Gear swap

[Marcus2000monster]

I’m throwing around the idea of swapping 4:10s for 3:73s to grab lower rpms and higher mpgs. Anyone here ever done it? Is it something that could be done myself or need to be taken to a shop? At that ratio difference is a new carrier necessary? Easiest way seems to swap entire front and rear end but it’s hard to find someone near me with what I want lol. 

[Ed ke6bnl]

TO much work and money for a 9% gear change. not a good ideal.

[Marcus2000monster]

2 minutes ago, Ed ke6bnl said:

TO much work and money for a 9% gear change. not a good ideal.

I have heard that bigger tires with 4:10s will actually increase mpg and lower rpms. Is this true? Normally big tires will greatly reduce mpg. Also big tires will reduce life of front end parts... 

[Ed ke6bnl]

I put 4:10 in my Dodge from 3:50 with the 35" tires close to original gear ration BUT the tires are far heavier and wider and the milage goes down in my opinion.

[Marcus2000monster]

I’m trying to get mpg UP and rpm DOWN. I considered  jumping from 285s to 315s but I think it will reduce mpg not gain. Anyone have experience with this size on 4:10s? 

[dripley]

Unless you have something odd on your truck you should have 3:55's on there. What rpm are you seeing at 70 mph? Mine sees 2000 rpm at 70 with 3:55 gears and 265 75 16's. 

 Your 285's ought to run a little lower than mine,

Edited March 18, 2018 by dripley

[Marcus2000monster]

14 minutes ago, dripley said:

Unless you have something odd on your truck you should have 3:55's on there. What rpm are you seeing at 70 mph? Mine sees 2000 rpm at 70 with 3:55 gears and 265 75 16's. 

 Your 285's ought to run a little lower than mine,

They ARe 4:10s. 2k at 60 Mph. 

[dripley]

53 minutes ago, Marcus2000monster said:

They ARe 4:10s. 2k at 60 Mph. 

I re reasd and stand corrected. May be I had too much coffee this morning. 

This does make better sense than what I thought you were trying to do. 

[AH64ID]

It will take tens of thousands of miles, or more, to offset the cost for just a mpg gain even if you do the work yourself. If you were to go from 14 to 16 mpg the CPM would be reduced by less the 0.03/mile at 3.00/gal. If you did the gear swap for $1000 it would take 33K miles to cover the cost. In my research for swapping from 3.73 to 4.10, for towing purposes, it would cost closer to $3K to do the swap and that would take 100K miles to recoup the cost. Going from 16 to 18 mpg would would be a 0.02/mile savings and thus take 150% longer to pay off. 

 

I think a 2mpg gain is unrealistically high... basically it's not going to save you any money unless you plan to put 250K more miles on the truck. 

 

If you've never setup gears before, which I gather you haven't, I wouldn't do it yourself. 

 

Go with a taller and skinnier tire on your next set, it will reduce rpms without a large increase in rolling resistance/weight. 

 

A 255/85R16 would be a 5% reduction in rpms over a 265/75R16, which is just over 1/2 of the change you would get with a gear swap. 

[Marcus2000monster]

48 minutes ago, AH64ID said:

It will take tens of thousands of miles, or more, to offset the cost for just a mpg gain even if you do the work yourself. If you were to go from 14 to 16 mpg the CPM would be reduced by less the 0.03/mile at 3.00/gal. If you did the gear swap for $1000 it would take 33K miles to cover the cost. In my research for swapping from 3.73 to 4.10, for towing purposes, it would cost closer to $3K to do the swap and that would take 100K miles to recoup the cost. Going from 16 to 18 mpg would would be a 0.02/mile savings and thus take 150% longer to pay off. 

 

I think a 2mpg gain is unrealistically high... basically it's not going to save you any money unless you plan to put 250K more miles on the truck. 

 

If you've never setup gears before, which I gather you haven't, I wouldn't do it yourself. 

 

Go with a taller and skinnier tire on your next set, it will reduce rpms without a large increase in rolling resistance/weight. 

 

A 255/85R16 would be a 5% reduction in rpms over a 265/75R16, which is just over 1/2 of the change you would get with a gear swap. 

Thanks for this! What’s the recommendation for tire size on 4:10s? Besides 255/85/16. 

 

3 hours ago, dripley said:

I re reasd and stand corrected. May be I had too much coffee this morning. 

This does make better sense than what I thought you were trying to do. 

All good buddy! 

[AH64ID]

Tall and skinny is the best way to drop rpms without drastically increasing the unsprung weight. 285/75R17 would also be a decent size, but they will be a bit heavier than the 255 series tires. 

 

IMHO 315' wouldn't be a good choice, as they are heavier and wider, both of which will increase the power required to spin them. 

Edited March 18, 2018 by AH64ID

[Marcus2000monster]

Just now, AH64ID said:

Tall and skinny is the best way to drop rpms without drastically increasing the unsprung weight. 285/75R17 would also be a decent size, but they will be a bit heavier than the 255 series tires. 

Gotcha. Currently have 285/75/16s. I would like to have a lighter yet taller tire. 

[AH64ID]

34 minutes ago, Marcus2000monster said:

Gotcha. Currently have 285/75/16s. I would like to have a lighter yet taller tire. 

 

If that's the size you currently run you aren't going to see much difference then. That's already an oversized tire and I can't think of anything that is taller without getting very heavy. A 315 is going to be about 130% the weight for a 4% reduction in rpm. 

[Marcus2000monster]

1 hour ago, AH64ID said:

 

If that's the size you currently run you aren't going to see much difference then. That's already an oversized tire and I can't think of anything that is taller without getting very heavy. A 315 is going to be about 130% the weight for a 4% reduction in rpm. 

Anyone know what rpm I would be running with 265s?

[dripley]

Mine came stock with the 265's and I see 2000 rpm at 70. Google "tire calculator" and you can compare sizes. You can get taller but you will have to get a lot skinnier to even come close to the same weight even if it is possible. New wheels would be in order also.

[Marcus2000monster]

30 minutes ago, dripley said:

Mine came stock with the 265's and I see 2000 rpm at 70. Google "tire calculator" and you can compare sizes. You can get taller but you will have to get a lot skinnier to even come close to the same weight even if it is possible. New wheels would be in order also.

You have 3:55 or 3:73?

[dripley]

5 minutes ago, Marcus2000monster said:

You have 3:55 or 3:73?

3:55. I don't think 3:73 was even an option.

Edited March 19, 2018 by dripley

[AH64ID]

42 minutes ago, dripley said:

3:55. I don't think 3:73 was even an option.

 

Correct, 3.73's are aftermarket only for 2nd gens. 

[Silverdodge]

U really want to play u could always put a set of 3rd gen axles in

[Marcus2000monster]

20 minutes ago, Silverdodge said:

U really want to play u could always put a set of 3rd gen axles in

Meh I wanna stay below 1k$ but that’s not gonna happen except To buy taller tires...