Tire Pressure

[ravens]

I have the Cont. Tires on my 2011 Jetta TDI and I checked the Tire Pressure at 40PSI. I see that the Tires are rated at 51PSI.

How high can I run them to better my MPG? Also, I see that in the door Jam of the drives side it states that that the Tires should be at 33PSI.

Is this correct? I'm interested in getting NITROGEN for the Tires. I spoke to a NITROGEN Dealer and he stated that he would do ALL four tires for 50 bucks. How much PSI will go into the tires and he said that he would go by the Sticker that is located on the drivers side door.

Seems to me that 33PSI NITROGEN will be to low....

 

[dieseldorf]

Many, many threads on this already, Raven. Welcome aboard!

 

[Plus 3 Golfer]

IMHO, skip the nitrogen. It's not worth $50. The benefits of nitrogen is overated for passenger tires.

Only you can determine whether you want to exceed the manufacturer's recommended pressure and by how much. I run 38 psi which provides a firm but not bone jaring ride and very even wear across the tire. I have seen no studies on how much mpg will increase by going from manufacturer's recommended to higher psi. But there are tests / studies on how mpg is affected when tires are deflated below recommended psi. CR said "Our own fuel economy testing showed a 1.3 mpg loss in highway fuel economy in a Toyota Camry when the tires were deflated by 10 psi" and The Rubber Manufacturers Association (RMA) "survey found that properly inflated tires can improve gas mileage by about 3.3%."

 

[dieseldorf]

.....

4. Over-inflated tires -- $200 wasted (minimum)

The Theory: Rounder tires roll easier, creating less work for the engine and therefore, better MPG.

The Facts: Again, this tip is true ... to a point. Over inflated tires will have less friction with the road, which lessens the effort the engine exerts to keep the car rolling, providing slight gas savings. However, overinflated tires will wear out quickly and irregularly, causing you to need early replacements at a cost of about $50 to $100 per tire. What's worse is that the decreased contact with the road increases stopping distances and limits handling capabilities. This all adds up to a large risk in costly accidents and injuries. Even if you are lucky and avoid a collision, it would take a lifetime (which could very well be short if you're riding on bald and bulbous tires) for your fuel savings to negate the cost of four new tires. According to Edmunds.com's testing, the fuel consumption difference between driving with over-inflated tires and tires at the recommended pressure is negligible. Sometimes, despite what GM's recent track record suggests, carmakers do know what they're doing and the recommended settings and levels do provide the best results.

 

[migbro]

Nitrogen provides no benefit whatsoever in passenger car tires.

There are two schools of thought at TDIClub on tire inflation pressure.
1. VW has considered all factors when recommending 33 psi and inflating tires to a higher pressure compromises safety in a somewhat difficult to define but important way.
2. The recommended tire pressure represents a trade-off between ride comfort and handling and fuel economy and should be viewed essentially as a minimum inflation pressure.

I subscribe to point of view #2. In my opinion, the important number is the tire manufacturer's maximum inflation pressure. This number is a cold inflation pressure and takes into account the tire temperature and pressure increase when the tire is in use. So I think that derating the tire manufacturer's maximum inflation pressure by 10% to 15% is a perfectly reasonable approach. After that, it boils down to ride comfort as higher tire inflation pressure does produce a harsher ride.

 

[dieseldorf]

Why aren't we all riding around on tires set at 51psi

.....

We’ve heard folks claim mileage gains by running their tire pressure above the manufacturer’s recommendations. In theory, that makes sense: With more inflation pressure, the tire bulges in the center of the tread and creates a smaller, skinnier contact patch with the road. This should mean less rolling resistance and increased mileage.

What’s more, we know under-inflated tires have a negative effect on fuel economy. The U.S. Department of Energy says that for every 1-psi drop in pressure, you can expect your gas mileage to lower by 0.4 percent.

If under-inflated tires drop your fuel economy, then over-inflated tires must give that mileage a boost—right?

We decided to find out. So, after saying goodbye to half our test car fleet, we took our long-term Honda Fit on an 800-mile road trip from Los Angeles to Phoenix and back again—setting our cruise control to 70 mph except for dips down to 65 mph in central Phoenix and downtown L.A.

