wheel weight. Is it a big deal?
04-19-02, 10:11 PM
#2
Yes, you can actually feel the decrease in acceleration from larger wheels that have even modestly more rotational inertia. Similarly, you can feel the ride get worse when you install wheels that simply weigh more (note the jarring feel of going over bumps in cars with heavy wheel/tire assemblies). The same thing that causes the ride to get worse also decreases performance because it is harder for the spring/shock assembly to control the motion of the wheel and keep it in contact with the ground.
How much worse it gets with weight depends on how much more the new wheels (and tires) weigh. I mention tires because they often weigh more that light wheels, and have a greater effect on rotational inertia both because of their weight and because they are farther from the wheel center (and rotational inertia is based on both weight and distance from the center). The value of light wheels also depends on the buyer's own valuation of the change versus the cost of going lighter. But lighter wheel/tire assemblies are absolutely better than heavier ones, all other things being equal. Getting heavier wheels and tires is worse in every regard, but often the advantage of wider tires or more room for brakes outweighs (a pun!) a modest increase in weight, and that is why people are frequently willing to go (a little) heavier.
The average buyer gets bigger wheels for cosmetic reasons that outweigh the costs of the weight increase to that buyer, or perhaps they don't care or are unaware of the downside of the increased weight. That's okay with me, too, after all it is their car so they can choose whatever they want. Unfortunately, the same buyers often think that they got an absolute increase in performance and don't even consider the weight issue.
-Max
How much worse it gets with weight depends on how much more the new wheels (and tires) weigh. I mention tires because they often weigh more that light wheels, and have a greater effect on rotational inertia both because of their weight and because they are farther from the wheel center (and rotational inertia is based on both weight and distance from the center). The value of light wheels also depends on the buyer's own valuation of the change versus the cost of going lighter. But lighter wheel/tire assemblies are absolutely better than heavier ones, all other things being equal. Getting heavier wheels and tires is worse in every regard, but often the advantage of wider tires or more room for brakes outweighs (a pun!) a modest increase in weight, and that is why people are frequently willing to go (a little) heavier.
The average buyer gets bigger wheels for cosmetic reasons that outweigh the costs of the weight increase to that buyer, or perhaps they don't care or are unaware of the downside of the increased weight. That's okay with me, too, after all it is their car so they can choose whatever they want. Unfortunately, the same buyers often think that they got an absolute increase in performance and don't even consider the weight issue.
-Max
Last edited by maxcooper; 04-19-02 at 10:13 PM.
04-19-02, 10:44 PM
#3
unless you buy larger wheels that are less weight than your smaller ones so you can get some kick *** road race tires on them 
I had to goto 17's so I could get the width I wanted.
not bad 13 pounds for 17X8
http://www.teamfc3s.org/main/members...R&img=rpf1.jpg
I had to goto 17's so I could get the width I wanted.
not bad 13 pounds for 17X8
http://www.teamfc3s.org/main/members...R&img=rpf1.jpg
04-19-02, 11:30 PM
#4
Lives on the Forum
I doubt you'd feel the difference in acceleration, unless you're doing timed runs or on a dyno.  Else, my butt dyno is just getting too old!
My experience has been the opposite of what maxcooper mentioned.  Heaviers wheels tends to "dull" the suspension reaction.  Lighter wheels actually "react faster" and cause more bumps in the ride.
This is comparing stock Zenki FC3S rims (16"x7") which weigh about 27# to GAB Sports rims (16"x7") which weigh about 15#.  You can throw out the tire weight theory, cause the same tires were dismounted and remounted on the new rims.
-Ted
My experience has been the opposite of what maxcooper mentioned.  Heaviers wheels tends to "dull" the suspension reaction.  Lighter wheels actually "react faster" and cause more bumps in the ride.
This is comparing stock Zenki FC3S rims (16"x7") which weigh about 27# to GAB Sports rims (16"x7") which weigh about 15#.  You can throw out the tire weight theory, cause the same tires were dismounted and remounted on the new rims.
-Ted
04-20-02, 01:00 AM
#5
I stand by my original post, on all counts.
