Formula to convert lighter wheels to HP??
06-24-16, 10:20 AM
#1
Instructor
Thread Starter
Formula to convert lighter wheels to HP??
I just got new 18in Niche Apex wheels on my car--weights are 26 lbs F and 27 lbs R. From what Ive seen on this forum the stock wheel weights are 28 F and 30 R.
Ive seen on other forums that the general formula is 1 lb lighter=3 hp extra
So Im saving 3 lbs per each rear wheel--x3=9 hp per wheel x2=18 extra hp
I also just had a Spectre CAI installed--that's maybe 4 to 5 extra hp
So theoretically my cars hp is 306+18+5=329
Anyone else ever formulate weight savings to HP gain??
Ive seen on other forums that the general formula is 1 lb lighter=3 hp extra
So Im saving 3 lbs per each rear wheel--x3=9 hp per wheel x2=18 extra hp
I also just had a Spectre CAI installed--that's maybe 4 to 5 extra hp
So theoretically my cars hp is 306+18+5=329
Anyone else ever formulate weight savings to HP gain??
06-24-16, 11:18 AM
#2
Super Moderator
I just got new 18in Niche Apex wheels on my car--weights are 26 lbs F and 27 lbs R. From what Ive seen on this forum the stock wheel weights are 28 F and 30 R.
Ive seen on other forums that the general formula is 1 lb lighter=3 hp extra
So Im saving 3 lbs per each rear wheel--x3=9 hp per wheel x2=18 extra hp
I also just had a Spectre CAI installed--that's maybe 4 to 5 extra hp
So theoretically my cars hp is 306+18+5=329
Anyone else ever formulate weight savings to HP gain??
Ive seen on other forums that the general formula is 1 lb lighter=3 hp extra
So Im saving 3 lbs per each rear wheel--x3=9 hp per wheel x2=18 extra hp
I also just had a Spectre CAI installed--that's maybe 4 to 5 extra hp
So theoretically my cars hp is 306+18+5=329
Anyone else ever formulate weight savings to HP gain??
06-24-16, 01:04 PM
#3
If the 1lb = 3hp equation were anywhere near correct my car would be making the equivalent of near 500hp! ~10lbs per wheel, ~20lbs for my battery. 60lbs*3=180+306=486HP!!!
Although reducing weight can make the car accelerate faster trying to equate pounds lost per horsepower gained is not going to get you anywhere. The only way to quantify the difference weight loss makes is to do back-to-back acceleration runs and see what the difference is. My two cents is that ~12lbs (or for you smart a$$e$ a less than 10% reduction in wheel rotational inertia) isn't going to make much if any difference in acceleration.
Although reducing weight can make the car accelerate faster trying to equate pounds lost per horsepower gained is not going to get you anywhere. The only way to quantify the difference weight loss makes is to do back-to-back acceleration runs and see what the difference is. My two cents is that ~12lbs (or for you smart a$$e$ a less than 10% reduction in wheel rotational inertia) isn't going to make much if any difference in acceleration.
06-24-16, 02:22 PM
#4
Lexus Champion
Formula to convert lighter wheels to HP??
Sorry to rain on your parade but that spectre intake most likely hurt your cars total power output. From what I've seen over the years on the forum, the only intake that's made a proven positive difference on our cars is the Joe Z intake and even at that it's not a difference that can be felt. Our Stock intake is almost perfect and swapping it out for something like the spectre intake only hurts your power not help it.
As for the wheel equals power thing, that's not true either. If it were, than my car would be pretty damn fact right now as my 19" Stance SF01's weigh approximately 22lbs F and 24lbs R. Which by your measurement (if I understand you correctly) would mean that I'm making about 18hp for each rear wheel extra. So about 36hp total by reducing the weight on the rear slightly... And I can 100% without a doubt tell you that's BS. If it were true I'd be a hell of a lot faster than what I am now, especially when you consider the fact that I also have the Joe Z intake (4-5hp) and Catback exhaust (7-8hp) to account for.
