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

[johnc]

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?

 

The spring rates you're ruining are fine for your current level of driving ability. As you increase spring rate the car becomes less forgiving because the tires are working harder (as Jon mentions above). Wait at least a year before bumping up the rates.

[zredbaron]

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.

 

I definitely aspire to improve my hand-to-wheel technique. And the thought of letting a wheel spin freely through my hands sounds like a broken wrist or finger waiting to happen...

 

 

The spring rates you're ruining are fine for your current level of driving ability. As you increase spring rate the car becomes less forgiving because the tires are working harder (as Jon mentions above). Wait at least a year before bumping up the rates.

 

loud and clear. if that's the case, then i will gladly wait the year. the car is more than a handful for me as it stands.

 

 

as to the less front vs. more rear sway balance, seems to me that less front would have more ultimate traction since the inside front tire wouldn't be lifted up as much powering out of an apex. am i correct? if so, this benefit comes at the cost of what?

[zredbaron]

i meant to include these stills of the car from this past weekend. another not-so-great surface, but more flat at least.

 

anyways, these images were cropped out of a medium-quality video from the bleachers. i remember before my suspension upgrade similar stills were requested. not sure if seeing these would change anyone's feedback, so i thought i'd submit them just in case.

 

 

 

 

 

 

(can anyone say LATE APEX!? haha)

 

 

 

 

 

[johnc]

as to the less front vs. more rear sway balance, seems to me that less front would have more ultimate traction since the inside front tire wouldn't be lifted up as much powering out of an apex. am i correct? if so, this benefit comes at the cost of what?

 

At the cost of more camber loss due to roll. The S30, being a strut suspension car, loses a lot of camber in roll and that's why you start out with over 3 degrees static in front. Reducing roll helps to keep the tire square with the road surface. But, too much roll stiffness through bars decreases compliance and makes the "independent" suspension less so. Its all a compromise.

[JMortensen]

You might read up on droop limiters. Looks like your lifting quite a bit on the inside rear

[DrSideways]

You might read up on droop limiters. Looks like your lifting quite a bit on the inside rear

 

A larger front bar will help to keep the inside rear on the road surface too. When installing a 1"+ front bar I always weld a plate to the bottom of the frame rail. This covers the bolt holes and runs about 5"-6" fore to aft with the center between the original holes. The width of the plate is just a bit less than the width of the rail. Then I weld a 4"x$' plate to that. The extra width sticks out to the inside of the rails. This is where I bolt the sway bar brackets. I think the plates were 3/16" thick. John C. may comment on that.

 

The larger bar can rip the threaded inserts right out of the frame. Of course that won't happen while in the paddock. Back in the day I ran a Suspension Techniques 1" front bar and 7/8" rear bar with a lot of success. Your mileage may vary.

 

Alan

[JMortensen]

If he's already having trouble with understeer and doesn't want to add a rear bar due to the traction issues with the Quaife, then I'd say a larger rear bar isn't a good solution to the jacking problem. Stiffer springs would reduce this a bit. I really like the idea of the droop limiters on struts because I think the angle of the struts cause the sprung mass to slide up the inside struts under lateral acceleration. I don't think any strut based suspension gets around this. If you have the strut straight up and down it would eliminate the jacking but the side load on the struts would probably cause a LOT of stiction. Not really possible to lean the struts out either due to packaging constraints. I don't think other suspension setups have nearly as bad a problem in this respect.

[260DET]

Looking at the pics above that car needs more front roll stiffness (and perhaps a stiffer chassis) to wedge weight back on to that inside rear to get some traction and keep the wheel angles within limits, car looks fairly awful really. Below is a pic of a car with a lot of front roll stiffness taking a slow right 180 degree corner, note the inside front is just off the ground, thats all due to a stiff chassis and a big front ARB holding the inside wheel up.

[DrSideways]

If he's already having trouble with understeer and doesn't want to add a rear bar due to the traction issues with the Quaife, then I'd say a larger rear bar isn't a good solution to the jacking problem. Stiffer springs would reduce this a bit. I really like the idea of the droop limiters on struts because I think the angle of the struts cause the sprung mass to slide up the inside struts under lateral acceleration. I don't think any strut based suspension gets around this. If you have the strut straight up and down it would eliminate the jacking but the side load on the struts would probably cause a LOT of stiction. Not really possible to lean the struts out either due to packaging constraints. I don't think other suspension setups have nearly as bad a problem in this respect.

 

This thing is leaning like a pig. Get the platform stable and then address understeer. Worse comes to worse throw some toe out at it.

 

Alan

[JMortensen]

You have a point Alan; he's got to get that roll under control. We're just talking about two different ways to get to the same place. I'm saying use stiffer springs all around (and especially if he's going to bigger yaw dampers [tires] I don't see a need to wait on the springs) or limit the jacking on the inside, you're suggesting a stiffer bar. If he wants to maintain the no rear bar setup, he really needs stiffer springs IMO, as going to a stiffer front bar will help, I just don't think it will do enough and I don't think it's going to help with the understeer. I've autoxed a truck that improved it's horrible understeer with the addition of a front bar, but I think Mark is past that point where the thing is set up SO bad that any reduction of roll will be a net benefit. I think droop limiters all around will be the more effective solution. Take a look at these cars with various spring rates and the last one with limiters.

