How is speed read?

rambunctious · 04-14-2012, 01:43 PM

So im taking the jump to increase the tire width on the stock rims..

Front 265-35-19
Rear 305-30-19

I know there are speed calculators out there, but since both tires are being changed? How would that affect what the speedo is reading? Is speed being read by rear or front tires? If there is already a post about this, please point me in the right direction...

370ZilverZ · 04-14-2012, 01:50 PM

Speed indicator usually comes from the transmission and the rear tire size changes the speed of the transmission output to the speedometer.

rambunctious · 04-14-2012, 09:04 PM

So speed is only read from rear wheels?

Waiz · 04-17-2012, 12:52 AM

Here is one for speed:

Tire size calculator

Here is one to ensure that you have the proper staggered sizing:

Tire Size Calculator - tire & wheel plus sizing

fuct · 04-17-2012, 11:29 AM

basically dont worry about it. the factory speedo is slow by 2-3 mph anyways.

04-14-2012, 01:43 PM	#1 (permalink)
rambunctious Base Member Join Date: Feb 2011 Location: in the cowboys stadium Posts: 183 Drives: your mom crazy.. Rep Power: 15	How is speed read? So im taking the jump to increase the tire width on the stock rims.. Front 265-35-19 Rear 305-30-19 I know there are speed calculators out there, but since both tires are being changed? How would that affect what the speedo is reading? Is speed being read by rear or front tires? If there is already a post about this, please point me in the right direction...

04-14-2012, 01:50 PM	#2 (permalink)
370ZilverZ A True Z Fanatic Join Date: Dec 2011 Location: DFW, TX Age: 67 Posts: 2,321 Drives: '11 BMW Z4 Rep Power: 19	Speed indicator usually comes from the transmission and the rear tire size changes the speed of the transmission output to the speedometer. __________________ 370ZilverZ Journal BMW Z4

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04-14-2012, 09:04 PM	#3 (permalink)
rambunctious Base Member Join Date: Feb 2011 Location: in the cowboys stadium Posts: 183 Drives: your mom crazy.. Rep Power: 15	So speed is only read from rear wheels?

04-17-2012, 12:52 AM	#4 (permalink)
Waiz A True Z Fanatic Join Date: Apr 2010 Location: SoCal Posts: 9,262 Drives: Z33 & GE8 Rep Power: 460	Here is one for speed: Tire size calculator Here is one to ensure that you have the proper staggered sizing: Tire Size Calculator - tire & wheel plus sizing

04-17-2012, 11:29 AM	#5 (permalink)
fuct A True Z Fanatic Join Date: May 2009 Location: Sugar Land Posts: 3,692 Drives: 97' Ranger :) Rep Power: 24	basically dont worry about it. the factory speedo is slow by 2-3 mph anyways.