No Calibration Needed!
 

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. :D :D

Re: No Calibration Needed!
 

Here are my calculations:

32's - 630.6 revolutions per mile

35's - 576.5 revolutions per mile

so, 630.6 minus 576.5 equals 54.1, which means 54.1 less revolution per mile for the 35's. Not much but it will add up...:D

Re: No Calibration Needed!
 

Re: No Calibration Needed!
 

Sounds wrong, but just keep good records so you can let the DMV know the odometer isn't accurate before you trade it in and you should be fine.

Re: No Calibration Needed!
 

You should also calculate how it effects your speed, as the speedo will also be off as well. You'll be going a bit faster then reflected by the speedo.. so watch out for speeding tickets.

32's - 638.6 revolutions per mile - ~8.6'/revolution

35's - 576.5 revolutions per mile - ~9.15'/revolution

My math says its about 6.6" diffference per revolution difference so
for every 638.6 revolutions (1 mile on your odometer) you've traveled 9.15 feet on the 35s or 638.6 * 9.15 = 5843 feet or 1.10 miles. Roughly an extra 600 feet.

Edit: Assuming your revolutions are correct...

Re: No Calibration Needed!
 

So, do you have other way to calculate it? Already tried the dealer if they could calibrate it but they can't do it. And I don't think I will trade it in...:D

Re: No Calibration Needed!
 

So for every 1056 miles you will save one mile on your odometer so if you average 12000 miles a year you'll beable to hide or save about 11.4 miles I gues it does kind of add up.
-But have mpg gone down?
-stayed the same?
-or gotten better?
-do you know?
-and what tires andwheels do you have?
-Oh and one more question what air pressure do you run them at?
Sorry for all the quetions but I'm trying to decied if it is worth going from the 33's to 35's thanks.

Re: No Calibration Needed!
 

I used this furmula to figure out - C = 2 pi r for the circumference. They are 63,360 inches a mile. Maybe I could be wrong...:D

Re: No Calibration Needed!
 

Just enjoy the better look and overall wheelability, and don't sweat the small stuff!
~11miles...your gonna lose that in wheel spin in a years worth of offroading anyway!:D

Re: No Calibration Needed!
 

That part is correct, but I think your closer to 1 extra mile for every 10 miles on the odometer. I don't know how you get 5 feet for every 1 mile on the odometer, if I am reading your second post correctly. Not exactly sure what you are saying in that post.

Re: No Calibration Needed!
 

with my calculations, 35's revolves 576.5 in a mile... and 32's 630.5, ... :D

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yeah, the 5 ft. was wrong. 54.1 less revolution a mile on the 35's comparing to the 32's..thanks. :D

Re: No Calibration Needed!
 

Too much math...my brain hurts! :D

Re: No Calibration Needed!
 

x 2.5 / 4^7 :D

Re: No Calibration Needed!
 

Use this calc...

http://www.miata.net/garage/tirecalc.html

Re: No Calibration Needed!
 

Ok the math is killing me to but just because I needed to figuer it all out so here it is. And yes I have a touch of OCD at times :D

32's: Cir=100.48" Rev. per. mile=630.57

33's: Cir=103.62" Rev. per. mile=611.46

35's: Cir=109.90" Rev. per. mile=576.52

and 1 mile = 63360"

So 33's will: Get you 1 extra mile for every 32 mile compared to 32's

and 35's will: Get you 1 extra mile for every 10.67 miles compared to 32's
and 1 extra mile for every 16.5 miles compared to 33's

sorry but I had to redo the math for my own sanity. lol...

Re: No Calibration Needed!
 

there you go!!.......and deiTai.. good find on the tire calc. :D

Re: No Calibration Needed!
 

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

Re: No Calibration Needed!
 

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

Re: No Calibration Needed!
 

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

Re: No Calibration Needed!
 

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... :D

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

Re: No Calibration Needed!
 

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

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.

Re: No Calibration Needed!
 

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.

Re: No Calibration Needed!
 

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.

Re: No Calibration Needed!
 

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

By the way good one FutureBeachBum

Re: No Calibration Needed!
 

LMFAO :D :eek:

Re: No Calibration Needed!
 

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.

Re: No Calibration Needed!
 

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

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... :rolleyes:

Re: No Calibration Needed!
 

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????

Re: No Calibration Needed!
 

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

Re: No Calibration Needed!
 

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

S.

Re: No Calibration Needed!
 

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

Re: No Calibration Needed!
 

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.

Re: No Calibration Needed!
 

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! :D :D

Re: No Calibration Needed!
 

And you trust the speedo in a Jaguar?:D

Re: No Calibration Needed!
 

Not really :D ....ok ok ok, I will do it again with my GPS ;) ;)

Re: No Calibration Needed!
 

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

Re: No Calibration Needed!
 

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.

Re: No Calibration Needed!
 

:perfect10s: