bar. The car feels much better without it with the exception of the rears spring rates feeling a bit too soft. I have no proof or hard evidence of this being the case with the exception of jacking the car up an noticing the wheel that's off the ground not having any droop or the simple fact that the car feels better without the rear hicas sway bar.

I'm running stock arms w/ urethane bushings. From what the corner workers told me it's only happening durnig braking and cornering.

Thanks for the feedback everyone. I managed to get the car to where I want and feel it needs to be over last weekends autoX. The spring rates need to be higher but it'll be okay for now while I learn to drive with consistency and for daily driving.

[AceInHole]

I don't think removing the rear sway bar is the answer, especially when it's a HICAS bar, they're stiffer than stock but not that stiff at all. The only reason this would help would be if your springs weren't captive and the load on the outside wheel was lifting the inside wheel due to the sway bar load transfer.
That's pretty much what's been happening to me, even with a stock rear sway (Whiteline bar up front). Tender springs would help, but only as much as the rear sway will allow them to (which reminds me, I need to order some tender springs before the season starts). The same thing happens on BMW's, which is why a bunch of those guys run without a rear sway (or a massive front bar).

What arms are you running in the back? And is this only happening during braking and cornering or under pure cornering as well?
I was lifting a rear with my car NA at the top of 2nd gear (fast for autox) through some sweepers. I just couldn't plant power with the HLSD, whereas now it's not nearly as much of a problem (even with boost).

Oddly enough, DJ McArdle up in NY would lift a front tire on his S13 with the rear bar removed... although I forgot his springrates (I think he posted them on NICO once). For reference, my setup has 600# fronts and 450# rears.

[racepar1]

What up ace! Nice to run into you here! You know that the whiteline front bar isn't really that stiff either? The largus bar is hollow shich gives it hoop strength, basically it just has waaaaayyyyyyy more surface area than a solid bar which translates to more surface tension which = stiffer. I plan on running the largus front bar with the whiteline rear bar. But I am working on re-locating the LCA mounting points on my spare subframe to pretty much eliminate the anti-squat. I think that that is the primary problem with the rear suspension on 240's (especially s-13's) WAAAAAAYYYYYYY too much anti-squat. As to the OP's question, try disconnecting the rear sway for sure and maybe stiffen up the front roll stiffness a bit. It is possible that the front is rolling too far and lifting the inside rear tire as a result. Your spring rates sound in the ballpark to me, but ace's rates are much higher and I can vouch that he knows what he is talking about.

[Wiisass]

What up ace! Nice to run into you here! You know that the whiteline front bar isn't really that stiff either? The largus bar is hollow shich gives it hoop strength, basically it just has waaaaayyyyyyy more surface area than a solid bar which translates to more surface tension which = stiffer. I plan on running the largus front bar with the whiteline rear bar. But I am working on re-locating the LCA mounting points on my spare subframe to pretty much eliminate the anti-squat. I think that that is the primary problem with the rear suspension on 240's (especially s-13's) WAAAAAAYYYYYYY too much anti-squat. As to the OP's question, try disconnecting the rear sway for sure and maybe stiffen up the front roll stiffness a bit. It is possible that the front is rolling too far and lifting the inside rear tire as a result. Your spring rates sound in the ballpark to me, but ace's rates are much higher and I can vouch that he knows what he is talking about.

Hoop strength? I didn't know sway bars were pressure vessels. A solid bar is always stiffer than a hollow bar of the same material and outer diameter.

Depending on the wall thickness on the Largus bar, it's probably too stiff, I don't know why people running already high spring rates feel the need to run a stiff sway bar. with the stiffer spring rates that people are running the sway bar has more negative effects that positive. It will decrease your roll gradient, but I mean we're talking less than 1.5deg/g with just springs alone.

I don't know, I still don't think this wheel lifting problem is totally rear sway bar related. I think there are other problems that people are overlooking and removing the rear sway makes it a little better, but there's still a deeper problem that is not being addressed. Binding in the suspension, too much rebound damping coupled with no preload or a non-captive spring, etc, something else seems to be happening. Especially with stock sway bars, I've measured them and I'm sure you guys have looked at them, those things couldn't lift the unsprung weight without the loaded wheel being compressed a lot.

