Machining a TRX wheel down to 15 inch ???

What you want to remove is probably close to the thickness of the wheel in that area. What is "TRX"?

 

Michelin TRX. This was a collaboration between Michelin and a few auto manufacturers (Ferrari, Ford come to mind) to use this specialty tire. It was probably "state of the art" back in 1979 - 1983, but Goodyear's introduction of the Gatorback (exclusive use on the Corvette in 1984) in a then-radical wheel diameter of 16" all but obsoleted the TRX.

As I recall, the Ferrari's TRX wheel (at least on my Mondial) may have enough material to remove 2/10 of an inch (really 9 mm in overall diameter, or 4.5 mm of material from the bead seat and lip.) But that would leave dangerously low amount of aluminum to form the bead seat for the rim. And besides, you end-up with a 15 in rim at that point...

 

MMMMmmmmmm,,,,,,,




Let's see Your custom wheel come apart at 140 MPH...?
ok?

 

I would think it would be an interesting experiment. Although there are a few folks that say no without getting any data it should be tried. Just need to find a shop who can do this and then put it through some tests to see where/if there are any weak spots. I would suspect that there is a large safety factor built into these so you would need to determine what that budget is and how you would affect it. Does anyone with the 390's willing to give one up for science???

 

It's an interesting idea but doesn't make a whole lot of sense. As was mentioned even if it is safe you still end up with a 15" rim! The whole point is to make tire choice and performance better...unfortunately 15" rims and rubber have neither...

 

Then why not just put the money into a set of metric tires? It just seems like a lot of work for little pay off. Or better still upgrade to QV or 328 rims...

 

Agreed! That's why I went with the 16"

 

I learned from the TV show Modern Marvels that Pirelli has a small run prototype dept. I contacted PTNA, and couldn't get a response. I don't know how many of those TRX Mustangs are around, but I would think there are still a good supply of 308's, Boxers, 400i etc that use them, that they might/could consider it. I remember buying a fresh set of VR rated 308 TRX's back in the day when they were about $175 each, and I thought they handled pretty descent. Now, those same tires are probably hard as a rock, and the options are aweful. I guess you can run on 14" rims, and the Goodyear GSCS.

One last thought is drawing up a cross section and giving it to a failure analysis company to consider fatigue, overload conditions etc.

I hope this works. It will open up some possibilities.

 

Hi David,

I think that's a bit harsh Despite the price, I think we have to give Michelin the thumbs up for still producing the tyre.....which clearly could hardly be an economic proposition given the volume they would be selling in 2008. We are VERY lucky to be in a position not to buy that tyre.

Regards,

Carl.

 

Hi David,

You probbaly can, and testing it shouldn't be a problem with the right engineer. The reason why the TRX size went metric was so that you could not mount a TRX tyre on an imperial rim. The rationale behind this was safety. The TRX tyre system used a significantly shallower rim flange and therefore had a much different bead structure in the tyre. To convert the rim, you would also need to reprofile the bead seat and rim flange to suit the imperial tyres.

Regards,

Carl.

 

Hi there..
For what it's worth I sell Mag Wheels for a living have done for 15years..
(Free plug www.magandturbo.com )

I have seen and heard of many things that people have done and my strong recommendation to you is DO NOT machine anything off those wheels..

Mag Wheels ( alloys ) are made and tested to withstand side impact force, pressure and weight, you remove any part of that rim and from that day on it will be sub standard... VERY DANGEROUS.

I have these TRX rims on my 85 308, I like the look of the rims but would love to fit a better performing tyre, Pirelli PZero Rosso, Good Year F1 anything but those horrid Michelin's.
I am going to buy an aftermarket set of 16ich copies of the same style and keep my TRX rims in the garage..

Cheers
Darren

 

So lets see if Dave can get the wheel cut and then get some data. I don't buy the "just don't do it " theory and if that were the case then there wouldn't be a TV program called "mythbusters". If it is feasible then lets take a look at the ROI. I suspect a good performance 15" tire will run between $70-$100 each and now would be the cost of getting the wheels turned down. So once again lets let the data talk.

 

Maybe I'm just more adventurous, I was just going to take my TRX wheels to a machine shop with a big chuck and have at them. Unfortunately, my tires are holding up well, and I don't put enough hard miles on them to get them scrubbed down where it's justified to start carving on them. By my advanced calculus, you would take about 0.177" of material off (total of 0.35" radius). I wouldn't reform the outer lip at all since by taking material off the bead area, you will be increasing the lip area. Just radius it like a standard 15" rim. Make sure there's a locking bead hump, and off ya go.

I'd then take it out on a track, or maybe mount it on a beater Volvo for a few hundred miles of thrashing. Now, if you curb it hard, it's not gonna stand up as well as the original. A 'defect' I am willing to live with to get away from - gulp, TRX.

 

I can't belive what im reading... seriously I have been to 4 alloy wheel factorys and watched the testing proccess at all of them. Melbourne , Milan, Tailand and so on and non of them put one more ounce of alloy in then they need too for cost reasons, all alloys are on the minimum fact.
I have seen wheels in the side impact tester the roller and the xray, all done for good reason, to find the limit of the rim and you want to go and mess with all that... great..

Hey for all I care fill your boots and carve your wheels up, but i just hope it's no one I know that youll crash into head on rounding a corner...


Jezzz

 

Don't bad-mouth 15" tires too much. You'll remember that L88 Corvettes came with 15" rims and tires. Indeed, the standard throughout the 1960s was 14". If you ordered a Tripower Pontiac GTO in 1964, it would have had 14" tires.

Miatas came stock with 14" tires, but a popular upgrade was 15".

 

Yes but now the standard is 16" and upgraded rims are 17-18" and higher. 15" is just not a performance tire anymore. If you keep the orginal 14" rim or even make 15" rims out of a metric ones you end up with a huge space in the wheel well or giant ballons on the rims, not very attractive or inspiring to drive. It may have been okay for the time but we have progressed since then. The 16" rim on the 308'/328's is the perfect size.

Why take the risk of killing yourself or someone else? It's just not worth it. I wouldn't feel to confident driving on converted rims at the track or on a highway. Spend the money once on a set of 16" rims and forget about it forever.

 

When wheels are tested, they generally fail at one of three locations. The spokes crack where they meet the rim, the spokes crack
where they meet the hub or the rim lip separates from the wheel. OEM wheels from large volume manufacturers are somewhat overbuilt as they see a lot of abuse.
I would bet Ferrari wheels are not. Taking that much material away from that critical location would be a big mistake. You would also want the wheels machined on
a CNC wheel machine and you would want a proper seat profile or they would probably not hold air. All this trouble and risk and then you can't get any good tires.
Right now there are only medium performance tires available for 16's. Think long term and get the 16's. You will be happier in the end.
Attached is a cross section of an OEM rim. Note the dimensions. According to what you have written, you would be removing more material then is there
off the back side bead seat.
Image Unavailable, Please Login

 

Actually, I probably did not give enough information, but I was not intending to be misleading in anyway. This rim section is a standard, non TRX rim. I was using it as a generalization of typical thicknesses of rims, not actual TRX dimensions. That said, I don't think there is any reason that a TRX rim would be much, if any thicker.
But you are saying the BMW wheels are thicker. So I have only my 2 cents to offer.

 

You meant to say "15's" here, right?

 

No, I was saying that even if the OP moved up to the 16 inch repos, the number of performance tires is very limited and getting less all the time. No tire company makes their highest performance tires in the normal upgraded 308 sizes of 225/50-16 and 245/45-16.