tire slippage due to suspension/quaiffe/torque...

[zredbaron]

i'm shifting this discussion to a new thread because it was beginning to hijack an engine build thread. i'm not sure if this belongs in the suspension or drivetrain section, but i picked suspension. drivetrain seemed more mechanical than handling, and my questions deal with handling.

 

this is what i posted after autocrossing this past sunday...

 

update--

i finally purchased some of that vp race gas, and man... it makes more of a difference than i had hoped for. i am getting a dramatically more complete (and faster) burn, and it hasn't even been tuned! not at all! i couldn't lay down the power anywhere, which was frustrating, but yet satisfying at the same time. that is, after all, proof that all of the time and money put into my engine has paid off!

 

here's a video from today's race:

 

(note the watch in high quality link)

 

as you may or may not be able to make out, i'm having a hard time with the power, both in terms of keeping the rear end hooked up and taming the beast. i'm really, really having a hard time being smooth. manual steering is a whole lot more varsity now.

 

question for you racers out there... the pulsing of rpms that you hear when i'm under load in a turn and going over a bump (ie the tires sometimes beginning to break loose and me having to be ginger with it)... to me, i think its the result of perhaps not the stiffest suspension (225# springs over illuminas) combined with my quaiffe hunting for where to put the power.

 

in my case, is the quaiffe doing me more harm than good, or is this just the challenge of having more power than you can use?

 

(if in the case the answer isn't so simple, i'll shift this to a new thread)

 

thanks!

[zredbaron]

If you're spinning the tires and have to back off, then the Quaife is hurting you. To what extent is hard to say. You can tune the suspension around the diff, but it is usually done with stiffer springs all around but stiffer in front, a smaller front bar, and no rear sway bar. I think if you tried to loosen the bar or delete the rear bar with the 225# springs you'll end up with excessive body roll. If you want the more technical version of suspension tuning, search "weight transfer worksheet".

 

There is also the matter of throttle control. There will come a point (sounds like you're there) at which you can't hit the apex and floor the throttle. You'll need to learn how to ease into it.

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[zredbaron]

yeah, i was afraid of that. hopefully johnc will pipe in, too. i still intend to experiment with no rear sway... but that will have to wait till next season.

 

 

 

uh... i couldn't floor it *anywhere.* in the turns, the tires were breaking loose at like 1/2" of pedal (or so it seemed with the adrenaline!). driving my Z now requires a level of finesse i don't yet have. it was all i could do to keep the car neutral in a turn and NOT break the tires loose. keep in mind this video was my best run, so this was the most finesse i was able to muster.

 

it might as well be 600hp or some other obscene number, because i feel like i cant use it.

 

(60 degree temps didnt help the traction dept, either)

 

if it sounds like i'm exaggerating, i don't blame you. that pedal was waaay too touchy today. i have no doubt the dyno will back up my claim.

 

how does that saying go? you reap what you sow... curses! my track times (relative to my competitors) are going down because its now so much more difficult to drive smoothly.

 

and by that i mean its soooo much more fun...

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[zredbaron]

So I looked again and it's hard to tell from your video. Are you spinning the inside tire, or both, or can you tell? If you're spinning the inside tire, then the Quaife is a problem. If you're spinning both, then you just need more tire back there, or some other method of getting more traction out of the tires you have.

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[TheNick]

Sounds like you are unloading the inside rear and spinning the diff. What size rear sway bar? Try unhooking it.

 

 

After watching the video - it could also be that you are bouncing off the bump stops in the front of the car - sounds like you brake and turn in and load up the outside front. Then the problems start happening. Are your shocks adjustable? Trying stiffening them up to limit the bouncing until you can go with stiffer front springs/front bar. What tires are you on?

[zredbaron]

i looked again too, and unfortunately that run didn't have any mistakes in terms of what happens with a touch of too much pedal.

 

if i had to guess, i'd say it was the outer tire that broke loose first, as the car would oversteer. if it were the inner tire, wouldnt it either understeer or be rather unresponsive and/or push?

 

also, my understanding is that the quaiffe biases the power to the outside tire in a turn.

 

that said, the video is what happens if i was being tender with the pedal. if i was being too aggressive, both tires would break loose. this handled a lot more like drifting, whereas the unbalanced tire slippage felt more like on the verge of loosing control.

 

so again, the concern is the pulsing that you hear in the race video. sometimes the pulsing was heard when the tires didnt break loose (or perhaps i didnt feel the slippage?). i interpret this as the suspension oscillating over the road, causing the quaiffe to hunt for the happy power distribution balance.

 

this hunting is what was screwing me, as the torque was surging up and down. if i were pushing grip of the tires, as soon as i hit the slightest bump, the tires would break loose. i understand that this is unavoidable to a certain extent, but i feel like this is happening waayyyy too easily.

