Michelin TRX tyres. One of the most surprising tyre models to ever hit the streets.
Most drivers have and will never hear about them.
For some enthusiasts like us, TRX is synonym with Michelin, metric sizes, weird tyres and A LOT of debate and hear-say in many communities.
Why is there so much talk about them when tyre talk almost always is about going one size higher or changing rim sizes?
I have been working in the classic car tyre industry for many years and I wanted to build a resource where any TRX-fitted car owner can go to and make an informed decision about whether to go for TRXs or not.
I wrote this guide exactly for that matter. Feel free to ask me any questions you might have. Enjoy!
I know many folks can or want to swap to imperial sizes, be it for money, looks or wider choice.
So I made this little tool to check the difference in outer diameter (and its effect on the final drive ratio).
If you are in the EU, you’re most likely bound to ECE R 30 regulation, which states that you have to be within +-3% of the outer diameter of the original tyre.
Please, bear in mind that any changes in original equipment is completely your responsibility and you should double check with your local inspection station, be it MoT, TUV, ITV or whatever it may be.
Economies of scale.
Like many manufactured goods, tyre price depends mainly on the size of the production run.
If there is great consumer demand, a big production run will bring the cost down because all the overhead costs will spread out among all the units produced.
In the tyre industry, this means that sizes that are mounted in tons of cars will inevitably be cheap.
To better frame production run sizes, more than 289 million tyres were sold in the European Union alone in 2016 (source here).
205/55R16 or 165/65R14 are perfect examples of tyres that are mounted on a million cars; you can ride on Bridgestone, Goodyear, Michelin or any first brand for roughly the same price as other discount tyres on these tyres.
That’s the reason you can even find Pilot Sports, Potenzas, P-Zeros and other high end models for surprisingly good prices on some sizes. They can be made cheaply because there is a lot of demand.
Complexity and performance are a factor, but they matter almost nothing in terms of cost.
Let’s go now to the other side of the spectrum: small production runs for low demand.
In this case, very few units are made on each run because there is no demand to support it.
However, the cost of setting up the line, the energy needed to make it run and the man hours do not differ much from the bigger production lines.
That cost is now spread among 100s to 1000s of tyres. In bigger production runs, roughly the same cost is spread out among 10k to 100k tyres.
That’s why the 365/710 R 540 Pilot Sport from the back of the Veyron is insanely expensive, even though there isn’t hundreds of times more tyre material nor technology than a contemporary Pilot Sport mounted on a GT3 RS.
Only 450 Veyrons in the entire world use that size. You can safely bet that not many tyres were made.
That’s why japanese cars from the 80s and 90s have more expensive tyres.
That’s why all classic car tyres are more expensive than regulars.
That’s why TRXs are expensive.
Economies of scale.
Like most times, we tend to judge past events with present information. Hindsight is 20/20.
In this case, we usually think of TRX as a crazy project that was obvious that it wasn’t going to take off.
After all, today, we still use good ol’ imperial wheels. How dare you Michelin try to rip us off with that weird tyres?
What we still use today are radial tyres. And Michelin did a similar move back in the ‘40s.
While today we think of radials as a normal tyre, it took decades to become the new normal.
Up until late 70s, a lot of cars outside Europe were being fitted with bias-ply as standards. That’s almost 30 years from when it became available.
Heck, even J-type wheels took years to adopt as standard. There were many others out there.
And then, there’s low profile radials.
Low profile today means something along the 30/35/40 percent aspect ratio. The kind of tyre you see fitted on a sports car or a sport-ish saloon fitted with 19-20” wheels.
It really didn’t used to mean that. By far.
Radials came out with an aspect ratio of 80/82 depending on the manufacturer.
Even though the nature of radials allowed the tyre to be designed with a shorter sidewall without compromising tread width, in the early days that proved tricky.
However, the need for performance that came with the cars of the ‘60s such as Miuras, Ghiblis, Daytonas and SEL 6.3 put pressure on manufacturers to develop and manufacture higher performance tyres.
Thus, the first 70 percent aspect ratio tyre, such as 205/70 VR 14, became available.
Michelin offered XWX, Pirelli offered Cinturato Serie 70 and P7, and many other brands followed.
The main issue back then was technology limitations.
With the technology available at the time, you could make a performance tyre with low sidewalls but you’d get a really harsh ride since the distance between the contact patch and the twisting S point of the imperial tyre would become closer and the suspension that the tyre would usually provide is now gone.
Michelin tried to innovate, and in 1975, few years after they release the XWX, they were able to offer a 55/60 and later even 45 percent aspect ratio tyre, that kept the same comfort.
That’s why it was so revolutionary.
The TRX was created to solve the performance/comfort dilemma that plagued 70s era design.
