Things I Learned From a Photo

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.
Taking the final corner at Wakefield Park

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.

The scars that proved the theory
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...


Neil Byers Mitsubishi 380 ran briefly in practice
Mumbo Racing visited Melbourne's Calder Park last weekend, and came away a little disappointed.

Problems began almost on arrival. Neil Byers' Mitsubishi 380 hit the circuit briefly on Friday, and was flying. It didn't last though, part way into the session the engine appeared to go into limp home mode - enough to get Neil back to the pits, but no further. Despite valiant efforts by the team, the problem could not be corrected. Something in the engine was: broken.

Sam Dale fired up the Reynard 94D for the mid-day session in Oz BOSS, he trundled to the dummy grid, and was told to shut down because a car from the previous session was going to take a long time to retrieve. When the signal was given to start engines, Sam went for the starter but achieved only a click. The car refused to start with or without the jump battery. The team attempted to push start the car, but the rear wheels would simply lock up when the clutch was released. Closer inspection revealed that the starter motor was stuck in the engaged position. The team pushed the car back to the garage for repairs, but on the way, Sam managed to get his right foot under the left-rear wheel of the car. Sam's foot lifted the rear of the car about 8 inches off the ground. The car had rolled over the top of his heel, and forced his foot over on itself. Sam hobbled back to the garage, and the rest of the team pushed the car.

The starter motor was easily fixed. Sam's foot on the other hand appeared to be: broken.

Strapping and race tape was applied to Sam's foot to make it fit inside his race boot, and he proceeded to teach himself how to left-foot brake, and downshift without the clutch. The biggest problem was that the swollen, purple right foot was very bad at providing feedback, making it hard to modulate the throttle application when exiting corners. Nevertheless, Sam qualified 3rd outright, and 2nd Oz BOSS car.

The output shaft from Sam's Reynard 94D
Raceday came, and it had rained heavily overnight - the circuit was still damp for the first race, and conditions were extremely slippery - calling for a delicate touch on the throttle... Sam took the rolling start gingerly, and gradually found a rhythm. Until 8 laps in, when the car lost all drive as Sam shifted into 5th gear on the main straight. He coasted to a stop, and retired from the race. A quick inspection revealed that no gears would engage, and there appeared to be terminal damage, with minimal gearbox spares carried, the car was loaded into the trailer: broken.

From a competitive standpoint it was a disappointing weekend for the team, with no races finished. But there are always positives, and they are what we prefer to focus on when there are problems. We all made it to and from the track safely (except for Sam's foot), we debuted a brand new trailer for the Reynard 94D, built by Roger Perkins from Ty Hanger's team - it performed faultlessly and is expected to serve the team well into the future. And most of all we got to enjoy the camaraderie that we look forward to leading into every race meeting. Everything else can be fixed for next time...