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why more air in rear tires

22K views 60 replies 17 participants last post by  Janni 
#1 ·
what is the reason for more air in rear tires, and what is best recomodation, or do I just use what is on door?
 
#5 ·
Nobody likes sitting on hold, but I would call VWoA and get their take on this. If the sticker says 46, yet the tires say 44, I'd be interested to hear what VW itself recommends. Are these tires in question 255/60-17 106H?

For the record, the sticker in my '05 V6 with 255/60-17 106H tires states 36 front and 44 rear. The stock Dunlop ST8000s I think maxed out at 51 psi, while the Pirelli STRs (which are now OEM, and what I ran before) were 44psi max. My current Nittos max at 35psi, but are oversized (265/70-17) with a higher load rating (113). So, they can actually support more weight with less air pressure.

Matt
 
#6 ·
:confused:I called vw,they said to go by the sticker on the door,I said I have two stickers,one on door itself,and one on door jamb.I waited for 20 minutes and he said I have optional tires,and go by the door sticker.I think I got a bad rep,at first he said 46 was ok,then 44,then he talked about some kind of optional tires,I said they came with the car,then he said 44.
 
#8 · (Edited)
I submitted a web support request to VW about a week ago, asking about the 46psi vs. 44psi max, and today I received a phone call, asking me for pictures of the stickers.

I took some pictures, and discovered a second sticker on the bottom side of the driver door, may be the same as reported by JKUCSMA. This sticker recommends 44psi for the rear, this still seems too high given the tire max is 44psi.

Here are some pics:
http://www.insanegenius.com/t2tires/


P.
 
#44 ·
I submitted a web support request to VW about a week ago, asking about the 46psi vs. 44psi max, and today I received a phone call, asking me for pictures of the stickers.

I took some pictures, and discovered a second sticker on the bottom side of the driver door, may be the same as reported by JKUCSMA. This sticker recommends 44psi for the rear, this still seems too high given the tire max is 44psi.

Here are some pics:
Volkswagen Touareg - Tire Overinflating Danger


P.
VW support eventualy called me back last week, and said they are still working on the issue, but to use the tires recommended rating. I explained to the person that there is no recommended rating on the tire, just a max rating.

They called me back again a today and said they do not have a recommended rating, just to inflate to less than the max rating on the tire. Not really much help.

I was adament that they keep the case open, for this is a pretty serious safety issue, imagine how many other T2 owners out there are following the sticker and inadvertently overinflating their tires.

P.
 
#12 ·
If it were me, I'd go with the sticker UNLESS that value were greater than what's on the tire. In that case, go with what's on the tire.

In the US, tire manufacturers are required to publish, on the tire's carcass, the maximum save inflation pressure for that carcass. Any overinflation can lead to damage to the carcass, especially if driven for extended periods.

Note that this maximum inflation pressure also applies to the pressures needed to seat the bead while installing the tire onto the wheel. We had a tire installer who had a lot of tires with belt separation issues on quality-brand tires (Dunlops, michelins and Goodyears, if I remember correctly. The shop owner did a little investigating and foind one of his installers using up to 100psi ov pressure to seat the bead -- WAY over what the tire was rated for. The tires got over-pressurized, and the carcass got damaged, leading to the belt failures.

Tires are complex beasts. It's best to adhere to the manufacturer's recomendations, in all cases. If you can find out the amount of load the front and rear tires will be carrying, you can always call the tire manufacturer to get a tire pressure recomendation. I'd use THAT in place of the VW recomendation. The manufacturer knows his tires better than VW does, ESPECIALLY if its a brand of model that VW doesn't normally install on the car.
 
#14 ·
What do you mean by "the wrong tires?"

If the tire can handle the vehicle load (i.e. the tire's loading at GVWR does not exceed the tire's load capacity,) then the tire is up to the load imposed by the vehicle, regardless of whether the tire's maximum pressure is above or below the manufacturer's recomended inflation pressure.
 
