Performance question...larger rims = slower car? Input on performance needed...
Performance question...larger rims = slower car? Input on performance needed...
I was under the impression that larger rims will slow your car down, regardless of their weight. But then I realized how is that possible when the overall diameter of the rim/tire will remain the same (profile decreases as rim size increases)?
So now I'm confused and I need some clarification on the issue...I don't believe this needs to be in the tire/rim forum, since that forum is about maintenence and asking for help, and I'm asking a question about performance.
So...to those who own 18'' rims, how do you feel about them? Have you ever 1/4 miled your car with the same mods but different sized rims -- any notable differences? Can anybody clear this issue up for me? =)
So now I'm confused and I need some clarification on the issue...I don't believe this needs to be in the tire/rim forum, since that forum is about maintenence and asking for help, and I'm asking a question about performance.
So...to those who own 18'' rims, how do you feel about them? Have you ever 1/4 miled your car with the same mods but different sized rims -- any notable differences? Can anybody clear this issue up for me? =)
Originally Posted by NmexMAX
I've seen many 3.5L run good times on street 18's ...
BUt that the difference between the auto 3.0L and 3.5L ...
Rotational mass
must chime in 
BUt that the difference between the auto 3.0L and 3.5L ...
Rotational mass
must chime in Rotational mass will only come into play if the overall wheel weight is different.
you may get light 18's however the tires are heavier, so you may end up where you started.
I personally am sticking with 17's when I switch my rims, I dont remember where it is, but it was said after test that 17's offered the best mix of handeling and light weight.
Keep in mind that larger rims, even if not heavier AT ALL, will slow a car down. This is also due to the rotational mass/inertia being described above. The ratio may not be much, but yes, effect on acceleration is greater, (by at least 2:1) when reducing rotational weight vs. overall weight. The farther rotational mass is from its axis, the more energy it takes to move that mass.....hence making reducing THAT weight, more effective. THEREFORE, on 18s the mass is farther away from its pivot = more energy even if not heavier. It's all leverage folks!
The following information was borrowed from another site, found by googling for rotational mass:
I figure 1# off the wheels is about 2# off the chassis:
Notes from physics --- Kinetic Energy = 1/2 I w^2 where
I = MxR^2 ... R being the radial center of mass, w is rotational speed,
which for a 24"; tire is 1.0xspeed in ft/sec...
use slugs for M (lbs/32.17) if you want to stay in the ft/lb/sec system and
lets you easily figure out hp (550 ft.lb./sec) to spin up to a given speed in
a certain # of seconds).
I crunched some numbers for a reality check.
For my wheel tire combo (SSR 16x7 GT1 - 15# and
BS SS-03 205/60/16 24#) it would take about
6 hp to get the 4 tires spinning to 60 mph in 7 seconds
and to accelerate them linearly to 60 mph as well, and it would take a 50# combo about 9 hp to do the
same... and takes about 78 hp (average) to propell the
remaining 2500 pounds of car and driver from 0 to 60 in 7 sec.
This doesn't include extra horsies to overcome rolling friction
and air resistance.
From these numbers, 1# off at the wheel is about as good as about 2.2# off the chassis
3 hp difference for the 44# wt savings from 39# to 50# per wheel, compared with
3 hp difference for 96# at the chassis. 78hp for 2500# chassis vs 81 hp for 2596#
chassis to do the same 7 second 0-60.
Some approximations were used (like the precise location of R).
Your results may vary.
Hope this helps!
J
The following information was borrowed from another site, found by googling for rotational mass:
I figure 1# off the wheels is about 2# off the chassis:
Notes from physics --- Kinetic Energy = 1/2 I w^2 where
I = MxR^2 ... R being the radial center of mass, w is rotational speed,
which for a 24"; tire is 1.0xspeed in ft/sec...
use slugs for M (lbs/32.17) if you want to stay in the ft/lb/sec system and
lets you easily figure out hp (550 ft.lb./sec) to spin up to a given speed in
a certain # of seconds).
