Rotational Inertia - Effects on Horsepower

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11 жыл бұрын

What effects does rotational inertia have on acceleration? Low moment of inertia components lead to more available horsepower. An explanation of rotational inertia, and why it's best to use low moment of inertia components in your drivetrain.
The next video will include additional information on rotational inertia.
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Пікірлер: 236

@TheMotownhustler 7 жыл бұрын

Thanks Professor. I'm 66 retired and drag racing for a hobby. I appreciate the information. 👍🏾😎

@EngineeringExplained 11 жыл бұрын

Thanks! I certainly will. The next two videos are basically math based (the next one mainly just words). Basically I just teach myself what I'm interested in, and then relay what I learn on my channel. Glad you guys enjoy it!

@IsmaelMartinezPR 9 жыл бұрын

Another example is an ice skater doing circles as the move their arms in the spin faster. Great series you have a great future as a teacher any day.

@jchafee1 4 жыл бұрын

Nice connection. I always wondered. Thank you.

@EngineeringExplained 11 жыл бұрын

A heavier flywheel will not improve acceleration at higher vehicle speeds; it would however reduce engine braking, so you'd have more inertia to overcome when stopping the vehicle, while in gear.

@n.s2833 6 жыл бұрын

its important to know that flywheel mass is calculated in ic engines to store kinetic energy permanently during combution strok and giving it back in the following stroks to give the engine smoth tourqe curve between stroks

@EngineeringExplained 11 жыл бұрын

No worries, the formulas and technical aspects certainly aren't for everyone. I will have plenty more videos which are more "traditional" and simply explain how things work. That said, I like to be thorough, and topics like these are needed to tell the whole story. In a few weeks I'll have a detailed exhaust story (basics, catalytic converters, mufflers, o2 sensors) and shortly after I hope to start getting into hybrids/electrics. The math will be minimal!

@MercedesAMGsRULE 7 жыл бұрын

I love this video. I have a Mini Cooper with the 'run flat' tyres on. I changed the tyres and weighed the old ones Vrs the new Non runflats. There is a huge 3.6kg per tyre difference due to the stiff tyre wall that the runflat has. Of course then I had it on the dyno, and the difference was 1.9 horsepower, (obviously it was dynoed on the front wheels so if I include the rear wheels I can double this figure) so the total Hp increase is 3.8. Also helps handing, it's comfort, quieter and more fuel efficient. The tyres are cheaper too! It was the Pirelli Runflats Vrs Continental Premium contact 2. I just carry an inflation kit in the boot if required.

@joonyaboy 7 жыл бұрын

Tires should be the first performance enhancement.

@EngineeringExplained 11 жыл бұрын

Thanks, glad to hear this! And I have no plans of stopping!

@EngineeringExplained 11 жыл бұрын

You simply have to provide enough power to power the engine continuously, this likely wouldn't change much with a different flywheel. Worse mileage in the city, roughly equivalent on the highway. A heavier flywheel could potentially provide a small benefit in drag racing, storing more "free" (doesn't take up time) energy to use once the light turns green.

@EngineeringExplained 11 жыл бұрын

Well if off-road vehicles never planned on going over 10 mph or so, ever, then 1 gear may be acceptable. But it's always nice to have a low gear set also for moving very slowly with maximum torque. You just want the versatility of multiple gears, in part so that it can also be used on the road or anywhere.

@EngineeringExplained 11 жыл бұрын

That's a great question, and something I try to discuss with professionals when I get the chance. I believe it does mean this, but I'm not certain the effects it may have on stability at higher speeds. Also, it depends what your pivot point is. If I had a track at my disposal I would play around with weight locations to see the effects. Abandoned airports are a tad pricey these days.

@EngineeringExplained 11 жыл бұрын

The answer to "why" is what I was attempting to explain in the analogy of the different bike wheels. Speed and velocity are the same here, as there's no directional change. Though both wheels move the same distance (and all the mass moves the same distance linearly) the rotational mass moves a greater distance in the first wheel.

@EngineeringExplained 11 жыл бұрын

Good to hear!

@EngineeringExplained 10 жыл бұрын

You'll likely want to get a different tire size to compensate for the lost 1" of the diameter. You'll definitely benefit from the change (assuming the weight of wheel + tire goes down, and rotational inertia goes down), but as to whether or not it will be noticeable is unknown.

@MisterBinx 8 жыл бұрын

About 4:10 is where it really clicked for me. Great explanation thanks.

