Spare Tire Over-inflation - How much is too much?

[TheGrrrrr]

Was thinking about redundancy for airing up if the ARB Compressors were to fail at an inopportune timed and was wondering if I would be able to carry my spare (max inflation pressure 50 psi) inflated to like 80 or 90 psi since there is no load. This would allow me to connect the 4 way Indeflate (on the source valve) to the spare and balance the air between all 5 tires. If I was at 20 psi on the main 4, in theory carrying 80 to 90 in the spare would allow me to balance all 5 tires at 32 - 34psi, which would be enough to get me back on the highway to a filling station of my choosing.

My assumption is that the max PSI for the tire is based on it being in use carrying the load of the vehicle and it seems like it takes over 200 psi to blow the tire so 80-90psi might carry just fine in a spare. I've certainly heard of people carrying extra air in the spare, just wasn't sure how much would be reasonably safe beyond the limit for use.

 

[grinchy]

I run my spare at max listed psi (in my case 65 psi). I don't think it has enough air in it to do much beyond top off a low tire, should probably try it out.

 

[BVE]

One time Discount tire over filled my spare and my TPMS system wouldn’t register at all until it was deflated closer to the 41psi I run on the others. I just have mine at 50 so I know which one on the dash is the spare.

 

[bhsdriller]

It doesn't work like that. Yes it has a lot of pressure, but not enough air volume for all 4 tires

I think lol

 

[bloc]

I periodically fill my spare to the sidewall limit so that despite it bleeding down slowly, it is more likely to be above the RCTIP when I actually need to use it. If it's still significantly over, I'll bleed it down to that pressure when/if I use it. Plus as @BVE said it makes it obvious which is the spare in the pressure readout on the gauge cluster.


Outside of that, even though a higher number may not blow up the tire, you don't know whether it is doing damage that could manifest into a blowout or other issue later when that tire is used on the road. So doubling the number for only one extra fill seems sketchy at best.. and if you are going to be below that, maybe just accept that either it is a low number for incidental top ups, or don't go above the sidewall pressure.

 

[TheGrrrrr]

It doesn't work like that. Yes it has a lot of pressure, but not enough air volume for all 4 tires

I think lol

If I have 5 identical containers with different psi in each and I connect them, they become one container with the air distributed evenly which would mean identical psi in each when disconnected. This is simple balancing. Now, I do not know if the extra PSI distributed on a 1:1 basis. Does 25 extra PSI in the 5th container get distributed evenly across the 5 containers? yes. Does that mean effectively delivering an additional 5 psi in each? I don't know. Its delivering what was enough air volume in the 5th container to provide 5 psi under that condition, but does that same volume of air add 5 PSI when distributed to a container at a lower starting psi? I don't know.

Edit: 7th grade physics was right after lunch and the girl sitting in front of me was a distraction. I regret nothing.

 

[Sandroad]

I'm ignorant of the safety considerations for filling over the max inflation pressure on the sidewall, but I do know from my RV life that wheels (trailers at least) have a pressure safety limit too.

IMHO, it seems this idea falls in the category of a solution in search of a problem. Maintain and check your ARB compressor/lines before every off road trip and you should be fine.

 

[kcjaz]

It doesn't work like that. Yes it has a lot of pressure, but not enough air volume for all 4 tires

I think lol

If I have 5 identical containers with different psi in each and I connect them, they become one container with the air distributed evenly which would mean identical psi in each when disconnected. This is simple balancing. Now, I do not know if the extra PSI distributed on a 1:1 basis. Does 25 extra PSI in the 5th container get distributed evenly across the 5 containers? yes. Does that mean effectively delivering an additional 5 psi in each? I don't know. Its delivering what was enough air volume in the 5th container to provide 5 psi under that condition, but does that same volume of air add 5 PSI when distributed to a container at a lower starting psi? I don't know.

Edit: 7th grade physics was right after lunch and the girl sitting in front of me was a distraction. I regret nothing.

Assuming all 5 tires are the same size (volume), 4 tires at 20 psi and one at 90 psi will balance at 34 psi. PV=nRT.

(I married the pretty girl who sat in front of me in 7th grade science class. Don’t regret that for a minute either!)

 

[Tex68w]

Counter to the OP's idea, I usually keep my spare at or around my standard on road psi knowing full and well that I have a dual compressor on board for adjustments if and when I should need the spare.

 

[manofthewoods]

If I have 5 identical containers with different psi in each and I connect them, they become one container with the air distributed evenly which would mean identical psi in each when disconnected. This is simple balancing. Now, I do not know if the extra PSI distributed on a 1:1 basis. Does 25 extra PSI in the 5th container get distributed evenly across the 5 containers? yes. Does that mean effectively delivering an additional 5 psi in each? I don't know. Its delivering what was enough air volume in the 5th container to provide 5 psi under that condition, but does that same volume of air add 5 PSI when distributed to a container at a lower starting psi? I don't know.

Edit: 7th grade physics was right after lunch and the girl sitting in front of me was a distraction. I regret nothing.

Female distraction IS the best excuse for pretty much anything and everything. For which recovery is NOT possible.
What was this thread about again?