Bigger rims = messed up MPH

Mechkiller31st · 11-14-2006, 12:39 AM

Ok Now if i remember my physics class well since my car had 15" tires my ECU was designed for that to help judge what my MPH was. So now that I hae 16" rims doesnt that mean that my speedometer will be off??

Patrick Olsen · 11-14-2006, 12:52 AM

Unless you're rolling around directly on the wheels, no. I'm assuming you have these rubber things called "tires" wrapped around your wheels, and if you did it properly, the outside diameter of your new tires should closely match the outside diameter of your old tires.

If not, your car will explode.

Pat

FuJi K · 11-14-2006, 01:02 AM

I've got to play with different sizes as well as different final drive ratio.
4.444FD with my RWD conversion I was 5mph off. STOCK it's 2mph off via "your speed" meters.

Mine is a MY99 and runs a speed sensor. This is very accurate IMO compared to the speed cable equipped cars.

02wrbrex · 11-14-2006, 01:09 AM

Quote:

Originally Posted by Patrick Olsen

If not, your car will explode.

Pat

He's right 100%

yzer · 11-14-2006, 02:09 AM

Quote:

Originally Posted by 02wrbrex

He's right 100%

And aftermarket rim-related explosions are not covered under warranty.

drivin blind · 11-14-2006, 11:11 AM

Get somebody to loan you a hand held GPS unit. It will read out your true speed. (If you don't, your car will explode and kill you!)

Mechkiller31st · 11-14-2006, 12:06 PM

Seriously what is with the whole car exploding thing. If i wanted to do that i would fill it with jet fuel

shwoop_soobie · 11-14-2006, 12:32 PM

speed wont be off by a certin mph. for tire sizes other than stock, it will be off by a percentage. sence it is a wheel being affected by acceleration and velocity. for example, say a slightly larger tire afects speed by an increase of 10 percent. so at 10 mph you would really be traveling 11, and at 100 mph, you would really be going 110...
however, car explosions due to tire size is at an all time high

11-14-2006, 12:39 AM	#1
Mechkiller31st Scooby Specialist Member#: 38474 Join Date: Jun 2003 Chapter/Region: MWSOC Location: Beach Park IL, USA Vehicle: 1998 Impreza Wagon L Brilliant Red	Bigger rims = messed up MPH Ok Now if i remember my physics class well since my car had 15" tires my ECU was designed for that to help judge what my MPH was. So now that I hae 16" rims doesnt that mean that my speedometer will be off??

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11-14-2006, 12:52 AM	#2
Patrick Olsen NASIOC Supporter Member#: 120 Join Date: Jul 1999 Chapter/Region: AKIC Location: Where the Navy sends me... Vehicle: 1997 Legacy 2.5GT QuickSilver Metallic	Unless you're rolling around directly on the wheels, no. I'm assuming you have these rubber things called "tires" wrapped around your wheels, and if you did it properly, the outside diameter of your new tires should closely match the outside diameter of your old tires. If not, your car will explode. Pat

11-14-2006, 01:02 AM	#3
FuJi K Scooby Guru Member#: 3687 Join Date: Jan 2001 Chapter/Region: MWSOC Location: St. Paul, MN Vehicle: MY99 GF4 JDM 6spd NF Performance	I've got to play with different sizes as well as different final drive ratio. 4.444FD with my RWD conversion I was 5mph off. STOCK it's 2mph off via "your speed" meters. Mine is a MY99 and runs a speed sensor. This is very accurate IMO compared to the speed cable equipped cars.

11-14-2006, 11:11 AM	#6
drivin blind Scooby Specialist Member#: 73043 Join Date: Oct 2004 Chapter/Region: MWSOC Location: Carson City, Michigan Vehicle: 2011 STI/2010 370Z Black/Black Cherry	Get somebody to loan you a hand held GPS unit. It will read out your true speed. (If you don't, your car will explode and kill you!)

11-14-2006, 12:06 PM	#7
Mechkiller31st Scooby Specialist Member#: 38474 Join Date: Jun 2003 Chapter/Region: MWSOC Location: Beach Park IL, USA Vehicle: 1998 Impreza Wagon L Brilliant Red	Seriously what is with the whole car exploding thing. If i wanted to do that i would fill it with jet fuel

11-14-2006, 12:32 PM	#8
shwoop_soobie Scooby Specialist Member#: 102323 Join Date: Dec 2005 Chapter/Region: SWIC Location: Prescott AZ Vehicle: 99 power poles beware	speed wont be off by a certin mph. for tire sizes other than stock, it will be off by a percentage. sence it is a wheel being affected by acceleration and velocity. for example, say a slightly larger tire afects speed by an increase of 10 percent. so at 10 mph you would really be traveling 11, and at 100 mph, you would really be going 110... however, car explosions due to tire size is at an all time high