you can run 70-75 all day long with the 4.10's and the only thing it will hurt is your mileage. for best mileage youll want to keep it below about 2k rpms, but for durability it doesnt really make a difference. whats bad for the turbo is shutting the truck down immediately after a hard drive. you need to give it time to cool down before shutting it off. if it was me id just leave the 4.10's in it.

if you dont have experience installing ring gears and dont want to pay someone else to do it, youre best bet would be to find a parts truck and just swap the entire rear/front ends out.

 

oh yeah.....if youre turning 2300 rpm at 60 mph you dont have 4.10's. that sounds like 4.30's to me. ive got 4.10's in mine and im turning 2k rpm at 60 mph. unless by "barely" over 60 you mean about 68 lol.

 

Do you have larger tires than stock by chance, because mine are the stock size. It could be more like 6150 or 6200. I guess when I need to change tires I can go larger to help....what size could I put on my stock rims to make a difference in the gearing?

Does anyone know the code on the Mfr Sticker on the door jamb to tell what gears I have?

 

im running stock tires. 265/75 16's. turning almost exactly 2k rpm at 60 mph. its closer to 2025 or so, but no where near 2300 rpm. if you want to make a difference in your gearing just by changing tire size, youre going to have to get some monsters on it. i had a set on it before these that were about 2.5-3" taller than stock and it only changed my speedo by about 2 or 3 mph and my tach by about 100 rpm at 60 mph.

here is an axle code chart.



Code Ratio Capacity Maker Type Yr

12 2.73 3800 FORD REG 1991
17 3.25 3300 FORD REG 1971
17 3.31 3800 FORD REG 1995
18 3.08 3800 FORD REG 1991
19 3.55 3800 FORD REG 1991
25 4.10. 5300 FORD REG 1991
29 3.55 5300 FORD REG 1991
35 4.10. 6250 FORD REG 1991
36 3.73 7400 DANA REG 1980
39 3.55 6250 FORD REG 1991
45 4.10. 7400 FORD REG 1991
49 3.55 7400 FORD REG 1991
65 4.10. 8250 FORD REG 1991
69 3.55 8250 FORD REG 1991
72 4.63 11000 DANA REG 1991
73 5.13 11000 DANA REG 1991
H5 4.10. 3800 FORD LIMITED SLIP 1991
H7 3.31 3800 FORD LIMITED SLIP 1995
H8 3.08 3800 FORD LIMITED SLIP 1991
H9 3.55 3800 FORD LIMITED SLIP 1991
B5 4.10. 5300 FORD LIMITED SLIP 1991
B9 3.55 5300 FORD LIMITED SLIP 1991
C5 4.10. 6250 FORD LIMITED SLIP 1991
C9 3.55 6250 FORD LIMITED SLIP 1987
D5 4.10. 7400 FORD LIMITED SLIP 1991
F5 4.10. 8250 FORD LIMITED SLIP 1991
W5 4.10 8250 FORD LIMITED SLIP 1995

 

Stock tires are 235 aren't they....thats what I have. So you would be larger making the difference in RPM's

Thanks for the chart, I'll check it out tonight.

 

sorry, forgot to clarify that. the 235 number applies to the width. i have wider tires than stock, but they are the same height. stock is a 235/85 if i remember correctly. but thats the same height as 265/75. so it wouldnt affect the rpms any.

 

a 235/85 means that your tire is 235 mm wide. 85 means that your sidewall is 85% as tall as your tire is wide. so 235 mm wide x 85%=199.75 mm tall sidewall.

a 265/75 means my tire is 265 mm wide. 265 mm wide x 75%=198.75 mm tall sidewall. so really, my tire is 1 mm shorter than yours. which would make me turn about 1 rpm more than you at 60 lol. either way, its the same as a stock tire when it comes to speedo/tach numbers.

 

Well, its trivial at this point but I THINK my tires are 235/75 but I can confirm that tonight.

 

im about 100% sure stock is 235/85. mine says 235/85 and so does goodyears website(for both 2 and 4 wheel drives) the f150/bronco/expedition/etc all have a 235/75 tire, but thats on a 15 inch rim, which is totally different than on a 16 inch rim. so if you confirm that you have a 235/75 you have just confirmed that you have the wrong tire size. thats about a two inch too small tire, even on a 16 inch rim.

your axle code will only tell you what gear it came with stock. your code may say 4.10, but that doesnt mean thats whats it has. but bottom line, if youre running the correct size tire and turning 2300 rpm at 60 mph, you dont have 4.10's. so no, your tire size isnt trivial. especially if youve got the wrong size.

 

Well, like I said I could be wrong....I'll check it out tonight. I find it hard to believe that anyone would take out 4.10's for 4.30's in a truck that is bone stock otherwise.

 

it all depends on what the person used it for really. if all i used it for was towing a 15-20k lb TT short distances, id put 4.30's in a stock truck. or a farm truck. anything thats not going to be run 70-75 mph. heck, in one month i put a 2.73, 3.55, 3.73, 4.10 and 4.56 in my mustang just to see the difference in the 1/4 mile times with the engine still stock before i built it.

 

If you have 235/75's on there now that'll cause your speedometer/odometer to be off by over 6% and give you an effective gear ratio of 4.35

 

thanks for the calculations. i knew it would be way off, but i wasnt sure what the exact ratio would end up being. but 4.35 sounds about right for those rpms. but its one of the two. either wrong tire size or someone has changed the gearing.

 

OK, looked at the truck and it is 235/85's. Also shows 45 (4.10) for the axle. Also, the MFR sticker shows the recommended tires are 215/85 so perhaps my speedo is a tad slow (I think I calculated it as being a little slow on my trip home from Florida), so that could make sense as to why I am turning a little over 2k at 60mph. I guess I just need to learn to keep the tach at 2k and not worry about the people going past me.

A half dozen or less tows a year at ~60mph, or spent $500+ to upgrade gears for marginal savings - six in one half dozen the other I recon

 

my truck only gets 11-12 hwy anyways and it has 3.55s i dont know if theres anything wrong with it, maybe lead foot or short in the drivers seat... there is a difference in rpms from standard to auto. autos are always a little less rpms for the same speed in od about 300 at 70. which is where you all are probly disagreeing about. reguardless of tire size, the speedos are all calibrated the same and correspond to the tachometer according to rear ratio. unless you compare auto to standard.
and it seems to me that a motor that is turning 2700 rpms over 200,000 miles would have far less life left than a motor that has been running 2200 for the same number of miles.