Spare Tire Speed Question

[Trustable]

Might be a dumb question , but it’s been bugging me - I took my spare tire down for the first time after 30k miles (shame on me, I know) to fill it up with air since I had the compressor out and noticed it had the 50mph max speed sticker on it. The spare is a full size tire almost exactly the same as the rest of my truck, baring the LT designation.

Main 4 - LT265/65r17 w/ aluminum
Spare 1 - 265/65r17 w/ steel

I looked online and found a few different reasons why spares may have different speed limits but most of those were due to different sizes of tires or wheels. The only thing I can think of is that the speed rating is due to the fact it isn’t balanced? I don’t recall seeing any weights but I really just flipped it to brush it off real quick as it had collected quite a bit of gravel. If it’s because it isn’t balanced, I would think I could get it balanced and treat just just like a normal tire/wheel combo. Just want to know if anyone else has any thoughts.

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[Frenchy]

When you get a chance, take the spare tire down again and look for a particular DOT type of markings on the tire. Most factory tires for many trucks SUVs and cars will be rated with an S or a T. Those letters are the speed rating. An S speed reading is 112 mph. A T speed reading is 118 mph. If you go into Tire Rack or simply Google tire speed ratings, you will find an easy way on how to look at the tire to identify the markings I'm talking about.

 

[Friday yet?]

I don't understand it either. When you are talking about one of the donuts spares I get it. Common sense. But when your spare is the same tire as the rest, just a steel rim, why?

 

[LawnMM]

It's so you don't damage the drivetrain. It's not because "oh it's a spare wheel etc etc" if you look at the manual regarding spares or it may be in the 4x4 section it talks about how if you were to put a fourth wheel that's essentially brand new on with three that are worn you're introducing a difference into the drive line.

Short distances at low (50 and under) speeds are unlikely to cause an issue but at higher speeds and longer distances you're rolling the dice. It even says DON'T engage 4x4 with a spare on the truck if I remember correctly.

Found it.

 

[Loweredon33s]

It's so you don't damage the drivetrain. It's not because "oh it's a spare wheel etc etc" if you look at the manual regarding spares or it may be in the 4x4 section it talks about how if you were to put a fourth wheel that's essentially brand new on with three that are worn you're introducing a difference into the drive line.

Short distances at low (50 and under) speeds are unlikely to cause an issue but at higher speeds and longer distances you're rolling the dice. It even says DON'T engage 4x4 with a spare on the truck if I remember correctly.

Found it.

But it’s the same tire height and in some cases the exact same tire as stock. There’s no reason for it to matter unless the sizes on the truck were changed.

 

[LawnMM]

But it’s the same tire height and in some cases the exact same tire as stock. There’s no reason for it to matter unless the sizes on the truck were changed.

I agree, doesn't make a whole lotta sense but that's what they say. I've also heard the 'beat up spare' explanation because it's under the truck and often poorly maintained ??‍ though it's not baking in the sun or climbing over rocks or rashing curbs or anything the main tires do so I'm not sure that one makes any MORE sense than the manual's explanation

One key phrase in there that might help us all is "full size dissimilar spare" they repeat that over and over. If it's the same size, height, width, everything, I can't see why there would be limits either.

 

[fjwlobo]

If you look at the RIM you'll see why. As stated, it's not balanced and I believe it is a two-piece welded rim.

These rims were not designed for extended use or the higher speeds you would normally drive with your one-piece rim.

If you hit too many potholes or drive on rough roads (your normal daily commute ) the weld could break and leave you in a bad place.

The tire and rim may be the same size as your other tires, unless you have 18 inch tires ?. The spare is a 17 inch tire and rim for all models.

 

[Chris M]

If you look at the RIM you'll see why. As stated, it's not balanced and I believe it is a two-piece welded rim.

These rims were not designed for extended use or the higher speeds you would normally drive with your one-piece rim.

If you hit too many potholes or drive on a rough roads (your normal daily commute ) the weld could break and leave you in a bad place.

The tire and rim may be the same size as your other tires, unless you have 18 inch tires ?. The spare is a 17 inch tire and rim for all models.

I had a tire shop tell me almost exactly that once. It's all about the rim not being able to hold up because of its construction.

 

[dozxab]

I think it is due to that cheap steel wheel they use, probably to reduce vehicle weight. I doubt that wheel would stand up to max loads or towing for long. I occasionally travel to remote areas and don't want to get stuck travelling long distances on that thing. When I replaced the OEM tires at 12K miles and went to 265/70R17, I bought a wheel that matched the other 4 (brand new take off on Ebay), bought 5 tires and sold the spare on Craigslist for $125. Now I can do a 5 tire rotation and not worry about being stuck at 50 MPH. Note, the manual states that the spare tire carrier is not rated for more weight so I added a ratchet strap to support the extra pounds.

 

[fob63]

When I looked at my spare on the 2019 FX4. It had the same tire as the four on the ground. The steel 2-piece rim had a caution sticker on it.
I bought an OEM wheel on Ebay, had a TPMS installed.

I have about 14k on factory tires, but I am wondering if I should mount spare on right front.

 

[Sojourner]

When I looked at my spare on the 2019 FX4. It had the same tire as the four on the ground. The steel 2-piece rim had a caution sticker on it.
I bought an OEM wheel on Ebay, had a TPMS installed.

I have about 14k on factory tires, but I am wondering if I should mount spare on right front.

This is what I did. Got an OEM rim to match the other four, mounted that tire on the new rim (it was identical to the other four), had a TPMS sensor installed, balanced rim/tire, relearned the TPMS, and added it to the tire rotation. So now I have a five tire rotation instead of four. To me, it makes sense; why waste a perfectly good tire just hanging there as a spare?

I did it at 3k miles so uneven wear wasn't an issue.

 

[Friday yet?]

the manual states that the spare tire carrier is not rated for more weight

Jeez! Just charge another $100 for the truck! Damn Ford. Come on.

 

[dtech]

Yeah I was on a road trip towing my 4,200 lbs TT and picked up a 3/8" inch bolt in a rear tire which went flat at the campground. Put the spare on and drove 4 hrs with it, kept it at 50mph at 1st then gradually went to 60 mph, thankfully made it home with no issues.

 

[Trustable]

When you get a chance, take the spare tire down again and look for a particular DOT type of markings on the tire. Most factory tires for many trucks SUVs and cars will be rated with an S or a T. Those letters are the speed rating. An S speed reading is 112 mph. A T speed reading is 118 mph. If you go into Tire Rack or simply Google tire speed ratings, you will find an easy way on how to look at the tire to identify the markings I'm talking about.

I totally forgot to see the speed rating! I’ll take a look next time I have some time in the garage!

 

[Trustable]

It's so you don't damage the drivetrain. It's not because "oh it's a spare wheel etc etc" if you look at the manual regarding spares or it may be in the 4x4 section it talks about how if you were to put a fourth wheel that's essentially brand new on with three that are worn you're introducing a difference into the drive line.

Short distances at low (50 and under) speeds are unlikely to cause an issue but at higher speeds and longer distances you're rolling the dice. It even says DON'T engage 4x4 with a spare on the truck if I remember correctly.

Found it.

Thanks for the explanation! I thought by dissimilar it meant more of a different style (at vs all season, etc) but I guess it makes sense. Now the question I have knowing that is how does it work for the people who have jeeps or other vehicles who do the tire rotations with all five, because at that point one tire would always have a bit more tread.

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