Measuring Tyre Widths

john xyz

Active Member
Location
East Kent
I purchased tyres from Ebay size 700x47. I wanted tyres that are 47mm wide.

The tyres that arrived were 28x1.75.... 1.75 equates to 45mm. The seller states that the tyres supplied are correct as both are 622x47.

Its only 2mm difference I know, but... If I had received tyres that actually were branded 700x47, would they be 47mm wide?

Thanks
 
Location
Loch side.
No tyres are almost never as wide as advertised. There are two reasons for this:

1) Rim width. A wider rim produces a wider tyre (measured across the widest part of the tyre, the bulge). Meaurements are according to a standard rim width used for ERTRO (European Tyre and Rim Organisation) classification purposes but your rim is almost never the same.
2) Weight Weenies. The scurge of the industry, these people weigh components on cocaine scales and then make decisions based on the lightest. Tyre manufacturers are fed-up with weight weenie editors choosing the best tyres in magazine "Shoot Outs" according to whichever tyre is the lightest, have evolved and now overstate the sizes of their tyres. In other words, their old 25mm is now a 28mm, for instance. This means the weight weenie editors now think it is the lightest 28mm tyre in the batch but actually, it is just an average 25mm tyre. This practice escalated out of proportion in a mini arms race. Some truce was called a few years back when one company, Avocet, said it will stop the practice. It subsequently went belly up or almost belly up. The rest of them still play this stupid game.

Having said that, a mm sizing is just nominal. You wanted a wide tyre and you got one. It doesn't matter whether it is 45 or 47mm. My next rant will be about the stupid mixing of systems - imperial and metric, on the same tyre i.e. 622 (mm) x 1.5".
 
U

User6179

Guest
I think it is the way they size them ,like shoes they go to the nearest recognisable size , they could measure 50mm in a wide rim at low psi or 45mm in narrow rim at a higher psi , the size is just a guide .
 
The whole thing is very confusing

There are several different methods of measuring tyres and tha similarities and differences can be staggering a 20" tyre can have a diameter difference of a couple of inches!

It should also be noted that the physical difference can be due to tyre pressure and rim width as well.

In this case according to the CTC, the 700X47 tyre is a 622-47

Schwalbe has a tyre calculator if you wish to investigate further
 
Location
Loch side.
Tyre pressure, above a nominal pressure, doesn't affect width. There is a magic angle for the cords in tyres and high pressure hoses (35.something degrees) that prevents tyres and hoses from lengthening or fattening under pressure.
The assumption is that the cords don't stretch under the recommended pressures calculated by the manufacturer.
 
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User6179

Guest
What? 40mm is not 40mm?

I cant quite remember, been a while but 40mm in say push fit is not compatible to say 40mm solvent weld or something like that ,one is sized by the bore of the pipe I think , hopefully a plumber will appear and explain but it is a fekin nightmare if your house has the old imperial pipes and your trying to put in a new bath or sink .
 
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john xyz

john xyz

Active Member
Location
East Kent
Thanks guys, I'll just put them on and see how I go... and will go research more for future purchases...
 
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OP
john xyz

john xyz

Active Member
Location
East Kent
Well I put the 28x1.75s (Continentals) on my Specialised Crosstrail Eilte and they;re a vast improvement on the tyres the bike came with. The TriggerSport tyres it came with were so bad I binned them not even keeping them for spares. The wider tyres are much better on the bad roads and along trails..

Thanks again
 
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john xyz

john xyz

Active Member
Location
East Kent
The stock tyres were 38s, the new ones 1.75...which equates to 45mm. So 7mm wider in total. Pumped to 50psi its a very nice ride..
 
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