"80R1383T" means 'aspect ratio of 80, radial construction', rim size 13 inches, load index 83, speed rating T. Aspect ratio is the height of the tyre, 80 is 'normal' anything less is generically termed 'low profile', load index is the max weight the tyre can carry, speed rating is the max speed the tyre can be used.
You must have misread "86R" as there is no such type.
Might be worth changing both to exactly the same type and considering "C" (Reinforced) type.
As I understand it, in the old days of crossply tyres the height was the same as the width. The width/height ratio is called the aspect ratio. When radial tyres were introduced the normal ratio became 80%, ie the height was 80% of the width, except the 80 wasn't usually shown on the tyre, so the tyre would have, say 185-14 on it. Later on, late 60's ish this ratio started to reduce, mainly in the interests of better handling as shallower walls dont flex as much, and to give a larger footprint on the road without increasing the overall diameter. It started at 70% aspect ratio, eg 185/70/13 as fitted to the early 3ltr Ford Capri, and is now down to the elastic bands seen on some cars. Any tyre below the "normal" 80% was known as "low profile" and to many people still is. So yes 265/70/17 could be called low profile.
Pete.
Post last edited on 29/04/2010 20:47:04
------------- Don't panic!
Hit it with a pointed stick!
Nostalgia's not what it used to be.
As I understand it and as said, Crossply sidewall heights used to be 100% of the widths, when Radials took over the side walls were first 82% of the width but this was not mentioned as part of the size.
You can still buy radial tyres of a particular size without the aspect ration mentioned and others saying 80%, I'm not sure if all are now 80% but those without the aspect ratio mentioned still differ in other ways, such as the load they can carry.
As for 'C' for Commercial or 'Reinforced' these are not the same tyres and are constructed differently, most importantly, they use very different tyre pressures for the same load.
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