I'm not gonna say that I don't feel the difference in my car compared to stock 18's because I do slightly feel like I may be just a tad bit quicker than before. But even if there really was a difference it would be something to small to properly measure or make anything out of it...
So basically what I'm trying to say is, with all your mods so far, or even with my mods for that matter. If you or I were to race a bone stock Is350 from a light, assuming equal circumstances, the stock IS would still be running about the same as you. That's all mainly due to the fact of how well tuned our cars are from factory. The only mods that would make an actual discernable difference that's not just in your head would be some PPE headers or a tune from RR Racing or TTFS. Other than that, I wouldn't mod the car for performance. At least not power wise anyway.. The only reason I even did what I have on my car currently is because I wanted my car to sound nicer and because I hate having stock wheels lol.
As for the wheel equals power thing, that's not true either. If it were, than my car would be pretty damn fact right now as my 19" Stance SF01's weigh approximately 22lbs F and 24lbs R. Which by your measurement (if I understand you correctly) would mean that I'm making about 18hp for each rear wheel extra. So about 36hp total by reducing the weight on the rear slightly... And I can 100% without a doubt tell you that's BS. If it were true I'd be a hell of a lot faster than what I am now, especially when you consider the fact that I also have the Joe Z intake (4-5hp) and Catback exhaust (7-8hp) to account for.
I'm not gonna say that I don't feel the difference in my car compared to stock 18's because I do slightly feel like I may be just a tad bit quicker than before. But even if there really was a difference it would be something to small to properly measure or make anything out of it...
So basically what I'm trying to say is, with all your mods so far, or even with my mods for that matter. If you or I were to race a bone stock Is350 from a light, assuming equal circumstances, the stock IS would still be running about the same as you. That's all mainly due to the fact of how well tuned our cars are from factory. The only mods that would make an actual discernable difference that's not just in your head would be some PPE headers or a tune from RR Racing or TTFS. Other than that, I wouldn't mod the car for performance. At least not power wise anyway.. The only reason I even did what I have on my car currently is because I wanted my car to sound nicer and because I hate having stock wheels lol.
06-24-16, 03:34 PM
#5
Instructor
Thread Starter
Sorry to rain on your parade but that spectre intake most likely hurt your cars total power output. From what I've seen over the years on the forum, the only intake that's made a proven positive difference on our cars is the Joe Z intake and even at that it's not a difference that can be felt. Our Stock intake is almost perfect and swapping it out for something like the spectre intake only hurts your power not help it.
As for the wheel equals power thing, that's not true either. If it were, than my car would be pretty damn fact right now as my 19" Stance SF01's weigh approximately 22lbs F and 24lbs R. Which by your measurement (if I understand you correctly) would mean that I'm making about 18hp for each rear wheel extra. So about 36hp total by reducing the weight on the rear slightly... And I can 100% without a doubt tell you that's BS. If it were true I'd be a hell of a lot faster than what I am now, especially when you consider the fact that I also have the Joe Z intake (4-5hp) and Catback exhaust (7-8hp) to account for.
I'm not gonna say that I don't feel the difference in my car compared to stock 18's because I do slightly feel like I may be just a tad bit quicker than before. But even if there really was a difference it would be something to small to properly measure or make anything out of it...
So basically what I'm trying to say is, with all your mods so far, or even with my mods for that matter. If you or I were to race a bone stock Is350 from a light, assuming equal circumstances, the stock IS would still be running about the same as you. That's all mainly due to the fact of how well tuned our cars are from factory. The only mods that would make an actual discernable difference that's not just in your head would be some PPE headers or a tune from RR Racing or TTFS. Other than that, I wouldn't mod the car for performance. At least not power wise anyway.. The only reason I even did what I have on my car currently is because I wanted my car to sound nicer and because I hate having stock wheels lol.
As for the wheel equals power thing, that's not true either. If it were, than my car would be pretty damn fact right now as my 19" Stance SF01's weigh approximately 22lbs F and 24lbs R. Which by your measurement (if I understand you correctly) would mean that I'm making about 18hp for each rear wheel extra. So about 36hp total by reducing the weight on the rear slightly... And I can 100% without a doubt tell you that's BS. If it were true I'd be a hell of a lot faster than what I am now, especially when you consider the fact that I also have the Joe Z intake (4-5hp) and Catback exhaust (7-8hp) to account for.
