Magura L476-21 bars with crossbrace on a 1979 Ritchey
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Motocross
Before Bullmoose bars, mountain bikes were usually equipped with motocross handlebars. Both motocross and mountain bikes needed the strength to tame the stresses fighting the rider to keep things going straight. Motocross offered affordable strength with perhaps more weight than needed for a bike.
1980 Trailmaster/Cove Bike Shop Catalog
mombat
Magura, Magura or GSM - nothing else would work.
1979 Ritchey equipped with Magura L476-21 motorcycle handlebars.
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Prior to 1980, the best handlebars were wide, flat & light motorcycle handlebars from Magura. Almost all Series I & II Breezers used Magura handlebars. See a gallery of 52 different Breezers: Vintagemtbworkshop Breezer gallery.
MX & MTB
Motocross handlebars found on early mountain bikes.
The 1977 Breezer #1 used a GSM Motorcycle (Germany) handlebar with an SR stem.
smithsonian
1980 Cook Bros Racing Cruiser. Modified by Steve Cook with Magura bars.
theradavist
1980 Koski Trailmaster, with Maguras. Magura and GSM were the only bars which Trailmaster would build with.
sfomuseum
1982 Breezer Series III. Joe stuck with motocross handlebars for all of his mountain bikes. See Breezer Gallery. theproscloset