Changing gear size

[TyCorr]

Jared, you say you felt that the 4.56s were too much. Care to elaborate?

Thanks

Im guessing that the rpms were stupid high...

Erik Claw said above that he's running 37's or 38's. He's got a 6 or 7hundred hp 6.4. He said the 4.30's are decent but he wants to regear to something smaller. Im guessing 4.10's.

I know the 7.3 is a totally different animal but Joe(csipsd) posted a video of his truck running along at 75 on 37's with 4.30 gears and he said that those gears are too much for a multiuse truck. He explained it as the 4.30's were great for in town driving and pulling. The 3.73's were good for highway but the towing and start stop driving were clumsy. Using that logic the 4.10 would be ideal especially if your driving consists of a mix of types. Towing from town, to a two lane, and then some interstate driving for example.

Another point that is in this discussion is the trans. If you modify you'll most likely be buying an upgraded auto or a clutch. For the auto guys, most builders inquire about tire size so the trans can be setup for that too. I know people in the 7.3 world find it cheaper with a built drivetrain to just add/apply more power to overcome taller gears.

Sorry this was so long 'a post but Id like to say that my 77 f350 needed 4.88 gears to turn the 40's. My 7.3 would do it stock, with a lift of course.

Ill stop now, Im in 6.4 waters....

 

[Charles]

Quickest way to destroy the driveability of a turbodiesel....


Listen to people always trying to regear to "stock"... As if stock was so perfect to begin with. One thing that will make a truck stay on top of the charger(s) better than anything else is a numerically LOWER gear.

If you want to make a truck a dog.... overgear it. With a 37 to 40" tire a 4.10 is probably ideal. Below a 37 a 3.73 is. With stock tires, probably a 3.55.

Not coincidentally the newer trucks keep coming with not numerically higher.... but numerically LOWER R&P ratios year after year. Even the OEM's are figuring this out. If you've got a gasser, then run a 4.56+ with a freakin 40" tire. If you've got a turbodiesel, run a 4.10.... or maaaaaaaybe a 4.30. Don't even think about a 4.56 or more unless you just like turning trucks into gutless pigs that burn up all the diesel in the surrounding 4 counties every time you crank them up.

IMO..... run a 4.10 or 4.30 with a TrueTrac and you will be very pleased. Run a 4.56 and you'll keeeeeeeeep yearning for another gear after you're already in OD, and you'll find that the truck takes forever to get on boost all the time. Run a 4.88 or 5.13 and you'll want to drive something else.

Good Luck.




(I'd run a 4.10.....)

 

[TANK'S 250]

Quickest way to destroy the driveability of a turbodiesel....


Listen to people always trying to regear to "stock"... As if stock was so perfect to begin with. One thing that will make a truck stay on top of the charger(s) better than anything else is a numerically LOWER gear.

If you want to make a truck a dog.... overgear it. With a 37 to 40" tire a 4.10 is probably ideal. Below a 37 a 3.73 is. With stock tires, probably a 3.55.

Not coincidentally the newer trucks keep coming with not numerically higher.... but numerically LOWER R&P ratios year after year. Even the OEM's are figuring this out. If you've got a gasser, then run a 4.56+ with a freakin 40" tire. If you've got a turbodiesel, run a 4.10.... or maaaaaaaybe a 4.30. Don't even think about a 4.56 or more unless you just like turning trucks into gutless pigs that burn up all the diesel in the surrounding 4 counties every time you crank them up.

IMO..... run a 4.10 or 4.30 with a TrueTrac and you will be very pleased. Run a 4.56 and you'll keeeeeeeeep yearning for another gear after you're already in OD, and you'll find that the truck takes forever to get on boost all the time. Run a 4.88 or 5.13 and you'll want to drive something else.

Good Luck.




(I'd run a 4.10.....)

well said...though I wouldn't go any lower than a 4:30 with 40's...for the exact reason you said...charger, rpm's, tranny

 

[tbsimmons]

I had 35's with 4.56's in my 04 and loved it. Truck was mainly used for towing. Now if it was a unloaded truck mostly I would have done 4.30's. But like Tank has stated the torque of a diesel makes people think they dont need to use gears with larger tires, which in turn puts more stress on the drivetrain. I dont think the reason for the taller gears in the new trucks is because of the torque but because of the EPA and mileage wars between the brands. Just my opinion but if I had 40's on a 6.4 250 it would have 4.56's. I have 4.88's with a 34" tire on my dually and it is a beast for towing. Throttle is not touchy while tuned in my opinion but you do have power all the time.
On what you would be compared to stock just use ratios that I posted above.
Example If you have 40's with 3.73's and are at say 1800 rpm. You regear to 4.30's your rpm would be around 2075.

 

[TyCorr]

I had 35's with 4.56's in my 04 and loved it. Truck was mainly used for towing. Now if it was a unloaded truck mostly I would have done 4.30's. But like Tank has stated the torque of a diesel makes people think they dont need to use gears with larger tires, which in turn puts more stress on the drivetrain. I dont think the reason for the taller gears in the new trucks is because of the torque but because of the EPA and mileage wars between the brands. Just my opinion but if I had 40's on a 6.4 250 it would have 4.56's. I have 4.88's with a 34" tire on my dually and it is a beast for towing. Throttle is not touchy while tuned in my opinion but you do have power all the time.
On what you would be compared to stock just use ratios that I posted above.
Example If you have 40's with 3.73's and are at say 1800 rpm. You regear to 4.30's your rpm would be around 2075.