I'm not gonna say that I don't feel the difference in my car compared to stock 18's because I do slightly feel like I may be just a tad bit quicker than before. But even if there really was a difference it would be something to small to properly measure or make anything out of it...
So basically what I'm trying to say is, with all your mods so far, or even with my mods for that matter. If you or I were to race a bone stock Is350 from a light, assuming equal circumstances, the stock IS would still be running about the same as you. That's all mainly due to the fact of how well tuned our cars are from factory. The only mods that would make an actual discernable difference that's not just in your head would be some PPE headers or a tune from RR Racing or TTFS. Other than that, I wouldn't mod the car for performance. At least not power wise anyway.. The only reason I even did what I have on my car currently is because I wanted my car to sound nicer and because I hate having stock wheels lol.
Im not looking to turn it into a race car--Im in my 40s and not a boy racer. That's why Im not doing springs or exhaust. But the engine is too quiet and I want some noise. And the wheel weight to HP formula is something I saw on another website. Spectre claims 13 hp gain--I doubt that. They would also probably deny it hurts performance. I don't care Im keeping it on. My mods to the car are done.
06-24-16, 04:12 PM
#6
Lexus Champion
Im not looking to turn it into a race car--Im in my 40s and not a boy racer. That's why Im not doing springs or exhaust. But the engine is too quiet and I want some noise. And the wheel weight to HP formula is something I saw on another website. Spectre claims 13 hp gain--I doubt that. They would also probably deny it hurts performance. I don't care Im keeping it on. My mods to the car are done.
Which is why I said don't mod for performance (engine wise) as thats not what our cars are for. But since you don't care for power than I guess we're good
06-24-16, 04:50 PM
#7
According to Enkei, "Every pound of unsprung weight savings has the effect of reducing overall vehicle weight by 20lbs."
Essentially, each pound of unsprung weight that you're able to reduce per wheel is equivalent to 5 pounds of sprung weight.
If you're able to reduce 10 pounds of unsprung weight per wheel (40 lbs total), the vehicle would supposedly feel like it reduced 200 pounds of its curb weight.
A general rule of thumb is every 100 pounds reduced from the curb weight is equivalent to gaining 8-10 HP and a reduction of 0.1 seconds off the quarter-mile time and 0-60 time.
Essentially, each pound of unsprung weight that you're able to reduce per wheel is equivalent to 5 pounds of sprung weight.
If you're able to reduce 10 pounds of unsprung weight per wheel (40 lbs total), the vehicle would supposedly feel like it reduced 200 pounds of its curb weight.
A general rule of thumb is every 100 pounds reduced from the curb weight is equivalent to gaining 8-10 HP and a reduction of 0.1 seconds off the quarter-mile time and 0-60 time.
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06-24-16, 04:54 PM
#8
Lexus Champion
Formula to convert lighter wheels to HP??
According to Enkei, "Every pound of unsprung weight savings has the effect of reducing overall vehicle weight by 20lbs."
Essentially, each pound of unsprung weight that you're able to reduce per wheel is equivalent to 5 pounds of sprung weight.
If you're able to reduce 10 pounds of unsprung weight per wheel (40 lbs total), the vehicle would supposedly feel like it reduced 200 pounds of its curb weight.
A general rule of thumb is every 100 pounds reduced from the curb weight is equivalent to gaining 8-10 HP and a reduction of 0.1 seconds off the quarter-mile time and 0-60 time.
Essentially, each pound of unsprung weight that you're able to reduce per wheel is equivalent to 5 pounds of sprung weight.
If you're able to reduce 10 pounds of unsprung weight per wheel (40 lbs total), the vehicle would supposedly feel like it reduced 200 pounds of its curb weight.
A general rule of thumb is every 100 pounds reduced from the curb weight is equivalent to gaining 8-10 HP and a reduction of 0.1 seconds off the quarter-mile time and 0-60 time.
