# Why no milage difference between 3.73 and 4.10 rear ends? **URL:** \ **Category:** Factual Questions\ **Created:** [June 9, 2003, 4:44pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665 "2003-06-09T16:44:50Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [June 9, 2003, 4:44pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/1 "2003-06-09T16:44:50Z")
I’m looking at a new vehicle (Explorer Sport Trac) They lhave the same milage rating for a 4.10 and 3.73 rear end. How can that be? The transmission gearing is the same either way, so the motor must be turning faster with the 4.10 than the 3.73, right? So, how can they have the same milage? ---
**Author:** ![ParentalAdvisory](https://avatars.discourse-cdn.com/v4/letter/p/53a042/32.png) [@ParentalAdvisory](https://boards.straightdope.com/u/ParentalAdvisory)\ **Post date:** [June 9, 2003, 5:15pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/2 "2003-06-09T17:15:08Z")
Were these rated with a manual or auto? That does make a difference. ---
**Author:** ![fuhoff](https://avatars.discourse-cdn.com/v4/letter/f/9d8465/32.png) [@fuhoff](https://boards.straightdope.com/u/fuhoff)\ **Post date:** [June 9, 2003, 5:22pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/3 "2003-06-09T17:22:22Z")
Simple physics math. Same mass traversing the same distance, overcoming the same resistance = same energy consumption. ---
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [June 9, 2003, 5:38pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/4 "2003-06-09T17:38:28Z")
I don’t believe it is that simple. Using your theory if a car were to stay in first gear it would get the same milage over the same distance. That’s not going to work. You are getting more torque to the ground with the higher gear (More work?) The higher gearing makes the engine turn at a higher RPM at the given speed. Higher RPM=more fuel consumed, ergo, _should_ = worse milage (less distance travelled per/gallon/liter of fuel) Right…? ---
**Author:** ![DiLLiGaF](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@DiLLiGaF](https://boards.straightdope.com/u/DiLLiGaF)\ **Post date:** [June 9, 2003, 5:40pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/5 "2003-06-09T17:40:19Z")
> [@](#): > > \*Originally posted by fuhoff \* > \*\*Simple physics math. Same mass traversing the same distance, overcoming the same resistance = same energy consumption. \*\* I don’t think that is accurate when you figure in the different gear ratios. **bernse** , was one of those gear ratios (3.73 possibly) the standard and the other an option? I’m just wondering if they based the fuel mileage off the standard package and didn’t make any changes for the optional package. The 4.10’s would definitly drop your mileage. ---
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [June 9, 2003, 5:52pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/6 "2003-06-09T17:52:00Z")
Well, the 4.10 is standard on certain packages. They don’t differentiate between the two for milage ratings. Interestingly enough, they rate the it at a fantastic 21MPG on the US website, and 25 in Canada. Must rate them differently here. ---
**Author:** ![DiLLiGaF](https://avatars.discourse-cdn.com/v4/letter/d/45deac/32.png) [@DiLLiGaF](https://boards.straightdope.com/u/DiLLiGaF)\ **Post date:** [June 9, 2003, 6:15pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/7 "2003-06-09T18:15:52Z")
> [@](#): > > \*Originally posted by fuhoff \* > \*\*Simple physics math. Same mass traversing the same distance, overcoming the same resistance = same energy consumption. \*\* I don’t think that is accurate when you figure in the different gear ratios. **bernse** , was one of those gear ratios (3.73 possibly) the standard and the other an option? I’m just wondering if they based the fuel mileage off the standard package and didn’t make any changes for the optional package. The 4.10’s would definitly drop your mileage. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [June 9, 2003, 6:16pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/8 "2003-06-09T18:16:09Z")
Does Canada use imperial gallons? ---
**Author:** ![zwede](https://avatars.discourse-cdn.com/v4/letter/z/ac91a4/32.png) [@zwede](https://boards.straightdope.com/u/zwede)\ **Post date:** [June 9, 2003, 8:48pm UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/9 "2003-06-09T20:48:59Z")
I think that’s the answer. They only go through the EPA mileage cycle for the standard equipment and don’t re-rate for the options. Quite a nice loop-hole, there. They could make some ridiculous final drive “standard” and then make better ratios a no-cost option. That way they would get better mileage to comply with fleet average rules. Of course, final drive ratio can only be taken so far until mileage no longer improves. /Markus ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [June 10, 2003, 10:48am UTC](https://boards.straightdope.com/t/why-no-milage-difference-between-3-73-and-4-10-rear-ends/180665/10 "2003-06-10T10:48:20Z")
Now that I think of it, most of the vehicle stickers I’ve seen state that the EPA values are estimates and real mileage is dependent upon driving habits and vehicle options. But… I’ve seen many of the same vehicle with different engines show different EPA estimates. I posted this on another thread a few days ago: > [@](#): > > US EPA FUEL ECONOMY EQUATION > The EPA equation for the calculation of EPA fuel economy mpg is derived indirectly from the city and highway HC, CO, and CO2 exhaust emission values, which are expressed in grams per mile of each exhaust pollutant, respectively. Consequently, EPA mpg certification label values are not based on direct measurements of fuel consumed by the engine. The EPA mpg equation is inferred from the exhaust total carbon balance. Fundamentally, this is a rational basis, and the method should determine the City and Highway fuel mpg correctly. However, EPA specifies that once the mpg values have been calculated by this carbon balance method, the city mpg is then multiplied by the arbitrary fraction 0,90; and, the highway mpg is multiplied by the fraction 0.78, to determine certification label values, see 40CFR600.209-85 page 751.