Unsprung & Rotating Mass: Why it Matters (FM Live)
"Unsprung Weight" and "Rotating Mass" are terms you hear quite often in the performance car community. This week on FM Live, Keith Tanner explains exactly what those terms are and why they matter, especially in a Miata.
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I really enjoyed this thanks my dude!
Thanks for your explanations. Very usefull
I've been waiting for you guys to cover this topic in this format! And the timing is great too- I just swapped out the heavier stock wheels on my 2003 SE for a slightly lighter stock set from a 2004- it isn't dramatic, but if the forums are correct (want to verify), this netted me about a 9lb reduction in unsprung weight. Still saving up for a set of Kokegi's or RPF1s..
I got a Kogeki set for my NC2 about a year an a half ago, and i could not be happier.
Thank you for the video
You're welcome
Love the videos guys!!! Can't wait to order a set of tobus for my ND!!
Awesome! Thank you! :)
Switching out the stock steel calipers with the powerlites in the Little Big Brake Kit was delightfully noticeable. ++ fun factor and feel
We love that kit, and it definitely changes the feel of the brakes!
I put 19x9.5 on my rx8 and they looked awesome but handled pretty bad. You can just tell how heavy they are through steering and bumps. That being said I put it back on stock wheels 😂
Great video! I have a set of 15x7 kogeki wheels i am looking forward to getting on the car. More grip, light weight, and stylish. What more could you ask for lol. However i have some leaking brake calipers that i would like to get fixed before the new wheels go on. With that being said, now that FM sells a caliper rebuild kit. Could you make a diy caliper rebuild video? 92’ NA
It's on the list for sure!
As someone who just rebuilt their rear calipers on an NB I will say it’s a fun learning experience and a lot easier than it seems. I plan on rebuilding my fronts soon just for peace of mind that both front and rears are good to go. Good luck!
I’ve been hoping for a silver version of the kogeki wheels, hope to get my hands on them soon
Check out the site, they're in stock now!
I changed over from steel springs to aluminum (swift) springs at the same time as upgrading from Tein to Ohlins suspension. The difference on the track was massive. How much of that was due to the Ohlins and how much was due to the springs. Do alloy springs react differently to steel ones? Does the weight difference add up to much?
That would be the change in damping you noticed unless you also changed spring rate. Springs are pretty simple devices. That said, it's pretty unlikely your Swift springs are aluminum as they would fatigue and break fairly quickly. They're probably spring steel like just about every other spring on the market.
Swift springs use less coils, which makes them slightly lighter and have less binding under full compression. They likely use some proprietary jdm steel, which makes them more durable.
1:02 17:40 Theoretical Question: If your upper & lower control arms had counter weights on the opposite end of the inner bushings (or, springs pushing up against the bottom of the car’s frames), would that decrease unsprung weight? And would counterweights on the LCA’s completely cancel the effects of the coilovers, or could there be an advantage there?
Any plans to bring deep silver to the 17x8 Kogekis? I'd prefer 215 tires to maintain nimble steering for street use. 9in wheels might be a bit wide for that.
If the color sells well in these two sizes (17x9, 15x8), and there seems to be demand for the other sizes, we'd love to offer deep silver for all fitments!
The question is not necessarily related to unsprung weight but I'm in a dilemma between two sets of items and they add some weight, so trying to choose between. On a pure canyon carver ND2 would one choose chassis bracing over the verus aero kit or vice versa. I can only choose one at the moment, due to budget constraints. Thanks, J
The ND2 doesn't need a lot of extra bracing, so from a performance point of view aero would be the first choice.
Excellent video. Now, if one considers getting aftermarket front calipers only for weight reduction, would that affect the overall weight balance of the car? If the near 50/50 weight distribution is a selling point of the Miata, wouldn't changing weight only on one side negatively affect that?
A 2300 lb car with 50:50 weight distribution has 1150 lbs at each end. Taking 5 lbs off each front corner would change the 50:50 to 49.78:50.22. You'll see a bigger shift (about 0.3) when you put the top up or down. Also, Miatas aren't perfectly 50:50 anyhow :) So don't worry about it.
On top of what FM said, remember these figures are not taking into account occupant weight, your bags, tools, stereo, how much fuel you carry etc etc... As FM said, get the low-hanging fruit first. That unnoticeable, fractional weight distribution change will be massively offset by objectively felt performance increases.
While on this topic, it would be good to discuss ride & handling difference between a stock 17" and a downsized 16" (or even 15", assuming brake fitment). Relate what the owner will feel in terms of shorter stiffer sidewall tires vs. taller more flexible sidewalls. How much steering response does a taller sidewall take away? How much ride comfort does it add? (subjective, I know) While researching an aftermarket tire/wheel solution for my stock 2019 GT-S, I went back & forth A LOT between 17" vs. 16" pros/cons. Ended up with 17" PF01s with -215 Conti ECS for my fun street car, and very happy, but there's always "What if?"
