Session at brands whilst I had 4 wheels

Good video! That white FRS looked quick in a straight line.

 

The flames made up for it though! You should teach that dru guy how to drive at a track day!

 

Nice video. Short circuit the Indy one but I really like it. As said the focus looked rapid on the straights.

Hope your car gets sorted quickly so you can get back out again.

 

He nearly fucked up @ 2:26 >.<

I think I recognise the car though, if it had a big brake kit I think I drove Cadwell with him last year some time. Bit annoying for you no doubt in the first half of the video as you seem to just be dodging or waiting behind traffic and you're taking much better lines than everyone else it seems.

 

Ouch!

There's no way I would use one of those stud kits on track!

 

I've been thinking of reasons why all the 5 bolts would have sheared in your hub (i'm a mechanical engineer by day and some of my day to day work involves part failure investigation on high-speed diesel engines - i'm also the guy on Facebook who wrongly surmised cold rears through Paddock punting you off...I can see from your laps in this vid that was never going to be the reason!!!) but did wonder if running/kissing the curbs through Surtees has massively increased the shock loading though wheel hub and in-turn caused stress fracturing of the studs. You can see that all the bolts sheared in the same way so maybe the cascade effect of one failing caused them all to fail under braking into Paddock as the front left was fully loaded. Just a theory...

 

Yep, that FRS was nippy, what power are you running?

 

I would say that racing studs would be 12.9’s and not 10.9’s, but even then they may have bespoke beefier hubs to cope with the additional forces. Rob Baker (who owns S2 Smarts in Watford and races and Fortwo and Forfour) showed me the O/S front wheel studs that sheared on his whilst he was shakedown testing at Bedford. The supplier was supposed to have sent 12.9’s studs but sent 10.9’s by accident. His sheared under braking approaching the left/right along the back straight. He’d correctly tightened them too as this wasn’t his first rodeo…like you!
It’s hard to see from the photos if one or two failed first and the others just let go fractions of a second later but it does look like two opposite bolts failed first due to fatigue and the others went with it but almost being twisted/torn out. The surfaces at two opposing bolts look different to the other three. The opposing two look to have one light and slightly grainy part (a tiny fraction of the surface) and one darker and more smooth (most of the surface). The rough grain is the final overload region and the shiny more uniform portion is the smooth fatigue region. The other three look to just have torn right out of the hub as the wheel tried to keep spinning but the brakes were slowing you down.

I wouldn’t have personally thought that these bolts should fatigue that easily as you’re hardly hammering the curbs, but it’s the only side you really touched it on. I would have thought that there should be a finite amount of times that a stud is torqued and re-torqued before they need to be replaced, but I’m guessing that David/Ktec wouldn’t know this unless specified by their manufacturer. With a critical component like this, we’d bin and replace after each use if using a bolt on one of our engine parts to prevent this exact situation from occurring – a bolt shear that is, not a wheel falling off on track. A bolt/stud has to stretch during torqueing so there is only so many times that you can reuse it.

What have Ktec said so far? I’m guessing they’ve no idea it’s probably a first for them too!

 

Very odd. I run 20mm spacers and longer studs on my Porsche 944 race car. The ones I/we use are the mega cheapo ones as you can see on the Demon Tweeks website, the spacer isn't even hubcentric but a generic 5 hole one. The outfit that built much of my car have used these on at least 20 Porsche race cars most of which have been hammered very hard over the past decade. I don't recall ever seeing or it being mentioned about a spacer/stud failure. What I have seen is Porsche's own over-engineered components failing, at least two cars snapped front alloy wishbones under hard braking. I know of another car ISTR a 924 where the rear wheel bearing (pressed in monster) had failed taking the wheel off.

Sounds like you were unlucky and had one of those 1:1000 or whatever their quality rate is duff studs but I am very interested to hear what the rating of those studs are as I am considering a set for my R26.

 

The Ktec ones are M12 x 1.25 10'9's so should really be more than up
to the task.

 

Does converting to studs and steel nuts make a difference? Its what I have on my 944 anyways and the guys running boxsters have that to think about as those cars like many modern cars run bolts as stock.

 

Just easier to change wheels. So easy that they'll even change themselves