Sponsored

Who is running 37"-40" tires on the diesel

ACAD_Cowboy

Well-Known Member
First Name
Francis
Joined
May 1, 2019
Threads
22
Messages
1,414
Reaction score
1,953
Location
NY
Vehicle(s)
15 jkur
I feel that you all might be missing the point I was getting at.

The lower the ratio (numerically larger difference) the more relative acceleration and throttle responce, aka felt torque, you will have.

Flipped the other way, you will have less felt power and increased fuel economy which can be exacerbated by not adjusting the tire size to speedometer relationship. If the computer still thinks the tires are short (relatively speaking) the revolutions per mile would be off by a lot leading to crazy phantom economy gains. But the computer needs that data to be spot on so it can inform the pcm about what to do.

Now I am not doubting that the diesel package is making the torque to haul the freight but I would recomend regearing ti get the snap back, sometimes you need to make horsepower not just torque.
Sponsored

 

Jefe1018

Well-Known Member
Joined
Mar 4, 2020
Threads
38
Messages
2,433
Reaction score
3,939
Location
NV
Vehicle(s)
21 JT Rubi Ecodiesel
Build Thread
Link
I don't know man... I'm getting 24mpg highway at 75-80 on 37's and plenty of pep. I'm sure a regear would bring it back, but for $1,500ish and a few days of my time I can do a lot of wheeling and not have to worry. If I go to 40's on my next set I will regear and reinforce the axels though.
 

CrazyCooter

Well-Known Member
First Name
Tony
Joined
Nov 1, 2020
Threads
10
Messages
1,892
Reaction score
1,959
Location
Far NorCal
Website
www.overlandvehicledynamics.com
Vehicle(s)
1991 JEEP YJ, 2021 JTR Ecodiesel
Occupation
Specialty Off Road Shop Owner
25k miles on 37s and 3.73s loving it except when towing heavy loads with wind resistance in mountains. 23-26mpg on the highway

5k miles on 37s and 4.10s....It feels slower out of the hole unloaded, but tows heavy a little better. Jumping up to 38s soon, so I expect that to be the balance. 21-24mpg on the highway.

Can't imagine wanting any lower gear without much larger tires.
 

Burghardphotography

Well-Known Member
First Name
Nick
Joined
Mar 14, 2022
Threads
15
Messages
318
Reaction score
429
Location
Portland, Oregon
Website
www.instagram.com
Vehicle(s)
'22 JTRD, '65 MBZ 220s, '66 Riviera GS, '72 F-250
Build Thread
Link
Occupation
Finding the will to live
I just did a road trip from portland, OR to Southern California by way of hwy 395. Carrying two people weighing 230 each, an ikamper 3.0, bed rack, winch, and our clothes and a cooler for a month long road trip. So a bit of extra weight, but not a ton. 3.5 inch lift and 37’s, speedometer calibrated with AEV procal.

Just put on 37s on Tuesday and left straight on the trip. Here’s my two cents:

i really wanted all those “you don’t have to regear the diesel” people to be right, but I’m not sold on that now that I’ve driven one on 37s.

Regardless of flat ground or hills, I almost never saw 8th unless I was on a steep downhill or going 70+ mph, which I just don’t do really, most speed limits up here top out at 65. Regardless, Any higher than 65 mph and my mpg was tanking into the mid teens. Across nothing but highways all the way down, I averaged 19.9 mpg. I mean that’s still good for a truck on 37s, but a far cry from these “I get 24 mpg going 75 on my 37’s” claims people throw out on here.

The slightest uphill would make the truck shift down, it did not want to stay in 8th gear, I’m talking so slight that the only way I knew it was uphill was by watching my altimeter slowly creep up. All in all, I wasn’t as impressed as I wanted to be, and am currently researching regearing to 4.56
 

M390

Well-Known Member
Joined
Apr 11, 2021
Threads
0
Messages
73
Reaction score
67
Location
TX
Vehicle(s)
2021 Gladiator Sport Ecodiesel
I feel that you all might be missing the point I was getting at.

The lower the ratio (numerically larger difference) the more relative acceleration and throttle responce, aka felt torque, you will have.

