With 30-9.50 15 tires, my speedometer reads two miles per hour too fast. I checked it with my GPS.
So how am I to read my odometer, or interpret it, to get a right read? For example, I have 115,000 miles on it supposedly. I must not have that many, but how do I calculate to figure it out? Also, in a trip of 100 miles, is there some way to calculate it?
It doesn't seem to matter if I am going 35 or 70, my speedometer always reads 2 miles an hour too fast.
Not sure how yours is showing the same mph offset regardless of speed. Usually it is a percentage difference.
I just went from 31's to 33's and purchased a kit from blue monkey motorsports. It is a kit that includes the device from healtech along with a plug n play harness. It is the best, least intrusive solution I could find.
Just to note- it's only 2mph off at one speed. A speedometer is not a linear instrument, therefore the faster you go, the more it reads incorrectly. It's inaccurate by a percentage, not by an actual unit of measure (mph).
The odometer will also be off by the same percentage as the speedo, at least for the amount of time you have been running bigger tires. Find out how many miles you have been running that size tire, figure the percentage your speedo is off and then multiply according. This will tell you how many miles to add/subtract from your odo reading.
Example: Mine is 10% off running 33's... speedo reads 50, Im actually going 55. Spedo reads 70, I'm actually going 77. Assuming the PO ran the 33's from day one, I would have 66K miles on my jeep. Odo reads 60K X 10% = add 6K miles to the current reading.
How can I tell what gears I'm running? (Please don't kill me...I looked...I PROMISE!)
If you can't find a tag, jack up the rear end and have someone turn a tire one full revolution while you count the number of revolutions your drive shaft makes. If the drive shaft makes a little over 3 revolutions, you have 3:07 gears, if it makes about 3 3/4 revolutions, you have 3:73, a little over 4 revs is 4:10 and so on.