Oversize Tire Speedo Differential

[snowtrooper1966]

Greetings!
Just pondering as I was driving the Dragon today....
If the oversize Nitto tires (285/60/18) affect the speedometer reading, that is I am actually travelling faster than the dash indicates, how does that affect the mileage reading? Do I have less than is on the readout? I wonder what the culminative affect of that discrepancy is over the years?
Best,

[rowhard]

Greetings!
Just pondering as I was driving the Dragon today....
If the oversize Nitto tires (285/60/18) affect the speedometer reading, that is I am actually travelling faster than the dash indicates, how does that affect the mileage reading? Do I have less than is on the readout? I wonder what the culminative affect of that discrepancy is over the years?
Best,

the 285 is a 6% difference, so you are traveling faster then indicated and you will actually be traveling father then indicated. So, recheck you gas mileage using the .06 times your indicated mileage, then add your indicated mileage to this figure to get the actually distance's traveled.

[snowtrooper1966]

So you are saying that I have traveled farther than my odometer is reading? Damn, I was trying to cheer myself up since I turned 70K this week, now it looks like I was 70K last year.....

[don moore]

ahhh...WHAT????.....

[rowhard]

So you are saying that I have traveled farther than my odometer is reading? Damn, I was trying to cheer myself up since I turned 70K this week, now it looks like I was 70K last year.....

yep, 2 inches every rpm of the tire, and if I did the math right, that would be 1 mile every 31680 rpm's.

sorry

P.S. I didn't take my shoes off when I figured that, so it could be off by who knows how much

[nfpgasmask]

Yup, I haven't done the calculations, but yeah, that's how it works. I guess I actually change my oil every 3500 or so, and not 3000. I still go by the ODO though.

With my tires my speed is 7% off, calculated by using a GPS. I set my Scangauge to reflect the difference and now all is good.

Bart

[snowtrooper1966]

So how could I calculate how far my ODO is off if I have had these tires on for say, 10K miles?
Best,

[rowhard]

So how could I calculate how far my ODO is off if I have had these tires on for say, 10K miles?
Best,

I'll get back to you, need to take my shoes off to figure that one

[rowhard]

I'll get back to you, need to take my shoes off to figure that one

got it, trying to explain it to me girlfriend who, bless her heart isn't into math, the answer popped into my head. it's 10k times .06 plus 10k SOOOOOOOOOOO

10000 x .06 = 600 + 10000 = 10600. So it was proable 3 weeks ago when you cracked 70k

Now I'm really sorry snowtrooper

[Gussie2000]

got it, trying to explain it to me girlfriend who, bless her heart isn't into math, the answer popped into my head. it's 10k times .06 plus 10k SOOOOOOOOOOO

10000 x .06 = 600 + 10000 = 10600. So it was proable 3 weeks ago when you cracked 70k

Now I'm really sorry snowtrooper

Wow that's sad though !

I replaced the stock shoes for 20x9 rims,the tyres are 275/45R20 which means my speedo are somehow outter the speedo angle

[rowhard]

Wow that's sad though !

I replaced the stock shoes for 20x9 rims,the tyres are 275/45R20 which means my speedo are somehow outter the speedo angle

would you believe there is only 1/10 of a inch difference between those rubber bands you call tires and the OEM tire:bgwg:

[VehiGAZ]

Greetings!
Just pondering as I was driving the Dragon today....
If the oversize Nitto tires (285/60/18) affect the speedometer reading, that is I am actually travelling faster than the dash indicates, how does that affect the mileage reading? Do I have less than is on the readout? I wonder what the culminative affect of that discrepancy is over the years?
Best,

The Great Goog answers all... http://www.miata.net/garage/tirecalc.html

[Riff Raff]

The Great Goog answers all... http://www.miata.net/garage/tirecalc.html

VehiGAZ--- Thanx!!! What a cool website. According to the calculator, ROWHARD's example should have been 6.4% (not 6.0%). However, ROWHARD was right there in the ball-park and gave a great 3rd grade explanation (I liked 3rd grade). Therefore, thanx goes out to you ROWHARD as well (AIM HIGH!!!).

[rowhard]

VehiGAZ--- Thanx!!! What a cool website. According to the calculator, ROWHARD's example should have been 6.4% (not 6.0%). However, ROWHARD was right there in the ball-park and gave a great 3rd grade explanation (I liked 3rd grade). Therefore, thanx goes out to you ROWHARD as well (AIM HIGH!!!).

Thanks Brian. That web site is the one I used to get these sizes.

Yes, the point 4.

Kind of like, measure it with a optical micrometer, mark it with a piece of chalk, and cut it with a axe.

and excuse me, that is 4th grade fingering

[Baxman]

Beware of the handy online tire calculators. They are acurate for passenger tires but not necessarily for off-road tires which are taller than same-size passenger tires.

After putting new, oversized BFG ATs on fresh new American Racing chromed alloys I made my way to Moab for ZuZoo. Before leaving, I checked the online tire calculator which told that the speedo would read 3% slow. As I was cutting across the NE corner of Oregon a very nice state cop used laser to show me the inacuracy of the online calculator. After months of letter-writing to the court in LaGrand, the very nice judge changed the charge from speeding, to "faulty equipment" but it still cost me something over $100.

Borrow or buy a GPS, then you'll know for sure!