And if you do remove the rear sway, increasing front roll stiffness is just going to make the car understeer more.

And this should probably be another thread, but what points are you relocating and why? I know you think you're going to be getting rid of the anti-squat that you have heard is designed into the rear suspension. But if you're just moving the points that you think should be moved, you're probably going to mess something up. I'm not trying to be an asshole, I just don't want you to waste a spare subframe just because you think you know what needs to be changed.

[AceInHole]

My next step is to run some tender springs in back. I'm planning on starting with a 50lb tender, although there seems to be a gap between 150 and 50 lbs according to the lists on some sites.

[racepar1]

I got that information from a guy that has been building racecars for about 40 years and before that he worked inthe aerospace industry, so it is pretty reliable info. I'll send you a PM discussing this though. I will also send you a PM about the mounting points as well. You are right though, for sure there is something else going on. I don't think it is shock related though as shocks are pretty much the smallest adjustments that you can make to the suspension. That's not to say that mis-adjusted shocks won't cause some problems, but I really don't think that they can cause a wheel to lift. To the O.P.: do you have adjustable arms and bearings in the uprights or is it just urethane bushings? If it is just bushings it could be binding the suspension some as the urethane bushings do not articulate very well since they are so stiff. Tender springs might help, but they will not hold as much pressure on the wheel as the rates are MUCH softer so you might still have problems hooking up off the corner. If you can find a way to get the car to squat more it will help keep that wheel down as well, but may start lifting the inside front.

[ckcadavona]

I agree with the assumptions that my rear suspension could be binding. But, I'm stuck with the urethane bushings due the the class I'm in. How would I decide what tender spring rates and lengths to go with? Is there another option to help the rear suspension binding problem that has not been mentioned? Eventually I will experiment with stiffer spring rates and tender springs. Hopefully I can find some used.

After driving the car without the rear sway bar for a few weeks I've noticed that I feel what seems to be the HICAS working. I could be wrong.

[Def]

Hoop strength isn't how you look at the stiffness of a bar loaded in torsion - I hope that guy didn't do structural work in aerospace.

The correct equation is I proportional to Do^4 - Di^4. Di being zero in a solid bar. This is assuming both bars have the same geometry, length, and material properties.

That said, a solid bar is only marginally stiffer than a hollow bar at the expense of MUCH more weight for that slight stiffness increase. The correct way to design a swaybar for a performance car is a hollow bar. Anything else is done for cost cutting reasons.


I guess I should post up some basics on tender springs, as there seems to be some confusion on them here. You don't want to run the tender springs unblocked for our purposes, you merely want them to give you more than the ~1-1.5" of droop travel the average stiff spring rates yield in the rear. When the tender spring is unblocked you get a rate equal to 1/final springrate = 1/primary springrate + 1/tender springrate. Easy rule of thumb is that you'll get a rate slightly below the tender rate when it's unblocked, then after it reaches coilbind you'll get a rate equal to your main spring.


As for wheel lifting, I did a quick test to see the friction on a stock rubber upright bushing out back with a stock arm. It max'd out my force scale at 20 lbs with likely less than 1/8" of movement at the end of the camber arm. Imagine 3 links plus a swaybar generating friction and it's not hard to see how reluctant wheels are to move back there. I think spherical bearings back there with tender springs to get some more travel are worth quite a bit on less than perfect surfaces.

[AceInHole]

My aim for the tender spring is for it to primarily be fully compressed (blocked?) under most driving condiions. It should really only provde a small bit of suspension travel to keep the wheel in contact with the pavement at the limit of travel, and nothing more.

As for the source of the problem, it's mostly a moot matter, as you're limited to what you can do about it in most cases (related to racing and staying within class rules). Removing the rear sway is the easiest method, and tender springs is the next best step (for which you'll actually have to buy things). If there's something else I can do within SCCA Street Mod rules, I'm all for it.

[Def]

Wrap the whole car in carbon fiber. Carbon fiber = fast.

Problem solved.

