Reducing weight
 

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

Also aluminum fuel tank, maybe to 4 gallon?

I understand if this thread is deleted for lack of substance..

Drilling rotors takes a very miniscule amount of mass out of them. Lathing the hats might be substantial but I am guessing cast iron hats are crack prone if they are too thin which is why manufacturers prefer casting them thicker?

I personally would much rather have a larger fuel tank that is heavier. Stopping for fuel is not a good use of time.

Reducing weight to make your car faster makes sense but it doesn't really save a lot of fuel for the effort.

A full tank lasts me 3-4 weeks so going down to 25 litres would still be very efficient timewise and even though E5 is relatively light. Thanks for the reply about the rotors. I also don't have a lathe or pillar drill...

https://ecomodder.com/forum/member-f...3-100-0884.jpg

I may or may not've refilled on the side of the road with the motor idling. Rather than drilling the rotors I cryogenically tempered them to extend the service life.

https://ecomodder.com/forum/member-f...5-100-0201.jpg

You want carbon ceramic rotors.

Thanks yes, freezing cast is really backwards for a density reduction technique. Or at worst floating discs with rivets. For now I will skim down 25%, crossdrill then look at ceramics when I have more time 👍

Are ceramic rotors generally available or is this thread about a specific application?

If it's backwards, you would find something to disagree with here:
Temper first and the machining should/will have less chatter.

I will have more data soon[-ish]. The car is at the shop and he will pull a rear drum and inspect it, The picture at Permalink #4 is from 2015.

The point with the gas cans is they can run full, empty or without, depending on circumstance. Usually, it's full in the right to balance the driver's weight.

Selecting the lightest tires and wheels possible would net far more benefits than anything with the brakes.

I have read that removing 1lb of rotational mass is like removing 3 lbs of regular mass in terms of acceleration and I'm sure mpg as well

I hate to be rude, but shaving the brake rotors for fuel economy sounds like a boondoggle.

There's a sticky thread at the top of the page, with a list of mods proven to improve fuel economy. That's a great place to start. Best of luck!

I just had rotors turned. New they are about 25mm, they are considered worn out at 24mm.

Tank
 

What is your current tank? Is it steel?

It is some kind of polymere in my Toyota. So, changing it too Alu will likely increase weight.

I remember reading something about drilling brake drums for better cooling and at least in theory improved braking under certain conditions, but I'd take it with a grain of salt.

Drum brakes are less effective when submerged in water. Drilling them helps with that.

My 1950 Studebaker lost it's brakes after fording some high water.

Best way to save weight with brakes is to get two piece rotors with aluminum hats, and to see if there are any calipers made of aluminum (if they aren't already) available for your vehicle.

Every fuel tank I've ever had has been plastic.

Wheels and especially tires are lower hanging fruit, however, since they're considerably farther away from the center of rotation.

Fuel economy gains from weight loss is virtually zero, but it does improve how the vehicle handles, accelerates, and stops.

I didn't know what a brake hat was... had to google it. Figured rotors and hats were all a single piece of metal, as I've never noticed them being separate pieces before.

Almost all OEM rotors are one piece, but you can get two piece ones. For example:

https://supermiata.com/SPM-2-piece-R...Miata-MX5.aspx

These save 3.9lbs per rotor over OEM single piece rotors (13.25lbs vs ~9.35lbs) . One advantage is that you can replace the frictional area and reuse the hat. I could see this being an advantage for something really expensive like, say, carbon ceramic.

Learned something today. Wish brakes were more interchangeable so the chance of needing the same hat on the next car was higher. Would make it a no-brainer then to purchase expensive hats that reduce weight, but last forever. I'm all about that.

Yeah unfortunately not even the hat offset and thickness are standard. And, on top of that, many of them are simply not published. You just buy for the car. We'd never know even if one IS interchangeable.

Odd enough, some operators still prefer all-around drum brakes for heavy off-road operation in countries such as Brazil, no wonder some entry-level dual-purpose motorcycles retained it until around 2018, including the Yamaha XTZ 150 Crosser which replaced the XTZ 125 (this one always fitted with a front disc even in the kick-start versions), and so many heavy-duty trucks still feature it. I still remember when the all-around drum brakes of the Honda XLR 125 were praised by an experienced reporter in a review for a magazine in 2001, and it was mentioned they had such a good sealing they didn't fail even while fording some creeks...

I'm a bit of a sceptic when it comes to weight reductions. Maybe reducing rotating mass would have a slight difference but in my opinion weight reduction only helps if you use your brakes allot. I remember driving home with 200kgs of compost in my boot, I decided to test a hypothesis that the extra weight could be used as an inertial battery in order to coast further and the car definitely did do this.... I usually get about 75mpg on my drive home.... That day with 200kgs of extra weight I got 80mpg. Granted it could've just been coincidental but I suspect driving style has allot more to do with the fuel savings by reducing weight. Sure it will increase rolling resistance slightly but the biggest difference is the amount of inertia your car will have at any given speed.