I can feel it on my car when I put the 18's on, even though the diameter is smaller than my 17s in the rear. It damps the acceleration in low gears. Other owners have commented about the same thing to me when they switched to bigger wheels. It feels much like a heavy flywheel versus a light one (as it is essentially the same issue -- rotational inertia).
My experience has been the opposite of what maxcooper mentioned.  Heaviers wheels tends to "dull" the suspension reaction.  Lighter wheels actually "react faster" and cause more bumps in the ride.
This is comparing stock Zenki FC3S rims (16"x7") which weigh about 27# to GAB Sports rims (16"x7") which weigh about 15#.  You can throw out the tire weight theory, cause the same tires were dismounted and remounted on the new rims.
-Ted
Lighter will change the frequency of the response, so it is possible that Ted's experience was a result of the response moving into a frequency range that is more perceptible/annoying to humans. But there isn't any debate about this topic in the Ride & Handling Engineering or racing communities. Lighter is better for ride and handling.
Consider that when the wheel is in the air, the sprung (chassis) and unsprung (wheel, suspension) weights are separated by the spring. If you let the spring do its work, it will push each body away from each other, and the amount that each moves depends on the ratio of their masses. Gravity is working on both of them equally, so it cancels out. The wheel will always move a lot more because it is always lighter, but a heavier wheel connected to the same chassis will result in more chassis motion. This is why ride degrades as unsprung weight increases -- the chassis moves more. It is also why cars with heavier chassis have a better ride. Load up your RX-7 with people, tires, and tools and things, and you'll see that the ride is better when it is laden with all that crap (until you bottom out). The effect is quite noticable.
It also takes longer for the wheel to get back to the ground if it is heavy, and this is part of the reason that handling degrades as wheel weight increases. The tire spends less time on the ground, because the suspension has a harder time keeping it there (while working against the chassis). If the chassis had inifinite mass, the situation becomes similar to valve float in piston engines -- heavier valves don't follow the cam profile as well as light ones, the same way that heavy wheels and tires don't follow the road as well when you hit bumps at speed. Having the tire off the ground in a turn reduces cornering limits. Bring chassis weight back into it, and it gets even worse -- much like having softer valve springs.
There is an effect with a heavier wheel that it will resist motion more, allowing the tire to deform more and move the wheel less. But the dominant effect is the one I described above, so the advantage is still with the lower unsprung weight setup. On the balance of things, lighter turns out to better in every way.
-Max
Originally posted by RETed
I doubt you'd feel the difference in acceleration, unless you're doing timed runs or on a dyno.  Else, my butt dyno is just getting too old!
I doubt you'd feel the difference in acceleration, unless you're doing timed runs or on a dyno.  Else, my butt dyno is just getting too old!
My experience has been the opposite of what maxcooper mentioned.  Heaviers wheels tends to "dull" the suspension reaction.  Lighter wheels actually "react faster" and cause more bumps in the ride.
This is comparing stock Zenki FC3S rims (16"x7") which weigh about 27# to GAB Sports rims (16"x7") which weigh about 15#.  You can throw out the tire weight theory, cause the same tires were dismounted and remounted on the new rims.
-Ted
Consider that when the wheel is in the air, the sprung (chassis) and unsprung (wheel, suspension) weights are separated by the spring. If you let the spring do its work, it will push each body away from each other, and the amount that each moves depends on the ratio of their masses. Gravity is working on both of them equally, so it cancels out. The wheel will always move a lot more because it is always lighter, but a heavier wheel connected to the same chassis will result in more chassis motion. This is why ride degrades as unsprung weight increases -- the chassis moves more. It is also why cars with heavier chassis have a better ride. Load up your RX-7 with people, tires, and tools and things, and you'll see that the ride is better when it is laden with all that crap (until you bottom out). The effect is quite noticable.
It also takes longer for the wheel to get back to the ground if it is heavy, and this is part of the reason that handling degrades as wheel weight increases. The tire spends less time on the ground, because the suspension has a harder time keeping it there (while working against the chassis). If the chassis had inifinite mass, the situation becomes similar to valve float in piston engines -- heavier valves don't follow the cam profile as well as light ones, the same way that heavy wheels and tires don't follow the road as well when you hit bumps at speed. Having the tire off the ground in a turn reduces cornering limits. Bring chassis weight back into it, and it gets even worse -- much like having softer valve springs.
