Datsun Roadster Forum-311s.org

For the fist time this year, the roadster was seen racing. New for this year, 14X7 Panasports, and 225/50/14 Hankook C71s. The results... I still cant catch a stockish 240z with V700s and an open diff, or, a 914 with some suspension tweaks. I did learn that the my tire pressure could have been too low. I hear that I should be running 38-40 psi, I was down about 22-24. Either way, I still couldn't get the back end to hook up. I still have a monster drift car. It did show some understeer issues, but only when I stuffed it into a really hard corner too fast. Power application caused more understeer, until the front end started to turn, then instant drift car.

I have some in car video, and I'll post it when I get it to download from my camera.



Will

Ok, why do the pictures not work?

Hi Will, lot's of questions....and a few assumptions.

Assumptions:

Your tires are not shaved
Your tire temps are 22-24 cold

Questions: Are you still running comp rear springs? How do you have your panhard rod set up? When your car pushes are you under braking? Is there evidence that you are hitting your bump rear stops though hard corners? What gears/trans are you running?

I am able to catch and pass a stock 240Z with my roadster, and I have a very mild cam in my roadster, you should be able to catch a stock 240Z with the right setup.

Ron

The tires are R compounds, tire pressure was hot, the car was not plowing on braking, but on 120 degree corners where I was getting on the power early trying to walk the back end around. The problem was I braking way too late (hindsight is 20/20) and carring too much speed into the corner. The tires did come off the used tire pile at Sears Point, but still seem to have a fair amount of stick left.

The track temp was only about 70 degrees when I ran. I did get 3 back to back runs, due to timing error issues.

I don't have the panhard on yet, I do still have the comp springs. I'm looking for a set of 66 springs, but I wanted to give my setup one last chance with the bigger tires.

Will

Lets try these pics:












Looking at these pictures, I can't see anything obviously off, but perhaps with this much tire, I could use a little more camber? I do think the car looks really good with that much tire under it.


And the what the heck car... Are you kidding me?


Any comments, ideas? I am actively looking for some 66 rear springs. I was hesitant to go that route as it would lift the rear back up, but since I have a panhard rod, that will bring the roll center back down to where it mounts which will be below the axle anyway.

I'll be picking on the Porsche crowd on Saturday so I will see how it goes on one of their more open and sweeping courses.

Will

Hi Will,

Your tire pressures (to me) are way too low. Your comp springs are a problem as they lower your roll center too much, and are inverted arches which causes problems with spring rate as well. Raising the roll center in the rear should help some. Panhard will give you adjustability for the roll center. I am not sure if I would like my roadster without the panhard rod. Or without an LSD or Locker.

In a couple of the photos it looks like you are too hot going into the turn and are turning so hard that you are turning past the effective point where the steering works and the car is plowing into the turn (read understeer) and then you are frying one of the rear tires on the exit, adding to a slippery condition in the rear with not enough pressure.

When you got three consecutive runs did your tires come in more or did they continue to go away as you kept going doing runs on them?

The tires did start to work a little better once I got the 3 back to back runs, that is when I posted my fastest time. I agree, I did have the front end turned to lock when I was understeering and was indeed to hot for the corner. I need more seat time in the car this year, I think I have partly forgotten how to drive it. In this case, I really needed to slow down to speed up. I guess that's what I get for racing that slow Italian thing...

Will

So I was thinking, what about having the comp springs rearched to mach a set of stock springs? That would allow more suspension travel and possibly soften the rear end up a little. I've been told that the 66 springs are the same as all the later springs (even though Bob Sharp and others say otherwise). With the comp springs rearched, the no longer sit concave on the car and can actually work rather than binding on each other.

Any thoughts?

Will

First things first, the tires look great!
If I remember correctly, having the spring arching up to the axle will make the car understeer, so the flatter or positive arch spring may help. You do have the locker in the car, correct? I was thinking if you could swap it for an LSD, it may give you smoother transitions as you put the power down. Might get lucky and trade even with someone looking for a locker. Only problem is your used to the locker, so your style may have to change.

If having the rear springs arch up causes understeer, than the spring arch isn't the issue since the car is still tail happy. I'm looking for more understeer so I can tune it out with either my 21mm front sway bar or my stock bar.

