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Tire PSI Exceeds Max When Warm

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R32REG

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Discussion starter · #1 ·
I know the proper way to inflate tires is when cold but the T2's 20' tires require 49 PSI in the rear.

My tires Max Pressure is 50 PSI.

When my tires heat up after driving they are above the max. (~52 PSI)

What's the consensus on what to do here? Deflate so the warmed up tires never exceed the max?
 
#2 ·
49psi is your maximum load pressure. Unless you're always loaded completely down and/or towing something heavy, you should use the half load pressure, or 44psi for the rears. Regardless, going over the tire maximum pressure is a bad idea for a number of reasons.
 
Discussion starter · #3 ·
TPMS is set to 49 from the factory. Never have I set tires to anything but the recommended max load.

Let's just say for sake of argument I was max loaded. My original question still applies.

Warm tire pressure exceeds max tire ratings. How does one handle that?
 
#4 ·
The tire does not have a max warm pressure of 50 psi. Just like the vehicle pressure recommendations, the max psi spec for your tires is quoted for cold tires that have not been warmed by driving or even sunlight. If you are at 49 psi cold, you are within spec even if it warms up 3-5 degrees when driving.
 
Discussion starter · #5 ·
m-fine said:
The tire does not have a max warm pressure of 50 psi. Just like the vehicle pressure recommendations, the max psi spec for your tires is quoted for cold tires that have not been warmed by driving or even sunlight. If you are at 49 psi cold, you are within spec even if it warms up 3-5 degrees when driving.
Click to expand...

That's what I was hoping to hear.

I figure they must account for the PSI increase if you are to inflate when cold.

It's just that I've never had a tire so close to the max PSI threshold limit. Pretty slim margin for error at 49 PSI and didn't want to have a blowout.
 
#8 ·
TPMS is set to max load for NA Touaregs, I assume for liability reasons. 49 is awfully
high for regular driving, and I'll bet you're wearing your rears unevenly for it.
Here's what the manual states:
Half Load Max Load (Bar/Psi)
F R F R
275/45 R19 M+S 2.8/41 2.8/41 3.0/44 3.2/46
275/40 R20 2.8/39 3.0/44 3.0/44 3.4/49
295/35 R21 2.7/39 2.9/42 2.8/39 3.4/49

I know that's hard to read, but the 275/40 R20 is at 39 front and 44 rear for half load, and 44 and 49 for max load.
 
Discussion starter · #9 ·
cb62fcni said:
TPMS is set to max load for NA Touaregs, I assume for liability reasons. 49 is awfully
high for regular driving, and I'll bet you're wearing your rears unevenly for it.
Here's what the manual states:
Half Load Max Load (Bar/Psi)
F R F R
275/45 R19 M+S 2.8/41 2.8/41 3.0/44 3.2/46
275/40 R20 2.8/39 3.0/44 3.0/44 3.4/49
295/35 R21 2.7/39 2.9/42 2.8/39 3.4/49

I know that's hard to read, but the 275/40 R20 is at 39 front and 44 rear for half load, and 44 and 49 for max load.
Click to expand...

Thanks for posting that.

Am I reading it correctly though? Does it list 39 for half load for the fronts?
 
#10 ·
I know my door card is not right for I don't have the 19" wheels it was built with. I had the dealer swap them for 17" before it was shipped to me. I wanted nothing to do with 19" wheels.
 
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#11 ·
R32REG said:
Thanks for posting that.

Am I reading it correctly though? Does it list 39 for half load for the fronts?
Click to expand...
It does, 39F/44R for half load, 44F/49R for max load. If you dig around, you find they also recommend 44F/44R for half load for the same tire size. To make sure you're not running overinflated, I recommend you do a quick chalk test. Get some sidewalk chalk or similar, and rub a thick line across the shoulder of the tire and into the tread blocks. Go for a quick spin around the block, and see where the chalk has been rubbed away. If it's not worn at all on the shoulder blocks of the tire, then you're overinflated for your current load. I'm actually genuinely curious now, but still leaning towards your TPMS being off.
 
Discussion starter · #12 ·
cb62fcni said:
It does, 39F/44R for half load, 44F/49R for max load. If you dig around, you find they also recommend 44F/44R for half load for the same tire size.
Click to expand...

What I find strange now is that my placard shows 39F / 49R.

Why would it give me the half-loaded value for fronts and full loaded for the rears?

Maybe another North American T2 owner with the 20 inch factory wheels can comment on their TPMS settings.

Need all this recent buyers of those beautiful Sapphire Blue T2's to give some feedback!
 
#13 ·
It is truly strange. Was it an oversight? Or a late design decision? Hard to say. If you can score some chalk, give the test a try and see how much of your contact patch is actually making good contact at 49psi. I think a 10psi split between front and rear for a vehicle with pretty good weight distribution is very odd, regardless. Maybe trying to fight understeer?
 
#15 ·
49 psi for the rear seems very high. I don't get why the T3 with 20" wheels is 33-38 and the T2 with a slightly smaller tire is 39-49. The front to rear difference seems excessive and the rear pressure seems high. I wonder if those numbers were specific to the OEM tires being near max load with 350kg on the hitch?
 
#17 ·
R32REG said:
I know the proper way to inflate tires is when cold but the T2's 20' tires require 49 PSI in the rear. My tires Max Pressure is 50 PSI. When my tires heat up after driving they are above the max. (~52 PSI) What's the consensus on what to do here? Deflate so the warmed up tires never exceed the max?
Click to expand...
Hi, what you are describing is normal. As a tyre flexes all the material warms up due to internal friction. This heat is transferred to the air inside. Increase the temperature of a fixed volume of air in a relatively low pressure vessel and you measured an increase in pressure from a cold tyre reading.

Take road racing of a motorcycle as an example. Cold psi is only a guide. After a few hard laps the tyre pressures may increase as much as say 8psi. The more important check is tyre temperature. If temp too low, reduce tyre pressure (= more tyre flex = hotter tyre). Too hot, increase tyre pressure (= less tyre flex = cooler tyre).

As long as your tyres are not too hot to touch, due to speed, load, etc, then you have nothing to worry about.

I run 35psi in my Treg tyres unless load, towing, etc dictate a higher cold pressure. I also do not have TPS and can run whatever pressure I like.

Your results may/will vary.

Mick
 
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