Car is square on the pad, alignment, ride height, camber, caster, all look to be as described on the setup sheet before we sent the car out.

Driver feedback after the session: mid-corner over steer during initial throttle application. I can see it on the video, it turns in fine, but mid corner the car looks nervous and his hands have to make small corrections all the time.

We had scrubs on for the session, the stickers were broken in during the previous day's test session. Two warm up laps, one hot lap, one cool down lap. Deflated and stored in the trailer.

Here's the funny part. The left rear and the front right was graining bad. Pad was checked for level before the car was put on the pad before the session and it was checked again. Setdown didnt' show anything wonky, not even corner weights.

Clockwise track, 5 right handers to 3 left handers. I know the track works the outside tires a lot more than the inside, but from all the times I've been there, I've never seen the car do that to the tires.

Single seater, pushrod suspension, treaded tires, no wings.

Have you checked each corner for binding thru full travel?

I am taking the approach that the car was fine and then suddenly went wrong this session -- you seem confident that setup was good and has not changed. Proceeding on that basis, first thing that comes to mind is diff failing but your car also sounds like a category that requires open diff, in which case never mind. Could have a dead rear shock, probably left side. As in no low bump force or damper is jacking down, car is falling over on left rear.

Another cause for this type of thing: something loose in the rear that is producing sudden change in camber or roll resistance under load. Bad bushing, mount, etc.

Yup, car was fine on Friday, and first half of the session on Sat. Put the tires on, didn't change a damn thing and then the tires came back in looking chewed.

Thanks for your suggestions.

I also vote for a problem with the diff and/or a damper playing up.

Based on that, I'd say a bum set of tires. What kind of tires are you running? Did the pressure come in as you would expect? How many miles on the old set? Did you see a good gain in lap time when you put fresh rubber on or was it about the same?

For the record I've had this happen more than once. It's probably not actually a bum set, probably just one is wonky and that's enough to throw the whole car off. I've had situations where I've stuck a set of 120 mile tires back on a car and gone 2 seconds faster with a better balance than the new set. It's frustrating as hell, but it happens.

I'd vote against a diff for a couple reasons. First, this is probably an open diff car. Second, most of the time when a modern diff goes south, it does so catastrophically. If you're running a cam and pawl, then I suppose it's possible, but I don't know a present day open wheel race car that even has a cam and pawl made for it.

Mac's dead shock idea is a possibility, and it's easy enough to run them across the dyno to see.

For the most part, we'll all just be making wild guesses without knowing more info.

Could very well be. Especially with treaded tires, hmm. I would be tempted to move them around just to see what happens, if only because it is so easy.

+1 and then put the old tyre set back on and then check shocks (have canisters? no gas?) - are they adjustable by the way? Had any kids around the car recently?

http://jackknight.co.uk/onlineshop/advance...hp?keywords=cam

I didn't say they aren't still made, but the fenders rusting off your Hillman Imp doesn't make it an open wheeler!

If you run Dunlops I like the sound of bust damper. Otherwise duff set of tyres sounds pretty plausible :-p

Ben

I knew what this was going to say as soon as I saw who had posted!

Boro do these look familiar?

http://www.autosport.com/gallery/photo.php/id/1314941

I rig tested a tin top a couple of years ago. It looked OK statically, but cross weighted badly dynamically. It also chewed tyres on track. The cause turned out to be a semi-seized drive shaft CVJ. I guess anything that is capable of X-weighting the car dynamically could have a similar effect. Hence I would resist blaming the tyres in the first instance.

Hi there

One of the easiest and quick method to check if anything is wrong:
Put the car on the set up pad
Note the corner weight
Have a heavy guy to climb on the front nose centered as much as he can
Note the corner weight
Repeat for the rear

It does not give the most accurate results but has some good conclusions in it
It is a static test, so dynamic effects are not taken in.
Doing that you can compare the load variation and if there is clear unbalance then you know something's off in the motion ratios somewhere.
Could be friction, dead rocker bearing, a bolt changed on a damper attachement that touches the chassis / gearbox and limit the suspension movements etc
Gives a pretty god idea if you car is straight in variations
If tires are a possible unbalance source, just repeat the test with the old set. That will give you comparison of their vertical stiffness.

Then if all this is correct see what can affect it dynamically.

Ben

You ever notice how the OP on these threads never returns? What's up with that?

Isn't this the free racecar troubleshooting forum?

The dampers have been pulled and sent to test. (Our shop doesn't have a shock dyno, and since this is a team that I'm new to, I don't know the history of these. No previous records)




Nope Too much rubber there. I think if you stack both our rears, you MIGHT get the equivalent of the front.




Thanks Ben, will give that a good go after the dampers come back. Testing on Monday with some new drivers, so it'll be good to see if this rears its head again.




Sorry FB, been busy of late with my other job outside of racing so I haven't had a chance to come back on.

Thank you very much to everyone who've replied here and gave me advice and suggestions, sincerely appreciated. Will update on what I find when the car's back out on track

Thanks!

Everyone here does it for the fun (including the tongue-in-cheek poke here and there.)

OK, we'll let you off this time, but you gotta come back and tell us what went wrong!

Hey Boro, can I ask a favour - can you repost your aero pic of the tufts going forward from the splitter?

Did you put the other set of tyres back on?

Reminds me of this old image. Chassis data monitored as the 70kg volunteer sat on the nose

Air PSI or bar correct? What about corner weights? Could the wheel not be balanced?

Quicker just to swap the dampers L<->R if they're set up symetrically. Since the handling problem is so obvious it should have been a good enough indicator.

But you should know what is was by now... we're waiting.