I crunched some numbers for a reality check.
For my wheel tire combo (SSR 16x7 GT1 - 15# and
BS SS-03 205/60/16 24#) it would take about
6 hp to get the 4 tires spinning to 60 mph in 7 seconds
and to accelerate them linearly to 60 mph as well, and it would take a 50# combo about 9 hp to do the
same... and takes about 78 hp (average) to propell the
remaining 2500 pounds of car and driver from 0 to 60 in 7 sec.
This doesn't include extra horsies to overcome rolling friction
and air resistance.
From these numbers, 1# off at the wheel is about as good as about 2.2# off the chassis
3 hp difference for the 44# wt savings from 39# to 50# per wheel, compared with
3 hp difference for 96# at the chassis. 78hp for 2500# chassis vs 81 hp for 2596#
chassis to do the same 7 second 0-60.
Some approximations were used (like the precise location of R).
Your results may vary.
Hope this helps!
J
it depends on weight, if you get 18s in the same weight as 17s...both with tires of course your 1/4 mi will be the same, BUT as upstatemax said, handeling will be worest because the tire is not rotating as much overall during the turn on a 17" rim than a 16"
Originally Posted by Jasovanni
Keep in mind that larger rims, even if not heavier AT ALL, will slow a car down. This is also due to the rotational mass/inertia being described above. The ratio may not be much, but yes, effect on acceleration is greater, (by at least 2:1) when reducing rotational weight vs. overall weight. The farther rotational mass is from its axis, the more energy it takes to move that mass.....hence making reducing THAT weight, more effective. THEREFORE, on 18s the mass is farther away from its pivot = more energy even if not heavier. It's all leverage folks!
The following information was borrowed from another site, found by googling for rotational mass:
I figure 1# off the wheels is about 2# off the chassis:
Notes from physics --- Kinetic Energy = 1/2 I w^2 where
I = MxR^2 ... R being the radial center of mass, w is rotational speed,
which for a 24"; tire is 1.0xspeed in ft/sec...
use slugs for M (lbs/32.17) if you want to stay in the ft/lb/sec system and
lets you easily figure out hp (550 ft.lb./sec) to spin up to a given speed in
a certain # of seconds).
I crunched some numbers for a reality check.
For my wheel tire combo (SSR 16x7 GT1 - 15# and
BS SS-03 205/60/16 24#) it would take about
6 hp to get the 4 tires spinning to 60 mph in 7 seconds
and to accelerate them linearly to 60 mph as well, and it would take a 50# combo about 9 hp to do the
same... and takes about 78 hp (average) to propell the
remaining 2500 pounds of car and driver from 0 to 60 in 7 sec.
This doesn't include extra horsies to overcome rolling friction
and air resistance.
From these numbers, 1# off at the wheel is about as good as about 2.2# off the chassis
3 hp difference for the 44# wt savings from 39# to 50# per wheel, compared with
3 hp difference for 96# at the chassis. 78hp for 2500# chassis vs 81 hp for 2596#
chassis to do the same 7 second 0-60.
Some approximations were used (like the precise location of R).
Your results may vary.
Hope this helps!
J
The following information was borrowed from another site, found by googling for rotational mass:
I figure 1# off the wheels is about 2# off the chassis:
Notes from physics --- Kinetic Energy = 1/2 I w^2 where
I = MxR^2 ... R being the radial center of mass, w is rotational speed,
which for a 24"; tire is 1.0xspeed in ft/sec...
use slugs for M (lbs/32.17) if you want to stay in the ft/lb/sec system and
lets you easily figure out hp (550 ft.lb./sec) to spin up to a given speed in
a certain # of seconds).
I crunched some numbers for a reality check.
For my wheel tire combo (SSR 16x7 GT1 - 15# and
BS SS-03 205/60/16 24#) it would take about
6 hp to get the 4 tires spinning to 60 mph in 7 seconds
and to accelerate them linearly to 60 mph as well, and it would take a 50# combo about 9 hp to do the
same... and takes about 78 hp (average) to propell the
remaining 2500 pounds of car and driver from 0 to 60 in 7 sec.