The door placard on the Honda recommends 32 psi in all four tires. The sidewall says the maximum pressure for the tires is 50 psi. So for the trip to Arizona, we inflated the tires to 45 psi. We figured 5 psi under that maximum inflation pressure would reduce drag enough to boost our mileage by some measurable amount. Before reaching Phoenix’s West Valley, we were able to travel 394.1 miles, then filled up in Glendale with 9.34 gallons and recorded 42.19 mpg. That’s the best mileage we’ve recorded so far in this car.

Two days later, we dropped the pressure back down to the recommended 32 psi and pointed the Fit’s nose home toward L.A. This time, over the exact same route, at the same speeds, the Fit went 411.3 miles. At the Chevron station in Santa Monica, our Fit drank 9.76 gallons, translating into 42.14 mpg—nearly the exact same mileage.

To invoke the MythBusters, we’d now consider the myth of increased fuel economy from over-inflated tires officially busted. So why didn’t the harder tires with less drag result in better mileage? Well, you’ve got to figure that, at 70 mph or so, the aerodynamic drag of the car’s body is probably outweighing the small improvements the tires gave us.

And we wouldn’t recommend anyone try this one at home either. The vehicle’s handling is compromised when the tires are over-inflated. At 45 psi, the ride was brittle. In fact, the tires were so stiff they nearly vibrated our garage-door opener right off the sun visor. Ouch. –Ben Stewart

Read more: Debunking a Mileage Myth: Can You Really "Pump Up" Your Fuel Economy? - Popular Mechanics

 

[migbro]

.....

Anecdotal. This cute story involves two trips two days apart over a different route (different directions) with undefined wind and temperature conditions AND two fills of less than 10 gallons each at two different gas stations. No meaningful conclusions can be drawn from this.

45 psi - first fill as reported: 394.1 miles, 9.34 gallons ---> 42.19 mpg
32 psi - second fill as reported: 411.3 miles, 9.76 gallons ---> 42.14 mpg

Let's do a little sensitivity analysis, with just a 3% error at each fill.

45 psi - first fill, 3% fill error: 394.1 miles, 9.06 gallons ---> 43.50 mpg
32 psi - second fill, 3% fill error: 411.3 miles, 10.05 gallons ---> 40.91 mpg

 

[ruking]

I have the Cont. Tires on my 2011 Jetta TDI and I checked the Tire Pressure at 40PSI. I see that the Tires are rated at 51PSI.

How high can I run them to better my MPG? Also, I see that in the door Jam of the drives side it states that that the Tires should be at 33PSI.

Is this correct? I'm interested in getting NITROGEN for the Tires. I spoke to a NITROGEN Dealer and he stated that he would do ALL four tires for 50 bucks. How much PSI will go into the tires and he said that he would go by the Sticker that is located on the drivers side door.

Seems to me that 33PSI NITROGEN will be to low....

Long and short on the nitrogen, stay AWAY unless it is free. Even if it is free, you might want to look up what percentage of nitrogen is in normal air.

I got 112,300 miles on a oem set of GY LS-H's. Tires were rotated every app 10,000 miles (which happens to be VW oem recommendations) Truly those tires came in a VERY distant 3rd place, only because VW selected 3 oem tires. On a more general ratings population (tirerack.com), they came in 28/32. Thanks to 4 lower rated GY tires, the GY LS-H's didn't dominate last place. Again as a corollary, I have never heard of anyone posting over 100,000 miles with VW oem TP recommendations of 26 psi. IF so, please FESS UP !!! Now some might see 112,300 miles as a fluke (or other pejorative word or phrase), but I am on the 2nd set and totally different oem and the 2nd set and totally different oem is on a 120 k pace.

So I think that after a certain set of mileages, the attitude really changes. So for example, I took 85% of max tire side wall pressure (or in my case) 38 psi. (37.4 actua/44 psi mswp) as the goal. I think all of us are acquainted in one way or another, how hard this is to do for 4/5 years with wildly varying temperature changes, etc. So truly in fact, I ignored the tp readings at times for 4 months. So that can be a low of 34 psi (77.3%). So the corollary: what are the LOWER to LOWEST PSI's you can get away with and still post very high mileages? Again, the tire oems are very opaque about this issue.

