Rear axle ratios

hemismith wrote:
Well, that's why it is faster to 60, but that doesn't account for off-the-line feel. HP is just a mathematical function of torque and rpms; it only has more HP because it revs higher. At 2000 rpm, the diesel is putting out 160 hp. With the hemi's torque peak higher and losing some due to my elevation, I estimate that it has at most 120 hp at 2000 rpm. This makes me question the diesels specs.

It's all about torque management. I doubt there is a truck on the market that allows full torque output in low gear, especially the diesels. Also, with the Ecodiesel there is some turbo lag although that's probably minimal.

MFL wrote:

blt2ski wrote:
What are the tire diameters. As that can make a difference too. A 2" diam change is like going from a 3.73 to a 4.10 if you go smaller, or a 4.10 to a 3.73 if you go to a larger tire.

Also torque plays a part in the take off part too. Not so much as HP when moving a road speed. One needs both.

Marty

When I ordered my new 250, I knew I wanted to stay with the smaller stock wheels/tires to keep my FW towing level, and to be sure to clear my garage door.

I was on the fence about 3.73 gearing, or going with the 4.30, with advertised 3,000 lbs more towing capacity. I discussed this with my dealer, who sells a lot of trucks. He said if I was getting the 18" wheels, with taller tires, he would get the 4.30 gears. Since I was staying with 17" wheels, smaller diameter tires, the 3.73 would work best for my needs.

I noticed that most all of the new 250 gas 6.2s on the lots, had the optional big tires/wheels, with the 3.73 gearing, which IMO, would mean gearing closer to 3.55, when compared to mine.

Jerry

My F250 came with 17" rims and 31" tall tires. I later went to 18" rims with 33" tall tires to gain additional wheel capacity. Even with the diesel, I noticed more downshifts in the hills/mountains but still stayed in top gear when towing mostly on flats.

So somehow I missed the boat on the Ram -- I didn't realize the Hemi came standard with 3.21 gears on most trims. I had been looking at the Tradesman Crew Cab 6'4" box model, which according to build and price comes standard with 3.55 gears like the Ecodiesel (that configuration also comes standard with the Hemi unlike most). But so far I haven't been able to find a window sticker for one of those to verify; only diesels. I see that the 6-speed transmission comes with 3.55 gears, which is the standard on that configuration, and it doesn't even give the 3.21 option when you specify the 8-speed, but I wonder if that's an error. Ram window stickers stupidly do not list the wheelbase or bed length so you have no idea what it is.

At any rate, that puts the normal Hemi's net first gear ratio at 15.13, more in line with other brands, and the difference between standard gears and the upgraded ones a whopping 22%.

Tachdriver wrote:
Back to your original question and adding that you will be towing a 6000 pound TT, I just traded in a 1996 C1500 with a 5.7L and 3.42 rear. I pull the trailer in my sig (6100 pounds) and with only 3 speeds to work with, it lugged off the line.

My new to me truck has max tow package, 3.73 rears and ecoboost it tows this trailer like it belongs here. There is a lot of good information above this post, however FWIW the newer EBs come with 3.55 or 3.31 you should be fine with either. The transmissions give you a wide variety of operating RPMs.

Don't know if this helps but I wanted to cut to the chase.

Thanks, we are really fortunate to have the newer transmissions with more gears.

Thanks for the comments on tire diameter; I was naively just assuming stock tires were all more or less the same size. I wish I could post a table of some numbers, but since this forum screws up all the formatting and doesn't allow attachment of pictures I can't. I guess I have to get a web page someday to link to. But here are a few numbers, differences all relative to a 265/70-17 tire:

Ram -- standard 265/70-17 height 31.6, Big Horn 20" wheels 33.0, difference 4.4%. One reason I don't like the Big Horn package. With my first Ram the tow rating was reduced with the 20" wheels, but that doesn't appear to be the case now.

Ford -- standard size same as Ram, XLT 18" 32.1, difference of 1.5%. Sport 20" wheels 31.9 (1.0%).

Toyota -- standard 18" 32.1, TRD 18" same height although different size, Limited 20" 31.9.

Here are some rear end differences:

Ford 150, 3.31 to 3.55, 7.3%
Ford 150, 3.55 to 3.73, 5.1%
Ford 250, 3.73 to 4.30, 15.3%
Chev 1500, 3.08 to 3.42, 11.0%
Ram 1500, 3.55 to 3.92, 10.4%
Ram 2500, 3.73 to 4.10, 9.9%

Turtle n Peeps wrote:

hemismith wrote:
Well, that's why it is faster to 60, but that doesn't account for off-the-line feel. HP is just a mathematical function of torque and rpms; it only has more HP because it revs higher. At 2000 rpm, the diesel is putting out 160 hp. With the hemi's torque peak higher and losing some due to my elevation, I estimate that it has at most 120 hp at 2000 rpm. This makes me question the diesels specs.

Taken to extreme. My BMW feels way faster off of the line then my tractor even though the tractor is putting out 15x+ the torque to the tires.