It just wasn’t possible to do so with the expertise of that era, so a new design was needed to overcome that spike in tension near the rim lip.
As years passed by and technology advanced, that issue was solved even using the regular type wheels, so lower and lower profile tyres that were also comfier became available.
Since not enough years passed to let the TRX become the new standard, it ultimately faded away into today’s Classic range.
However, the concept is still valid and is a technically superior design that gets rid of fundamental flaws of the traditional design.
It’s one of those instances were a superior/revolutionary technology doesn’t get adopted because the market has bridged the gap close enough by evolved, pre-existing technology.
The TRX tyre can only be mounted in TRX wheels. They were conceived to work as a unit from the start.
TRX wheels are built in metric sizes instead of inches and the inner shape of the wheel is different than regular J-type imperial wheels.
Instead of the usual 15”, 16” or 17” wheels, TRX wheels came in 315mm, 340mm, 365mm and so on.
A TRX tyre can not be fitted to an imperial sized wheel and viceversa. Nor the diameter or the tyre bead fit.
Do not even try, you’ll waste your time. They made it that way to avoid fatal confusion (or stubbornness), since the tyre would pop-up in an J-type tyre and you’d crash, obviously.
I’ve seen 400mm tyres from the 30s fitted into a 16” tyre many times due to poor tolerance control in manufacturing typical of that era.
Not a good idea, many crashes have been due to this fact and most of them unbeknownst to the driver/owner since, hey, it fitted!
Decades before the TRX, there were many wheels and tyres made in metric sizes, but the market eventually settled to imperial measures.
Since the birth of the pneumatic tyre, engineers have been improving the way the tyre fits into the wheel.
Nowadays, we can ride along in low pressure tyres (1-2 bar, 20-30 psi).
But in the early days, much higher pressures were required to keep the tyres inside the rim. It was very easy to lose pressure and pop the tyre out of the wheel.
The way the wheel interacts with the tyre radically changes the behavior of the vehicle.
The TRX was a new proposal in which the wheel and the tyre were designed from scratch to fit each other, and not what was on the market.
A TRX wheel works like this:
Source: Michelin Classic
Imperial wheels have a high outer flange to help keep the tyre in place.
That has the side effect of producing a “S” shape in the tyre once mounted in the car due to its weight.
This can be minimized if we use a lower, stiffer sidewall for better handling, but the car becomes more harsh and uncomfortable the lower and stiffer we go.
Conversely, we gain comfort and smoothness the higher and softer we make the sidewall.
The conventional design has this drawback. The TRX set out to precisely remove this sticking point.
By lowering the flange and redesigning the tyre bead to fit the new flange safely, the TRX tyre had a fully spread out tension throughout the sidewall, hence the name in french TRX (Tension Repartie X).
This allowed to better control the reaction and have both good lateral handling capabilities paired with smooth and quiet ride qualities.
There’s a lot of confusion about availability of TRX.
I’ve seen and heard many stories about it, ranging from “out of stock for years” to “someone bought the moulds for dirt cheap and does small runs back in his workshop”.
The truth is simpler.
Michelin has NEVER dropped it from its range and it is available for sale, though in much smaller and infrequent runs.
TRX are among the few tyres that Michelin has kept in its offer since day one, and the price has stayed mostly the same from where they first came out (adjusted for inflation).
When they shifted it to its Collection range, they made sure to incorporate all the new knowledge gained from decades of experience to improve the tyres.
The current production range is the following:
190/55 VR 340 81V MICHELIN TRX
220/55 VR 365 92V MICHELIN TRX
190/65 HR 390 89H MICHELIN TRX
200/60 VR 390 90V MICHELIN TRX
210/55 VR 390 91V MICHELIN TRX
220/55 VR 390 88W MICHELIN TRX
240/55 VR 390 89W MICHELIN TRX
240/45 ZR 415 94W MICHELIN TRX
240/55 VR 415 94W MICHELIN TRX
“I just found out that Michelin no longer manufactures the tires any more for this car. Is that true?”
See the answer above. That’s not true.
At most, your precise size is replaced by a fully equivalent TRX size that’s out of stock right now, but will surely be available as soon as Michelin does a new batch.
“I have heard the metric TRX tyres are rubbish with regard to the handling and grip of the car?!”
The engineers at Ferrari, BMW, Renault Sport and more used TRX to enhance the capabilities of their projected cars.
Personally, I think it is safe to say that, performance-wise at least, the engineers at Ferrari, BMW, Renault Sport and other brands might know a thing or two more than me about designing a powertrain, suspension and braking system.
The hear-say about TRX has a main reason. TRX are and were expensive compared to regular tyres.
Most original owners of TRX-fitted cars didn’t care about the price of the tyres since they were very expensive cars to begin with.
