AP, I hit a curb this weekend and broke two of my tires. In the process of repairing the damage, I had many questions but little time to ask. I am sorry to throw so many questions out at once.
1. Can two tires that are not the same (ie. made by different companies) be placed on the same axle if they are the same size?
2. What did it mean when someone told me I had a directional tire?
3. What does the speed rating mean? Does it matter if two tires have different speed ratings? What speeds do the speed rating letters represent?
4. Does a damaged rim:
a. increase the risk of damage to my car/tires?
b. create unsafe driving conditions?
5. Why are tires so expensive?
Thanks!
ANSWER PERSON RESPONDS: Uh, oh. I see liability issues here. Just for this one question, pretend that AP is like the TV psychics who function for entertainment purposes only. You should really ask an honest tire dealer, or perhaps a mechanical engineer here at Duke!
My dad used to purchase used tires for $5 or $10 each, so none of them would match (except the size). This was for an old beater car that he just drove around town. It didn’t seem to matter. I’ve been told that it really *does* matter, certainly for the front axle (or any axle that steers).
Directional tread will point differently depending on which way you mount the tire. Even with non-directional tread designs I’ve always heard that with radial tires they get used to revolving a certain direction. That’s why you rotate radials front to back, never side to side (although for short distances at reasonable speeds, like when you put on a spare, it shouldn’t matter).
Speed ratings indicate the highest recommended speed, and there’s usually a huge safety margin (e.g., the tires can go faster than your car can safely go). I’m sure it’s advisable to use the same speed ratings all the way around (one corner of your car isn’t going to be slower, hopefully), and you certainly want all of them to surpass the capabilities of your car.
F = 50 mph
G = 56 mph
J = 62 mph
K = 68 mph
L = 75 mph
M = 81 mph
N = 87 mph
P = 93 mph
Q = 100 mph
R = 106 mph
S = 112 mph
T = 118 mph
U = 124 mph
H = 130 mph
V = 149 mph
Z = 149+ mph
You should replace the wheel that has a damaged rim, or see if the rim can be repaired. Get a mechanic to look at it (I don’t know the extent or location of the damage.) It could lead to losing air pressure or making it more likely that the tire will catastrophically blow. Yes, this is unsafe.
There’s probably profit in the price somewhere, but there’s also a lot of engineering and rubber. It’s pretty amazing that they can run over abrasive surfaces for tens of thousands of miles before wearing out.