MOMBAT: 1983 Olsen Trials Bike

1983 Olsen

This bike was built as a collaboration between John Olsen and Joel Jensen, a frame builder in Bellingham, WA. The stays were made of straight tubing since John didn't have the ability to bend tubing yet. He is also responsible for his early signature Ford Engine Blue paint job. According to John:

"The bike was originally built with a Sturmey Archer 5
speed internal hub, but that blew up literally on the first ride in the
parking lot of the Tiger Mountain riding area near Issaquah. The intent
had been to use this hub, so all of the braze-ons were designed for that rather than a derailleur. At this time, I never used a front derailleur, and if you saw our trails, you'd know why! Remember, at this time, there were no strong enough freewheels, no good brakes, no good sealed bearings (that I could afford), and I broke rear derailleurs off like popcorn."

It was designed to mimic John's Kos Kruiser but has a 68 degree head tube with a 62 degree seat tube which moves the rider way over the rear wheel. John on the geometry:

"We didn't really care where the saddle was or what the seatpost
angle was, because the bike was designed for very technical trails or
observed trials competitions, so you never sat down, except for long
trudges up logging roads to get to the next nasty section."

The bottom bracket is 13" tall for clearance and the outer chainring was originally just a bashguard. The previous owner added the larger chainring and switched the gears by hand. One quirk is the backwards bottom bracket which John explains:

"That was an accident, shared by several of my frames, very annoyingly. I ultimately took to brazing the BB shell to the seat tube, cleaning it up, then installing a fixed cup while I fixtured and tacked the frame so I wouldn't make this mess up. I bet I made 4 or 5 frames before I figured this out."

Click on thumbnails below for larger images:

Frame		Cro-Moly, fillet brazed

Fork		Cro-Moly BMX style

Rear Shock		NA

Rims		Araya 7X 24" rear, 26" front

Hubs		Specialized, nutted axles

Spokes		Stainless Steel and zinc

Tires		Tioga Comp III 24" rear, 26" front

Pedals		MKS Grafight X

Crank		SR Apex

Chain		Sedis

Rear Cogs		Suntour 5 speed freewheel

Bottom Bracket		Sugino

Front Derailleur		NA

Rear Derailleur		Suntour Honor

Shifters		Suntour Mighty thumb

Handlebars		motorcycle trials

Stem		SR, drilled for brake

Headset		Tange Ritzy Light Alloy

Brake set		Shimano Deore XT

Brake levers		Shimano Deore XT M700 (4 finger)

Saddle		Avocet Touring II

Seat Post		Alloy

Colors		Ford Engine Blue

Size		19.5"

Serial #		NA