What's wrong with tyre specs?

What are you measuring between?

And… what pressures are you using?

if you mean I'm not taking knobbles into account the first 2 are slick tyres

all with regular pressure, maybe the second wasn't spot on but no way it would gain the extra centimeter even at full pressure

It's like chocolate bars, making them smaller but still paying the same price.

I seem to remember reading (in the pages of the mag possibly) many moons ago that when the tooling is made for the tyre its hard to predict exactly what size the tyre will be when inflated on a rim. You're making a solid die for something that is going to be flexible and take its shape under pressure. But the text on the tyre needs to be part of the  making of that mould too. So the size stated on the side of the tyre is their target they had when they made the mould but might not the the exact size of the tyre that comes out at manufacture when mounted and inflated - but then its too late to change it.

this has always been the case, my expectations after 15 years mountain biking is that Maxxis come up small, Conti tend to run a little bigger (depending on the model), Schwalbe are usually on the smaller side but its all hit and miss and any two tyres models of the same size from the same manufacturer can be vastly different.
expecting them to reach spec on a 24-25mm rim is probably ambitious though.

34mm rim is huge, it's ever bigger than the recommendation from the producer itself.
62mm is what I'd expect from a 2,35" tyre, not a 2,6".

I understand there might be differences between batches, but this is far off tolerances.

The latest gen Schwalbe 2.35s were designed around a 30mm id rim so might come up a bit small on 25mm id. However, I've had them measure up anywhere between 58mm - 61mm on said 30mm rims so there's definitely some manufacturing variation going on.

I've noticed that my latest Continental road tyres are 37-622 on one stamp, 35mm is stamped elsewhere on same tyre. 🤷

That can't be right can it Maccruiskeen?
They will know that when we make a mould it comes up 3% bigger or 2% smaller than the mold or whatever it changes by, that should be consistent?
Also, do the they make prototypes? Your theory stands for the first preproduction ones but once they've made those they'll know that a mold of x size gives a tyre of y size?

Tyre specs have always been horseshit. It's not inaccuracy- though there will be a little- and it's not the rim width, it's just lies. One person designs a tyre, someone else decides what market segment they want it to target, so if they have a cool new 2.5 but this year it's all about 2.6 rears and mullets, then it'll be stamped up 2.6. If, like the old swampthings, people expect 2.35 for trailbikes and 2.5 for downhill, then the singleply will be sold as a 2.35 and the dualply will be sold as 2.5 even though they're exactly the same size.

A few years back I did a bunch of real comparisons with wide and narrow rims, and the difference it makes in overall tyre width is pretty trivial, and when you look at what actually changes it's obvious why- it's almost (though not exactly) like adding to the circumference of the tyre, so 5mm of extra rim really only changes it by 1mm or so.

It's always been bollocks but it's worse now imo since we're in an age where stuff really gets marketed on tyre size more than it did 10 years or so ago.

Fun thing is my smaller-than-expected 2.35" schwalbe barely fits (with no mud clearance) a frame specd for 2.5" tyres.

Total randomness, tyre size must be referenced to a given ERTO rim size.

I'm pretty sure we did a tyre grouptest a bunch of years ago where we measured the flat, bead to bead distance of the tyres, just as a constant. Then at least you can see if there'll be a bigger volume, regardless of rim width. It obviously didn't catch on 🙂

Oh yeah, should add that the media are part of the problem (sorry Chipps, not pointing fingers at anyone here, just the wider "the media" as a whole. I've seen in the past "the tyre is heavy for its size" or "the tyre comes up large" way too many times when it's actually just honestly sized, meanwhile undersized tyres were praised for their light weight. Dishonesty and undersizing is such standard practice that the rare honest tyres are often criticised for it.

That can’t be right can it Maccruiskeen?
They will know that when we make a mould it comes up 3% bigger or 2% smaller than the mold or whatever it changes by, that should be consistent?

wherever it was I read it it was a manufacturers own account of the disparity between the stamped and measured size in a tour of the factory / see how it’s made type article. If there’s no consistency in the discrepancy then it doesn’t really seem to be a deliberate strategy.

MSC tyres are the width they say they are… it’s problematic though if you’re used to other brands.
I recently tried a 2.4 as a rear in my Stanton. Couldn’t turn the wheel! It fits a Maxxis 2.5 though!

I like the bead to bead measurement idea, otherwise all tyre widths should be based on a set rim width.

Schwalbe always used to come up large, their 2.35 26" tyres were always bigger than a Maxxis 2.5". My WTB tyres are supposedly 36c but measured 38c. My 25c Continental's are different sizes, different tyres but meant to be the same width.

Why are you measuring them, what's the purpose?
Does it in any way matter, is a 62mm wide tyre more or less suitable for a thing than a 65mm one?
Without calipers, can you tell?

surely anyone who has ever worn shoes or clothes is well aware that manufacturer sizes are just a made-up thing.

The sizes are, as Northwind says, just a guide to intended use, the physical size doesn't directly have that much function, they could just as easily label them with a colour or a made-up word like cosmetic ingredients so long as the end user gets the idea of what is intended for from that description.

One person designs a tyre, someone else decides what market segment they want it to target, so if they have a cool new 2.5 but this year it’s all about 2.6 rears and mullets, then it’ll be stamped up 2.6.

That’s been my suspicion, with a bit of weight management for good measure. That one is too heavy to be a competitive 2.4. Easy, sell it as a 2.5.

I've been and checked this morning -

Continental Top Contact "35mm" actually comes in at 37mm.
Continental Contact "35mm" actually comes in at 32mm.

The Top Contact is noticeably taller than the Contact.

Both on same rims/bike, both same pressure. One of the carcasses is 10% smaller than the other(!).

I know they are moulded differently, steel Vs folding, Black Chilli Vs ordinary rubber, but still..

@chipps, do you have a link to that article? It sounds like a really good idea 🙂

What makes me laugh is the stating the size to two decimal places. I even have a tube that states it's usable range to three decimal places, so a thousandth of an inch could take you out of the range!

In my tyre store I have Schwalbe 2.4 that are smaller than 2.35, Conti 2.5 narrower that a Conti 2.2...etc.

I agree it is more like marketing segments. In my memory it at least goes back to when 26*1.9 = XC race tyre, 2.1 = Normal MTB tyre, 2.2 = DH Tyre.

My MSC Grippers in 2.35 are waay chunkier than a 2,4 Wide Trail Maxxis - which I knew when I bought them!

Its not just bike tyres though, same on the car. A 195mm track style tyre like a Yokohama Advan is noticeably squarer and wider than another companies all seasons in 195mm.

Why are you measuring them, what’s the purpose?

The purpose is to buy the right component to match other components.

A pair of tyres nowadays goes for 150€ (not talking about forks), is it that hard to mention the actual size related to a given ERTO?

This is not a t-shirt, specs are specs, this is technical and it's often a matter of mm in che tyre clearance department, such wide tolerances aren't acceptable.

Does it in any way matter, is a 62mm wide tyre more or less suitable for a thing than a 65mm one?

Appartently it is, since same tyre can be produced in 2,35" and 2,6" and priced differently

Appartently it is, since same tyre can be produced in 2,35″ and 2,6″ and priced differently

But does it alter the function if its an accurate number of not? Yes if you bought a 2.6" and actually got a 2.6cm tyre it will but the handful of mm you're looking at will be imperceptible.

The purpose is to buy the right component to match other components

Which other components? Are you worried your 2.6 front will be narrower than the 2.35 rear?

This is not a t-shirt, specs are specs, this is technical

No its not, there's not even a standardised method for measuring them. It's marketing. It's not a bearing or an air seal, it's not critical and the accuracy to a few mm isn't important to its function. The numbers are an indicator nothing more, nothing less.

and it’s often a matter of mm in che tyre clearance department, such wide tolerances aren’t acceptable.

You've already accepted in your op that rim and pressure will change the width, as will carcass and tread.
The frame clearance is based on a manufacturer's choice of tyre on their choice of rim at their choice of pressure. Just like they famously weigh an unpainted xs frame to get low weights I'll wager they choose a skinny tyre on a narrow rim because better clearance sells.
If a frame fits a 2.6semi slick, should it fit a 2.6 mud spike? Can they reasonably say it takes a 2.6?
There's a reason those max clearances all come with small print.

They give [mtb] tyre sizes to 0.1", a measuring system which is only accurate to 2.5mm at best assuming no creative rounding. If they measure centre to edge then double it, that could be 5mm.
Oh and there's no standard for measuring them.

You're expecting something beyond what's available or indeed reasonable.

Appartently it is, since same tyre can be produced in 2,35″ and 2,6″ and priced differently

Same carcass, bead, rubber etc? Different RRP or just the 2.35 is discounted more heavily because its less fashionable?

Does it in any way matter, is a 62mm wide tyre more or less suitable for a thing than a 65mm one?

Maybe.
A 25mm Maxxis Highroad rubs on the frame of my TT bike. A 23mm version of the same has loads of clearance, not measured it but way more than 2mm

True, but that same tyre might fit mounted on a different rim.
Case in point my front and rear are the same tyre (2.6), if I try my front wheel it won't fit into the rear, that's on a 31mm internal rim. The rear is on a 25mm internal and fits with mud clearance.

Which other components?

Frame and fork for example?

I already have 2.6 at the front and 2.35 at the rear, but it turned out the front is much smaller (I could have saved money on the fork) and the rear rubs despite declared 2.5" tyre clearance.

GF wanted bigger tires than actual 38mm so I got 47mm on a new 25 rim but they barely make 42mm.

Bottom line: money and time wasted.

This is beyond natural tolerances.
Producers should make specs right and true, I believe they can afford some QC for this amount of money.

This is beyond natural tolerances, make specs right

To do this there would need to be a standard system for sizing them.
So what size rim do you use to check the width of tyres? What pressure? With tread or without? Tubes or tubeless? What type of tubes? With inserts or not etc etc etc.

Say you choose 19mm rims, once you've done that you need to decide if tyre a, which measures 35mm on a 19mm rim & measures up at 36mm on a 23mm rim is the same star (35) as tyre b, which also came up at 35 on a 19mm rim but its now 39 on a 23mm one. What about tyre c which is 39 on the 23mm rim but only 33 on the standard 19. Which tyre is the bigger size?

You then need to get all manufacturers to follow the same standard, which so far they have achieved with erm, pedal thread?

For example there's an organization (ETRTO) publishing recommened rim/tyre width.
Producers could declare tyre size depending on a given pressure on the recommended rim width.

From there you might get a much closer idea depending if you have bigger/smaller rim and different pressure.
Not rocket science, man.

Today is just wild nonsense

I'd quite like to know the tyre depth as well as the width as this can have quite an effect on the tyres performance. But if they can't even get the width measurement right then maybe not.

Not rocket science, man.

Today is just wild nonsense

Or, it just doesn’t matter that much?

Assuming the tyre is fit for purpose the things that sell to the masses are lighter weight and wider/ bigger volume. Both are at odds with each other so why not lie a bit on each in the favourable direction? Tyres sold, job done.

Every company does it so it has become the norm*

* Except Bontrager MTB tyres IME

dc1988 wrote,

Schwalbe always used to come up large, their 2.35 26″ tyres were always bigger than a Maxxis 2.5″.

Schwalbe 26ers were pretty accurate, Maxxis 2.5s were usually close to 2.35. It wasn't schwalbe that came up large. Not having a poke at you just to be clear, it's just this is a perfect example of the traps we fall into where doing it wrong is so commonplace that doing it right seems weird.

Dangeourbrain

Does it in any way matter, is a 62mm wide tyre more or less suitable for a thing than a 65mm one?

Of course it can matter! Sometimes a 65mm tyre won't physically fit and a 62mm will. Or more likely, a 65mm will have no mud clearance but a 62mm might. False sizing means it's impossible to compare like with like so other things like claimed weight also become less meaningful.

And tyre volume and size is a matter of choice. Sometimes you specifically want a larger tyre. Sometimes you want all the tyre you can fit in the frame.

Comparing with clothes sizes is interesting. Because "medium" means nothing but if an item of clothes says 32 inch waist it bloody ought to have a 32 inch waist. We don't buy medium tyres. A medium frame can vary in size but if it's a 21 inch frame and it measures 18 inches it matters.

The sizes are, as Northwind says, just a guide to intended use

I did not say that.