Tires in their sizes usually have letters on them, you might have come across “P” or “LT” letters. These letters sometimes show up at the beginning of the size, and the “R” letter right before the wheel size. For instance you come across P245/40R18 or LT315/70R17. But what could it possibly mean when the tire says “P245/40ZR18”? And so, you need to know what speed ratings are.
Now, speed ratings are expressed in letters and are usually listed alongside load index for a tire after the size. For instance, 245/40R18 93H. H appears to be the speed rating and 93 the load index. Both the load index and speed rating could be described as service description.
Also, it is important to know that anything rated for more than 149mph is considered a Z-speed rated tire. Most times, the manufacturer could attach the Z in the size right before the R. This helps to denote a Z-speed rated tire. Not all Z-speed rated tires have a Z listed on the sidewall in this manner because it is not mandatory. The service description is more specific about the speed rating, in adding the Z may be an aesthetic choice.
Therefore, ZR is a category of speed rating. It was first introduced for speeds over 149mph. Although car speeds have increased beyond what was required as maximum. ZR was later subdivided into Y, W and Z due to the capabilities of cars going faster than 149mph.
Do I Need Zr Tires?
Many people consider if it is often advisable to use ZR tires, hence the question is asked. Obviously, tire speed ratings are taken by running the tire, under load or at speed. Performance from 1mph on up could indirectly affect the speed rating of the tire. The lower the speed rating, the softer the tire carcass is. Because lower speed rated tires are meant for normal cars and not performance cars.
Thus, they tend to have harder tread compounds (longer tread life and less dry road traction). Understanding this is critical in making an informed decision about tires.
Consequently, tires which have a max speed capability of over 149mph could have ZR in size designation. Tires with a maximum speed capability over 186mph could be required to include “ZR” in the designation. But tire designations have changed tremendously over time.
Back then they had just come out with the Z rating for cars like the Corvette, Vipers, and the exotics. Now they have a lot more ratings that are more specific on the speeds they are designed for – W, Z, V, H, U, T etc.
What Is A ZR Tire Rating?
ZR-rated tires are designed to go faster than 149 mph. And as such top speed has emerged in the past three decades. This prompted manufacturers to create something more specific. Thereby leading to the introduction of W-168 and Y-186 rated tires. In the description, If the W or Y-rated tire’s service is in parentheses, then the tire is rated for speed greater than 168 and 186 respectively.
Because W and Y tires are rated for more than 149 mph, they are also Z-rated. Though this marking is sometimes omitted in the size. In describing the letter construction, the letter R which is radial; ZR stands for a Z-rated radial. ZR basically means the tire is adapted for speed above 149mph. Before 1990, the manufacturers used “ZR” to mean high performance tires until it was redeveloped into W, Y, and so on.
Can You Repair ZR Rated Tires?
Yes. ZR rated tires they can be repaired. British standard on motorcycle tire repairs (BSAU159f) states that no repairs are allowed on sidewalls. Hence, the standard says repairs are not allowed on high speed Z-rated tires. According to the standard, only certain areas can be repaired.
It says a tire must be inspected by an expert for any secondary damage. For instance, if a nail punctures your tire, it might have also damaged the sidewall inside. Also, a run-flat exposed cords and so on. Repairs can only be made in the center of the tread area. With 25% of each side of the center line.
To this, ensure that repairs are done with a mushroom-type plug. This should fit into the punctured hole from inside. It should bound with the tire by vulcanization. If for anything else and the British standard says the tire must be chucked. And if your tire repairer says the same thereby quoting similar reasons, then he’s being honest.
It is important to note, it is often dangerous to re-inflate a tire which has gone flat. For any serious under-inflation then such tires should be taken by a specialist for thorough examination. On no account should a tube be considered as a puncture repair remedy.
A permanent repair could be carried out to check if there is an external or internal damage. This can only be done by a specialist. To avoid hazard of any kind, neither externally applied plug type nor liquid sealants should be used. Tire manufacturers may not be liable to problems resulting in their unrecommended use.
ZR shown on the sidewall of your tire is a reference to the tire’s speed rating. Historically, the speed rating ZR on a tire meant that the construction of the tire could reach 150 miles or 240 kilometers per hour.
Today, a tire labeled ZR, has more capabilities than before. ZR can be classified into 3 different speed ratings, which can be either W, Y or Z.
If you’re replacing your tires, you may want a low or high-speed-rated tire. It is best not to mix and match them. When mounting differently rated tires, techs prefer you put the lower-speed-rated ones at the front to prevent over steering. This can conflict with the best practice of putting the tires with the most tread on the rear. And could also be important for wet traction.