The choice of tire can have a significant effect there as well. Keith used to have a set of 17" and 14" wheels/tires for his NA, and the 17" setup rode better than the performance-biased 14" one because of the sidewall stiffness.
Ouuiuu
Thanks Keith for another great video. Quick question…there’s a myth saying that every kg saved on unsprung masses is equal to 20 kg of sprung mass. What is the real ratio? Tx, Andrew
Call that more of a guideline or a rule of thumb than a real ratio. The effect will depend on what you're measuring. I would hate to try to put numbers to it.
A little late but would you ever make a 5x100 version of your wheels for other cars?
Never say never, but we don't have any coming at the moment.
Not that I've looked all that hard, but after years on grm ,car lounge, vw/Audi and miata tech forums I don't recall any spread sheets covering tire weights. Seems like we confirm every other number we could measure. For my part, I downsized my fist to 16's konig flow form. The wheel is 10lb lighter but with neo gens the overall is only 4lb. That's a lot of tire weight.
Manufacturers publish tire weights and you can also get them from Tire Rack, so they’re pretty easy to find if you look. In the video, we were comparing different widths of the same tire with a similar sidewall height. Increasing sidewall height will definitely have an effect, that’s where a lot of the tires structure lives.
@@FlyinMiataVideo I've never seen a tire weight listed at a point of sale. Individual manufacture web searches is where I draw the line on effort. I'll admit my experience is well in line with expectations. The extra sidewall and frankly the neos just Looked heavier. Also flyin miata's community engagement always on point. Tanner and crew straight deliver!
On Tire Rack, click on “Specs” in the tire listing. The weight is there. It’s in a similar place on Discount Tire.
I thought unsprung weight matters a lot on acceleration/flywheel effect as evident on 1/4 mile of same car but different wheel size 15" vs 18".
Is there a deep silver version for the 15x9?
Not yet. If the deep silver sells well in 15x8 & 17x9, then we would love to offer them in other sizes in the future if the demand is there.
I upvoted to help the algorythm
Thanks!
how much hp does it take to move 1lb of unsprung weight?
Something I don't see talked about (that's easily found anyway) is the wheel/tire width to track time performance curve. If the sky is the limit then where exactly does the point of diminishing returns start as they get wider and wider? Would love to see this covered in depth with real tests!
Good question! I see this as traction vs. added weight of the tire/wheel combo. Let's say we're entering a 90 degree corner at 60mph and we spin out. The first thing to do is get the stickiest tire to see if that'll help, if not, start adding tire width until you don't spin. Tire sizes have a recommended wheel width range and that'll determine, mostly, the wheel width one should consider. Shoot us an email and I can narrow down some general starting points per generations.
If you don't need more traction and increase the size of your tire/wheel combo, you're just adding weight. If you're adding weight to get more traction which lowers your times, it's worth it.
Feet and the shoes we put on them are the perfect example of "unsprung weight".
That's a good one!
With regard to unsprung weight, knowing that manufacturer tire pressure specs involve multiple factors what would a reduction in unsprung weight have on the stock tire pressure spec ?
Interesting question. The choice of tire (construction and compound) and tire size is going to be a much bigger factor. Any effects of the unsprung weight will likely be dwarfed by those.
What is the most comfortable and driver friendly miata as far as visibility
If the top is down, visibility can’t be better! Other than that it depends on the type of top you have installed
What happens if your left/right wheels have slightly different weights (because you cheaped out and used two different wheels)? Will this effect braking?
Now that's an interesting one. It might be harder to threshold brake with more inertia on one side, and there's the possibility you'll also have less traction on the heavier wheel. Will it be significantly biased to one side? Probably not. It may end up being more of a theoretical difference than an actual one, especially if there isn't a big difference in weight.
Do the rotational forces from the engine and driveline also create a gyroscopic effect?
How would you incorporate this information?
@@LARSENBISQUITS I wouldn’t but I’m curious anyways, what if you got light weight internals? Or drop in a small block v8?
Look into the reverse rotation Indy car that Smokey Yunick built. If you decreased your rotating drivetrain mass (ie, install a lighter flywheel) you’ll probably notice the drop in inertia via free rev throttle response more than any gyroscopic effects.
Question: all things being equal (specifically manufacturer, rim/tire width, and overall diameter of rim/tire combination) what weighs less, larger diameter wheels with smaller sidewall tires or smaller diameter wheels with larger sidewall tires? In other words, what tends to be “heavier” rims or tires? Also, how does density and distribution of weight about the center of rotation compare in each case?
