Datsun Roadster Forum-311s.org

Traction bars prevent spring wrapup, but that could be a bit of Will's issue as the net effect is that the front half of the spring no longer springs...

Sid, you might be right. I know Ron runs them on his car, but his springs are softer to start with. I guess I could pull them off and put the torque rod back on and see how it does. I've never run the car with fresh tires with them, but as is its not as fast as it was last year. I've got way more tire, and seemingly less control. It points the finger as causing the spring rate to be way too high. I've thought about this, but as I said, I haven't had known new tires on the car with them. Perhaps I will pull them and go back to the torque rod for the next PCA even in July. I get axle hop with and without them, although the burnout is much more controlled in a straight line with them.

Perhaps with stock springs they will be good, but with the current setup I think they are only making things worse. I have noticed that not many other racing roadsters use them, or I just can't see them in pictures. I do need to get the panhard rod welded in. I just need to find the time.

Will

They help as they prevent wheel hop. They also help locate the rear axles. I feel that they make a positive difference. Although the panhard rod makes more of a difference in my opinion.

I think it is a combination of items, and perhaps a little testing is in order. I did not try the traction bars on the comp springs, but I had other issues with the comp springs.

Ron

I'll pull the traction bars before I run with the PCA again. Same tires, same course (more or less, perhaps different directions but not much of a change). If the car sticks better, the traction bars are overstiffening the already overstiff rear end. No UFO event for July, so I only have the PCA to run with. If I manage to get down to see Mark and pick up his stock '70 leaf springs, I'll put them in and add the traction bars back on. I might even find the time to get the panhard done. I need to drop the tank anyway to weld up my trunk (lots of cracks) If I have everything out and setup I might as well get to it.

Will

Hi will

I just started auto-x my roadster this year and am starting to play with different setups to see what works. I am using comp springs as well and am also very confident that they aren’t bottoming. I also thought about rearching the springs to raise the rear but I think you would then have a hard time bolting the spring to the car due to the arch taking away length. Flipping the shackles will add roll steer due to the mount points being different heights.

I Have a 68 with a R16 stroker and no LSD at this time I am using Avon tech R’s 205 50 R14 at 28 psi. For the first three events I tried the rear comp sway bar I had a fair amount of over steer and would spin the inside tire on exit constantly. For this last event I removed the rear bar and had no problem with inside tire spin and little over steer and just a little push that I could manage with a little brake input.

Your track bars were something a fellow racer recommended and I am curious what your experience has been with them. I am overall happy with my cars handling at this time but unless I try something else I will never know the difference. I race with the Siskiyou sports car club in southern Oregon and blessed with lots of practice time. To try new things and record lap times. Here is a link to one of our photo pages they may be of use for comparison. http://ssccmedford.org/2009_event_2_pix.aspx" onclick="window.open(this.href);return false; your photos do definitely show positive camber gain during your turns. A book that I have been reading is how to Make Your Car Handle by Fred Puhn It was recommended in the book Secrets of Solo Racing and I have found the info helpful.

Hope this wasn’t to long for a first post.

John

P.s. If your are racing with Sonoma P.C.A. say hi to Jim Winston driving the black z he is a good freind.

How to digest all this stuff, lots of speculation....not a lot of really hard data...and different drivers & cars. All lead to confusion.

Will, I am seeing you start down one direction, you don't complete the suggested setup and then wonder why your car does not handle right. Now you are undoing what your started....Traction bars are probably not effecting your car that much. The lack of a LSD or Locker and the lack of a Panhard rod are probably a much larger issue. Finish the panhard rod, try it on your car, it works well on mine and the adjustment of the panhard makes a difference. Install softer rear springs with a panhard rod and a well shimmed LSD or a Locker, that should do the trick.

Do one thing at a time, and test, see if the car improves, stays basically the same or is worse and go from there. Scientific method will go a long way here.

Fred Puhn's book is good, Fred lives down here in San Diego, and we see him from time to time at different racing events. Although it has been a few years since I have seen him...

Ron

I HAVE a locker on the rear. Since adding the traction bars, the car has gotten more difficult to drive. Last year I thought it was due to the tires being totally dead. Now I have lots of tire, and huge amounts of oversteer. More than I had without the traction bars. I light both tires up the moment I put my foot into it, they stay lit till I lift or I find a tall enough gear that I cant spin them (3rd) If I'm trying to turn while on the power, I'm simply rotating like I have a rear sway bar on the car (I don't) I figure its not that hard to pull the traction bars off, and if I find an improvement, it tells me that the rear is too stiff, the traction bars add more spring rate (through pivot drag or what have you) and the panhard will just possibly add more things to up the spring rate. With the stock springs, this might also happen but the degree is less since the spring rate is already far less than the comp springs. (In other words the effective spring rate goes up through bind/drag from the lack of rod ends in the traction bars. I just have rubber bushings.)

Will

RC240z wrote:I did not try the traction bars on the comp springs, but I had other issues with the comp springs.

Ron, what were your other issues with the comp springs? I'm wondering also if I made a mistake going with the comp springs. So, why did Nissan make such stiff springs if they don't work as well? If they made them, and marketed them as competition springs, wouldn't you think they would perform better than stock?

Kyle

Kyle,

If you are on a glass smooth surface, they may work fine. According to the Datsun Competition manual, the hot tip was to use the early 1600 springs...

spl310 wrote:Kyle,

If you are on a glass smooth surface, they may work fine. According to the Datsun Competition manual, the hot tip was to use the early 1600 springs...

