Michelin invented the steel-belted radial tire, which it introduced in 1946. That turned out rather well for them. In the early seventies, anticipating the trend to ever lower-profile tires, Michelin made a bold gamble to reinvent the genre, with a proprietary metric wheel-tire combination that was not interchangeable with conventional wheels and tires. Although it made considerable inroads for a few years, including a lot of American Fords, in the end the TRX concept went flat.
Michelin’s ideas behind the TRX tire were very valid. As tires moved to lower profiles, their smaller sidewalls naturally resulted in substantially stiffer rides. Michelin, being based in France and so associated with the smooth-riding French cars, looked for a compromise, to gain the performance benefits of a low aspect ratio tire and maintain good ride quality.
The solution was the TRX flange and tire (the TDX was a similar design but also included limited run-flat capability). The wheel flange is angled outward, and not so deep. That allows a more gradual transition from the tire bead to the sidewall, maximizing its ability to flex, even with a limited sidewall height.
The TRX was made in three wheel diameters: 365 mm (14.37″), 390 mm (15.35″) and 415 mm (16.3386″). They generally replaced 70-series tires more than one inch smaller in diameter. In the case of the Mustang and Thunderbird Turbo Coupe, their 220/55 390 TRXs replaced the standard 205/70 R14 tires. That was a big jump in diameter size and aspect ratio, but the TRXs did the job admirably, in terms of no noticeable reduction in ride harshness.
TRX tires were used by a number of European manufacturers, including BMW, Audi, Citroen, Peugeot, Ferrari, Alfa Romeo, Renault , Saab and possibly others. Ford of course, adopted them not only in Europe, but made a major push with them in the US, during the late seventies and early eighties.
In addition to Michelin, Avon and even Goodyear made TRX tires; but not for long (in the case of Goodyear). As tire technology improved with conventional rims and radials, the advantages of the proprietary TRX system soon became insignificant, and the TRX system petered out as OEM tires in the mid eighties or so. Most owners with TRX tires have switched to modern conventional wheels and tires, as replacement TRX tires became ever more expensive. At some point, Michelin sold the molds to Coker, who continues to make them for purists, at a price.
But in 1983, the distinctive graceful large wheels and thin TRX tires were not only desirable from an aesthetic viewpoint, they also functioned superbly. All things must pass, except perhaps for conventional inch-size wheel rims, it seems.
Something else I never knew about. Over $2K for a set of tires would certainly hurt.
I remember my ’82 Escort GT had the option. Replacement tyres were something like 20% more expensive than equivalent tyres, and the only other retail outlet who made the tyres were Sears. Fortunately, they were a bit cheaper than the Michelin’s.
79 Mustang, silver with orange graphics and TRX tires. One of the many Revell or Testor 1/18 scale models I built.
Mine always had excess glue and fingerprints on them as my handiwork got sloppier and sloppier due to the glue high I invariably got.
I always liked the Mustang’s TRX wheels, but not enough to pay 500 bucks a tire to keep them on the car. Yikes.
Agreed. I loved Ford’s 6 spoke copies of the Lancia Scorpion’s 4 spokes, but the TRX diameter means that the vast majority of them are long gone. Michelin and various OEMs did it to their customers again when runflats became common, this time under the PAX brand name. Sadly for ignorant customers, the result is going to be the same. Tire technology keeps marching forward, and buying tires for metric wheels keeps freezing people in time, expensively.
But look at how much the tires cost on today’s equivalent cars. My dad has a Taurus SHO with the optional 20″ wheels. Very short tire life + expensive tires.
at the Tire Rack, the OE 20 inch Goodyears are $164 a tire and the highly rated Continental DWS is $264 a piece. The tires aren’t cheap, but you have options. The only option for TRX and PAX victims involves buying new wheels.
I’m just laughing that the tires at $500 a piece have almost 2000 likes on Facebook!
Likes are free.
I think the early BMW 6 series also used TRX tires.
