Going on a trip, best tire pressure?

[fierodough]

Car: 1999 Beetle TDI

It will be pretty loaded with 4 people and luggage.

It's a 900km drive each way.

What would be the most fuel efficient tire pressure to run (front and back) without risking a blowout?

I just got a fresh tire alignment yesterday.

I'm old school and always set my tires to the recommended PSI on the door.. I understand going a bit higher would improve fuel economy but may also reduce braking capabilities (smaller contact patch) and a bumpier ride.

Thanks in advance!

 

[PressEnter[]]

I don't think you'll experience any safety issues going up to sidewall max pressure, or even 10% over...but at that point the ride may already be unbearably harsh for your passengers. 45 PSI isn't bad in my new Jetta, but in my old car with its old suspension, going over a manhole cover could be teeth-jarring.

 

[Joe_Meehan]

I would recommend 2-4 psi increase.

 

[fierodough]

Thanks guys! My tires are rated for 49psi MAX. I'm running 35psi now. I'm thinking 40psi in all 4 corners. Should be good?

Cheers!

 

[jayb79]

45 in the front 40 in the back, assuming you are running stock 16s blowout will be much less of an issue with more pressure

 

[Whitecloud1]

Always ran 40 PSI

....In my 02 Jetta. With a full load, I would put a couple extra PSI in the rears... 40 front/42 rear YMMV

Let us know what you get for the trip....

 

[ffemtp]

I always run the sidewall max. I am usually alone in the car so I make a decision to trade quality of ride for economy. In your case you will have 4 people so help dampen the higher pressures. You have a nice opportunity to test this out - run your current pressure on the way out, then run side wall max on the return trip. See for yourself which works best for you....

Have a good trip!

 

[fruitcakesa]

I do 39 psi all around

 

[tikal]

80% to 90% of the maximum sidewall tire pressure.

 

[fabed23]

I would go at about 40psi. I drove a pretty loaded car across the southeast and was a pleasant ride

 

[Joe_Meehan]

80% to 90% of the maximum sidewall tire pressure.

While there is nothing wrong with that, but you really need to consider that there may be a great difference in what might be a good safe pressure and the max on the sidewall.

Other than doing some serious road testing under different temps, road conditions etc. I suggest you stick with a pressure that meets both the max (and minimum) and the recommendations for both the car and the tyres.

 

[fierodough]

45 in the front 40 in the back, assuming you are running stock 16s blowout will be much less of an issue with more pressure

I'm running 225/45R17 94W. So not stock.

 

[jayb79]

Still should be fine. Less chance of pinching it with more air pressure. Low profile tires usually have a pothole failure because the rim cuts into the sidewall.

 

[tikal]

While there is nothing wrong with that, but you really need to consider that there may be a great difference in what might be a good safe pressure and the max on the sidewall.

Other than doing some serious road testing under different temps, road conditions etc. I suggest you stick with a pressure that meets both the max (and minimum) and the recommendations for both the car and the tyres.

I do not disagree with the above statement.

 

[fierodough]

Back from my road trip! thanks for the advice guys! Not sure if my data will be helpful to anyone but here it is:

@ 35 PSI, mixed city and highway I used to average 37.9 MPG as per Fuelly.
@ 41 PSI, mostly highway at 100Km/h (60 MPH) I averaged 45.2 MPG as per Fuelly.

The ride was acceptable, not much harsher than at 35 PSI. Handling did not really seem to change but I was not pushing the car to its limits.

I did notice a few interesting things on my trip.. In the US (specifically Shell in Boston MA. Diesel is colored or tinted yellow? Here in Ontario, diesel is pretty much clear.
And what is with this stupid law in the US that your "worst" tires have to be in the front?? My front tires had some camber wear. I got an alignment and got new tires installed at Pepboys. They refused to install the tires in the front. They rotated my back tires to the front and mounted the new tires in the back. ***??

Anyhow, that was my trip!

 

[roadhard1960]

http://www.youtube.com/watch?v=--Hb5kQCaTg

 

[fierodough]

http://www.youtube.com/watch?v=--Hb5kQCaTg

I guess they don't take into account that the front does 90% of the braking. More accidents are from collisions than from fishtailing.

The owner should have the final say. As long as the thread depth is legal, put them where you want.

 

[Ski in NC]

I run my Jetta mk4 at 40 all around. Seems like a good compromise, tried 45psi and every little crack in the pavement came through. Also, pulling into my shop with wet tires I could see contact patch was not full width. At 40, the whole tread is contacting and ride is ok.

 

[Mike in Anchorage]

And what is with this stupid law in the US that your "worst" tires have to be in the front?? My front tires had some camber wear. I got an alignment and got new tires installed at Pepboys. They refused to install the tires in the front. They rotated my back tires to the front and mounted the new tires in the back. ***??

This is hardly a law. You got advice from some simplistic sales folks. As the others say, do what you feel comfortable with. I agree that on a road trip with multiple occupants, I'll have the best tires on the front of the car.

 

[MikeMars]

... And what is with this stupid law in the US that your "worst" tires have to be in the front?? ...

Supposed to be safer that way (due to understeer versus oversteer I think).

 

[Thermo1223]

This is hardly a law. You got advice from some simplistic sales folks. As the others say, do what you feel comfortable with. I agree that on a road trip with multiple occupants, I'll have the best tires on the front of the car.

Technically it is an unwritten law, it was mandated to some extent after the Firestone fiasco with the tire industry. We all know had nothing to do with this situation but someone just figured they knew best.
No tire dealer I've ever been sans a few independents will put only 2 new tires on the front. They don't want the liability if you decide to sue them for not making your car "as safe as possible". Why? People don't drive safe, they speed, and when they take the corner to fast they will fishtail with bald tires on the back. Since we are really idiots in that regard according to some we won't be able to recover from said spin.
I am not saying I agree or disagree but it is a fact now.
It is safer if you are an inexperience driver or just a fool but if you know what you & the car are capable of, well then you make the decision.