So they usually were wealthy individuals.
Fast forward some years. The second-third-fourth owners of these cars buy the car at a steep discount since it’s been used for years now.
They stretch the tyres as far as they can to save money because they are surprised when they see the price of a new set, which in many cases in the past, could cost more than the car itself.
Many times, this means riding on very old, crystallized TRXs. They still have tread on it, but won’t grip because they are 25 years old.
“TRX are rubbish, they don’t grip on any conditions!!!”
I dare you to push ANY car with ANY set of regular tyres that are 25 years old.
Most of us will blame the poor handling on the age in the case of regular tyres, not on the tyre itself, but the opposite would be true in the case of TRX.
A new set of TRX handles beautifully, and the suspension is designed to work in conjunction with the reaction of the TRX.
“TRX tire technology is now over 40 years old.”
Yes it is.
It’s also true that regular radial technology is over 70 years old and I don’t see anybody throwing that around.
That argument by itself is not enough.
I agree that most modern tyres have better overall handling characteristics simply by the R&D invested in all those years.
That’s an undeniable fact.
It’s also true that it really varies from brand to brand, size and even models within the brand.
I think we can all agree that a PS4 will grip a tad better than an Energy Saver.
That brings us to consider which options we have to replace our classic tyres.
In the case of the TRX, when we opt for replacement wheels, which is possible in most cases, we have to check what’s available for our car and if it’s an equivalent size.
I’ve seen many swaps which were nice, but I’ve seen others which put a poor modern tyre that wouldn’t stand a chance against a new set of TRX.
As a side note, even though the original design and the tread pattern remains the same, TRX have also benefited from R&D improvements of all these years, mainly in manufacturing precision, materials and compounds.
The following Ferrari were equipped with TRX as standard or as an option:
|Ferrari 208 GTB/GTS Turbo||220/55 VR 390||220/55 VR 390 TRX|
|Ferrari 308 GTBi/GTSi||220/55 VR 390||220/55 VR 390 TRX|
|Ferrari Mondial T (front)||220/55 VR 390||220/55 VR 390 TRX|
|Ferrari Mondial T (rear)||240/55 VR 390||240/55 VR 390 TRX|
|Ferrari Mondial 3.2 (front)||220/55 VR 390||220/55 VR 390 TRX|
|Ferrari Mondial 3.2 (rear)||240/55 VR 390||240/55 VR 390 TRX|
|Ferrari Mondial 8||240/55 VR 390||240/55 VR 390 TRX|
|Ferrari Mondial QV||240/55 VR 390||240/55 VR 390 TRX|
|Ferrari BB 512i||240/55 VR 415||240/55 VR 415 TRX|
|Ferrari 412||240/55 VR 415||240/55 VR 415 TRX|
|Ferrari Testarossa (front)||240/45 VR 415||240/45 VR 415 TRX|
|Ferrari Testarossa (rear)||280/45 VR 415||280/45 VR 415|
The following BMW were equipped with TRX as standard or as an option:
|BMW E28 (non-M535i/M5)||200/60 HR 390||200/60 VR 390 TRX|
|BMW E30||200/60 HR 365||220/55 VR 365 TRX|
|BMW E28 (M5/M535i)||220/55 VR 390||220/55 VR 390 TRX|
|BMW E24 (non-M635/M6)||220/55 VR 390||220/55 VR 390 TRX|
|BMW E24 (M635CSi)||240/45 VR 415||240/45 VR 415 TRX|
|BMW E23||220/55 HR 390||220/55 VR 390 TRX|
The following Renault were equipped with TRX as standard or as an option:
|Renault 5 Turbo (front)||190/55 VR 340||190/55 VR 340 TRX|
|Renault 5 Turbo (rear)||220/55 VR 365||220/55 VR 365 TRX|
|Renault A310 V6 (front)||190/55 VR 340||190/55 VR 340 TRX|
|Renault A310 V6 (rear)||220/55 VR 365||220/55 VR 365 TRX|
The following Citröen were equipped with TRX as standard or as an option:
|Citröen BX GT||170/65 R 365||170/65 R 365|
|Citröen BX 4TC||210/55 R 390||210/55 VR 390 TRX|
|Citröen CX 2400/25 GTi/2500 Turbo Diesel||190/65 HR 390||190/65 HR 390 TRX|
|Citröen CX 25 Gti/Prestige Turbo||210/55 R 390||210/55 VR 390 TRX|
The following Ford were equipped with TRX as standard or as an option:
|Ford Fairmont||200/60 R 390||200/60 VR 390 TRX|
|Ford Granada||200/60 R 390||200/60 VR 390 TRX|
|Ford Mustang||220/55 VR 390||220/55 VR 390 TRX|