Newbie tyre size advice

[luusac]

Hello,

I am looking for a new tyre and am a bit lost with the sizing.
Rear tyre (newish), 37-622 (28x1 5/8 x 1 3/8 - 700 x 35C) HS348
Front (old, to be replaced) 40-622 (700 x 38C) - I think these are correct, but some of it is hard to make out

I suspect that originally both tyres were the same as the front. If I have understood tyre sizing correctly it is the tyre width that is different between these two tyres, and that the difference is only 3mm. Does it matter, can I just get another 37-622, or should I replace the rear as well to the original 40-622? Bike is used for short distance commuting and short family rides only, in case that makes a difference.

If I were to replace one or more wheels too what size for the above tyres, 28"?

Thanks

 

[raleighnut]

700c tyres, and ones a 35 the other a 38 so I'd match the front to the newish rear but make sure you fit the new tyre to the front wheel.

 

[luusac]

So it doesn't matter too much whether is is a 35 or 38? What size of wheel if I want to replace that too?
Thank you.

 

[andrew_s]

It's OK to mix tyre sizes, so long as the difference isn't excessive. The difference between 35 and 38 (or 37 and 40) is minor, and within the range of differences between what tyres actually measure, and what they say on the side. If you deliberately mismatch sizes, it's usual to put the larger tyre on the rear, as there's more weight on the back of the bike.

I'd get another 37-622 to match the rear.

Any new wheel has to be a 700c (iso 622) wheel, or your brakes won't be in the right place for the rim. If you have disc brakes, you can swap wheel size, but you want to change both or the resulting tilt forwards or backwards will affect the bike handling.
Rim sizes are given as (eg) 17-622, where 17 mm is the internal width. The external width is generally about 6mm more than the internal width. Width limits what tyres you can fit - the absolute narrowest tyre would be about the same as the external width, or a bit more, and you shouldn't go wider than double the narrowest.