360 wheels now milled 18MM and looking good

I have now milled 18MM off the back of each of my rear wheels. They look much better now, I have attached pictures, but I took them with my cell phone, so they aren't that great but you can see the difference from before on the rear.

What I have learned is that 93 and up 348s have a 43mm offset and just bolting on 360 wheels works fine. 1992 and older 348s have a 68mm offset and you need to mill off about 18mm for them to look right and fit underneath the fender well, unless you like the 4X4 look I had before I machined them.

Procedure:
First, you need access to a pretty large mill or bore. I used our old boring machine to do the job because it has a large table to mount to. This is not for folks who have no machining experience by the way...

First, if you have the tires on make sure to remove the valve stems so the tires won't cause the rim to not seat on the table. Make sure to tape up the wheel edge with masking tape so you don't scratch the wheel on the table. make sure your tape is even, as we are dealing in thousands of an inch in run-out here (or mils for your metric folks).

Next indicate the wheel surface in. I used several clamps on the inside of the spokes to hold the wheel down. By ever so slight adjustment on each on get the hub surface down to no more than one tenth flatness - this will make sure your wheel is true.

Use a mill, fly cutter or boring head to machine off 18mm - I actually machined off .700". You will then need to re-bore the wheel hub clearance. I milled it out to 2.64" - what it was before, and .350" deep. Make sure you re-indicate the center position of the hub before you bore or you will get it off center and have major problems!

Finally, you will need to remove the wheel alignment/rotor position studs as there is now not enough room for them to stick into the wheel forging. I suppose you could cut them off a little, I just removed them for now.

I just threaded my old 348 bolts (14X1.5mm) on down and cut them off to length (cut about .75" off of them) and they work great. Bolt it all up and you are ready to go.

I will lower and set my suspension up in a few days, just wanted to get the wheels fixed so they wouldn't hit the fenders for now. Whole process probably took ~6 hours and no cost at all, just some sweat equity and an old boring machine.
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Excellent work Dave!!

 

Simply unbelievable ! You are da man !

 

Looking good! Much better than before.

 

Very nice! Did you feel that "point of no return" when you started to shave the metal?

 

That's what I'm talking about. Good job....

 

well done son

 

Awesome! Must be great to have access to such equipment! I would take about 12-15mm off my aftermarket rears if I knew someone with a milling machine.

 

Does this part of my wheel size document look correct? Seems to match what you found, Dave. If you are sure the change was made in 1993, I will add it in.

Wheels look great on your car.

Taz
Terry Phillips




348

Five Spoke 17” Early, 5 X 108 mm
Front 7.5J X 17 ET 49 mm, Rear 9J X 17 ET 68 mm
Five Spoke 17” Late, 5 X 108 mm
Front 7.5J X 17 ET 49 mm, Rear 9J X 17 ET 43.05 mm

 

Dave, this is excellent info. Thanks for posting. I must now find someone locally who can do this for me -- I don't have access to toys like that big milling machine of yours.

Just to clarify, the only difference between the early 348s and the 93 and up cars is in the offset of the wheels. The later cars used a 43mm wheel offset to provide a wider track. This was the factory equivalent of the 25mm spacers that most owners have added to their early cars. The suspension and body geometry is the same, so this milling procedure is applicable to any year 348 (including the newer ones).

Now having said that, there do seem to be car-to-car variations when people bolt on the 360 wheels. Some don't appear to stick out much at all, while others are very pronounced. I haven't been able to work out why this is. Some of it must be down to specific tire choice I think.

- Eric

 

Terry, I think this is correct. The change to the rear wheel offset (at least in the states) was cut in with the 1993 Serie Speciale models and the spiders. After that, the only exception I know of was the 1994 factory challenge cars, which for some reason were still delivered with the original 68mm offset wheels.

- Eric

 

Looks fantastic! Nice work!

 

Looking good! I would still probably lower the rear springs maybe 3/4" or so when the car is in the shop for servicing or whatever. Enjoy it!

BT

 

wow. NICE WORK Dave! Very nice indeed!

 

You did this with the tire on? How can you insure the wheel is square to the millhead? Did you start by checking the runout of the wheel before you mounted it? I'd be curious to see the runout at the rimface post cut. If you are off you will get weird vibrations at speed and encourage bolt lossening if not exactly square to the hubface.

 

This was my first thought, also.

Remember, guys, these are 180 MPH capable cars. There is not room for 1/2mm or even 1/4mm errors, here.

 

I believe this is the relevant part of his procedure:

Now, I don't speak machinist, but this sounds like adjusting the clamp load on the spokes to keep the hub surface flat (i.e level) to within 0.0001". This would leave you with a new face parallel to the old face.

 

Looks good.

 

Excellent points - Dave, we don't want to be reading a future thread about you losing a wheel while in action

 

Nice work Dave.

Does it handle different now?

Cheers

 

First, it was a little scary to take that first cut, but I'm used to that kind of scary thing - like cutting out the old light supports to install Huskers LeMans tail light assembly.

Secondly, of the 6 hours it took to do the job probably 3 hours were spent setting up the wheels before machining. Proper set up is the key to any machining project. We manufacture compressors with bearing sizes ground to millionths of an inch, so I've got that figured out.

As to the tire question, I removed the valve stems so the tires would easily roll away from the rim - I checked them by hand before actually trying this. I have P-Zero tires and they moved easily, if you have run flats with really hard sidewalls I suspect you might have to remove them first.

I didn't put an indicator on the car after re-assembly, however, I did clamp a straight edge to the car and spun the wheels to check them. By this method I did not see any run -out in either the diameter (which you wouldn't expect anyway with boltcentric mounts) and I couldn't detect any run -out in the in-out direction either. I suspect there may be a thousanth or so, but without an indicator mounted on the car I couldn't tell. I can tell you have I have done the same type test on our excursion looking for a vibration on our 33-12-50 tires. You can actually see some movement in those wheels from the factory - one of those big rough tires was actually moving up and down about 1/16"- so that is probably the reason for a slight vibration on that vehicle. I realize the Ferrari is capable of much higher speeds, but I couldn't detect any run-out - so I'd say they are probably as good or better than they were stock from the factory.

I also compared the rim bolt area to my Corvette wheels and I still have more meat on the Ferrari wheels than the Corvette - so no worry there. Also the vette has about 100HP on the Ferrari, so I have no worries at all about wheel strength. By quick calculation the wheels have a huge factor of safety against bending or fatigue cracking.

Several other people have done this same wheel machining and I have not heard of any problems - so further comfort that all is well.

The car doesn't handle any different that I can tell. Where I live there are cops about every 100 yards (they get paid $25/hr to radar on their days off) so you have to be careful when going fast. There is no vibration detected from any of the wheels and I drifted a turn or two with it today close to the factory to make sure everything was clamped up good to the car with no issues after coming out of the drift. Better to stress those things at low speed before getting up to high speeds.

All in all I am satisfied with the 360 wheels and my set-up. I do need to lower the car at some point in the future though.

 

yup, 4 years ago, no problems. Plenty of track time on them since I have Road America in my backyard.

 

Dave- Thanks. Will update the list. Will leave the weird exceptions to the experts. My list is just for proles like me trying to swap wheels.

Taz
Terry Phillips

 

You are absolutely right and I asked my self the same question ... why my 360 rims don't stick out as much as Dave 's prior shaving off 18mm ?

 

And here is a pic that I took last week during the Las Vegas Lake Meade run ....
My 360 rims are not machined off.
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