The lunacy of the tire shops

[kunkstyle]

So after a loss of almost 100km a tank from my usual gas mileage, I thought it might be an idea to check the tire pressure. Lo and behold, after getting my winter tires put on, the shop (which will remain un-named for now) set the tire pressure to 50 psi.Max on the tire is 44, and the OEM tires were 36/32. I've let the pressure out since. Should I set them back to the OEM pressure? Would over inflation lead to that poor of mileage? I always thought over-inflation would have the reverse effect. Opinions/comments/help?

[zionzr2]

over inflation usually yields better mileage and a harsher ride and premature wear.A little over oem is not bad but you definalty should stay under tires max Cold pressure. also remember even after the car has been driven a mile the tires are no longer considered cold.

[Mavrik]

100km a tank? I suffered that every winter. would go from 500-600km a tank to 300-400 a tank in the winter. I doubt it had to do with my tire inflation and I doubt 50psi (though bad for your tires) would decrease it by that much.

[kunkstyle]

Quote, originally posted by Mavrik »100km a tank? I suffered that every winter. would go from 500-600km a tank to 300-400 a tank in the winter.Sorry should have clarified; I'm comparing it to last winter's results. I had never actually hit over 10L/100km until now. And it's only the beginning of winter

[mistertwo]

yay for winter gas.. my mileage has been crap too. And yikes! overinflated tires is risky business.

[kunkstyle]

Quote, originally posted by mistertwo »yay for winter gas.. my mileage has been crap too. I thought that only certain stations used a winter blend in Canada (husky & mohawk)? That's why I always fill up @ Shell. Quote, originally posted by mistertwo »And yikes! overinflated tires is risky business. Thanks for the heads up - I'll make sure they're back in operating range. I should have checked them as soon as they were out of the shop.

[Mavrik]

Well if its 100km less then what you got last winter I'd say there could be something else wrong. When is the last time you changed your air filter or got a fuel injector flush? Might just be due for a mini tune up.

[kunkstyle]

Hmmm, CAI installed in October, so the filter shouldn't be a problem (unless that's what's causing the drop in winter?)Fuel injector cleaner would have been done in the summer (6 months ago), and the oil was just changed.I've got a bad ground somewhere which I'm attacking this week, but I can't imagine that changing it that drastically.

[Mavrik]

Well I know the cold air intake in the winter cold weather hurt my fuel economy. did you have that cai on last winter? This could be of how I drive but I got about 100km less a tank with it on then I did with it off. So that really hurt in the winter time and with running the car to warm it up in the mornings or after work.Your injector flush the bottle dumped into the tank or the flush where a bottle is air pressured and connected to your fuel system for 20 mins or so?

[kunkstyle]

Dumped into the tank. Didn't know there was another way to do it. Maybe I should take it in for a fuel system clean?Nope, didn't have the CAI on last winter, although I don't usually drive a whole lot different with it on (there's some tanks when I do, and take that into account.)

[mistertwo]

Oh I didnt know that some gas stations dont use a winter blend.. I think pretty much everywhere around me does. Opps!and about the tire pressure:Maintaining correct tire inflation pressure helps optimize tire performance and fuel economy. Correct tire inflation pressure allows drivers to experience tire comfort, durability and performance designed to match the needs of their vehicles. Tire deflection (the tread and sidewall flexing where the tread comes into contact with the road) will remain as originally designed and excessive sidewall flexing and tread squirm will be avoided. Heat buildup will be managed and rolling resistance will be appropriate. Proper tire inflation pressure also stabilizes the tire's structure, blending the tire's responsiveness, traction and handling.Disadvantages of UnderinflationAn underinflated tire can't maintain its shape and becomes flatter than intended while in contact with the road. If a vehicle's tires are underinflated by only 6 psi it could weaken the tire's internal structure and eventually lead to tire failure. Lower inflation pressures will allow more deflection as the tire rolls. This will build up more internal heat, increase rolling resistance (causing a reduction in fuel economy of up to 5%) and reduce the tire's tread life by as much as 25% while increasing the probability of irregular treadwear. Drivers would also find a noteworthy loss of steering precision and cornering stability. While 6 psi doesn't seem excessively low, it typically represents about 20% of a passenger car tire's recommended pressure.Disadvantages of OverinflationAn overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when encountering potholes or debris in the road, as well as experience irregular tread wear. Higher inflated tires cannot isolate road irregularities as well causing the vehicle to ride harsher and transmit more noise into its interior. However, higher inflation pressures reduce rolling resistance slightly and typically provide a slight improvement in steering response and cornering stability. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures.

[kunkstyle]

Quote, originally posted by mistertwo »Oh I didnt know that some gas stations dont use a winter blend.. I think pretty much everywhere around me does. Opps! They very well might all use a winter blend south of the 49. I'm not too sure. Here the stations advertise if they've got an ethanol/winter blend, so that's what makes me assume not all of them use it here.Thanks for the inflation info!

[keithvibe]

i too had a simmilar problem with a shop... had my wifes car inspected.. they checked the tire pressure and "adjusted" it as they said... to 55psi... her cavalier runs at 32-33psishe questioned it when she said the car road funny and that she went threw an entire week an only used 1/3 of a tank of gas instead of the usual 3/4 of a tank. I did the math back then when it happened... that tank of gas she got close to 45mpg... when she normal gets 25-30.. After I reset the tires to the correct pressure you can be dame sure I gave the shop two ear fulls.