Myx
Senior Member
- Joined
- Mar 6, 2016
- Threads
- 79
- Messages
- 2,166
- Reaction score
- 2,042
- Location
- Delaware
- Vehicle(s)
- 2018 Honda Civic EX (Hatchback/CVT)
- Vehicle Showcase
- 1
- Thread starter
- #1
Rotating Mass, Available Horsepower and Acceleration
This is probably one of the most uncool wheel/tire posts in this forum and I'm probably a 1%'er here. It is absolutely not for looks. Just tests with acceleration.
**I am not recommending anyone do or try this.**
Anyways....
Car: 1.5ltr 2018 Honda Civic EX turbo (Hatchback/CVT)
Stock wheel/tire: 215/50-17 Continental Procontact TX, 17X7" Alloys
Stock Tire Weight: 21lbs
Stock Wheel Weight: 27.8lbs
Stock wheel/tire weight: 48.8lbs.
New wheel/tire: 225/50-15 Kumho Ecsta AST, 15X7 Enkei J10.
Tire weight: 21lbs (Tirerack)
Wheel weight: 14.6lbs (Tirerack)
Wheel/Tire weight (weighed on bathroom scale): 35.6lbs.
Total weight reduction: -13.2lbs per wheel.
Total reduction of rotating wheel mass: -48.8lbs total
Miata Tire Size Calculator shows a -6.3% change. Speedometer will be affected. So available wheel hp/torque to the wheels estimated at an extra 6.3%. I'll test for results in 1/4 mile times. Not hp/tq numbers anymore. Dropped 4/10ths of a second doing something similar to this in my Rav4. 3/10ths in my Honda Fit. Who knows where this will go. I'm no engineer. I'm sure there's cool math to calculate this.
I picked these tires to experiment with the effects of changing final drive gear ratio. There are better tires to use but these are the only all season tires I could find @15" to affect this much change in gear ratio.
Stock final drive gear ratio is: 4.81:1
Kumho Tire gear ratio: 5.13:1 Gear Ratio Calculator
How Does Gear Ratio Affect Torque
Pounds Per Horsepower
Rotational Inertia - Equivalent Mass
Is Bigger Better - 15" vs 17"
Gear Ratio Calculator
CVT - A Simulated Tuning Approach
This is just my personal experiment with rotational mass reduction and gear ratio. Just one of the ways I improve acceleration. Putting this up for personal documentation (In case computer hard drive fails, paper notes become lost, etc). Just sharing though!
Disclaimer: I don't recommend anyone do this. Stick to your stock tire diameter. You will throw off your speedometer, odometer and possibly affect your suspension geometry in strange ways not intended by your manufacturer. Hell, you may suffer seizures, disorientation, heart failure and permanent hearing loss. Just don't do it.
Additional Info:
Inertia Calculator
General formula: I = mr^2 = mass * radius * radius
Inertia = Inerita of wheel + Inertia of the tire
Inertia = m1 * (r1²) + m2 * (r2²)
Mass of stock wheel: m1 = 27.8 lb
Radius of stock wheel: r1 = 8.5"
stock tire: Continental 215/50-17
Mass of stock tire: m2 = 21 lb
Radius of stock tire: r2 = 12.75"
Stock Inertia = 27.8 * (8.5²) + 21 * (12.75²)
Stock Inertia = 2008 + 3413
Stock Inertia = 5421 ********
New wheel: Enkei J10 15X6.5"
Radius of new wheel: r1 = 7.5"
new tire: Kumho Ecsta AST 225/50-15
Mass of new tire: m2 = 21 lb
Radius of new tire: r2 = 11.95"
New Inertia = 14.4 * (7.5²) + 21 * (11.95²)
New Inertia = 810 + 2999
New Inertia = 3809 *******
Total reduction in Inertia:
3809/5421 = 0.70 .....70%
30% Reduction in Rotating Inertia
The Effects of Rotational Inertia on Automotive Acceleration
More Personal Notes - 9/21/19
New wheel/tire: 205/50-15 Vredestein Quatrac 5
Tire weight: 17lbs (Tirerack) {-4lbs Lost}
Wheel weight: 14.6lbs (Tirerack) {-13.2lbs Lost}
Wheel/Tire weight: 31.6lbs.
Total weight reduction (Per Wheel): -17.2lbs per wheel.
Total reduction of rotating wheel mass (All four wheels): -68.8lbs total
Stock final drive gear ratio is: 4.81:1
Vredestein Quatrac 5 Tire gear ratio: 5.31:1 Gear Ratio Calculator
Miata Tire Size Calculator shows a -9.4% change from stock and a -1.7% from current setup. Speedometer will be affected. So available wheel hp/torque to the wheels estimated at an extra +9.4% (Instead of 6.3%). This is ONLY based on the change in wheel/tire size (Diameter = Gearing) alone, not the change in weight.
Guesstimate is that since change in rotational mass is 5lbs per wheel for a total of 20lbs (From lighter tire now), this is the equivalent to gaining +6.5whp (Myxal Math).