It's the last part that matters - the further away the mass is from the center, the more effect it has on rotational inertia. It's like an ice skater pulling their arms in to spin faster. Tire weight seems to be more tied to carcass width than sidewall height, at least in the case of Miata sizes. So going from a 15" to a 16" wheel on a Miata with a corresponding change in the tire size will only change tire weight by a pound or two - you can see this by looking at Tire Rack and viewing the spec sheets for a certain tire model. In some cases, it makes no difference at all - a Toyo R1R in 205/50-15 weighs the same as a Toyo R1R in 215/45-17. The 205/45-16 is slightly lighter. But you'll definitely pick up some wheel weight going from a 15" to a 17" wheel, all else being equal.
@@FlyinMiataVideo gotcha. So, more or less, more sidewall and smaller rim to achieve a given overall diameter is lighter, but that’s not nearly as important as the fact that more mass is concentrated near the center of rotation. Full disclosure, here I’m targeting a specific larger overall diameter (~26.5”) for a lifted Miata. I’m glad I don’t have to sacrifice sidewall.
@@johnnyk5 When we specified "Miata tires", we meant performance-oriented road tires. There can be a very large difference in the weights of off-road tires because they often have heavily reinforced sidewalls. Might want to take that into consideration when shopping for rubber. The increased diameter of your overall wheel/tire combo will result in an increased polar moment of inertia, effectively making them heavier when it comes to flywheel effects.
Something that occurred to me while watching this is that changes in unsprung weight changes the dampening of the suspension. Is shedding 10 pounds per corner enough that it would merit changes to shock valving or a coilover click? What is the difference between changing unsprung weight and changing shock valving?
The shock valving is there to control the spring first of all, so if you're not changing the spring rate the valving will remain much the same. Same with the difference between unsprung weight and valving, an underdamped spring feels very different than a light wheel/tire setup. It could be possible to confuse an overdamped shock and too much unspring weight, though.
@@FlyinMiataVideo I think that makes sense but I'll have to think about it a bit.
Fuel savings are also noticeable?
We have not done any testing on fuel savings.
Nothing to do with unsprung weight, but I have to ask the Miata Professor (not mocking). I see guys putting 1.6 clutches, pressure plate and flywheel into 1.8's, is having A/C make any difference? I know guys have said that too light of flywheel on an A/C car can mess things up a bit, but I wasn't sure about using a smaller clutch disk, pressure plate and flywheel? Please advise. Best Always,
It's sort of related, because that gets into the same idea as rotational inertia. A smaller flywheel of the same weight will act "lighter" than a larger diameter one because that weight is closer to the center of rotation. The pressure plate is effectively part of the flywheel, but it has a different job so it's easier to specify the pressure plate that does the best job and then adjust the rotating mass with the flywheel. The disk only spins when the clutch is engaged, so it's part of the flywheel sometimes. A 1.8 clutch setup can have the same rotational inertia as a 1.6 unit does if it's specified correctly. Dropping a smaller diameter 1.6 unit in there is away to get less flywheel effect from the same total mass (ie, cheap and easy), but it has the downside of decreasing your holding power so you need to run a heavier spring on the pressure plate for the same torque handling capability, which means a heavier pedal. A flywheel effectively resists a change in speed, so one of the most noticeable things it does it prevent the idle from dipping too far when the AC compressor kicks on or the alternator suddenly pulls a lot of power. Go too light and you could end up with a car that stalls when the AC comes on or when you come up to a stop sign. That's also why positive displacement supercharged cars don't like to run as light a flywheel as naturally aspirated or turbo cars, that supercharger adds some extra drag that tries to pull down the idle speed.
@@FlyinMiataVideo That said, what would The Miata Professor do? I've noticed too that the smaller pressure plate can only handle 175 torque where as the larger one can handle 289. I'm putting in a 2.0 with 225ish hp. I don't know where it will be as far as torque. Thank You for your input.
Use the 1.8 parts and just use a lighter flywheel if you want less rotating mass. That’s exactly what it’s for. If you go too light, you can end up with idle problems or a decrease in driveability.
One topic I was hoping to hear with the ratio between unsprung weight to sprung weight. For example, if each wheel is 5 pounds lighter than stock wheels, that’s a total of 20 pounds unsprung weight savings. How many pounds savings is that equivalent to sprung weight? 👍
There's not really an equivalency formula like that. Wheels are not just unsprung, they're also rotating. So they'll have a larger effect than, say, a lighter caliper. But the savings will show up in different ways, so you can't really say that 5 lbs off each wheel is equivalent to 50 lbs off the chassis or anything like that.
If Al lug nuts and metals stems aren't significant enough for weight savings, then what are they good for?
I think it’s good for that “it’s lighter so it’s gotta be doing something !”
@@singerfpv9044 That's part of it! You need lug nuts, so why not make them lighter? Metal stems are also more reliable than rubber, especially with the heat being put into the wheel on track use.
