Two Questions that I've been curious about


#1
  1. From a brake pad longevity stand point. Is it better to press the brake harder for a shorter period of time or lightly ride the brakes?

  2. My car appears to get its best gas mileage at around 2500 rpm. In town that is attained by leaving it in 4th gear ( manual tranny ) Shifting to 5th drops the rpm down to about 1600. So from a fuel economy stand point would it be better to leave it in 4th or drop it into 5th?

Thanks in advance.
Bill


#2

My philosophy is anytime you are using your brakes, you are wasting money. I try to look ahead and adjust my speed using the throttle only to minimize the use of brakes. Leave plenty of room for slowing down and often a complete stop is not necessary.

But the longer lighter touch I believe will take off less brake material, but it has the affect of leaving residues on the rotor which leads to brake pedal shuddering (pulsing). The higher heat generated by the harder stop burns off the residues so I think a mix of the two is best. Mostly the longer stops but an occasional hard stop when you first start to feel the pedal pulsing.

Generally the highest gear usually gets you the best gas mileage, but there are so many factors involved including the cam profile, bore/stroke ratio, gear ratios, combustion chamber design etc. that there is no one rule that applies to all.


#3

As above, I have what I call my own hybrid system-which is try to drive with bare minimum brake use. Braking hard not only wears the brakes faster, also has bad effect on suspension, engine and transmission mounts and passengers :slight_smile:

I have the gas mileage gizmo and less than 2000 RPM seems to be the sweet spot for my car, so it varies. You have to use the correct gear for speed/incline though. Clutch and transmission repairs are more costly than a few gallons of gas.


#4

There are other factors besides the force of the pads on the rotors that slow the car down. For example, if you just took your foot off the gas you’d eventually stop without ever using the brakes at all. I think the longer the distance you take to slow down, the less you’ll wear the pads, as the other factors will contribute a higher % to the stopping force.

Given a desired speed, whether it is better mpg-wise to use 4th or 5th is dependent on the design of the power train. Every make/model/year is different.


#5

For most cars, driving at low rpm with the throttle opened as much as appropriate is the most efficient because pumping loss and friction loss are minimized. However, you can also waste fuel when your rpm is too low. That’s when the combusted fuel and air stay inside the cylinder for too long and a significant part of the fuel’s energy heats up the coolant instead of expanding the air. This thermal loss is more than the efficiency gain you get with the low rpm. To find your optimal rpm, you have to experiment over a few tanks of gas. However, don’t be a cheapskate when climbing a hill. Use a gear lower than necessary to get the hot air out and the coolant to circulate quickly. Using a high gear for a prolong climb can overheat the engine.


#6
So from a fuel economy stand point would it be better to leave it in 4th or drop it into 5th?

It’s best to keep it in the highest gear possible, but not too high that the engine is straining or knocking (which can cause serious engine damage). 5th gear is not usually for city driving.

For example, if you just took your foot off the gas you'd eventually stop without ever using the brakes at all. I think the longer the distance you take to slow down, the less you'll wear the pads,

And the more you’ll p*ss off the people behind you.


#7

I think it is good to be aware of your surroundings and use the brakes as little as possible. Just don’t take this to extremes and forget that other people behind you may be trying to get to work on time. As for what gear to use, 1,600 RPM is fine for situations which require little to no power, such as maintaining your speed on a slight downhill, but asking the engine to put out a lot of torque at 1,600 RPM is hard on bearings, cylinder walls, and piston rings.


#8

Good questions. It really brings to light why many computer controlled autos get better mileage then manuals. There are general rules for best economy and using the highest gear but there are times when you shouldn’t.

To minimize braking whether it be a manual or standard, I would shift it into the most appropriate gear for the speed limit to ensure their is always some engine braking.

Even if the car will easily cruise in top gear at 35 mph on level ground, it goes into a lower gear, especially where speed limits are well enforced. There comes a time when max mileage takes a back seat to speeding tickets. Interesting but my new truck with an auto will downshift “automatically and aggressively” under heavy braking and when the speed crawls above what the cruise is set at. Still, the car gets better mileage then a manual. That tells me that using lower gears often and discriminatory where possible instead of always being in the highest gear…can’t hurt too much and is safer.


#9

Another negative for a CVT. When I drive at a steady 20-30 MPH, the CVT stays in the “top gear” and the RPM is around 1000. I can’t change that except by manually downshifting, in which case the RPMs jump to 3000, too high.

So I get good gas mileage, but the car jerks and can’t hold a steady speed.

(2015 Forester)


#10

I have no problem holding a steady speed with my Insight’s CVT.