This doesn't include extra horsies to overcome rolling friction
and air resistance.
From these numbers, 1# off at the wheel is about as good as about 2.2# off the chassis
3 hp difference for the 44# wt savings from 39# to 50# per wheel, compared with
3 hp difference for 96# at the chassis. 78hp for 2500# chassis vs 81 hp for 2596#
chassis to do the same 7 second 0-60.
Some approximations were used (like the precise location of R).
Your results may vary.
Hope this helps!
J
thnks for the info, this only makes it dead certain, I am sticking with 17's....
Originally Posted by Jasovanni
Keep in mind that larger rims, even if not heavier AT ALL, will slow a car down. This is also due to the rotational mass/inertia being described above. The ratio may not be much, but yes, effect on acceleration is greater, (by at least 2:1) when reducing rotational weight vs. overall weight. The farther rotational mass is from its axis, the more energy it takes to move that mass.....hence making reducing THAT weight, more effective. THEREFORE, on 18s the mass is farther away from its pivot = more energy even if not heavier. It's all leverage folks!
The following information was borrowed from another site, found by googling for rotational mass:
I figure 1# off the wheels is about 2# off the chassis:
Notes from physics --- Kinetic Energy = 1/2 I w^2 where
I = MxR^2 ... R being the radial center of mass, w is rotational speed,
which for a 24"; tire is 1.0xspeed in ft/sec...
use slugs for M (lbs/32.17) if you want to stay in the ft/lb/sec system and
lets you easily figure out hp (550 ft.lb./sec) to spin up to a given speed in
a certain # of seconds).
I crunched some numbers for a reality check.
For my wheel tire combo (SSR 16x7 GT1 - 15# and
BS SS-03 205/60/16 24#) it would take about
6 hp to get the 4 tires spinning to 60 mph in 7 seconds
and to accelerate them linearly to 60 mph as well, and it would take a 50# combo about 9 hp to do the
same... and takes about 78 hp (average) to propell the
remaining 2500 pounds of car and driver from 0 to 60 in 7 sec.
This doesn't include extra horsies to overcome rolling friction
and air resistance.
From these numbers, 1# off at the wheel is about as good as about 2.2# off the chassis
3 hp difference for the 44# wt savings from 39# to 50# per wheel, compared with
3 hp difference for 96# at the chassis. 78hp for 2500# chassis vs 81 hp for 2596#
chassis to do the same 7 second 0-60.
Some approximations were used (like the precise location of R).
Your results may vary.
Hope this helps!
J
The following information was borrowed from another site, found by googling for rotational mass:
I figure 1# off the wheels is about 2# off the chassis:
Notes from physics --- Kinetic Energy = 1/2 I w^2 where
I = MxR^2 ... R being the radial center of mass, w is rotational speed,
which for a 24"; tire is 1.0xspeed in ft/sec...
use slugs for M (lbs/32.17) if you want to stay in the ft/lb/sec system and
lets you easily figure out hp (550 ft.lb./sec) to spin up to a given speed in
a certain # of seconds).
I crunched some numbers for a reality check.
For my wheel tire combo (SSR 16x7 GT1 - 15# and
BS SS-03 205/60/16 24#) it would take about
6 hp to get the 4 tires spinning to 60 mph in 7 seconds
and to accelerate them linearly to 60 mph as well, and it would take a 50# combo about 9 hp to do the
same... and takes about 78 hp (average) to propell the
remaining 2500 pounds of car and driver from 0 to 60 in 7 sec.
This doesn't include extra horsies to overcome rolling friction
and air resistance.
From these numbers, 1# off at the wheel is about as good as about 2.2# off the chassis
3 hp difference for the 44# wt savings from 39# to 50# per wheel, compared with
3 hp difference for 96# at the chassis. 78hp for 2500# chassis vs 81 hp for 2596#
chassis to do the same 7 second 0-60.
