Question about tyres

[OldPedaller]

Having had a couple of problems with punctures with my current Powabyke, I'm thinking that I might need wider tyres. I'm trying to get my head round the issue of what tyres the tyre sizes mean.

The Powabyke has 28"/700c tyres. I'm not clear what the 700c means? (It's close to 700 mm, but that doesn't seem to be much of a match with the 'c')

Also, on mountain bike descriptions, I've seen 26" x 1.75. Is the 1.75 = 1.75 inches?

And my last question: If the 1.75 = 1.75 inches, is that the rim size or the inflated tyre width?

Thanks for any help.

 

[flecc]

Sorry you haven't had a reply yet. As you've gathered, the whole business of tyre sizes is a mess, partly due to various national interests wanting to do their own thing and partly due to metric versus imperial measure. Some sizes refer to the approximate overall tyre diameter, some to the rim diameter and some to tyre widths. You can ignore that "c".

The 700 is millimetres, being an approximation of the overall diameter of a sport bike wheel and skinny tyre, sometimes called 27" but a bit nearer to 28"when a fatter tyre is fitted to that type of narrow rim. Thus you will also see references to 27" and 28" wheels, though strictly speaking the rims for this size band come in two diameters.

As well as these tyre diameters, tyres and wheel can also be marked with the nominal rim diameter in millimetres in another continental system, confusingly more than one diameter for each inch size tyre diameter in some instances. Here's the equivalents of imperial tyre diameter and continental rim diameter methods:

27" = 630
700c = 622
26" = 559
24" = 540 or 507
20" = 451 0r 406
18" = 355
16" = 349 or 305

There are some others like 12" and 17", but we don't have them so I've left them out.

The other dimension in inches or mm is the tyre width, such as 1.75 (") or 38 (mm). For stabilty reasons and ease of fitting, it's best not to stray too far from rim width when specifying a tyre, but in some cases very wide tyres are made specifically for narrow rims. For example, Kenda of China make a 1.95" wide tyre as a replacemnt for the usually much thinner 700c size tyre's rim.

This link shows a chart for a typical tyre and the various sizes for it. The nominal diameter column is followed by the ETRTO measure column and the imperial equivalent column in each case.

 

[fatts]

Hi I hope this will help www.sheldonbrown.com/tyre-sizing.

regards
Fatts

 

[flecc]

Sorry, left the link out above:

Schwalbe tyres