Here are some thoughts from the Engineer:
Hi Patrick
I’ve been analysing some of the data in more detail and what I have discovered is the following.
We have been using 45mm of rear damper travel at the track. This probably equates to around 70mm of wheel travel.
Unfortunately the car needs to have more droop travel through some of the higher G force turns. The inside rear wheel is lifting off the ground, this is the jacking effect that Paul was talking about, at the time we thought it was being caused by too much rebound damping and we removed some.
Factory setup have the droop controlled by the bolts retaining the outer torsion bar bush, your application probably has the rear droop controlled by a spacer above the piston within the damper so some damper or rear suspension setup mods will be required before the next outing.
If you look at the data particularly suspension position [position each corner in a new graph on the page] you will see that the lr suspension pots flat lines during some corners at around -22.
At this time the rear wheel is starting to lift of the ground and the rear will start to become unstable.
Your video also confirms this as you have to correct your line on entry , you were travelling 16 klms quicker than the previous lap and the gpsmap shows you wider on entry before the apex which all added to the event.
The rear end appears to be rolling more that the front but a more accurate measurement of motion ratios would be required before you could call this a fact.
Everywhere that the lr suspension starts to bounce off the full droop point is where you were complaining about a lack of rear grip so we need to rectify this before next outing.
If there are no spacers within the damper then we may need to get extended rose joints, Im a bit surprised that this has occured given that you bought the dampers to suit this application.
Mark
Rsport Race Engineering
When I put the concept of disbelief to the engineer that we were getting inside wheel lift on this corner he replied with the below paragraph. Unfortunately I can't upload .pdfs so I have put in a link to a thread on Rennlist for those that want to see the screen capture data from the shock pots.
See post #578
Patrick's build thread. (IT RUNS!) - Page 39 - Rennlist Discussion Forums
Hi Patrick
Please see attached screen capture. Unless the rear wheel managed to hold at exactly the same height for over a second on each of the three occasions as you turned in I would believe my comments to be correct. I think the wheel lifted on entry and you were a victim of the grip slide shimmy scenario on entry to the corner which caused your mid corner correction and subsequent running wide on exit. I'm not saying that the rear shock has definitely bottomed out but something has definitely stopped suspension droop at that point, the most likely scenario is that the shock has runout of travel but regardless the situation needs to be reviewed to see what has caused the suspension to stop its travel and cause wheel lifting at that point.
Please note if you look at the capture you can see a similar trait in the right rear shock as you leave the track at about the same level of droop.
The 'grip-slide shimmy' is when the rear end grips and then slides and requires steering correction to maintain line through the corner.
Also to note the car was running on 10.5" x 18" 285/645 front and 11.5" x 18" 305s rear. Brand new Hoosier R80 slicks. Also while we had a pretty decent front splitter on we haven't had time to put on the large rear wing so have only had what is known as a Hoop spoiler from the Factory. This could also have affected the balance front to rear.