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

[260DET]

A couple of quotes from those who know a lot more than I on the subject of big front/no rear ARB's.

 

'My own opinion is that on most road courses a rear anti-roll bar is a bad thing. Anti-roll bars transfer lateral load from the unladen tyre to the laden tyre - exactly what we don't want at the rear. I would much rather use enough spring to support the rear of the car.' Carrol Smith

 

'The hidden power of the (stiff front) ARB is wedge at corner exit.' Paul Haney

 

All I'll add to that is that the fastest S30's I know of do not use a rear ARB and that the basic problem with the S30 is turn in, or lack of it, which often is bandaided by using a rear ARB.

[G-rib-73-240z]

if you want better tires you could try these, i "hear" they are bery nice when warm to the touch, and stick well. but ive never used them because i havent had a need yet haha.

 

http://www.discounttiredirect.com/direct/findTireDetail.do?pc=28793&counter=1&ar=50&rd=16&sw=false&cs=225

 

i hope you fix your problem i think its the tire hopping problem to me.

[zredbaron]

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...

 

when you're right, you're right. cutting the car is currently about as uncomfortable as getting married.

 

reality: each passing week i get closer to the idea of truly cutting the car. and i get closer to getting married.

 

to the car. haha. [still selling carbon fiber body parts, jon? lol.]

 

in all seriousness, thanks for taking the time to lift the fog for me on all points, john. i'll definitely raise the car and soften the struts and report my results here. if there are enough runs, i'd like to experiment with no ARB, too. i do have an event this weekend, but the navy might have other plans for me. here's hoping...

 

speaking of ARB experimentation, is there any problem with simply disconnecting one end of it to simulate no rear bar at all? this would have that effect, right?

 

thanks again to all!

[heavy85]

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.

 

Well I dont have the gigantic slicks but I do run the softest compound 9.5" wide slicks. I'm running 225/250 with a little bigger front bar but similar rear. I do not have any hopping issues like in the video. My biggest limiting factor is my driving ability not the car. I'm convinced you can be damn fast ... at least locally ... with this set-up. Of course I also have chassis stiffeners welded in, 'bumpsteer' spacers, cut bumps stops, relocated LCA, it's gutted so fairly light weight, sectioned struts, clutch LSD, etc so in reality I'm similar but possibly quite a bit away in detail from your set-up. It seems your problem is the mid corner bounce and the corner exit traction is just a result. My speculation is your bouncing off the bump stops. If you go with slicks they suck when it's cold and your better off with R-compound. They are nice when it's hot though. Other thing is I've had really bad tire wear with the radial slicks but very good luck with the bias plies. I think I need more spring to make the radials live but since I drive my to and front the track I can't really go where I probably need to so I'm going back to bias plies if I can still get them. I've got 5.7 liters worth of V8 power so I have to ginger the throttle or it pitches sideways. That's just something you need to learn to manage. With this set-up my only real issue other than traction is mid corner push which I think I need more front spring to help because I think I'm loosing too much camber in bump. Next year I'm going to try upping the front to 300 lb. Hope this rambling helped.

 

Cameron

[JMortensen]

speaking of ARB experimentation, is there any problem with simply disconnecting one end of it to simulate no rear bar at all? this would have that effect, right?

Yes, that should work.

 

Cameron, I think even with the 9.5 inch slicks you're going to have a hard time controlling roll. Roll = less camber with independent suspension. I don't think you'll be able to get enough camber in there to compensate.

 

I agree that he's probably bouncing on the bumpstops. I think if he cuts the bumpstops and raises the car a bit he's still going to be on the bumpstops when the car rolls with that spring rate and losing camber due to roll to boot, that was my point. It may not be as obvious because it may not be slamming the bump stops, but it might cause a mid corner push.

[johnc]

It may not be as obvious because it may not be slamming the bump stops, but it might cause a mid corner push.

 

That would be a good thing because now Mark's got the suspension to actually do some suspending! He's back in the ballpark.

[rxsleeper]

Hi Mark,

 

I can't offer much to help you out since I have only Autox'd the Z one time.

 

I am curious though on your tire pressures. Most of the guys that I autox'd with (in theRX8) and I found that the Kuhmo's like much higher pressures than what you listed. Just something else to think about. I will go back and look at my set up notes but 37 psi sticks in my mind for some reason.

 

Next autox look for the Yellow RX8, walk up to Pat and tell him, "look ahead, look ahead, look ahead!" and tell him that is from some old guy in Alabama.