If the comp springs arching upward causes oversteer, than having them rearched might do the trick. I might also look into a set of sliders to replace the rear shackles. Those would allow the springs to compress/rebound with less friction as well.

There has to be a reason the comp springs are flat, I can't see Nissan keeping a bad product around for 40+years. Yes Bob Sharp states they are too stiff, but if they are, why hasn't something been done to correct the issue. Were they designed to be run with a set of Bilstein rear dampers that are high pressure gas units rather than hydrolic? If that were the case, I can see the Bilsteins raising the rear a little (They do on Alfas) if they were only used in the rear. With the shocks raising the rear some, the springs then have arch to them, or at least sit flat under load rather than arching up.

Does anyone know for sure what the spring rates between the 66 springs, the late stock springs and the comp springs are?

I'd be happy to throw a set of stock late springs on just to see what happens, but I don't have any. I'm a little afraid it will cause the car to wallow around and cause other issues. The lower spring rate might give me the traction I'm looking for, but by raising the rear up more it could cause more oversteer, or cause so much understeer that I can't dial it out with changing swaybars.

Will

Hi Will,

This is my interpretation, and it is worth what you pay for it.

Going into a turn your car is understeering some. Once you get back on the throttle it is oversteering badly.

There are two problems here. Your roll center is too low in the rear, de-arched or comp springs have effectively lowered your roll center to the point that the car will understeer into a corner because the REAR of the car is too low.

Exiting a corner, your rear springs increase spring rate as they compress further and hit the bumpstop effectively removing any suspension travel, that will cause lots of power-on oversteer.

Raising the roll center with the properly arched springs will make the car more manageable, and more linear from a handling standpoint.

Eliminating the car from bottoming out on the bumpstop or frame will help your oversteer issue.

I know you look at the comp springs and say this is the cool set up, but remember tire technology was much different back then, and with more grip comes different handling characteristics requiring a different spring setups.

Going one step further you can place a block spacer under the rear shackles with your existing springs and test, to see how that effects the handling. (I would suggest an inch or two of spacer) and then we can talk about it further.

I have photos of racing roadsters with inverted shackles in order to raise the rear of the car with the comp springs. The spring rate might not be as much of the problem, the height, in my opinion is the issue.

Also, please follow up with us, are you running an LSD diff, Locker diff or Panhard rod? if you are running an LSD what is the break away on the LSD?

I'm not hitting the bumpstops, I've checked this several times. I am 99% sure I have a locker for a rear end, no LSD. I have not installed the panhard yet. Its on the list of things to do sooner than later. Most of the time the car is neutral on corner entry, and oversteers on exit on throttle, or is neutral off. The only time it understeers is when I have way over cooked a corner, turned the wheel to lock, way past the ability for the tire to do anything. In this case, its all driver error.

I'd rather get the comp springs rearched rather than buying new ones. If the ride height is the cause, sweet, I'll spend the $ to have them redone and get them powder coated while I'm at it.

I'm going to see if Nissan still has any of the 55020-10500 leafs, depending on the price, I might go that route, and before I install them, have the comp ones rearched to match. At this point, I'm looking at options, obviously the rear springs are the issue, the question is what is the most effective way to deal with them. Yes, slapping a set of 10500 springs on is the quick and easy way, however finding a good set of used ones might be tough. Running the stock late springs might also be a hot setup since they are even softer, and I might be able to correct for the softness by upping the stiffness on the rear shocks (not ideal but it might work.) Rearching the comp springs, again possible, but why hasn't anyone else tried it? Is it not worth the effort, or has someone tried it and found that they are still too stiff?

I'm going to bounce some thoughts off people before I spring into action on this.

Thanks for the input.
Will

Will the car looks mean!
Did you work the rear fenders to fit?
Is that a sway bar link in the back?

Alvin, that should be his traction bars you are seeing.

R

Yes Alvin, I worked the rear fenders a bit, hence the reason there is bare metal on the flares. I started working with a baseball bat, finished with a glasspack muffler and a sledge hammer. The fit is very close.

Those are traction bars you see. I'm still not sure why I painted them white, but they show up under the car pretty well.

Will

hmm I thought traction bars were for drag racing. Did they help or hinder on the auto-x?