Guys, first, there is no point in re-gearing for a tire that is only an inch larger in diameter. Actually, after proper inflation, that tire that is an inch larger usually is no more that .6" higher. Second, when you say 255's and 275's and all sizes like that, I would hope you guys know that you are talking about the tire WIDTH, not the height.

This is how it works:
255 <---- Tire width (in mm)
70 <---- Percentage of width taken to equal height
R17 <---- belongs on 17" rim.

So...

A 265/70R17 is a tire that is 265 mm wide, 70% of 265 as sidewall height, and is designed to fit a 17"x8"wheel.

The stock 16" wheels can fit up to a 32" without any need for changes. The stock 17" is designed for up to 34".

Hope that this helps you guys.

-Flea

 

The attached link to tire calculator is very helpful in determining the changes to expect when changing size
tire size calculator

 

With all this talk of tires I'm going to ask a question here but may start a new thread if I don't get a response.

I have a '98 Jeep Wrangler and recently put on 31" Pro Comp M/T's. Awesome tires, but with my 3.06 rear gear my speedo/odo are about 10% off. I bought the transfer case gear (28 tooth) for 30" tires because that's the largest tire "supported" by Chrysler's parts dept. I want to do a before and after comparison so I decided that I'll have my wife drive 60mph in the F-150 while I drive the Jeep. Before that though I wanted to check the Ford to see how accurate the speedo is. I have the ORP with the LT265/70R17 Goodyear Wrangler AT/S tires. Yesterday with my wife running the stopwatch we tested the speedo between mile markers on the freeway. The results ... 52 seconds to travel 1 mile at 60 mph .... HUH!!! I come up with 69.2mph. Is this possible?

Are mile markers notoriously inaccurate or did Ford screw up?

 

I don't have a calculator handy... otherwise, I'd double check your math to make sure... Have you installed any superchips? Have you done anything that may have altered pinion angles or CV angles? Have Ford check it the next time you get your vehicle alligned.

 

Fleas:
I just got back from doing a retest on a different stretch of freeway. 1mile @ 60mph -> 1min 1sec, 1min 1sec, 1min 2sec then 2miles @ 60mph -> 2min 3sec and so on for about nine miles. What a difference a day makes. I really have no explanation other than either the mile markers are off on the first stretch of freeway, or me and my wife messed up somehow. Probably the driver’s fault (according to the wife) but I used cruise control both times.

Sorry to waste your time. Good job Ford!!

 

If you guys would keep your trucks stock you wouldn't have all these headaches.....

 

Supercrew2001red5.4
Keep it stock! No mods... Now that just wouldn't be any fun now would it. Half the fun is cussing it and getting everything fixed the way you want it. Seriously though in some ways you are right, that's why I didn't go ahead with any kind of lift or at least not yet.

MitchF150
Thanks again. I wasn't for sure if your tires were 70 or 75 series, it makes a big difference as FleasF-150eatshondas mentioned. It's always important to remember that aspect ratio on tires. I am going to call the tire shop and ask what they think (they seem pretty knowledgeable). I just know my tire sizes and things not how much difference there would be in a 265 or 285 tire. Either way I will check out my front end and have a shop do the same and either the shop or I can replace whats needed. I did learn something else from your post, I didn't know the TC could be locked or unlocked in basically all the gears. I thought it only locked up after 3rd. I was under the impression that the TC locking up was the OD. Makes sense though. I have no problems making the truck move. Heck I can keep up with my girlfriends little 86 Honda Accord on the interstate. It still has the get up and go if you mash it a little. It's the up and down shift on the interstate (mainly uphills) that somewhat bothers me. I think if the shaking is fixed I could live with the power loss, the two combined make me want the stock Hot wheels sixed tires back. Oh, by the way, check out the tire forums, got those new pics up.

If anyone wnats to use the tire program I found it's at http://www.dakota-truck.net/TIRECALC/tirecalc.html
Some guy with a Dodge made it but it's still pretty good.

 

Howdy KYFordFreak,

In regards to durability, well , let me just say this. In 1988 I ordered a new Ford F-150 Lariat 4x4. I knew before I bought it that I was going to run 33"x 12.2" tires with 10" rims on it. So I ordered the truck with 4.10 gears. When the truck came in I put the tires and rims on the same day.