@mackchannel6348 2 жыл бұрын

Old content is still good content. This helped me understand much about my vehicle that I did not know. Thank you for taking the time to put out this video!

@EngineeringExplained 11 жыл бұрын

Lifetime eh?? Sounds good to me! As long as you're out there I'll keep making videos.

@modestcody123 8 жыл бұрын

That made a lot of sense man. Really good job!!

@nolimeplease 3 жыл бұрын

I just love the way you explain things. I have just been given a solid concept in physics that will be a tool I carry for years. Thanks!

@EngineeringExplained 11 жыл бұрын

There are no simple disciplines of engineering, your knowledge is sound. :)

@francisgaliegue6645 8 жыл бұрын

This video does not have enough views. I have never figured out what inertia really was until I saw this video... Excellent job. Congratulations!

@stephenkeighley7993 11 жыл бұрын

I truly enjoy these videos. Doing a great job, please be sure to keep it up.

@karynthurston4304 2 жыл бұрын

This is the first time the concept has been made clear to me. The explanation was great and I really understood it since being aware of it for 3 years now. 5 STARS!! Thank you. :)

@EngineeringExplained 11 жыл бұрын

Thanks!

@EngineeringExplained 11 жыл бұрын

Basically it could be any rotating component which is out of balance. My first inclination would be the wheels/tires, as this is probably the easiest location for something to get out of balance. Even if there was just simply a clump of dirt stuck in one of the rims, it could cause a significant vibration at speed. First I'd just check to make sure everything is clean and how it should look; then perhaps take it somewhere to get the wheels balanced.

@EngineeringExplained 11 жыл бұрын

If you check out my video on flywheels, I explain why they have a certain mass. Regarding reducing rotational inertia, the real reason why it isn't done (to a greater extent) is cost. To get equally strong components, the materials are going to be expensive.

@JeffThePoustman 8 жыл бұрын

I can concur that most cylindrical components in an engine would be better off with a lower relational moment. In my opinion, the flywheel may be an exception. In a comment below EE mentions a key reason for a heavy flywheel: smooth power delivery. I want to watch the follow-up video treating traction, but it would at this point intuitively seem to me that too-abrupt power delivery would be a greater threat of traction compromise. Anyway, another excellent video! Thanks EE.

@-_addy_- 10 жыл бұрын

Very good and informative video!

@SavageJim01 11 жыл бұрын

Excellent review of MoI! Brings back memories of my highschool physics teacher using a pipe &rod of the same wt rolling down his inclined physics book on a desk! When I got to university to learn materials science, I had to use the Polar Moment of Inertia to calculate torsional stresses. I always thought back to examples like yours to remember that a pipe will take more torsional stress than a rod of the same area on the plane perpendicular to the moment vector.

@EngineeringExplained 11 жыл бұрын

I would say check out my videos on HP vs Torque. Specifically "Formula 1 vs NASCAR, Horsepower vs Torque" as this shows the difference of high revving engines to lower revving engines, with torque being the altering factor.

@rickitickidicki 11 жыл бұрын

another concept flawlessly explained! I'm gettin' this! Thanks man, You!, You've got a gift you!

@oliobgmoti-bulgaria8401 Жыл бұрын

Incredibly well explained, the drawings and logical follow up were on point!

@EngineeringExplained 11 жыл бұрын

That's a good idea!

@EngineeringExplained 11 жыл бұрын

Check out my video on flywheels, which explains there purpose. They are useful for a smooth power delivery. And yes, you wouldn't want it smaller than the clutch.

@EngineeringExplained 11 жыл бұрын

Yes, as it is the object's resistance to rotation.

@EngineeringExplained 11 жыл бұрын

Lightweight rotational components, and try to locate the mass towards the axis of rotation.

@williamdutoit9585 9 жыл бұрын

This explains well why cars tend to spin their front wheels when shifting from 1st to 2nd, It's all that inertia that is "stored" in the engines high speed. when shifting to second the engine has to rotate slower but it doesn't want to causing a peak in torque at the wheels resulting in loss of traction. This also explains why my motorcycle doesn't wheelie in 1st but shifting fast to 2nd lifts the front wheel momentarily.

@yamaharacer308 10 жыл бұрын

Keep up the good work dude.