Last edited by Tro209; 06-24-16 at 05:01 PM.
06-24-16, 05:02 PM
#10
Lexus Champion
06-24-16, 05:51 PM
#11
Lexus Champion
I don't know where these figures come from, but they are misleading.
1. Unsprung weight (as opposed to sprung weight) has the following effect on acceleration: none whatever. On a road course with surface irregularities reduced unsprung weight may (if the suspension is adjusted) reduce lap times and improve average speed, but this advantage decays to zero with a flat surface. Read my article: http://victorylibrary.com/mopar/sprung.htm
2. Dead (absolute) weight loss from a wheel change of course affects the overall mass of the car - less is better, but it has nothing to do with it being a wheel or a cinder block. 5 lbs. per wheel removed from a 3,000 lb. car is .67% (less than 1%). You can't feel it, because the change is wayyy too small. Your senses are very poor at quantifying force, better at changes in force. The threshold of human perception for a F1 driver is about 2%, for an average driver 5%, which would require wheels weighing 37.5 lbs. less per wheel (the actual ET and MPH would improve much before this point).
3. The change in inertial loss from accelerating a lighter wheel (or tire, or brake rotor) is not proportionate to the weight or the diameter, but to the 4th power of the effective radius of mass, which can be somewhere near the center of the radius but varies greatly with the design. Two wheels with the same diameter and weight may have very different centers of mass (viz. less weight in the hub is worthless). Inertia goes up very quickly with increased mass radius, and also as the square of the RPM. Wheels are fairly large (compared to the flywheel or ring gear) but turn very slowly (compared to engine and driveline parts), so while it's an advantage it's pretty small. There is no "1 lb. = 3 lbs." fixed number, it's not possible. Read Vizard for some examples with math.
Enkei sells wheels. That comment was from the sales department, not the engineering department.
CAI intakes are a high profit center, very few do as well as the factory system.
1. Unsprung weight (as opposed to sprung weight) has the following effect on acceleration: none whatever. On a road course with surface irregularities reduced unsprung weight may (if the suspension is adjusted) reduce lap times and improve average speed, but this advantage decays to zero with a flat surface. Read my article: http://victorylibrary.com/mopar/sprung.htm
2. Dead (absolute) weight loss from a wheel change of course affects the overall mass of the car - less is better, but it has nothing to do with it being a wheel or a cinder block. 5 lbs. per wheel removed from a 3,000 lb. car is .67% (less than 1%). You can't feel it, because the change is wayyy too small. Your senses are very poor at quantifying force, better at changes in force. The threshold of human perception for a F1 driver is about 2%, for an average driver 5%, which would require wheels weighing 37.5 lbs. less per wheel (the actual ET and MPH would improve much before this point).
3. The change in inertial loss from accelerating a lighter wheel (or tire, or brake rotor) is not proportionate to the weight or the diameter, but to the 4th power of the effective radius of mass, which can be somewhere near the center of the radius but varies greatly with the design. Two wheels with the same diameter and weight may have very different centers of mass (viz. less weight in the hub is worthless). Inertia goes up very quickly with increased mass radius, and also as the square of the RPM. Wheels are fairly large (compared to the flywheel or ring gear) but turn very slowly (compared to engine and driveline parts), so while it's an advantage it's pretty small. There is no "1 lb. = 3 lbs." fixed number, it's not possible. Read Vizard for some examples with math.
Enkei sells wheels. That comment was from the sales department, not the engineering department.
CAI intakes are a high profit center, very few do as well as the factory system.
06-24-16, 06:56 PM
#12
FYI, Grassroot Motorsports did a test back in May 2014 comparing a miata equipped with a heavy set of wheels vs a lightweight set of wheels (12 pounds lighter per wheel). To minimize variables, tires were the same model and width and the wheels were the same diameter and width. The miata was Vbox confirmed to consistently be up to 0.3 seconds faster from 0-60 with the lighter set of wheels vs the heavier set.
Last edited by redspencer; 06-24-16 at 07:09 PM.
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