Reducing unsprung mass has been often praised as a low-hanging fruit when it comes to a more spirited driving, and it also may increase fuel-efficiency, yet a weight reduction on other parts of the vehicle may not become so negligible at all. Finding the amount of places to get rid of a few ounces at each may take longer than choosing one single place to take some pounds away at once. Well, maybe you were more concerned while hauling an unusual load, so it might've been more a matter of driving style than relying on the load as some sort of an "innertial battery". Just consider the example of a big-rig going a long stretch downhill, with Jake Brakes on and some low gear in order to avoid overheating the brakes, I'm sure such conditions would prevent much of the innertia to be recovered in order to increase fuel savings...

Thanks Ecky, the fuel tank will be 25ltr aluminum, if I ever get time to change it. Early next year likely. It's position will be right at the very rear inside the cabin, rear to where I replaced the wheel well. As long as it's fuel tight upside down and vents outside I'm allowed. It will help with weight distribution too. Thanks also for replies, I may have to cast my own al brake bells at some future point and yes drilling helps with heat dissipation and reduces weight and wear however it takes time and effort, rarely see it these days except on motorbikes. The Prius calipers do have ceramic pistons on the front but small aluminum units may be an improvement when it's time

Plus stuff in this car is becoming so old replacing a tank with a new one fitted with a new pump is no problem, and will likely be cheaper than just a OE pump

Thanks again for thoughts. I have two Prius and the lighter one consistently brings back a 22-24mpg improvement driven with identical variables

When I'm hauling a 2nd car on a dolly with my truck going similar speeds, sometimes I see an increase in MPG. I think it's more of the boat tail effect than the weight. I've hauled scrap and all kind of misc stuff in my truck, weighted down it coasts farther, adjusting the driving style for that and I normally don't see much of an MPG effect unless I have unpredictable stops like driving through the city with stop lights.

There's a saying I heard that sprung weight reduction is like 10x that of unsprung, but I'm pretty sure the context of the saying is for racing and probably relates to handling + acceleration + braking. Spinning weight has a larger effect than non spinning effectively when you're trying to change speed.

There's "batteries" designed as a spinning mass in a vacuum on magnet bearings to have as little friction as possible. Google says those flywheel batteries can be up to 90% efficient. Clearly the longer the time between charge and discharge (self discharge rate) will hurt that figure.

Either case, with more weight, just pumping up the tires to max sidewall helps offset the rolling resistance added by the weight. There's clearly an advantage with going lighter but for steady state speeds weight doesn't have much of an effect.

Most extreme example I can think of is a semi truck, fully loaded it looks like they loose around 30-35% fuel econ due to weight, but they are running around with and extra 24 tons using the figured posted. My Prius is just under 1.5 tons to give context. I'd say the areo effect is much much larger lol.

https://www.quora.com/What-s-the-mil...l-trailer-load

IIRC the only production car resorting to it was a Porsche. I don't remember its name, but I remember seeing one roaming around in my hometown.

Formula One Kinetic Energy Recovery System (KERS):

The flywheel has been used as a battery a bit in history. This is pretty old tech, check out the gyrobus.

https://en.wikipedia.org/wiki/Gyrobus

It's interesting to hear a flywheel based energy storage was developed, the negatives are really bad for racing, resistance of changing direction, and added weight. I'm sure their efforts were focused on a small weight that spins at very high rpm. The one in the bus only spun at 3000 rpm, but it was around 3 tons too.

I was looking for a vid I saw before on these, and this one came up, seems to cover a little bit of everything. One I was thinking of was the power grid flywheel based energy storage where a guy tours the place and talks about the weight, rpm etc. Pretty crazy setup really. There's even a mention of the F1 system near the end, 6500 rpm seems quite low, but probably a lot safer than something half the weight spinning twice the speed.


https://www.youtube.com/watch?v=_QLEERYS5C8

One of the great quotes I love;
Drum brakes would be great, if they worked!

I was able to do handbrake slides with my Insight's 180mm rear drums. They were only ~5lbs (2.2kg) each.

I don't understand the big hype behind disc brakes, drum brakes have always worked great for me. It's easier to make "big" brakes in the disc config by using 4 or 6 piston calipers and such. Disc front drum rear is my fav brake layout. Bonus is the drum setup shields the brake parts from the weather some, so generally speaking there's less rust related issues up here in Michigan for drum brakes. Slides are always rusting up and freezing up, caliper pin issues, etc. It's quite common to have the brake pads not slide correctly and wear at an angle. If a vehicle sits, the drum brakes do have more issues with the shoes rusting to the drum, but popping the tire off and hitting the drum with a hammer generally frees them up pretty easily.

For a race car, I could see the desire for disc all around as they can be over sized easier and such, but for a consumer grade vehicle, I don't mind rear drum.

Fun, but....
My old Australian Falcon wagon (1971) used to do the same.....but not always when you wanted it to :-o

In the "old days" driving around Aus, creek crossings were common, and drying out your drum brakes was a necessary task.....usually just with judicious use of the brakes, but many an unwary traveler ended up red-faced (or worse) with brake failure.

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...

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. :D

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.?

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.

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

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

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

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 =).

http://mirrors.arcadecontrols.com/ww...s/brakes19.jpg

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.

https://i.gyazo.com/f3a66656df2a7d28...1160c716a9.png