Round 2 - The View From the Garage
Updated: Sep 7, 2022
By now most people will have seen our round 2 results and be aware that things did not go as smoothly as planned. However, from the tougher events does come some of the most valuable information - and 3 Sisters was no exception to this.
The first bit of info we were able to gather at 3 Sisters was a second chance to try the car out with the Whiteline front antiroll bar. We first ran it at Pembrey with some undesirable results, and 3 Sisters was a second chance to run it after Ian had been able to familiarise himself with the new front end setup.
After a couple of runs we can only conclude that the Whiteline is just way too stiff for the job; it kills the front weight transfer so much that he was having trouble initiating with it connected. We have managed to source a lighter sprung ARB and will look into reducing the spring rates at the front before round 4, when we can re-run some of that testing at Pembrey.
At the heart of the trouble we had at 3 Sisters was the failure of a custom front steering component that we have been developing, this pushed us to refit the old pre 2020 setup and go back to the old castor and trail settings. While an interesting bit of A-B-A testing I cannot say it is something we ever want to repeat, the old setup is just so much worse that it was immediately obvious in the way the car moved on track.
Sometimes it's only when you are forced to go backwards can you really see how far things have come. The lack of front end performance we believe is part of the reason for the rear end shaft and diff cup failure we saw, as the driver was having to work the car so hard just to keep it sliding around the tarmac.
The smoke stops when the drive shaft quits.
Which leads me on to the big one, our broken prototype.
Some time back in 2018 we undertook some work to resolve the issues around the e36 non-m hub on the e30 chassis, the work and learning there spawing a package of changes to improve the front end of the FPP e30 drift car. Part of that has been the development of a set of roll center spacers that modify the geometry of the front end, slightly adjust the ackerman and cure some of the issues the E30 chassis has when sliding.
The spacers we have had on the car for the first couple of round this season were a first gen prototype that were quickly machined during the winter of 2021, it was only ever intended as a short lived part before a better revision 2 was done - however we were not expecting to be replacing it this quickly. With some careful analysis of the broken part we think there have been two key things contributing to the issue, as the base design was well under the max stress we would expect to be required to break one this quickly.
Firstly we think there may have been a mixup with the material. When designed it was spec'd as 8062-T6 aluminium, however it is possible it was machined from 6063 due to supply issues during 2021's winter. Not ideal as this will have knocked off near 30% of the expected strength. Secondly it looks like the bolt through the hub may have worked loose. It was torqued up when fitted but was not checked between rounds, admittedly that one is on us. A close look reveals wear marks between the round spacer and the main body of the roll spacer, additionally there is a piece of aluminium that has peeled from the surface inside the counter bore just where the head of the bolt rests.
There is a high chance with a slackened bolt and some movement happening on the back of the hub, that the spacer was subjected to loading that it was just never designed for resulting in rapid fatigue on the far side of the counter sink.
Armed with this knowledge we have been able to return to the shop, run through some FEA simulations to figure out what was needed, and get a version two machined in time for the upcoming round at DriftLand.
While we still think the V1 was strong enough for its designed loadings, we cannot accept a part with the potential to fail like this so the V2 has been beefed up in all the critical areas, peak stress in breaking and cornering has been reduced by 70% and certified 6082-T6 bar stock has been used to machine them. Roll on Round 3!