Add 40 WHP with one simple trick! (Story by: Dynodad.com)
TLDR: A massive change in rotational mass resulted in ~40whp drop in horsepower measured at the tires of a Jeep Gladiator. With the stock 32” tire and rim combo I measured 352whp & 346wtq at 7.3psi. The sneakers were swapped for a much heavier set of 37” tires and rims. With no changes to the calibration besides the tire height parameter I measured 313whp & 316wtq at 7.3psi! Want to easily gain 40whp in your Jeep? All you must do is put the stock wheels and tires back on 🙂
As enthusiasts we all know heavy wheels and/or tires suck… they suck power down, they suck braking force away, and they suck motion control from the suspension. Common sense, gut feel, and science all confirm this; however, we rarely get to see the real results in a semi-controlled A-B testing scenario. Well today is a special day!
Despite the tagline of this page referring to LSX/LTX dyno results, I am going to share some interesting results and calculations from a recent Jeep tuning session. The beast in reference is a 2020 Jeep Gladiator Rubicon 8-speed automatic with a Prodigy Turbo Kit set for ~7 pounds of boost.
The tuning session occurred with the factory Jeep Rubicon wheels and Falken Wildpeak MT 285/70-17 tires. The wheels weigh ~23lbs and the tires weigh ~62lbs for a total package weight of ~85lbs per corner.
The result of tuning this combination was 352whp & 346wtq at 7.3psi. The chart below shows the nice torque curve and solid pull of power. This setup made the Gladiator feel light on its feet.
Once the tuning session was completed with the stock wheel and tire package, I swapped to the 37” setup: Toyo Open Country MT 37×12.5-17 tires mounted on Black Rhino Armory 17×9.5 wheels. The wheels weigh ~35lbs and the tires weigh ~84lbs for a total package weight of ~119lbs per corner.
No tune changes were made besides the tire height parameters. The results of the dyno pull with the 37” sneaker package was 313whp & 316wtq at 7.3psi. As expected, this setup made the Gladiator feel like a stock Gladiator Rubicon on the road with regards to power and acceleration… as indicated by the 30+whp and 30+wtq drop across the main section of the powerband!
With the 37” tire setup the powertrain was turning an additional 68lbs at the rear axle. Additionally, the taller tire height moves the weight further from the point of rotation at the axle. After seeing the big drop in power and torque measured at the tires I decided to see if the numbers would match some physics calculations; I calculated the torque delta for the two wheel and tire packages.
Here is a quick overview of the math and assumptions made:
- Since a wheel/tire package is neither a perfect ring or a perfect disk I decided to calculate both and average the results.
- I made wheel speed calculations from 4,000rpm to 5,000rpm since the torque curve is flat-ish in that range.
- I used simplified physics calculations and assumptions… this is def undergrad level math, feel free to nitpick and comment away 😉
The resulting torque delta calculation is 38 torques… not too far off from our measured value of 33wtq at 5,000rpm! Yay math!!
Anyways, now that I spent hours of my Sunday morning making a wheel/tire/torque calculator in Excel and writing this post… I hope you’ve been truly entertained. Now I’ve gotta go entertain the children I’m ignoring. Thanks for reading, and please like/share/comment away!
P.S. I plugged some data into the calculator based on my personal 2017 Chevy SS sedan. The Weld 17” wheels with MT ET Street R 275s gains ~10wtq over the stock GM 19” wheels and Potenza RE050As. I’ll toss the car on the dyno some day and see if this holds water.