There is an acrid smell of welded steel at Jeremy SyCip's small shop in Railroad Square, where a dozen bicycle frames are in the process of being built and more are on a rack awaiting repair.

He is part of a resurgence in custom bike building, and an interest in old-school steel frames, that has become a cottage industry in Sonoma County.

"Some people want something handmade and something local. Local is a big thing right now," SyCip said. "The main difference is I size people up. It's like a custom-fitted suit."

SyCip will be one of eight bike builders who will be featured Sunday at the third annual Sonoma County Bicycle Expo in Santa Rosa, where they will raffle off and then actually construct a bike frame.

"Most people are not aware of this wonderful industry in Sonoma County," said Gary Helfrich, executive director of the Sonoma County Bicycle Coalition, which is staging the event. "Sonoma County is such a cycling mecca. But not only is Sonoma County a great place to ride, some of the best bikes in the world are being built here."

The expo is from 10 a.m. to 4 p.m. on Second Street between D and E streets and in the E Street parking lot. Admission is free.

It will feature vendors with new and used bike parts and gear, clothing and accessories, music and food and drink.

There will be BMX stunt performances, a 10-mile ride at 8 a.m., a kinetic art bike parade at 11 a.m. and skills programs for children from 10 a.m. to 1 p.m., with low-cost bike helmets for children.

Bike Monkey, which stages dirt bike races in Sonoma County and also the Levi Leipheimer King Ridge GranFondo, is holding low-key races for fat-tire bikes all day on Second Street.

Bike builders are being featured for the first time. It includes SyCip, Bruce Gordon Cycles of Petaluma, Gary Helfrich of Camp Meeker, Inglis & Retrotec of Napa, Raphael Cycles of San Francisco, Rebolledo Cycles of Glen Ellen, Soulcraft of Petaluma and Calfee Design of Monterey.

"It all starts with the bike," Helfrich said. "Otherwise we would all be pedestrians."

SyCip said that steel was the frame of choice when he began building bikes in the 1990s. It was supplanted by lighter carbon-fiber frames, but steel is now making a comeback.

Part of the appeal is the feel of a frame made of steel, which has the right amount of stiffness for performance and also the right amount of flexibility for comfort.

Unlike carbon-fiber, steel doesn't have a lifespan and can be easily repaired.

To get the perfect fit, SyCip said he takes seven measurements of a customer's body, from their height to the length of their thigh.

"Everything is made around their measurements or riding style or if they have had injury," SyCip said.

The bike frames and forks start at $1,800 and, because he is a one-man shop, there is a four- to five-month wait.

"When I moved up here 10 years ago from San Francisco, I was really worried there would not be enough business, but it's a big cycling community," SyCip said.