Anyone running 32"+ tires with 3.73's?

daspes · **Posted:** Tue Apr 13, 2010 8:21 pm

tommudd wrote:

Get ready for less than 1/2 the power on hills, or feels like it
have to run with the OD off to maintain anything around 65 MPH
MPG drop of at least 2 to 3 MPG or MORE
this is according to the scan gauge before and after the change

Anyone who says different is full of crap
unless of course you live on completely flat ground, never go where there are any hills, never want to pull a trailer etc.

I'm full of crap then. I have more than enough power and have no problem seting the cruise at 70 and being able to hold it on level ground. Hills it will downshift, but that is to be expected. I'm getting @ 21 mpg on the high way, stick to 60 and I can pull 25 mpg. City is about 16-17. I think the thing that is really helping out is the light weight tires I'm rolling on.

tommudd · **Posted:** Tue Apr 13, 2010 8:59 pm

daspes wrote:

tommudd wrote:

Get ready for less than 1/2 the power on hills, or feels like it
have to run with the OD off to maintain anything around 65 MPH
MPG drop of at least 2 to 3 MPG or MORE
this is according to the scan gauge before and after the change

Anyone who says different is full of crap
unless of course you live on completely flat ground, never go where there are any hills, never want to pull a trailer etc.

I'm full of crap then. I have more than enough power and have no problem seting the cruise at 70 and being able to hold it on level ground. Hills it will downshift, but that is to be expected. I'm getting @ 21 mpg on the high way, stick to 60 and I can pull 25 mpg. City is about 16-17. I think the thing that is really helping out is the light weight tires I'm rolling on.

But won't you admit that 4.10s would be way better?
I can set mine at 70 also but you can tell it is not happy at that with it shifting back and forth.
I can run 65 with the cruise on with the OD off and get 20 MPGs easy . 4.10s will be so nice to have as soon as someone gets to it.

daspes · **Posted:** Tue Apr 13, 2010 9:05 pm

tommudd wrote:

But won't you admit that 4.10s would be way better?
I can set mine at 70 also but you can tell it is not happy at that with it shifting back and forth.
I can run 65 with the cruise on with the OD off and get 20 MPGs easy . 4.10s will be so nice to have as soon as someone gets to it.

That wasn't the question though. I absolutely think that 4.10's would be better. I'm just making the statement that depending on where you live, your current set up, and your driving styles 3.73's are completely livable. Some posts just make it sound like 3.73's on any tire over a 29 is the devils work. Yes if you are at high elevation or in a very hilly area you will definitely notice a difference, otherwise, it can be lived with until you regear.

ATXKJ · **Posted:** Tue Apr 13, 2010 9:12 pm

daspes wrote:

I think the thing that is really helping out is the light weight tires I'm rolling on.

I don't think folks appreciate how much tire weight impacts performance.

Boiler · **Posted:** Tue Apr 13, 2010 9:47 pm

Diameter has as much to do with it. It takes more torque applied through the axle to apply the same force at the road when you have a larger tire. Also, rotational moment of inertia (how hard it is to get an object moving) is increased as mass is moved outward. So here you're putting more weight on, AND your moving it out. So you're raising your gear ratio and increasing the amount of inertia you have to overcome. All of this makes the drivetrain work harder to get it rolling....or in another view, makes it get rolling slower under the same amount of effort.

So now you've got a power loss, and your next issue is that the engine turns slower at the same highway speed due to the ratio change. Hence the downshifting. I'm wanting to regear badly even with my 245/75-16 tires because mine used to downshift on just the slightest hills stock. Imagine what its doing now. I personally believe thats why my milage has always sucked. That combined with what seems like extra engine braking coming from somewhere. Unfortunately I don't have k's to drop on a regear.

VoodooMann · **Posted:** Tue Apr 13, 2010 9:48 pm

Tom,

You are STILL running 3.73s?!

tommudd · **Posted:** Tue Apr 13, 2010 10:18 pm

Afraid so and hating every mile!
Have had the parts sitting here a year but catching the guy that's going to do it when both our schedules work out is hard.
I will be so happy when I can. :banghead:

I drove to the Badlands and back with the OD off, 65 MPH and 20 MPGs , overdrive on, went to 14/15 MPGs and shifting all of the time :furious:

I can run 75 plus and the RPMs seem to be enough to be OK almost, any lower and say at 70/72 I'm turning 1850/1900 RPMs just too low for it to run right

NOTE:all speeds by the GPS and MPGs by the scan gauge

VoodooMann · **Posted:** Tue Apr 13, 2010 10:35 pm

better mileage with overdrive off?

stumpjumper_09 · **Posted:** Tue Apr 13, 2010 10:48 pm

less shifting cause it keeps the rpm's in the power band where the 3.7 most efficiently make power.

VoodooMann · **Posted:** Tue Apr 13, 2010 11:07 pm

I could see that, wierd part is mine hardly ever shifts when I'm going between 65/70 at 75 I'm at 2200 RPMs at 70 I'm right at about 2K

Tokyojoe · **Posted:** Tue Apr 13, 2010 11:08 pm

I had 32's Maxxis Bighorns with my 3.73 gears. Bad mpg but no problem running them. I am back to 245/75/16 Firestone AT's for regular daily driving. Need to get wheels for the Bighorns for this Summer's off-roading trips.

