I recently bought a 2015 F350 SRW for towing a couple horses around when needed. It will also do some around-town driving when my wife needs to go somewhere and the eldest daughter has already taken the van. The truck will do no off-road driving, except for the occasional gravel road.

The truck came with 17" wheels. I might wait until the factory tires wear out and then make a decision about wheels/tires, but I'm also considering getting some aftermarket wheels now. Naturally, new tires would accompany new rims.

I don't know anything about the "best" wheel size or tire size. I've done some searches here regarding tires. Most threads discuss primarily brands/models of tires. I'd like to know the math behind choosing the best wheel size and the best tire for a given wheel.

I understand that shorter sidewalls handle better but give a bumpier ride, and that taller sidewalls give a better ride but won't handle as well. But, how much of a difference does it make? How much does towing factor into the decision? Are there any proven mathematical formulas for determining the best wheel/tire combo for a desired use?

For a truck, is there an ideal wheel size and an ideal tire size to put on the ideal wheel?? Is there anything functionally wrong with 17" wheels, or is it simply that they don't fill up the wheel well nice and appear too small? How about width? I'm not hoping to get tires so wide I have to add fenders to the truck to cover them, but I'll do what is necessary.

Thanks in advance for your input!

Any thoughts on this article:
http://www.consumerreports.org/cro/2012/12/plus-size-tires-when-more-is-less/index.htm

I would stick with the stock wheel/tire size combo. A bigger *tire* has the same effect as raising your final gear ratio, reducing towing performance. If the truck has lots of power and you are towing fairly light, one tire size up is usually ok.

Wheel size has nothing to do with drive ratios, has a fairly small effect on ride, but it can limiting the tire choices available to you. I have had trucks 15, 16, 17, and 20 inch wheels. I like the looks for a smaller wheel and a tire with more sidewall.

My current Duramax has stock 20's, as that's what was on it when I bought it. I really wanted the stock 18's. The ride is fine and sidewall flex isn't an issue, but paying twice as much for a tire the same size as a 16 but with a bigger hole in the middle really sucks, and it severely limits my choice of acceptable tires. I knew that going in, but it was the only truck that had everything else I wanted. I still wish it had 18's, even now.

Other than a small change in overall wheel/tire weight, wheel size is more about aesthetics than anything else. If you do change wheel size, be sure to investigate the proper offset/backspacing and width, otherwise you may find a tire size that fits a stock wheel rubs on an aftermarket.

One more addition just to illustrate the cost differential, I can almost buy aftermarket 18's and tires to fit for the same price as just tires for my stock 20's.

The above CR article is mostly in reference to cars. A 16-20 inch wheel is fine for a real truck, but again, I would likely avoid 20's just because of the tire choices. Spend some time looking at wheels and tires on tire rack.

For the best handling, especially in snow, stay with a narrower tire.

For pure functionality stay with the stock tire size. The trend of people putting bigger rims & tires on trucks is purely for fashion, it doesn't help performance. To figure out what a tire is capable of the construction is what's important, not the size. You've got to look at the load, traction, & wear ratings. Going to a bigger rim and lower aspect ratio is what sportscars use for better handling, but it's an F350 so you're not gonna make it handle like a corvette. For towing you don't want a narrow sidewall tire, not enough flex to absorb the punishment. Look at tractor trailers, their tires are usually kind of tall & skinny like the ones on your F350, that's generally what you want for weight bearing ability.

Also, if you get new rims you need to look at whether they're rated for the pressure & load of the E rated tires. The E rated tires that came on your truck are rated for 80 psi, not all aftermarket rims will take that pressure.

In a nutshell, the only reason to go changing rim size or tire size from stock is for looks, there's nothing to be gained functionally.

The Consumer Reports link is mostly BS. Keep the 17" factory wheels. You can buy tires to fit 16", 17", 18", and 20" wheels and still end up with the same overall tire size within 1/2" in both height and width. The bigger the wheel, the more tires cost and the fewer options

Not sure exactly which size comes from the factroy, but I'm gonna guess 265/75/17. If you really want to go bigger you could go 285/75/17 and get a tire about 1" taller and wider. It would fit your factory wheels.

I might go up one size, but no more. You'd be looking at $100-$150 more for 4 tires in the next larger size. It would effectively change your gear ratio and give a little less power and your speedometer and odometer will be off unless you recalibrate.

If you want to run tire chains you may have clearance issues with larger tires too.

Unless you need more ground clearance , I would stick with stock tire size. As others have mentioned ,bigger tires equal more $ and more weight equals less mpg.

Ford already provided them for your intended use.

My factory tires are 245/75/17. They look fairly small.

But, I hear what everybody is saying: No need to go bigger than a 17" wheel. I guess I'll just leave them alone. When the factory tires wear out, I'll consider a taller 17" tire but not go crazy.

Thanks all!

Wade;
Good evening to you sir, hopefully this finds you and your fine family doing well.

So while I'm not familiar with the specific truck you've got, I do know that most of the vehicles in the small work fleet that it's my job to look after can't have their tire size varied much from stock without getting the computer reset.

With all the sensors in the newer vehicles, if you go much more than an inch higher than stock it begins to effect the shift points and in extreme cases can apparently cause issues with the transmission.

On our own 2003 Dodge we were able to go up to 285's from the stock height 265's without resetting the computer, but if we'd have gone to 305's we'd have needed to get it reset.

The other issue one can run into is that if you have a flat and use the stock spare - it could cause undue stress on the rear diff if the difference in height is too great.

Then too, on our Dodge you can't stick a 305 into the spare holder....

Anyway these are all things to consider when changing tires from stock diameters these days.

Hopefully that was somewhat useful for you or someone out there tonight sir. Good luck with your pickup whichever way you decide.

