Like the title says. Who is running 40" tires and what gears are you running.

I have read about most guys running 4.56's... but recently heard 4.30's are better??? What RPM are you at going 60 and 70 mph? I have a chart but some guys are not matching up to that.

Thanks!

 

I vote 4.56's with 40" tires.


I run 4.30's, but I only have 36" tires. With this setup, I'm almost dead on with MPH vs RPM's as a stock truck is. So if you are wanting to get closer to a stock "feel" on 40's, get 4.56's.

That's my 2 cents.

 

What is the intended purpose / purposes of the truck? Listed in order from highest priority to lowest, and frequency would be good lol.

IE

#1 Towing - 6 days a week
#2 Hi-way trips - 2 months a year
#3 Street "racer" - 2 weekends a year
#4 offroader - once a year.

average obviously

 

#1 Hi-way trips
#2 Street Racer (a few times a year)
#3 Towing (several times a year)
#4 offroader... sees some snow that is about it.

 

Here is a calc that Neil posted on the RHN

http://spreadsheets.google.com/ccc?k...wHiiSIG5YpxQcA

 

I have seen the calc... but the more I talk to guys, it isn't matching up quite well. Thanks though!

 

No Problem. We will have to let Neil know and maybe he can adjust it.

 

Here is what I got

Stock
33" tire, 3.73 gears, 2000rpm, .71 ratio OD. 74.2 MPH

4.88s
40" tire, 4.88 gears, 2000rpm, .71 ratio OD, 68.7 MPH

4.56s
40" tire, 4.56 gears, 2000rpm, .71 ratio OD, 73.5 MPH

4.30s
40" tire, 4.30 gears, 2000rpm, .71 ratio OD, 78 MPH


#1 Hi-way trips
#2 Street Racer (a few times a year)
#3 Towing (several times a year)
#4 offroader... sees some snow that is about it.

Using this order, I would go with 4.56 gears. It is just .7 MPH different per rpm. If the truck is empty on the highway, that is the route I would want. Similar unloaded characteristics. Cruising EGTs will be slightly higher then now /normal, do to more load on the drivetrain, due to the heavier tires / more rolling friction. MPG should be similar to stock, I would guess a possibility of a -.5 to -1 mpg change over stock gears, and tires.

If the top priority was towing or offroading, I would go with 4.88s.
More rpms, lower egts, poorer fuel mileage on the highway.

If the only thing the truck ever did was cruise the highway, and go to show and shines, I would do the 4.30s, to keep rpms down, EGTs would probably be a little higher cruising per rpm, but you can always downshift for hills. Since you would still like to tow, and race a little, I would personally not go this route. But that is ultimately your call.

EDIT: Actually thinking ahead, how much weight do you tow? If its light enough you could go 4.30s, then also, if down the road you think you will run smaller tires, you wont need to regear again, otherwise I would go with 4.56s.

 

I tried it, and it's pretty darn close to what I see.

My tires are 325/60r20, and I'm running 4.30's on a 4r100 automatic.

I hit 2000 RPM's at about 68mph, and the calculator shows I'm at 2000 RPM's at 69 mph. If I input the stock values (3.73 gears, and 265/75r16 tires), it says that 2000 RPM's is 71 mph. Most folks would find that to be pretty close I would think.

Of course, tire manufactures have variances when it comes to overall tire diameter. My tires measure slightly larger than most other 325/60r20's, so I'm sure that will have an effect on calculations vs. real world.


Anyway, I still vote for 4.56's with 40's

 

I have talked to two guys running 40's and it doesn't match up. One guy has run 4.88's, 4.56's, and now 4.30's he is finally happy. At 75 he is seeing about 2200 rpm's...

then I talked to another guy and he said 4.30's were perfect and he had practically the same power as I do... He hated the 4.56's...??

So I am hoping guys that are running these tire combo's will post up.

A few days ago I was set on 4.56's... now I am on the edge...

 

One more thing to mention... it would be sweet to stick some 37's back on there and hit up the drag strip... LOL

 

I'm a gear head and I 100% agree with this.
Go with the 4.56 gears. It will give you the best all around package.

 

Well thanks!! Hopefully someone rolling 40's will post up.

Like I said above, I was dead set on 4.56's.... Then after talking with guys running 40's they said they didn't like it. So I want to make sure.

I have been running 3.73's and 37's for a long time now and I am pretty happy with it... I can still crank out between 15-17 mpg...

 

To give yourself a little preview, go drive around with the OD switched off. It will be similar to that in high gear.

 

X2 Steven.

I want 4.30's when I get the moola.