Nice job mate still bringing the coupe to classic japan on Sunday?

Simon my car pretty much uses the specs right out of 1200 competition manual.

I gravitate towards soft spring larger bars, I pound over the curbs so the softer springs help. I'm running 225-250 fronts, the rear springs should be 160lb mark. I say should because stock rear is 109 the 1200 suspension manual says use Nismo spring set and remove 3rd / short leaf which is 10% stiffer than stock but 25% softer than Nismo 3 leaf set up. I have the all 3 leafs so that should be 160lb spring.I run a 22mm front bar and 16mm rear bar (both Addco brand) The manual specs 25mm front 22 rear which seem a bit large to me.

The track width on my car is much wider than stock, I'm running the 510 wagon / roadster H190 (1350mm ?) the front track is 1365mm. I'm running 25mm roll center spacers under the 280zx struts. The 280ZX control arms are using the standard pick up points but they've been lengthened 19mm.

Alignment of the top of my head is -1.3 camber (Hoosier street TD bias ply spec no more than -1.5) 2 mm toe in and 4.5 degrees of caster. Ride as measured from the body join below the sill is 125mm front,( I could lower but risk the control arms traveling past horizontal and reducing the camber) the rear is a at 140mm. I can't lower the rear without having to modify the floor otherwise the H190 diff will small the sheet metal.

My car has what I'd call moderate oversteer; most folks would so a lot of oversteer but like most guys who started on motorcycles first I tend to like a car on the loose side. My local track is mostly low to medium speed corners it's an issue. The other factor is the car has got all of 105-110 whp, so being gutless as it is I'm pretty much floored from mid corner to exit in any corner over 60mph. If it had any real power I'd change the set up.

OK back to your car; the spring rates aren't that alarming after I thought about it, 2100 pound Spec Miata uses 750 front 450 rear springs. If you can snag a test day I would try go back tosofter springs combined with larger front bar in combination with small rear bar. Finally on the front springs if the car will take a set on low speed corner entry than I wouldn't worry about it. It one of those things you have test.

As for the roll centers I do seem remember that the rear should be slightly higher than the front otherwise the car tends toward oversteer.

I may have misread the post but how are you getting rear toe and camber? Is that a style,of axle that similar to what V8 super cars have?

One question I have is the car turning faster lap times with the new set up? If it is then I would work on the balance. As previously stated I'd adjust the rear, be if softer spring rate or roll center. If the car was slower I'd go back to the baseline. With it being Alan's first drive in the car I realize it maybe a moot point as far as lap times go. One thing I always go back to is the did the problem occur before I made changes. I also try not to make any changes before any events that I haven't had a chance to run at a track day. I don't like making anything more than minor adjustments on race weekends, my attitude is one of if you have work on the car more than 10-15 minutes to make a change you're not adjusting the car you're fixing it. I try to keep it to damper adjustments, sway bar adjustments and tire pressures.

The big thing is you are always chipping away at it, people don't realize how much that contributes to being a top notch car.

(Note I edited the ride height spec before I installed the H190 the car was 110mm front 120mm rear)

Thanks so much for your input Tom. The softer front springs and heavier front bar makes good sense to me. I think the 120Y bar is 19mm. I might also remove the extra rear leaf and add a soft bar.

The camber and toe at the rear is from just bending the diff housing. I use a length of rail iron and some risers and clamps to secure the housing at the right pinion angle. Then use a bottle jack to bend the camber into it using vertical straight edges clamped to the outer flanges to measure the camber as im bending. The housing is rotated 90 degress to adjust the toe.

I also have a much larger difference in front to rear track than you. My front is about 70mm wider. I can adjust this with rear spacers though. Absolutely worth a try as well.

My car works well at the tighter tracks, but ive always struggled at Phillip Island. The four fastest corners are from between 160 and 180Kmh. It needs to have a little push through these to be able to pick up the throttle early. Its not fun when the back wants to swap ends at these speeds!

Im also wondering if a little more rake may help as well. These things seem to get light in the rear with the shape they are. If I lift the rear slightly it may reduce the rear lift.

I'll go out now and measure some bars to see what may work.

The car was slightly slower now with the extra rear leaf and the stiffer springs, but it was someone else driving the car that hasn't driven it before, so its hard to say definitively if the car is faster or not.

Thanks again

Quote:

Yeah, I'd agree with your thoughts on the roll centers. Rear should be higher than the front, so the roll axis has some rake. With your LCA angles I'd say the front RC is too high. Some people make high front RCs work, but I reckon it's better off and easier to sort with a lower front RC.

WRT to the rear toe out feeling, how much camber is in your rear leaf pack? The more curved they are at static height, the greater the rear steer effect is with any body roll - ie as the leaf compresses it will get longer, while the inside unloaded leaf shortens.

I just watched the vid - great to see the little Datto in action. Shame about the issues over the weekend, it certainly looks rapid the way it blitzed past the guys for that 10th place battle! Love it!

Simon always happy to share, great thing about 1200.com is that we can all bounce ideas around. I'm always learning from these threads.

Tom

Hi Simon , I was at PI with a couple of RX7's and was watching all 3 of you Dato coupes , for a old car they certainly get going , we too had our rear roll centre much lower than ever before , even to the point that a Mumford link was discussed to lower it even further , of course we are much wider than you at the rear , we did also put blade adjustable rear sway bars on the to do list

One more thought; is,it possible or allowable to put a bit more rear downforce since it would seem that Phillip Island is the one place where the oversteer really becomes an issue?

Tom

Yes Tom , we noticed that the "locals " had very different rear spoilers than the visitors , little winglets at the front and max height at the back with directional veins or as I called them " Sprintcar sideboards" , and a decent wickerbill or gurney on the rear edge , must have been something in it

The rear spoiler is maxed out for the rules. If anything, the front could be too effective. The only obvious aero thing to do would be raise the rear of the car to give it more rake, to try to reduce rear lift. Maybe try a shorter front splitter too.
Wards, I had a blade from Harrop eng to make the front bar in adjustable from in the car, but never got around to building the rest of it. Might have to go back on the to do list as well.

Simon because the Addco bars only have the one hole like the stock bar my fabricator made the mounting point on the control arm adjustable. There are two flat plates welded on top of the control with 5 holes; the middle hole lines up with the stock mounting point, the ones either side are in board or out board of that, moving the mount changes the leverage the control arm exerts on the sway bar. When I had him lengthen the control arms and when it was done added the the brackets for adjustability.

Tom