 

i intend to experiment with the sway bar next season, but would very much appreciate any input anyone has!

 

thanks!

[zredbaron]

seems we were both posting at the same time.

 

hmm... dont think its the front. not the bump stops, anyway. the car is quite neutral until i'm at apex and post-apex and either have neutral pedal or attempting to accellerate.

 

then i feel like i'm on ice. grip is being completely lost in the rear, and is due to too much damn torque. perhaps i'll try reducing my rear camber?

 

then again, maybe i'm missing what you're saying entirely. if so, please explain! (i watched the video again and not sure i follow what you're referring to...)

 

the suspension isn't that aggressive. tokico illuminas (all 4 corners on stiffest setting) with 225/200# springs. i do have camber plates. 1" front sway and 3/4" rear. tires are kuhmo v710 225/50r16.

 

theres no question i need a bigger footprint, but i refuse to cut my car (i think! sigh...), and my brakes mandate a minimum 16" rim.

[Flexicoker]

You're lifting the inside rear tire, you can combat that by moving the roll stiffness distribution forwards. Less rear bar, and stiffer rear springs. Or more front bar, and softer front springs.

 

The tire hop is a different problem, exacerbated by the inside wheel spinning. The "tire hop frequency" is mainly of function of tire spring rate, car spring rate, and unsprung mass. I think that softer or no rear bar, and stiffer rear springs is your best bet, this should help with both problems. Changing damper settings might help, but its only a bandaid for tire hop. (in my opinion)

 

You do need to tune your suspension to the Quaife. you need to tune your suspension to work with whatever differential you have, and with a Quaife, that means keeping the inside rear tire on the ground.

[tube80z]

question for you racers out there... the pulsing of rpms that you hear when i'm under load in a turn and going over a bump (ie the tires sometimes beginning to break loose and me having to be ginger with it)... to me, i think its the result of perhaps not the stiffest suspension (225# springs over illuminas) combined with my quaiffe hunting for where to put the power.

 

It's sorta hard for me to tell what is causing what in your video. But to me it looks like the front starts hopping, probably ran out of suspension travel, and then your right foot starts tapping along. And as you make more power and have a more responsive engine you pay the penalty.

 

A few things to try that aren't too hard. Put zip ties on the shock shafts and see if they are being pushed into the bumpstops. If they are then I'd fix this before moving too far along

 

Next thing, which may be a little harder. Add a quadrant to you throttle linkage and slow down the lower opening movement. You want to have to move your foot more at the lower openings. This can really be important with a V8 car.

 

And if you can get us some pics of the car in a corner. Preferably a front three-quarter shot so we can see the inside front and rear tires.

 

Cary

[Daeron]

 

Next thing, which may be a little harder. Add a quadrant to you throttle linkage and slow down the lower opening movement. You want to have to move your foot more at the lower openings. This can really be important with a V8 car.

 

 

I was thinking of suggesting this same thing, but I didn't last night because it was in the sticky "max power stroker" thread.

 

since I wanted to subscribe to this thread anyway, I figured I would give this a +1

[zredbaron]

here are the most recent pics i have. none of them are ideal, but it's what i have...

 

looking at this first pic again, i'd have to agree with flexicoker in that i'm dead wrong about spinning the outside tire... this clearly shows the inside tire having minimal contact.

 

after this first pic, i decided to reduce my camber (both front and rear) and raise my ride height about a 1/2" or so:

 

the rest are after these changes.

 

 

 

ok, so if i'm not mistaken my front springs are 25# stiffer than the rear. i can swap those easily enough. i could also reduce the dampening slightly in the rear, and possibly experiment with no sway bar.

 

thats the in the meantime stuff. sounds like i want to invest in new springs and shocks. recommendations? what does the quaife want to see? (4.37 r180)

 

also, i'm considering (for real this time) ditching these tires and rims and going bigger, possibly entering prepared classes and moving away from DOTs. would going to true slicks change my spring/strut selection?

 

as for rear sway bar, would a smaller sway be more ideal than no rear sway at all? i think stock was 1/2". i'm at 3/4".

 

the throttle quadrant sounds very cool. i did a search or two and found a couple explanations, but my lack of experience requires pictures! hah. is there a thread/tutorial here or anywhere else that could steer me in a better direction? thanks!

 

i'll do the zip tie experiment this weekend...

 

thanks guys!

[zredbaron]

oh and as a reference, here is the car at rest. this was taken the day of the video (this past sunday).

 

 

i've heard the stern warnings of over-lowering the car, and i did measure to make sure it wasn't below 5" from the ground and that the arms weren't level or below level (forgive the lack of proper terminology!), but i do wonder if it still isn't too low. i also suspect i might have too much camber in rear.

 

and no, i don't have degrees. i've simply been making adjustments between runs (i liked that, didn't like that). i can hold more speed in sweeping turns because of my rear camber, but i think with power i can't afford that camber leaving the apex and for the rest of the course....

