Originally Posted by
ron.jace
You don't need one. If you are renting a somewhat decent car you will be fine with it. I been to the summit in a Ford Fusion in 2009 and Saturn Vue in 2008. You don't need an SUV to drive to the top. It's a simple dirt road pretty much any car will get to the top. When coming back down shift the transmission into second gear (both automatic and manual cars can do this). Even if you don't shift down and just use the breaks on the way down you will still be fine. There is no point spending extra money on getting an SUV just to get to the summit.
Worst advice ever.
I have personally seen cars and 4wd vehicles that had crashed coming down the Mauna Kea summit road. I have seen vehicles in the visitor center parking lot with smoke pouring out of the wheel wells due to over using the brakes.
I have been to the summit 100+ times over the past 12 years. Always in a 4wd pickup. On the un-paved section, I use 4-low range and 2nd gear. This allows me to use both my brakes and my transmission to control the downhill speed. On the paved sections I use 2nd or 1st in 2wd, and use my brakes as necessary.
What happens if you just use brakes downhill at altitude?
The friction of the brakes creates lots of heat.
The heat is conducted to the brake system lines, caliper parts, and wheel cylinders.
This heat, combined with the low atmospheric pressure at high altitude, causes the brake fluid to boil off. *Liquids boil at lower temperatures at high altitudes. Refer to the baking instructions of a cake mix in your pantry. You will see separate instructions for folks who live at higher altitudes.
So now your brake lines contain a
gas instead of a liquid. This results in soft, mushy brakes, and if you continue to do this, you will lose the stopping power of the brakes completely.
Its the density of
liquid brake fluid that allows sufficient pressure to squeeze the brake calipers, and push out the wheel cylinders. When you replace part/all of this liquid with a gas, you cannot reach sufficient pressures to grip the brake discs/drums.
Nuff said.