Tire Pressure Question
 

So...

My 1999 Suzuki Swift says in the manual to fill the tires too 32 psi, and my front tires have a max of 35 PSI and my rear are around 50 psi.

...What should I fill them too for better fuel economy?

Welcome to the fourm!

I would start with 40-44PSI or max sidewall if they are lower than that.

For other mod ideas take a look at the wiki: Main Page - EcoModder

Thanks!

So I should go over the max stated on the front tires (35)?

Can I set the tires at different pressures (higher for the back, lower for the front)?

Also, is the max sidewall different from the max PSI listed on the tire?

What tire has a max side wall of only 35PSI? You can go higher but you run risks of handling issues, and tire wear. Try it and see if it helps. If the back is rated for higher I would try them all at 40PSI.

The fronts are rated at 35. I'll try them all at 35 first, and then try to bring them up too around 40.

As a Noob, you have not experienced the sometimes acrimonious discussions concerning inflation pressure in tires. Here's what we agree on:

Increasing inflation pressure:

1) Improves fuel economy
2) Hurts ride quality

Here's what we have disagreement on:

Increasing inflation pressure:

3) Hurts tire wear
4) Hurts traction (This can be subdivided into dry traction, wet traction, hydroplaning resistance, and snow traction)
5) Increases the risk of impact damage
6) Increases the risk of vehicle rollover

You should read the discussion threads so you get a sense of the degree of disagreement and why there is disagreement. That way you can make up your own mind.

I've increased the tire pressure to 44psi and saw better mpgs
but once @ 50psi or so, bounces to much with **** on the road it actually hurt my mpgs

Personally I would never go over the sidewall max. If you want to go over the 35psi you're sidewalls say is max, then get new sidewalls.

Secondly, while we're talking replacing front tyres, always put new tyres on the back (unless you're chaning all 4), regardless of wether the car is FWD, RWD or 4x4. Rear end skids can be fatal, front end skids are much much safer.. unless your name is michael schumacher.

Derek
(running 45psi all round on 50psi max sidewalls... oh and my owners manual for my merc says if you pump the tyres up for a max load, you can safely drive after unloading without dropping pressures.. max load pressure at rear is 50% higher than min pressure)

put the front tires on the back and the backs on the front. The front should have more weight on it and would take the extra pressure better. I would swap tires and run 45 front and 35 rear.

I agree.

i know this is a fuel econ forum but as a certified mechanic youre asking for a blowout. theres gonna have to be a compromise between safety and fuel economy if you value your life and those around you.

i drive a jeep liberty and have already increased the mpg 3mpg city and 2mpg highway just by doing my own little bout of mods. in no way would i ever change the psi of my tires to other than what the factory recommends

List of fallacious argument techniques

(picks up a stick and sets about belaboring the cadaverous equine)

http://i144.photobucket.com/albums/r...tdeadhorse.gif

Again, please read the discussions on this topic. As with most dynamic systems, there is probably not going to be a simple blanket answer that applies in all situations, regardless whether it's issued by the manufacturer or anyone else.

As the Ford Explorer/Firestone debacle indicated, low pressures are probably more likely to lead to tire failure, crash, death & dismemberment, than are high pressures.

Running the manufacturer's recommended pressure will only optimize one thing: your ability to blame the manufacturer if something goes wrong.

For best economy or smoothest ride or longest tire wear or "safety" (best handling on snow? Best handling (turning or braking?) on dry pavement? Best wet traction? Best impact resistance? Best heat resistance?) it's very unlikely that any single pressure will be optimal.

Certainly.
But the rated max. psi is what the tyres are constructed and certified for.

Well, on my Volvo those recommendations are blatantly wrong.

The recommended pressure for light loads - 2.3bar / 33psi - is way too low, leading to increased tyre wear on the shoulders, tramlining and an uncertain feel to the steering.
Originally, I started increasing the pressure to cure these handling and wear issues, as recommended by some folks on a car forum.
That brought me to 41 psi - still having the uneven wear issue, though reduced.

After joining ecomodder, I increased the pressure to sidewall max, 51 psi.
Guess what, the uneven wear is gone.
No alignment work has been done on the car.


I probably picked up a rubber fetish in my motorcycling years, as I fairly often feel the tyre temperature when checking them for signs of wear.
With the increased pressure and hypermiling, the tyres are a lot cooler than they used to be at lower pressures.
Yes, so much cooler that you can actually, unscientifically, feel it ...

just because you can do it doesnt mean its the smartest thing to do. like with many things on cars, the optimal tire pressure is what the factory writes on the inside of the b-pillar near the drivers seat. the recommended tire inflation chart there (for my libby, its 33psi all around) is the best compromise between safety, ride comfort, handling, and fuel economy. its posted at that number because psi fluctuates and the rec. pressure is the middle ground for that. to say that its purely put there so you can blame the manufacturer is one of the most absurd statements ive heard in a while. NO company wants to take the blame for someones mistakes so they put that there to avoid conflict and do everything they can to not be liable.

think about it this way:

youre not saving enough money from overinflating ur rubbers to offset the medical expenses when they blow out and you hit another car.

and believe me, im all for this website and the message it advocates (maximizing the efficiency of your vehicle) but i draw the line at risking my life and others around me

If I have a tire blow out by running it at the sidewall max, then I'm going after the tire manufacturer. Going above the max is where it gets sketchy, but at the max, if you have a problem, it is probably from a defective tire. It says "max", not "max, but you'll probably have a blowout".

I run 44psi in my 44psi max sidewall tires, no problems.

I think there is plenty of data on this site, as well as others, to conclude it not only can be done safely, but IS being done safely by many, with benefits of increased tire wear, increased tire life, better hydroplaning resistance and better mileage.

The increase in harshness of ride only shows that the majority of vehicles on the road have suspension that is horribly calibrated, ie- CHEAP.
Some Penske's or Ohlins would help the ride immensely.

No, it is not optimal.
Then again, neither is running sidewall max on my car/tyre combination, as the ride is fairly harsh on an unloaden car.

Having increased the pressure gradually, I'd say 3bar / 43.5 psi is the optimum instead of 2.3bar / 33.5psi on my car.
It retains most of the comfort, yet returns good mileage.


Chances are good you'll get to see increases in the recommended pressures over the coming years as fuel efficiency becomes a more pressing need.
It's an easy win.


Actually, the (cold) pressure rating takes into account that the tyre will heat up during use.
Hypermiling, your tyres won't heat up much.


Using rated max is not overinflating the tyres.
Tyres seldom blow out because of too high pressure.

Typically, they blow out at low pressure as soft tyres heat up a lot more than when properly or higher inflated; sidewall deformations are far bigger @ low pressure, and can lead to structural failure of the tyre's core.


Same here.

At 24,000 miles on the Michelin X replacement tires on my Civic VX, the tread wear measured 5% of the available tread. Wear was even across the tread and I even drove them on ice with that pressure and survived.
That was at 44 PSI, the same pressure I have my current tires on my Altima.
If you check previous threads or the net in general, a lot of Police forces use similar pressures and if you are carrying a maximum load the pressure recommendations are higher in some cases. I have heard of tires lasting over 100k miles when driven the way hyper milers do with sidewall max pressures.

Try measuring your coasting distance, then try it with sidewall max pressure. I have driven over 70k miles with tires at sidewall max without any issues, and I will continue to do so because it lowers heat retention, increases tire life, saves gas, and does not significantly affect handling. In fact it may improve it, in case I ever need to use the maximum capability.

regards
Mech

regards
Mech