I'm concerned about safety--not so much ride comfort or mpg. Normal tire pressure is 35 psi in the front and 33 psi in the rear. BUT, the roads are icy and I have the studded tires installed now. I just got the 10,000 mile service and discovered that the rear tires were now 35 psi. The dealer said this was better in cold weather. Wouldn't lower pressure in the rear give me better traction there? Can someone detail/theorize why the dealer is right? Also, the dealer added hydraulic fluid to the brake master cylinder reservoir saying it was normal. During normal brake usage and with no brake leakage why would the reservoir loose fluid? I'm trying to learn to trust my Toyota dealer but I'm having some trouble with doing this. Thanks.
Fluid in the brake reservoir falls as brake pads wear and the pistons in the disk brake calipers are left more extended. The calipers are in fact holding the "missing" fluid. Various mechanics have handled that differently on different cars of mine. I believe it is best practice not to refill so that you don't have fluid spills when the calipers are repositioned to allow the installation of new pads. The tire pressure is hocus-pocus in my opinion. There are valid reasons to adjust tire pressure. I think 40/38 gives me the best handling, wet traction and snow traction without subjecting the tires to too much pothole hazard. If the dealer did not leave a 2 psi differential between front and rear, they don't know what they are talking about, at least in this area, and their opinions can be disregarded.
My Goodyear Nordic studded snow tires have a higher load rating than the Michelin Harmony I usually run. I like to leave them at 30-32 with 2 psi less in the rear From the post I'm unclear where you live, what sort of winter tires you're running, and how old your Prius is. I've never added brake fluid to my '04 How are the tires working in the weather? CBC Marketplace has run another show this week on winter tires. Sadly, the tire companies are still telling customers that "all season" is good for winter. If you have broadband, the show is here CBC.ca - Marketplace - Don't rent a car this February without winter tires. Oh, wait...
-Most- tire manufacturers and tire engineers will tell you to use higher pressure for better traction. It helps the tire clear better (get the excess snow out of the tread). Within reason, of course. If you put in enough pressure most tires will balloon, reducing the tread on the road. This requires a lot, however, usually above the max. recommended pressure. Based on a tire engineers recommendation I like to run a bit under the max pressure to ensure I don't damage the tire on sharp road irregularities. I run my Nokian WRs at 40PSI front and 38 PSI rear. I get very good traction, both on ice and in snow. They also work very well on dry roads. If I remember correctly, they are rated for 50 something max pressure.
When we run studs on our hybrid SUV tire pressure, versus MPG goes out the window. We normally run appz 40lbs all the way around in the summer. But shiny slick ice? All bets are off. We just worry about getting from point A to point B and keep the pressure at 35.
I once read on one of these threads that increasing the tire pressure with the OEM Goodyear tires helps traction in winter weather. I tried this and found it does improve the traction in winter weather.
As mine is about 4 months old, I'm still on the factory Goodyear Integras. I pump them up to 42 front, 40 rear. Im positive this makes a very noticable difference in mileage. I also just put in Mobil 1 synthetic for the last oil change (the first change, 6000 mi!) and i think that made a huge difference in fuel economy.
the brake reservoir system is designed so that when both the front brakes and the rear brakes are worn out completely, the fluid will not be below the "minimum" mark. if the level is above "minimum" then no fluid needs to be added. it's an indicator of brake wear over a long period of time, or a leak. fluid should never be added until it drops below the "minimum" mark. brakes should not be worn out at 10k miles. you NEVER EVER EVER just add fluid and shrug your shoulders. unless it was some dumb tech adding more fluid to the system than was really necessary. too much fluid makes a mess when you go to compress a caliper piston.
Given the very slow rate of Prius brake wear, any noticeable reduction in the fluid reservoir level would send me right under the car in search of slow leaks. If you have them, it is very important to find and correct them.
