How off will my speed be off?
![LS1[CHEVY]'s Avatar](data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 50 50'><circle class='avatar-circle-default' fill='%234d8769' cx='25px' cy='25px' r='20px'></circle><text class='avatar-text-default' x='49%' y='53%' fill='white' text-anchor='middle' alignment-baseline='middle'>L</text></svg>)
Thread Starter
On The Tree
Joined: Nov 2001
Posts: 151
Likes: 0
From: NJ
How off will my speed be ? 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]; Mar 28, 2005 at 10:21 AM.
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.
TECH Enthusiast
Joined: Oct 2004
Posts: 578
Likes: 0
From: Lincoln, Ne
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?
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.
Very well explained . Thanks guys 