[Dtsnlvrs]

I agree with JC, you are too stiff. The nose is bouncing under braking. I Auto-x on street tires and 150f / 175r springs....nice and soft..but then again, when I show up at an auto-x, i lower my tire pressures too...It is all about keeping it plyable.

[zredbaron]

hey guys. sorry for the delays... hard to stay up on things here in the middle east...

 

i never did have another race before i deployed (the event was cancelled), but i *did* raise the ride height and soften the springs to 3 in the front and 2 in the rear. i think.

 

the car handled wonderfully in comparison. you guys were right; the struts weren't allowing my suspension to do any 'suspending'...

 

even though the car handled light years better, i think i'll be taking the advice to jump up the spring rates and get rid of the illuminas and move to a more proper strut for a purpose built car. i'll be back in the states this summer and intend to experiment with unbolting the rear ARB, too...

 

again, thanks so much for the responses!

[gnosez]

I didn't see any mention whatsoever of your Z ever being corner balanced, aligned or the many changes you've made recorded so that you know where you started and what effect each change makes,

 

Having a 240 with a 3.2L and running it at just under 6 inches at the rockers I have had no issues similar to the ones you are experiencing. Looking at your Z and what I see is too tall tires and a too low Z.

 

My set-up includes 8-inch GC 275lb springs, Tokico HTSs (mid point setting), cut struts, 3/4-inch poly bump stops, 2.25 neg camber front and 2 rear. I run a 25mm front sway bar and no rear bar. Street tires are 245/45/16 and track are 225/50/15.

 

The 250rwhp go through my Quaife (3:90) and I have run the car hard on the street, AX and track events.

[drmiller100]

front shocks being too stiff makes sense to me.

 

You might (should???) read about late apex.

Then you should work on getting close to the inside cones.

Between these two issues, by definition you will be late coming off corners.

 

If it were mine, I would put stiffer springs on the front of the car. Stiffer springs will do a lot of interesting things. It will reduce body roll. It will let you power out of corners a LOT better. It will plant the inside rear corner. It will speed up your turn in.

 

I also can't tell how good your brakes are. If you late apex, you will focus more on braking straight.

 

just thoughts.....

[260DET]

This post may be a bit off topic but looking at the video again I was struck by: how fast you want steering response and turn in, how directional change is virtually constant, how smooth the pavement is and how power down is so crucial and how its all happening at a relatively low speed.

 

So: heavy springs carefully matched with quality dampers; no rear ARB, front ARB only; wide, soft tyres on suitable rim width wheels; power steering; modest camber angles; Ackermann steering; ATB diff.

 

For that sort of work you want a stiff car flat on the deck which will slide rather than roll. Flat on the deck to get instant steering response and full face tyre contact with the pavement. So it won't slide either.

[Dtsnlvrs]

Not to re-hash an old thread, but are there any updates on this issue?

[zredbaron]

hey, fancy meeting you here, russell!

 

yeah, the update is that my koni struts and stiffer springs have been in my garage since last summer, still waiting to be installed.

 

[car has been in the body shop for over 7 months now being repainted...]

 

but thanks for the reminder that i still need to follow up on this thread once i'm finally able to.

[zredbaron]

18 months later, i can finally report back! autox video at the bottom.

 

suspension upgrades:

koni yellow race struts installed

new springs - 300 fr / 250 rear

 

weight reduction (+ associated weight savings estimate):

braille battery (20 lbs)

carbon fiber hood / hatch / lexan (80-85 lbs)

removal of stereo, speakers, amp (33 lbs)

removal of carpets, floor mats, etc (20 lbs)

 

setup changes:

removed oem rear brake proportioning valve (the T fitting with the restrictor)

used brake booster that works so far (prev one was shot)

removed rear sway bar (5 lbs?)

ride height raised (not sure by how much, 1" or so?)

corner balanced (50.0% corner balance, 50.9% front)

front camber (maxed)

rear camber (about 2/3 in)

recommended koni settings as per johnc

 

total weight, with ~7 gals fuel and 160 lb driver: 2380

 

(i regret having the car balanced with 7 gals of fuel now, but oh well.)

 

 

my report: the car drives like a dream in comparison. granted, i have no experience to draw from other than my previous setup and other racer's cars that i've driven.

