How off will my speed be off?
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Im getting some 18X9 Evos this week. I picked a 275/35/18 for the rims. Im currently running stock 16in wheels and tires. How much will my speedo be off when I put the new rims and tires on?
Last edited by LS1[CHEVY]; 03-28-2005 at 10:21 AM.
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I can't remember the exact tire size on the 16's so I did two different ones for you. Hopefully you have one of these sizes already on the car.
275/35/18 is 25.578 inches tall
245/45/16 is 24.68 inches tall
245/50/16 is 25.646 inches tall
Either one of those you will be fine with. The 275 might make it a LITTLE bit off, but as already said, not enough to make a big enough difference.
275/35/18 is 25.578 inches tall
245/45/16 is 24.68 inches tall
245/50/16 is 25.646 inches tall
Either one of those you will be fine with. The 275 might make it a LITTLE bit off, but as already said, not enough to make a big enough difference.
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why would the 275 tire width cause it to be off? I would guess that the overall diameter would cause the speedometer to be off so wouldnt it matter more if you are increasing wheel size or sideway size?
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Originally Posted by C.J.
why would the 275 tire width cause it to be off? I would guess that the overall diameter would cause the speedometer to be off so wouldnt it matter more if you are increasing wheel size or sideway size?
So a tire that is 275mm across has a sidewall of (35%) 90.75mm which is roughly 3.8 inches. So with a 18" bead diameter + 3.8" top sidewall + 3.8" bottom sidwall = 25.6" diameter total
now that will be 25.6"*pi= 80.384" around (circumference)
SO you see if you have a say... 315/35/18 it will be taller and have a larger circumference which will make the speedo read SLOWER than the 275/35/18 but only by 4.3% or if you are going 60 that would make the speedo read 62.6mph.
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