I dont know about you but I thought stock gearing was way too high to do anything but tow up to about 60mph. Running 75 or 80 was miserable.

In a 450 with 4.88's Id have to get a GV overdrive. That sucker has to be screamin running 75 or 80 on the interstate/tollways

 

[MadDiesel73]

Brian at Bts told me to go one gear size smaller (numerically) then the one that would put you back closest to stock rpm.

 

[tbsimmons]

I dont know about you but I thought stock gearing was way too high to do anything but tow up to about 60mph. Running 75 or 80 was miserable.

In a 450 with 4.88's Id have to get a GV overdrive. That sucker has to be screamin running 75 or 80 on the interstate/tollways

Nope thought the stock was great for the stock tires, I would have liked to have 4.10's with the stock tires.

The 450 yes it is high, I dont drive much over 65 though with the truck. I didnt by the truck to set land speed records, I have a car for that.

 

[tbsimmons]

Oh forgot on the GV, they would be fine. But from what I have read are not good for towing while in OD, engine braking, etc. For me it would only be used for about 5-10% of my driving in the truck.

 

[TANK'S 250]

Brian at Bts told me to go one gear size smaller (numerically) then the one that would put you back closest to stock rpm.

Stock it technically between 4: 56 & 4: 88...so....looks like I'm right again

 

[AKHILF]

Another 6.0 guy in the big hp side of the forum, I have 37's on with 3:73's I liked it better on the highway because of the rpm drop but i can also vouch my tranny dosnt like it. But even with the droped R's my milage still blows. But I think thats just from the extra weight of the 37x22's at almost 150 each corner. What would I see if i went to a 4:10? Would better milage be one of them?

 

[TANK'S 250]

As a rule...only going up 1 gear set isn't worth it.

...when you say " Big HP", how much are we talking?....you may have too much for the stock tranny, or your tuning might need to be tweaked.

4:30's would put you back to stock....but I wouldn't go more than 4:10's with 37's.

Like I said,.. gear changes depend on preference, and how you drive your vehicle(tow/race/city/hwy)

 

[MadDiesel73]

Yea I may trade these 4:30's in for 4:10's with these 37's. Just got toyo 37 13.50 20's. 85% of my day to day is city stop and go. But I dont want to regret it when I travel.

 

[MadDiesel73]

I like doing 80 at 2k

 

[Erikclaw]

That is what I want, I hate turning 2250 or so at 80.
I am putting down 776hp with a fully built tranny. So I figure with 4:10's I would be happier. Don't think my drive train would suffer much with that set up.

 

[TyCorr]

Stock it technically between 4: 56 & 4: 88...so....looks like I'm right again

I thought you were claiming to get the one closest to stock then pick the lower(numerically higher)? Thats not what Brian says. He'd pick 4.10's where you're picking 4.30's. When you put a bts in so much more power makes it to the rear wheels that you dont need all the gear. Plus he sets the trans up for whatever gears and tires you're running.

 

[TyCorr]

As a rule...only going up 1 gear set isn't worth it.
...when you say " Big HP", how much are we talking?....you may have too much for the stock tranny, or your tuning might need to be tweaked.

4:30's would put you back to stock....but I wouldn't go more than 4:10's with 37's.

Like I said,.. gear changes depend on preference, and how you drive your vehicle(tow/race/city/hwy)

I agree but if you're redoing the rear differential it isnt that much more work/time/money to swap to a different gear, regardless of the ratio. Additionally if a 3.73 is too high and a 4.30 is too high, you wouldnt go to the 4.30 anyway because "its a waste of time" to run the 4.10.

ErikClaw did just that and now he's wishing/planning on going to the 4.10. That certainly isnt anymore cost effective to do it a second time because you didnt pick the right gear the first time, no offense to anyones rig or their choices.

Im gonna stay outta this one...Ive said the same thing too many times LOL

 

[Erikclaw]

I will probably change mine since I hate seeing it rev so high when cruising 80 for hrs some times. The occasional buz to 100 makes it hit 3000rpm. But I probably shouldn't be doing that much anyway.

 

[tbsimmons]

Here are some numbers all at 2000 rpm. ***Estimates***
35's
3.55 - 83
3.73 - 79
4.10 - 72
37's
3.73 - 84
4.10 - 75
4.30 - 72
40's
3.73 - 90
4.10 - 82
4.30 - 78
4.56 - 74

To the original poster. Gears are a compromise to what the truck is used for most of the time. If it is towing, you want more gear, if it is a highway gear you want less. Only you can make that decision.

 

[tbsimmons]

Here is 4.88's with 34's at 2000 - 58
I usually cruise around 2250 - 65

 

[Tim @ P.I.S.]

I have to admit I didnt read every page here, but you guys trip me out.

THe best place for tire/gearing info is from a REAL 4x4 shop. Before I owned a diesel i was big into the offroad world.

First to get the best possible mileage you need to be in the powerband while at cruising speed. 3.73's have no place with a 40" tire. Neither does a 4.10 for that matter.


Second, i dont want to hear about people complaining of mileage while daily driving a "RACE" tune, running 40" tires and running 80mph. There are three things right there you can change to get better mileage.

My truck would net me 14mpg bone stock. I now run 46" tires(445/65/22.5) with 22.5 alcoas and adapters. This combo weighs in at nearly 1200lbs of rotating mass.
And guess what, i still get 13mpg............because I run 5.38 gears:shocked:

I am 100rpms under stock at 65mph. Still have plenty of acceration even in od.

Either suck it up and get the proper gears to match your tires and make for a nice drivable rig or downsize to get better mileage.