the performance of 17s
the performance of 17s
ok I have enkei rs7 17" rims. There has been alot going around about the issues of weight when compared to 15s. Today I was changing my rims to put on my winter tires. My winter tires are 15" steal rims that I got + 250 in exchange for my 04 ex rims. I weighted each tire and got the following rs7 37lbs with tire. Winter tires 41lbs. I know that performance 15s will be lighter than steel rims, but I think this would put them about even with my 17s. maybe a bit lighter. I really don't think that 15s will perform better than 17s
Yes, it's an Acura EL
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Keep in mind too that the majority of mass on a 17" rim is further from the rotational center, thus making it harder to get the car moving from stop. A 15" rim of the same weight (even if the total weight with rubber is identical for both rims) will be easier to start motion on, because the mass is closer to the rotational center of the wheel. I got this info a long time ago from this link: Clicky
Will you notice the difference on the track? Maybe, maybe not. You do gain a little bit of cornering ability from the fact that a 17" tire has less sidewall, and thus will flex less on a hard turn.
Will you notice the difference on the track? Maybe, maybe not. You do gain a little bit of cornering ability from the fact that a 17" tire has less sidewall, and thus will flex less on a hard turn.
Last edited by TeLLy; Dec 14, 2004 at 01:27 PM.
Autocross Junky
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Rep Power: 380 To reinforce Telly, The issue isnt with the Actual weight of the wheel, its with how far that weight is from the center of rotation... This influences whats called the Moment of Inertia. Inertia is the resistance an object has to a change in its state of motion. The more inertia an object has the harder it is to change its state of motoin, or in our case its harder to get that wheel to spin or stop from spinning.
A simpllified equation to Determin a wheels Moment of Inertia is this
I=m(r^2)
I = Inertia
M= Mass (weight)
r = Radius
So, For a 17" wheel to have approximatly the same inertia as the stock 15" wheel (18-19 LBS for the steel wheels) that 17" would need to weigh about 15 LBS... Compair that to the 15" alloys (16.5 lbs) that some have and that 17 now Needs to weigh about 13 LBS. Compair that to my Rotas @ 11.8lbs.... and a 17 would need to weigh about 9.1 LBS...
Now Tire does play a part, and Heavy tires can hinder you'r acceleration.. But Remember, a tire will a taller side wall will have a Higher ammount of its weight Closer to the center of rotation so its total weight will count for less.
Conclusion, a Light 17 is better then a Heavy 17, as you will have close to the stock wheels moment of Inertia, so you havent lost any thing... But a Light 15 is so much better... Will you notice this much on the street? probably not so much. But if you are racing the clock you will see a difference.
A simpllified equation to Determin a wheels Moment of Inertia is this
I=m(r^2)
I = Inertia
M= Mass (weight)
r = Radius
So, For a 17" wheel to have approximatly the same inertia as the stock 15" wheel (18-19 LBS for the steel wheels) that 17" would need to weigh about 15 LBS... Compair that to the 15" alloys (16.5 lbs) that some have and that 17 now Needs to weigh about 13 LBS. Compair that to my Rotas @ 11.8lbs.... and a 17 would need to weigh about 9.1 LBS...
Now Tire does play a part, and Heavy tires can hinder you'r acceleration.. But Remember, a tire will a taller side wall will have a Higher ammount of its weight Closer to the center of rotation so its total weight will count for less.
Conclusion, a Light 17 is better then a Heavy 17, as you will have close to the stock wheels moment of Inertia, so you havent lost any thing... But a Light 15 is so much better... Will you notice this much on the street? probably not so much. But if you are racing the clock you will see a difference.
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Zzyzx, it's nice to finally see a reply from someone who actually understands the issue. You must be an engineer? I'm guessing because I'm a Mec E, and usually nobody know what the hell I'm talking about when I explain it that way!
(SnOwBoArDeR | FoReVeR)
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From: Mission Viejo
Rep Power: 303 here is an example:
u have seen figure iceskater right....u know when they spin, their arms spread out....but when they bring the arms closer to their body, they spin faster.
another one.
hold a 10lbs weight w/ ur arm xtended.....now hold it closer to ur body. u can hold the weight longer w/ it closer to ur body.
done
laws of physics
u have seen figure iceskater right....u know when they spin, their arms spread out....but when they bring the arms closer to their body, they spin faster.
another one.
hold a 10lbs weight w/ ur arm xtended.....now hold it closer to ur body. u can hold the weight longer w/ it closer to ur body.
done
laws of physics
Originally Posted by Zzyzx
To reinforce Telly, The issue isnt with the Actual weight of the wheel, its with how far that weight is from the center of rotation... This influences whats called the Moment of Inertia. Inertia is the resistance an object has to a change in its state of motion. The more inertia an object has the harder it is to change its state of motoin, or in our case its harder to get that wheel to spin or stop from spinning.
A simpllified equation to Determin a wheels Moment of Inertia is this
I=m(r^2)
I = Inertia
M= Mass (weight)
r = Radius
So, For a 17" wheel to have approximatly the same inertia as the stock 15" wheel (18-19 LBS for the steel wheels) that 17" would need to weigh about 15 LBS... Compair that to the 15" alloys (16.5 lbs) that some have and that 17 now Needs to weigh about 13 LBS. Compair that to my Rotas @ 11.8lbs.... and a 17 would need to weigh about 9.1 LBS...
