MPG hit with Toyo AT3s 35x11.5x17 with 3.73s??

[AmishMike]

@Garemlin Sorry that no body actually answered your question.
I have a Rubicon so 4.10's but went from factory Falken M/T's 285/70R17 to Nitto Trail Grapplers in 35x11.5 and have had no noticeable change in mpg. The tread pattern of both are very similar.
DO read @Gren71 's link

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[NachoRuby]

@Garemlin Sorry that no body actually answered your question.
I have a Rubicon so 4.10's but went from factory Falken M/T's 285/70R17 to Nitto Trail Grapplers in 35x11.5 and have had no noticeable change in mpg. The tread pattern of both are very similar.
DO read @Gren71 's link

Same here. I went from the stock 285/70/17 MTs to a 315/70/17 AT. Gas mileage is unaffected. I think it's because the tires weigh the same (both are 61 lbs each) due to the construction of the old MTs vs the new ATs, and also due the tread pattern of the MTs introducing more rolling resistance into the equation. The 35s weigh the same and roll better. RPMs are also slightly down on the interstate due to the larger tire, which helps as well.

 

[Garemlin]

@Garemlin Sorry that no body actually answered your question.
I have a Rubicon so 4.10's but went from factory Falken M/T's 285/70R17 to Nitto Trail Grapplers in 35x11.5 and have had no noticeable change in mpg. The tread pattern of both are very similar.
DO read @Gren71 's link

Wondering what effect the 3.73s will have if any.

 

[ShadowsPapa]

Moving from non-A/T tires, say you have highway or all-weather tires, A/T tires will drop your MPG just because.
Then factor in weight, size, impact on engine being in the sweet spot RPM-wise, etc.
Going from my stock tires to even the exact same diameter A/T tires I took a hit. Dealer said any time they put A/T tires on a vehicle that didn't have them, they see mpg drop.
Mine has dropped a couple mpg since my first year.

Keep watch for those to change tires and talk about mpg changes but have never bothered to change the setting in their system. You can pretty much ignore those because they are running with false numbers.

 

[ShadowsPapa]

Turning an engine faster almost ALWAYS results in a higher specific fuel consumption. (gal per hour per hp)

Sooo glad you said "almost". Mine did better with higher RPM when hauling a load. It struggled to pull at a lower RPM and mpg dropped.
There's a sweet spot.
Unloaded when mine runs higher rpm for the same road speed, the mpg drops.
That sweet spot, again.

It's similar to how we saw larger engines get better mpg than a smaller engine in the exact same car, same gear ratio, etc.

 

[dcmdon]

Sooo glad you said "almost". Mine did better with higher RPM when hauling a load. It struggled to pull at a lower RPM and mpg dropped.
There's a sweet spot.
Unloaded when mine runs higher rpm for the same road speed, the mpg drops.
That sweet spot, again.

It's similar to how we saw larger engines get better mpg than a smaller engine in the exact same car, same gear ratio, etc.

As you know Cam timing is optimized for a certain RPM. Even with variable cam timing. (Does the pentastar have variable valve timing? And if yes, is it continuously variable or does it just shift from a low RPM timing to a high RPM timing??)

If you get too much below where timing is optimized you lose efficiency. But with most engines at most manifold pressures you are driving close enough to that optimal RPM that lower still is better.

 

[ShadowsPapa]

As you know Cam timing is optimized for a certain RPM. Even with variable cam timing. (Does the pentastar have variable valve timing? And if yes, is it continuously variable or does it just shift from a low RPM timing to a high RPM timing??)

If you get too much below where timing is optimized you lose efficiency. But with most engines at most manifold pressures you are driving close enough to that optimal RPM that lower still is better.

VVT and VVL (variable valve timing/variable valve lift)
It's not like the old centrifugal cam setups where the timing changed based on RPM.
The cam phasers that handle timing shift the cams using oil pressure.

 

[dcmdon]

VVT and VVL (variable valve timing/variable valve lift)
It's not like the old centrifugal cam setups where the timing changed based on RPM.
The cam phasers that handle timing shift the cams using oil pressure.

Does it vary lift as kind of a throttle? I know BMW has completely eliminated throttle butterflies in their engines. They throttle the engine entirely by reducing intake valve lift.

 

[Gren71]

Does it vary lift as kind of a throttle? I know BMW has completely eliminated throttle butterflies in their engines. They throttle the engine entirely by reducing intake valve lift.

 

[redriderjf87]

Gearing down (higher numerical ratio) will NOT help fuel economy. The engine will rev higher in top gear which will hurt highway fuel economy.

This may even out if you aren't currently even running in 8th on the highway. But the bottom line is that the slower the motor is turning at a given speed, the better your fuel economy is.

Engineers and manufacturers work to balance this fact with the need for decent acceleration. If all you cared about was fuel economy, you would be geared to run at full throttle at something like 1300 rpm when you were on the highway.

Shorter gears will help in town driving and speeds up until when youre just able to hold high gear. And also some highway situations where you're getting more into the throttle or having to downshift. Which will happen significantly I'd bet with 3.73s on 35s.

 

[Daddiator54]

I saw about a 5mpg hit going from the stock Bridgestone tires to Toyo AT III 34x11.5x17 and the same with Kenda 35x10.5x17s. Stock was about 23 in mixed driving, now at around 18mpg, have 22k on my JT.
I have 4.10s though not 3.73s.

Same. Took about a 5mpg hit as well with same tires. Was super sad but also it was expected so It’s worth mentioning that i also upgraded my rims to fuel beast (unknown weight) so that probably has some factor into the loss.

 

[Caraholic]

Remember, rpm's lower, better mileage



what about throttle positioning?

 

[USMC-SSGT]

I averaged maybe 21ish on 3.73 stock overland setup. Feel like I lose more everyday. Maybe high 15s now on a good day with some boat anchor Mickey 35s and 20s with a lift…but damn it looks good!

Really wanted and was 100% sold on diesel. They happened to have a fully loaded overland on the lot that I got for $6k under Msrp. Still consider ordering a new one (mine only has 7k miles) and getting the diesel. Issue is I don’t tow and it’s more of a fun want. Id get better mpg AND not need a re gear, but I’d still never break even fuel wise if that were my goal. I also sold all my OEM stuff so I’d need to swap 1 for 1 with the new one or start all over again adding $8 k in parts.

 

[Dave-G]

when you go to bigger tires- it is like you lowered ( higher number) gearing- going from 3.73 to 4.11 when going to 35" tires with keep you 60mph rpms the same. And keep the motor in best torque curve. chart below is 1-1 no over drive

 

[IOS-XR]

I switched our High Altitude Diesel from the factory 20” Dueler HL’s to JL Rubicon take offs last week. Went to 17” with 33-ish inch BFGoodrich KO2’s. Very minor overall diameter difference. So far I’m hovering around loosing 1.5mpg. I attribute that to weight and rolling resistance. I’ll just be leaving them on for the winter and if I do some minor off-roading.

They do look much better though…..

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