TPMS saved me, plus a bonus rant

[RickLightning]

Okay. Why do you think the limit is 50 mph when the Owner's Manual says it's 70?

Spare tires different trim, and tire size. Lower the tire and read it.

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[Henry Ford]

Spare tires different trim, and tire size. Lower the tire and read it.

It says max speed is 50 mph?

I'm pushing this because you are contradicting what I read the in the Owner's Manual when I needed to use a spare. I don't know another source to reference in that situation.

My understanding is the spare that comes on a Lightning or any F150 (maybe Rapter is different) is not the same size as stock tires but is close. I assume they don't match the spare to the stock tires for cost savings. The difference in tire circumference across Lightning trims is about 3%, a difference a differential can easily handle. Maybe at some speed the differential can no longer handle slightly different tire size, hence the speed limit.

Another reason for a speed limit might be tire construction. I'm certain Ford doesn't spend 1¢ more on a spare tire than is necessary and there are limits on what a spare is capable of. My assumption is they publish those limits in the Owner's Manual. I'm open to another explanation.

 

[Pioneer74]

Apparently AWD systems don't like the mismatch.

That doesn't apply to the Lightning. The front and rear axles aren't linked through a transfer case like traditional AWD vehicles

 

[Zprime29]

That doesn't apply to the Lightning. The front and rear axles aren't linked through a transfer case like traditional AWD vehicles

Ah, so AWD from an EV is not the same as AWD from an ICE? I'll have to research that, I'm barely familiar with the difference between 4 wheel drive and standard ICE AWD.

 

[Zprime29]

Spare tires different trim, and tire size. Lower the tire and read it.

That doesn't answer the question. Why does it say 70mph in the manual?

 

[Ricks Lightning]

The information stamped on the tire is the ultimate answer. sure you can cheat a bit, but what the manufacturer designed the tire for is the ultimate safety factor. No different than what the Ford stamps the tire pressure on the door jamb, the tire manufacturer stamps the maximum tire pressure on the tire. Owners manuals are not updated as well as they should be. Maybe the truck can handle the 70mph as printed, but the tire was not designed to handle that speed.

Rick

 

[mrau]

Checked my spare today. It is stamped Temporary Use Only. However I did not see any speed limitations. It is a Maxxis Bravo 771 N that was designed as a spare for F150 & Lightnings. No speed limit info on the Maxxis page either.

Also the valve stem is pointed up. Still easily accessible for checking tire pressure. (36 psi).

 

[Zprime29]

The information stamped on the tire is the ultimate answer. sure you can cheat a bit, but what the manufacturer designed the tire for is the ultimate safety factor. No different than what the Ford stamps the tire pressure on the door jamb, the tire manufacturer stamps the maximum tire pressure on the tire. Owners manuals are not updated as well as they should be. Maybe the truck can handle the 70mph as printed, but the tire was not designed to handle that speed.

Rick

I'm definitely not a lawyer, but it seems to me that Ford would be opening themselves up to litigation if I follow the direction on the owners manual and that results in an accident. I found several other Ford owners manuals that all say 70mph for a dissimilar full sized spare. I feel like my compromised speed of 60mph was a good choice.

 

[Maquis]

That doesn't answer the question. Why does it say 70mph in the manual?

The manual for my 2023 states 70 MPH, but 50 MPH in 4 wheel drive. Probably a carryover from the ICE manual.

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