Reducing weight

[cRiPpLe_rOoStEr]

Odd enough, all-around drum brakes are still prefered by most commercial truck operators in Brazil, even for severe off-road usage. Sealing might've improved considerably through the last decades, which may render some new drum brakes more reliable than their older counterparts...

[Talos Woten]

Originally Posted by Nathan jones

Drilling brake disks/rotors or lathed for weight, has anybody done it themselves?

For those interested, we can estimate how much we power we gain from weight reduction.

Let's use my 2009 Toyota Prius as an example. At highway speeds (65mph ~ 29m/s) the car needs around 10kW+ of power to maintain speed. Around 7kW of that is to overcome aero drag (unmodded), 3kW is rolling resistance (stock tires), and + is whatever else we have on. This is at least 250W (just the car circuitry being powered) but can easily be 2kW with AC cranking, radio blaring, headlights on, etc.

So right off the bat, we see that rolling resistance is a major factor in power consumption. Even in a highly optimized car like the Prius, it's a quarter to a third of the total. It's not uncommon in other vehicles for it to be nearly half of the power loss even at cruising speeds. This is why low rolling resistance tires have such a profound impact on fuel economy.

Returning to the estimation, rolling resistance is mostly linear with weight (barring subtleties like heat and tire chemistry changes with use). The Prius is around 3,000 lbs, which means that for it each pound of weight reduction results in one watt less running power needed. This conversion will be different for each vehicle, but it's going to be around that ballpark. 1 lb = x Watts, where x is small.

So a few pounds here or there isn't significant, but serious changes are. I ripped out around 500 lbs from Champrius and it improved her mpg by almost 3%, as expected. And when I camp I add on +900 lbs of gear and I instead see a -7%+ worsening of FE.

Even if the weight you are trying to reduce is rotating, unsprung, etc. it has a small effect on power consumption. Of course, it has a huge effect on things like acceleration, handling, braking, and other performance aspects. But as far as fuel economy goes, it's still the same order of magnitude.

By the way, I just recently changed my headlight to 15W LEDs from 60W Halogens. Not only are they brighter and safer, that's the equivalent of dropping 90 lbs from the vehicle at nighttime. There's lots of ways to improve fuel economy, and by converting everything into the same scale (say power wattage) we can then rate how effective different approaches will be.

If you are riding the bleeding edge to reduce your brakes by 20 lbs... I'd say there are easier, safer ways to get an extra 20W of power in your vehicle.

[Ecky]

Originally Posted by Talos Woten

If you are riding the bleeding edge to reduce your brakes by 20 lbs... I'd say there are easier, safer ways to get an extra 20W of power in your vehicle.

That's a fair point. As you say, economy is not the only thing affected by weight, but brakes are probably not the first place to look if economy is your goal.

[65whitelion]

Originally Posted by Ecky

That's a fair point. As you say, economy is not the only thing affected by weight, but brakes are probably not the first place to look if economy is your goal.

So long as your brakes are in good order....not dragging, releasing properly after use.
Which system (drum vs disc ) has the most parasitic loss.?

[Ecky]

Originally Posted by 65whitelion

So long as your brakes are in good order....not dragging, releasing properly after use.
Which system (drum vs disc ) has the most parasitic loss.?

I'm almost certain discs have the most parasitic loss. They generally don't have a way to retract the pads from the friction surface safety braking.

[65whitelion]

https://www.autoevolution.com/news/w...vs-149568.html
"For his part, VW spokesman Jochen Tekotte motivates the company’s decision by citing the lower rolling resistance of the drum brake setup, its superior corrosion resistance, and effectiveness."
Goes on to talk about use with re-gen braking

[65whitelion]

....or, if you want a headache! ;-)

https://www.mathworks.com/help/autob...inalwheel.html

[ps2fixer]

Originally Posted by Ecky

I'm almost certain discs have the most parasitic loss. They generally don't have a way to retract the pads from the friction surface safety braking.

If adjusted right, I suspect disc and drum are very similar for parasitic losses. For long term issues and such, I'd say disc is more likely to cause a drag over drum. Normally drums "go out of adjustment" and you have to press the brake pedal farther for the rear shoes to touch the drum. When adjusted up, they should just barely have resistance.

Disc brakes on the other hand sometimes do have a spring to push the pads out a little, but the slides need to be in perfect working order, good caliper pin slides if it's a caliper with pistons on one side. I'm not sure how the 4 and 6 piston calipers are setup for the return system, but my Lexus LS400 front brakes have a spring that clips into the pads to help seperate them a little after braking. Here's a pic of the little springs, I suspect some mechanics would just throw them in the trash since they probably don't do a whole lot. The brakes are pretty undersized in that car too. I swapped the front rotors and clipers with bracket out from a 94, around 1 inch larger disc. It helped a little with braking, but it really needs a 4 piston caliper or similar since it's a large car. My prius on the other hand has very responsive brakes... did I mention the LS400 is 4 wheel disc, and the prius has rear drum =).

[cRiPpLe_rOoStEr]

Originally Posted by ps2fixer

Normally drums "go out of adjustment" and you have to press the brake pedal farther for the rear shoes to touch the drum.

Not anymore. Self-adjusting drums have been fitted since late '60s.

[ps2fixer]

Originally Posted by cRiPpLe_rOoStEr

Not anymore. Self-adjusting drums have been fitted since late '60s.

Still happens all the time up here in Michigan, rust doesn't help anything lol. I just adjusted the brakes up on my 1995 F250, was a good 5 turns out of adjustment on each side, pedal much higher now.

Even better, look at a Toyota echo rear drum brakes, there's no adjustment! You adjust them by replacing the shoes, pretty crazy design, super budget/cheap car.