Tyre size?

[atrick]

Please help me? Just got a new bike and trying to set computer, the tyres on my bike are Schwalbe silento and the size is
37- 622 (28x1.40) 700 x 35c. Surely it is either 37 or 35 ? It's the width isn't it? But according to Sheldon website the setting is different so which do I go for?
Thank you, kind regards, Patrick

 

[Tim Hall]

Measure the circumference by a dab of paint on the tyre and rolling the bike along the drive or road. Measure the distance between the dots of paint on the road. On the other hand, the difference in effective circumference between a 35mm and 37mm section tyre is 12mm. Or about 0.5% of the tyre circumference. Use 36 and the job's a good 'un. (Waits for someone to correct my sums)

 

[atrick]

Thanks Tim, got that and will measure it. Just don't understand why the tyre is marked with the two different sizes?

 

[wam68]

Thanks Tim, got that and will measure it. Just don't understand why the tyre is marked with the two different sizes?

Yeh, it's confusing but the 622 x 37 will be the ETRTO measurement and will refer to the inner diameter of the rim ( 622mm from the inner edge to the inner edge). The 700 x 35 refers to the outside edge tyre diameter ( 700mm from tyre tread to tyre tread ). That will be the most accurate reading for your computer setting

 

[atrick]

I understand the 622 and 700 bit, but why the 35 and 37? No where online is this shown as the same thing, all the charts I have seen are either 35 or 37, never both, whereas the 622 is same as 700

 

[sreten]

Hi,

700C refers to the 622mm rim size and is not the diameter of the tyre.
The diameter depends on the 700C/622m tyre width mainly, and to
a lesser extent the width of the rims. For Sheldons calculator 37mm
is likely best, though actual tyre width is likely 35mm. Tyres aren't
perfectly round, such that width always implied the extra height.

rgds, sreten

 

[raleighnut]

The rolling measurement is the best way IMO

 

[John the Monkey]

The rolling measurement is the best way IMO

Yup. I've seen enough claimed 23c tyres that give different sizes when measured using this method to distrust manufacturer sizing.