Something that you have to keep in mind is that by design the leaf spring rear end already has a built in roll centre. By fitting a pan hard,watts, Mumford or other, a fixed point of roll centre doesn't magically appear. The built in rc will still be there but you will be working with or against it depending on were you set the height.
You will probably find that you end up very close to where silly old mr Datsun set it 40+ years ago. I would say he was a pretty smart bloke.
It is pretty easy to work out your rc, diagrams on google.

Is lateral location needed, probably not in such a light car.

whilst I agree with your comment regarding roll centre conflicts and making radical changes.
I disagree regarding the light car and need for lateral diff stability.
Once you start putting lateral load into these cars locating the diff laterally, irrespective of the Roll centre location, is important to reducing lap times and provide a predictable handling car.
Also the roll centre can still be tweaked with a lateral device which is another way to dial the response you want.

This doesn't need to be radical variation from standard. But these millimetre/centimetre changes are enough to change handling characteristics, as such it is an important tuning tool.

Quote:
When you add a lateral link, you don't end up with two conflicting roll centers. It changes the Rc location.

Mr Nissan designed it for the stock car's Cg, height, spring rate, 155SR12 tyre, and front Rc height. On a track car you do not want it anywhere near where Mr Nissan put it. But that's alright, because unless your car is standard height the roll center will no longer be where Mr Nissan designed it to be anyway. eg my 120Y: Stock rear Rc is about 38mm above the top of the axle housing. Lowering it 48mm moved the Rc 66mm lower than standard and about 285mm from the ground with a 185/60 R14 tyre.

Lateral location of the diff is nice if it's done properly, but there' no guarantee it will improve your lap times, and it certainly isn't important to provide a predictable handling car. You can (and should) have a perfectly predictable handling car without one. The instability Tom's car has is not because there's no lateral location members.

I'm with LOWTECH, I never had any need for one either from 116rwbhp L18 up to 300rwbhp CA18DET. No shortage of lateral grip or problems with stability here:

Harry, nice pictures.

On the tires they drop a few tenths at as they get old, note I do strategically buy them so I can run them for 12 months (or more). By the last track day my overpowered wonder turns into a drift car.

The sway bar it is an ADCO bar, the bushings attach to the frame rail near the front spring shackle, the end links attach to the spring like in the competition manual.

I should also clarify on the traction bars as I've had them on the car for many years; the original ones were exactly like the manual, T-shaped with the rod end bolted to the bracket under the axle. The ones on the car now have a rod end on both sides, the front spring shackle mount for the bar has a set of machined spacers/bushings. It is possible this change is causing a bind, perhaps it's pinching the busing in the front spring eye etc.

The only bump rubbers on the car are the ones on the shocks, I also have done exactly as you suggested and used a dab of grease to see if parts are making contact, nothing obvious.

It's ironic you mentioned the rear shackle, because I dragged out my copy of Tune To Win in an effort to see if I overlooked something obvious.............I checked the rear shackle and it is swept toward the back of the car. I have not measured the angle but somewhere between 15-30 degrees.

Also on the subject Smith books, he wrote that he felt that the complication of properly installing a Watts Linkage wasn't worth the bother over doing a proper Panhard Rod.

In corner in the video the car is pulling about 1.3-1.4G (based on guys who have telemetry and run at a similar speed), that really isn't well beyond what other 1200's are doing. I will have a better idea on Saturday after it gets inspected, if nothing obvious is found we will likely install a panhard rod. At next months track day I will try the car with and with out the bar hooked up. I am also going to try undoing the traction bars to see what that does (I use track days for testing). I will also have my fabricator take a look at the front end just for good measure. I am fairly sure that the instability may also be the nut behind the wheel, to be honest had I not seen the video I would very likely continued to just drive the snot out of it, especially since I have a single seater in the garage again. Happily fixing this should at the very least make it easier to drive but I do expect to trim the lap time. I have been telling a friend for some time that I feel there is more speed in the car.

On the subject of single seater, the Novakar Formula 500 I have now uses a solid axle like a Kart but with suspension, it weighs 725lbs with me in it and the car is perfectly capable of pulling 2.5Gs and the lateral locating device is quite stout for such a small car.


Tom

I should have been clearer with my wording, I never intended to imply/support a dual roll centre concept. Actually i didn't read retrorally post as implying that either. Funny how we read the same thing but come to different conclusions. I read it to imply that leaf and other lateral restraint can either assist or work against each other. Which I agree with, poorly implemented watts linkage would be worse then without one.

