Vintage Dirt Bike Q & A

Hello,
I have just had the rear shock overhauled and a higher rated spring fitted. The static sag is 25mm and the race sag is 115mm. The rear end of the bike seems very low with the rear tyre level with the exhaust muffler. The guy at the shop thinks that this is o.k but I am not so sure. The last motocross bike that I had was a 84 CR500 and I can't remember the rear end feeling so low. I have wound up the preload to max. Could the spring still be too light? Does the shock internals play any part in supporting the weight of me and the bike in the static position?

You should worry less about what it looks like more about the specific settings. If you set the race sag OK, but then can't get the right static sag, then the spring rate is off. Too little static sag means too softer rate over-compensated with pre-load. The reverse holds true. Too account for stiction and damping, you measure static sag twice; push-down and pull-up. Use the average of the two measurements. You don't say what you weigh, but 185-190lb riders here are running .63kg/mm springs up from .44kg/mm stock.

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

Red Rocket,
I'm 217lbs of Scottish muscle, so I guess that I will need quite a bit above standard. Don't know the rate of the new spring fitted but I did give the guy at the shop my weight. I'll try your advice and see what the results are. Still have a feeling that the spring is too soft.

It would be useful to know the specific rate for the new spring. If you visit http://www.racetech.com you can enter your, bike, all-up weight, and riding style and it will suggest the correct shock spring rate. The following comments apply the 1983 CR480R and I know that Honda was making subtle changes to the shock and linkage during this time. You may be told that there are not after-market heavier springs available. However I learned that there is a range of Eibach springs 883.00XX.1 which are 55mm x 273mm in size. These are not specifically for the CR480R but they fit just fine. I am running a 883.0067.1 which is .67kg/mm. I am still playing with the sag, but can get in the ball-park with almost no pre-load. The .44kg/mm spring that came stock with the bike had the pre-load cranked all the way down. The other tip I'll pass on is that the damping needs work and Tru Technologies is the place to go. Rich Truinski - the owner - has a rocket-ship CR480R that runs in SoCal historic events.

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