| Spec | Old | New | Diff |
|---|---|---|---|
| Diameter | 614.6 mm | 603 mm | -11.6 mm |
| Revs/km | 518 | 528 | 10 |
This tire size is within the safe range. Your handling will remain stable.
When your speedometer shows 100 km/h, you are actually traveling at 98.11 km/h.
Welcome back to the garage! I’m your resident Senior Tire Engineer, and today we’re tackling a comparison that looks incredibly simple on paper, yet results in two completely different driving experiences. We’re comparing two common sizing options often found on entry-level sedans and hatchbacks: Tire A (185/70 R14) and Tire B (185/60 R15).
At first glance, you might think, "It’s only an inch difference in the wheel, how big of a deal can it be?" Trust me, those small adjustments to the aspect ratio and rim diameter fundamentally alter everything from your speedometer reading to how your coffee stays in the cup on a bumpy road. Let’s break down these two heavy hitters.
Before we hit the road, we need a quick primer on the sizing nomenclature. Both tires share the same width, which simplifies one key aspect of the comparison.
The numbers that truly define the performance difference are the profile (the middle number) and the rim diameter (the last number):
The key takeaway here is that Tire A (185/70 R14) uses a much taller cushion of air to bridge the gap between the rim and the road, while Tire B (185/60 R15) replaces some of that air cushion with metal (the larger rim) for stability.
In a properly engineered vehicle, the replacement tire should maintain the exact overall rolling diameter as the original equipment tire (OEM). When you deviate, you mess with the vehicle’s calibration.
Let’s look at the math, because this comparison is sneaky:
Wait, what? Despite having a smaller rim, Tire A (the R14) is actually about 1.9% TALLER than Tire B (the R15). This is critical for your speedometer.
If your car was originally calibrated for the smaller Tire B, switching to Tire A means the wheels turn fewer times for a given distance. Your speedometer will therefore underreport your actual speed. If your dash says 60 mph, you are actually traveling closer to 61.15 mph. This is a legal and safety concern, especially near speed cameras!
This is where the difference between the high profile (Tire A) and the lower profile (Tire B) becomes impossible to ignore.
Tire A, with its large 70-series sidewall, is designed to absorb vertical impacts. Think of that huge sidewall as a secondary suspension unit. It cushions the blow from potholes, bumps, and rough road surfaces before that impact energy even reaches your primary shock absorbers.
When you reduce the aspect ratio to 60 (Tire B), you significantly reduce sidewall deflection. A shorter sidewall is stiffer and less prone to 'rolling over' during hard cornering. The tire can transmit steering inputs to the road faster and more accurately.
If you enjoy pushing your car even slightly through curves, the 185/60 R15 will offer a more engaged and connected driving experience.
Determining fuel efficiency between these two is complex, as it involves two major engineering variables: Unsprung Weight and Gearing Effect.
Tire B requires a 15-inch rim, which is typically made of alloy. Even if the tire itself is slightly lighter due to the shorter sidewall, the larger rim usually outweighs the weight savings. Heavier unsprung mass (the weight not supported by the suspension) requires more energy to get rolling and stop, marginally hurting fuel economy.
Because Tire A is taller, it effectively acts like a longer final drive gear ratio. The engine doesn't have to work as hard (fewer revolutions per minute) to maintain a consistent highway speed compared to the smaller Tire B.
The Verdict on Efficiency: For pure highway efficiency, the taller Tire A (185/70 R14) often holds a marginal advantage due to the gearing effect and potentially lower overall unsprung weight (assuming the 14-inch rim is steel or a very light alloy). Tire B requires the engine to spin slightly faster to maintain the same actual speed.
Choosing between the 185/70 R14 and the 185/60 R15 is ultimately a choice about your priorities on the road.
Remember, changing your tire size from the manufacturer's specification should always be done carefully, keeping the overall diameter as close to the OEM size as possible to avoid major speedometer errors!