newmoon

I have that exact air compressor. Works great. I prefer it over the 12 V ones because they are slower and I'm worried that they will drain the car battery. But I still keep a cheapo $5 12 V Harbor Freight air compressor in the trunk for emergencies.

KevinGary

Yes and yes

thehaviet

thanks. i will start with 38 front and 35 rear and see how that goes.

porksoda

Another thing i found while i was shopping for tires was that tirerack recommends:

"XL/RF tires required. Customer must maintain higher tire pressure levels of 42psi for proper load. *********PLEASE COPY THIS NOTE ONTO INVOICE************"

There have been countless threads everywhere on this and as far as i understand they recommend the air pressure to guarantee sidewall rigidness.

Currently as recommended by another member i am running 39 front and 39 rear on my pirelle with size: 255/35R20 97Y XL

thehaviet

I am confused. You said Tireack recommend/requires XL tires to run at least 42psi, but you're running 39psi?

porksoda

Hi, to clarify there was a thread about this last year sometime (https://www.audiworld.com/forums/a6-...ssure-2821098/).

Basically the dealers overfill the tires to 44/46 and it makes the ride teeth chattering. Lots of users experimented with lower pressures safely and various recommendations were made between 38 and 42 psi.

My comment was that manufacturer recommend to keep these at 42psi, and i suspect it is because of the shorter sidewall to maintain rigidity.

I am not 100% of my 39psi causes any warranty related or safety related issues but i ran 38 last year. I will be confirming with a manufacturer and a tire vendor about the minimum recommendation of 42psi.

newmoon

There are load and inflation tables that you can use like this one, right at the end pp 29-32:
https://toyotires2-1524598101.netdna...s_20151020.pdf

Basically the load capacity increases with increased pressure. A standard tire meets the stated load index at 36 psi. So if it has a load index of 100, it can carry 1764 lb, but it has to be inflated to 36 psi. If you use lower pressures, e.g. 32 psi, it will only be able to carry 1587 lb.

A tire that has XL or Reinforced on it meets the stated load index at 42 psi. But the capacity in pounds that each load index corresponds to is still the same as standard tires. So if you have a 100 XL tire, you need to inflate it to 42 psi to carry 1764 lb.

Because different tires have different load indices even in the same size, and different car manufacturers tune their recommended tire pressures differently, places like Tire Rack probably just recommend 42 psi to make sure that you get the maximum load carrying capacity of the tire.

If you want to go lower than 42 psi, that's fine. Audi does it right there in their recommended pressures. But the proper way to do it is to look up the table and make sure you meet the same load capacity in pounds at the pressures you want to use, as the original Audi specs.

thehaviet

Thanks. I follow what you're saying, but do people actually do the math to add up the weight of their cars and passengers in order to have a total load requirement to match to the corresponding psi?

snagitseven

No. Most use (and should) the recommended psi for standard and max as outlined in the manual or somewhere in between depanding on the load. Audi's recommendations, common sense and drive/ride feel should be adequate for just about any tire assuming it is OEM sized.

porksoda

As snagit7 said, I usually am the only passenger in the vehicle with little to no load in the trunk so my pressure happens to be within the range of recommended psi.