I heard that if you buy new wheels and tires, they should stay as close to the factory total diameter as possible. Is this true? So if you have 20 inch diameter wheels and tires, and you buy a set of 19 inch wheels, you need as close to 1 inch tires to (hypothetical here) as possible to keep good speedometer calibration.

So, I'm looking to get new wheels, and I need tires soon (tread's wearing out--won't pass inspection soon), so should I keep the overall diameter roughly the same? I have an '01 with 15" wheels. I want maybe 17 or 18's on there, so do I need to look at lower profile tires for my beast?

 

As your tires/rims get larger in diameter it will throw your speedometer off, and your acceleration will suffer.
When you go larger, you will actually be going faster than your speedometer is reading...example your speedometer is reading 60 mph, but your actual speed is 65 mph.
Your actual speed will be dependent on the size tire you eventually get. Also, your acceleration will suffer, again dependent
on how large your tire is.
There is a way to offset the change, but it requires changing your rear axle gearing.
Going up in overall diameter by an inch, maybe two won't throw it off too badly, but it will affect the truck.
There are formulas on line to figure out what your change will be when you change tire/rim/axle gearing.and what gearing you will need to re calibrate your speedo.
Remember when you go to a larger overall diameter, lets say 4 inches, your also going to raise the truck by two inches, and that in turn may interfere with your front wheels contacting the sheet metal and/or front suspension components.
You also have to look at the width of the tire/rims you want. Going to a larger 17 or 18 inch tire/rim combo will mean the offset of the rims will be "deeper" which in turn means that when you make a turn, there is the possibility that the tire will contact the truck/suspension.
You can go to a larger rim with a lower profile tire sidewall to keep overall diameter close to original, but remember, lower profile means stiffer sidewalls, and now you get into having a "stiffer" ride. And, these older Rangers had suspensions that were never designed for a smooth ride to begin with...its a truck, with a truck suspension. Stiffer sidewall won't help the ride at all.
It is really a balancing act between tire/rim size, offset, and backspacing of the wheel.

Grumpaw

 

Good read, Grumpaw. Thanks. That's what I was told, so it's been confirmed. What I think I'm going to do is match up a set of rims with tires and keep the same overall wheel/rim diameter. Should be a smooth transition that way.

 

I have a 2009, pretty much same as yours, and had the 15 x 7 inch steel rims.
I just got a set of alloys, same 15 x 7 inch , and the back space was almost the same as the stock rims...1/2 inch more.
Kept the tires the same size as originals, 225/70/15. . I know they look "small", but I was after the "old school" look with a lot of sidewall on the tires.
Being that I kept thw wheels stock size, I can always go to a slightly taller or wider in size as there won't be any interference with the truck/suspension.
Of course, with them being almost stock size, I run 30 psi (don't carry any load) and the ride, even for a pick up, is nice.
Grumpaw

 

What do you mean by "backspace"?

I am pretty set on increasing wheel size--maybe up to 18's. A guy showed me some stock 18 inch Hyundai's with tires that matched the overall diameter of my tires/wheels. Now, I'm not too interested in stock Hyundai's, but the thought of 18's that make a near-seamless transition from my old wheel/tires intrigues me. The tires were of a lower profile, but not that bad.

Ride is horrendous now, so it may get worse, but I have plans to tweak the suspension for a softer ride. My truck rarely hauls a load.

 

Back space is the distance, in inches or mm measured from the back of the wheel face to the edge of the rim at the rear.. The more the back space, the deeper the wheel/tire will fit into the wheel opening.
Lot easier if you just google up "wheel back spacing and wheel offset" Will have pics and diagrams to assist.
Example...your stock steel rim has a backspace of right at 3 3/4 inches. If you take the same wheel, but with a 2 inch backspace it will then "stick out" of your wheel well that 1 3/4 inch.
The reverse is true if you go with more backspace with the same rim...it will "intrude" into the wheel well and the tire may hit the fender liner or front suspension component.
The guys that run 4 x4's can get away with a lot of large tire/wheel combos because the suspensions were designed for larger rims/tires, and the lifted trucks go way larger..
Not saying you can't go with a 17-18 inch rim with wider/low profile tires, you just have to be careful of how big/wide you go before you have problems. Just check...on this forum and others a lot of guys are running oversize
tires/rims on stock 2 wheel drive Rangers.
And as for that Hyundai...it was designed for and the suspension designed for a 17 or 18 inch rim with a low profile tire...The Ranger suspension was designed to be a truck suspension and no thought was ever put into running a 17/18 inch rim with a low profile stiff sidewall tire.
Guarantee the ride difference between a Hyundai with 18 inchers and your Ranger with 18 inchers/low profile tires will be totally different. Soft car suspension vs. truck suspension.
Grumpaw

 

Sweet. Thanks.

 

Remember, if you go with a 17/18 inch rim, it will probably be wider than the stock 7 inch rim. Would almost have to be wider to accommodate a 17 or 18 inch low profile tire.
Lets say it's an 8 inch wide rim. That extra inch in width has to go somewhere, either with less backspace which will have that wide tire "sticking out" or with an inch more backspace which will have that tire "intruding" further into the wheel well.
Usually, intruding may bring problems with the tire hitting the fender liner or front suspension, and if it sticks out, it may cause the tire to hit the front or back of the fender sheet metal Just depends on how big you go.
The Ranger has some fairly large wheel wells so if you don't go nutso you'll probably be ok.
Google up "Ford Rangers with 18 inch wheels"...whole bunch of pictures come up...will give you an idea of what you dealing with.
Grumpaw

 

Thanks again, Grumpaw. I found a site called Custom Offsets that has some handy info for me to peruse. I think if I take my time and find the right wheel, I should stay close to factory dimensions.

 

You can re-calibrate the speedometer, either through 4 wheel ABS(if you have that option) or Body Computer, most tire shops have that software now, 1998 and up Rangers
1997 and older Rangers can be re-calibrated by change a gear on transmission or transfer case, its an easy to change gear

The rear axle ratio does change lower with larger diameter tires and higher with smaller diameter

Read here and get your AXLE code and find out what you have now: https://therangerstation.com/tech_li...le_codes.shtml

 

Cool. So I could take it to a decent tire shop and have them re-calibrate the speedo?

Thanks for the link.

 

Yes, just call around, Ford Dealer can it too, call to get a price, have VIN handy they will ask for that

 

Great. Thanks.

 

Yes rumor is true. You can go up in rim / wheel size from 15 to ........ this is called + size, so going from stock 15 to 16 is called +1 and to 17 + 2 and so on. The correct way to do it is to keep the overall circumference of the tire the same. In other words as you go up in size of the wheel from let's say 15 to 17 your new tire on the 17" rim will have a smaller sidewall but the overall circumference of the 17" + tire should remain the same. This way your speedometer will remain accurate. You would be trading some sidewall height to the increase wheel diameter size. In essence you increased your wheel size from 15 to 17" that's 2 inches more so your new tire size will have a 2" less overall in sidewall now taken up by your increased wheel size

I hope this helps answer your question, also google tire calculator and plug in your factory tire size and see what a +1, 2 and so on tells you you should replace it with.

 

Cool, thanks for confirming. I will proceed buying my new wheels and tires with all of this helpful information in mind.