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Suspension Modifications from Cycle World
- August 1976 Edition
HONDA CB400 SUPERSPORT
Initial Impressions: Hondaís smallest Supersport is a compact machine that isnít overly comfortable to ride for long distances. In addition, it wiggles some when pushed, particularly when the road surface is not smooth. There are three reasons for this. First, there isnít enough rebound damping in the front forks. Second, the front forks flex too much because of insufficient stanchion tube diameter. Finally, the rear shocks lack sufficient oil capacity to prevent overheating and subsequent loss of damping control. Correcting the rebound damping and changing rear shocks helps handling a great deal, but does nothing for the harsh ride. Softer spring rates help here but the effect is minimal due to limited fork travel. The forks cannot be extended using the stock damper rod because the standard guide bushing causes the forks to bind as they flex under frontal loading. In other words, this is a difficult bike to fix.
Damper Rod Modifications: Handling can be improved by increasing rebound damping. To do this, braze the upper rebound hole shut in each damper rod. File the damper rods smooth and redrill the top hole in the same location to .060 in. A 1/16 in. drill bit is roughly equivalent to that diameter. If you are not content with improving handling alone, you must exchange the stock damper rods for ones that will not bind in the stanchion tubes as the forks flex. Number One Products has designed a rod with a floating guide bushing that does not bind nearly as easily as the stock rod. With the binding problem lessened, it was possible to use a longer rod that extends travel 1 in. This complete damper rod is available in a kit that includes springs.
Fork Springs: If you choose to modify the stock rods in the interest of handling, use the stock springs. The Number One Products kit includes progressive springs with an average weight in the vicinity of 30 lb. No preload spacers are required with this set-up.
Suggested Rear Suspension Modifications: Without question, the spring rate is too high. Even if the stock shocks are retained, substitute 90-lb. springs the same length as stock. Better yet, replace the stock shock with a Koni, part number 76F1302. Again, 90-lb. springs should be used. Springs are available from Ken Ross, S&W, Koni or Girling.
Results And Cost: Koni shocks with 90-lb springs and an increase in fork rebound damping help handling considerably. There is no wallow in turns and the bike will hold a line when pushed to the limit. Ride, however, remains harsh. Because of fork flex, fork action remains less than perfect, even with a complete damper rod and spring change. Nevertheless, the improvement in ride on rough roads is considerable. On smooth streets there is little difference. If you want to go the handling route, modifying the stock damper rods should cost around $10. Koni shocks are $34. each. Springs again start at $8.40. If you like to ride long distances or commute on rough surface streets, the Number One damper rod kit and springs are worthwhile. Part Number is H400-14. Cost is $44.95.
Excerpt from article in Cycle World - August 1976