 

my first event after two seasons was the SCCA NE Divisional Championship. my dumb ass entered the car into XP and was thoroughly beaten. (haha!)

 

i knew that going into it, so it's all good. the race was at FedEx field in washington dc. the lot was much worse than i remember that club using. the lot was slanted, gravel-infested, had two different types of asphault, had a trickle of algae / water going down one corner of the course, and to top it all off had had long grooves where presumably electrical wires were run underground and patched poorly. inverted speed bump, basically.

 

as crappy and frustrating as the course was, it was for the best. it let me throw my new suspension setup through the whole gamut, not just a solid course design but fun challenges like negative camber offset cones in a slalom right after driving through a wet patch. oh, and the negative speed bumps just before the apex of a slanted sweeper was fun, too.

 

the conditions were, however, great for helping me shake some rust off of my driving. i was definitely over-driving the car at first, but i smoothed out a little as the seat time started to add up. each run had about 20 mins between runs, so the tires were always cold until halfway through the run. i was first heat, it was cool out, and my kumhos just wouldn't warm up. hoosiers didn't seem to have a problem. oh, well. made me a more careful driver though, which is what i needed. same problem the next day, but it was probably 20 degrees warmer so it wasn't as drastic an impact.

 

tires aside, the car was perfectly balanced and 100% predictable. it was compliant to the bumpy course and surprisingly responsive. really the only harsh critique i would have for the car is contact patch. 225mm tires are just too small for the performance capability of the rest of the car. i think i can get away with 245 or 255 A6s. they have a slightly smaller profile, and in my repaint project i cut the fenders out slightly.

 

luckily, the driver still sucks, so there's lots of free time to gain out there in the meantime!

 

tuning between runs was limited to tire pressures and camber angles. i have the front camber maxed out, producing about a 7 degree F spread from inside to outside of the tires. i was able to get the rears pretty much even. (using a probe type tire pyrometer). i kept tire pressures around 22.5 psi rear and 24 psi front where i've learned like them.

 

here are my findings with removing the rear sway bar:

removing the rear bar with the quaiffe atb is INCREDIBLY beneficial to putting power down in a turn. not beneficial to a medium hp car, but if you're making power, this definitely lets you put it down well before the apex. hell, it helped me turn harder. basically as soon as you've changed the direction of the car you can put the power back down. i'm still getting used to it, as you have to be even farther ahead of the course with your throttle inputs. the problem is turn in. it feels like it slaloms half as well as it used too. i think going down to an oem thickness rear bar (the one i removed was the 3/4" MSA bar) and having it adjustable (probably to tune it down, even) would be ideal. i don't feel like i need/want much, but a touch might really help turn in.

 

perhaps toe adjustment or spring rates would help, too. opinions wanted!

 

i *feel* as though by the end of the event i have a decent grasp of my car's new performance envelope. studying my race video revealed a ton of time left out on the track.

 

seat time, seat time, autox school, seat time.

 

anywho, here's the video i spent way too much time playing with my mac to create:

 

 

if you're paying close attention, you can catch the spots where the car's acceleration gets to make up for the driver's poor line through a given turn. i may not have been competitive as much of the grid, but probably had just as much if not more fun on course than any of them!

[JMortensen]

Sounds like you made some nice improvements in the handling dept. I would suggest that when you go to a bigger tire you might need to up the spring rate again because the increased traction will generate more lean, nose dive under braking, etc. As an alternative to putting a rear bar back on, you could go stiffer springs and smaller front bar to balance the car without gaining a whole lot of roll. Front toe out would help turn in, maybe try 1/8 or 1/4" total and see if that is of any benefit. If you're driving to the event that's going to rip up tires, so what I used to do was have a mark on the left tie rod for street and one for race, and then I'd just adjust that one side. Makes the steering very slightly off center, but you don't have to adjust both sides that way.

 

Any instructors ever talked to you about shuffle steering? Takes some getting used to, but it's a good idea to (almost) never to have your hands cross on the wheel like that. Also that steering wheel looks huge; what is that, a 15" wheel? I'd swap it out for a 13 if it were my car, and get something grippier than wood. I tried a 14" wheel and my hands kept hitting the door panels, not sure if you have that problem or not but it drove me crazy.

 

Your car looks faster than my car ever was, and sounds great when it's not backfiring.

