Lightweight Wheel Tire Size and Gear Ratio Change

Myx

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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
.36whp per extra pound of unsprung weight. or "For each 3 lbs extra unsprung weight, you will lose 1 rwhp."
Rotational Inertia - Effect on Power
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.

Honda Civic 10th gen Lightweight Wheel Tire Size and Gear Ratio Change White Civic



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
 

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Myx

Myx

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I have been looking for a little over an hour searching on the internet. No more than 5 minutes after posting this question, I found a link to what I was looking for. Thanks! I found all the information I needed.

TireSize Effective/New Gear Ratios
 
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Myx

Myx

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Updated thread with what I was really thinking about instead of letting it be a wasted thread.
 
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Myx

Myx

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Went out earlier to do some test runs with this setup to record 1/4 mile data on the difference of before and after wheel/tire changes. I forgot to tell the shop that install it to put higher air pressure in the wheels vs 32psi (I have my own psi for smaller wheels). None of the three gas station air pumps seems to be working. Guess the drop in temperature tonight into the 20's-30's is affecting them. So looks like I won't know the direct affect of making this change since I have plans on making a few other modifications tomorrow.
 


davemarco

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Do
Went out earlier to do some test runs with this setup to record 1/4 mile data on the difference of before and after wheel/tire changes. I forgot to tell the shop that install it to put higher air pressure in the wheels vs 32psi (I have my own psi for smaller wheels). None of the three gas station air pumps seems to be working. Guess the drop in temperature tonight into the 20's-30's is affecting them. So looks like I won't know the direct affect of making this change since I have plans on making a few other modifications tomorrow.
You think that upgrading from 18 in wheels to 19 in would change the ratio in the SI enough to hit 60 mph in 2nd gear? I think that second tops out at 58 or 59 now, and I think that it would be a cool (and totally arbitrary) goal to try and hit 60 in 2nd. Should really improve the 0-60 time if possible.
 
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You think that upgrading from 18 in wheels to 19 in would change the ratio in the SI enough to hit 60 mph in 2nd gear? I think that second tops out at 58 or 59 now, and I think that it would be a cool (and totally arbitrary) goal to try and hit 60 in 2nd. Should really improve the 0-60 time if possible.
If you change your tire diameter to a larger tire diameter, then yes.
Something like this may help with the specifics though ---> Simple RPM Calculator
 

BarracksSi

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You think that upgrading from 18 in wheels to 19 in would change the ratio in the SI enough to hit 60 mph in 2nd gear? I think that second tops out at 58 or 59 now, and I think that it would be a cool (and totally arbitrary) goal to try and hit 60 in 2nd. Should really improve the 0-60 time if possible.
It probably would (and as long as you get tires taller than stock), but you wouldn't know that it was 60 mph from the speedometer because it doesn't know how far you're going -- only how many RPMs the wheels are turning.

That is, your car knows that so-and-so wheel RPM equates to 60 mph, and that's it. It doesn't know whether your car is traveling sixty miles an hour along the ground (what airplane pilots would call "ground speed").

You could put skateboard wheels on it, drive at an indicated 60 mph, and you'll really be going at maybe 10 mph.

Or you could use tall monster truck tires, drive at an indicated 60 mph, but you'll be traveling over 100.

Anyways, getting taller tires to get a lower cruising RPM (or change the shift point a bit higher) also brings the drawbacks of less wheel well clearance, greater speedometer error (makes a difference if you like to push the speed limit), and a bit of a higher stance.
 
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TrippyPancakes

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Yo Myx,

I'm going to hijack this thread for half a second. Are you still running the quatrac 5's? And if so are yours super loud in terms of tire/road noise? I have had a set on my stock rims for around half a year now and they seem to keep getting louder and louder and it's slowly starting to drive me insane. I can't hear any engine/intake/turbo noise over the tire noise in some cases
 
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gtman

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TrippyPancakes

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I don't have them but researched them for a while. Overall great tire but about the loudest tire in their category.

Here's a detailed test done in Europe. Great tire in the wet but noise is kind of abysmal.

https://alltyretests.com/vredestein-quatrac-5-test-review/
Yeah, they're a beast in wet and snow and a super capable all season tire for place that have some rough winters. But I did not realize how much louder they would be than the OEM continentals. I also had never seen that website before and will certainly be using it before future tire purchases
 
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Myx

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Yo Myx,

I'm going to hijack this thread for half a second. Are you still running the quatrac 5's? And if so are yours super loud in terms of tire/road noise? I have had a set on my stock rims for around half a year now and they seem to keep getting louder and louder and it's slowly starting to drive me insane. I can't hear any engine/intake/turbo noise over the tire noise in some cases
Yes! I haven't thought about it but now that you pointed it out, yes, they are louder than what I am typically used too.
 
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Myx

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