[tube80z]

You're lifting the inside rear tire, you can combat that by moving the roll stiffness distribution forwards. Less rear bar, and stiffer rear springs. Or more front bar, and softer front springs.

 

It may also come from changing RC locations and/or using devices like droop limiters to control the load transfer distribution.

 

The tire hop is a different problem, exacerbated by the inside wheel spinning. The "tire hop frequency" is mainly of function of tire spring rate, car spring rate, and unsprung mass. I think that softer or no rear bar, and stiffer rear springs is your best bet. Changing damper settings might help, but its only a bandaid for tire hop. (in my opinion) this should help with both problems.

 

I'm not saying this isn't the issue but unless you see it in person it is unlikely in my opinion. I've seen a number of cars setup just like this and they don't have this issue unless an insert isn't working.

 

Cary

[johnc]

I watched the video a few times and here are some things I noticed:

 

1. You car seems to have a pitch problem where the front seems to porpoise or bounce. It appears you have too much compression damping in the front shocks or not enough rebound damping and you can hear the front tires chirp under braking as you go over bumps and paint stripes. Or, is the car on its bump stops under braking?

 

2. You're lifting the inside rear wheel and the Quaife is going open for a second. Listen for a whirring sound inside the car which is a very characteristic sound from a Quiafe when it goes open.

 

3. Is the bumping/pitching causing you're right foot to move on the gas pedal?

 

How far do you want to go with the suspension tuning? Here's what I'm thinking:

 

1. Bump the springs rates up all around to 300 front and 250 rear.

2. Upgade to Koni or Bilstien shocks which drop the compression damping and give more rebound control.

3. Run a 1" front ARB and a 5/8" adjustable rear ARB.

4. Don't change wheels and tires, stick with what you have for now.

[johnc]

I watched again and I really think the main problem is a pitch control. The car gets bouncing front to back and I think your foot bounces in sync on the gas pedal.

 

Are you spring rates the same?

What settings are the Tokico's on?

What are your air pressures?

 

The car seems very stiff and bound up. There doesn't seem to be much compliance in the suspension, its not absorbing the bumps and transmitting even small suspension movements into the sprung weight.

[JMortensen]

i've heard the stern warnings of over-lowering the car, and i did measure to make sure it wasn't below 5" from the ground and that the arms weren't level or below level (forgive the lack of proper terminology!), but i do wonder if it still isn't too low. i also suspect i might have too much camber in rear.

Do the zip tie test that cary mentioned and you'll know if you're lowered too far. I think the measurements at the rockers are somewhat suspect because the tire height isn't taken into account. Your tires look pretty tall, so you'd have to lower the car further to get the same 5" at the rocker. Checking at the strut shaft eliminates the confusion.

 

One thing that absolutely amazed me is how much suspension travel Dave Kipperman's Z is using with 5-600 lb springs in it. Cary has posted pics of it leaned pretty far over in corners. Just mind boggling to me. Of course his car has gigantic slicks too so it can generate a lot more lateral g, but still I think it's unrealistic to expect 250 lb springs to control the roll on a well set up Z. I think this same problem is something Cameron (heavy85) is also running into right now.

[tube80z]

looking at this first pic again, i'd have to agree with flexicoker in that i'm dead wrong about spinning the outside tire... this clearly shows the inside tire having minimal contact.

 

It will be good to note how much travel you have before we go too much farther in advice. I would like to point out that in the pic above you're on the brakes and not the gas. So you can't really say for sure how planted the rear is or not.

 

As John mentions above the issue we're all seeing is a pitching of the car. What we don't know is if that's caused from the from the car running out of travel or some other cause. Once you fix that I think you'll find car works much better. The static pics make it look like you're fairly low.

 

Cary

[zredbaron]

as usual, lots of wonderful responses. thanks to all who are participating.

 

How far do you want to go with the suspension tuning?

haha. remember how far i went with my engine? that far. no holds barred. (still wondering about cutting the fenders, if i do it will likely be in the subtle z direction... either that or just let the tires stick out.)

 

i do recall when i was installing my camber plates that the bump stops weren't looking new anymore, but rather that they have been bumped a number of times and perhaps should be replaced before too long. i also had to replace a front strut that was completely shot. don't remember if the worn stop was one side or both, but definitely front. i'll report on that. i dont know how tall bump stops normally are, but these are from msa and were about 1.5-2" if my memory serves. is this about normal or is there another type/brand that i should install?

 

i predict i'll find my zip ties all the way at the top this weekend. if so, how can i determine if the blame is spring rate alone, as opposed to ride height or bump stop design?

 

i pulled out my receipts. the front springs are 225s and the rear are 200. as a refresher, tokico illuminas have settings 1-5, with 5 being stiffest. i used to run with the front at a 4 and 3 rear. after putting in camber plates i switched it to 5 front 4 rear, and a few events ago i switched it to 5 and 5.