Now 13 years and 98,000 miles later, I still have the same truck with the same rims. Only difference is I'm now running Super Swampers instead of B.F. Goodrich all terrians. I just had my first mechinical problem. I need to replace one of the brake caliburs on the front.

I've never had any front end problems at all, no engine problems, transmission. Nada. And yes, she's been off road, plenty. But I've always used common sence and I've always been big on maintaince.

So IMHO, don't be afraid of mods and given a choice between gears and engine mods. You will get more out of the gears in your case. You have to remember that the taller tires will not only reduce your gearing but being wider they offer more wind resistance and they are heavier. Unsprung weight is a performance killer.

Good luck with whatever you decide.

 

KYFordFreak;
I think the "locking" is only in third. I figured that out on the same hill. When the tranny downshifts into second, I would let up just a bit and then it would shift into "third", but at about 2000 rpms. The engine works much better and really has some pull to it, even up the hill. At the top of the hill, it would shift again, and drop to 1500 rpms. I had the OD disingaged, so I just figured it had some lockup feature for third. Anyway, I just wish it would drop to "unlocked" third, before going all the way to second. Yes, even on the highway, in OD, It will want to downshift going up slight inclines. I'm just getting used to hitting the OD button before the incline and going from there. Not worried about it.

Flea;

Thanks for the input. I'm aware of the numbers on the tires, but that's good info for those who may not be that familar with the numbers. I was just getting tired of typing out the whole tire size. We had been discussing it so much, it was pretty much just assumed we had the 75 series. I figured we all knew that the stock tires from Ford were usually the 70 series.

 

My $.02 (and worth every penny) as to the priority order (assuming on & off road use without bias) & what to expect:

1. Intake (K&n probably fine) - small (if any) HP gain, no troque gain/loss, better throttle response, small (if any) MPG gain; easy mod, not expensive, do it yourself.
2. Chip (Superchip?) - much cleaner shifting, small (if any) HP gain, small (if any) torque gain, little better gas mileage; easy mod, do it yourself, requires premium fuel, little pricy (compared to the other mods in list).
3. Flowmaster Y-pipe - noticable (measured by others - first handers please comment) HP & Torque gain, better gas mileage, cheap mod even with labor charges (unless you are a welder).
4. Flowmaster muffler (3" I/O, series 40 or 50 depending upon sound desired) & 3" back from Y-Pipe - small HP gain, no torque loss, less expensive than cat-back or dual systems (I personally don't think duals are worth the expense & weight & if done wrong, rob low end torque for HP), no too expensive a mod
5. Gears - 4.10 with 33" tires - better 60' times, better towing, better in the muck (as long as you know how the drive the taller gears), loss of MPH at the 1/4, loss of MPG although not as much as you would think with OD & hills as you won't downshift as much.

Unless you are making heads/cam changes I don't headers are worth it in general. Someone with experience cutting open the stock manfolds please contradict me if they are POS (like the Y-pipe). There are other things to consider like high flow CATs as well but I have no experience on these cars.

If you are looking for off road performance, then next up would be a good set of lockers. Air lockers provide nice flexibility, like the ARB's. Depending upon the terrain type of off roading, sucha s sand versus deep mud, you may consider lockers before gears. Air lockers (or just front lockers) will have no deleterious effects on the road, i.e., no lost MPG or MPH.

Chuck

 

Conocoan
Just the news to hear, glad that at least your older Ford held up that well. Now if the newer ones are built to half that standard I should be ok. We have had 2 Broncos. A 84 with the 2.8 which was ok but seemed very weak, we traded it off for moms minivan. Then we still have dads old 73. Man that thing is a tank, we hual a fullsize trailer load of wood out of the farm with no problems, and the old 302 motor (replaced about 10 yrs ago) still chugs away, the C4 tranny in it has never been touched, body is just a little rough.

MitchF150
Well, thanks for all your help,. Guess you and I both need to find somewhere to read up on our trannies. I don't know about you but I like knowing how everything works and runs. I noticed toady that if I kick out OD up hill it will run about 3000 RPM's then dron down to about 2 at the top of the hill.

Anyone know a good place to find info on transmissions?