Rear view of a Dallara DW12 IndyCar showing the Xtrac gearbox casing mounted between the rear wheels beneath the rear wing

IndyCar Gearbox Explained: Six Gears and No Clutch Pedal

September 23, 2026

Welcome to the Happy Hour Racing IndyCar Tech Breakdown - where we take one confusing part of the NTT IndyCar Series and make it make sense. No engineering degree required.

The Short Version

Every car in the IndyCar paddock runs the same gearbox: an Xtrac P1011, six forward gears plus a reverse, shifted by paddles on the steering wheel. There is no clutch pedal in the car at all. The clutch is a hand paddle, and the driver only touches it to launch from a standstill. Teams are allowed to change the gear ratios and almost nothing else. Here is how the whole thing works.

One Gearbox, Every Car

IndyCar is a spec series in the places where spending money would not make the racing better, and the transmission is one of those places. Xtrac has been the series' exclusive gearbox supplier since 2000, and the current P1011 specification arrived with the Dallara DW12 in 2012. Penske runs it. Ganassi runs it. The smallest team on the grid runs the identical part.

It bolts to the back of the engine and carries the rear suspension, which is why the back of an Indy car looks so bare. The gearbox is the back of the car. The whole assembly weighs about 154 pounds, the casing is aluminium, and it is rated to handle up to 650 Newton meters of torque coming out of the 2.2-liter twin-turbo V6.

Engine, then the bellhousing that now holds the hybrid unit, then the gearbox, then the differential and the rear wheels. All of it hangs off the back of the tub.

Sequential Means One Gear at a Time

Your car at home, if it has a stick, uses an H-pattern. You can go from fifth straight to second by moving the lever across the gate. An Indy car cannot do that. It is sequential, which means gears come in order: 1, 2, 3, 4, 5, 6 going up, and the same list in reverse coming down. Want fourth from sixth? That is two pulls of the paddle, one after the other.

Inside, it does not use the synchronizers that make a road car shift smoothly. It uses dog gears: chunky teeth that slam together. They are noisy, they are harsh, and they wear out, but they engage almost instantly. The gears themselves are straight cut rather than angled, which is louder and stronger. That whine you hear on an onboard camera is the gearbox, not the engine.

The shift itself is pneumatic. Pull the paddle, compressed air throws the selector, and the next gear is in. The driver keeps the throttle pinned through an upshift. There is no lifting and no clutch work.

So Where Is the Clutch Pedal

There is not one. An Indy car has two pedals, throttle and brake. The clutch is a paddle on the steering wheel, and it has been that way since 2012.

The driver squeezes it exactly twice in a normal race: once to launch off the grid, and once if the car has to pull away from a standstill in the pits. Every other shift of the day happens with no clutch input at all, because a dog gearbox does not need one. There is also an anti-stall function, so a driver who releases the clutch paddle too fast does not kill the engine and sit there blocking a lane.

IndyCar cockpit showing the removable steering wheel where the shift paddles and hand clutch paddles are mounted on the back of the rim — Everything the driver needs to shift is on the back of this wheel. Upshift and downshift paddles, plus the clutch paddle used only to get moving. (Photo: Kalvin Chan, CC BY 2.0, via Wikimedia Commons)

That wheel keeps getting busier. IndyCar approved the Cosworth Mk 3 steering wheel for 2025, an optional upgrade that eight of the series' 11 full-time teams ordered. The rim grew from 284mm to 310mm so drivers get more leverage without power steering, and it carries a bigger display plus more buttons and rotary dials, largely because the hybrid gave drivers more to manage on the fly. It costs roughly 19,000 dollars per wheel.

A closer look at an @IndyCar steering wheel with @townsendbell and @hinchtown. #Indy500 #INDYCAR
- INDYCAR on FOX (@IndyCarOnFOX) May 15, 2025

The Ratios Are Part of the Setup

Here is the one thing teams actually get to change. The internals are built so first gear lives on the layshaft and second through sixth slide on, which means a crew can swap gear ratios in the garage in about five to ten minutes. Beyond the ratios and the differential settings, teams are not allowed to modify the transmission.

Ratios matter more than most fans realize, because IndyCar races on three completely different kinds of track. A tight street circuit needs short, closely stacked gears so the car accelerates hard out of 40 mph corners. A superspeedway needs long gears so the engine is not screaming past its limit at 230 mph. Get it wrong and the driver either runs out of revs down the straight or bogs off every corner.

The hardware never changes. The spacing between the gears does, and that is what tailors one spec gearbox to a street circuit and to Indianapolis.

What the Hybrid Changed

When IndyCar added hybrid power in 2024, it did not redesign the gearbox. The motor generator unit and the energy store were dropped into the bellhousing, the short section that joins the engine to the transmission. The driveshaft runs straight through the motor on its way into the gearbox.

It is a 48-volt system storing up to 320 kilojoules per lap in 20 ultracapacitors rather than a battery, because capacitors fill and empty far faster. The whole store can charge and deploy in about 4.5 seconds. Because that motor sits directly on the driveline, it can also spin the engine over, which is why drivers have been allowed to restart the car themselves on pit lane since 2025 instead of waiting for a crew member with a starter.

What You Will Hear and See

Turn up an onboard. The rising whine under acceleration is straight-cut gears. The hard mechanical bang at every upshift is a dog ring engaging. Watch the driver's fingers on a road course and you will see a pull for every corner, one gear at a time, with both feet still doing only throttle and brake. And on the grid, watch the hand on the back of the wheel right before the green. That is the only clutch input anybody is going to make all day.

The Bottom Line

Six gears, one spec Xtrac box, paddles instead of a lever, and a clutch that lives on the steering wheel and gets used twice. Teams can change the ratios and the diff, and that is about it. Everything else on the grid is identical, which is exactly the point: when the gearbox is identical in every car on the grid, the difference you are watching is the driver.

If you are the person in the room who now knows why an Indy car has two pedals, you may as well dress the part. The Indy 500 car flag tee, the Snake Pit tee and the race logo long sleeve are in stock, and there is a Colton Herta 1:18 diecast if you would rather have the car itself. The rest is in the IndyCar collection. New tech breakdowns drop every week, so bookmark the blog and stop guessing at the jargon.