Tyre Sizing Misunderstanding

[Deleted member 35268]

I always thought (and never sought to clarify) that the second number for a 700c tyre e.g. 23, 25, 28 was additional extra diameter or thickness of the tyre and not the width!

Reason I thought this was a 28c is usually a longer diameter than a 25c for clearance etc.

What a numbnut

 

[Spiderweb]

I'm confused now, does the 23/25/28 number not refer to both width and depth of a tyre?
So if you move from a 23mm tyre to a 28mm tyre then the latter will be both 5mm wider and 5mm deeper?

 

[Deleted member 35268]

I'm confused now, does the 23/25/28 number not refer to both width and depth of a tyre?
So if you move from a 23mm tyre to a 28mm tyre then the latter will be both 5mm wider and 5mm deeper?

maybe ?

 

[mjr]

It's actually far worse than that. The c on 700c indicates the height and means 39mm (to result in an outer diameter of 700mm) and that's usually also the width, so 39mm. 700b tyres are still 700mm tread-to-tread but 635mm bead-to-bead, so lower/narrower tyres on a slightly bigger wheel. Measuring tread-to-tread makes some sort of sense as you could put a 700b wheel+tyre in most frames designed for 700c or 700d as long as rim brakes have enough height adjustment.

Sizes like 700x25c and so on are all sorts of confused (because it's no longer 700mm tread-to-tread) and confusing and that's why the ISO sizes are the only ones to use, written width dash bead in mm, so 25-622 or whatever.

 

[mjr]

Oh and if you really look for them, there are a few tyres with different width and height when mounted on the recommended rims, written as width/height-bead. I've had some 28/32-630.

 

[Milkfloat]

I'm confused now, does the 23/25/28 number not refer to both width and depth of a tyre?
So if you move from a 23mm tyre to a 28mm tyre then the latter will be both 5mm wider and 5mm deeper?

Depends how much you inflate it

 

[Globalti]

I always thought (and never sought to clarify) that the second number for a 700c tyre e.g. 23, 25, 28 was additional extra diameter or thickness of the tyre and not the width!

Reason I thought this was a 28c is usually a longer diameter than a 25c for clearance etc.

What a numbnut

Hey! This comment is discriminatory against @numbnuts of this parish and other poor folk suffering from loss of feeling in the gonads.

 

[rogerzilla]

This is the most confusing thread ever. Best option is to ignore the meaningless names like 700c, 26", 20" etc and use the ETRTO/ISO code like 23-622, 54-559 or 28-406. The first number is the nominal diameter of the inflated tyre and the second number is the bead seat diameter. All rims and tyres have these codes.

Otherwise you might not realise that a 700c and 29er rim are the same size and that there are two common - and totally incompatible - 20" rim sizes and three 16" rim sizes.

 

[raleighnut]

This is the most confusing thread ever. Best option is to ignore the meaningless names like 700c, 26", 20" etc and use the ETRTO/ISO code like 23-622, 54-559 or 28-406. The first number is the nominal diameter of the inflated tyre and the second number is the bead seat diameter. All rims and tyres have these codes.

Otherwise you might not realise that a 700c and 29er rim are the same size and that there are two common - and totally incompatible - 20" rim sizes and three 16" rim sizes.

There is about 5 different sizes of 26 inch tyre non of which are compatible

 

[Ming the Merciless]

Hey! This comment is discriminatory against @numbnuts of this parish and other poor folk suffering from loss of feeling in the gonads.

You are talking balls

 

[Ajax Bay]

https://www.sheldonbrown.com/tire-sizing.html

I'm confused now, does the 23/25/28 number not refer to both width and depth of a tyre?
So if you move from a 23mm tyre to a 28mm tyre then the latter will be both 5mm wider and 5mm deeper?

Depends on how close those different tyres are to their nominal width. Also depends on inflation pressure and the wheel's inner rim width.
I've found the bicyclerollingresistance.com site useful for finding out which tyres/models come up narrow and which come up wide. This is their Conti-gp4000s-ii-23-25-28 comparison.
Quoting:
For 23mm, 25mm, 28mm tyres (on a 17mm rim at 100psi):
Measured Width: 25 mm 27 mm 31 mm
Measured Height: 23 mm 25 mm 29 mm

 

[Levo-Lon]

The 26" wheel debate trundles on...and on...and on

It's like a Celine Dion song and on

 

[mjr]

Don't you mean 559mm?

590mm aka 26"x1⅜" is the only true 26" size!

 

[Ming the Merciless]

37-622