FLA997

In looking at the original edition 2010 Cup manual, the center bolt torque specs are cited to be 490nm. (see below circled in red from the manual).

Three years later Porsche Motorsports sends out a bulletin updating the torque specs for the center bolt to be 50nm (and subsequent torque procedure for replacing a center bolt).

My question is, what did Porsche learn in three years that significantly reduced the torque spec on the center bolt from 490nm to 50nm?

Failures from such high torque loads?....or am I missing something here?

McRae

Performance. PAG finally caught on to what all the top cup teams had been doing for many years.

CRex

^ Would you mind explaining... how would a looser center bolt (assuming we're talking about the spindle to which the wheel nut mounts) contribute to performance? I'm still scratching my head as to how the wheels can stay together with merely 50Nm...

smf32s

The higher turning force on initial install pushes the bearing on. Then you back off and tighten to 50. Then you put the collar on which holds it in place. The lower force causes less distortion and wear on the bearing you just forced on.

This must have caused issues in wear on the bearing over time.

Stu

McRae

The higher preload of the wheel bearing is what's recommended from the bearing manufacturer for maximum lifespan of the bearing, hence why it has been the Porsche recommendation.

What we figured out is that it also makes the rolling resistance from the bearing much higher, i.e. the car is a bitch to push around in the paddock. Go down on the preload and it will roll easier, which means you gain speed. It's not a huge difference, but in hardfought championships every little thing counts, when you have 20 cars qualifying within a second those things matter.

It was quite fun to always lend a hand helping move cars around on lineup/parc ferme, to see who had done the same to their cars, because you can feel it...


BTW, the bearing lifetime will go down with the looser preload, but still within the set lifelength of 30H normally.

claykos

Does this also apply to the earlier 996/997 style centerlocks which use the smaller wheel nut?

FLA997

Thanks McRae...makes sense now. Quite a swing in torque spec.

McRae

Yes. We first did it on 996's, so its been around a while...

cid042

I fear that I do not really understand. Does that mean that I should tighten my wheels (08 cup) to nearly 10 times less than I do now ?!!!

McRae

No Cedric, absolutely not! This is not about the wheelnut torque, this is for the stub axle that you then put the wheelnut on. Try to use that little torque on a wheelnut and you'll end up with a Morgan! Morgan as in three wheeler...

Bill Farrell

Does the Stub Axle need to be re-torqued after approx 100km (to adjust for stretching of the components during stress ?).

Is the Stub Axle torque reduction a response to the left rear Stub Axle Failures that have impacted so many cup cars ?

amso3

The above stated torque requirement change was not a performance issue, but a drive flange issue on the 10 and 11 cars, just as Bill has suggested. Porsche has never (to my knowledge) suggested that these torques be used on 09 and earlier cars. If in doubt ask PMNA before you do this on earlier cars! Not everything you read on the internet is true.......

fstockcarrera

Crazy. I just broke the end of the LR axel today @ Lime Rock in the down hill @ 100mph. I manage to keep it off the wall. BTW Blk 996tt axel with about 40hrs. Guess they are a one season disposal item. Dan J did suggest a much lower torque. about 100 ftbl i believe. I don't think the center bolt torque was the issue , but what do i know. Ideas? Bill also broke the same in the toe @ WGlen last year. I replace the center bolt each winter.

cid042

Thanks Ranald. I was quite sure I had misunderstood something... ;-)

claykos

I'm somewhat intrigued by this because my 996 seems ridiculously difficult to push.