Load Index and Speed Rating: The Safety Stats Most Drivers Ignore

The tow truck driver dropped the Ford F-250 at the shop. The left rear tire had exploded on I-75. The sidewall was shredded. The owner, a guy named Rick, was standing next to the truck, arms crossed, face red. He kept saying the same thing: “I just bought those tires six months ago. They had plenty of tread.” I walked over to the destroyed tire. It was a standard passenger tire, P-metric, with a load index of 107 and a speed rating of S. The sidewall clearly showed “P265/70R17 107S.” Rick’s truck was a heavy-duty F-250, not a light-duty F-150. The wrong vehicle. The wrong tire. I asked him if the tire shop had asked what truck he drove. He said “yeah, I told them F-250.” I asked if they looked up the correct load rating. He said “they just handed me the same size as my old tires.” The old tires were also the wrong rating. Whoever owned the truck before Rick had put P-metric tires on it. Rick never checked. He assumed the tire shop knew what they were doing. The F-250 has a gross vehicle weight rating around 9,000 pounds. That’s about 2,250 pounds per wheel on average. A load index of 107 is rated for about 2,150 pounds per tire. That’s close – but the rear axle carries more weight than the front, especially when towing. Rick had been hauling a landscaping trailer that week. The extra tongue weight pushed the rear tires over their limit. Heat built up. The sidewall failed. The tire blew. The Load Index Calculator would have shown him the problem before he ever left the shop.

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Tire Load Index Calculator

Enter your tire size and load index — see maximum weight per tire and recommended load for your vehicle.

All data stays in your browser — we never see it.

I pulled up the calculator on my phone and showed Rick. His truck needed a load index of at least 115 – about 2,680 pounds per tire. The 107 tires were rated for only 2,150 pounds. That’s a 20% deficit. He was overloading them every time he drove with a full tank of gas and a passenger. Rick’s face went from angry to confused to embarrassed. “How was I supposed to know that?” he asked. That’s the problem. Nobody tells you. The door jamb sticker shows the recommended tire size and inflation pressure. It also shows the load range – but most people don’t know what that means. A “load range E” tire has a higher load capacity than “load range C.” The P-metric tires on Rick’s truck were “load range SL” – standard load. That’s for passenger cars, not heavy trucks. The Tire Speed Rating Guide is another stat that gets ignored.

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Tire Speed Rating Guide

Enter your tire speed rating — see maximum safe speed and performance characteristics.

All data stays in your browser — we never see it.

A few years ago, a guy named Steve brought his BMW M5 to a track day. The car had new tires – same size as stock, same brand, everything matched. But the speed rating was wrong. His M5 came with Y-rated tires (186 mph). The shop sold him V-rated tires (149 mph). On the track, Steve hit 140 mph on the straight. The tires overheated. The tread started separating. He felt a vibration, backed off, and drove slowly to the pits. The tire was ruined. A few more laps and it would have blown. Steve checked the sidewall after. He saw the V rating. He was furious – at himself for not checking, and at the shop for selling him the wrong tires. Speed ratings aren’t just about top speed. They’re about heat dissipation. A tire rated for 186 mph can handle higher internal temperatures than a tire rated for 149 mph. On a track, in hot weather, with heavy braking and hard cornering, that extra heat tolerance matters. On the highway, driving 75 mph, it doesn’t. But if you ever push your car – track days, mountain roads, even sustained high-speed cruising – the speed rating is critical. Rick’s truck didn’t need a high speed rating. He drove 70 mph. The S rating (112 mph) was fine. His problem was load index. Steve’s problem was speed rating. Two different vehicles, two different mistakes. The Tire Size Comparator isn’t directly about load or speed, but it helps you see if the tire size is correct.

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Tire Size Comparator

Compare two tire sizes side by side — see diameter, width, sidewall, and revs per mile.

All data stays in your browser — we never see it.

Both Rick and Steve had the correct tire size. That wasn’t the issue. The issue was the numbers after the size – the load index and speed rating. Those are easy to overlook. They’re printed on the sidewall, but they’re smaller. Most people don’t even know what they mean. Rick ended up buying a set of LT265/70R17 tires with load index 121 and speed rating R (106 mph). He also bought a tire pressure monitoring system for his trailer. He said “I’m not taking any chances anymore.” That’s the right attitude. Load index and speed rating are not optional features. They’re safety specifications. Ignoring them is like ignoring the weight limit on a bridge. The bridge might hold your truck. Might not. The tire might survive. Might not. Check your door jamb sticker. Find the recommended load index and speed rating. Look at your tire sidewall. Compare the numbers. If they don’t match, replace the tires. Not next month. Now. A guy named Tom had a Nissan Leaf. He put cheap tires on it with a lower load index than stock. The tires looked fine. But when he had three passengers and a full trunk, the rear tires were overloaded. He didn’t know. He drove from Detroit to Chicago. One of the rear tires blew. He was fine, but the tire was toast. He checked the load index after – 89 instead of 94. He said “I didn’t think it mattered.” It matters. The Load Index Calculator is free. The Speed Rating Guide is free. Use them before you buy. Not after.