So 85% is still a good target (your case being 43.35 psi) . Some folks would dismiss this for any number of reasons. However they choose to ignore that even VW oem recommendations are a percentage of max side wall pressure !!! Again if your 33 psi is true, it is 64.7% of max side wall pressure. Now don't get me wrong, there are any number of reasons for that specific oem recommendation, but VW (most other oem's also) is/are quite opaque on the issue. My 09 TDI is 35 psi/51 psi (68.6%). My 03 TDI is 26 psi/44psi (59%).

 

[dieseldorf]

Anecdotal.

And i'll agree with you. Their test routine was bordering on meaningless.

Big, broader scope: if there was one or two or three MPGs to be gained by inflating our tires to 50psi, don't you think the tire and auto mfrs would have put it together by now? Seriously?

 

[ruking]

And i'll agree with you. Their test routine was bordering on meaningless.

Big, broader scope: if there was one or two or three MPGs to be gained by inflating our tires to 50psi, don't you think the tire and auto mfrs would have put it together by now? Seriously?

I think pretty obviously.... NOT. Would an oem want a sale @ 112,300 miles or 4 sales @ 30,000 miles?

 

[dieseldorf]

Oh, yeah, how could I forget the conspiracy angle! How foolish of me

 

[migbro]

Oh, yeah, how could I forget the conspiracy angle! How foolish of me

Why is that a conspiracy? Tire manufacturers aim to maximize profits just like any other business. Have you ever asked yourself why you can't buy a tire with 14/32 tread depth instead of 10/32 or 11/32? Why do ALL tire manufacturers use this tread depth for passenger car tires? There's no technical reason why a new tire shouldn't have seven sixteenths of an inch of tread depth.

 

[ruking]

Oh, yeah, how could I forget the conspiracy angle! How foolish of me

Their is NOTHING illegal about that sentiment and/or comment nor implemention nor reality: ergo no conspiracy.

 

[Joe_Meehan]

Generally I agree with almost all of the above. Looking at the available hard facts seems to lead me to the opinion that there is very little hard facts available to us. My education and career was determining what all those numbers meant. More often than not, while they sounded great, they were really not very meaningful. Numbers don't lie but they can be used to infer many things.

In this case I believe one of the best (if not the best) data comes from the tyre companies.

Here is another from the Goodyear site.

Tire Inflation
Proper tire inflation is a key ingredient in driving safety and long tire life. It is wise to check your tire's inflation at least once a month with an accurate tire pressure gauge. Continuous loss of inflation pressure is an indication of a possible tire/wheel assembly problem; consult your tire professional immediately if you encounter this situation. Be sure to check the pressure while the tires are cold, and have not been used recently. If you drive even a mile this will cause your tire pressure to increase and give you an inaccurate reading.

Check Your Air Pressure
Keep your tires properly inflated and you could improve gas mileage by more than $1.50 every time you fill your tank. The recommended tire pressure for your vehicle is located on a sticker inside your driver-side door or noted in your owner's manual.

You might also try the US Department of transportation.

http://www.nhtsa.gov/cars/problems/E...intenances.htm

They say:
You can find the correct tire pressure for your tow vehicle in the ownerís manual or on the tire information placard.

 

[timwagon]

I would put in at least 100 PSI, and only fill with pure hydrogen.

Since hydrogen is the lightest element, you'll float down the highway and probably get over 90 MPG.

 

[pipes p]

i would put in at least 100 psi, and only fill with pure hydrogen.

Since hydrogen is the lightest element, you'll float down the highway and probably get over 90 mpg.

lmfao

 

[Joe_Meehan]

I would put in at least 100 PSI, and only fill with pure hydrogen.

Since hydrogen is the lightest element, you'll float down the highway and probably get over 90 MPG.

Fill up the passenger compartment and you could float over traffic jams.

 

[dieseldorf]

or use it as your yacht on weekends!

 

[timwagon]

Fill up the passenger compartment and you could float over traffic jams.

...and sing Alvin and the Chipmunks songs all day...