What tyres do I need ?

[Michael bmx]

I have a set of alex rim dr13 they measure 18" in diameter and 1 " wide, I brought some 20" tyres thinking they were considerdd as 20" then found that 20" only measure 16" across, so do I need to try and find a 22" tyre?

[Michael bmx]

Also forgot to say that the original tyres say 20x 1 1/8 and the new ones say 20 x 1, the wide isnt the issue so could someone explain why the 20 is?

[CustardLips]

What's the actual size of rhe rim... 20 x 1 3/8 ?

[Michael bmx]

The wheel itself measures 18" in diameter and 1 1/8 in diameter, I just found out that this is a 451mm tyre where a standard 20" wheel uses a 406 I made a mistake

[BMX1973]

I remember selling some 20"  Weinmann rims on here and the irate buyer (newbie) said I sold them 18" child's wheels . They will not fit my repop Comp3s which Im getting

 I said when tyres arrive see if they fit, which they did. 

The wheel will be 20" when the tyres are put on 

[Michael bmx]

Thanks again for the reply, yes they are 20" with tyres, there where I made the mistake, I thought all 20" wheels where the same size, but they are not lol, a standard 20" wheel seems to be 16" in diameter but my alex rims are 18" but both are 20" with tyres on, so when I brought 20" wheel tyres I was sent a set for the standard instead of the 451 mm type I needed guess im stuck in the 80s/90s lol before mm was used ha ha. All sorted now 👍

[brettypeeps]

The tyre size is 20 x 1 3/8.

[Spen69]

20" is the maximum OUTSIDE diameter of the tyre once fitted 

Narrow 1-1/8"  & 1-3/8" rims use different tyres but are still only 20" max when inflated.

I could be wrong but I think it has something to do with very early racing rules but either way there are two sizes, one is denoted with a fraction in the notation and the other uses a decimal. A standard rim is termed 20x1.75" or 20x1.5" and will fit any tyre from 20x1.5" upwards, seen newschool running 20x2.4" fairly often. The other rim is noted 20x1-1/8" and will run 20x1-1/8" or 20-3/8" tyres

Hope that helps - can probably post a few pictures if it's still not clear but for example my kids race bikes have a 1-1/8" narrow rear tyre and slightly wider 1-3/8" front for better grip

Oh, and don't forget you will need different size brake caliper - probably 610 size not standard 890/900/1000/1020's - if you're not sure what I mean the measure the centre of the brake spindle hole to the middle of the rim brake surface in mm then add a zero which will give you a number to aim for in the serial size of the caliper

[Michael bmx]

Thank you so much for the info it is a great help, I have converted to disc breaks but that info will help in the future. Thank you guys

[Michael bmx]

I have alex rims and these ankie ones