Flipped the other way, you will have less felt power and increased fuel economy which can be exacerbated by not adjusting the tire size to speedometer relationship. If the computer still thinks the tires are short (relatively speaking) the revolutions per mile would be off by a lot leading to crazy phantom economy gains. But the computer needs that data to be spot on so it can inform the pcm about what to do.

Now I am not doubting that the diesel package is making the torque to haul the freight but I would recomend regearing ti get the snap back, sometimes you need to make horsepower not just torque.
I run 4.56’s and 35’s and couldn’t be happier. I do pull a 6500 gvwr travel trailer occasionally however. I saw no loss of mileage whatsoever from 3.73’s and 35’s. What did get lower were EGT’s and boost numbers though. Folks that don’t think you need to regear don’t haul much around I’m guessing.
 

Sponsored

Burghardphotography

Well-Known Member
First Name
Nick
Joined
Mar 14, 2022
Threads
15
Messages
318
Reaction score
429
Location
Portland, Oregon
Website
www.instagram.com
Vehicle(s)
'22 JTRD, '65 MBZ 220s, '66 Riviera GS, '72 F-250
Build Thread
Link
Occupation
Finding the will to live
37s and 4.10s for the last 7k miles. Sometimes, i forget that I'm on 37s.
see I want to go 4.10s, but I’m afraid I’ll spend all that money and end up wanting more. How’s your mpg with the 4.10’s?
 

Vtur

Well-Known Member
Joined
Mar 6, 2021
Threads
11
Messages
1,055
Reaction score
1,102
Location
Norcal
Vehicle(s)
JTOD
I just did a road trip from portland, OR to Southern California by way of hwy 395. Carrying two people weighing 230 each, an ikamper 3.0, bed rack, winch, and our clothes and a cooler for a month long road trip. So a bit of extra weight, but not a ton. 3.5 inch lift and 37’s, speedometer calibrated with AEV procal.

Just put on 37s on Tuesday and left straight on the trip. Here’s my two cents:

i really wanted all those “you don’t have to regear the diesel” people to be right, but I’m not sold on that now that I’ve driven one on 37s.

Regardless of flat ground or hills, I almost never saw 8th unless I was on a steep downhill or going 70+ mph, which I just don’t do really, most speed limits up here top out at 65. Regardless, Any higher than 65 mph and my mpg was tanking into the mid teens. Across nothing but highways all the way down, I averaged 19.9 mpg. I mean that’s still good for a truck on 37s, but a far cry from these “I get 24 mpg going 75 on my 37’s” claims people throw out on here.

The slightest uphill would make the truck shift down, it did not want to stay in 8th gear, I’m talking so slight that the only way I knew it was uphill was by watching my altimeter slowly creep up. All in all, I wasn’t as impressed as I wanted to be, and am currently researching regearing to 4.56
I know exactly what you mean, the incline near June Lake going NB on 395 is quite long. What i found is that, doing 80+ mph before hitting the hills and maintain speeds of atleast 75+ will consume less fuel and also less of a load, lower boost too.
 

Pescatoral Pursuit

Banned
Banned
First Name
Chuck
Joined
Jun 19, 2021
Threads
73
Messages
1,301
Reaction score
1,825
Location
Orlando!
Vehicle(s)
‘06 F-150, ‘15 CTS, ‘21 JT Urban Rubicon Diesel
Occupation
Plumba
Regearing returns engine rpms at a given speed to optimum (factory) levels, NTM reducing strain on the drivetrain.
The question isn't whether the diesel can perform without a regear; it's: can it perform optimally without a regear, and that answer is no.

We already see a loss from the factory with an increase in tire size from 32" to 33" so it stands to reason those losses continue to increase with tire diameter and then compound that with increased loads (added weight.)
 

Sponsored

Burghardphotography

Well-Known Member
First Name
Nick
Joined
Mar 14, 2022
Threads
15
Messages
318
Reaction score
429
Location
Portland, Oregon
Website
www.instagram.com
Vehicle(s)
'22 JTRD, '65 MBZ 220s, '66 Riviera GS, '72 F-250
Build Thread
Link
Occupation
Finding the will to live
I know exactly what you mean, the incline near June Lake going NB on 395 is quite long. What i found is that, doing 80+ mph before hitting the hills and maintain speeds of atleast 75+ will consume less fuel and also less of a load, lower boost too.
Damn 80?? With the amount of hwy patrol I saw I don’t know if I’d risk that haha. Thanks for the tip though!
 

