Need help figuring MPG
Thread Starter
|
Freshman User
Joined: Dec 2007
Posts: 38
Likes: 0
From: North Las Vegas NV
Need help figuring MPG
I have a 2008 f 250 V10 with 4.30 gearing. I just replaced the stock wheels and tires with after market. Stock wheels were 17" and tires 265/70/17. I replaced them with 18' wheels and 35/12.5/18 Toyo M/T's. So roughly I went from a 31.6" tire to a 35" tire. It looks like my speedometer is off about 10.5%. Does this sound right? How in the heck do I hand calcukate my MPG's? Any help would be appreciated. I'm not worried about MPG's but am curious.
Senior User
Joined: Apr 2004
Posts: 203
Likes: 0
You need to get on an interstate and drive about 30 miles. Record your odometer reading at the first mile post and at the last. Subtract the difference and then you know what percentage your odometer is off.
My '04 is off 2.5% low. I take miles traveled, times 1.025 then divide by the gallons.
Example= My trip odometer says 273 miles and I put 22.7 gallons in. 273 x 1.025 = 279.83.
279.8 / 22.7 = 12.33 mpg
My '04 is off 2.5% low. I take miles traveled, times 1.025 then divide by the gallons.
Example= My trip odometer says 273 miles and I put 22.7 gallons in. 273 x 1.025 = 279.83.
279.8 / 22.7 = 12.33 mpg
Hotshot
Joined: Mar 2007
Posts: 10,101
Likes: 40
From: Pa
Originally Posted by Bug1964
I have a 2008 f 250 V10 with 4.30 gearing. I just replaced the stock wheels and tires with after market. Stock wheels were 17" and tires 265/70/17. I replaced them with 18' wheels and 35/12.5/18 Toyo M/T's. So roughly I went from a 31.6" tire to a 35" tire. It looks like my speedometer is off about 10.5%. Does this sound right? How in the heck do I hand calcukate my MPG's? Any help would be appreciated. I'm not worried about MPG's but am curious.
Senior User
Joined: Feb 2006
Posts: 396
Likes: 2
I know the dealer can only do up to 34.5" tires on a truck like mine "2003" but on the 08 I dont know what they can flash up to.
I do know there are "programmers" out there that claim to be able to change the tire size but I also know for my truck the same thing was true and the programmer did not change anything.
I use a speed wizard speedometer correction device, and I know people with this in 08's and it works. I think the truspeed also works in the 08's though I cant remember.
to find the percentage do like above and look at speedo vs gps
kenny
I do know there are "programmers" out there that claim to be able to change the tire size but I also know for my truck the same thing was true and the programmer did not change anything.
I use a speed wizard speedometer correction device, and I know people with this in 08's and it works. I think the truspeed also works in the 08's though I cant remember.
to find the percentage do like above and look at speedo vs gps
kenny
Thread Starter
|
Freshman User
Joined: Dec 2007
Posts: 38
Likes: 0
From: North Las Vegas NV
How will reflashing make the truck run better? I'm not getting that. LOL. With the 4.30 gears and the bigger tires the truck is running much better than with the stock go kart tires. That is why I got the 4.30 gearing. Will the dealer charge for reflashing?
Hotshot
Joined: Mar 2007
Posts: 10,101
Likes: 40
From: Pa
Originally Posted by Bug1964
How will reflashing make the truck run better? I'm not getting that. LOL. With the 4.30 gears and the bigger tires the truck is running much better than with the stock go kart tires. That is why I got the 4.30 gearing. Will the dealer charge for reflashing?
I reflashed my truck with my SCT tuner for my larger tires and the truck will hold the gear slightly longer before shifting. The speedo and trip meter was corrected by the tuner as well.
Whether you believe it or not your truck is slower with the 35s on it compared to a smaller stock tires. It may not be noticable but the truck will be slightly slower and the braking distance will more than likly be slightly longer. Thats just negative effects of larger and heavier wheels and tires.
A reflash at the dealer should cost around $100. You paid all kinds of $$$ for the new wheels and tires so $100 is a drop in the bucket to do the job right. Thats part of adding bigger tires, many people neglect it though. The new SDs with 20" wheels and tires are around 34" in diameter so the dealer should be able to reflash for 35's, if not you may have to find something from the aftermarket.