 

Softly sprung no droop limiters:

http://lh3.ggpht.com/tube80z/R_0JCYGU_4I/AAAAAAAAAgk/fh6n7KdzxNs/s800/IMG_4064.JPG

 

Stiffly sprung no droop limiters:

http://lh6.ggpht.com/tube80z/R_0JL4GVANI/AAAAAAAAAjM/yKjNKjbtDOQ/s800/IMG_4088.JPG

 

 

http://lh3.ggpht.com/tube80z/R_0JvIGVBSI/AAAAAAAAAr8/iD1JWzenIsw/s800/IMG_4172.JPG

 

 

Stiffly sprung with droop limiters:

http://lh4.ggpht.com/tube80z/R_0JlYGVA-I/AAAAAAAAApY/eMo310K4iho/s800/IMG_4146.JPG

Edited June 11, 2010 by JMortensen

[zredbaron]

for display purposes:

 

 

 

Softly sprung no droop limiters:

 

 

 

Stiffly sprung no droop limiters:

 

 

 

Stiffly sprung with droop limiters:

 

it was a shame to not see the progression of images all on one screen to scroll back and forth between.

Edited June 11, 2010 by zredbaron

[DrSideways]

You have a point Alan; he's got to get that roll under control. We're just talking about two different ways to get to the same place. I'm saying use stiffer springs all around (and especially if he's going to bigger yaw dampers [tires] I don't see a need to wait on the springs) or limit the jacking on the inside, you're suggesting a stiffer bar. If he wants to maintain the no rear bar setup, he really needs stiffer springs IMO, as going to a stiffer front bar will help, I just don't think it will do enough and I don't think it's going to help with the understeer. I've autoxed a truck that improved it's horrible understeer with the addition of a front bar, but I think Mark is past that point where the thing is set up SO bad that any reduction of roll will be a net benefit. I think droop limiters all around will be the more effective solution. Take a look at these cars with various spring rates and the last one with limiters.

 

Softly sprung no droop limiters:

http://lh3.ggpht.com/tube80z/R_0JCYGU_4I/AAAAAAAAAgk/fh6n7KdzxNs/s800/IMG_4064.JPG

 

Stiffly sprung no droop limiters:

http://lh6.ggpht.com/tube80z/R_0JL4GVANI/AAAAAAAAAjM/yKjNKjbtDOQ/s800/IMG_4088.JPG

 

 

http://lh3.ggpht.com/tube80z/R_0JvIGVBSI/AAAAAAAAAr8/iD1JWzenIsw/s800/IMG_4172.JPG

 

 

Stiffly sprung with droop limiters:

http://lh4.ggpht.com/tube80z/R_0JlYGVA-I/AAAAAAAAApY/eMo310K4iho/s800/IMG_4146.JPG

 

 

The droop limiters sure would be an inexpensive way to go about it. Try it and see.

 

Alan

[DrSideways]

I did some more thinking on this. Your car is pretty low. The spring rates are not real stiff. Then there are the Tokico shocks. Are they the shorter units? If not, might they be bottoming out and taking the spring out of the equation? Those can be at their limit anyway under some less than extreme conditions. Autocross on a slick lot can be some of the toughest conditions.

 

So to test this out just raise the car back up to something just less than stock ride height. Realign and re-scale the car. Go to an event and see how it does. This would be an inexpensive way to test.

 

Keep us posted,

 

Alan

[DrSideways]

Any new developments?

 

Alan

[zredbaron]

Any new developments?

 

Alan

 

unfortunately, no. next event is an autox school in two weeks, and I hope to have either a skinny rear bar or a thinner front bar to play with that day since there will be no shortage of seat time. adjustable, of course.

 

haven't had a chance to investigate into S30 droop limiting options, either.

[zredbaron]

ok, so i was looking for a skinnier rear bar, and was told that there was no OEM bar until late '73. that blew my mind!

Edited July 8, 2010 by zredbaron

[Lazeum]

This is true only for US

 

Here in Europe, 240z has got rear sway bar since the begininig but the fixtures were different, there were 2 brackets that hold the stab bar in front of the rear suspension on the 2 lateral frame rails.

 

 

[zredbaron]

really? mounts backwards? interesting.

 

damn, i want one. i don't want to reduce my front ARB, that will will only exacerbate my roll issues...

Edited July 9, 2010 by zredbaron

[johnc]

You can install the ST 3/4" rear bar or get an adjustable 5/8" bar from Design Products: http://designproductsracing.com/Z_Suspension1.html

[zredbaron]

very nice. my searches thus far have found nothing, and this looks to be exactly what i was asking for. thanks john!

 

looks like the price tag will also motivate me to finally get around to putting the previous parts up for sale somewhere.