RED_KJ_666 · **Posted:** Tue Apr 13, 2010 11:15 pm

Is thinking odd MPG numbers? Sorry to Semi Jack the Thread but on Stuck tires 235/70/16 and regular maintenance I am getting more like 16-17MPG. 31's are seeming like they will be the SUCK. My RPM's always seem way too low when OD is on.

daspes · **Posted:** Tue Apr 13, 2010 11:26 pm

RED_KJ_666 wrote:

Is thinking odd MPG numbers? Sorry to Semi Jack the Thread but on Stuck tires 235/70/16 and regular maintenance I am getting more like 16-17MPG. 31's are seeming like they will be the SUCK. My RPM's always seem way too low when OD is on.

Is that city or highway?

VoodooMann · **Posted:** Tue Apr 13, 2010 11:27 pm

try changing the plugs, I did mine yesterday and my mileage skyrocketed

tjkj2002 · **Posted:** Tue Apr 13, 2010 11:51 pm

Boiler wrote:

Diameter has as much to do with it. It takes more torque applied through the axle to apply the same force at the road when you have a larger tire. Also, rotational moment of inertia (how hard it is to get an object moving) is increased as mass is moved outward. So here you're putting more weight on, AND your moving it out. So you're raising your gear ratio and increasing the amount of inertia you have to overcome. All of this makes the drivetrain work harder to get it rolling....or in another view, makes it get rolling slower under the same amount of effort.

So now you've got a power loss, and your next issue is that the engine turns slower at the same highway speed due to the ratio change. Hence the downshifting. I'm wanting to regear badly even with my 245/75-16 tires because mine used to downshift on just the slightest hills stock. Imagine what its doing now. I personally believe thats why my milage has always sucked. That combined with what seems like extra engine braking coming from somewhere. Unfortunately I don't have k's to drop on a regear.

Yes but the added weight has a far more drastic effect,it's something like every 1lbs of rotating weight is like adding 10lbs to your overall vehicle weight.

"P" rated 265/75's are about 20lbs or so less then a load range "D" 265/75 tires,running the "D" range tires is like adding 800lbs extra weight to your KJ over the "P" rated tires of the same size.

VoodooMann · **Posted:** Tue Apr 13, 2010 11:54 pm

Also, most 245/75s are Load Range E, and are UNGODLY heavy for their size.

tjkj2002 · **Posted:** Wed Apr 14, 2010 12:26 am

VoodooMann wrote:

Also, most 245/75s are Load Range E, and are UNGODLY heavy for their size.

Yep.

Before the SFA swap I was running 265/75 Trxus MT's(load range "D") and 16x7 Unique Steel series 297 rims(soft 8's) and weighed 89lbs each(wheel and tire) and the OEM 16x7 alloy rims and 235/70 GoodYears tipped the scales at about 45lbs.4.10's helped alot for me,not the greatest but no 4.56's for the D30A meant that 4.10's had to do and why I SFA'd so I could gear better as my wheel/tire combo now weighs about 116lbs each.

VoodooMann · **Posted:** Wed Apr 14, 2010 12:49 am

I've already started to plan my SFA as you've probably seen.

So I'm trying to decide what I really want to do.

I'll probably end up with Built HP D60s (Probably Junkyard D60s or D44/60, worst case scenario I swap the front first, and then save for D60s, etc)

I don't want to spend a Buttload of money on parts and stuff I won't be able to run in 2-3 years...

but if I happen across some money (via second job, or if my dad helps out, we were supposed to have a project vehicle for us both to work on, maybe I can convince him it is the Liberty)

I might do a temporary solution to the GOBS of space in my wheel wells without regearing, and then start accumulating SFA stuff.

BUT if not regearing isn't realistic (which considering Tom and some others are running big tires on 3.73, seems like it can't be THAT bad)

Then I will postpone my SFA for a few MORE years, and go from there.

tjkj2002 · **Posted:** Wed Apr 14, 2010 1:05 am

VoodooMann wrote:

I'll probably end up with Built HP D60s (Probably Junkyard D60s or D44/60, worst case scenario I swap the front first, and then save for D60s, etc)

I don't want to spend a Buttload of money on parts and stuff I won't be able to run in 2-3 years...

The second part is funny when you stated the top part 1st."Built" D60's,more so for HP60's,can reach about $9,000 for the front and about $3000-$6000 for the rear for junkyard D60's and not customs ones like from Dynatrac(those are more for really built ones).For the front you want a HP60 from a Ford,'78-'79 F350 preferred,and rarely seen for under $1000 for a used complete axle.For the rear a matching D60 rear from the same '78-'79 F350 good,there are many less the desirable D60's.A D70 from a mid '80's E350 is another great rear axle,will accept most D60 parts.

VoodooMann · **Posted:** Wed Apr 14, 2010 1:18 am

I'm not looking for full custom, I have seen how ridiculous that can get as far as price. I figure I probably won't want to spend more than 3k per axle, unless I get a sweet job, win lottery, learn how to $#!% Gold Bricks etc.

I will probably start out as a Budget SAS like Inc did. Start by only swapping the front and reworking the rear suspension, and then save/sell/trade up from there

Are you referring to this part:

"I don't want to spend a Buttload of money on parts and stuff I won't be able to run in 2-3 years..."

That was only in reference to paying to regear/lock up an IFS front end I will end up junking. :jester:

Anyone running 32"+ tires with 3.73's?

Who is online