BTW, Marty is on the money about the tire diameter. I was going to bring that up but he pulled a hole shot on me. :B

True, when I woke up this morning I thought I better add to my post but you beat me to it. Obviously I can't spend my whole life at 2000 rpm, but I spend very little above 4000 too. Any rate, during that range, the diesel's torque is decreasing whereas the Hemi's is increasing, and then of course you've already shifted into 2nd in the diesel and lost 33%.

I don't know about your tractor but I have a 335i and it's great. But the 335d is faster off the line even though the 335i will beat it ultimately. Acceleration is simply a function of the net torque (including tire diameter and everything else) at any given moment in time and the weight it is trying to move, assuming traction of course. But I don't think it's worth belaboring this issue.

hemismith wrote:
I've had a hard time finding a truck with everything I want on it, so I'm debating the need for higher rear axle ratios. Here are the net 1st gear ratios for various half-ton trucks:

Make Rear 1st
Toyota 4.30 14.32
Ford 3.31 13.80
Ford 3.55 14.80
Ford 3.73 15.55
Chevy 3.08 12.41
Chevy 3.42 13.78
Ram 3.55 16.73
Ram 3.92 18.48

The Chevy seems like it definitely ought to have the optional gears.

The Ram is for the 8-speed; the 6-speed definitely needs them but it appears the 8-speed compensates sufficiently, especially since the 2nd gear drop is much less than the others.

The Ford 3.5 only comes with 3.31; does the turbo give it enough torque so it doesn't really need the 3.55s?

Thanks.

Back to your original question and adding that you will be towing a 6000 pound TT, I just traded in a 1996 C1500 with a 5.7L and 3.42 rear. I pull the trailer in my sig (6100 pounds) and with only 3 speeds to work with, it lugged off the line.

My new to me truck has max tow package, 3.73 rears and ecoboost it tows this trailer like it belongs here. There is a lot of good information above this post, however FWIW the newer EBs come with 3.55 or 3.31 you should be fine with either. The transmissions give you a wide variety of operating RPMs.

Don't know if this helps but I wanted to cut to the chase.

blt2ski wrote:
What are the tire diameters. As that can make a difference too. A 2" diam change is like going from a 3.73 to a 4.10 if you go smaller, or a 4.10 to a 3.73 if you go to a larger tire.

Also torque plays a part in the take off part too. Not so much as HP when moving a road speed. One needs both.

Marty

When I ordered my new 250, I knew I wanted to stay with the smaller stock wheels/tires to keep my FW towing level, and to be sure to clear my garage door.

I was on the fence about 3.73 gearing, or going with the 4.30, with advertised 3,000 lbs more towing capacity. I discussed this with my dealer, who sells a lot of trucks. He said if I was getting the 18" wheels, with taller tires, he would get the 4.30 gears. Since I was staying with 17" wheels, smaller diameter tires, the 3.73 would work best for my needs.

I noticed that most all of the new 250 gas 6.2s on the lots, had the optional big tires/wheels, with the 3.73 gearing, which IMO, would mean gearing closer to 3.55, when compared to mine.

Jerry

hemismith wrote:

Turtle n Peeps wrote:

Exactly. So as a rule I'd expect turbo-charged engines not to need to much gearing because of their low-end torque. For some reason though the 5.7 Hemi felt faster off the line than the Ecodiesel even with the same transmission/rear end ratio and with less torque down low.

Because the Hemi has WAY more HP.

Well, that's why it is faster to 60, but that doesn't account for off-the-line feel. HP is just a mathematical function of torque and rpms; it only has more HP because it revs higher. At 2000 rpm, the diesel is putting out 160 hp. With the hemi's torque peak higher and losing some due to my elevation, I estimate that it has at most 120 hp at 2000 rpm. This makes me question the diesels specs.

Taken to extreme. My BMW feels way faster off of the line then my tractor even though the tractor is putting out 15x+ the torque to the tires.

BTW, Marty is on the money about the tire diameter. I was going to bring that up but he pulled a hole shot on me. :B

hemismith wrote:

blt2ski wrote:
What are the tire diameters. As that can make a difference too. A 2" diam change is like going from a 3.73 to a 4.10 if you go smaller, or a 4.10 to a 3.73 if you go to a larger tire.

I'm just considering stock tire diameters. If I were to change up to large off road tires then I think a gear change would be important.

blt2ski wrote:
Also torque plays a part in the take off part too.

Exactly. So as a rule I'd expect turbo-charged engines not to need to much gearing because of their low-end torque. For some reason though the 5.7 Hemi felt faster off the line than the Ecodiesel even with the same transmission/rear end ratio and with less torque down low.

You need to look at the stock diam of tires from EA manufacture, even from with in manufactures. One may have an 18" rim, another a 20" rim. They may or may not be the same diam. ALong with the 20", is also possible depending upon the sidewall ratio to be smaller in diam. Some like the 265-75-16 and a 265-70-17 are literally the same tire, just a different rim size to handle larger brake setups. Many GM's have either a 31, 32 or 33" diam option, depending upon the size. A 31" setup with the 3.73 gears will be on par with a 33" diam setup with 4.10's, No difference in shift points assuming the same motor, trans etc.

Stock or not, the tires may be different diameters!

Marty