Why 1964? Do tell me more about your preference for old, hardtail springer bikes. You seem to have a lot of interesting ideas to share.

Now you've got my attention.

That makes a certain sense, one day i may have to try actually riding a rigid myself

Good questions. Choosing fork oil and spring rates is both art and science. Damping Rod forks have significant limitations. From Race Tech's website:

"Damping rods while inexpensive to manufacture have major limitations. To create compression damping, oil is shoved through a hole or holes. Shoving oil through holes creates very little resistance to flow at low vertical wheel velocities as when hitting a dip or gully or applying the front brakes. This allows the forks to shoot through the travel fairly easily, diving or bottoming in these situations. On the other hand when the wheel hits something square edge, especially at speed, it needs a lot of oil to pass through the damping holes very quickly. Unfortunately the nature of shoving oil through holes is that as the wheel velocity increases the damping force increases with the square of the velocity. In other words if you double the velocity you get four times the force. This means the hole basically "hydraulic locks" resulting in a harsh spike. Damping rods give the worst of both worlds; they are both too mushy and too harsh at the same time."

What is the condition that you are trying to "improve" with thicker fork oil? One thing is for sure, the suspension will become harsher on sharp-edged bumps. If you are committed to thicker (heavier) oil, you might consider reworking the compression holes in the Damping Rod to keep the forks from hydrolocking.

Regarding spring rates, are you looking for progressively wound springs or straight rates? Since Damping Rod forks don't have any rate-based valving, they sometimes use progressive rate springs to compensate for the lack of rate reaction. But progressive rate spring react in undesirable and sometimes unpredictable ways. For example under braking they can produce significant initial dive, followed by harshness. Straight rate springs must be carefully chosen to find the sweet spot between ride and handling.

Springers have dampers built in
on the earliest models, they were friction dampers, and later units used hydraulic ones
The magic is in the geometry, not a lack of damping ability
as to suspension stiffness vs compliance, there's a magic spot there
too soft and you wallow around like you're riding an over ripe tomato
too stiff and your tire 'skips' over road imperfections
Like I said in another thread, race bike teams will spend $1000s to save a single lb, suspension is heavy
There are no hardtail GP bikes

Make that 6 outta 8,
while I use air springs and oil, it's from a different bike, so not stock.

Like I asked in my post above, what are you trying to accomplish with the suspension changes? If you can provide specific things that you'd like to change, along with your weight and bike modifications, we might be able to suggest incremental changes.

Just going to a 15-40 wt oil is a rather unscientific approach. My guess is that you wont like the effect.

cheapnewb24 wrote on 01/20/16 at 09:36:34:

Here's an interesting question....

Is it better regarding safety and performance (not comfort) to have the suspension too stiff or too soft? Will hitting a high speed bump with a stiff (thick oil) front be worse than hitting it with a mushy front (thin oil)? Is there a fine goldilocks zone for safety here or can I just add thicker oil until my kidneys fall off. Again, I'll probably have to experiment. There's probably a very good reason that front suspension was standard procedure before rear suspension. Those forks need to give don't they? Don't want to go flying over the handlebars at 60 mph just because I hit a little pothole. .

I've listened to a video on suspension tuning which considered getting rid of bounciness. WD likes springers. How on earth do those things not bounce all over the place and not cause real problems?

cheapnewb24 wrote on 01/21/16 at 11:27:21:


I'm not sure if you have the tool to get to the bottom of the forks.  Look over the threads in the tech section.  I made the one where I combined 2 long bolts and used jb weld.  You'll also need some pvc to push the new seals in place, that is in the thread as well.  It wasn't to bad, if I can do it anyone can.

Best regards,

My 2003 has 12.5" Progressive rear shocks. Set as stiff as they can get, and I routinely bottom them out. Very distinct sound and feel, readily noticed. Have bottomed out hard enough to scrape the emissions canister mount on the road surface.

A springer fork is a whole different world versus glide forks. Throttle knowledge and control are critical to safe handling. Tire pressure front and rear literally make or break a rigid frame and its handling characteristics. You have to know your machine stem to stern and pay attention. Modern bikes are get on and go. Traditional bikes require bolt checks, tire checks and tire alignment checks pretty much before every ride.

As soon as I can swing it my spare frame will get a rigid conversion. I need to swap from torsion bar IFS to a real axle and leaf springs under my K1500 first.