Michael Yount
Mustang Master
Was the speedo corrected for the gears? Your tires are the same size as mine, and they're a bit shorter than the standard height on the Stangs; so the car is actually behaving more like it's got 3.91 gears.
Gears??
- Thread starter Drago
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Kurt2002
New Member
Drago, take a look at your A/F ratio, you may be running rich. That would result in poor gas mileage.
willys1
Active Member
Michael Yount
Mustang Master
The math is all simple ratios. The standard Stang tire was about 25.9" tall. The 225/50/16 is about 24.9" tall. 24.9/25.9=.96; the shorter tire gives you a numerically higher effective rear end ratio by the same %. So, 3.73/.96= 3.89 or about a 3.90.
To calculate tire height differences based on size - you take the section width in mm - 225, divide it by the conversion to inches - 25.4mm/inch = 8.86". The sidewall height is the section width (8.86") X the aspect ratio (50 series means 50%). So, 8.86" X .50 = 4.43". The height of the tire is the diameter of the wheel (16") + twice the sidewall height (sidewall at the bottom and at the top) -- 16 + (2 X 4.43) = 24.86" -- that's where my 24.9" tire height estimate came from.
With those formulas, you can play with tire height and rear ratios til the cows come home. By the way, your engine rpm changes proportionally with the gear change or the tire diameter change. So if your tire is 5% taller, the engine revs at a given road speed slow down by 5%. 5% shorter tire, the engine revs speed up by 5% at a given road speed. So you can see how a tire size change throws off your speedo/odo, and throws off your gas mileage calculations. Hope that helps.
To calculate tire height differences based on size - you take the section width in mm - 225, divide it by the conversion to inches - 25.4mm/inch = 8.86". The sidewall height is the section width (8.86") X the aspect ratio (50 series means 50%). So, 8.86" X .50 = 4.43". The height of the tire is the diameter of the wheel (16") + twice the sidewall height (sidewall at the bottom and at the top) -- 16 + (2 X 4.43) = 24.86" -- that's where my 24.9" tire height estimate came from.
With those formulas, you can play with tire height and rear ratios til the cows come home. By the way, your engine rpm changes proportionally with the gear change or the tire diameter change. So if your tire is 5% taller, the engine revs at a given road speed slow down by 5%. 5% shorter tire, the engine revs speed up by 5% at a given road speed. So you can see how a tire size change throws off your speedo/odo, and throws off your gas mileage calculations. Hope that helps.
