360 wheels: Shaving the back pad of the wheel to change the offset?

Fred,
I am curious about this altering of the wheels. Isn't there a big liability issue to get past by anyone "shaving" material off a wheel? It would seem to me that any alteration that could result in a weakening of the strength of the wheel is exposing one's self to a big lawsuit no?


Sent from my iPhone using Tapatalk

 

There is a shaved set of 360 modulars available above in Ferrari Ads.

 

If you were shaving off a couple of mm I could see it, but what percent of the thickness is 10mm? Seems like that could significantly weaken the wheel and if you drive the car hard the thing could fail.

 

No problem. Just don't forget to shorten the lug bolts!

 

I have a 1990 Mondial T. The previous owner put 360 Starfish rims on the car. He had 10mm shaved off the inside of the rear rims so the tires would clear the fenders. The fronts are not modified.
I don't track the car or race in any way. I have had the rims off the car and inspected them for anything that might show crack, etc. Nothing shows. I have had the car for 18 months. I believe the PO had the car for 13 years. I don't know how long or how many miles these particular rims have been on the car.
I will say that front rims are subject to much more stress than the rears especially when turning. I would have a master machinist give an opinion before assuming the fronts can be shaved 10mm without consequence.

DavdiJ
Image Unavailable, Please Login

 

If you are talking about removing material on the inner surface of the hub it is a big mass of material. I can't imagine that it would be a problem but I am not an FEA type engineer. Just the gut feeling says you are OK. Of course there are brake calipers and inner fender features that could put the kibosh on the deal.

 

I was not formally educated as a machinist. My education is that of an engineer. I can tell you that answering your question with absolute certainty would be very difficult if not impossible for a design engineer who makes his living studying such things. That's why testing is such an important part of wheel design when the "real guys" do it and I doubt if you intend to test your wheels on some sort of test rig.

Yes, good machinists have a "feel" for the strength of materials, but relying on a machinist for a real answer is likely to be less reliable than getting an answer on the Internet, keeping in mind that anyone can post anything they like on the Internet. Nothing against machinists, but your question is quite far outside the educational background and expertise of a machinist.

The fact that someone has done this, or something similar to this, is a data point. But it may or may not be a "good" data point and it is far from a guarantee of success.

If I had to guess, I'd say you'll most likely be OK. But that advice is worth exactly what you're paying for it. The advice to not put too much faith in the opinion of your machinist is more valuable, even though it's also free.

 

What Ferrari do you want that you'll shave the front rims? They should fit as is for most...

 

FredWhiteAndBlue:
As part of a ongoing maintenance program I would have the rims checked at least once a year after taking the material off. Look for small cracks at the lug nut holes. Extra checks if you hit a big pot hole. You would not be happy if the rim broke at speed.

I glad you now appreciate the Mondial. The car is much better looking in person than photos.
One more for ya (I know I'm a show off!):

DavidJ
Image Unavailable, Please Login

 

Here is my 1995 348 Spider with Starfish wheels (unshaven/ no mods for fit).
I feel the same about showing off my baby!
Image Unavailable, Please Login
Image Unavailable, Please Login

 

My gut feel is that this is a bad idea. However, if the machined part is only the hub and not into the spokes -- then maybe it's okay.

 

I had 360 wheels on my 348, and will probably put them back on next time I need tires.

What I remember is that the front wheels did not have any excess hub material, and there was very little clearance between the wheel spokes and the brake caliper. In other words, no possibility of shaving the front wheels, at least for the 348 application.

- Eric

 

I have a 1991 348tb and in order to have the 360 modular wheels fit properly in the wheel wells I did what others have done, which was shave off 18mm.

http://www.ferrarichat.com/forum/348-355/333963-360-modular-wheels-348-speciale-done.html

http://www.ferrarichat.com/forum/348-355/194194-348-before-after-wheel-upgrade-2.html

The hub on the 360 rear wheels is huge. The wheel guy I've used for several years, showed me the rears still had more material left after shaving then most stock wheels he has seen. My understanding is that if you have a 93SS or 94-95 spider, you don't need to shave off anything as the stock wheels will fit fine. The car felt great and looked awesome.
That being said I decided I liked the smoother look of the 355 wheels and went back to them. My 360 modulars are currently on sale in the classifieds section which includes 20 non OEM chrome bolts that work perfectly for 89-92 348's.

http://www.ferrarichat.com/forum/ferrari-parts-collectibles/428091-ferrari-360-modular-wheels-348-a.html

If I don't sell them I'm toying with the idea of having the centers painted gold and just keeping a second set
Image Unavailable, Please Login
Image Unavailable, Please Login

 

360 wheels make just about any Ferrari look better, even my 308.

But shaving any metal on such a highly stressed part is something that needs an engineer to assess.

When wheels are designed, there are all kinds of considerations taken into account:
vehicle weight, tire adhesion capability, metal fatigue, margin of error for "acceptable" manufacturing defects or variance in tolerances, allowing for some amount of curb rash, pot hole, curb impact degradation yet still maintaining "enough" strength to carry on.

BBS is a very highly respected wheel manufacturer, producing some of the best production wheels.

Any honest engineer is going to be very reluctant to accept the liability for sanctioning a wheel modification.

So, perhaps the next best approach would be to talk to those who do modify wheels for a living.

I was a bit apprehensive about narrowing the rear 360 10.5x18 rims to fit my car and also equally concerned about installing spacers and longer wheel bolts.

I liked the look and needed more room for bigger brakes as well as being able to fit modern high performance tires.

my best recommendation is to talk to guys who do wheel mods every day, professionally. The peace of mind would be priceless.

I will post the wheel mod company when I have the chance to go back and get the info.

Meanwhile, here is my baby
Image Unavailable, Please Login

 

How thick is the back hub? I would do some research on various wheel companies and see what their hub thickness is. Find wheels using the same wheel material, construction, and spoke shape.
Good luck
CK

 

I think what happens when you start modifying is that you start chipping away at the safety margins. Lets say that a detailed analysis reveals that a certain mass is required to hold the forces that are expected. A safety margin of three would make the part or section 3 times as thick. It's been years but I recall a safety margin of three when we designed for fighter pilots (for the portions of airplanes that I worked on disclaimer). You should be able to make a reasonable shave to a hub if similar safety margins are employed for autos. Someone from Detroit please chime in. So this means that the rim will fail before an over designed rim but with safety being what it is I would think that normal use is not going to be a problem. Non-track use I see no problem. Just as was pointed out earlier my opinion is worth what you paid for it but I would do it if I wasn't cutting into the spokes including the transition area between the hub and spokes. If its a radius transition and I was leaving a little material on the hub before the radius begins I would not have any issue myself, but that's me. Sure you slide into a curb at 110 the rim will fail, but a failure at this point should be expected. YMMV

 

Fred,

I bet Daniel at Ricambi would have all the wheel info you need & may know of a potential source to obtain the drawings for the wheels. Which would help for the machining/mod material removal calculations.

 

It will probably be fine.
I looked at my 360 fronts, and they appear to have 9-9.7mm of pure spacer material. You've got big lightening pockets left cast in there already, the first level of which is that depth.

How does removing that much material affect your hub depth for centering? That may require attention so it will still fit on the hub.

It's dark and cold in my garage. I didn't give a ton of thought to load paths.

I've removed material from the hubs of a set of wheels before; the pros at Weldcraft Weldcraft Wheels Wheel Widening Wheel Repairs Wheel Restoration shared my assessment that those particular wheels had plenty of material to spare.

P.S.- I may or may not upload a photo of what we're talking about since the site is making me manually resize my photo instead of doing it for me. Is that new?