Personal Note:
Spoon Sports SW388 15" - 9.4lbs
This is probably one of the most uncool wheel/tire posts in this forum and I'm probably a 1%'er here. It is absolutely not for looks. Just tests with acceleration.
**I am not recommending anyone do or try this.**
Anyways....
Car: 1.5ltr 2018 Honda Civic EX turbo (Hatchback/CVT)
Stock wheel/tire: 215/50-17 Continental Procontact TX, 17X7" Alloys
Stock Tire Weight: 21lbs
Stock Wheel Weight: 27.8lbs
Stock wheel/tire weight: 48.8lbs.
New wheel/tire: 225/50-15 Kumho Ecsta AST, 15X7 Enkei J10.
Tire weight: 21lbs (Tirerack)
Wheel weight: 14.6lbs (Tirerack)
Wheel/Tire weight (weighed on bathroom scale): 35.6lbs.
Total weight reduction: -13.2lbs per wheel.
Total reduction of rotating wheel mass: -48.8lbs total
Miata Tire Size Calculator shows a -6.3% change. Speedometer will be affected. So available wheel hp/torque to the wheels estimated at an extra 6.3%. I'll test for results in 1/4 mile times. Not hp/tq numbers anymore. Dropped 4/10ths of a second doing something similar to this in my Rav4. 3/10ths in my Honda Fit. Who knows where this will go. I'm no engineer. I'm sure there's cool math to calculate this.
I picked these tires to experiment with the effects of changing final drive gear ratio. There are better tires to use but these are the only all season tires I could find @15" to affect this much change in gear ratio.
Stock final drive gear ratio is: 4.81:1
Kumho Tire gear ratio: 5.13:1 Gear Ratio Calculator
How Does Gear Ratio Affect Torque
Pounds Per Horsepower
Rotational Inertia - Effect on Power.36whp per extra pound of unsprung weight. or "For each 3 lbs extra unsprung weight, you will lose 1 rwhp."
Rotational Inertia - Equivalent Mass
Is Bigger Better - 15" vs 17"
Gear Ratio Calculator
CVT - A Simulated Tuning Approach
This is just my personal experiment with rotational mass reduction and gear ratio. Just one of the ways I improve acceleration. Putting this up for personal documentation (In case computer hard drive fails, paper notes become lost, etc). Just sharing though!
Disclaimer: I don't recommend anyone do this. Stick to your stock tire diameter. You will throw off your speedometer, odometer and possibly affect your suspension geometry in strange ways not intended by your manufacturer. Hell, you may suffer seizures, disorientation, heart failure and permanent hearing loss. Just don't do it.
Additional Info:
Inertia Calculator
General formula: I = mr^2 = mass * radius * radius
Inertia = Inerita of wheel + Inertia of the tire
Inertia = m1 * (r1²) + m2 * (r2²)
Mass of stock wheel: m1 = 27.8 lb
Radius of stock wheel: r1 = 8.5"
stock tire: Continental 215/50-17
Mass of stock tire: m2 = 21 lb
Radius of stock tire: r2 = 12.75"
Stock Inertia = 27.8 * (8.5²) + 21 * (12.75²)
Stock Inertia = 2008 + 3413
Stock Inertia = 5421 ********
New wheel: Enkei J10 15X6.5"
Radius of new wheel: r1 = 7.5"
new tire: Kumho Ecsta AST 225/50-15
Mass of new tire: m2 = 21 lb
Radius of new tire: r2 = 11.95"
New Inertia = 14.4 * (7.5²) + 21 * (11.95²)
New Inertia = 810 + 2999
New Inertia = 3809 *******
Total reduction in Inertia:
3809/5421 = 0.70 .....70%
30% Reduction in Rotating Inertia
The Effects of Rotational Inertia on Automotive Acceleration
More Personal Notes - 9/21/19
New wheel/tire: 205/50-15 Vredestein Quatrac 5
Tire weight: 17lbs (Tirerack) {-4lbs Lost}
Wheel weight: 14.6lbs (Tirerack) {-13.2lbs Lost}
Wheel/Tire weight: 31.6lbs.
Total weight reduction (Per Wheel): -17.2lbs per wheel.
Total reduction of rotating wheel mass (All four wheels): -68.8lbs total
Stock final drive gear ratio is: 4.81:1
Vredestein Quatrac 5 Tire gear ratio: 5.31:1 Gear Ratio Calculator
Miata Tire Size Calculator shows a -9.4% change from stock and a -1.7% from current setup. Speedometer will be affected. So available wheel hp/torque to the wheels estimated at an extra +9.4% (Instead of 6.3%). This is ONLY based on the change in wheel/tire size (Diameter = Gearing) alone, not the change in weight.
Guesstimate is that since change in rotational mass is 5lbs per wheel for a total of 20lbs (From lighter tire now), this is the equivalent to gaining +6.5whp (Myxal Math).
Personal Note:
Spoon Sports SW388 15" - 9.4lbs
Attachments
-
11 KB Views: 153
-
187.5 KB Views: 271
Last edited: