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So, I read your review on all the confusing sizes with all the tire manufacturers.   Here in the states most cyclists use the French measurements, i.e. 700c x 25.  I just ordered some Continental tires for my gravel riding.  I like some knobs on the tread, so I order "Continental Extra Puncture Resistant 700c x 28."  

This has happened a few times as I remember.  What I receive on the label is 28 x 1 5/8 x 1 1/8.  That is another measurement for 700c x 28, I understand.

But what is odd is that on the tire the orange & gray logo reads is "Continental, RIDE TOUR , electric plug graphic, then 25, then EXTRA, Puncture BELT".  When painstakingly read the black imprint on black tire info, it reads my good ol' 700 x 28.

So, when my ride buddies see that visible 25, they tell me that I should go at least to 28's.  So, what does that "25" mean on the Continental logo?

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John Stevenson [436 posts] 7 months ago
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Quote:

what does that "25" mean on the Continental logo?

As far as sizing goes: nothing. See Simon E's comment below.

As far as tyre sizing goes:

Look for a marking like '622-28' on the tyre somewhere. That's the ISO/ETRTO designation and gives you the actual bead diameter and nominal width.

Nominal because the actual width of a tyre in use depends on the width of the rim you fit it to, and as far as I can tell the ISO/ETRTO system either fails to set a reference rim width, or manufacturers ignore it. 

I've got nominal 28mm tyres that measure 26mm on older, narrow rims, and I've seen the opposite happen too.

To keep things nice and complicated, Continental's latest tyres, the Grand Prix 5000 series, appear to be sized for 17mm internal-width rims rather than 15mm, so everyone who got used to Contis coming up big on modern rims is going to have to recalibrate their expectations.

The only way to be sure of the width of a tyre in use is to put a caliper across it and measure it.

If your friends' comments are annoying, black out the tyre label with permanent marker!

[Edited to clarify I was talking abut sizing]

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Simon E [3792 posts] 7 months ago
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Continental UK's page for that tyre shows sizes etc, the ETRTO size of 622mm is the one to look for if you have 700c rims (yes, it's somehwat confusing):

https://conti-tyres.co.uk/commuting-touring/ride-tour

28 x 1 5/8 is inches, which is 40mm width while 1 1/4 is 31mm. If you fit the tyre (presuming it is the right size for your rims) then, as John says, the real-world tyre width will vary a little depending on the width of your rims.

The plug icon & 25 probably indicates its suitability for e-bikes and a rating.

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John Stevenson [436 posts] 7 months ago
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Simon E wrote:

The plug icon & 25 probably indicates its suitability for e-bikes and a rating.

Oh bollocks, you're absolutely right, it indicates suitability for electric-assist e-bikes limited to 25km/h.

I had my head stuck in 'sizing' and missed the reference to a plug logo. Mea culpa.

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IanEdward [321 posts] 7 months ago
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Just to add my recent experience, a Continental 700x25 measures up as 27mm on a DT R460 rim. A 700x28 measures up as 31mm.

When frame manufacturers advertise clearance for 28mm tyres, they mean tyres which actually measure 28mm, so not a tyre badged as 700x28mm, d'uh! 

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Simon E [3792 posts] 7 months ago
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John Stevenson wrote:

I had my head stuck in 'sizing' and missed the reference to a plug logo. Mea culpa.

So easily done. I call it 'forum tunnel vision', where you inadvertently focus solely on one phrase or part of the previous post. We've all done it... well, I certainly have!

To the OP - wider tyres usually offer better comfort. However, if your ride buddies don't actually understand tyre sidewall markings then this kind of (well-intended) 'advice' can be less than helpful.

Legacy imperial measurements might seem to make sense for smaller tyre sizes but even 20", 24" and 26" have multiple incompatible sizes. ETRTO metric numbering is the way to go and with the return of the '650' series alongside 700 (and now 27.5" and 29" in MTB) it is the only sensible system.

Some info & FAQs from Schwalbe:

Tyre sizes - https://www.schwalbe.com/en/groessenbezeichnung.html

Tyre dimensions - https://www.schwalbe.com/en/reifenmasse.html

There are more useful links in the footer of each page under 'Technology / FAQ'.