Dwayne

The stock tires on my Dodge 2500 are 265/70/17. When I bought it used from a dealer, they'd installed 245/75/17's. They're the same diameter and weight capacity as stock but they're narrower. That gives a bit more room for tire chains. I think the narrower ones handle better on slick roads and in rocks.

They only look small because it is a big truck. Those tires are about 31.5" tall and 10" wide

A set of 265/70/17's will be about the same height, but 1" wider.

A set of 285/70/17's will be roughly 33" tall and 11" wide. That is as big as I'd go.

Here's a great tire size calculator to make short work of research:

Tire Size Comparison

I like 245's for width on my Dakota for deeper snow, but I think I'd probably go a bit wider on a 1 ton. Going bigger will have the same effect as running taller gears, but you could haul a couple of horses around with a half ton, so I wouldn't worry about that. I'd probably stick with the 17's. I don't like running anything you can't run over a curb without wrecking the rim.

Run it till you decide what you want. You probably have room to increase or decrease OD enough to change drive rpm. If you like how the gearing works for you keep the same size, if not adjust.

If your Dakota is like my Dakota 4x4 factory specs are 245/70Rx16 up to 265/70R16. I went half way to 255/70R16 because I could save $10 a tire, weird that a bigger tire was cheaper but it is a more common size at Costco so they get a break.

The negative about going to a size was my speedometer is 4 miles off ever hundred miles (4%) and the gas mileage dropped 10%. Thinking of dropping back next time around now that it is reaching 300k I could use that 4% drop in gearing

Really the only reason to get different size wheels on a truck is if you want a particular tire that will not fit on your current wheels. Lets say you wanted to run 33 inch tires. Your current wheels may not be wide enough for the tire you want unless you go the tall, skinny route.

I personally hate the move to bigger wheels. I want sidewall for flex. These trucks coming with 20-22 inch wheels are rough riding and no good off road. A good 16 inch wheel with proper size tires is what I prefer on a truck. Of course, load rating also plays a part on sidewall flex.

Now a performance car is a bit different. Bigger wheels and less sidewall is sometimes prefered for cornering and traction, but they do ride rough.

What you need to decide is what size tire you want to run and how that will affect your final gear ratio and towing ability and if that fits your current wheel or not. The taller the tire, the less power for towing but increases clearance. The "mathmatical formulas" are the gear ratio charts that show how changing the size tire affects rpms. Depending on your motor and transmission, you want to do most of your work in a given rpm range. Here is an application that will show you what changing tire size does to overall size. http://www.tacomaworld.com/forum/tirecalc.php
Here is a chart that shows how tire size affects rpms: http://www.rmr-offroad.com/interco/chart.jpg

If you have no preference and just want something that seems to fill up the wheelwell a bit more, just get the next size bigger tire. It will still fit your wheels and will not affect towing very much.

Just replaced tires/wheels on my '02 2500 Chev gas crew..

stayed with the stock 16"

16" BFG KO2's are pricey enough...

20" tires are insane !

I'm gonna disagree with the others - I love the 20" wheels/tires that came on my F350 CC 4x4 SRW. There's still plenty of tire and sidewall for flex, not like running 20's on a car or smaller truck. If mine had come with anything less, I would have moved up. My stock Michelins will make 50k easy, and handle great. Most folks can't believe their riding in a 1 ton 4wd pickup when they ride in it.

I do lower the pressure to ~60psi when not towing, and up it to 80psi when towing our 5th wheel. Had to get the dealer to reset the TPMS to alarm on the rear same as the front - set to like 60psi and they alarm when 10% low I think (was a pain to convince them, service mgr argued it couldn't be done so I finally complained the the general mgr who made him check anyway - voila, he learned he could do it!).

And 20" tires are about $200-300 per set more than 17 or 18" tires I would run that would give me equivalent height/width. It's a $50k truck...

Wade, you may want to consider a 265/70/17 10 ply all terrain for your truck. Talk to your tire dealer and see what they recommend...

Both huge wheels and the BS TPMS are unnecessary on a big work truck... Flaunting a $50,000 truck around is also childish... Nuff said..

This!

As others have said, on a truck or 4x4, you really want tires with a decent abount of sidewall. For that reason and the lack of availability, I would avoid 20" rim all together..

If you are looking for new rims for appearance sake, I would still stay with 16" or 17"..

Although you sake you won't use it for off roading, I note over here many of the folks who do off road do with comparitively small rims and tires with very large side walls..I have to say on a truck or 4x4, I like that look very much...Usually the rim are steel and are not particularly "flash" but look functional/business like and IMHO are better suit than fancy alloy 20" rim off a brothel creeper...

That is a very popular upgrade size and usually works very well. Mine are only 9.5" wide though.

I think they call them cappuccino cowboys

TPMS is not BS in any way. What's wrong with a system that let's you know your tire is low before you can detect it visually or by feel?

I only wish that all systems (some do) actually read out the pressure. The TPMS on my truck only goes off if the pressure is low, but I have no way to know what the actual pressure is.

I guess low is better than nothing. Mine reads out in PSI and throws an idiot light if too low. I have caught three different punctures on three different vehicles with TPMS. It also makes it easy to cheek the pressure, assuming it is accurate (mine have been). Wife's car only does low or not and I don't like that as much.

Childish? That I point out the cost of the truck vs the difference in cost for tires? If you gotta worry about $300 extra on a set of tires, shouldn't be driving a $50k truck was my point.

And never said they were necessary (other than the fact you cannot buy a 1 ton or less truck without TPMS), just that 20" wheels on a truck this big are not bad, work fine, etc., and are my preference - to each their own.

I don't know chit about towing tires.

Just wanted to say hi to Wade.

Hi Wade!