My wheel fell off on a trackday

At 137 km/h coming into a long right turn, my inner rear wheel fell off. A loud clonk and I could see how the inner rear wheel was bypassing me! I slowed down slowly standing on three wheels and could keep the car on track the whole time. A guy ran out on the track to help me, and we could easily push the car out from the track by lifting at one corner while pushing.

The loose wheel had hit the rear wing rivets loose. Other than that, no damages at all! No scrape marks, nothing. I put the other set of wheels on and continued driving the rest of the day as nothing happened.

But how could this happen?

The wheels have been used three seasons. Magnesium centres are known for the need to be inspected every season - but this is aluminium and they're supposed to hold together. Then I noticed that the rear centres had larger bolt holes than the fronts!

I've emailed the manufacturer and got the following replies:

Cracks forming on the other rear

I have spoken to two other owners  with the very same design billets,  I think I only made 5-6 sets like your before changing to the later profile as  the power and weight of customer cars was  going up so I thought to beef them up a little, The two I have spoken to  have no problems and have used them now for three seasons hill climbing here in the uk. I do not have an answer for you why  there has been a failure, but I can Only assume fatigue, The later billets you have are now used on lots of similar cars to your including some saloon circuit  cars around the 850kg mark with no problems reported 
I am of course more than happy to send out replacement centres .

And later:

I see the  old wheel bolt holes are larger, this is because when I originally worked with Meteor  we were going tom use floating taper washer that needed a bigger hole, using these washer didn't work out so I changed the hole to smaller dia, the set you have were simply a set form stock that were used up.

I see the damaged inner rim. No problem for me to send a replacement under the circumstances.

After investigating the new design I'm confident they're much stronger than the one that broke, and I feel assured they'll hold. If you have similar wheels, I suggest you check them and see if you have the larger or smaller holes, and replace them if you do. If you have the new style centres I wouldn't worry.

I must say I got an immediate and professional response from the manufacturer, and they did everything they could have done in this situation. However, I don't think I should have gotten the weaker style centres in the first place.

New style centre from the inside.
 Note that this picture doesn't show that the centres are also thicker than before.

Old centre, with big bolt holes.

Tierp Arena

Great day! Great fun racing with some other sevens. Probably the last outing for the season.

My car is both wonderful and terrifying at the same time! Especially in the morning on a wet track with cold slicks... Ehh... The concrete barriers added another dimension to it. During the day the track dried up and I could start pushing, but I had most fun trying to overtake the red Westfield. I was faster but still it is very hard to overtake someone.

The alternator broke again. Since last time I let a local mechanic fix it 'as new' to a reasonable price but it didn't last long. I'm probably over revving it. In the winter I must change the pulleys so it rotates a bit slower.

My shoulders will be sore tomorrow!

Mantorp first time 2013

This years first trackday was a warm day with blue skies on Mantorp and a huge mix of different types of cars.

Things didn't go that well. It started with me being a bit late.

Then there was a Porsche that spilled oil on a long section of the track. (Those German cars....)
Then someone else went off and one corner was covered with gravel and the track was closed again.
When I finally got the tires warm there was too much traffic and no clear laps.

Engine problems

Lost top end power and the top speed on the straight was a bit too low. It got worse and worse, so I stopped driving and went home instead, worried that there was something very wrong with the engine.

When I got home I did some troubleshooting and found out the alternator warning light connector was broken, and that prevented the battery being charged. (Stupid design!) My speculation is that the battery's voltage went down during the day and caused the fuel pump not being able to keep up the pressure when the fuel demand was peaking, making the engine run lean. Running an engine like this lean is not good at all and could cause fatal pre-ignition.

I need some way to prevent this from happening again.

I would like to be able to log the fuel pressure, and have some warning system for a fuel or oil pressure drop.

Here is a video I found describing how voltage affects the fuel pump flow:
http://www.youtube.com/watch?v=RjykWzDr1Kk

Noise check

A couple of months ago I bought a cheap noise meter from Hong Kong, and today I asked someone to measure the drive-by noise of my car.

The guy told me it made 106.4 dbA!

In many race circuits in this country have from this season a drive-by noise limit of 95dbA.

I started measuring the other cars, and no-one, except a stock Corvette, was below that limit.

