Motorcycle Tire Speed Ratings: Reading the Chart and Matching the Required Code

Establish the symptoms

Start by writing down what prompted the question. Common triggers include: • a tire shop quoting a replacement with a different letter; • a used bike arriving with different codes on the front and rear tires; • a recent tire change after which the bike feels vague, weaves or wobbles at highway speed; • a sidewall marking you can't decode; If there is a handling complaint, note when it appears. It may show up only above a certain speed, only with a passenger or luggage, or only after a long run when the tires are hot.

Record recent changes as well. A new tire brand or model, a different size, a puncture repair, a pressure change, added luggage or a passenger, and recent wheel or suspension work all matter. Write down the full sidewall marking for both tires, including the date code, not just the letter. That record helps you tell a specification mismatch apart from a riding symptom. These are two different problems, although they sometimes appear together.

Reading the sidewall code and the chart

On a typical radial sport tire you might see a marking such as 120/70ZR17 M/C (58W). The first part is the tire size: width in millimeters, aspect ratio, a construction letter and rim diameter in inches. M/C identifies a motorcycle tire. In the service description, the number is the load index and the letter after it is the speed rating. Bias-ply tires show a dash or a B where radials show an R. Some older or touring sizes present the code differently, so always read the whole string rather than hunting for one letter.

The common letters in a motorcycle tire speed rating chart are J 100 km/h (62 mph), K 110 km/h (68 mph), L 120 km/h (75 mph), M 130 km/h (81 mph), N 140 km/h (87 mph), P 150 km/h (93 mph), Q 160 km/h (99 mph), R 170 km/h (106 mph), S 180 km/h (112 mph), T 190 km/h (118 mph), U 200 km/h (124 mph), H 210 km/h (130 mph), V 240 km/h (149 mph), W 270 km/h (168 mph) and Y 300 km/h (186 mph). H sits between U and V rather than in alphabetical order. A ZR in the size means the tire is rated above 240 km/h (149 mph). If the service description is shown in parentheses, as in (58W), the tire can exceed that letter's value, and the tire manufacturer sets the actual limit.

These figures describe what the tire withstood in a laboratory test at a specified load and inflation pressure. They are not a recommended riding speed. The rating also assumes the tire is undamaged, correctly inflated and carrying no more than its rated load.

Distinguish plausible causes

When the fitted code doesn't match the required one, the usual explanation is simple. A previous owner or shop fitted a cheaper or easier-to-find tire with a lower letter. Two observations support this: the code is lower than the one in the owner's manual or on the vehicle placard, and the brand or model differs from the original fitment. If the letter is higher than required and the size and load index are correct, that is generally acceptable and unlikely to be the source of a problem.

Sometimes the code is correct, but the conditions the rating depends on are not. Underinflation, overloading, a plug or patch repair, impact damage, worn or uneven tread and age-hardened rubber all erode the margin the rating assumes. Many tire makers state that a repaired tire no longer carries its original speed rating. Evidence for these causes includes low pressure readings, visible damage, repair marks, squared-off tread or an old date code. A new, undamaged, correctly inflated tire makes them unlikely.

If the bike weaves or wobbles at speed, the speed rating may be a coincidence rather than the cause. Other possibilities produce similar symptoms: • an unapproved front-to-rear pairing; • mixed bias and radial construction the maker doesn't permit; • an incorrect tire size; • worn or loose steering head or wheel bearings; • suspension setup, wheel balance or luggage loading; A complaint that began right after a tire change points toward fitment. One that developed gradually points toward wear or mechanical components.

Checks in a useful order

Begin with checks that need no tools. Find the required size, load index and speed rating in the owner's manual or on the tire information label. On many motorcycles that label is on the swingarm, the frame or under the seat. Compare it with both sidewalls. Then check the date code and look for cuts, bulges, embedded objects, repair plugs and cracking. Also check whether the tread wear indicators are close to level with the surrounding tread.

Next, check cold inflation pressure with a reliable gauge and compare it with the manufacturer's specification. Use the solo or two-up figure if the manual lists both. Measure tread depth at the center and on the shoulders. Then confirm that the tire manufacturer's fitment list approves the exact size, construction and front-rear combination for your model. Some makers require a specific front tire to be paired with a specific rear.

Leave anything that requires lifting or partly dismantling the bike to a qualified technician. That includes checking steering head and wheel bearings, wheel runout and balance, rim condition, and internal tire damage that can only be seen with the tire dismounted. If the tire has been repaired, the technician can tell you whether the tire maker permits that repair and what restrictions apply.

Interpret the findings

If the fitted letter is lower than the required code, the fitment does not meet specification, however the bike feels. The fix is a correctly rated tire; adjusting pressure does not change the rating. If the letter matches or exceeds the requirement and the size, load index and construction are approved, you can rule out the speed rating. Move on to the other findings.

Low pressure or overloading shows the tire lost some of its safety margin, but it doesn't show whether the tire was damaged. A tire that has been ridden significantly underinflated should be inspected inside before you trust it again. Visible damage, a repair, worn tread or an old date code each justify replacement on their own. If every tire check passes and the wobble or weave persists, the tires have not been shown to be the problem. Replacing them would be a guess, so the mechanical inspection should come first.

Urgency and next action

Stop riding and arrange transport or a tire replacement if you find any of the following: • a bulge or a cut reaching the cords; • exposed cords; • tread at or below the wear indicators; • a tire that keeps losing pressure; • a wobble that appears suddenly; If a tire is rated lower than required, keep speeds and loads modest until it is replaced. That precaution is not a safe distance or time limit for continued use.

When you contact a tire shop or technician, bring the following information: • the motorcycle's make, model and year; • the required size, load index and speed rating from the manual or label; • the full sidewall markings and date codes of both tires; • your measured pressures and any repair history; • a description of when the symptom happens; With that, they can confirm an approved replacement and decide what else needs inspection.