Regearing to 3.21 Like the RAM for best MPG

[Ericshere03]

I was thinking of installing a new rubber ring gear on my rear axle, ok a pair, ok ok ok, let me start over...

I was thinking since the RAM gets its best MPG with 3.21 gearing (3-4MPG better), why not "regear" the Gladiator for an effective ratio of 3.21? It turns out mathematically a 3.73 rear gear effectively becomes 3.23 when going from 32" tires to 37" tires. Drag and weight aside, going to 37's may be a boost in MPG, obviously at higher speeds additional drag will cause a hit and when accelerating in the city the weight will cause another hit...

I am slowly justifying 37's this time, i had 35's on my 2020 Gas 6 speed Gladiator, I "want" 37's but I LOVE the performance (power/MPG) of the crappy 32's that came stock on my 80th Anniversary.

What are you folks seeing with 37's, please only respond with CALIBRATED speedometers, hand calculations are a plus!

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[PDiddy]

I think you will have zero torque and it will be like swimming with shoes on. No fun at all.

 

[Ericshere03]

I think you will have zero torque and it will be like swimming with shoes on. No fun at all.

The math suggests that even with 37's the gear ratio is still a hair better than the RAM, so a little more torque to the ground... Also the weight of a BFG KO2 37 is only 12lbs more than a stock 33. That only leaves drag, which I cannot calculate without a wind tunnel.... Actually not true, i can calculate roughly based on a coast down test. Also our 8 speed 4.71 first gear, taking off isnt much an issue.

This has been answered many times before, I was sort of thinking about the issue justifying 37's in a different way.

 

[Jefe1018]

I think you will have zero torque and it will be like swimming with shoes on. No fun at all.

Negative, lack of torque is not an issue with 37s and 3.73 on an eco-diesel, at least nothing to complain about too much considering the big difference. However, I highly doubt any vehicle becomes more efficient with bigger, heavier tires.

Edit: OP has a gas engine with a soon to be 3 speed manual trans

 

[Panthers65]

in theory it'll work, but in practice I hardly ever see it turn out that way.

Use to be the same theory with smaller V6 engines in full size trucks. In perfect conditions with a 75 year old woman driving, you would see better MPGs. 95% of real world situations you wouldn't.

If you do 99% of your driving on the interstate, completely flat ground, never towing, you might see a bump. if you do any city driving your mileage will drop, any towing and your mileage will drop, get into a really strong headwind and your mileage will drop, ect.....

Plus with the cost to regear, it'd take you 15 years to break even...

 

[Hipbilly]

With a 6MT??
You'll hate it. I went from 285s to 315s with 3.73 and dropped from 17mph to 14, could barely take off without smoking the clutch, the wife stalled it all the time, had zero torque and had to keep revs up to climb hills, completely lost 6th gear, and HAD to use 4lo to drive off-road.

Re-geared to 4.56 and all is happy again, back up to 15mpg, cruise in 6th with plenty of power to pass w/o downshifting, the only thing I lost was cruising at 85. I can cruise at 80, but usually keep it at 75 now.

I told my self that with a 4yo son and a new one on the way, I have no business cruising at 85 on 35s and a 3" lift, anyway....

 

[FutureOdin]

Folks need to read where these threads sit before replying. This is related to the EcoDiesel.

So I'm confused, you want to go with 37s with 3.21 gears with the EcoDiesel?

OR are you saying 3.21s on the RAM is like 37s with 3.73 with the Gladiator?

 

[Ericshere03]

Folks need to read where these threads sit before replying. This is related to the EcoDiesel.

So I'm confused, you want to go with 37s with 3.21 gears with the EcoDiesel?

OR are you saying 3.21s on the RAM is like 37s with 3.73 with the Gladiator?

I was trying to be funny, but I was suggesting that 37’s may put the motor in an efficiency sweet spot with an effective ratio equal to a ram with 3.21 gears.

for the record, I had a stock JKu 6 speed with the 3.21 gears and was a SLUG!

 

[Jocww]

I was trying to be funny, but I was suggesting that 37’s may put the motor in an efficiency sweet spot with an effective ratio equal to a ram with 3.21 gears.

for the record, I had a stock JKu 6 speed with the 3.21 gears and was a SLUG!

yea but the diesel if you had one would make not as much of a slug.

 

[Ericshere03]

yea but the diesel if you had one would make not as much of a slug.

I know, that’s sort of my point, gladiator on 37’s equals RAM on 32’s … gearing-wise.
And for the record I do have an ecodiesel, it’s a rocket ship compared to every Jeep I’ve owned, and drinks diesel like a Honda.

 

[Terminus33]

You are missing one of the most important part of fuel efficiency of which can not be changed on our trucks. If you have an identical powertrain and weight between the Gladiator and Ram the ram will get better mileage because its not a brick in the wind.

 

[Hipbilly]

This right here is where I got lost... as you were.

 

[dcmdon]

I know, that’s sort of my point, gladiator on 37’s equals RAM on 32’s … gearing-wise.
And for the record I do have an ecodiesel, it’s a rocket ship compared to every Jeep I’ve owned, and drinks diesel like a Honda.

Yes, but a completely different engine.

If they are turning the same rpm and one engine makes 600 ft-lbs at the crank, it will be easy to livewtih. If the other makes 260 ft lbs, it will be miserable.

you have also neglected to account for the fact that what matters is OVERAL gear ratio. You have no idea what the Ram vs Jeep's transmission ratio is in top gear.

Which leads to another thing. The AT will most likely notice the lugging and will max out in 7th.

What you are suggesting makes no sense on so many levels. I'll write more when I have time.

 

[Ericshere03]

Yes, but a completely different engine.

If they are turning the same rpm and one engine makes 600 ft-lbs at the crank, it will be easy to livewtih. If the other makes 260 ft lbs, it will be miserable.

you have also neglected to account for the fact that what matters is OVERAL gear ratio. You have no idea what the Ram vs Jeep's transmission ratio is in top gear.

Which leads to another thing. The AT will most likely notice the lugging and will max out in 7th.

What you are suggesting makes no sense on so many levels. I'll write more when I have time.

Yes I do, the RAM and the Gladiator have the same tranny, same ratios;
1st 4.71 2nd 3.13 3rd 2.10 4th 1.67 5th 1.28 6th 1.00 7th 0.84 8th 0.67

 

[Ericshere03]

This right here is where I got lost... as you were.

Whoops! Traded that for the ecodiesel … I’ll fix it! Thanks for the heads up.

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