Tyre Sizes

[Paul Narramore]

I've just returned to cycling after seventeen years away and I'm amazed at all the new innovations which have come into bikes since those day. In 'my' day tyres were 27 x 1 1/4 for sports bike, 27 x 1 3/8 for roadsters and tubs for racing.

I now find that tyre sizes are an utter nightmare to understand. My Marin had old 700x32C tyres which needed replacing. I was sold Continental City Contacts which seem to be 28 x 1 1/4 or 32x622 or 700x32. If that wasn't confusing enough the Panaracer inner tubes are 700x18-32C, 27x1, 1 1/8, 1 1/4, 18 - 32 - 622 - 630.

It seems that the inner tubes fit a heck of a lot of different sized tyres.

Would someone care to try to explain this to me?

Is it possible to get a tyre gauge for Presta valves? I know I have a pressure gauge on my track pump but I always lose too much air when removing it from the valve so never quite know the exact pressure.

My cycling book says I 'should' be able to replace a tyre on a rim using just thumb pressure. Really? I've tried every possible way excluding using a lubricant and I HAVE to resort to a tyre lever. What's the secret?

 

[al78]

There are two numbers associated with tyre sizes. One is the tyre diameter and the other is the tyre width.

For example, 700x23C means a 700C tyre diameter which is 23 mm wide (a 700C tyre is actually 622 mm in diameter and is a typical tyre diameter for a road bike).

The tyre widths you can use depend on the width of your rim. The tyres you can use with various rim widths are detailed here:

http://www.sheldonbrown.com/tire_sizing.html

Similarily for inner tubes, the diameter must be the same as the tyre diameter so if you have a 700C tyre you need a 700C sized inner tube. Inner tubes have a certain amount of leeway regarding the width of tyre that they can be used with so an inner tube pack will typically state 700x20-28C which means the tube is to be used with a 700C tyre, minimum width 20mm and max width 28mm.

Regarding tyre replacement some tyres you can remove and replace without tools, others you will need levers. It depends on how tight a fit the tyre is with the rim (tyres marked with the same diameter will have small variances in actual diameter), how flexible the tyre is and how strong your fingers are.

 

[MajorMantra]

Further to what al78 said, when it comes to your Contis, the 700 is the nominal diameter of the whole tyre whilst the 622 is the actual rim diameter. 622-32 is the ISO designation for the size whilst the 28x1 1/4 nomenclature is one mainly used on the continent I think.

You really don't need a pressure gauge if you've got a track pump. The amount of air you are actually losing when you pull the pump off is pretty negligible.

As to your fitting question, every tyre/rim combination is different and some will go on relatively easily with just your thumbs whilst others will be an absolute bugger even with levers. Don't be ashamed if you need the levers!

Matthew

 

[Paul Narramore]

Ashamed? Well I've caused to punctures by nipping the inner tubes in the last fortnight even though I was ultra careful.

Thanks very much for that information. It did make sense even though my small brain will never remember it all.