The Totalspan Soapbox Derby will be back for Whanganui's Vintage Weekend, with the biggest field of carts to date.

Organiser Denise Vincent said the number of registered karts this year had exceeded expectations.

"It's growing and growing ... we've opened up a can of worms."

With 38 entrants at Whanganui's first Soapbox Derby in 2014, the numbers have steadily increased.

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"They're coming in thick and fast and - ones that we know of - we're probably hitting 50."

Last year's floods put a damper on the derby, so this year she is eager to make up for lost time.

She says the 4000 spectators can expect to see carts of all sorts - basic jobs put together over a weekend to something a bit more impressive.

"Some of these guys have just gone well out, over and above with what they've designed. Absolutely just top of the bloody range."

Others have opted for something a bit more creative.

"Karts that look like chuck shoes ... there's old vintage looking cars, there's fire engines, there's Postman Pat, just amazing what's people can do out there."

For the uninitiated a soapbox derby is a race between unpowered karts down a slope.

For the Whanganui event there will be three categories for children, starting at 5, a drift trike class, and a category allowing adults to get in on the fun.

There will even be a wheelie bin race made up of the Derby volunteer committee.

"I think that one's going to be carnage galore to be honest.

"We might pull some brave souls from the audience who want to have a go."

Garmac Engineering will provide three jump ramps for the event, and the "Wall of Death" will make a return.

Karters are urged to make their way to the inspection pit at Drews Ave by 8am.

You must wear a helmet, clothes and shoes, and your kart must have decent brakes.

Thanks to support from local businesses there will be no shortage of spot prizes for the event.

It's free for all those under 5 and between $10 and $20 entry for all other entrants.

"That's per cart, so there's some families that might have three kids, but they're going to use the one cart so that would be a one-off $10 or $20," said Mrs Vincent.

"Obviously to watch it's free."

Entries are open up to the day, and Mrs Vincent expects a final tally of about 60 karts.

"Thank to all businesses and shops that made this possible," she said.

The race will kick off at Queens Park raceway at 9.30am on January 23.