Vintage Dirt Bike Q & A

Has anyone compared (ridden) the Banana type swingarms with the straight aluminum CR250 swingarms?

They all seem so different (Mugen, Fox Factory, DG w/ tilted axle). Does anyone have an article/s explaining the concept of each one or a comparison test?

J

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

Some time back this was a discussion subject on one of the Elsinore-related boards. Someone had done an analysis and posted a link to it. I grabbed the diagram but lost the link (sorry). Net net the CR250R 1978 and 1979 rear suspension has a falling rate geometry. Many are of the opinion MX bikes need rising rate suspensions that are supple to small bumps early in the stroke but stiffen up at the end to resist bottoming. The diagram only considers the leverage of the swing arm, not what shocks are used. Shocks with four springs - two steel, gas(nitrogen) spring in the resevoir, bumper - can offset this geometry by using stiffer springs later in the stroke. Anyway, the purpose of the banana arms from Fox etc. was to change the geometry to be more rising rate-like, and at the same time had the benefit of lowering the rear of the bike. I believe Novation Racing has today a swing arm that achieves the same with a straight arm, but needs to use 15" shocks to compensate. If (a big if!) you can get a Mugen or Fox arm no doubt it is the best for this bike, but don't sweat it in the meanwhile

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

Michael,

Thanks for the info! Everyone seems to be sold out of replica swingarms and finding good original ones seems to be a quest. Vintage Elsinores has been promising Thor replicas since last year and nothing yet.

I had Novation build a swingarm for my CR125 from their CR250 design with different pivot mounts and a different length, but they forgot to take the different shock angle into account and I will need to send it back for modifications. I seem to be foiled at every turn.

I know where I can get a Fox arm, but I'm not quite ready to take that hit yet ($$$$).

J

_________________
#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

The last Fox swing arm on eBay fetched $1,200 if my memory serves me correctly...

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF