high mph then glide

[trebuchet03]

I agree with rh77 - and it really does depends on conditions.

For braking ability - the max force you can place is related to the weight of your vehicle and the coefficient of static friction (which is related to your tire compound and road surface).

Considering the road doesn't really change (so your static friction coefficient will remain nearly constant) - increasing the weight of the vehicle increases the amount of braking force you can apply before the wheels start skidding.

Which brings me to... Bodies that are skidding have a different friction coefficient (coefficient of dynamic friction) that is ALWAYS lower than static friction. This is why it's so difficult to regain control of a skidding vehicle. This is why ABS will stop a vehicle much faster than a vehicle that's skidding even though the ABS vehicle won't have the brakes on full all the time.

I'd bet their comparing an emergency stop condition - where an empty truck will skid while a heavier truck will be able to maintain traction for a little longer. But has rh77 said - brakes will only go so far when it comes to large masses of stuff to stop, there's just a lot of energy/momentum there.

[skewbe]

Originally Posted by trebuchet03

...This is why ABS will stop a vehicle much faster than a vehicle that's skidding even though the ABS vehicle won't have the brakes on full all the time...

I'm not sure that holds true for dry pavement, but I'm biased against automatic brakes and transmissions and all that other drive my car for me stuff too. I like driving, especially in winter.

http://www-nrd.nhtsa.dot.gov/vrtc/ca...99-01-1288.pdf

[trebuchet03]

Originally Posted by skewbe

I'm not sure that holds true for dry pavement,

The dry pavement findings were found not to be statistically significant which does not mean you can say "there's no difference." The problem with statistic analysis is that you can't use it to find a zero difference between two sets - regardless of control. At the same time, a statistically significant finding doesn't mean there's a practical significance (large visibility in the real world)


I, for one, will continue using ABS - it's saved my butt once already (wet pavement) But really, at the heart of it - the purpose of ABS is to increase brake steer traction (a kid runs in front of you sorta thing) - straight line stopping isn't real world emergency stopping I can't think of anyone that can pump their brakes at 60Hz or pump the one offending wheel :/

[omgwtfbyobbq]

Yeah, AFAIK there's no way a human can compete with ABS since it pumps the brakes hundreds of times during which a human can only pump a few times. It can keep a car on the threshold for more maximal braking way better than a human can.

Regarding unloaded versus loaded semi braking, like rh77 said, w/o a load in back, the rear brakes won't do nearly as much as they are designed to since there isn't nearly as much weight on them and the fronts may get more weight on them than they are designed to and lock up/skid. I don't know if the distance in an unloaded truck would actually be greater than a loaded one, but the distance in an unloaded truck with brake bias setup for a greater load would likely be greater than if it was setup for no load.

[1993CivicVX]

I think the VX's sweet spot with P&G is pulse 35 glide 25 or pulse 40mph glide to 29mph which is prolly in the neighborhood of 90+mpg if finagled just right. (Pure conjecture, but I wouldn't be surprised.)

[2TonJellyBean]

VX, what would be the approximate load on the pulse?

[1993CivicVX]

Thanks for the link Larry. I only saw now that you posted. Haven't visited this thread in awhile. I've driven my mom's Prius quite a bit.

The article said: Most Prius drivers are delightedly familiar with "glide" or "stealth"
mode, where the car moves solely under electric power without the engine
running. Electric traction and the ability to bring the engine in and
out of play based on go-pedal demand is one of the major hallmarks of
such a hybrid system, and contributes to its ability to use very little
fuel at lower speeds with a foot technique called "pulse & glide". But
alas, this game seems to cease at 42 miles per hour, when the engine comes
on and stays on as long as the car is going faster than that. For most
people, mileage suffers somewhat since even at idle or lower power demand,
the engine is consuming *some* fuel. The concept of a good "glide" seems
to be inaccessible at those higher speeds.

The article says that after 42mph the engine comes on. Not always. I've elec motored up a hill up to 50mph with no engine. This was after going down a very long, winding hill where the battery pack was positively topped off. But other times I've gotten the prius to go over 42mph without the engine coming on. And as far as I know, when you take off the gas at any speed, the engine turns off, but you get the drag of the auto battery recharge (since the prius doesn't automatically go into neutral) Very interesting and informative article, tho. So when you put in neutral the ICE is running? Strange.