[Wiisass]

One thing that I think could be contributing to this problem is people setting the height with the mounting points on the arms, both inboard and outboard, tight. Like Def was saying about bushing friction. Stock bushings are not meant to rotate, they're a spring/damper system at every pivot point. So if you have yours tight from putting everything together at some random height, this is where the suspension will want to be statically due to the bushings. So this could be contributing to the problem.

And Def was right on, I hope that aerospace guy wasn't doing anything other than cleaning up. I guess reliable doesn't mean right.

And with the damping coefficients and general stiction and hysteresis present in a lot of dampers, you would be surprised at the amount of force it can take to fully extend a damper. I have noticed that the 8610/11 does take a lot of force to extend from a compressed position to full rebound. This is probably because there is no positive pressure in the shock due to the twin tube design. And then for any asian dampers, I'm just assuming it's a crappy seal/too much rebound/they're junk problem that can not be fixed.

For tender springs and the 8611, I would think about going much stiffer. Something very stiff, but short, so it coilbinds/becomes blocked as soon as the car is put on the ground. It would take some quick calcs, but they shouldn't be too hard to figure out.

PJ, the source should not be a moot matter if people don't even know what the source is. You can't say that something can not be fixed if you don't know what needs to be fixed. It could be something that you can change within whatever rules you are in and would allow you to keep a rear sway bar. Or it could be something that you can better accomodate through some other method. Don't say it doesn't matter if you don't know what it is.

[Def]

I made this up a few months ago real quick for myself, so excuse the somewhat random nature the data is presented. The force vs. travel curves explain a lot though(scale changes on the last one). I didn't take into account motion ratios, this is purely force on the spring.

These were setup around typical Eibach tender spring rates, but if you want to look at the equations you can change things around as needed.


I'm too pissed off at school to give an explanation for those that don't understand it all right now. But post them up and I'll get to them tomorrow if things aren't too cryptic and no one else posts up an answer.

[Wiisass]

Def, looks pretty good. I love seeing nerdy excel stuff.

Now what would make that better would be to incorporate installation ratios and actual car weights and throw in some lateral load transfer stuff and figure out at what lateral acceleration the tender spring becomes un-coilbound to figure out if it's worth it and what it would do.

But I think the most important thing would be getting a definitive answer on what causes this.

Stock S13 rear sway has an endlink rate of about 45lb/in and S13 HICAS rear bar has an endlink rate of about 175lb/in. This is the rate to move one end of the bar with the other end fixed. Both of those rates are pretty soft in comparison to everything else. I don't have any S14 numbers, but I'm assuming rear bar would be pretty close, most stock rear bars are really soft. So if people are running a stock rear bar, I don't see that being the problem.

I don't know, more analysis or testing is required to figure this out. But it would be nice to have an actual answer on why this is happening. I'm still leaning towards bushings being a big issue. Which is something that can be remedied in a variety of ways no matter what setup you're running, stock arms/bushings, aftermarket arms/rod ends, etc.

[veilside180sx]

Out of curiousity, when was the last time you lubed up your ES bushings in the rear?

[Def]

Out of curiousity, when was the last time you lubed up your ES bushings in the rear?

To whom is this directed Sir Richard?

[Def]

Def, looks pretty good. I love seeing nerdy excel stuff.

Now what would make that better would be to incorporate installation ratios and actual car weights and throw in some lateral load transfer stuff and figure out at what lateral acceleration the tender spring becomes un-coilbound to figure out if it's worth it and what it would do.

But I think the most important thing would be getting a definitive answer on what causes this.

Stock S13 rear sway has an endlink rate of about 45lb/in and S13 HICAS rear bar has an endlink rate of about 175lb/in. This is the rate to move one end of the bar with the other end fixed. Both of those rates are pretty soft in comparison to everything else. I don't have any S14 numbers, but I'm assuming rear bar would be pretty close, most stock rear bars are really soft. So if people are running a stock rear bar, I don't see that being the problem.

I don't know, more analysis or testing is required to figure this out. But it would be nice to have an actual answer on why this is happening. I'm still leaning towards bushings being a big issue. Which is something that can be remedied in a variety of ways no matter what setup you're running, stock arms/bushings, aftermarket arms/rod ends, etc.

