Tire size question
#1
Senior Member
Thread Starter
Tire size question
I've ordered my GLE with 21" rims. I was playing with tire and rim size's this morning and realized that the rim size changes the number of revolutions per mile. I always thought that larger rims offset with less tire rubber height. did I miscalculate something?
19" rim with 255/50 tires. Rubber height is 255mm * 50%, or 127mm. Total diameter is 19" + 2*127mm/25.4 = 29"
21" rim with 275/45 tires. Rubber height is 275mm * 45% or 124mm. Total diameter is 21" +2*124mm/25.4 = 30.8" (similar result with the 315/40 rear)
Almost a 2" difference, which explains why I felt the larger rim filled out the wheel well better. But how does the car compensate when calculating speed, etc.
19" rim with 255/50 tires. Rubber height is 255mm * 50%, or 127mm. Total diameter is 19" + 2*127mm/25.4 = 29"
21" rim with 275/45 tires. Rubber height is 275mm * 45% or 124mm. Total diameter is 21" +2*124mm/25.4 = 30.8" (similar result with the 315/40 rear)
Almost a 2" difference, which explains why I felt the larger rim filled out the wheel well better. But how does the car compensate when calculating speed, etc.
#2
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2020 GLE 450; 2023 BMW M2 Coupe
Tire size diameter differences
I've ordered my GLE with 21" rims. I was playing with tire and rim size's this morning and realized that the rim size changes the number of revolutions per mile. I always thought that larger rims offset with less tire rubber height. did I miscalculate something?
19" rim with 255/50 tires. Rubber height is 255mm * 50%, or 127mm. Total diameter is 19" + 2*127mm/25.4 = 29"
21" rim with 275/45 tires. Rubber height is 275mm * 45% or 124mm. Total diameter is 21" +2*124mm/25.4 = 30.8" (similar result with the 315/40 rear)
Almost a 2" difference, which explains why I felt the larger rim filled out the wheel well better. But how does the car compensate when calculating speed, etc.
19" rim with 255/50 tires. Rubber height is 255mm * 50%, or 127mm. Total diameter is 19" + 2*127mm/25.4 = 29"
21" rim with 275/45 tires. Rubber height is 275mm * 45% or 124mm. Total diameter is 21" +2*124mm/25.4 = 30.8" (similar result with the 315/40 rear)
Almost a 2" difference, which explains why I felt the larger rim filled out the wheel well better. But how does the car compensate when calculating speed, etc.
#3
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Join Date: May 2019
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2020 GLE 450 AMG exterior
Years ago, I upgraded from 15-inch stock wheels to 18-inch Cobra R rims on my Mustang. One day, I set the cruise control 5 mph over the posted limit, got pulled over and ticketed for doing like 11 or 12 mph over the limit. You'd have to think they'd calibrate the speedometer for whatever wheels the car leaves the factory wearing. The speedo is digital now, so it would seem like a simple setting adjustment, but I'm just spitballing.
#4
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2020 GLE 450; 2023 BMW M2 Coupe
Tire size diameter differences
Years ago, I upgraded from 15-inch stock wheels to 18-inch Cobra R rims on my Mustang. One day, I set the cruise control 5 mph over the posted limit, got pulled over and ticketed for doing like 11 or 12 mph over the limit. You'd have to think they'd calibrate the speedometer for whatever wheels the car leaves the factory wearing. The speedo is digital now, so it would seem like a simple setting adjustment, but I'm just spitballing.
#5
Senior Member
Thread Starter
Exactly. I'm waiting on tirerack to offer winter tire/rim package, hopefully they will have something on a 20" rim.