Custom Semi-Truck Transmissions
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Uphill Semi-Truck Racing Transmissions

Built to climb. Built to win.

Uphill racing is the ultimate test of power, gearing, and durability. We build transmissions that keep your engine in the power band and put the power to the ground.

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Use Gear Analyzer
mountains

Extreme Grades

Designed for steep inclines and heavy loads.

gearbox

Power Band Control

Keep your engine in the power sweet spot.

Optimized Ratios

Custom gear spacing for maximum pull.

Durability

Built to handle heat, stress, and shock loads.

Loaded vs Bobtail

Loaded Competition

  • More weight = More traction
  • Requires lower gearing
  • Focus on steady power
  • Maximize pulling force

Bobtail Competition

  • Less weight = Higher RPM potential
  • Requires taller gearing
  • Focus on speed through the hill
  • Maximize speed & RPM
We build custom transmissions for your exact setup.

Why Gearing Matters Uphill

Maintain Usable RPM

Stay in the power band from start to finish.

bullet-hole

Correct Shift Recovery

Optimized ratios provide quicker recovery between shifts.

gearbox

Engine Load Control

Proper gearing keeps your engine under control.

Traction & Consistency

The right gear spacing keeps you moving forward.

Finish Strong

The right setup helps you carry RPM to the finish.

Custom Uphill Race Transmissions

  • Custom gear ratios for your terrain
  • Eaton Fuller based platforms
  • Strong CNC machined gears & shafts
  • Heavy duty synchronization
  • Custom rear sections
  • Precision assembly & setup
  • Tested for real world conditions

Find the Perfect Setup

Use our Gear Analyzer

Calculate tire sizes, differential ratios, shift points, and MPH by gear.

Tire Diameter

Differential Ratio

Shift RPM

MPH by Gear

Generate printable reports and compare setups instantly.
Launch Gear Analyzer

BUILT FOR THE LAUNCH

Raw power. No trailer. No excuses.

“This Dodge bobtail puts the power down when it matters. A hard launch, heavy smoke, and serious diesel performance—exactly what you expect when the lights drop.”

SETUP

BOBTAIL

POWER

DIESEL

LAUNCH

Hard

THROTTLE

FULL

Frequently Asked Questions

What transmission is best for uphill racing?
It depends on your class, weight, and power band. Loaded trucks want tighter, lower gearing for steady pull; bobtails run taller ratios to carry speed. We build both on Eaton Fuller platforms.
What RPM should I shift at uphill races?
Shift so recovery RPM lands at the bottom of your power band — the Gear Analyzer shows exactly where each shift drops you.
How do loaded and bobtail setups differ?
Loaded setups prioritize pulling force and lower overall gearing; bobtail setups prioritize speed and RPM with taller gearing and wider steps up top.
Can you help me choose the correct gear ratios?
Yes — that’s what we do. Run your numbers in the Gear Analyzer, then call Jimmy and we’ll dial in a ratio set for your exact hill and truck.
Do you build transmissions for all hill types?
Yes — short steep hills, long grades, dirt, and pavement. Ratios and clutch setup are matched to the terrain.
What clutch works best for hill climbing?
A properly set 12.5″ slipper clutch (Crower or Atlas) protects the drivetrain and keeps power delivery smooth.

Not an Automotive Shop

We focus 100% on semi-truck racing and heavy-duty applications.

Ready to conquer the hill?

Get the transmission that gets you there.
Request a Build
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