A bad way of analyzing things, but the stock swaybar "feels" like more rate than that. I think the actual rate is higher once you take into account the bushing friction and hysterisis(quite sure I misspelled that), which means that once the rear suspension isn't rolling, all the bushings are still fighting your suspension from doing its thing.


As for throwing other stuff in the spreadsheet, that would be cool, but beyond just sitting there plugging in some numbers for 30 mins. So by all means, go ahead and embellish upon it. :D

[veilside180sx]

To whom is this directed Sir Richard?

The original poster=)

[AceInHole]

I put some actual thought into it, and I guess the next step would be to adjust roll centers, specifically in terms of front versus rear. Off the top of my head, wouldn't it help to raise the front roll center higher than the rear?

[ckcadavona]

I greased them when I installed them in December. I'm not sure what type of grease was supplied with them. I've been using marine grease on my front upper mounts so that is what's going to be used to regrease them when I get some free time.

[Wiisass]

A bad way of analyzing things, but the stock swaybar "feels" like more rate than that. I think the actual rate is higher once you take into account the bushing friction and hysterisis(quite sure I misspelled that), which means that once the rear suspension isn't rolling, all the bushings are still fighting your suspension from doing its thing.


As for throwing other stuff in the spreadsheet, that would be cool, but beyond just sitting there plugging in some numbers for 30 mins. So by all means, go ahead and embellish upon it. :D

All bars were measured in the stock bushings. Usually just as they were when they came off the car. It will be a little different on the car, but it shouldn't be much. I designed the test rig to as closely approximate them being mounted on the car as possible.

But there can be a lot of hysteresis in those bushing, so if you were to load and unload a bar and show force versus displacement, there would be an offset. How much, I really can't say, but just by design, you know it is there.

[Def]

Interesting. Got any pics of said rig? Sounds like a fun setup.

[racepar1]

I put some actual thought into it, and I guess the next step would be to adjust roll centers, specifically in terms of front versus rear. Off the top of my head, wouldn't it help to raise the front roll center higher than the rear?

I did a little, and I do mean a little, reaserch on this question. Raising the front roll center above the rear will make the car more prone to oversteer. It will tilt the roll axis towards the rear of the car which will cause more weight to be transfered towards the rear. This will make the lifting wheel problem worse. With the roll axis tilted towards the front of the car it makes the car more prone to understeer. Most racecars are set-up like this as it allows the car to be set-up to have slight understeer at high speed and more oversteer at low speed.

[AceInHole]

I did a little, and I do mean a little, reaserch on this question. Raising the front roll center above the rear will make the car more prone to oversteer. It will tilt the roll axis towards the rear of the car which will cause more weight to be transfered towards the rear. This will make the lifting wheel problem worse. With the roll axis tilted towards the front of the car it makes the car more prone to understeer. Most racecars are set-up like this as it allows the car to be set-up to have slight understeer at high speed and more oversteer at low speed.

Wouldn't weight transfered to the rear help plant both rear wheels, thus keeping more weight on the inside rear tire?

[racepar1]

Wouldn't weight transfered to the rear help plant both rear wheels, thus keeping more weight on the inside rear tire?

But there would be more weight transfered to the outside rear tire. Which would most likely result in lifting the inside tire just the same. Most of the extra weight that would be transferred to the rear would end up on the outside tire since you are cornering. This will result in more compression of the suspension on that side. So unless the other tire can droop more it will still be the same thing. It will also have negative impacts on the handling in other ways. I really think he needs to find some way to reduce the binding in the rear suspension and some helper springs to give him more droop would be good.

[ckcadavona]

Would adding thrust, needle, torrington, whatever bearings work in this situation? It probably wouldn't be legal in my class but I'm curious. Does anyone know of a grease that would work better then marine grease?

