Tried the gear diff, but...

[yellowshark]

We tried the gear diff for the 1st time this afternoon (XRAY diff with 1000 oil).
It was very planted on the fast corners, i.e. the 1st and the last but somewhat loose elsewhere. I am kind of assuming the niceness of the fast corners was due to both wheels spinning together and of course helped by the rear wing downforce. The handling on these two corners seemed better than with the ball diff.

For the 2nd run I corrected the front two body mounts which were lazily one notch higher than they should have been and I laid the rear shocks down one notch (never had them laid down that far before).
The result was a bit more bite on turn in, guessing the lower bodyshell, and whilst the rear was still loose it was smoother, more predictable.

So what to do?; I put the stopwatch on the 2nd run and the car was real slow with at least half of the 20 laps or so in excess of 16 secs with the rest between 16secs and 15.7. Last Friday we were doing sub 15 secs on most laps. I was going to fit the ball diff for the 3rd run to make a comparison but the rain came down.

With a loose rear end I would loosen a ball diff but going to 2000 oil is the reverse so my brain hurts. Could it be that with 1000 it is just too loose and one of the wheels is spinning right up as we exit the corner?
Any comments appreciated

[lesbaldry]

Pete I wont delve into the Xrays handling as my experiance is only with the 008.
From what I remember and see of the Xray its a very"steery" car anyway so a gear diff will only exaggerate this and TBH your set up's always look a little twitchy to me and hard to drive
Fitting a gear diff to my TC6 for the first time some while back was an eye opening experience,basically I had to de-tune the steering some,set the car up "a little dull" to drive, fit the gear diff and the car then comes alive
As for oils,they make a big difference! Presuming the Xray diff has roughly the same size internal gears as my Spec R, 1000 is a little light,it will certainly feel smooth and free but will "diff up"(spin up the unloaded wheel) very easily in low grip,bumpy tracks dont help mater's either should a wheel get lite or airborn!! 2000 on the other hand will feel a little "gummy" but should give better traction,this may sound a little odd and opposite thinking but it works! you may want to try a compromise between the two grades!
It took a while for me to get used to the gear diff and an adjustment in driving style may be needed

As for set up changes to suit the gear diff's feel, try killing the steering a little(dial in some understeer) and let the chassis roll with geometry rather than springs, IE low roll points but slightly heavier springs ,especially on the rear! this worked on the TC6 " for me"... Basically I run quite low roll points and fit the same rate front spring to the rear.Also depending upon track and conditions I sometimes favor quite a heavy rear roll bar,1.5mm same as the front,this "I feel" helps to keep the rear "flater" and the rubber on the deck with less chance of "diffing up" during the on power roll... This may sound a contradiction for better grip/traction and my suggestion of increasing the chassis roll but a roll bar affects the chassis roll in a different way to roll points as do springs,good luck and I hope this helps some .......Failing that ask Reuben his seems to work well

Ps Ian Newton "the original throttle jammer" tried one a little while back and loves it!.....but I did break his thumb in three places befor he fitted it ;D

[yellowshark]

Thanks Les that was really helpful. As you say Craig likes to live on the edge ;D and we can and do get caught out by rapid track or tyre changes.

Now I know that the gear diff will be adding steering and it is not just us I can start working on it.

It wil be interesting to see what Reuben says as an XRAY owner

Unfortunately though with the rain today I am rapidly running out of time to get some testing in before Aldershot

[lesbaldry]

Aug 18, 2011 13:14:26 GMT yellowshark said:

Thanks Les that was really helpful. As you say Craig likes to live on the edge ;D and we can and do get caught out by rapid track or tyre changes.

Now I know that the gear diff will be adding steering and it is not just us I can start working on it.

It wil be interesting to see what Reuben says as an XRAY owner

Unfortunately though with the rain today I am rapidly running out of time to get some testing in before Aldershot

No prob Pete....The gear diff I feel is an advantage at Aldershot with its good power on steering so is prob worth you trying in sat's three timed practice rounds....see you there,Ian will be there fri to get the Gay bo up in pole position

[Reuben]

On the Xray I do the following when fitting the Gear Diff:

Remove 0.5mm from the front Outside hub shim (to induce a little understeer, stop on-exit break aways)

Increase rear roll bar to 1.4mm from 1.2mm (you will be carrying more speed into the corner with a GD, so need to stiffen the rear roll, this is to stop it reaching its maximum load as fast and breaking traction)

Increase rear droop by 0.5 - 1mm to prevent it diffing up.

But my Gear Diff is the Spec R one so I use the 50mm rear drive axels (which give less grip than the standard 52mm ones).

1000 weight oil and learn to live with it.