Some approximations were used (like the precise location of R).
Your results may vary.
Hope this helps!
J
You see...that's where I got the notion that because the rim is now moving further away from the center axis, the harder it will be to spin them. It's the same concept as say...taking a loop earring and spining it on your finger...and then taking a hoolahop and trying to spin that. I got into an arguement with Jeff92SE which I bowed out of...he made the point that a larger rim will not slow down performance because the overall tire-diameter remains the same.
I had some 16" rims, the OEM's that were dipped in chrome or chrome plated. With tires that combo was about 46lbs. I now have some 17's that are lighter and weigh 39lbs. The car feels a little lighter when accelerating especially in the lower rpms, but then again that is according to my inaccurate butt dyno. The only numbers I do have are from my gas mileage, which are better than the stock 16's.
larger but lighter wheels may achieve better acceleration because the radius in I=MR^2 is the radial center of mass which may change depending on the wheel design. If you can form a wheel that is much lighter than a wheel of a smaller diameter and get the radial center of mass smaller than the wheel of smaller diameter, then your energy required to rotate that wheel decreases. This also is dependent upon the weight of the tire. Generally, a larger wheel will result in more power required to rotate the wheel, but if you can get a wheel with substantially reduced rotational mass and a lighter weight tire, then you might be able to free up some power.
If we were to take two different wheels (with tires) of the same diameter and the same weight the performance numbers could still be different. The problem is that we don’t know how far the center of rotational mass is located from the actual center of mass (the center of the rim.) The further away the heaviest part of the wheel is located the more energy it takes to accelerate that wheel.
My guess is that most rims have the center of rotational mass closer to the sides. Therefore, your car should be slower with 18’s (considering that the tires weight stays the same)
On the other hand, by increasing the size of the rim you are also decreasing the profile (and the weight) of the tire which is just as important as the weight of the rim. (if not more important since the center of rotational mass of the tire is further away while the tires usually weigh just as much as the rims)
My guess is that most rims have the center of rotational mass closer to the sides. Therefore, your car should be slower with 18’s (considering that the tires weight stays the same)
On the other hand, by increasing the size of the rim you are also decreasing the profile (and the weight) of the tire which is just as important as the weight of the rim. (if not more important since the center of rotational mass of the tire is further away while the tires usually weigh just as much as the rims)
Member
Joined: Feb 2004
Posts: 116
The 2# off the rims = 1# off the tires as a rule of thumb can be thought of this way.
1st - Assume that your car somehow magically can accellerate without the tires spinning. In this case adding 1# to the rims would be the same as adding it to any other part of the car as far as accelleration is concerned.
Now, come back to reality. Your extra 1# on the rims still has the same affect as adding it to any other part of the car. However, now that your wheel is spinning, the outside of the tire is actually traveling around it's axis (for simplicity, assuming no deformation of the tire) at the exact same mph as the car. The rim's a little bit inside this and is traveling around the axel at a little less than the mph of the car (the ratio is the tire rim diameter divided by the outside tire diameter). The energy to accellerate this mass in a rotational way is in addition to the energy to accellerate this mass linearly along with the car body.
Since a large percentage of the wheel mass is concentrated in the rims, even if you keep the total tire/wheel mass the same, as you increase the wheel size, you move that mass of the rim outward and increase the rotational inertia, therfore theorhetically slowing accelleration.
If you wanted to run an experiment on this you could fabricate heavy iron or lead hoops that could bolt to your wheels. 1st, put these in the car and accellerate. Try and place them in the car near the center of the wheelbase so you maintain normal weight balance between the front and back. Then bolt the hoops to the wheels so they spin with the tires. Accellerate again. Despite the fact that the car in both cases weighs exactly the same, accelleration will be faster with the hoops in the car.
1st - Assume that your car somehow magically can accellerate without the tires spinning. In this case adding 1# to the rims would be the same as adding it to any other part of the car as far as accelleration is concerned.
