3.42 Gears with 37" Tires

[TCoopSC]

I posted this to an older thread but didn't get any responses.

I have an '18 2500 with 3.42 gears, 5" lift with 37x13.5" tires on 20s. The truck drives fine in my opinion but i was wondering how different things would be if changed to 4.10---4.56 gears.

1) How much better would the truck feel driving it? Off the start and passing someone?

2) How much would my MPG go down? Currently im 19-20 (Some good info: Stock truck was around 20. Added DRD 60hp tune with deletes and it went up to around 23. Added 5" lift with 37" tires and where im at now)

3) Is it harming my trans with the lower gears? I don't tow much and only under 5k.

Thanks for any replies!!

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[F350Cummins]

I posted this to an older thread but didn't get any responses.

I have an '18 2500 with 3.42 gears, 5" lift with 37x13.5" tires on 20s. The truck drives fine in my opinion but i was wondering how different things would be if changed to 4.10---4.56 gears.

1) How much better would the truck feel driving it? Off the start and passing someone?

2) How much would my MPG go down? Currently im 19-20 (Some good info: Stock truck was around 20. Added DRD 60hp tune with deletes and it went up to around 23. Added 5" lift with 37" tires and where im at now)

3) Is it harming my trans with the lower gears? I don't tow much and only under 5k.

Thanks for any replies!!

it does add stress to the trans to get rolling. I am not a gearing expert, but I think 4:10 may be a bit extreme, where 3:73 would be a happier medium. 4:56 would be way too extreme.

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[TCoopSC]

Screen Shot 2019-03-26 at 7.18.32 AM.png

Thanks F350Cummins!

Yea, if you look at this chart, 3.73 or 3.90 would put me back in the RPM range of stock but im wondering if the truck would need a little more gear to help with the larger tires. The larger the gear, the higher the RPM which would hurt highway MPGs but the larger gear may help with "city" driving and backroads which is 95% of my driving....

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[DDP]

it does add stress to the trans to get rolling. I am not a gearing expert, but I think 4:10 may be a bit extreme, where 3:73 would be a happier medium. 4:56 would be way too extreme.

I agree, 4:10 should be perfectly fine. Once you get to about 40’s is when your looking at a little higher. 37’s aren’t even too bad on 4:10’s. Well worth the money for sure as your truck will not feel like a dog.


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[TCoopSC]

I’m getting 4.10s put in. I’ll let y’all know how it drives in a few days.


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[BrentM]

Subscribed... I am running 3.42's on 38's. I am considering a regear. Keep us posted

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[TCoopSC]

Ok, i got the truck back last Friday. The truck feels a lot better even to the point that i lowered the HP tune from 120 to 60! The gears change a lot sooner which gets you into 6st gear at 50mph if the engine load is low enough. I didn't care for this when i had stock tires but with the 4.10 gears, 6st gear feels a lot stronger! Before the gear change and with the larger tires, it would stay in 4th till around 50mph and wouldn't go into 6st until over 60mph. MPG so far has increased. I haven't been on the intestate yet, only city and back roads (0-55mph). I'll drive it some at 70+mph and update y'all.

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[TCoopSC]

Drove the interstate this morning. Below are the RPMs for everyone's knowledge. Note: The truck felt really good in 6st gear at interstate speeds.

MPH RPMs with 4.10 gears
60 - 1425
65 - 1550
70 - 1650
75 - 1800

With the 3.42 gears, i was around 1500 at 75mph.

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[RamHunter18]

Looks like you made a good choice

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[CMB]

It's been a while but I once did some figuring much as the charts show. Im currently running .410 with 35 and the final ratio is the same as stock tires on .372. To tow is a dream. .456 is too much on 37s but .410 would be in the sweet spot.

Cheers

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