Edited June 5, 2010 by JMortensen

[johnc]

Looks orders of magnitude better then before. You are getting a lot of push so here are a couple suggestions:

 

1. Brake a little earlier and don't pop off the brake pedal. Ease off the brake pedal as you're turning in.

2. Slower hands on corner entry, don't throw in steering and overload the front tires.

3. Shorten your steering arms.

4. Increase front rebound by 1/2 turn.

[260DET]

Without contradicting John's #2 point above, I've found that with weight transfer to the front still happening it is possible to initially flick the steering quickly to get the front of the car to turn in. Timing is everything with such a move, its a quick flick to get the response before lateral weight transfer kicks in to make things difficult. Its best used for relatively slow speed corners, I would not use it in a high speed corner.

[zredbaron]

great replies, as usual guys. thank you! i'm quite proud of the progress we've made. i say we because well, i took your collective advice and you were right on all counts.

 

john, i continue to admire your succinct, step by step recipes for success.

 

jon, i'm having a hard time distinguishing between the difference between reducing front sway bar vs. increasing [adding] rear sway bar. would the former necessitate an increase in spring rate to equate to the latter? which is more ideal and why?

 

speaking of spring rates, after noting the difference in handling in bumping up the spring rates, i find myself wondering if i should bump them up slightly again. i don't drive the car on the street, so who cares, right? seems to me i read about a chassis stiffness limitation (such as above xxx# springs, tube framing was req'd else the chassis would eventually flex and fatigue itself). what is the recommended spring limit if my only chassis stiffeners are triangular strut braces in both front and rear?

 

as for the steering wheel, the wheel is 13" and with the leather gloves grabbing the lacquered finish, the grip is phenomenal, actually. to me, the slick wooden wheel and leather gloves and a speed racer helmet are one with the theme of the car.

 

shuffle steering: yes, my technique could be better. that said, it also seems to me that there are transitions on the track that the shuffle isn't appropriate with manual steering. that is to stay, when you have to *muscle* the wheel, the shuffle technique doesn't have the torque to generate a timely steering input. right?

 

i find that on the hairpin turns, the car likes a *very* slight flick to turn in, too. problem is if i flick too much, then i lose traction on the front tires and push. overall, though, when i watch the video again i see parts where my inputs are unnecessarily jerky, either because i didn't study the track enough or i'm correcting for an over-aggressive throttle input.

 

and btw jon, i laughed embarrassingly loud after reading this:

and sounds great when it's not backfiring.

Edited June 9, 2010 by zredbaron

[JMortensen]

jon, i'm having a hard time distinguishing between the difference between reducing front sway bar vs. increasing [adding] rear sway bar. would the former necessitate an increase in spring rate to equate to the latter? which is more ideal and why?

You can get the same balance on the car with softer or stiffer springs. Stiffer springs will work the tires harder and will allow less roll, so less loss of neg camber under roll. Softer springs will give you more compliance for bumpy surfaces.

 

speaking of spring rates, after noting the difference in handling in bumping up the spring rates, i find myself wondering if i should bump them up slightly again. i don't drive the car on the street, so who cares, right? seems to me i read about a chassis stiffness limitation (such as above xxx# springs, tube framing was req'd else the chassis would eventually flex and fatigue itself). what is the recommended spring limit if my only chassis stiffeners are triangular strut braces in both front and rear?

John Coffey has posted a lot more about structural stiffness and spring rates than anyone else, but the bottom line is that at some point you'll go to a stiffer bar or stiffer springs and there won't be a change in how the car handles because the chassis will flex as the spring deflects, masking the change.

 

as for the steering wheel, the wheel is 13" and with the leather gloves grabbing the lacquered finish, the grip is phenomenal, actually. to me, the slick wooden wheel and leather gloves and a speed racer helmet are one with the theme of the car.

Weird. Looked big, but 13" is the way to go for autox IMO, so I guess you're there already.

 

 

shuffle steering: yes, my technique could be better. that said, it also seems to me that there are transitions on the track that the shuffle isn't appropriate with manual steering. that is to stay, when you have to *muscle* the wheel, the shuffle technique doesn't have the torque to generate a timely steering input. right?

I never had a problem with shuffle steering, but I know Cary and I have talked about it and he has one part of a track he runs regularly where he actually lets go of the wheel and lets it spin. That's not the way I was taught to do it, but I guess if it works for him it's kind of tough to argue. For me, I try not to cross hands and not to let the wheel spin in my hands. I was taught that relatively late in the game and only used it for a couple years of my 8 years of autoxing, but it works for me so far.