@DENicholsAutoBravado 10 жыл бұрын

Thanks for the great video. Here's my reaction when I found a practical application of this video's information. Wow. You have to read the description on the video link I'm sharing here. 3 grams on the pistons assembly equals 100 lbs. of torque at redline. Watch the following engine rebuild presentation. His goal isn't to reduce weight so much as to balance his pistons. It's better to have the piston heads balanced, but that takes instrumentation beyond his ability. Hyundai Assembly 4 - Balancing Rods This modification is completely within my ability. I want to do it first on my vehicle that isn't a daily driver.

@samrattomar7552 6 жыл бұрын

Great Jason, Again a very beautiful and effective video content on moment of inertia. I would request you to prepare a video on selecting/designing the AVM (ANTI VIBRATION MOUNT) for engines. I would like to understand as how do we define as what is the amount of frequency which we need to damp w.r.t engine or how to define the percentage of isolation for the chassis from the vibrations of engine. I would request you to prepare a content on it Best Regards! Samrat Tomar

@chadmellor 11 жыл бұрын

Love these videos, keep it up :)

@danb3e3 4 жыл бұрын

Good analogy talking about the distance the mass has to travel. Cheers!

@philwright1233 5 жыл бұрын

Excellence in explanation! Thank you sir!!

@aaihamm 11 жыл бұрын

Great video as always :)

@jackrios4040 4 жыл бұрын

This video convinced me to get lightweight pulleys and lightweight wheels lol great explanation 🙂

@leebaidyanathan1 11 жыл бұрын

The topics are getting better by the day :)

@EngineeringExplained 11 жыл бұрын

Yes, and the opposite, depending on the mass and dimensions.

@EngineeringExplained 11 жыл бұрын

Lighter flywheels for more power, but you're power delivery will not be as smooth.

@trillionare7 10 жыл бұрын

Hey man, I am thinking of getting 17 inch wheels weighting 16 lbs each, over stock 18 inch wheels which weights 23 lbs each. Size difference is 225/50 R17 vs 225/50-18. Will I benefit from the this mod in terms of gas mileage and acceleration? Thanks

@jamesseaton7033 2 жыл бұрын

great video and weird seeing the old content! glad you kept the whiteboard 😎

@sadsismint 11 жыл бұрын

really liked this one! very clear :D

@EngineeringExplained 11 жыл бұрын

I think it's honestly just the room that I film in. It's kinda cramped and I think it just echoes a bit around the room. I'll have to think of a solution.

@ingeniousx2581 4 жыл бұрын

I actually had a idea of using that principle in racing cars ....u contract the mass towards the centre after a car is about 50 miles an hour and its speed would increase by too much

@DENicholsAutoBravado 10 жыл бұрын

Uh oh! Late last night, I was thinking about this, and now I want cross drilled brakes. For my car's design theoretically it won't help with braking much, but it'll reduce the rotational inertia that has to be overcome for acceleration. ....when I'm up for the mod, I'll be weighing it and new ones to be sure the difference I expect is actually there.

@EngineeringExplained 9 жыл бұрын

***** Umm.. yes they do. Your brake calipers remain stationary.

@chincemagnet 8 жыл бұрын

+DE “AutoBravado” Nichols You're not gonna lose much weight from a few drill holes.

@DENicholsAutoBravado 8 жыл бұрын

chincemagnet Nope. But inertia is inertia. Hey, this is the least effective brake mod, so why not try it for weight? I'm thinking more about how lighter rotational items mean a lot more than overall weight. Still haven't done it. I'm so excited as to wait for newish rotors to wear out. Lol. Get the likelihood and time frame? Lol

@LawrenceTimme 11 жыл бұрын

This was really helpful as i can apply this to my push bike wheels.

@EngineeringExplained 11 жыл бұрын

I doubt light weight pulley's are going to give you 5 hp more, but if you've seen the dyno that proves it then yeah it could be worth it.

@fifthgear93 11 жыл бұрын

Keep making videos about complicated things. Your videos have a lot of educational value. Make a video please, about the differences between diesel and petrol engines. Which is better for everyday use and why.

@shananagans5 11 жыл бұрын

Great vid. Many people discount the importance of rotational inertia.They understand weight overall but they don't really understand how you are kind of doubly penalized by weight that also spins. One time I was buying lighter wheels & tires for my buggy (1,200lbs) & I said "this should make a huge difference." The guy said "it's only 40lbs you won't notice it" I said it's 40 less lbs of unsprung weight & 40lbs less rotating weight. He didn't understand & looked at me like I was a crazy woman

@metodraginii 10 жыл бұрын

SuperB video!!! :)

@SheldonCowles 9 жыл бұрын

Excellent video.