Now Tire does play a part, and Heavy tires can hinder you'r acceleration.. But Remember, a tire will a taller side wall will have a Higher ammount of its weight Closer to the center of rotation so its total weight will count for less.
Conclusion, a Light 17 is better then a Heavy 17, as you will have close to the stock wheels moment of Inertia, so you havent lost any thing... But a Light 15 is so much better... Will you notice this much on the street? probably not so much. But if you are racing the clock you will see a difference.
A simpllified equation to Determin a wheels Moment of Inertia is this
I=m(r^2)
I = Inertia
M= Mass (weight)
r = Radius
So, For a 17" wheel to have approximatly the same inertia as the stock 15" wheel (18-19 LBS for the steel wheels) that 17" would need to weigh about 15 LBS... Compair that to the 15" alloys (16.5 lbs) that some have and that 17 now Needs to weigh about 13 LBS. Compair that to my Rotas @ 11.8lbs.... and a 17 would need to weigh about 9.1 LBS...
Now Tire does play a part, and Heavy tires can hinder you'r acceleration.. But Remember, a tire will a taller side wall will have a Higher ammount of its weight Closer to the center of rotation so its total weight will count for less.
Conclusion, a Light 17 is better then a Heavy 17, as you will have close to the stock wheels moment of Inertia, so you havent lost any thing... But a Light 15 is so much better... Will you notice this much on the street? probably not so much. But if you are racing the clock you will see a difference.
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Originally Posted by Civic_Racer9
here is an example:
u have seen figure iceskater right....u know when they spin, their arms spread out....but when they bring the arms closer to their body, they spin faster.
another one.
hold a 10lbs weight w/ ur arm xtended.....now hold it closer to ur body. u can hold the weight longer w/ it closer to ur body.
done laws of physics
u have seen figure iceskater right....u know when they spin, their arms spread out....but when they bring the arms closer to their body, they spin faster.
another one.
hold a 10lbs weight w/ ur arm xtended.....now hold it closer to ur body. u can hold the weight longer w/ it closer to ur body.
done
laws of physics
Autocross Junky
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Originally Posted by Mr.EL
Zzyzx, it's nice to finally see a reply from someone who actually understands the issue. You must be an engineer? I'm guessing because I'm a Mec E, and usually nobody know what the hell I'm talking about when I explain it that way!
No engineer here.... I'm just an Avid Racer (Legal, Sanctioned and Insured) with an aptitude for Physics/mechanics..
Originally Posted by bgoetz
I was really just focusing on the overall weight, but I do understand what you are saying. However this would be more dependant on the overall design of the wheel vs the size. As long as you get a 17 that will match the same overall size as your stock tires the weight from the center of the tire will not be that much difference. But yes I understand this concept
Heres a better explination:
For a typical wheel, approximatly 80% of its weight will be found in the rim it self (the farthest point on the wheel away from the center of rotation). For a tire... that depends on the profile of the tire. Simply put, a tire with a Higher profile will have more of its weight closer to the center of rotation, making more of that tires wieght effect the wheel/tires combos inertia Less.
Example: say we have a 17" wheel with a 205/40-17 Tire (fairly common) that would give us a side wall of 3.23" a Radious of 11.73". compair that to a 15" wheel with a 205/50-15 tire (also Fairly common) that would aive you a side wall of 4.06" and a radius of 11.57" (Just over 1% smaller then the 17)
Now, assuming both wheel/tire combos weighed the same, your still better off with the 15" wheel/tire combo simply because more of the wheels weight is closer to the center of rotation Plus, more of the tires weight is closer to the center of rotation..
and to reiterate, you will probably not notice a difference in the above by using your butt dyno, but if you are racing a clock you will see a difference.
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Rep Power: 0 Not only should you think about weight and how it is distributed about the wheel but you should also think about how a larger wheel/tire combination will affect your gear ratio. I personally drive on 14s with some chubby falkens and i wish i had 13s, gear ratio, weight, and braking.
Julian
Julian
Originally Posted by 87MugenProCR-X
Not only should you think about weight and how it is distributed about the wheel but you should also think about how a larger wheel/tire combination will affect your gear ratio. I personally drive on 14s with some chubby falkens and i wish i had 13s, gear ratio, weight, and braking.
Julian
Julian
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Rep Power: 380 He's talking about altering the final gear ratio by running Tires that are of a different overall diamiter then Stock, thus altering your acceleration and shift points.
and I agree.. if there were decently wide and sticky tires in 14" I'd be running them... if I could run 13's and there were decent tires for them... I'd run those too.
and I agree.. if there were decently wide and sticky tires in 14" I'd be running them... if I could run 13's and there were decent tires for them... I'd run those too.
. 
I too was debating 15" Rota's or 17" Arospeeds. I had some 18" Enkei's awhile back and I noticed a slight drop in acceleration from a stop with those. The rims were 24lbs a piece. I figure the Arospeeds weight 17.2 a piece, and should give me about the same as my stockers plus a wider tire. They look pretty good too. You just gotta compromise.
Originally Posted by mootlif3
I too was debating 15" Rota's or 17" Arospeeds. I had some 18" Enkei's awhile back and I noticed a slight drop in acceleration from a stop with those. The rims were 24lbs a piece. I figure the Arospeeds weight 17.2 a piece, and should give me about the same as my stockers plus a wider tire. They look pretty good too. You just gotta compromise.
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