There is an effect with a heavier wheel that it will resist motion more, allowing the tire to deform more and move the wheel less. But the dominant effect is the one I described above, so the advantage is still with the lower unsprung weight setup. On the balance of things, lighter turns out to better in every way.
-Max
04-20-02, 08:24 AM
#6
Lives on the Forum
Excellent posts, Max...FWIW, I agree in every way...
In my experience, my acceleration HAS suffered on the public roads SINCE I've converted to 9 x 17, 45-mm offset SSR Integral A2s shod with 255/40-17 Yokohama AVS Intermediates all the way around; compared with my old "stock" setup of 8 x 16, 38-mm offset SSR IA2s shod with 225/50-16 Pirelli P-Zero Asimmetricos.
The weight difference between the 17 and 16 inch setups is about 10 lbs. The 17s weigh 45 lbs each corner, while the 16s were 35 lbs each corner.
While I don't feel too much degradation in the ride quality, I definitely feel a loss in acceleration (which is why I don't street race anymore)
The upshot with the new road setup is the increased grip levels during on/off ramp entry/exits! Unbelievable--my FD is just glued, and I don't hear ANY tire squeal...I plan on track testing the road setup for a few laps to see if the wider road rubber (despite the heavier weights) will turn decent laptimes at Putnam Park!
One note to keep in mind, is that my car is 100 hp down from Max's FD, so my problem is magnified vs what Max feels with 18s vs 17s.
Interestingly enough, I don't feel the acceleration loss when I switch to my track 17-inch track setup--8.5 fr and 9.5 rr x 17 SSR Competitions with 245/45 fr and 275/40 rr -17 Hoosier R3S03s. Each corner weighs--you guessed it--35 to 36 lbs! The upside to the track setup is I get the increased traction of the sticky Hoosiers complemented with the wider contact patches (from the wider tire sizes)...while still maintaining the stock wheel/tire weights--I got my cake and am enjoying it too
Anyhow, I just wanted to chime in and say that my experience is very similar to Max's experience.
FWIW, the wheel weight differences are as follows:
8 x 16, 38-mm SSR IA2--16 lbs
9 x 17, 45-mm SSR IA2--19 lbs
8.5 x 17, 42-mm SSR Comp--15 lbs
9.5 x 17, 42-mm SSR Comp--16 lbs
Tire weights are as follows:
225/50-16 Pirelli P-Zeros--20 lbs
255/40-17 Yokohama AVS Intermediates--26 lbs
245/45-17 Hoosier R3S03--20 lbs
275/40-17 Hoosier R3S03--21 lbs
TRUST US--WEIGHT MATTERS--LESS is BETTER (MORE?)
Have you lifted a Champ car wheel/tire setup?--they're feather light relative to their huge sizes!
In my experience, my acceleration HAS suffered on the public roads SINCE I've converted to 9 x 17, 45-mm offset SSR Integral A2s shod with 255/40-17 Yokohama AVS Intermediates all the way around; compared with my old "stock" setup of 8 x 16, 38-mm offset SSR IA2s shod with 225/50-16 Pirelli P-Zero Asimmetricos.
The weight difference between the 17 and 16 inch setups is about 10 lbs. The 17s weigh 45 lbs each corner, while the 16s were 35 lbs each corner.
While I don't feel too much degradation in the ride quality, I definitely feel a loss in acceleration (which is why I don't street race anymore)
The upshot with the new road setup is the increased grip levels during on/off ramp entry/exits! Unbelievable--my FD is just glued, and I don't hear ANY tire squeal...I plan on track testing the road setup for a few laps to see if the wider road rubber (despite the heavier weights) will turn decent laptimes at Putnam Park!
One note to keep in mind, is that my car is 100 hp down from Max's FD, so my problem is magnified vs what Max feels with 18s vs 17s.