I agree that Toms issues are not caused by a lack of lateral restraint, will be interesting to see what the cause ends up being.
I also agree it is perfectly resonable to race without one, many have with great success.

I think however, without evidence, it's a long bow to draw to say that better control of the diff location wouldn't have made a difference in lap times. Maybe out of the box, just lowering a 1200 hits the rear roll centre sweet spot? If so great, saves a heap of time and money.
I have strugged to find subjective/objective evidence of how much of a difference, if any, a lateral restraint would make. I can't find any for 1200s, but the escort community has talked about it. Page three of this link does have some subjective discussions on watts with leafs. http://www.rsmotorsport.com.au/forums/viewtopic.php?f=25&t=3292&start=40


I like doing experiments and a lateral restraint is something that I would like to do in a future upgrade, but that will be some time off yet and a little down the list of priorities.
Having just installed an adjustable rear swaybar, I would like to do some back to back testing with that first.

all these escort links are pretty funnny. I know Danny personally. The one time I raced against him on decent tyres was at Mt Cotton in 2004 (before that I was using $50 out of date and hard as nails rubbish). I beat him despite being over 100rwbhp down on his big dollar engine and having none of his fancy expensive suspension bits and pieces, just literally junkyard stuff I whacked together myself. He'll have a list of excuses as long as your arm - at the time he blamed his big dollar Proflex shocks. Funny using that as an excuse against a bloke with Monroe and Peddders comfort gas shocks...

Tom, that's the way to go I reckon. remove pieces until you can isolate what's causing the bind. If that oscilation is due to a suspension problem, it has to be a bind condition IMO.

Like I said, I have strugged to find either subjective or objective evidence to support either way and that link was one case of subjective evidence supported by someone who has actually done the upgrade and in his case, found benefit in the change.
I am pretty sure there is a U2L IPRA 1200 in Vic runs a watts linkage, would be interesting to here from him why he installed one and what the differences are, I think his name is Simon Phillips. I also think he holds some U2L lap records?

Harry.
Did you end up selling the red car? If so do you know how it is going these days? It was certainly an inspirational build for many of us out there, I have always liked how it looked on the track.

Bryan

Hi Tom(and everyone else),

I also don't think this is a lateral location issue.

I'd be checking for front spring eye bush wear, too much front toe out, Uncouple rear springs to prevent bind(I can help with this). Check rear toe(you want toe in) ensure enough bump and droop travel at each corner. Check all the Caster rod bushes, ball joints, tie rods and steering box for play. And lastly, it may need some more rebound in the shocks.

Putting the watts on my car made a significant difference to knowing what the rear was doing. It didn't initially give me more speed but gave me the confidence with predictability in the rear that enabled me to drive it faster. But as Retrorally has touched on, any lateral location device MUST be a lot more rigid(rod ends etc) than the spring location.

The other huge advantage is you can very quickly adjust the oversteer/understeer balance. Mine has a ball screw adjustment that takes less than 30 seconds to change.

My car used to do something similar. Mine was too soft in the rear and the second it lifted the front wheel, the outside rear would overload and would snap oversteer.

Quote:

Thanks, yeah sold it to some guys in SA. Now has SR20DET and just about everything else changed too. Looks better than ever I reckon.

Attach file:

---

  600.jpg (43.81 KB)

All,

I got my fabricator pal to look at the video and he also believes there is either something binding or something loose working like a hinge. The plan is to inspect everything including down checking the shell. With all that said we will be installing a lateral location device because it won't do any harm. When I get it on track we'll disconnect each component and notemthe effect.

My reason for think lateral movement is it does "feel" like something in the back is moving, having experienced the bottoming in the Miata it just doesn't feel the same.

Simon please explain uncoupling the springs, I think I know but not sure. Also you are correct making the car more predictable will let the driver get the last bit out of the car. It's not the car is way faster it's just that you can zero in on maximum grip immediately. I am pretty good at catching a car but doing that 12 times a lap for 15 laps is going to result in losing time even if it is only a couple of tenths.

Harry I am a big fan of low buck low tech ingenuity; case in point was my old Volvo 144 car that I used for rallycross. The suspension was a mix of other model stock parts, 164 front springs, wagon rear springs etc. I even ran used rally tires. I kicked butt with it, many a Subaru driver were left wonder how the old brick went so well.

Tom