Not quite correct.
This is about speed ratings and the load information just complicates things and has nothing to do with speed rating. I would leave it out.
SR, HR, VR, and ZR are not the speed designation. The R is for radial construction.
From the nhtsa.dot.gov web site:
Letter Rating
Speed Rating
Q 99 mph
R 106 mph
S 112 mph
T 118 mph
U 124 mph
H 130 mph
V 149 mph
W 168* mph
Y 186* mph
* For tires with a maximum speed capability over 149 mph, tire manufacturers sometimes use the letters ZR. For those with a maximum speed capability over 186 mph, tire manufacturers always use the letters ZR.
Note: You may not find this information on all tires because it is not required by law.
And even the NHTSA gets it wrong. The R is for radial. Although all tires are radial these days, it still is only to denote radial construction.
"R" means radial. "D" means diagonal, referring to bias ply tires. "B" means belted for belted-bias ply tires.
The Z is always in the description, as in P225/50
ZR16. All other speed ratings are shown in the tire's load index & speed symbol description. P225/50R16 100
WW 168 mph 225/50R16 89W
Y 186 mph 225/50R16 89Y
Y over 186 mph 225/50ZR16 89Y
(Y) over 186 mph 225/50ZR16 (89Y)
Note: There are citations of parentheses around the Y for over 186 mph, but I couldn't find a factual basis for it.
And although the speeds are based on km/h, I would delete the km/h because the SCTA doesn't use it.
So it looks like this:
Speed ratings are European Commission for Europe Regulation 30 (ECE 30) European Indoor Wheel Test Standards.
Tire speed ratings are not required by U.S. law.
Pre-1991 speed rating:
225/50
SR16 - 112mph
225/50
HR16 - 130mph
225/50
VR16 - over 130mph (unspecified test speed)
225/50
ZR16 - over 149mph (unspecified test speed)
Post 1991 Speed Ratings:
There are numerous speed ratings below M, but rarely shown in lists.
The Z is always in the description, as in P225/50
ZR16. All other speed ratings are shown in the tire's load index & speed symbol description. P225/50R16 89
WM 81 mph SCTA - Not allowed - lowest speed rating is Q - 225/50R16 89
MN 87 mph SCTA - Not allowed - lowest speed rating is Q - 225/50R16 89
NP 93 mph SCTA - Not allowed - lowest speed rating is Q - 225/50R16 89
PQ 99 mph SCTA -100 mph - 225/50R16 89
QR 106 mph SCTA - Not in rule book, counts as Q rating. - 225/50R16 89
RS 112 mph SCTA -115 mph - 225/50R16 89
ST 118 mph SCTA -120 mph - 225/50R16 89
TU 124 mph SCTA -130 mph - 225/50R16 89
UH 130 mph SCTA -150 mph - 225/50R16 89
HV 149 mph SCTA - Up to 200 mph - 225/50R16 89
VW 168 mph SCTA - Up to 200 mph - 225/50R16 89
WY 186 mph SCTA - Up to 200 mph - 225/50R16 89
YY over 186 mph SCTA - Up to 200 mph - 225/50
ZR16 89
YOver 200 mph - Tire speed ratings no longer apply.
And a reminder that it is not the speed you think you will go, but the current record for the class.
If you break a record that takes you over the speed rating for the tire, you are still good for the remainder of the meet. Subject to safety concerns and an inspection of the tires.
On the other hand, if the record is open and you have Q rated tires on a AA motor you may have difficulties in tech inspection.
And we are not done yet . . . On to motorcycles.
The speed ratings of the tires are as noted above. Motorcycle tires use either the speed rating in the body of the designation or in the load index and speed symbol.
Speed ratings are European Commission for Europe Regulation 30 (ECE 30) European Indoor Wheel Test Standards.
Tire speed ratings are not required by U.S. law.
Tire speed ratings M,N,O,P,Q,R,S,T and U - SCTA - Any tire designated for motorcycle use is permitted 0-70 mph
H 130 mph SCTA 71-130 mph
V 149 mph SCTA 131-150 mph - If shaved, up to 200 mph. Generally, shaving removes the bulk of the rubber and only leaves a thin layer with no cords showing. This reduces the centrifugal forces on the tire.
Z (Listed as ZR in the rule book) SCTA - Up to 200 mph - This would include Y and W rating as they are above Z.
Over 200 mph - speed ratings no longer apply.
Don't forget the date. Tires rated V and above must be manufactured in the last 10 years. Look on the side for a raised block with four digits; it's usually next to the U.S. DOT tire identification number. The first two indicate the week of its manufacture, and the last two are for the year. For example, 1702 would indicate the tire was manufactured in April, 2002. Prior to 2000, there were only three digits, with the last one indicating the year.
