No Calibration Needed!

[rkcrawl]

Originally Posted by evldave

Don't forget that 32"/33"/35" tires aren't really that size. You should go to the mfrs website or tire rack to get actual dimensions.

here's an example for tire rack & BFG AT KOs, 35" is really 34.5"

http://www.tirerack.com/tires/Spec.j...rrain+T%2FA+KO

While true, you're just gonna to confuse more people. Want to really confuse people? Not only are they not really the advertised size, but if you REALLY want to be accurate you have to consider the true tire radius with WEIGHT on it...

f5fstop's idea about the GPS is easier if ya have one

[f5fstop]

Originally Posted by rkcrawl

What, my math wasn't good enough for you?

I have a headache; nothing against the math, I never even looked.

I should also mention that on my trip to TN last fall, I checked my speedo and it was running two miles under the registered speedometer speed at 70 mph (thus I was doing 68). I confirmed this with two different GPS units; a Magellan Sportrack TOPO, and a Garmin iQue 3600.

[evldave]

I believe there is a federal law that requires the speedometer, from the factory, not be more than x% below the actual speed (don't know the value). This is so you can be absolutely sure you aren't going faster than indicated on the speedo. Mfrs adjust their speedos high (low) to make sure they meet the guidelines.

Also, European regs have a tighter guidelines, meaning they are more restrictive for the 'too high' guidelines. So EU mfrs adjust their speedos high (so your speed is lower than indicated) even more - my BMW was 3-4 mph low, I checked the H3 on the way home from work today and it was 1-2 mph low.

So why does that matter? Because no math you can do will adjust for the factory fudge, so just wing it. Since the factory builds in a fudge, technically your odometer is off anyway, so an extra bit here or there is moot.

[FutureBeachBum]

With all the calculations, you have forgotten the most important factor:
LPM (looks per mile)
95.7 percent of H3 owners think the 35?s are 27 percent better than the 33?s.
This represents an increase in the damn fine coefficient of 1.37 pi squared per inch of increased tire diameter.

However the LPM rating is not limited to fellow H3 owners, for example card carrying Sierra Club members will view the larger and therefore more dangerous tires as 18 percent more likely to run over Bambi. Netting you an easy increase in (dirty) Looks Per Mile of 7.9

This is on the opposite end of the spectrum of the Mini-van driving soccer moms who won?t notice you at all unless you are sporting a ?I break for Garage Sales? bumper sticker. Subtract 1.2 LPM

Of course all of this proves the theory that there are 3 kinds of people in the world?those who understand math and those who don?t.

[deserth3]

I need a beer (or several) after reading this thread. Looks like FutureBeachBum may be ahead of me.

By the way good one FutureBeachBum

[NEOCON1]

Originally Posted by The Green Lantern

Ok, I went from 32's to 35's and I have been trying to figure out the exact number of my MPG. But here's my theory - so my mpg is off 3 inches, larger tires are making less revolutions per mile which means I'm going a bit farther than a mile when my odometer shows I went a mile. I think it's a great thing as far as warranty wise.

LMFAO

[f5fstop]

Originally Posted by evldave

I believe there is a federal law that requires the speedometer, from the factory, not be more than x% below the actual speed (don't know the value). This is so you can be absolutely sure you aren't going faster than indicated on the speedo. Mfrs adjust their speedos high (low) to make sure they meet the guidelines.

Also, European regs have a tighter guidelines, meaning they are more restrictive for the 'too high' guidelines. So EU mfrs adjust their speedos high (so your speed is lower than indicated) even more - my BMW was 3-4 mph low, I checked the H3 on the way home from work today and it was 1-2 mph low.

So why does that matter? Because no math you can do will adjust for the factory fudge, so just wing it. Since the factory builds in a fudge, technically your odometer is off anyway, so an extra bit here or there is moot.

Yes there is a Fed regulation. I believe it is 5 percent +/-, but can't be sure; been awhile since I was working in that area.

[Ipedog]

My gawd you people are making this hard. Way harder than it needs to be (Although that might be the idea ).