#18 ·
According to Pirelli USA'a web site, the load index for that tire is 106, meaning a load capacity of 2094 lbs per tire.

Ubnfortunately, their techinical data page does not include your size, but most other similarly-sized tires in that line are spec'd to 44psi.

I'd inflate to no more than 44.

(And truthfully, I'd probably air mine up to 42, check wear patterns and tire temps, and adjust from there. As a racer, I have the gear to do that properly -- most folks don't.)
 
#21 ·
I good get a temp reader and check the center and outer edges for any differences...
If you're going to read the tire's temps, get yourself a good probe-type pyrometer. these have a small spike at the end of the probe that is stuck into the tire and measures the temperature a few millimeters below the tire's surface (the surrface cools down much too quickly for its temperature to be of any value -- by tyhe time you've gotten out to take your first measurement, the tires have already started to cool, and by the time you thake your third measurement, the tires a MUCH too cool.)

Tire temperatures are an important tool in setting up a race car, so many manufacturers make excellent pyrometers. Unfortunately, they are not cheap.

 
#22 ·
This probably isn't the same reason, but in auto-x we used to fill the back tires with more air to encourage oversteer (the slightly under-pressured fronts would grip longer than the over-pressured rears).

Although, if you add weight to the rear I could see this creating similarly-sized contact patches for all tires, making the TCS on a full-time 4x4 more reliable.
 
#25 ·
Mine came with 106-rated Dunlop ST8000's. I then put on 106-rated Pirelli Scorpion STRs. Both of these tires are OEM for the V6's. The 17" wheels get the 106 rated tires. I think the 18's take a 108 XL (extra load) and the 19's are 109, but I'm not sure on those off the top of my head. I'd assume the lack of sidewall dictates a higher load rating.

Matt
 
#27 ·
I'd assume the lack of sidewall dictates a higher load rating.
Nope -- the load index is the load index. If the sidewall height affects the tire's load capacity, its reflected in a higher load index.

OEM's buy tires based on a number of reasons, only one of which is the load rating. You can be sure they all are capable of coping with the GVWR and GAWR of the vehicle, however.
 
#28 ·
Just checked the tires on my '08 V8 (19" wheels.) They're load index 105, so obviously VW is installing a mix of load ranges. Having something other than 109 does NOT necessarily mean you have the wrong tires, unless VW is screwing up, and after the Explorer/Firestone sillyness, I doubt it.
 
#34 ·
Just checked the tires on my '08 V8 (19" wheels.) They're load index 105
That's really odd, and much lower than I've heard before for a 19 on a Touareg. What size/brand/etc are these tires?

Matt
 
#30 ·
I run 43-44 (cold) in the front and 45-46 (cold) in the rear. At one time I had to drop the pressures for some beach driving and when I pumped them up again they were already hot so I under inflated (41-42 front and 42-43 rear) compared to what I would normally have. After a week or two I noticed scrubbing on the outer edges of the tyres - put the pressures back up again and alls well.

When I originally picked up the vehicle new from the dealer the pressures were 44 front and 46 rear.
 
#32 ·
One point to ponder. The recommended inflation pressure (46#) is very close to the maximum inflation pressure for my Goodyears (50#) If I fill up cold, then the tires will easily go over 50# with some driving.

I'm going to see how much I need to drop the pressure to stay safely under 50# (I'll probably shoot for 48,) and keep the cold pressures acceptable.

If you're seeing a big difference between your cols and hot pressures, you have a lot of moisture in the tire's air. See if you can get a vacuum pulled on the tire (or at least least all the air out,) and have air put in that's bee run through an air dryer (common on compressed air systems used for painting -- adding one to your home compressor will cost between $10 and $300). The less moisture, the less pressure change.

Or, if you want to get really fancy, many high-end dealerships and tire shops now have the equipment to evacuate the air in your tires and replace it with nitrogen. Nitrogen doesn't increase pressure when hot nearly as much as air does. Race cars have been using this trick for years.
 
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