I am seeing some similar thinking in rims made for tubeless bicycle tires where Stan’s Notubes isusing different shapes in the bead hook and spoke area to suit low pressure tubeless applcations.
A lot of ’80s BMWs had TRX rubber. It makes the prospect of owning one of those cars rather daunting because I imagine tire replacement is a hassle. I don’t know how available TRX tires are today, but I’m guessing they aren’t necessarily going to be stocked in your average rural tire shop.
Early BMW 6 Series used 14″ wheels, just like all other large BMWs of the ’70s. They got TRX wheels in the ’80s, which many of us still regret when we end up owning them because someone didn’t have the foresight to simply replace the wheels. Fortunately, there are many, many other wheels that fit just fine. One can usually pick up a set of used wheels – often with serviceable tires – for less than the cost of a single TRX tire.
I remember an 80′s Monte Carlo with 365 or 390 wheels, but darned if I can find anything about them now…
Never heard of GM using them.
They even came to Australia on the XE Falcon ESP (European Special Pack)
Also Jaguar had the horrible things to upto about 88 ;o)
And on the XE equivalent LTD?
The Fairmont Ghia ESP’s had 15×7″ rims, it was only on the 82-84 FD LTD’s that used the metric wheels. Just under 3500 produced.
My first radials were a set of XZXs that replaced the worn-out Firestones on my Vega. It was an epiphinal moment.
I had TRXs on my 79 Mustang 5.0L and they handled great. Looked great too.
The only thing I didn’t like was the premature wear on the fronts. The outer shoulders got worn away in no time due to the soft tire compound and nose-heavy layout of the car. The 5.0L (302) was cast iron back then. The rears looked like new.
A few months ago I saw a Ferrari Boxer at a local car show with aftermarket wheels. I asked the owner why he had those on the car and he said the stock wheels were TRX type. I said what’s wrong with that and he said something like there are no replacement tires available and wasn’t taking any chances!
The 1986 Peugeot 505 STI had a distinctive 6 spoke alloy rim that came in either a TRX or 15 inch version. Still causing problems years later as these rims are in demand for all varieties of Peugeots (and some Subarus), as long as its the 15 inch and not the TRX. They’re NOT interchangeable and given the lack of availability and price of TRX tires, the TRX rims are good only as paperweights. If you are still running TRX tires you, sir, are a purist of the highest order.
The Austin/MG Montego from the 1980s had metric alloy wheels and tyres on the up spec models. A common DIY car upgrade here (and I guess worldwide) is to buy a lower spec car and dress it up by swapping the tyres onto the wheels of the higher spec model. Second-hand factory alloy wheels aren’t expensive. One of my friends found that didn’t work on his low spec Montego, as the low spec cars wear conventional non-metric wheels and tyres, whereas when he went to upgrade to the factory alloys, they were cheap but new metric tyres were going to cost practically more than the car was worth.
I was a fan of the 79 Fox bodied Mustang Cobra and thought the TRX rims were the perfect look for that new car design. I’d like to think it is a rim that has aged well and is an iconic design in it’s own right, right up there with Detroit’s best. Just a shame the metric tire that goes with it is made of almost-unobtanium! Many thanks for the indepth look at this wheel and tire. Stuff like this I can count on finding here at Curbside!
Funny how metric measuring works nearly everywhere, we went metric here in the 70s I have French Michelin steel rims on both my cars but in inch sizes 14s on my Citroen and 15inch Peugeot rims on my Minx
One solution to the tire debacle…
http://forums.corral.net/forums/wheels-tires/977655-ford-thunderbird-cougar-trx-wheels-modified.html
I love the wheels on that T-Bird!! Don’t think I’ve ever seen them before… way cool.
I didn’t know you could actually still buy these anywhere, that’s pretty neat.
I have a few michelin trx tires sizes 165/70/365 about 6 of them and 8 200/65/365 if anyone is lookin to buy them