not happy with my 4.56 gears
#46
11-06-2011, 04:37 PM
#47
11-06-2011, 05:09 PM
Member
HAHA okay, you're right if you make the corrections a different way than the way I've explained then your MPG calculation will be correct as long as corrected numbers are being used. Bottom line if you make changes to tire size and/or gear ratio, you can use a $300 programmer or a $3 calculator, you still have to factor in the changes from the factory set up to get an accurate MPG rating.
#49
11-06-2011, 08:24 PM
Member
My truck has stock tires and gears so I can't give you actual numbers... maybe someone with non-stock tires and gears and a GPS could go out and drive down the road and hold a speed to 50 MPH as shown on the GPS and record the speed listed on their speedo. Then maybe I can show this a little better... a bonus if your truck displays MPG on the dash, Lets see what that says.
I'll either clear this up or really confuse you now
With only a tire size increase you could use an online calculator to figure out how far off your speedo/odometer are. With both tires and gears, a GPS comparison will make this MUCH easier!
My trucks stock tire size acording to tirerack.com is 275/65/18 or about a 32" tall tire.
Say I put 37's on. What would I have to do to figure out my MPG after that?
For a baseline we'll say with the stock tire size 50 MPH on the GPS = 50 MPH on the Speedo and We'll say it takes me 16 gallons of gas to drive 250 miles as recorded by the odometer.
(((Speedo Reading - 50 MPH GPS Reading) * 2) + Odometer Reading) / Gallons Used = MPG
Stock would be like this.
(((50 - 50) * 2) + 250) / 16 = ~15.6 MPG
50 - 50 = 0
0 * 2 = 0
0 = 250 = 250
250 / 16 = 15.625
Now change to 37" tall tires (~16% larger)
This will make the Speedo read off just a little. The GPS will still read 50 MPH but according to 4lo.com the Speedo will only show 43.5 MPH (give or take) I'll use the same MPG math as in the example above, 16 gallons on a 250 mile reading from your now incorrect odometer. First correct the odometer reading, subtract the 50 MPH GPS reading from the 43.5 MPH speedo reading and multiply that by 2 and then add that answer (probably a negative number) to the 250 miles shown on your odometer. This number is the actual miles traveled. You'll take that number and divide it by the number of gallons you used. The same as you would figure your MPG in any other car. For this example I used the same 16 gallons for the math, but we all know you would probably be using maybe 18 or 19 to fill the tank back up because the larger tires, weight and rolling resistance will also add to fuel consumption. I'll show that next.
(((43.5 - 50) * 2) + 250) / 16 = ~14.8 MPG
43.5 - 50 = -6.5
-6.5 * 2 = -13
-13 + 250 = 237
237 / 16 = 14.8125
Still with 37's if it realistically took 18 gallons to fill up after driving 250 miles as shown on your odometer you would figure it the same way.
(((43.5 - 50) * 2) + 250) / 18 = ~13.2 MPG
Go fill up your tank and reset your trip odometer. Then go drive around all day, at least 100 miles or so and then fill up again and record your trip miles and number of gallons it took to fill up. Then copy this into a Google search and edit it with your numbers.
or just click this link ===> (((S - A) * 2) + O) / G = and make the changes as listed below.
Change S to your Speedometer reading at a predetermined GPS speed
Change A to your Actual Speed Shown on the GPS (50 MPH)
Change O to the trip Odometer reading at fill up
Change G to the number of Gallons it took to top off the tank.
Hit search. Google will do the math for you.
I'm sure I could figure out about what the MPG display in your truck might say without it knowing what changes you made to the truck, but my brain hurts now! At first glance I'd bet it shows about 12.3 using the numbers from above. Figuring that it would show somewhere around the % difference between stock 32's and new 37's (16%) from the actual MPG. Meaning The MPG you figure using this math minus 16% difference in tire size that it does not know about. Then even less figuring in extra weight and resistance.
So I say, Someone please gather the info needed to do actual math and we'll see how I make out.
I'll either clear this up or really confuse you now With only a tire size increase you could use an online calculator to figure out how far off your speedo/odometer are. With both tires and gears, a GPS comparison will make this MUCH easier!
My trucks stock tire size acording to tirerack.com is 275/65/18 or about a 32" tall tire.
Say I put 37's on. What would I have to do to figure out my MPG after that?
For a baseline we'll say with the stock tire size 50 MPH on the GPS = 50 MPH on the Speedo and We'll say it takes me 16 gallons of gas to drive 250 miles as recorded by the odometer.
(((Speedo Reading - 50 MPH GPS Reading) * 2) + Odometer Reading) / Gallons Used = MPG
Stock would be like this.
(((50 - 50) * 2) + 250) / 16 = ~15.6 MPG
50 - 50 = 0
0 * 2 = 0
0 = 250 = 250
250 / 16 = 15.625
Now change to 37" tall tires (~16% larger)
This will make the Speedo read off just a little. The GPS will still read 50 MPH but according to 4lo.com the Speedo will only show 43.5 MPH (give or take) I'll use the same MPG math as in the example above, 16 gallons on a 250 mile reading from your now incorrect odometer. First correct the odometer reading, subtract the 50 MPH GPS reading from the 43.5 MPH speedo reading and multiply that by 2 and then add that answer (probably a negative number) to the 250 miles shown on your odometer. This number is the actual miles traveled. You'll take that number and divide it by the number of gallons you used. The same as you would figure your MPG in any other car. For this example I used the same 16 gallons for the math, but we all know you would probably be using maybe 18 or 19 to fill the tank back up because the larger tires, weight and rolling resistance will also add to fuel consumption. I'll show that next.
