Hi All,

So, just got a new bike for my Son, a Frog 70 Team Sky: 


Now trying to find some suitable inner tubes, but struggling.

The tyres and tubes are marked as 25x1 25-559


I just can't seem to find any inner tubes of that size online anywhere.  Can anyone suggest somewhere to get them from?


The bike also came with some cyclocross tyres, marked as 26x1.35 (35-559)


I'm confused as to why both have diameters of 559, but the cyclocross tyres also say 26"....The wheel diameter, without tyres, appears to be 559mm.  The tyre diametere appears to be 25".



Rod Marton [130 posts] 1 year ago
1 like

Traditional tyre size measurements are highly confusing, the only systematic indicator of tyre size is the ISO size (the xx-xxx figures). First two digits show the tyre width, the last three the bead diameter (all in mm). So your rims will need a tyre with 559mm bead diameter, but can accommodate different tyre widths.

As for inner tubes, they will generally fit a range of sizes: what you will need is something for a narrow 26" (559) tyre (note that there are several different tyre diameters all called 26"). You should be able to find one without too much difficulty, but if you have problems SJS cycles stock tyres and tubes in every imaginable size.

Canyon48 [1147 posts] 1 year ago

559 is the ISO 5775 (ETRTO) measurement of the BSD (bead seat diameter - how big the actual wheel rim is). https://www.youtube.com/watch?v=aYY7fGpnecE

The 26 x 1.35 is the old way of measuring tyre size, measuring by the outside tyre diameter, not inside BSD - see the older markings conversion table


The difference between 25" and 26" is the difference between the outside diameters of road and off road tyres - the archaic imperial system of measuring outside diameter really is a pain!

Buy tyres/tubes based in the ISO measurement, i.e. any 559 tyre will fit on the rim.


kil0ran [1688 posts] 1 year ago

+1 for SJS. Spa Cycles might also be a help

Went through similar pain trying to find tyres and rims for a bike requiring a 520 rim recently, it might be worth looking at LBS/sites specialising in selling folders and recumbants.

ChasP [68 posts] 1 year ago

Slightly wider  (narrower than your cx tyres)



A bit more expensive


Also used by Islabikes, better than the 650 size sometimes used as cx sizes available.


gsf600y [2 posts] 1 year ago

Hi everyone,

Thanks for the advice.  What a pain in the bum it all is.


I'd already ordered a tube before posting this, and just had a 26" innertube delived - it definitely bigger than the 559 25" innertube, as it sits around the 25" one, and now you've explained it to me, I realise it's actually bigger than 559 - the box says "650A" on it, which looks like it eqates to ISO size of 590, hence why it fits around the 559.



So, yes, sticking to the ISO standards seems like the only reliable method of doing it  1


I did also take a punt on these on Amazon:


Not sure how tall the valves are...hopefully tall enough!


So, where some of your suggestions are for 559 tubes, BUT the tubes are wider than the existing 25x1.0  (1.0 = 25mm I assume?), e.g ChasP's suggestion of 


It's for 32mm to 50mm tyres, so would it fit in that 25x1.0 tyre OK, or would it be difficult stuffing it into the tyre?


Thanks again all  1



BehindTheBikesheds [3322 posts] 1 year ago

the 26" tube you ordered is the old 26" that came on British club bikes and roadsters some 50 years ago, with a few ladies bikes still having them fitted up until the 80s.

The now older MTB 26" (559) standard was always designated as 26x x.x or 26x x.xx in decimal format and the narrow variants 26x1 or 26x1 1/8 but never in the triple fractional format.

there's not many narrow 26" tyres around these days as the marketing has now reverted back to other obselete sizes and rim sizes that was perfectly fine are being left without tyre choice so they can push punters to buy completely new frames/bikes otherwise they have little or very expensive tyres to locate.I used to have a pair of Mavic MA40 559 rims mounted on Campag hubs and a 559-25 tyre for my Kona MTB, as you'll have found the choice is ridiculously limited and/or expensive.

hope the links help.


Folding and non folding versions


UK based seller of 28mm https://www.ebay.co.uk/itm/Continental-Grand-Prix-26-x-1-1-8-28mm-Road-B...

Amazon https://www.amazon.co.uk/Continental-Grand-Prix-Clincher-Tire/dp/B00FZQMXLS

Schwalbe pro One https://www.sjscycles.co.uk/tyres-large/26-x-110-inch-28559-schwalbe-pro...