Suspension setting difficulty

Ross Nicol · 05-06-07, 10:16 AM

Found a major difference between front and left suspension.While trying to set the camber to the same setting, I found the rose joints on the left wishbone had to be wound out 5.5 turns and the right zero turns as the photos show.
Ross

Ron Earp · 05-06-07, 11:35 AM

Are the arms the same length? How about the location of the ball join on the arm, are they in exactly the same place left to right? And the mounting locations on the chassis, the same? Certainly there will be variations from left to right, not sure it is a lot to be worried about. Something would have to be different I'd think, but I'm not sure any car is perfect with respect to variations.

R

Malcolm · 05-06-07, 02:45 PM

On GTD's (yes I know its not RF!) there is a difference between sides of the car. Maybe 3mm is typical? I never really worried about it. I know that it was never recommended that when setting castor that you set one side via turn plates etc and then measured to set the other by a reference measurement! Maybe hand made chassis in jigs get variations in them after all? Maybe this is typical for all types of replica 40's?

Russ Noble · 05-06-07, 02:59 PM

Ross,

If this has recently changed, then something has got bent.

On the other hand, if it's just the first time you've setup your front caster accurately then it's probably just compensating for some cumulative manufacturing tolerances. Thats one of the reasons we use rod ends as opposed to spherical bearings or bushes. Adjustability. It'll be fine.

Cheers

Ross Nicol · 05-06-07, 08:22 PM

No nothing is bent and prior to this, each time the suspension has been worked on, this problem of running out of camber adjustment on the right has been noticed.I tried 1/2 width lock nuts but resorted to cutting back the arms ( a crude job with a cut off wheel).This shortening of the arms did allow more camber but I had lost the Datum from the original arms.2 weeks ago I got Will to remove the threaded ferrules and shorten the arms further.This he did and restored the Datum so both arms were now xmm shorter than the original length.I refitted the rose joints and set them 3 turns out.Checked camber 4.6 degrees neg left, 3.1 degrees neg right.Obviously I did some fiddling to make both sides the same and the result as I have shown seems extreme at 13mm or 1/2". I will get to the bottom of what the cause is but for now at least my settings are ok and ready for this weekends race meeting.
Ross

Malcolm · 05-07-07, 03:46 AM

That is some serious neg camber Ross. I guess the tyres are radials and you need that much to generate the heat?

Ron Earp · 05-07-07, 08:11 AM

Quote:

Originally Posted by Malcolm

That is some serious neg camber Ross. I guess the tyres are radials and you need that much to generate the heat?

I was looking at that too. Hoosier recommends -2.25 to -2.5 on the R tires we race with up to the 225 front size we use, no more for most applications but that will depend on other factors. But I think Ross must have it sorted, it has been on track a lot and running well I think.

R

Ross Nicol · 05-07-07, 10:22 AM

Yes Malc they are Dunlop Radials. Ron I don't think tyre guys are best placed to recommend camber settings for any race car as all cars will react differently. Increasing the negative camber on my car has transformed it's handling and improved grip to such an extent it's becoming a Jet. If you look at that right front tyre in the photo you can see some rubber pickup from the cool down lap but if you ignore that the grain across the tread shows wear across the full width of the tread.Now this is no accident as I have increased neg camber until this even tread wear became apparent. I have used a temp gauge as well but reading the tyres is a good start. It feels so good to be racing a car with so much grip and my corner speed is much better.I've just spent tonight working on the rear suspension and found 2mm of toe out on the right rear and that's now corrected but I have to shorten my top links to allow more neg camber at the rear. These cars were not built as race cars with allowance for this much camber that's for sure.
Ross

Ron Earp · 05-07-07, 10:28 AM

Sorry, I wasn't clear on my recommendation as it comes from our race tire supplier on track, who are racers in similar cars, and is a ballpark for sure. I run about -2.0 to -2.5 which seems to work well at most tracks, but I run all I can, about -2.5 to -2.7 on the technical track we run when I get a bunch of roll and corner forces etc. but watch the temps and pressure to make sure it jives. Track temp has a good bit to do with "perfect" setup on the car, as well as a lot of other things. Normal tire people, yep, I agree good for selling tires.

If you're using the temp gauge and watching pressures then I'm sure it is right on. What sort of toe do you run in the front on that car? I've run a bit of toe out that seems to help turn in and haven't experienced the wandering that some claim to have on the straights doing this. Just wondering what you saw on the GT40 with a lighter front end than anything I have now.

Ron

Ross Nicol · 05-07-07, 09:15 PM

A picture is worth a million words so here are 2 of my front wheels.Note the rubber on the inside edge. This edge has not been in touch with the track and I have increased neg camber to cure this next time out. There was a time when I only had 1/2 the tyre width on the track so improvements are coming.Unlike yourself Ron I have no one racing a similar car to compare notes.
Ross

Jim c · 05-08-07, 06:24 AM

Ross

I have the same problem but it runs out on the left.

My arm jig is left and right handed
So I know mine is not in the arms.
I used 3 joints in the top arm and this gives more scope.
Another in the bottom gives even more scope to push the wheel out at the bottom.

Jim

Ross Nicol · 05-08-07, 10:00 AM

Being able to shift the lower wishbone out is a good Idea Jim as I have moved the top in so far that spring/wishbone clearance is a concern at droop.Sorry Ron didn't answer your question, I have 1mm of toe in on the front.Have heard of improved turn in with toe out but never tried it myself. Makes you wonder sometimes if stories about handling are only applicable to certain cars.It seems what may make a car handle badly can make another handle well. Just got back from a Lotus club meeting at Holinger Engineering,they make 6 speed close ratio boxes H pattern or sequential for Getrag (Porsche Carrera), and other high end sports cars. they also make boxes for Australian Premier Series V8 Supercars. Very interesting.
Ross