I still have my stock springs just in case. When you say early 1600, could you be more specific? Do you mean earlier than 67.5? Or earlier than 67?

Kyle

The pre-67.5 springs were slightly stiffer than the 67.5-70s, but not as stiff as the comp springs. With less power, the comp springs might be fine for racing. With more power you are more likely to break the back end free and then it becomes hard to get it settled (at least in an autoX format that is almost constant turning different directions.) If you get the back end too stiff, it starts skipping around and becomes slower that it would be with a full stock setup The suspension must work inorder to transfer power to the ground. Another thing with the comp springs is that you have less suspension travel before you hit the bumpstops. (You can cut them way down however.) When you bottom out, the spring rate goes to infinity and you end up with snap oversteer. (Not what my car is doing.) Another thing that comes into play is the rear roll center and the roll couple. Roll center is an imaginary spot in space where the car pivots around the front has its own. As a rule of thumb, you want the RC to be above ground level other wise you run into issues such as camber loss and the suspension compresses, along with the need for crazy high spring rates to compensate. Case in point, my Alfa. The front has a roll center that is well below ground level and requires 1300lb coils in the front. The rear has 180lb springs, however the roll center is higher than the axle itself. (Hence the reason the really fast Alfa GTVs have a lower back end than the front. Its an attempt make the Roll Couple better.) R Couple is an imaginary line that runs between the front and rear roll centers, and the closer to level it is, the less body lean the car will have, especially if the R Cent. is low. (Anyone feel free to correct me if I'm off here someplace. Bad info is worse than no info.)

I'm not exactly sure how to calculate roll center on a live axle with leaf springs. In my case, Ron seems to think that the roll center is already too low with the comp rear springs, so with a panhard rod the roll center would be even lower. This doesn't make a whole lot of sense to me and there for I haven't installed the one I have for fear of making a bad thing worse. Now with comp springs, the roll center rises to the stock location, and with the panhard comes back down to someplace near the center of the panhard. (Which sits below the centerline of the axle, but still higher than where it would be with the comp springs.)

Also, with the flat comp springs, strange things happen when you load the spring backward (such as with the car sitting on the ground bending the springs upward rather than flat.) I'm not sure if the spring rate goes up exponentially or if it goes down

I wonder the same thing, why would Nissan market a bad product? There has to be a reason they have stuck with the springs like this rather than reaching them. Even Bob Sharp mentions that the springs are too stiff.

If one wanted a drift roadster, I have the setup, no e-brake ripping needed, just apply power and drift. I don't want to know what its like to drive a SR20 DET powered roadster with comp springs and an open diff. Way too much power and not nearly enough grip. I cant use what I have now, why the heck would I want more?

Will

Will, you have something unique going on with your car. All your issues appear to be low speed and perhaps they don't factor into the same charactoristics that my car has....

This is not an attack, and I am sorry if my post came across as one. I still feel strongly that the comp springs are your culprit, but who knows for sure. A panhard rod set up correctly is adjustable, and can adjust the roll center up and down from what I understand. A panhard rod with the 66 springs seem to be the ticket for my car.

To answer other questions. The comp springs were designed when tire technology was completely different, and at that time drivers would sling a roadster around with oversteer and a tight LSD or Locker. Tire tech is different now and race tires are too. time to look for what works with current technology. Again, this is my opinion, and it is worth what you paid for it.

Ron

Ron,
I didn't take it as an attack. Yes it does seem to be a low speed thing. At the PCA event I did I picked up 3 seconds by short shifting to 3rd and more or less keeping the engine below 5k rpm. The car was nicely settled and ripped through the slalom section flat on the floor. First gear is basicly useless, 2nd results in rear tire spin everywhere if the engine is above 4K rpm (thats straight line, left and right turns) Corners in 2nd are best done slowly before the engine gets into the power band, otherwise its tail-out full lock drift time. On the track the car is usually a 3rd 4th shift unless its a really tight hairpin and then sometimes 2nd gets used. The car is rarely going slow enough to warrent 2nd gear, so the drift monster stays put.

Ill try and post some incar footage of the last race I did so you can see and hear how much drifting is really going on

Will

We have video...

http://vimeo.com/5402196" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

This is more or less the same course that I just missed TTOD at last year before the traction bars were added on tired tires. As you can see, the moment the power comes on I'm chasing the car around. This shouldn't happen with 225/50 R compound tires. Its a low speed low gear thing and I think the traction bars have actually made it worse. I'll find out when I pull them and go back to the original setup.

Side note, I just scored a nearly new set of Hoosier Street TDs. I don't know what the tire compound is (guessing its the R6) but I'll be giving these a shot as well. Free tires, what the heck? One has a flat spot, but I'm not out to win a National Championship so who cares as long as they hold air and don't self destruct. I know they are a popular vintage track tire (as apposed to autoX) but with a tread wear of 0, they should stick pretty well.

Will

Will,

I will take a look at your video. I have street TD's and they are a pretty hard compound for a race tire. I know that my Toyo RA-1's out perform the street TD's by quite a bit. Looking at my cornering G's on my videos, I only get about .86 with the street TD's and just over 1.0 with the Toyos. Everything I am hearing is that the new 888 Toyo would be a good all around solution for you. A street tire that does not have to be shaved and holds up well for a race tire. Not sure if they are available in a 14" though.

Interesting, perhaps addressing your gearing might be a better scenario. What differential gears are you running? 3.7, 3.9, 4.11?

R