Hotshot
Joined: Mar 2007
Posts: 10,101
Likes: 40
From: Pa
Originally Posted by Mercury45
I know the dealer can only do up to 34.5" tires on a truck like mine "2003" but on the 08 I dont know what they can flash up to.
I do know there are "programmers" out there that claim to be able to change the tire size but I also know for my truck the same thing was true and the programmer did not change anything.
I use a speed wizard speedometer correction device, and I know people with this in 08's and it works. I think the truspeed also works in the 08's though I cant remember.
to find the percentage do like above and look at speedo vs gps
kenny
I do know there are "programmers" out there that claim to be able to change the tire size but I also know for my truck the same thing was true and the programmer did not change anything.
I use a speed wizard speedometer correction device, and I know people with this in 08's and it works. I think the truspeed also works in the 08's though I cant remember.
to find the percentage do like above and look at speedo vs gps
kenny
Certain tuners for SD and other vehicles for that matter won't correct for tires size.
My SCT corrected mine and I confirmed it with GPS. My tuner asks for the revs per mile and axle ratio.
Trending Topics
Senior User
Joined: Feb 2006
Posts: 396
Likes: 2
i have a diablo sport predator, i bought it back in 03 early 04 .. around that time, after many many conversations and basically having arguments back and forth with diablo sport they helped me out in other ways but the tuner / programmer did not correct tire size at all.
As mentioned before as far as I know standard programmers will only do up to 34.5" tires, and this is also the limit of the dealer (or at least what most dealers will do)
Now there is a thing called the "accupro" but again I have no experience with it PLUS it is more expensive then the inline boxes anyway.
If you ever are going to consider switching the tires back to stock, or ever go bigger then i think the dealer is a poor option - it may cost up to 100$ each time for a flash, while with the device I use (speed wizard) it takes less then one minute and it is very accurate.
Hey dkf - what size tires did you end up with? just wondering
kenny
As mentioned before as far as I know standard programmers will only do up to 34.5" tires, and this is also the limit of the dealer (or at least what most dealers will do)
Now there is a thing called the "accupro" but again I have no experience with it PLUS it is more expensive then the inline boxes anyway.
If you ever are going to consider switching the tires back to stock, or ever go bigger then i think the dealer is a poor option - it may cost up to 100$ each time for a flash, while with the device I use (speed wizard) it takes less then one minute and it is very accurate.
Hey dkf - what size tires did you end up with? just wondering
kenny
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Ford Super Duty: 5 Things Owners LOVE, 5 Things They LOATHE!
Joe Kucinski
Every 2026 Ford Truck Engine RANKED from WORST to FIRST!
Michael S. Palmer
The Best F-150 Deal of Every Trim Level (XL through Raptor)
Joe Kucinski
Hotshot
Joined: Mar 2007
Posts: 10,101
Likes: 40
From: Pa
Originally Posted by Mercury45
Hey dkf - what size tires did you end up with? just wondering
kenny
Team Mudd is running 37s on his and uses a Superlift Truespeed to correct for the tires as well as others on his site.
Link
http://www.team-mudd-racing.com/Readers%20Pics.htm
Posting Guru
Joined: Nov 2004
Posts: 1,708
Likes: 3
From: North Dakota
I actually found that my speedo was a bit optamistic with the stock tires, in other words it was reading a bit faster than I was actually going. Going from 265/75/16s to 285/75/16s actually put it just about spot on acording to to my Lowrance I-Finder H20C.
Senior User
Joined: Feb 2006
Posts: 396
Likes: 2
from the factory the trucks are setup usually to read a little faster -
and badhabin... 2mph fast but at what speed. You should really give a percentage of how fast it is reading because just saying 2mph does not make it really clear. Cause 2mph fast at 100 is 2% fast but 2 mph fast at 10mph is 20% fast - see my point?
Kenny
and badhabin... 2mph fast but at what speed. You should really give a percentage of how fast it is reading because just saying 2mph does not make it really clear. Cause 2mph fast at 100 is 2% fast but 2 mph fast at 10mph is 20% fast - see my point?
Kenny