(((43.5 - 50) * 2) + 250) / 16 = ~14.8 MPG
43.5 - 50 = -6.5
-6.5 * 2 = -13
-13 + 250 = 237
237 / 16 = 14.8125
Still with 37's if it realistically took 18 gallons to fill up after driving 250 miles as shown on your odometer you would figure it the same way.
(((43.5 - 50) * 2) + 250) / 18 = ~13.2 MPG
Go fill up your tank and reset your trip odometer. Then go drive around all day, at least 100 miles or so and then fill up again and record your trip miles and number of gallons it took to fill up. Then copy this into a Google search and edit it with your numbers.
or just click this link ===> (((S - A) * 2) + O) / G = and make the changes as listed below.
Change S to your Speedometer reading at a predetermined GPS speed
Change A to your Actual Speed Shown on the GPS (50 MPH)
Change O to the trip Odometer reading at fill up
Change G to the number of Gallons it took to top off the tank.
Hit search. Google will do the math for you.
I'm sure I could figure out about what the MPG display in your truck might say without it knowing what changes you made to the truck, but my brain hurts now! At first glance I'd bet it shows about 12.3 using the numbers from above. Figuring that it would show somewhere around the % difference between stock 32's and new 37's (16%) from the actual MPG. Meaning The MPG you figure using this math minus 16% difference in tire size that it does not know about. Then even less figuring in extra weight and resistance.
So I say, Someone please gather the info needed to do actual math and we'll see how I make out.
#51
11-06-2011, 11:25 PM
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Man! I've tried to sort of explain this before in another thread. If you have made changes to your tire size and/or gear ratios, you HAVE TO figure out the percentage of your combined over all change to calculate your MPG. You can not use ANY numbers your truck is giving you to calculate MPG, not RPM???? not the odometer, not the speedometer and most of all NOT THE MPG display on your dash
Use a GPS and drive your truck at 50 MPH (GPS speed). Read your trucks odometer speed at the same time your GPS says 50 MPH. Take your odometer speed minus 50 MPH and multiply by 2. This will tell you the % your odometer is off.
If your vehicle odometer registers "M" miles and it takes "G" gallons to fill up…
Multiply "M" miles by the amount the odometer is off calculated above. Add that number to your odometer reading to get total miles. Divide the total miles by "G" gallons. This will equal ACTUAL MPG.
Use a GPS and drive your truck at 50 MPH (GPS speed). Read your trucks odometer speed at the same time your GPS says 50 MPH. Take your odometer speed minus 50 MPH and multiply by 2. This will tell you the % your odometer is off.
If your vehicle odometer registers "M" miles and it takes "G" gallons to fill up…
Multiply "M" miles by the amount the odometer is off calculated above. Add that number to your odometer reading to get total miles. Divide the total miles by "G" gallons. This will equal ACTUAL MPG.
#52
11-07-2011, 12:19 AM
Member
I'm kinda curious as well.. I bought my second KR stock about a year ago.. The difference in power is night and day.. Same year model.... Same size tire and rim combo... I'm curious to if the previous owner regeared the truck.. With my 35's at 70mph my rpm reads a little less than 2000.. The gas gauged tells me i'm at 14.4mpg... My 35's break loose easily and it pulls effortlessly.
Originally Posted by 5speedtransmissions.com
Put rear on jack stands (safety first!)
Wrap a long cable tie around the driveshaft, but don't cut the 'tail'. Point it straight up at the 12:00 position.
Put a mark on a tire, like at 6:00 position.
Put the trans in Neutral.
Turn the wheel exactly 1 revolution, noting how many times the driveshaft turns by watching the cable tie. The key is to be as exact as possible.
Note the position of the cable tie tail.
Now, if the cable tie made 3 revolutions, and is at about the 1:00 position, then it's likely a 3.08 gear. 3.5 revolutions, then a 3.55. 4 revolutions, 4.10, etc.
Wrap a long cable tie around the driveshaft, but don't cut the 'tail'. Point it straight up at the 12:00 position.
Put a mark on a tire, like at 6:00 position.
Put the trans in Neutral.
Turn the wheel exactly 1 revolution, noting how many times the driveshaft turns by watching the cable tie. The key is to be as exact as possible.
Note the position of the cable tie tail.
Now, if the cable tie made 3 revolutions, and is at about the 1:00 position, then it's likely a 3.08 gear. 3.5 revolutions, then a 3.55. 4 revolutions, 4.10, etc.
#53
11-07-2011, 12:28 AM
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ha i guess i picked the right gear tire combo because i get from 11-13+ mpg on heavy 41's.
#54
11-07-2011, 06:12 AM
#55
11-07-2011, 10:51 AM
Member
Yeah, thats what the whole calculation is about, correcting the odometer reading before figuring the MPG. Reading the speedo at a known accurate speed and converting the odometer based on the now known difference, I guess it would be the same as if you drove a known accurate distance and then did the math to figure the difference between that known difference and the distance shown on your odometer. Using the speedo to gauge the inaccuracies is just a lot faster than driving a known distance. You know 0-50 and record the numbers Vs. driving a known distance to get the numbers. Plus 50mph is repeatable over and over exactly the same every time.
#56
11-07-2011, 07:28 PM
#57
11-08-2011, 12:00 AM
#58
11-08-2011, 12:02 AM
#59
11-08-2011, 10:02 PM
Member
yeah, I'm not saying you shouldn't, All I'm saying is that your MPG is wrong unless your odometer is corrected before MPG is calculated. So for all the guys running larger tires and/or lower gears, I've shown how to figure it out if you didn't have a programmer to do it for you.
#60
01-30-2012, 05:24 AM
Senior Member