Rotation mass front vs rear
- Thread starter nsxsupra
- Start date
Yes. When you are accelerating, some force is used to accelerate the wheels - it does not matter if the wheel is a drive wheel or not. Although, compared to the rear, the fronts use up less force due to the smaller MOI (moment of inertia).
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nsxsupra said:
Not only do lighter wheels allow a car to accelerate quicker, but also the can will handle better. By having less mass to move up and down, less "unsprung weight", the suspension is able to act more efficiently, and is able to keep the tire in contact with the road surface better.
How perceptible these differences are is up to debate, but going from a light combination to a heavy one is very noticeable.
-Jeremy
You will benefit from reducing weight front and rear for suspension etc as stated above.nsxsupra said:
For acceleration, the rears are more important due to the fact the motor has to turn the wheels from the center, so the more mass you remove from the outer rim/tire etc that faster it can accelerate with the same force. The fronts have the radius to act as a fulcrum therefor requiring less effort under acceleration only.
Edgemts said:
This is incorrect. It takes the same amount of torque to spin an object, no matter how it is applied. I can see how you might think intuitively that it's different, but it's not.
Clarification
I just realized what I wrote, although still true for stock tires on NSX (and probably most other cases), is a little misleading since it makes no mention of different tire diameters...
Anyway, this is not the case with the stock wheels and tires: The rears have much greater MOI than the fronts.
I don’t have any figures for MOI of the wheels and tires, but if you assume MOI is roughly proportional to weight of the wheel and tire, out of the torque needed to spin stock 16"/17" wheel and tires (about 39 lbs. front and 48 lbs. rear according to the FAQ), about 46% is absorbed in the front and 54% in the rears.
At least I think this correct - it’s been a while since I took physics.
I just realized what I wrote, although still true for stock tires on NSX (and probably most other cases), is a little misleading since it makes no mention of different tire diameters...
In stock 16"/17" sizes, the outer diameter of the rear is about 4.7% greater than that of the front, so front wheel spins faster than the rear by the same factor. Since torque is proportional to the product of MOI and acceleration and since the fronts will always accelerate 4.7% faster than the rears, the front wheels would "hurt" acceleration exactly as much as the rears if the MOI of the rear wheel was exactly 4.7% greater than the MOI of the front wheel.Ojas said:
Anyway, this is not the case with the stock wheels and tires: The rears have much greater MOI than the fronts.
I don’t have any figures for MOI of the wheels and tires, but if you assume MOI is roughly proportional to weight of the wheel and tire, out of the torque needed to spin stock 16"/17" wheel and tires (about 39 lbs. front and 48 lbs. rear according to the FAQ), about 46% is absorbed in the front and 54% in the rears.
At least I think this correct - it’s been a while since I took physics.
Great link - I didn't laugh so much the whole year! :biggrin:ANYTIME said:
rbirling said:
Really,
So if thats true then its just as easy to tighten a bolt with a one inch ratchet as it is with a 20 inch ratchet????
Once again I said accelerate not maintain.
Take a kids merry go round, load it full of kids, try to turn it from the center, now try the outside edge, were you able to make it accelerate at the same rate with the same effort? Now take the kids off.
Shoot if that's the case let me throw away my flywheel, the starter should be just fine connected right to a real small gear on the crank.Right?
Talk to you later, need to pull my tranny to get started.
:smile:
No!
rbirling is obviously not talking about applying tangential force at different points along the radius.
The drive shaft provides a certain amount of torque. Most of the torque is used to accelerate the mass of the vehicle (by tangential force applied to the ground via the moment arm of the wheel).
Some torque is need to accelerate wheels at both ends of the car. Afterall, when the vehicle accelerates, all four wheels accelerate. rbirling’s point is that it makes no difference if a wheel is accelerated directly from torque applied to its shaft or indirectly from tangential force exerted by the ground, which came from tangential force from the other wheel, which came from torque applied to the drive shaft of the other wheel. Regardless of where the torque is applied, the wheel will accelerate at the exact same rate.
rbirling is obviously not talking about applying tangential force at different points along the radius.
The drive shaft provides a certain amount of torque. Most of the torque is used to accelerate the mass of the vehicle (by tangential force applied to the ground via the moment arm of the wheel).
Some torque is need to accelerate wheels at both ends of the car. Afterall, when the vehicle accelerates, all four wheels accelerate. rbirling’s point is that it makes no difference if a wheel is accelerated directly from torque applied to its shaft or indirectly from tangential force exerted by the ground, which came from tangential force from the other wheel, which came from torque applied to the drive shaft of the other wheel. Regardless of where the torque is applied, the wheel will accelerate at the exact same rate.
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Edgemts said:Really,
So if thats true then its just as easy to tighten a bolt with a one inch ratchet as it is with a 20 inch ratchet????
Once again I said accelerate not maintain.
Take a kids merry go round, load it full of kids, try to turn it from the center, now try the outside edge, were you able to make it accelerate at the same rate with the same effort? Now take the kids off.
Shoot if that's the case let me throw away my flywheel, the starter should be just fine connected right to a real small gear on the crank.Right?
Talk to you later, need to pull my tranny to get started.
:smile:
Didn't mean to start an argument just point out an error. I'll stand behind the physics, but I'm not sure I'm good enough to explain them properly. :smile:
Smaller wheels have a lower moment of inertia, but smaller diameter wheels also turn at higher RPM.Ojas said:
Mass at the edge of a wheel takes 2x the energy to accelerate as non-rotating mass. This is true no matter what the wheel diameter is.
Yep
Yes. In my original post, I neglected to mention the effect of the smaller diameter wheel. However, as soon as I realized this, I did post a <a href="http://www.nsxprime.com/forums/showthread.php?p=451758#post451758">follow-up</a> to clarify.Tom239 said:
NSX-Racer said:
Absolutely, thanks for the link. The Milwaukee Sawzall is cool.
Yes you would think so... However, a lower profile tyre will need stiffer sidewalls... Therefore thicker and heavier as well...nsxhk said:
Another factor to consider is the volume of air in the tyre. Porsche went to the trouble of making hollow spokes in some of their turbo rims to maximise the air volume and reduce weight at the same time...
nsxhk said:
The weight was obtained from Toyo official site. The weight of tires are probably equally as important as weight of the wheels if not more.
Weight of OEM tires:
15/16 94.6lbs total for all 4 tires
16/17 98lbs total for all 4 tires
#Oem Yokohama tires do weight a few lbs less than Oem Potenza.
Toyo T1-S weight 82.6 lbs total for 4 tires.
205/45/16
245/40/17