Interestingly enough, I don't feel the acceleration loss when I switch to my track 17-inch track setup--8.5 fr and 9.5 rr x 17 SSR Competitions with 245/45 fr and 275/40 rr -17 Hoosier R3S03s. Each corner weighs--you guessed it--35 to 36 lbs! The upside to the track setup is I get the increased traction of the sticky Hoosiers complemented with the wider contact patches (from the wider tire sizes)...while still maintaining the stock wheel/tire weights--I got my cake and am enjoying it too
Anyhow, I just wanted to chime in and say that my experience is very similar to Max's experience.
FWIW, the wheel weight differences are as follows:
8 x 16, 38-mm SSR IA2--16 lbs
9 x 17, 45-mm SSR IA2--19 lbs
8.5 x 17, 42-mm SSR Comp--15 lbs
9.5 x 17, 42-mm SSR Comp--16 lbs
Tire weights are as follows:
225/50-16 Pirelli P-Zeros--20 lbs
255/40-17 Yokohama AVS Intermediates--26 lbs
245/45-17 Hoosier R3S03--20 lbs
275/40-17 Hoosier R3S03--21 lbs
TRUST US--WEIGHT MATTERS--LESS is BETTER (MORE?)
Have you lifted a Champ car wheel/tire setup?--they're feather light relative to their huge sizes!
Last edited by SleepR1; 04-20-02 at 08:34 AM.
04-20-02, 02:52 PM
#7
All out Track Freak!
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Max when the intermediates wear out go with some toyo's I have the same size 255 40 17 and they weigh 22lbs not bad for a street tire. Not too expensive either I paid about 680 shipped.
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04-20-02, 05:12 PM
#8
Ghost Ride the Whip
Keep in mind that another important thing to consider when purchasing wheels is the strength of the wheels. Just because a wheel is light does not automatically mean that its' the best choice, if the wheel bends when you run over a pothole or a bump then it will upset the balance of the car and ruin the handling. Make sure whatever wheel you get is forged so that you know it's strong.
04-20-02, 05:47 PM
#9
Lives on the Forum
Tite FD,
Absolutely! I agree with striking a balance between lightness and strength. This is EXACTLY the reason why I'm using the SSR Integral IA2s for the road, and the SSR Comps for the track. I'm not saying the Comps wouldn't be able to handle road duty, but I'd rather use the lightest possible for race, and use the heavier and probably stronger wheel for the road.
Your point comes strongly into view when you begin considering 18 or 19-inch wheels. As the tire sidewall decreases, more and more, there's less and less cushioning the car between road and wheel, and if the wheel is too light then you'll most likely bend them running over a chuckhole!
Absolutely! I agree with striking a balance between lightness and strength. This is EXACTLY the reason why I'm using the SSR Integral IA2s for the road, and the SSR Comps for the track. I'm not saying the Comps wouldn't be able to handle road duty, but I'd rather use the lightest possible for race, and use the heavier and probably stronger wheel for the road.
Your point comes strongly into view when you begin considering 18 or 19-inch wheels. As the tire sidewall decreases, more and more, there's less and less cushioning the car between road and wheel, and if the wheel is too light then you'll most likely bend them running over a chuckhole!
04-20-02, 05:58 PM
#10
Lives on the Forum
Now, one obvious that hasn't come up yet is that fact I'm comparing my FC to your FD's.  Suspensions type is obviously different, so this could be a major point.
The vibration frequency is a good point - it could also connect with the fact that the suspension types are different.
I agree with the fact that lighter is better!
-Ted
The vibration frequency is a good point - it could also connect with the fact that the suspension types are different.
I agree with the fact that lighter is better!
-Ted
04-20-02, 06:23 PM
#11
Lives on the Forum
Fritz,
My AVS I's in 255/40-17 were $515 for a set of 5...with the '99 FD Rx7 Type RS brakes, I carry around an extra 9 x 17, 45-mm SSR IA2 with Yoko AVS I in back for a full-size spare, since the 16-inch temp spare will not fit over the larger calipers...
My AVS I's in 255/40-17 were $515 for a set of 5...with the '99 FD Rx7 Type RS brakes, I carry around an extra 9 x 17, 45-mm SSR IA2 with Yoko AVS I in back for a full-size spare, since the 16-inch temp spare will not fit over the larger calipers...
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