[cb400tcol]

Asking for feedback on a rough front fork ride over medium to hard bumps. The last owner installed Hagon front springs listed on receipt as "214MM 10 weight oil with 140MM air gap". I'm not a suspension guy, so new info to digest. Would like to know if this was set up to be this firm/rough or is there room to explore a smoother ride???

Although it handles good - but a less rigid ride would sure be nice to complete this fun machine. Any help or re-direct to a post that addresses would help.

Thanks in advance!

 

[Old Putz]

Could be any number of things.
The receipt doesn't reveal anything about the springs themselves, particularly the spring rate. Was the previous owner a 280 lb guy, who installed stiffer springs to compensate for his size? If so, and particularly if you're, say 125 pounds, the springs are going to be way too stiff. Any idea why he replaced the springs in the first place?
A rough ride can also be the result of springs that are too soft, and underdamped. I bought an SV650 when they first came out in 1999. The bike, as delivered, had a horrible tendency to have a jackhammer-like front end while riding through rough corners. I thought at first that the springs were too stiff, but when I looked into it I found out that the stock spring rate was ideal for a 130 lb rider, and I weighed more like 160. When I tore into the forks I found that they came from the factory with less than half of the oil that was supposed to be in them, and what came out looked a lot more like rusty water than fork oil. Simply putting in the right amount and viscosity of fork oil made a nearly miraculous improvement in the bike's behavior. Up to that point, the front end was moving in an essentially uncontrolled manner- the front wheel was thrashing around over bumps, losing contact with the asphalt (the bike would run wide in bumpy turns) and delivering a really rough ride. The new fork oil got rid of all of this behavior.
So... what's the spring rate of the springs you've got? Is it appropriate to your weight? Is that 10W fork oil appropriate for the springs? Did the previous owner actually install the oil? Was the work done so long or so many miles ago that the oil is no longer providing adequate damping?

Start here: RT - Digital Product Search

 

[cb400tcol]

Thanks for the reply, many things to consider. Some assumptions are the 160 lbs previous owner undoubtedly bought the new springs to match the new Hagon rear shocks to complete the bike for knowing re-sale, so some unknowns on spring rate, amount, weight of oil, and air gap installed when I took ownership last month. You mentioned how improved your previous bike’s ride was with just the fork oil improvements, so I will research and do sensible additions of just that for the first pass to see how to improve. It handles and feels so good on smooth surfaces so I do not think I need to “re-invent the wheel” (pardon the pun) as to just getting the “jarring” feel on hard bumps smoothed out. Air gap is worth my research and I assume the proper qty of lighter weight oil would “soften” the ride from just the common sense of it???
I am 200 lbs and ride with medium aggressiveness on the twisty’ s out West some will check into matching everything up for a better riding experience. Thanks for your input and any other tips or links you or anyone else has on this topic.

This bike has been good fun sorting out and cruising around on!!!!

JH

 

[Boomer343]

Check your tire pressure and try lowering it a couple pounds or even a single pound at a time. Quite often people over inflate their tires.

To a point you will get better braking and smoother ride with lower air pressure. Don't forget that tire pressure is set cold.

 

[Old Putz]

One other thing to consider. The forks on a CB400 are pretty basic; they're a compromise in terms of both cost and character (neither touring bike cushy or track bike stiff). You can change damping characteristics by changing the weight of the fork oil. Go with a thicker (larger viscosity number) oil and the rebound will be slower, which keeps the front end from being bouncy but also can cause problems with 1) the front end "packing down" over a series of bumps as it doesn't get the chance to fully extend before the next bump, and/or 2) the ride being harsh as the thick oil keeps the forks from compressing readily. Go lighter and the bike is more responsive over repeated bumps, but go too light and the ride can be harsh as the wheel travels up and down with little control. What I'm describing is the difference between high and low speed damping, "speed" referring to the motion of the fork, and not the bike's velocity.
A more sophisticated fork will run thicker oil for better control, but have adjustable, spring-loaded blowoff valves that allow the forks to move quickly if a sharp bump is encountered. Adjusting the spring tension on the blowoff valves allows the rider to customize the ride quality, hopefully achieving a best-of-both-worlds ride. The nice thing is that you can add this adjustability to many of the simpler damping rod type forks by installing cartridge emulators. These allow you to install a means of dialing in both low speed damping (through oil viscosity) and high speed damping (by providing adjustability to when the low speed damping is defeated). Race Tech makes such pieces:
Emulators
No, I'm not affiliated with them in any way, but I've installed them on other bikes, and they work really nicely if you take the time to dial them in (the company provides extensive instructions on doing just that).
Maybe not something you want to do right now, but a possible solution farther down the line if you're unable to reach an adequate setup with what you've got.

 

[Alan F.]

There are cartridge emulators by other makers on ebay, same principle often the exact same part dimensions as well, but lower prices.