Burghardphotography

Well-Known Member
First Name
Nick
Joined
Mar 14, 2022
Threads
15
Messages
318
Reaction score
429
Location
Portland, Oregon
Website
www.instagram.com
Vehicle(s)
'22 JTRD, '65 MBZ 220s, '66 Riviera GS, '72 F-250
Build Thread
Link
Occupation
Finding the will to live
Regearing returns engine rpms at a given speed to optimum (factory) levels, NTM reducing strain on the drivetrain.
The question isn't whether the diesel can perform without a regear; it's: can it perform optimally without a regear, and that answer is no.

We already see a loss from the factory with an increase in tire size from 32" to 33" so it stands to reason those losses continue to increase with tire diameter and then compound that with increased loads (added weight.)
Bingo
 

@californiajeeping

Well-Known Member
Joined
Apr 1, 2020
Threads
16
Messages
916
Reaction score
922
Location
California
Vehicle(s)
2022 Jeep Gladiator diesel, 1977 cj5 LS swapped
I feel that you all might be missing the point I was getting at.

The lower the ratio (numerically larger difference) the more relative acceleration and throttle responce, aka felt torque, you will have.

Flipped the other way, you will have less felt power and increased fuel economy which can be exacerbated by not adjusting the tire size to speedometer relationship. If the computer still thinks the tires are short (relatively speaking) the revolutions per mile would be off by a lot leading to crazy phantom economy gains. But the computer needs that data to be spot on so it can inform the pcm about what to do.

Now I am not doubting that the diesel package is making the torque to haul the freight but I would recomend regearing ti get the snap back, sometimes you need to make horsepower not just torque.

The diesel is torque limited in first and second gear. Plus under full power the 3.0L rev's up faster than it can reach full boost. You put larger tires on and it has more time at full power in 1st and 2nd.

It really does go good even with the huge tires. On the highway it does need to hit 7th on moderate hills but pulls in 8th usually. Works perfectly. The thing is 4.10's are too little gear and 4.56 is too much unless your on 40s so the factory 3.73 is worth keeping around.
 

mrmo

Well-Known Member
First Name
Mrmo
Joined
Jan 26, 2021
Threads
50
Messages
809
Reaction score
496
Location
East Tn
Vehicle(s)
2022 Gladiator
Occupation
nuke
No way those fuel mileage numbers are right. I travel a lot. Normally approximately 800 mile round trip for work. I have the diesel Willys with the stock Firestone MTs (32's?), and I have purposely worked with highway mileage, using the cruise control, setting it for approx. 76mph or so, which equates to around 2000rpm, and I can squeeze 23.5-24mpg out of it. I guess if you have 37's and cruise at 55mph you might be able to pull in the 20's....
 

CrazyCooter

Well-Known Member
First Name
Tony
Joined
Nov 1, 2020
Threads
10
Messages
1,892
Reaction score
1,959
Location
Far NorCal
Website
www.overlandvehicledynamics.com
Vehicle(s)
1991 JEEP YJ, 2021 JTR Ecodiesel
Occupation
Specialty Off Road Shop Owner
No way those fuel mileage numbers are right. I travel a lot. Normally approximately 800 mile round trip for work. I have the diesel Willys with the stock Firestone MTs (32's?), and I have purposely worked with highway mileage, using the cruise control, setting it for approx. 76mph or so, which equates to around 2000rpm, and I can squeeze 23.5-24mpg out of it. I guess if you have 37's and cruise at 55mph you might be able to pull in the 20's....
Yes, totally speed dependent. Our speed limits here in CA never exceed 70mph. I have seen over 30mpg over a 60 mile period where I was driving a back road at 35-45 mph. At 70-75 its in the 19mpg area.

Just like other diesel engines I've owned, they prefer to be loaded down at low RPM vs revved up with no load for best fuel economy.
Sponsored

 
 



Top