[racepar1]

You would have to run spherical bearings in all the arms except the RLCA's as they have no articulation, just up and down. But yes that would elininate any bind issues that you are having and the suspension would travel very freely. SPL (splparts.com) sells rear multiling bearings so there is a drop in solution if it is legal in your class. As far as the grease goes I really don't think that anything would make much of a difference there. Just grease them regularly. It may be a good idea to install grease fittings to make it easier to do, then you could do it before every event. You would have to remove all of the arms, remove the metal sleeves from the bushings, and drill a hole (that is the correct size for a grease fitting) through the arm and the bushing. It would be a good idea to chamfer the inside of the hole on the bushing too.

[ckcadavona]

I knew about the sphericals but I was suggesting an alternative.

[racepar1]

Sphericals are the only option for all of the control arms except for the RLCA as far as I know as they need the ability to pivot in every direction.

[Def]

I'm going to be making Z32 rear upright spherical bearings soon(3 pivots and the rear shock mount) - they'll be cheaper than the going solution.


You should never grease a spherical bearing if it's a PTFE(teflon) lined bearing, which I'd assume it would be in an automotive application if it's intended to last any length of time.

[Def]

Sphericals are the only option for all of the control arms except for the RLCA as far as I know as they need the ability to pivot in every direction.

You can put spherical bearings in place of the RLCA stock bushings(2 per side).

[racepar1]

You can put spherical bearings in place of the RLCA stock bushings(2 per side).

I know that. What I was attempting to say was that the RLCA is the only arm on the car that can use any sort of rollerbearing as it is the only arm that moves straight up and down. The other arms travel in arc which makes anything other than a sperical bearing useless. If you finish those upright bearings LMK, I would be VERY interested.

[AceInHole]

But there would be more weight transfered to the outside rear tire. Which would most likely result in lifting the inside tire just the same. Most of the extra weight that would be transferred to the rear would end up on the outside tire since you are cornering. This will result in more compression of the suspension on that side. So unless the other tire can droop more it will still be the same thing. It will also have negative impacts on the handling in other ways. I really think he needs to find some way to reduce the binding in the rear suspension and some helper springs to give him more droop would be good.

Ah, I read it differently as an overall load transfer to the rear, not increased transfer at the rear. Even then, the way I imagine it is the car generally balances itself across a diagonal (outside front to inside rear, or inside front to outside rear) and basically "see-saws" across it. If you're transferring the majority of the load to the outside rear, the car must be balanced across the inside rear and outside front, lifting the front tire. At least, that's what seems to happen with the BMW's (E36s generally lift the front tire before 2-wheeling, at which point you're either killing your clutch diff or spinning a tire).

[AceInHole]

You should never grease a spherical bearing if it's a PTFE(teflon) lined bearing, which I'd assume it would be in an automotive application if it's intended to last any length of time.

I followed that rule for a while, but always wondered why OEM ball-joints used grease. In a sealed bearing, it shouldn't be a bad thing.

[Def]

I don't thing OEM balljoints have PTFE liners, I think it's a metal ball on a metal race, which will necessitate grease.

Spherical bearings aren't sealed, so even if you put a boot/seals over them you'll still get a little dirt finding its way in. You put grease on the ball and the grit just builds up in the liner, making friction skyrocket, and destroying both the liner and ball. PTFE liners also need some play to work by design, so the clearances are not "close to zero" which makes the contaimination problem worse.

[racepar1]

Ah, I read it differently as an overall load transfer to the rear, not increased transfer at the rear. Even then, the way I imagine it is the car generally balances itself across a diagonal (outside front to inside rear, or inside front to outside rear) and basically "see-saws" across it. If you're transferring the majority of the load to the outside rear, the car must be balanced across the inside rear and outside front, lifting the front tire. At least, that's what seems to happen with the BMW's (E36s generally lift the front tire before 2-wheeling, at which point you're either killing your clutch diff or spinning a tire).

You read it correctly as I understand it. There will be more overall load transfer to the rear, but unless you change the load transfer across the rear as well then you will end up with the same thing. Actually with a lower roll center it will most likely roll even more than it originally did which will once again lift the tire, probably more. This is all really just theory untill someone puts it to the test, but that is the way I understand it.

[a_ahmed]

I was on youtube and came upon this:

http://www.youtube.com/watch?v=UeVNZyCjqrw

kind of had to post this in the lifting wheel thread to scare some newb people :P