Then I moved a little, and all readings changed. Then the wind changed, and the readings changed as well. Then I realized I could not get the same reading twice for the same car.

It seems like measuring noise at a race track is not an exact science.

I refuse to think my car makes as much noise as 106db, but I'm not surprised I have to do something about it if I'd like to drive on other circuits. I just don't know what yet.

What about all the work done this winter?

All good!

The roll cage... stayed in place. 

The suspension bushes hold together. The car felt nice and precise.

The exhaust manifold was not leaking!

The silencer mounts did not break.

No oil spew from the catch tank.

Engine did not leak oil from the front cover

Overall the car feels wonderful. Too bad I was worrying about the engine instead of enjoying myself.

I did not have the aeroscreen mounted as I didn't think it would do much difference. At the end of the straight the force against the helmet was overwhelming. I must put the aeroscreen back on.

Gelleråsen end of season

Beautiful crisp autumn day at Gelleråsen. Crisp indeed. In the morning the temperature was -4 degrees C and there was frozen water on the puddles. I was running an old and square set of slicks, and the grip was close to nothing until the afternoon when the temperature rise to about +5.

It was several years ago I visited Gelleråsen and I can't say I know the circuit very well. It was lots of traffic and mixed slow and fast cars, and for some reason some of the slower cars refused to move aside when someone faster came from behind. One cars even used to block me. Why is  that? It is so easy to leave some room, and it it nothing worse than to wait the entire lap until the straight. At the end of the day I got a couple of clear laps and managed a good 1:10.1 lap! I'm sure that time can be improved by several seconds with some practice and better circumstances, but it is a fast time and I'm really satisfied.

Sleep tight

 A wash, a last short ride to dry the brakes and into the garage for the winter. No big plans for this winter, at least not yet...

Mantorp wear and tear

An humid day at Mantorp with rain in the morning and dry after lunch. One of those days when nothing felt good. I pushed harder and harder but the lap times stayed high and today's best time was 1:23.0. A Camaro cup team confirmed that the track was slower than usual because of slippery rubber from drift cars the days before. Still I didn't feel like I drove as good as I could have.

A couple of other things didn't go very well either.

Cracked wing with zip tie

First my right front wing went loose and cracked. Back in the pit I drilled a small hole and put it back with a zip tie. The next lap the left wing went loose...

The oil catch tank got full and spew oil in the engine bay. I don't know how that is possible but that is what happened.

The exhaust manifold sealant didn't hold and the leak is back. Another winter project.

The orange colour is where the pad material ends.

Rear brake pads worn out completely. I have ordered a new rear set of Pagid RS4-2 (1158 for my calipers). When the front pads wear out I'll try a different brand and see how they compare. I'm also considering installing a pressure reducer valve to rears and use the same compound on both ends. (Right now I use Pagid RS14 on the fronts and RS4-2 on the rears)

The A frame bushings are worn. At least I think so. When I brake I can see the wings move much more than they did before. I'm thinking of replacing them with Powerflex bushings during the winter, but they sure are expensive!?

One more trackday before the winter, this time at Gelleråsen. Lets hope it doesn't rain.

Mantorp - slicks vs CR500

Mantorp, again. A new personal best, again - 1.21,8!!! That is 1.5 seconds faster than last time, and I haven't changed anything except put on a new set of (second hand) rubber. I never thought I could reach laptimes like that!

At the end of the day I mounted a set of standard 15" rims with Avon CR500 tires just to see the difference compared to the Dunlop Radical slicks. 1.24,8 or 3 seconds. That is a big difference, no questions about it, but with the CR500 the car suffered tremendously from understeer and I think the difference would be less if I took the time to adjust the suspension to suit the tires better. Not to mention tires with better dry performance than CR500.

Slicks in red, CR500 in blue.

I also put zip-ties on the damper rods and that confirmed my suspicion that the front dampers bottoms out onto the bump stops. I don't know if it is while cornering or while braking, but that is something I should look into next time.

Riding on the bump stops is not necessary a bad thing. Read an article here.

Mantorp trackday movie

Movie clip from Mantorp this summer. Personal best 1:27.94!

Avon ACB10 tyres
Filmed with a GoPro HD