Looking at the wheels I have I noticed that there is a lot of extra weight in the center hub area and in the spokes that looks like it could be cut off or out to reduce the weight of the wheel.
Has anyone ever done this or know of someone that has??

 

Sounds too risky to try, imagine the failure that could happen. Balancing it could be difficult as well.

 

Are you serious?

Assuming you are .... It would be a massive job to do the engineering calcs to verify your safety (unless you are a mech engineer and familiar with the calcs).

Would be easier to buy new wheels where engineers have already done the calculations. The OZ Alleggerita from Tirerack are light & cheap.

 

You would better off finding some magnesium wheels. I would not alter anything that has to do with a wheel. There are numerous ways to reduce weight in the 964, hacking a wheel to do it would be the most unsafe thing to do.

 

Ok - I hear what you are saying and understand your concerns. But, the point is that the wheels we buy are cast wheel for the most part and then machined to fit the hub on a certain type of car. In doing so they leave a lot of extra material in the center hub area and they also leave the wheel itself thicker than necessary - wheels are over engineered, on the safety side. There is room for weight reduction without crossing a safety threshold.

 

I would think that you would want to minimize rotational mass. Cutting weight from the center of the hub wouldn't do that. I'd focus on lightweight rims, tires or both. Cutting away the margin of safety would be extremely difficult (for reasons other have stated) and provide little benefit. This is my opinion and I have little education or real world experience to support it.

 

Weight reduction benefits would be gained closer to the diameter of the rolling mass, not the center. That is why you see cast "pockets" toward the bases of the spokes (nearest the rim portion of the wheel) on "hollow spoke" porsche rims.

 

There is both science and art to getting aluminum castings to solidify and cool without cracking or warping. Release some residual casting stresses, and you may cause problems even remote from the cuts.

Unless you have a lot of knowledge and experience with that exact casting, I would recommend leaving it alone.

 

When I was racing off road and rallye I have seen a lot of folks turning their wheels to reduce weight. Momentum but also reduce suspended mass. I've seen factory team doing that (Porsche was providing drivetrains for Lada and I remember well chating with a guy from PMS telling me these wheels were turned differently depending on the application - lighter to stronger) so while the liability is high and you should really consider this if you plan to put some modify wheels on the road, there's nothing against that if you know what you're doing, at least on track. I've retained myself from building carbon wheel for the this reason.
The momentum will not change a lot on acceleration/braking however the weight of the wheel becomes more important - especially on a lightweight car- on bumpy road which is what rallye and off road are about.
I don't see the interest in the street or on track where huge brakes are tolerated (look at the weight of big red setup including the heavy rotor) while we use smaller brakes for rallye and baja.

 

If you're really serious, go mag. I couldn't believe it when I held to identical wheels, one mag, and one aluminum. Guesstimate is 1/3 to 1/2 lighter. I'm sure someone can give you real numb ers.

 

Where do you find those magnesium wheels? I saw a set that went for $5K - I think.

 

You may want to study this table. It shows the relative weights of different wheel designs.

http://members.rennlist.com/911pcars/wheelwts.html

 

A general rule of thumb is cast magnesium is 1/3rd lighter than an identical cast aluminum wheel. However the magnesium versions vary in design over their cast brothers and the alloy they use is high in aluminum content so on average we see about 20% weight reduction for factory aluminum vs magnesium wheels.

example cup I 9 x 17 factory wheels
aluminum weight is 25.96 pounds
Magnesium weight is 20.46 pounds
So roughly a 21.5% in actual weight savings of its aluminum counterpart.

I would never consider altering any wheel. If everything is not done perfectly (inferior machining alone) can cause a stress riser that could result in wheel failure. It would also render the wheel unsellable to the average buyer. You might as well consider a light weight wheel replacement but then you have to consider where the weight was reduced and will that result in bent or damaged wheels from average driving.

 

Not so sure of the accuracy of this chart. if they are talking factory speedlines 3.6 wheels in the sizes they have listed the are not close to the 50 & 56 pounds they are claiming. Actual weight is 25.4 pounds for the 8" and 28.6 pounds for the 10" wheels.

 

The Mags in Europe go for $8K plus depending on condition. Fikses are a great alternative.