Now, come back to reality. Your extra 1# on the rims still has the same affect as adding it to any other part of the car. However, now that your wheel is spinning, the outside of the tire is actually traveling around it's axis (for simplicity, assuming no deformation of the tire) at the exact same mph as the car. The rim's a little bit inside this and is traveling around the axel at a little less than the mph of the car (the ratio is the tire rim diameter divided by the outside tire diameter). The energy to accellerate this mass in a rotational way is in addition to the energy to accellerate this mass linearly along with the car body.
Since a large percentage of the wheel mass is concentrated in the rims, even if you keep the total tire/wheel mass the same, as you increase the wheel size, you move that mass of the rim outward and increase the rotational inertia, therfore theorhetically slowing accelleration.
If you wanted to run an experiment on this you could fabricate heavy iron or lead hoops that could bolt to your wheels. 1st, put these in the car and accellerate. Try and place them in the car near the center of the wheelbase so you maintain normal weight balance between the front and back. Then bolt the hoops to the wheels so they spin with the tires. Accellerate again. Despite the fact that the car in both cases weighs exactly the same, accelleration will be faster with the hoops in the car.
Supporting Maxima.org Member
Joined: Oct 2005
Posts: 64
i was thinking of getting 17's stock for my '00; i have 16's non-oem (dunno what they are cuz i bought it used with them on) and so my question is besides the visual aesthetics, what kind of change can i expect with performance and is it worth it?
Originally Posted by Jasovanni
Keep in mind that larger rims, even if not heavier AT ALL, will slow a car down.
i think lightweight wheels are designed through research and not that it's simply overall "lighter". the heaver part of the wheel would be closer to the center of rotation (center of rim) therefore having less rotational inertia. so it's not only lighter, but will help accelerate even if it's larger than your stock wheels.
think about weights for balancing your wheels. the further it is from the center of the wheel, the more of a difference it makes, hence that's where they put the weights. try putting those same amount of weights closer to the center of the rim to see if it actually makes a difference. you'd have to put a lot more.
Get some SSR CompH rims and forget bout stock 17s, they weight very little.
I am rocking 15" Sawblades from a 4th gen now for winter, and there is really no acceleration diff between them and my 17" Enkei RPO1, which weight the same as the Sawblades. I am selling my Enkeis too if anyone is interested
I am rocking 15" Sawblades from a 4th gen now for winter, and there is really no acceleration diff between them and my 17" Enkei RPO1, which weight the same as the Sawblades. I am selling my Enkeis too if anyone is interested
Originally Posted by VRod
what's the bottomline between 16s and 17s; major change worth doing to buy stock 17s?
The 17's look better and will handle better; on the flip side, they are heavier...
I think they are worth buying, however, I would look for a better 17" than the stockers. They are heavy at around 26lbs each... not to mention they are only 7" wide, I would look for at least a 17x7.5 so you can throw wider tires on and not have to worry about it.
Supporting Maxima.org Member
Joined: Oct 2005
Posts: 64
Originally Posted by upstatemax
The 17's look better and will handle better; on the flip side, they are heavier...
I think they are worth buying, however, I would look for a better 17" than the stockers. They are heavy at around 26lbs each... not to mention they are only 7" wide, I would look for at least a 17x7.5 so you can throw wider tires on and not have to worry about it.
I think they are worth buying, however, I would look for a better 17" than the stockers. They are heavy at around 26lbs each... not to mention they are only 7" wide, I would look for at least a 17x7.5 so you can throw wider tires on and not have to worry about it.
thanks for the help dude
Bigger tires will make your speedometer read slower
http://www.miata.net/garage/tirecalc.html
- thus the car will 'move' faster as per the speedo... however, we all know that the lighter and smaller the tires, the quicker the car... that's why a lot of guys have some 15" steelies hanging around for track runs...
http://www.miata.net/garage/tirecalc.html
- thus the car will 'move' faster as per the speedo... however, we all know that the lighter and smaller the tires, the quicker the car... that's why a lot of guys have some 15" steelies hanging around for track runs...
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