RacingFlyer

pm sent.

AScholtes

I would agree, but not with the reasons you stated... instead, here are a few reasons that would be more of and explanation..

1: age (metal fatigue)
2: driving conditions (hmmm, sports car, corners, spirited driving goes hand in hand)
3: suspension upgrades (stiffer) transferring greater loads onto the hubs...

IMO, this would be the most likely causes for this type of failure...

m73m95

Well, Metal doesn't "age" like you're thinking. If anything, it becomes stronger with use. Are you afraid to rev your ~25 year old engine to 6k rpm? What if the rods/pistons are "old"?

The driving conditions are indeed part of the equation... But, Porsche's are designed with the track in mind. The problem is that "go fast" technology has evolved past our 25 year old cars. Stickier tires, and not only stiffer springs, but lowered cars, solid bushings all contribute to the stress the hubs weren't intended to absorb.

And, I did mention springs being a contributing factor.

225 isn't that wide of tire. Slicks are indeed sticky, but I'm leaning more toward the 500lb springs. That is STIFF dude!


I wonder how much time is lost per lap with #300 springs, instead of #400-500 springs? What springs did the "real" 944 turbo, or 968 RSR race cars use? (asking all of RL with actual track time... not just the OP). I'd like Tony G's comments, if he's reading this.

I don't have the track time as a lot of our RL members, but I am a decent fabricator. With some really good feedback, I think something could be done to improve the suspension for track cars....if its something track guys would be interested in. Using the monster springs to correct the camber is just chasing your own tail. With #500 springs, you could just throw the front sway bar in the trash, to save weight. New GT3RSs don't use #500 springs.

Oddjob

Hub failure rates may potentially increase with the number of bearing race changes, which is common on track cars. Pounding the races in and out of the alum casting, along with the high loading of track use can and does generate fatigue failures in the hubs. The cracks often start at or near the inner bearing race lands.

Cyclic loading will not work harden an aluminum casting: http://en.wikipedia.org/wiki/Fatigue_(material)

500 lb/in spring rate is quite moderate these days. A lot of 944 track cars have been up in the 700-900 lb/in spring rates for several years now, and all are using sway bars....

AScholtes

Not saying age as in its old and fails just because it is old. Age as in, it has seen alot of miles and stress placed on it, and yes, since it is a sports car designed to be pushed, which is exactly what fatigue failure comes from.

As to your stronger thinking, do not confuse stronger with brittle. Metal does not become stronger by getting used, it gets more brittle, yes.. It also gets more brittle as it oxidizes and ages, aluminum is especially famous for this. Every time a cast part flexes it develops micro-fractures in the metal that eventually leads to failure.

I see this type of stuff every day in my line of work with old machines.

Lemming

+1, most of the non-spec racing 944's are well past the 500 lb mark.

m73m95

Cast anything doesn't work harden.... but it doesn't age either.

The bearing/race idea is something to consider though.... I would think that the reason all of the hubs start to crack there, is because that's where the load is....

I understand that, but that doesn't mean its right. Using that heavy of spring is missing the point of what suspension is supposed to do in cornering. Its not about weight transfer at that point. Why not just run high bump stops, and run the car on those, like NASCAR sprint cup?

From what I've read here on RL, and heard from people that have talked to him, Tony G's "goal" has been to keep up with modern GT3 cars...which I think he pretty much does. However, the places around the track that he loses time, is due to 1. our dated suspension design, and 2. having to use too much spring to compensate for our dated suspension.

If something could be done to our cars to allow the use of "proper" springs, it would be easier on components, easier on tires, and drop lap times.

reno808

What kind of wheels are those?

Oddjob

Old thread on the hub failure subject:

https://rennlist.com/forums/showthre...ferrerid=15894




Since Lemming and I apparently have no internet credibility, go test this theory over on the racing board. 996/997 Cups are running up to 1500-2000 lb/in spring rates.

Useable spring rates have a lot to do with tires. The more grip the more spring you can or need to use. The higher cornering loads (from higher grip tires) will increase fatigue on the car. Running lower spring rates, lower grip tires, etc (driving slower on the track) will decrease loading and therefore reduce failure rates of the suspension components and tub itself. But then you end up at the back of the pack, so why bother racing if you do not want to be competitive?

AScholtes

You have to remember that youa re dealing with a kid here that has no real experience in suspension setups for racing... Experience comes from racing and years behind how to do it without breaking things

I've had my share of breaking things in other makes that were't as expensive to repair and it nearly drove me into bankruptcy... I have since learned that my pockets are nowhere near deep enough to do it anymore, and especially not on a P-car...

ehall

Lol.
That's the thread I mentioned back in my post. Glad you were able to find it. I thought you had a prominent role in it.
I hope you get some "racin sperience" soon.