Ok..with 285/75-16's on my truck...the speedo is 4 miles per hour SLOW...so when going 70 it's ACTUALLY going 74.That being said, can anyone figure out how much behind the Odometer/Trip meter is? does this mean i'm getting MORE than the calculated 17mpg highway/empty since it's clicking off LESS miles than actually traveled?

 

Your speedometer is reading at 94.5% of what the actual speed is. Your odometer should be off the same amount. So if you are getting 650 miles to a tank of fuel, you would divide 650 by 94.5% and your actual miles traveled for that tank would be 687.8

It's getting late for me, but I think that is correct.

 

I found out on my personal truck that when im doing....
10mph im doing 11mph
20 doing 22
30 doing 33
etc
etc. Just going from 29's to 33's

 

Your about 10% off. So add 10% into your mileage and you'll get what you actually drove.

 

What was your grade in math class?

 

Straight A's

 

Actually there are several tire sites on the web tirecalc.com I believe is one where you can feed that information and get the results the formula is pretty easy though just take actual speed divided by speed on odometer and that will give you the formula as in 60actual and 62 shown = 60/62= .968 so if you are traveling 60 on the speedo and 62 in reality then you have traveled further than the speedo shows and you mileage is better than calculated. if that makes any sense.

 

Not you. Heck I even had Strait A's and B's through HS. Greg What was your grade?

 

Do they even grade that low?

 

i never finished business math... ...something about Algebra and trying to mix numbers with letters doesn't make sense to me..or else we'd be speaking in numbers

 

We dont speak with numbers so we shouldnt do math with letters!!!

 

10% is a pretty good estimate but it may be a little higher, of course each truck is different and there will be some instrument error. I've been running 285's for 2 years now. At 65, I'm actually running closer to 73-75. And, I may be wrong, but the faster you go, the further from the acutal mph your truck indicates

 

That would be correct. Just for a giggle check when you wonder about something like this and don't know the answer, take it to an extreme and see what happens. In this case, one extreme is zero miles per hour. When you are stopped, your speedometer is reading accurately even with larger tires. So, from that information, you know the variance in mph between actual speed and what your speedometer reads is a function of the speed you are going.

 

haven't played with hexidecimal numbers have ya... then there is algerbra


and my math grade in college was 100%, and in HS was +90%

don't remember any of it anymore though

 

OK, it took me a while but here is the formula that you use for the conversion.



3x-2y+(4y-11)(3x+22) -/ a + (9x -2) + (3y -4)

Hope this helps.