My truck came with the package that has 20" wheels and tires. The spare is an 18" wheel and tire. Is this normal? With 4 wheel drive, we are not supposed to put different size tires on the same axle.

 

different size tires. not different size rims. if the 20 and 18 inch tires are both the same height, that is all that matters. taller rim size has a smaller tire sidewall.
so a 20 inch tire that is 35 inches tall and a 18 inch tire that is 35 inches tall are the same size, the 20 just has a smaller sidewall.

 

Thanks for the feedback. I understand that one could have different diameter wheels with same diameter tires. I'm just wondering if Ford is using 18" wheels as spares--and why? If they are same diameter, then why not a 20" wheel and tire. They can't say a 20 won't fit!

 

because plain jane stock work trucks use 18's.
why put a $400 alloy wheel under a truck when you can put a $35 steel wheel under there?

 

I'll take a $35 steel wheel that holds a 20" spare tire.

 

A 20" tire costs way more than an 18" tire also. With a steel wheel, it's not gonna spend much time on the road unless you do a 5-tire rotation that involves remounting tires.

A 20" steel wheel is gonna weigh a LOT and if a small person actually needs to change a tire it would be really hard to handle; I don't think Ford even makes a steel 20" wheel because these big wheel sizes have nothing to do with function--they actually reduce the load capacity of the truck in exchange for the "look".

For instance, the Raptor (actually made for performance) uses 17" wheels because it's meant to function, not for ghetto bling like the 20's.

The 18" tire/wheel will hold the same load and as has been said, the tire is the same diameter as the 20's. Most cars and smaller SUV's get a temp donut spare.

George

 

I can't get anybody at Ford to explain that to me. They just shrug their collective shoulders and don't answer the question.

 

What does "at Ford" mean? In their main corporate engineering or corporate accounting department? That is where the decision is made. Your dealer did not design the equipment that the factory puts on trucks.

I thought I answered your question. For a spare, there is zero reason to use a 20" wheel and I doubt that anyone even produces a steel 20 because 20" wheels are meant for bling and that is not what steel wheels would be used for.

Most cars and SUV's get a donut temporary spare. It is more likely that a pickup will be towing and/or using 4WD, so an equal tire diameter spare that will hold similar weight as the regular tires is better and that's what you have. You're not gonna rotate it in a 5-tire pattern unless you dismount tires, etc, so think of it as a temporary spare. With all the tire/wheel combos used on an F150, they are NOT gonna have 10 different spare tire assemblies on the line if 1 will do.

A 20" steel wheel and tire will weigh 100 lbs...is a small woman or a guy with a bad back gonna want to change it? And with the massive and expensive efforts that Ford is making to reduce vehicle weight where every ounce counts, why would they want to add weight with a 100 lb 20" spare?

George

 

Thank you for your answer. I understand exactly what you are saying. But I have an F-350, not an F-150, and I use it to tow a 5th wheel trailer. I don't think that the 18" wheel and tire that are under the truck now weighs any less than a 20" wheel and tire--I could be wrong.

The 20's are 275/65R20, and the spare is a 275/70R18. Yes, they are within an inch or so of being the same diameter. I don't know about the "bling" reference, but I have what I have. It would be nice, if I have a flat and need the spare, to be able to install it and continue to a point of convenience to have the flat repaired/replaced. The way it is now, I'll have to go from convenience to necessity.

I don't do five-tire rotations, but I do use the spare as the "fourth" tire when buying replacement tires. I could just buy three and put the best used one on the steel wheel for a spare.

As for tire weight, all of these tires and wheels are heavy. One has to develop techniques using the lever to install, uninstall, and store them.

Thanks again.

 

An inch of diameter difference is not a lot and when your 20" tires wear down, the diameter difference will be less than a half inch. If you get a flat on the road, I would say you are good to travel a significant distance using the spare. You can certainly see what the owner's manual says about any restrictions when using the spare.

People who buy cars and SUV's get donut spares and those are far more than an inch shorter and are truly temporary/emergency use items. Chrysler minivans give you a can of fix a flat and charge $3-400 for a donut spare and a jack as an option.

George

 

Yeah, I know. The owner's manual calls the tires on the ground "road wheels" and the spare is the spare. It says get the road wheel repaired as soon as possible.

I found the answer, though, by looking at the door post. The placard that specifies the tire pressure lists the spare as an 18". So you are right, it is an expensive temporary spare.

On a side note, every 4 wheel drive vehicle that I have owned had a full size spare, never a doughnut. The wheel was a steelie, and didn't match the others, but it was the same size.

Thanks again.

 

I was just looking at my tires yesterday. I have four BFG's on aluminum wheels and a four year old full sized Michelin that has never been on the road on a full size steel rim. It really bugs me to have a tire just sitting, getting older by the day, with no chance of being used. I'm thinking I'm going to buy another rim to match the four I have, and next tire change make all five match and institute the five tire rotation. It's funny that my owner's manual calls for a five tire rotation, but the spare tire and wheel don't match.
While a 20" aluminum rim is going to be harder (and pricier) to find, you might want to consider shifting to the same tactic next tire change. It'll provide you with more peace of mind, and should pay for itself in increased mileage on your tires.

 

I think you are right.

 

Will the 20" wheel fit in the spare area under the bed where the 18" steel wheel and tire are now?

 

Like others have said I've had several Ford Trucks and all but this one had a spare tire the same brand and size as what's on the truck, even though it's a steel rim. It's just a way for Ford to save a buck by giving you an 18" tire rather than a 20" tire. You can quickly see what tires were provided by looking at the factory plate on the drivers side door jam. Mine has 275/55 R20 113t and 275/65 R18 116t spare. I'm one who like to do a 5 tire rotation. I don't like leaving a new spare tire set under my truck. I have had several trucks get 80K miles doing this 5 tire rotation.