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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?

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  • Are you asking why the letters aren't in alphabetical order? I'm just trying to understand. Jan 7, 2016 at 21:44
  • @Paulster2 I have edited my question. Sorry it wasn't very clear before. Jan 7, 2016 at 21:52
  • Thanks! And I think @JPhi1618 answered about as good as anyone can :D Jan 7, 2016 at 21:53
  • @Paulster2 That is a fair point. Jan 7, 2016 at 21:59

1 Answer 1

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+50

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".

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  • 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! Jan 7, 2016 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, 2016 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. Jan 7, 2016 at 21:57
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    @JPhi1618 vote, not upvote ;)
    – Zaid
    Jan 7, 2016 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, 2016 at 22:05

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