Going with your estimate of 631 revs per mile for the 32" tires (which seems low - per their web site, Toyo says their Open Country AT 265/75R16 gets 656/revs/mile)

AND your 315/75R16 Toyo's get 595/rev/mile - per the Toyo site

You can divide the GY revs by the Toyo revs to get your mileage factor ratio. In this case (assuming that the GY calc is correct - doubtful) you get a milage factor of 1:1.060504202.

So for every mile indicated on the odomiter you have actually traveled 1.060504202 miles. This difference in mileage does add up quicker than you think.

For any given tank of gas I get about 280 miles indicated on the odomiter. My BFG's have a mileage factor ratio of 1:1.053244592. In my case this means that in actuality I have traveled 280 miles multiplied by 1.053244592 or 294.91 miles.

A difference of 14.91 miles. While not a ton, it does add up to about 53 miles saved per 1000.

I would be willing to bet that the GY 265/75R16 turns close to 650/rev/mile so your mileage factor ratio sould be closer to 1.09.

Hope this helps...

[Agriv8r]

Aren't the speedometer for the HUMMER's now electronic, meaning there are no longer cables? And the speed is now computed throught the PCM? If this is correct then there is the possibility that the PCM may have enough variance input into it that it recalculates automatically. Have you paced the truck with another vehicle to see if the speedometer is wrong????

[Agriv8r]

Not now electronic, but electronic. They have been the same since release.

Now what's needed is some shorter gearing (higher numerical) so that the acceleration on the street is reasonable.

S.

[RubHer Yellow Ducky]

There are 2 additional ways to figure it:

1. E = MC2

2. as long as the angle of the dangle is equal to the heat of the meat you make sure that both are firm enough to transverse the curve of the canyon to reach the upper recesses of the ...

RYD

[f5fstop]

Originally Posted by Agriv8r

Aren't the speedometer for the HUMMER's now electronic, meaning there are no longer cables? And the speed is now computed throught the PCM? If this is correct then there is the possibility that the PCM may have enough variance input into it that it recalculates automatically. Have you paced the truck with another vehicle to see if the speedometer is wrong????

Electronic and the speedo and odo are fed via the BCM, which calculates the PCM speed signal, and stores the information internally.

There are devices you can place inline with the vehicle speed sensor to fool the system.

[The Green Lantern]

Originally Posted by f5fstop

All this math and there is an easier way. Just use your GPS, or borrow one.

Ok, I used GPS and a Jaguar to measure my mileage. It seems I am off about 10 mph. The Jaquar, which followed right behind me, was showing 65 mph to my 55 mph. After we had arrived at our destination, the Jaquar showed a traveling distance of 46 miles, while mine only showed 41. That's a 5 mile difference in my favor!

[f5fstop]

And you trust the speedo in a Jaguar?

[The Green Lantern]

Originally Posted by f5fstop

And you trust the speedo in a Jaguar?

Not really ....ok ok ok, I will do it again with my GPS

[deserth3]

Here's another way to do it.

Keep a constant speed between mile markers. Measure the time in seconds. divide this number into 3600 and the result will be your average speed between those two mile markers.

i.e. 3600/60 sec.=60 mph
3600/65 sec.= 55.38 mph
3600/55 sec.=65.45 mph

[WVHummer]

I purchased 37x13.5x17 Toyo's earlier this year for my vehicle. The Toyo's are actually 37.1" in diam. compared to my bfg, which were 34.5. I did the math and here is what I came up with.

---------Toyo's------- BFG's
diam.----37.1"---------34.5"
circum.--116.553"-----108.835"--------(63360 in = 1 mile)
rev/mi.--543.615-------584.58

584.58/543.615=1.075
So, the Toyos travel 0.075 mile greater than the BFGs do in 1 mile.
So, when my speedometer says I am traveling at 60 mph, I am really going 64.5 mph.
@40 = 43.00 mph
@50 = 53.75 mph
@60 = 64.50 mph
@70 = 75.25 mph
@80 = 86.00 mph

Also, for every 13.33 miles, I am traveling 14.33 miles
1 mile saved every 13 1/3 miles.

[The Green Lantern]

Originally Posted by WVHummer

1 mile saved every 13 1/3 miles.