Hitchcocks Forum

Hello,

I just bought new tyres Dunlop K70 and I need some explanation on markings on side of tyres.
Front tyre is 3.25/19 54p and back tyre is 3.50/19 57p.

The thing I don't unterstand is that when I put tyres side by side, the rear one is bigger - taller (even thou they have same diameter - 19).
Why is that? Is this normal or I made some mistake when buying tyres?

Thanks
Peter

3.50 is wider than 3.25
Tyre sidewall wall markings explained:-

http://dustcap.co.uk/images/sidewallmarkings.gif

The aspect ratio determines the diameter a 100 aspect ratio has a bigger diameter that a 70 aspect ratio.
Plus a 3.50 tyre and a 3.25 tyre will have different diameters even if the aspect ratios are the same.

No Peter, you have not made a mistake. But it may be helpful to explain what "aspect ratio" means. On a metric sized tyre it's normal to see the size expressed as something like - 90/90 x 19 - the second 90 is the aspect ratio, which is expressed as a percentage of the width. Hence this tyre is 90mm wide, and the sidewall height is 90% of 90mm. Normally for the imperial sizes you quote the aspect ratio would be 100, i.e. 100% of the width. So a 3.25 would have a sidewall of 3.25" and a 3.50 a sidewall height of 3.5". It's the hole in the middle that's 19" because that's where the 19" wheel fits,,,,,,,,,,,,, Hope that makes sense.

Thank you all. What does 54p or 57p stand for?

The 54 is the load index:-
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http://www.tyresave.co.uk/tyreload.html
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The P is the speed rating:-

http://www.tyresave.co.uk/tyrspeed.html

As Papa says its known as the service description.

speed rating / load.

So how does load index work? Is it like front tyre + rear tyre? (In my example 54 load index + 57 load index)? That would be 467lbs + 507lbs = 974lbs. Is that all the load tyres can take and then minus motorcycle weight, minus rider weight, etc?

It is the maximum weight on the tyre. Add front an rear tyre load weights up that that will probably exceed the maximum makers allowed gross vehicle weight of the motorcycle.
It does on my BMW K75S by a big margin, manufacturers GVW 992lbs(450 kilos)add the maximums for each tyre 1188lbs (539kilos)