Tire size confusion

[homeiss]

So I've realized that the tires on my car are not stock size which would mean my speedometer and odometer readings are slightly off.

My car's stock tires would be 175/70R13 and the ones on my car are 195/60R14.

When I plug those numbers into this site it says when the speedo says 100 I'm actually going 102.5.

However, when I use the calculator on this site it says when the speedo says 100 I'm actually going 97.56.

Not sure why I'm getting different numbers here. Any help would be appreciated, thanks!

[pletby]

If you have a GPS or even a cell phone with GPS you can set your cruise at 100km/hr and read how fast you are really going then apply the correction to your speedometer.

As a strange sidebar my speedometer is optimistic by around 4km/hr, but when I read the speed off my Ultragauge accessing my car's computer it matches the GPS exactly. Weird eh?

I'm not an expert on reading tire sizes, someone else will chime in I'm sure.

[jray3]

I've seen bad speedometer readings on two hondas now (with stock size tires). My Odyssey reads 4-5 mph high at highway speed, but the odometer and OBD readouts are spot on, whether counting mile markers or using GPS.

[vskid3]

I think your issue is that the two sites compare things backwards from each other. Your second site is actually saying that when your speed is 100, your speedo will say 97.56. The tire you're running is a little bigger, so you'll go farther for each revolution compared to the stock size. That means your speedo will read lower than actual (or at least lower than it would read compared to the stock tires). GPS is the way to go, especially to check the odometer (more important for MPG calculation).

Originally Posted by pletby

As a strange sidebar my speedometer is optimistic by around 4km/hr, but when I read the speed off my Ultragauge accessing my car's computer it matches the GPS exactly. Weird eh?

A lot of cars will read a little high on the speedometer, but the odometer and speed from the OBD-II port are right on. Supposedly it's so you can't blame the manufacturer if you get caught speeding.

[darcane]

Originally Posted by homeiss

So I've realized that the tires on my car are not stock size which would mean my speedometer and odometer readings are slightly off.

My car's stock tires would be 175/70R13 and the ones on my car are 195/60R14.

When I plug those numbers into this site it says when the speedo says 100 I'm actually going 102.5.

However, when I use the calculator on this site it says when the speedo says 100 I'm actually going 97.56.

Not sure why I'm getting different numbers here. Any help would be appreciated, thanks!

Both answers are identical, just inverted in how they are displayed... change the order you plug them in and you will get the same numbers.

Ignore the numbers for a moment. Your current tires are taller than stock. Because of that, you are going faster than you would be going with the stock tires.

[iveyjh]

The second one is correct, all things considered.

[homeiss]

Thanks everyone. So does that mean I can just multiply the odometer by 2.5% for correct readings?

I'll try downloading an app to check my gauges with as well.

[ChazInMT]

I have noticed that tires of the same size by differing makes have slightly different diameters when I shop on Tire Rack.I ALWAYS use Tire Rack as a guide for the tires I'm going to buy for my cars since 1992 or so to get the best price. When they started putting performance and review ratings up it is just an amazing site to find the best value. I would never have bought General tires were it not for them.

[homeiss]

Ok so I ran a GPS speedometer app on my way home today. The second site appears to be right while the speedometer says 100 the app was saying around 97.5 km/h.

I reset the tripmeter and the car says 38.7 while the app reports 38.67, so almost bang on.