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Home > Visual / Audio Mods > Wheels & Tires > bigger wheel diameter = inaccurate speedometer

bigger wheel diameter = inaccurate speedometer

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tc1stgen Killeen Texas, US Scion Guru	I know that when you change the wheel size from the factory it causes the speedometer to be inaccurate. Meaning your not going the actual speed it is indicating. So if you put an 18" wheel on are you going faster or slower than what your speedometer reads? Ask me about Innovative Car Works! LED's is their specialty! http://www.ItsMyScion.com/tc1stgen http://www.myspace.com/tc1stgen http://www.tunerfriends.c...mber.php?u=13341&8685 http://www.cardomain.com/ride/3084016 "NOS is like a hot girl with STD's, you want to hit it but are afraid of the consequences!"
[#] May 15, 2008 11:00am
rainbowflag Spring Texas, US Chief Mechanic	Try this: http://www.discounttire.com/dtcs/infoTireMath.dos
[#] May 15, 2008 11:03am
krdshrk New Brunswick New Jersey, US Godlike Advisor	It depends on the tire size you use. Scikotics NJ is sponsored by Lawrence Scion 2006 GReddy Turbocharged Automatic tC 220+ WHP - 14.044 @ 97.02 MPH
[#] May 15, 2008 11:10am
FrAnkRYzzO Perry Hall Maryland, US $upervillain for Hire	A bigger tire will increase make your actual speed faster then what your speedometer tells you. This is not caused by switching from 17's to 18's though. It has to do with the actual height of the tire. The wheel size is irrelevant. ............... Search or one of these adorable kittens WILL DIE!
[#] May 15, 2008 11:12am
psiewert Gurnee Illinois, US Vehicle Designer	The speedometer reads the revolutions of the drive shaft per minute. If you put on a larger tire, it means you have a larger circumference. That means that with a larger tire, you are moving a further distance in 1 revolution. Lets say with your tire profile will be equal between both tires. With a 17 inch rim you have a 3 inch profile tire and with an 18 inch rim you have a 1.5 inch profile also. This means that the circumference of the 17+3 inch wheel = 62.83 inches. The circumference of the 18+3 inch wheel is 65.97. Every revolution you will be moving 3 inches further with an 18 inch rim. At 1 MPH you will actually be traveling 1.05 MPH.
[#] May 15, 2008 11:15am
tc1stgen Killeen Texas, US Scion Guru	they are gonna be 225/40/R18 Ask me about Innovative Car Works! LED's is their specialty! http://www.ItsMyScion.com/tc1stgen http://www.myspace.com/tc1stgen http://www.tunerfriends.c...mber.php?u=13341&8685 http://www.cardomain.com/ride/3084016 "NOS is like a hot girl with STD's, you want to hit it but are afraid of the consequences!"
[#] May 15, 2008 11:18am
rainbowflag Spring Texas, US Chief Mechanic	If you use the calculator in my previous post it will tell you the difference.
[#] May 15, 2008 11:25am
krdshrk New Brunswick New Jersey, US Godlike Advisor	tc1stgen wrote: they are gonna be 225/40/R18 I give you EddNog's Wheel/Tire Chart: At 60mph you'll really be going 61. It's not bad. Heck, I run 225/45R17 on my car. Speedo's are pretty innacurate anyway.. Scikotics NJ is sponsored by Lawrence Scion 2006 GReddy Turbocharged Automatic tC 220+ WHP - 14.044 @ 97.02 MPH
[#] May 15, 2008 11:27am
tc1stgen Killeen Texas, US Scion Guru	yeah I did. It said I would be going 65.3 mph when my speedometer reads 65 mph. Thanks! Ask me about Innovative Car Works! LED's is their specialty! http://www.ItsMyScion.com/tc1stgen http://www.myspace.com/tc1stgen http://www.tunerfriends.c...mber.php?u=13341&8685 http://www.cardomain.com/ride/3084016 "NOS is like a hot girl with STD's, you want to hit it but are afraid of the consequences!"
[#] May 15, 2008 11:29am
psiewert Gurnee Illinois, US Vehicle Designer	haha, i deleted my post cause I was doing it all by hand, and I was way off.
[#] May 15, 2008 11:29am
tc1stgen Killeen Texas, US Scion Guru	LOL Ask me about Innovative Car Works! LED's is their specialty! http://www.ItsMyScion.com/tc1stgen http://www.myspace.com/tc1stgen http://www.tunerfriends.c...mber.php?u=13341&8685 http://www.cardomain.com/ride/3084016 "NOS is like a hot girl with STD's, you want to hit it but are afraid of the consequences!"
[#] May 15, 2008 11:39am
Beckaz_tC Mesa Arizona, US Scion Guru	Actually.... When I had my stocks on my speedometer was off about 2-3. Now that I put 18's on it is just right.
[#] May 15, 2008 11:41am
Orin Auburn Alabama, US	good information to have and great post
[#] May 15, 2008 12:02pm
FrAnkRYzzO Perry Hall Maryland, US $upervillain for Hire	For those of you that are running different size tires then stock and are bothered by the slight difference in speed due to anal retentive OCD tendencies, if you purchase a scangauge2 you can adjust the speedometer reading to compensate for the difference in tire size. You would just need access to a GPS to get your actual speed and then adjust accordingly. ............... Search or one of these adorable kittens WILL DIE!
[#] May 15, 2008 12:24pm
krdshrk New Brunswick New Jersey, US Godlike Advisor	FrAnkRYzzO wrote: For those of you that are running different size tires then stock and are bothered by the slight difference in speed due to anal retentive OCD tendencies, if you purchase a scangauge2 you can adjust the speedometer reading to compensate for the difference in tire size. You would just need access to a GPS to get your actual speed and then adjust accordingly. Yeah I check my GPS speed vs my speedo... it's about right. Scikotics NJ is sponsored by Lawrence Scion 2006 GReddy Turbocharged Automatic tC 220+ WHP - 14.044 @ 97.02 MPH
[#] May 15, 2008 01:28pm
MrScion07 Rochester Massachusetts, US Godlike Advisor	rainbowflag GOOD FIND! thats cool. Def a good thread
[#] May 15, 2008 01:42pm

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