This is the page for climbs starting from Ashby BART in Berkeley, part of a comprehensive index of climbs to Grizzly Peak Boulevard from BART stations.
My fist choice route is via Tunnel Road. The classic Tunnel climb is heavily used by cyclists of all abilities thanks to a consistent and moderate grade and good options to continue on Grizzly Peak.
via Tunnel Road 6.4 miles, +1,330 feet
The first 2/3 of the way up is extremely consistent and moderate, it used to lead to the first tunnel between Berkeley and Orinda (Kennedy Tunnel). The last third where the name changes to Skyline Boulevard after the old tunnel is steeper but not unreasonable. There are bathrooms and water at the top.
Claremont runs up Claremont Canyon from Berkeley to intersect Grizzly Peak Boulevard at the top of today's Fish Ranch Road. For novelty you could drop down Fish Ranch and take the freeway into Orinda. You could hit 55 on that downhill.
via Claremont Avenue 3.8 miles, +1,165 feet
This route used to be a busy pass between the ports and commercial facilities in the East Bay and the vast ranches in Contra Costa ("opposite shore") county. The Pony Express used this trail in it's very brief history before the new transcontinental telegraph, which used the same Fish Ranch to Claremont canyon route, made the pony service obsolete. Wagon haulers and cattle drivers could rest and quaff a beverage or two at the saloon before starting down the hill.