Will the 4.7 final drive ratio kill MPG and TOP end speed for use as practical daily driver?

[The Bronze]

TOP speed is electronically limited by fuel or throttle body electronically, but based on tire type and 10 speed auto it will be around 99-105 MPH. So around 3075 RPM for LT315/70R17s and 4.70s and 2875 RPM for LT285/70R17s and 4.46 gears. With RPMs off the table, that just leaves mileage, acceleration, stability, looks, and replacement cost to debate!

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[grimmjeeper]

TOP speed is electronically limited by fuel or throttle body electronically, but based on tire type and 10 speed auto it will be around 99-105 MPH. So around 3075 RPM for LT315/70R17s and 4.70s and 2875 RPM for LT285/70R17s and 4.46 gears. With RPMs off the table, that just leaves mileage, acceleration, stability, looks, and replacement cost to debate!

Turns out that the speed limiter in most vehicles is set based on the speed rating of the factory tires. They don't want you running faster than the tires can handle.

 

[HoosierDaddy]

Not to sound like im coming off rude but if you are one of the people worried about your mpg's i would really think hard if the bronco is the vehicle for you, because some people say 4.7 wont hurt that much but its definitely noticeable, i went from 3.55 to 4.10 in my mustang and noticed a difference, so having 4.7 on a big heavy vehicle with 35's.... well MPG is not going to be that great, but the Bronco wasn't made with good gas mileage in mind.

But did you increase tire size also? That is what is happening at the factory, get taller tires, they install a lower gear and it all equals out in the end.

Run the RPM calculator over at GrimmJeeper.com using all the info provided to us by Ford in respect to what tires get which gear. ...I have.

After all the tire and gearing changes, the RPM at any given speed is literally with several RPM .
The biggest "Give" is going to be the increased mass of the 35"s ...that super low 4.7 will cancel out almost all of it.

 

[Trilifter7]

Left side is 4.7 rear axle ratio with LT315/70R17 tires. Right side is 4.7 rear axle ratio with LT285/70R17 tires. Chart is automatic transmission gear vs speed (I picked 3 speeds) to give engine RPM. "Aint nobody" going to be worried about being stuck at high rpms with 3 overdrive gears!

View attachment 65028

Left side is 4.7 axle ratio with LT315/70R17 tires. Right side is 4.46 axle ratio with LT285/70R17 tires.

View attachment 65026

I don't think you used the right transmission for these charts. Should be the 10R80 10 speed. yours shows 9 gears. for the 10 speed, 4.46 gears and 285 tires should be at 2346 rpm at 80mph

 

[The Bronze]

I don't think you used the right transmission for these charts. Should be the 10R80 10 speed. yours shows 9 gears. for the 10 speed, 4.46 gears and 285 tires should be at 2346 rpm at 80mph

Funny, I missed a line somewhere when I made an edit. I will edit that. Good catch.

 

[Jak]

Would it be over simplifying to say, keep 4.46 if you plan to use 33s, or, upgrade to 4.7 if you want 35s?

 

[Austin26]

Yea but when you add bigger tires doesnt your MPG drop lower also?

Maybe im not understanding something here, in my experience changing to a higher number gear 4.10 or 4.7 hurts your fuel economy, also the bigger your tires are 33 to 35inch hurts your fuel economy so why together would it be a wash? I'm not a mechanic but my simple logic would tell me together they would make your fuel economy even worse not wash each other out. But please let me know if my understanding is wrong.

Larger diameter tires will weigh more which makes fuel economy worse. However, the larger diameter alters the final drive ratio as it has a larger circumference which improves fuel economy. This is why he or she said it was a wash, which I agree with.

If you're concerned about fuel economy get some relatively lightweight P-metric all terrains or even all seasons in a stock tire diameter.

I drive slowly and get at or above sticker rated fuel economy with my cars. It'll be the same with the Bronco. This is the biggest factor in my opinion but also kills the fun if speeding or rapidly accelerating and braking is your thing.

 

[jswan]

Sounds like I'm going Squatch Badlands, and adding Rotopax with two 5 gallon jugs on board.
Should be nearly no worries depending on where I'm going.

I'm and engineer (civil, not mechanical) and all this gearing talk has my head spinning! LOL!

 

[Austin26]

Not to sound like im coming off rude but if you are one of the people worried about your mpg's i would really think hard if the bronco is the vehicle for you, because some people say 4.7 wont hurt that much but its definitely noticeable, i went from 3.55 to 4.10 in my mustang and noticed a difference, so having 4.7 on a big heavy vehicle with 35's.... well MPG is not going to be that great, but the Bronco wasn't made with good gas mileage in mind.

I agree with your sentiment but you're forgetting the wheel circumference is itself another gear. They're close to the same as already stated by others.

 

[djp]

With the slightly bigger tires and the slightly bigger gears, it’s basically a washout.
There might be a small difference but not anything you should notice very much.

Above is very true, but lets also do the cost of gas over time, I suspect it to be < $100 per year (even if it wasnt a wash out)

10,000 miles / at 25mpg * $2.20/gal = $900 is gas spent per year

now let's say 2.5 mpg reduction because of gearing....

10,000 mikes / 22.5mpg * $2.20/gal = $977 in gas per year

Ouch, $77. Killer, perhaps a prius?

 

[Wizard1183]

THey shouldve had 2.7L with MT. Stupid not to as the transmission can handle what comes in 2.7L. Now if someone was to reprogram it? It may not handle the power then. But factory it most certainly can.

 

[North7]

THey shouldve had 2.7L with MT. Stupid not to as the transmission can handle what comes in 2.7L. Now if someone was to reprogram it? It may not handle the power then. But factory it most certainly can.

Different adapters, they don't bolt together. It will take further development by Ford to do it.

There are a 1,000 posts on this subject if you want to dive deeper.

https://www.bronco6g.com/forum/search/

 

[Broncodave]

A lot of talk of MPGs only, but the reason I'll probably go 33" instead of 35" is the ability to change my own tire (Hopefully. The 33 is still a big, heavy tire) and the stopping distance (for us freeway speed travelers). 33's for me hit the sweet spot between coolness factor (big tire) and better performance (small tire).

This video should start at 14:40 (brake test).

 

[Wizard1183]

Different adapters, they don't bolt together. It will take further development by Ford to do it.

There are a 1,000 posts on this subject if you want to dive deeper.

https://www.bronco6g.com/forum/search/

Adapters or bell housings?

Different adapters, they don't bolt together. It will take further development by Ford to do it.

There are a 1,000 posts on this subject if you want to dive deeper.

https://www.bronco6g.com/forum/search/

Ummmm I know they dont bolt together. Could they? Absolutely. But its more along the lines of mounts moved ect so that they could bolt together. And outputshaft splines are same count as the 2.7L. I just think Ford failed to deliver a manual Transmission in 2.7L. Its not like it wasnt a given people wouldnt want that. If youre gonna pay homage? Then pay homage and stop slipping in tidbits where it doesnt matter as much and fail where it matters most....

 

[BossMann]

With the higher gears, the EV Wrangler goes from 50 miles per charge to 35...

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