Budget speed guide

The stock motor is a 24 V motor. Its speed depends on the voltage it gets: at 24 V it spins about 2,500 RPM, at 48 V about 5,000 RPM. Double the voltage and you roughly double the top speed.

The stock cart runs on two 12 V batteries in series (24 V). Add two more and wire all four in series to get 48 V. With a 48 V controller and everything else stock, the cart goes from about 12 mph to about 20 mph, for roughly the price of two batteries and a cheap controller.

The controller has to be rated for your new voltage. One extra battery (36 V) on the stock 24 V controller gives a small bump, but you won't get the full speed until the controller matches the battery.

A 36 V 500 W XL motor sounds like an easy upgrade, but a motor rated for 36 V spins at 36 V about as fast as the stock motor does at 24 V. You get more torque, not much more speed.

The better trick is to overvolt a 24 V motor: run a stronger 24 V motor (higher watts) at 48 V. You get double the RPM, plus more torque, and a bigger motor handles the heat better.

Also check the shaft and sprocket. The stock motor has a small 8 mm shaft and a sprocket for #25 chain. The XL motor he tried came with a bigger shaft and a sprocket for T8 (8 mm) chain, so it didn't work with the stock chain.

• Motor: 24 V 350 W motor that came with a #25 sprocket, so he could keep the stock chain.
• Fitting it: trimmed the motor frame so the bolt holes line up, and ground down the flat side of the D-shaft so the sprocket could slide back in line with the chain.
• Gearing: rear sprocket from 55T to 47T (R34 three-bolt pattern fits the stock hub) with an 11T front sprocket. That changes the ratio from about 6:1 to 4.29:1.
• Chain: took about 3 links out of the stock chain (around 84 links) so it fits the new sprockets.
• Result: about 29 mph at 48 V with a 48 V controller.

Just swapping the 55T rear sprocket for a 47T on an otherwise 48 V stock cart gets you about 24 mph.

Headset bearing: treat it as mandatory once you go fast. It's a pain to install (you have to hammer off the lower ring at the bottom of the fork), but afterwards you can tighten the fork as much as you want and it still steers smoothly.

Solid front tire: a big part of the wobble comes from the air-filled tire. With a solid tire he has no speed wobble at all.

• A new 48 V controller is not plug and play. Cut off the old plugs, splice the wires and add male/female connectors so everything plugs straight in.
• You need a 48 V charger. The stock 24 V charger can't charge the new pack. Put the same connectors on the charger so you just unplug the battery from the controller and plug in the charger. His charges a flat pack in about 1 to 1.5 hours.
• A small spark or pop when you connect the battery is normal. It's the capacitors in the controller filling up. Connect the battery with the cart switched off.
• A cheap voltage display shows how much battery is left (his read 53 V on a full 48 V pack).

Apollo caster mod: casters from Apollo Caster (about $16 each) come without a kingpin, so you fit your own. You have to grind the kingpin down to fit. He also welded the kingpin and the caster rivet, because the bolts kept breaking and the rivet can work loose on bumps.

Wide soft wheels spread the weight and soak up bumps, so the ride is much smoother. They also grip sideways: the cart goes straight until you pull the drift bar. Stock narrow casters slide more easily, which is more forgiving for kids at low speed but feels loose at 29 mph.

When fitting new wheels, keep the spacer between the bearings (grind it to length if needed). Then you can tighten the bolt hard without pressing on the bearings, and the wheel still spins freely.

• LED strips under the cart, wired to 12 V from the battery pack (about $10).
• Seat cushion from Walmart (about $5) with double-sided tape in the middle, so you can lift a corner to reach the seat bolts.
• Homemade battery box from metal strips bent in a vice and riveted together, held on with self-tapping screws.

Lithium iron phosphate (LiFePO4) packs hold less energy than regular lithium for their size, but they are more stable, you can fully charge and drain them, and the fire risk is much lower. They cost more, but they are the safest lithium choice for a fast cart.