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

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 The one time I raced against him on decent tyres was at Mt Cotton in 2004 (before that I was using $50 out of date and hard as nails rubbish).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.

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.

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

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:

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.

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.

For solid rear axle location, I like the Mumford link the best. It allows you to set your roll center wherever you want. By changing the angle of the outer links, the roll center is where the links would meet in in middle. This could even be below the ground if you wanted.
I have not found it necessary so far. My car has Delrin bushings at the front of the spring, and Urethane on all the other mounts. Koni Single adjustables. It pulled just over 1G at the Streets of Willow Skid pad on Toyo R888's 225/45-13's No noticeable rear axle movement.

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lol, 6mth old tyres are brand new! I thought you said you had old tyres?

Yes, bump stops binding will do something like this too. You can smear grease on the surface they strike to check if they hit. Are you not using bump stops in the standard location above the diff?

Other things binding suspension movement will cause it too. You could try disconnecting the traction arms to see if they're the cause,but it sounds like it was doing it before they were fitted.

Quote:
got a picture of this? sounds like a pretty unusual setup.

what angle are the rear spring hangers on. The lower end isn't further towards the front of the car than the top is it?

Harry, you are correct, the video really only shows that some of condition exists. I will attempt brief answers but will likely prattle on as usual.

Tires were six months old, I’ve run a cooked/really old set at a track day and these were not that far gone.

There is less oversteer as the tires heat up but the oscillation is still there just not to the same degree and it was pretty consistent throughout the race.

The oscillation has been there but I do not believe to this degree; with the wider track the corner speed is higher. “Displaying” the issue is the operative word. Previous video clips show the car moving around 4-5 inches (more like McGee’s car) but not 10-12 inches. On my admittedly subjective scale of 1-10 with the video being a 5-6 I’d call what it did before a 4.

Rear suspension is Nissan Competition Springs, with traction bars, 5/8 (16mm?) sway bar. The rear bar bushings attach to the frame with the bar ends clamping to the springs. The sway bar has been on the car since day one.

Benny’s question on the bump stops would have been my train of thought but the axle snubber has been removed, the bump rubbers on the shock are not bottomed. As previously mentioned I raced a stock class car which cornered on the bump rubbers and this behaves somewhat similar but not quite the same.

My thought is that there is a cyclical wind up and release like Benny mentioned. If the axle deflects say 10-15mm how much rear steer does this cause and would the axle movement create this cycle? The bushings are Polyurethane except the aluminum ones for the front shackle to frame mounting point.

I want another set of eyes to inspect everything, so it’s going to my buddies shop, it’s obvious the car can be improved.

Bert as for scary part, as someone who used to road race motorcycles and still does some desert and motocross, this rates about .09 on my admittedly skued fright scale.

If you go to minute 6:50 to 7:30 of this video you can kind see how the car responded before.

https://www.youtube.com/watch?v=9NE5zGOs76A


Tom