@nunyabizness2433 6 жыл бұрын

Good video. Thanks.

@BouncingHope 11 жыл бұрын

Wow! I like this explanation of Moment of Inertia! Makes so much sense now. So would that mean, in linear terms, mass can be seen as an object's resistance to acceleration?

@shananagans5 11 жыл бұрын

I like you going into detail. The math isn't really my thing but,taking the time to actually work it out, lets me see how much difference it really makes. Granted I am ill & stuck at home with nothing better to do but I am sure several of your viewers are engineers or in school to become engineers. Those details are more important to them than most but the average person can understand the concept or principal without doing the math.Going into detail you to give both the simple & complex answer

@swansmeister 5 жыл бұрын

Hi there sir. First of all, love all your vids, very informational, I tend to believe the things you claim in most of your vids. I have a question I want to buy gruvzn parts one piece billet lightweight pulleys, 4 of em, crankpulley, servopulley, airconpulley and one other which I dont know anymore, its a kit. They claim 5-7hp gains and heard a lot of good things about them. Would you recommend these and could they realy give that high of hp gains as they claim. My car is heavely tuned (NA).

@EngineeringExplained 11 жыл бұрын

Well it of course depends on multiple things, including the weight of the car and the current power. Regardless, every bit helps. Increase a 5 hp go-kart to 10 hp, and you will surely feel it. Increase a 300 hp car to 305 and it's unlikely you'll notice.

@siedpe13 4 жыл бұрын

I understand how this video explains benefits of a lighter flywheel. I was hoping this video would cover the purpose and benefits of a heavy flywheel. When replacing the clutch on my daily driver, I learned that yes, a light flywheel would increase my acceleration, but it would have a negative effect for stop and go driving as I regularly engage my clutch to inch forward. I think some information as to why vehicles use heavy flywheels to begin with, would be useful

@balazsrepasi8035 6 жыл бұрын

Great video, thanks. Couldnt get it before

@EngineeringExplained 11 жыл бұрын

Punching holes in brakes for the sole purpose of reducing inertia sounds a bit dangerous. You want a large surface area for good cooling. Sometimes they are slotted/drilled for cooling as well. But basically they are sized for the car.

@EngineeringExplained 11 жыл бұрын

No, it is a plus. If it were a minus the moment of inertia would decrease as the mass moved away from the axis of rotation, which is not the case.

@yardman0001 11 жыл бұрын

Awesome video man, I have a degree in Aeronautics and didn't know this!!

@EngineeringExplained 11 жыл бұрын

Yep, graduated ME.

@swayingGrass 11 жыл бұрын

Clear!! Thanks ^^

@PranavHosangadi 11 жыл бұрын

Simple way of putting it: Moment of Inertia is to Torque as Mass is to Force. Since people are more used to thinking of masses and forces than MI and torque, it becomes really easy to remember.

@EngineeringExplained 11 жыл бұрын

Well, fatter tires are going to have increased rotational inertia. But if you're traction limited then it could help acceleration.

@EngMadison 11 жыл бұрын

I think of the moment of inertia as sitting on a spinning chair with your arms out vs. arms in...which one is easier/faster at spinning? But I dropped out of Mechanical for Civil Engineering...so maybe I'm not the one to be giving advice. Great videos, watch them all the time!

@MrIrrepressible 11 жыл бұрын

Thanks for the answers. Regarding the pulleys I meant that they free up an extra 4-5 hp to the wheels not that they add extra hp. 250 dollars for a set of 3. Still considering the purchase

@garysmart1 6 жыл бұрын

Hey Sir please reply... if I leave in a hilly road is that means smaller rim diameter is better in climbing up the hill compare to big rim??? please reply

@alexander2093 3 жыл бұрын

Great video I'm currently lifting my truck and am choosing between 3 sets of tires..each have slightly different height and weight. Would you be kind enough to do the math for me to see which one has the least rotational mass and more suitable for fuel savings... My math is very weak, your help would be greatly appreciated Thank you, Alexander

@Bluegogglesonadog 11 жыл бұрын

Hey man, really nice vid. I just had one small "negative" comment i thought you might want to know. Lately I've been getting, i would'nt say bored, but not so enthused from your videos. I really liked the ones you did in the beginning, explaining how engines, and brakes and turbos and suspension, etc. work with very clear drawings. Although i liked this vid in particular, ever since you started explaining with formulas and stuff (basically your "new" videos) i've felt lost most of the time... *

@oorhood 11 жыл бұрын

you're my hero

@XWMaster 10 жыл бұрын

I was wondering about 2-piece brake rotors. I see that they are on all SuperCars and when I was researching I saw that they are the best kind.. Why is that? Because they would have a much larger rotational inertia?. Or does the weight lose make up for it?

