derbi progress


the derbi monster has sadly been at a halt since before christmas. the main obstacle of the project, figuring out a rear sprocket/wheel situation, turned out to be some real trouble. here it is with the original YZ80 rear wheel.

sneak peak

there were two problems with that wheel. first, the 12″ wheel looked goofy and non-moped like. second, it took a 428 chain (motorcycle grade) and my derbi takes 418. the rear hub is also huge on that dirt bike wheel, so lacing a 17″ rim onto the hub and getting a custom 418 sprocket made to bolt onto it in a small enough size to keep a good gear ratio was out of the question. stock derbi gearing was 19×30. the smallest i could go on the rear was in the mid to upper 30’s and i didn’t have the room in the front to go much larger than a 20/21 without hitting the cases. here’s the dirt bike tire with the stock derbi front and rear sprockets.


another complication was the super thick axel on the yz80. i wanted to use it so i could keep the sweet chain tensioners and beefiness of rad motorcycle parts. i went through at least 4-5 different pitbike, motorcycle and moped wheels trying find a wheel that i could get bearings for to fit the inner diameter of the hub and the outer diameter of the axel. NO DICE. the sprocket and axel problem was getting frustrating. this weekend nate and i set off to a junkyard determined to find a solution. after some digging around i found a gnarly 18″ rear wheel from a 1974 kawasaki motorcycle that worked! it had a small enough hub that i’ll be able to get a custom 418 sprocket made that will bolt right up to the wheel. the only caveat is it comes super close to the front of the swingarm. i’m going to have to get some low profile racing slicks to make sure i have clearance. worse case scenario we’ll just weld aluminum to the back of the swingarm and extend the axel slots to make it work. i’m really excited to see it with a huge tire on the back.

rear wheel solution

i also scored that laguna sport tank (i freaked out when i saw it just sitting there, unfortunately there was no frame/motor/anything else to be found) and am going to use it instead of the trac tank on this bike.

new tank

i’m going to be welding up the engine, tank and seat mounts this week. then just need to get the rear sprocket made and a tire and this little buddy will be ready to go! quick question for derbi pros, what are my front sprocket options? do they share the same spline pattern as another bike? it’s a z-sprocket so i’m hoping that’s the case, but if not where can i find derbi front sprockets?


2 Responses to “derbi progress”

  1. Looking excellent! Can’t wait to see it!

    • 2 gabeb

      thanks phil! more progress made tonight. i’ll have it waiting for a joy ride when you get here!

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