Earlier in the year Mumbo Racing visited Wakefield Park for the opening round of the AMRC. The circuit had just been resurfaced, and I was looking forward to driving on the smooth, grippy tarmac.
The meeting turned out to be a little confusing, and it wasn't until I received a CD of photos from the guys at Oz Event Photo that I was able to figure out what had been going on.
It all started on the Friday unofficial practice. My usually reliable Reynard 94D suffered an overheating problem in the first session. One of the coolant hoses changed position slightly and came in contact with the alternator pulley - the pulley wore a hole in the hose, and the coolant escaped. Some quick repairs to the car on Friday afternoon had it up and running again, but I had missed out on some track time, and not really had a chance to get an idea about the circuit - all I could tell was that it seemed quite slippery.
On Saturday morning, the official practice session came to a premature end after the car continued to overheat - although the problem encountered on Friday had been solved, we hadn't been able to completely bleed to the coolant system, and the airlock caused the engine to overheat. We were unable to bleed the airlock out in time to rejoin the session. We were confident that the problem had been fixed though, and were looking forward to qualifying.
Well, qualifying came, and I had trouble coping with how slippery the circuit seemed. I completed a couple of uncharacteristic spins, that happened in a way I could not explain. I managed third fastest, but was disappointed with the time I had set, and unsure why I was slow.
Raceday came, and the first race started reasonably well. I moved up to third place, but on the seventh lap I spun part-way through the fish-hook corner. It felt like I was nowhere near the limit of rear-end grip when the rear lost grip and the car spin. In the course of making sure I moved clear of the racing line I stalled the car, and was unable to restart. I was out of the race. And out of ideas as to why I had spun.
In this case, and the couple of other spins I'd had during the weekend it seemed to happen in each case as I released the brakes. The car seemed to have quite a lot of understeer on corner entry, and just as rear grip should have been increasing (as I eased off the brakes into the corner), the rear would break away and I would spin. It didn't make sense.
I started from the rear of the field for the second race, and made my way forward to fourth before the earlier problem with the coolant hose reared its head again - the coolant hose was punctured and I was out of the race.
When I got the car back to the workshop, I solved the coolant hose problem very quickly - I fitted a bracket to keep the hose clear of the alternator pulley.
I was still pulling my hair out over the handling problem when the CD of photos arrived from Oz Event Photo. On the CD was the photo that appears above. As soon as I saw it something caught my eye: The front wing looks like it is touching the ground.
As soon as I noticed that I came up with a theory. I thought it may have been possible that the front wing was touching the ground under brakes. This would unload the front tyres, causing them to loose grip, leading to understeer. The understeer would only be present while the wing touched the ground (ie; under brakes). As soon as the brakes were released, the understeer would disappear, and the front tyres would be turned at a greater angle than normal (to overcome the understeer) - this would have the effect of very quickly moving the front of the car in the direction it was being steered, and possibly cause the rear tyres to exceed their maximum grip - ultimately leading to a spin. This sequence fitted exactly with what had been happening at Wakefield Park - just at the moment I would expect rear grip to increase (easing off brakes to transfer a little weight back to the rear), the car would spin.
Another sequence of photos from the CD showed the whole thing happening. Click here to view the sequence.
I thought there would be one easy way to prove this, and I raced to the workshop to have a look at the underside of the front wing.
Sure enough, a hole had worn through the underside of the wing where it had been contacting the circuit. I set about repairing the underside of the wing, and altering the mounting of the wing to make sure it was high enough above ground level.
So, how had this happened? I suspect there are two factors:
1) The wing had been a little low for a while but the increased grip on the new Wakefield surface allowed caused a little extra deflection in the suspension, allowing the wing to come in contact with the surface - more grip making it look like there was less grip!
2) I fitted new Yokohama tyres for this meeting - whilst they appear to have a very slightly higher sidewall than the Dunlops I had been using, it's possible the Yokohamas have a slightly softer sidewall, allowing more deflection, and allowing the wing to get low enough to contact the circuit.
Why didn't I figure it out sooner? With the other distractions (holed coolant hose, overheating), and limited track time, I attributed the spins to my own difficulty coming to terms with the new surface. It didn't even occur to me at the time to look at the underside of the wing - if I had, I probably would have figured it out.
Next time around, you can be sure the same mistake won't happen again...