ok... So I bought this truck and it has 33 in tires, a 3 inch lift and a bunch more stuff... it also has 4-10 gears.... What does that mean? My truck is very slow right now with the 5.0 engine.. would changing the gearing help me get around faster? or give me better MPG?

 

4.10 gears mean for 1 rotation of the tire, the driveshaft rotates 4.10 times. Changing your gears will only hinder your truck, not help. It takes a lot of power to turn those tires, so you shouldn't expect rocket sled performance. If you want to get more power and better mileage out of your truck, put smaller tires on.

Trevor

 

How it works is this:

The higher the number, the lower the gear. Lower gears make your engine spin faster (which equals less mileage), but give you more power.

Tires are just another type of gear as far as the engine is concerned. Bigger tires equal a taller (i.e. higher) gear.

So it has to balance out in the end. If you put bigger tires on it, you're effectively changing the gearing of the truck. You have to compensate for that by putting lower gears in it.

 

what gears does a 1990 f150 4x4 come with?

 

what is the rest of the size. 33's aren't that big. and what brand are they. some tires are made with a heavy sidewall for offroading. that makes then heavier and harder for the motor to turn. as for what gears you should have in your truck you can get the code from the door post.

 

You have the correct size gears for the size tires you have on there. Stock the trucks typically come with 235/75/15 tires (about 28-29" tires) and 3.73 gears. Putting 33" tires on it and going to 4.10 gears makes the gearing roughly the same. You're truck is just higher off the ground. My truck is the same as yours. I have the 33" tires with 4.11 gears. I bought it from my brother like this. I remember when he first lifted the truck and put the 33" tires on it without changing the gears the truck really ran strange. It wouldn't shift correctly, it was real jerky and it got about 4 mpg. It took him a while to learn that he needed the gear change and now the truck runs better. When you're balancing gearing and tire size you can opt for more power (quicker start which is done with smaller tires or larger gearing) or fuel economy (larger tires or smaller gearing and a slower start). The combo you and I have on our trucks falls right in the middle. There are some websites out there that will show you the typical gearing/tire combos and how you get more/less power/fuel economy. But you can't have both. I'm assuming that your truck is lifted so if you put smaller tires on it it will look real weird (I know cause when I bought my truck my brother had put 31" tires on it.) And if you change the gearing it isn't cheap. Especially if you have a 4x4 because then you have to do both front and back rear-ends.

 

there pro comp 33 in All Terrain tires 33 X 12.5... I looked at the inner door jam... and found a lot of different numbers... and warnings.. but nothing about stock gear ratios.

 

Under axle it will have a letter and number or just a number it is code for the ratio.
Now for power and mpg. This gets kind of tough. The motor in your truck is made to run at a certain speed I beleive between 2000 and 2500 rpm's you get the best gas mileage when you are there. Thats also where your trans should shift unless your nailing the gas pedal. I beleive you will get the most economic power if you change your gears to acheive that rpm range.
I will explain it for a bicycle. You start off in 8th gear it takes alot of work to get to and maintain the speed you want no take off power to speak of. Now start off in first gear, great to get going but real tough to maintain a higher speed. Start off in 4th gear good take off power and easy to maintain a higher speed.
Here is a link to help you figure the right gears for you. http://www.tyres1.com/calculators.html
You need to know your t case high gear ratio and your final drive ratio on your trans. Then you can start changing the axle ratio on the calculator until your rpms are where they are supposed to be.
I hope I expained this well enough for you. If not let me know and I will try again.

 

The gear ratios are not on the door jamb. The tire size should have been there though. It would have been like I typed above. 235/75/15 or maybe P235/75R15 or something like that. If those were your stock tires then the gears were most likely 3.73. Those gears go way back are are in my 72 F100. So was that tire size. But in your original post you said it had 4.10 gears. How did you know that. And the 33 inch tires are about right for 4.10 gears. What more are you looking for?

 

The axle code is on the tag on the drivers door jamb. The code will tell you what axle ratio you have. It will look something like this one. It's the top picture.

http://www.clubfte.com/users/mil1ion...ruckCodes.html


This link is from Mil1ions web site. Making sure he gets the credit.

 

Wow, there's a lot of misinformation on this thread.

One, there is no such thing as a stock ratio. I've seen trucks with 2.73, 3.08, 3.55, 3.73, and 4.11 rear axle ratios. It just depends on what the truck was ordered with and what was available that year. 3.73 is a very odd ratio and I'd consider it rare.

*All* transfer cases have a 1:1 high-range ratio.

Transmissions are different, of course. If you look on that sticker, (someone didn't explain this very well) there are two rows at the bottom. One row reads things like TRANS and AXLE and SPRING. Post the codes under TRANS and AXLE and someone can decode them. You can also look in your owner's manual to get them decoded.

Next depends on what you want to use the truck for. 4.10's with 33 are great for the freeway, but it sounds like you want a little more get up and go. If you have an overdrive trans, you can go with lower (numerically higher, remember) gears like 4.88 or so. The lower you go, the faster your engine will spin on the highway. This translates to worse gas mileage, and if it's low enough, premature engine wear.

If it's a 4x4 truck, you have to change both axles, or you will tear the truck apart if you try to use 4x4. Figure on about $500 an axle to have a shop do the work for you.

 

They are on every Ford truck I've ever owned or looked at.

 

Thats what I thought but didn't want to say that if I was not correct.

My fingers were getting tired.LOL

 

i put 33 thornbirds on my 91 and it didn't hurt too bad. orig. 373 gears and still got 12 mpg. those procomps are a heavy tire too. they weigh in at 53lbs each.

 

I agree with almost everything andym said, 3.73 in the F-150 isn't the most common. I think 3.55 is the most common in the F-150 for a 4x4, although you could get a variety of different gears for 4x4's (3.08, 3.55, 3.73, 4.11, probly more) A Ranger however, only came with 3.73 gears in the 4x4's.

Turboguy - I am guessing you would have had 3.55, like I said, I think they were the most common in 4x4's.

Where I disagree with andy is in transmissions. All manual transmission will have a top gear (unless its overdrive) of 1:1. But thats a mute point here, he has an auto. Just so people know for in the future.

Trevor