Tyre Sizing

[kevberlin]

My Cb250rs requires a new rear tyre. The owners manual gives the tyre size as 400s 18 4PR. My current tyre shows itself to be 110/90/18.
I understand the 110/90/18 description, but haven’t a clue regarding the 400s 18 4PR.
Can anyone enlighten me please so I can be assured when I purchase the tyre.
Thanks a lot.
Kev

[xbally]

Sorry Kev I have no idea but when I get some time I intend to look into this as the tyres on my RS250 will need replacing soon too.

[xbally]

My Haynes says 4.10 S18-4PR for the rear. Mr. Honda's owners' manual also says the same.

[Ian]

I'm no expert on tyre information but I believe the 4PR is 4 ply rating. This is an index that measures the tyre's capacity to withstand the load at a given pressure.

[kevberlin]

It seems the 400 sizing shown in the manual is the imperial measurement.
In the case of the cb250rs 110/90/18 is appropriate.
Kev

[Itsme]

Being pre-metric I was always used to buying tyres in sizes like 3.25, 3.50 and 4.00 x 18 or 19. The 4.00 refers to the width of the tyre in inches (remember them?) and confusingly the .25, .50 etc was a fraction of an inch in metric! or at least that's what I always was told and if you measure the width of old tyres it seems to be right. In those days we didn't care about aspect ratios, the middle number of a modern tyre size, we just bought the right rim size and a suitable width for the bike and how we were going to use it. So on a 250 a 4.00x18 sounds about right and I would have expected the front tyre to be a 3.25 or 3.50.

Ian

[iansoady]

I prettty much agree Ian, although I would use a size lower - 3.50 for the back and 3.25 for the front. I need a back tyre for the dreaded Yam and intend to fit a 3.50x19 Mitas H01 which I've had success with in the past.

[Itsme]

Hi Ian

To be fair on reflection I agree with your choice of tyre sizes. I remember my 350 JAWA using a 3.50 x 18 rear and a 3.25 x 18 front. I think looking back the only time I used a 4.00 x 18 on any of my CZ/JAWA machines was when using them with trials tyres and then I used a 21" front wheel with the 18" rear.

Ian