 

obviously its not working very well for me...

 

tires are kuhmo v710s, 225/50r16. i find the best traction with pressure at 24.5 front and 23.0 rear.

 

please forgive my lack of complete understanding here, but i'm trying!

 

i found and read this thread:

http://forums.hybridz.org/showthread.php?t=128079

(Near Zero Front Suspension Droop)

 

the light bulb is slowly beginning to turn on, but is still too dim to be useful!

 

cary, you seem to be voicing a lot about drooping, but after reading the whole thread, i never heard any explanation as to what droop was, and google didn't help either. with regard to limiting droop... sounds wonderful, but droop of WHAT!? haha. do you mean compression of a spring because the car is rolling? i get that drooping is bad, but what *part* physically is drooping?

 

The car gets bouncing front to back and I think your foot bounces in sync on the gas pedal.

yes, that's *exactly* whats happening! the surging of the car is causing my foot to move, which is trying to be neutral on the pedal, but instead causing the oscillation to worsen unless i back off immediately. the throttle response of our torquey L6s is wonderful, just a tad frustrating with my current setup.

 

Do the zip tie test that cary mentioned and you'll know if you're lowered too far. I think the measurements at the rockers are somewhat suspect because the tire height isn't taken into account. Your tires look pretty tall, so you'd have to lower the car further to get the same 5" at the rocker. Checking at the strut shaft eliminates the confusion.

 

checking the strut shaft? do you mean the zip tie test or something else? i thought the over-lowering problem was because of control arm geometry, and not bump stops bottoming out. or is it both?

 

thanks again!

 

-mark

[JMortensen]

haha. remember how far i went with my engine? that far. no holds barred. (still wondering about cutting the fenders, if i do it will likely be in the subtle z direction... either that or just let the tires stick out.)

Let go of the idea of half-assing the flares. If you're going to cut up the car you might as well go big. Just my $.02...

 

i dont know how tall bump stops normally are, but these are from msa and were about 1.5-2" if my memory serves. is this about normal or is there another type/brand that i should install?

You can get better materials that are more linear in their spring rate, but you need room for them. I would guess that the ones you got from MSA are the Energy Suspension poly bumpstops. You can cut them down so that they're smaller.

 

i predict i'll find my zip ties all the way at the top this weekend. if so, how can i determine if the blame is spring rate alone, as opposed to ride height or bump stop design?

These issues are all inter-related. Too low = roll center underground = not enough travel. You can section struts to gain travel, but you may still have issues with the RC being low. The RC can be raised by raising the LCA pivots on the front. On the back it's a little tougher to deal with. Terry (blueovalz) lengthened the bottom of the strut housing to raise the rear RC. I've only seen a few people go that far.

 

i pulled out my receipts. the front springs are 225s and the rear are 200. as a refresher, tokico illuminas have settings 1-5, with 5 being stiffest. i used to run with the front at a 4 and 3 rear. after putting in camber plates i switched it to 5 front 4 rear, and a few events ago i switched it to 5 and 5.

I didn't like 5 on the Illuminas. Didn't seem good for anything. I almost always ran on 3 or 4 at autox.

 

cary, you seem to be voicing a lot about drooping, but after reading the whole thread, i never heard any explanation as to what droop was, and google didn't help either. with regard to limiting droop... sounds wonderful, but droop of WHAT!? haha. do you mean compression of a spring because the car is rolling? i get that drooping is bad, but what *part* physically is drooping?

Droop is the same thing as sag, but look at from the opposite end. When have the car on a jack for instance and you set it down on the ground, the suspension sags. The suspension might compress 4 or 5 inches before it stops as the suspension gets to the actual ride height. Droop is another name the same 4 or 5 inches of suspension travel that is used up when the car is at ride height. When you put a jack under the crossmember and lift the front of the car, the amount that the car can lift before the tire leaves the ground is the droop. When the car rolls in a corner, it can lay really far over because there is so much droop. If you limit the droop then the car will roll over until it runs out of droop, and then it stops (or bicycles). The rest of the roll at this point comes from the outer suspension compressing.

[johnc]

As Jon posted above.

 

1. Your shocks are set way too stiff. 3 or 4 max for the springs you have. I would try 3 front and 2 rear to start with.

 

2. Your bump stops are too long. Next time the struts are apart, cut those MSA urethane bumpstops down to 3/4".

 

3. 225/50-16s are tall tires (24.7"). I suggest you raise the ride height of your car 1.25" all around. That 5" ride height discussed in context of good handling S30s relates to the ITS minumum ride height rule and its for cars running 225/50-14 tires which are 22.8" tall.

 

Make changes 1 and 3 before your next event and then report back here. If you can make change 2, all the better.