According to an answer on this page the speed ratings that can appear on the end of a tire specification (like "195/65R15 91 V") include almost all of the letters of the alphalphabet in almost the correct order...

A1-A8 - Steps from 3 mph to 25 mph
B - Up to 31 mph
C - Up to 37 mph
D - Up to 40 mph
E - Up to 43 mph
F - Up to 50 mph
G - Up to 56 mph
J - Up to 62 mph
K - Up to 68 mph
L - Up to 75 mph
M - Up to 81 mph
N - Up to 87 mph
P - Up to 94 mph
Q - Up to 100 mph
R - Up to 106 mph
S - Up to 112 mph
T - Up to 118 mph
U - Up to 124 mph
H - Up to 130 mph
V - Up to 149 mph
W - Up to 168 mph
Y - Up to 186 mph
Z - 149 mph and over

Why are not all of the letters in the alphabet included and why is one of the letters, H, in the wrong order?

  • Are you asking why the letters aren't in alphabetical order? I'm just trying to understand. – Pᴀᴜʟsᴛᴇʀ2 Jan 7 '16 at 21:44
  • @Paulster2 I have edited my question. Sorry it wasn't very clear before. – Max Goodridge Jan 7 '16 at 21:52
  • Thanks! And I think @JPhi1618 answered about as good as anyone can :D – Pᴀᴜʟsᴛᴇʀ2 Jan 7 '16 at 21:53
  • @Paulster2 That is a fair point. – Max Goodridge Jan 7 '16 at 21:59

I don't have and sources for this, so please, post 'em if you got 'em, but it's my understanding that H was originally used to designate either Highway rated tire or High speed. Even I'm not clear on this...

Also, the letters I and O are commonly left out of lettering schemes because of their cousins, the numbers 1 and 0.

And to speculate further, X is missing because before standard, metric tire sizes, the X appeared as a separator between the tire height and width like: 29.0"x 9.3".

  • That would explain the missing I and O, but surely logic would suggest that X would also have a speed rating? Considering that the rest of the alphabet does! – Max Goodridge Jan 7 '16 at 21:24
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    X is being reserved for when a tire with an eXtreme enough speed rating is manufactured. – JPhi1618 Jan 7 '16 at 21:26
  • That sounds feasible. It would just be nice to know how that originated or who came up with it or when. Maybe that is just me. – Max Goodridge Jan 7 '16 at 21:57
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    @JPhi1618 vote, not upvote ;) – Zaid Jan 7 '16 at 22:02
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    You're not too new to be able to chat. Come on over to the chat room with any questions like that, or just to... chat. – JPhi1618 Jan 7 '16 at 22:05

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