@chancemonagon9688 4 жыл бұрын

Even though I’m going back to a video you made six years ago I am still wondering if this hurts the lifespan of the engine and why?

@tarkin1980apa 7 жыл бұрын

This is a great video, but I don't think you made it clear why you can't just make the flywheel smaller and thicker (ie reducing the diameter while keeping the mass the same). Thanks for a great channel. I like these theoretical videos as I am interested in engines and egineering but don't really care much about cars :)

@mohammadenteshariun1629 11 жыл бұрын

that is probably just a typo but the equation in red is I=1/2 M ( r1^2 - r2^2 ) there should be a minus instead of plus

@RBfarming 11 жыл бұрын

You go into detail about why you would want less rotational inertia but made no argument as to why it's there in the first place. Absolutely fantastic channel though, watched every single video ;)

@PavelShevchuk 10 жыл бұрын

Oh, changing wheels is so underrated! If you decrease overall diameter of wheels, you'll get more torque at expense of top speed and speedometer precision. If you fit narrower tires - you can decrease grip and have more fun with rwd/awd car. Watch "The Mercedes C63 AMG Experiment - /CHRIS HARRIS ON CARS" video to get the idea.

@williambob245 4 жыл бұрын

Just to get this all straight. I have a 01 single cab z71, I'm planning to swap an 8.1L 8100 vortec from a 03 crew cab long bed. From factory that truck makes around 340hp and 450lbs of tq. So I should be able to expect slight a slight gain beach of the shorter drivetrain?

@shananagans5 11 жыл бұрын

Yes. Depending on the diameter & overall weights of course. If the diameter is larger a lighter hollow cylinder can have a higher moment of inertia than a slightly heavier cylinder with a smaller diameter. Think of a weight on the end of a single bicycle spoke. The closer the weight is to your hand the easier it is to move. Now put that spoke in a completed wheel. The farther the weight is from the axle the harder it is to make it spin.

@EngineeringExplained 11 жыл бұрын

That's what my flywheel video is for :)

@neko_789 3 жыл бұрын

Would you prefer a lightweight flywheel or a stock flywheel on a car that has a lot of rev hang like a subaru? Would the lightweight flywheel make the rev hang worse? Thanks.

@EngineeringExplained 11 жыл бұрын

I think I used all caps, simply to spite you! :)

@alexi077 3 жыл бұрын

You should Remake that Video. Please maka a Video what impact on Performance and mileage it has when saving mass on wheels. 0-100 times and consumption messuerments would be great!

@xxTONEMOxx 11 жыл бұрын

Can you make a video talking about Ls/Vtec Thanks i would really appreciate it! :)

@kevinjeeves1634 5 жыл бұрын

What would be the 'hauled equivalent' of rotational mass? Ie power to spin one extra pound vs hauling that same pound?

@marcholler4047 6 жыл бұрын

So is a bigger rim and wider tire decrease horsepower due to weight?

@destin842 5 жыл бұрын

Pretty much, in drag/street racing Your goal is to be able to get traction on the smallest tire possible.

@lelouchbritannia8728 5 жыл бұрын

Can u make a video about sprocket ratio for Motorcycle

@shik20v 11 жыл бұрын

Hi bud heavier or lighter flywheel for better acceleration? I have a 4age silvertop and want to swop out to lighter 4age blacktop fly, wil i lose torque?

@EngineeringExplained 11 жыл бұрын

Yes, it's hollow, and yes, it's a "+" sign. May not be entirely intuitive, but MOI increases as the mass is located further away from the center of rotation.

@nuk3man 11 жыл бұрын

I have a couple of questions (I might have missed it in your video), *why* is it that objects with lesser moment of inertia would travel down the hill faster than an object of comparable dimensions but with higher MOI? I understand that it represents the resistance to change, but from where does this force of resistance arise? Also, do the two wheels have the same *speed* but different velocity? Isn't it higher in the smaller diameter one as a result of less distance travelled?