@@FlyinMiataVideo everything has its benifits for its specific use ! Thanks for the great video, helps me stay informed and learn new things about these cars
I personally like the FM aluminum lugnuts because they look nice but aren't in your face like many aftermarket lugnuts, the textured ends help a ton of you don't use/don't have power tools, and and I don't have to Google torque specs every time I take a wheel off
I'm getting a set of forged magnesium wheels made for my 370Z that will shave off about 9 lbs per corner. In the near future, I'm going to replace my all-steel one piece brake rotors with a two piece rotor that has an aluminum hat, for an additional weight savings of 5 to 10 lbs per corner. I'm looking forward to seeing how the combination will affect handling.
Hey did you end up doing this? I'm thinking of doing this to my car with similar weight savings and curious what it'll be like with lighter wheels and rotors taking off 13lbs on each corner
@@nickyp2627 I haven't done the installation yet, as the manufacturer made a mistake on the front wheels and had to remanufacture them. I just got them back and am getting ready to have the front wheels ceramic coated. I got some custom fabricated aluminum alloy lug nuts made and am fitting some aluminum washers under them for spacing purposes. I'm looking at probably a month before I get them installed on the car.
I just got the wheels installed, with some billet aluminum lug nuts. The difference in how the suspension handles is noticeably improved. Bumps and cracks are much less noticeable and the steering response is a lot quicker. The acceleration is a little better, with the coast down faster. I think I've gained as much as 1 mog on the gas mileage. I'm hoping that there will be less impact stress on my sus PO ension components. I can't wait to see how it does when I get the lighter brake rotors on the car. I expect the main benefit will be better wheel tracking over bumps and less inpact shock through the suspension.@@nickyp2627
I need a set of these for a GT86..😜
We keep a log of all wheel requests, and if we see enough demand, the wheels will be brought to the site! Unfortunately, a 5x100 bolt pattern isn't common for us Miata folk.
Watched this vid at least twice….. maybe third time I finally noticed his lab coat reads “Professor Batshit”. 😂
How about rotors? You mentioned calipers, but I didn't hear anything about light rotors.
The mass of rotors is actually functional - they’re a heat sink.
@@FlyinMiataVideo Ha, thanks for the reply. I thought two piece rotors would help dissipate help quicker. Maybe I'll just get regular slotted rotors then. I was going for unsprung weight savings.
Ive got a V6 camaro, so more accleration would be awesome as i understand ligheter wheels could mean about 1% more HP/TQ, about 3.25 Hp, BUT with a LOW MILEAGE 2015 2LT [42,000 miles] & living in a neighborhood with really bad roads, i mean washboards in every direction, will lightweight wheels ALSO help save my car from premature rattletrap shitbox synndrome? or moving at the cost of 500$ extra per month into a nicer roads but less safe neighborhood since i may not have a garage there. cuz in one year 500/month extra adds up to 6000$ cdn but if i can get a set of lightweight wheels for 3000 cdn thats a bargain paying for itself in 6 months if i dont have to move residences, and i will need that gARAGE for extra security with those wheels on there.
Going with a smaller diameter wheels and thus more tire sidewall would probably have a greater effect than just making them lighter. Also, choosing a tire with a softer sidewall will help. Light weight is certainly a good thing in your situation but it's not the only thing.
OK, why 2 mics?
This video was shot for Facebook Live, which doesn't let us save in full 4k. So we run two cameras and two mics to have better quality for KZhead. Gives us some redundancy as well.
try to put your table on top of the camera filming you..
Why didn’t you manufacture a 7 and 7.5” wide rims to help keep weight down? It’s a shame these wheels are only available in 8 and 9 inches. This means a larger tire to keep it square which means more weight.
Each mold has the potential of X amount of widths which limits us on how wide or narrow a wheel can be from a single mold. We might have some more widths available for the NC and ND later if we have enough interest.
@@FlyinMiataVideo thanks for replying. I’d be very interested in a lighter wheel / narrower width. Only reason I didn’t want to purchase is the 8” means a heavy rim and a heavy tire to square it off.
@@TheScottishDad I agree; however, is the Kogeki heavier than a stock smaller size? If this is what you're comparing it too?
@@FlyinMiataVideo I struggle to get accurate weights on my stock 17x7 ND2 wheels. I think they’re around 8.1kg. So I don’t think there’s much in it on pure rim weights, but a 225 tire would weigh more than the 205, but I’ll do some research on tire weights. It may not be too much of a weight increase overall? I appreciate that a small amount of static unsprung mass can mean more rotating mass but the aesthetics would be worth that compromise :-)
@@TheScottishDad Agreed. If you don't need the increased contact patch, a bigger tire is really hurting your performance.....unless it's about aesthetics. Here are some factory wheel weights from our shop cars. 2016 GT 18 lbs. 2016 Club w/Brembo trim 16.15 lbs. I'm not sure what wheel Mazda offered then but.....
Do what Jaguar used to do, mount the brakes inboard!