Suspension

As most of you already know the suspension components on the RC51 were for its time some of the best OEM parts ever put on a production motorcycle. A click here or there makes a difference in contrast to other period suspension parts like on my old 900RR where you could basically turn any adjuster you like from lock to lock without really affecting anything… However the springs rates are still designed around riding 2 up and the valving is completely out of spec for serious riding

Ultimately the bare minimum requirements for getting the RC51 to be compliant enough to keep you out of the ditch or gravel trap is a 20mm fork rework to revalve the forks to a more usable spec along with new fork springs and slap an Ohlins Shock on the rear of the bike. Those two items will give you both compliancy for traction keeping the tires in contact with the road and proper range of adjustment so that you can tune the geometry of the bike

Additonally depending on your needs you might find an aftermarket suspension linkage is beneficial as well
I used to receive many e-mails inquiring about suspension set-up on the RC51 & at the time this website was started I was barely able to accurately convey just how much improvement quality aftermarket suspension made to the bike let alone be able to tune it. Funny enough now almost a decade later I am a test rider, track instructor and suspension technician and can pretty much work out any possible problem one might encounter with suspension or geometry set-ups, but prior to my very steep learning curve I started with the very basic knowledge listed below and written by Dave Hodgespension here, as it seems that alot of people simply do not know what the adjusters do or even where they are located. So I went looking for all the answers & I believe I found a pretty good article written by Dave Hodges.
 

Circuit One Suspension
Suspension Tuning Guide by Dave Hodges
Street Bike or Road Racing Applications

With incorrect suspension setup, tire wear is increased and handling suffers, resulting in rider fatigue. Lap times can be dramatically slower and overall safety for both street and race enthusiasts is another issue. Add the frustration factor and it just makes sense to properly setup your suspension. The following guide will help you dial in your suspension for faster and safer riding both on and off the track.

Basic Setup: Check the following

: Forks/Rear Shock - Race sag 25-30 mm, 1 - 1 3/16 inch
: Forks/Rear Shock - Street sag 30-35 mm, 1 3/16 - 1 3/8 inch
: Check chain alignment. If not correct, sprocket wear is increased.
: Proper tire balance and pressure. If out of balance, there will be vibration in either wheel
: Steering head bearings and torque specifications, If too loose, head will shake at high speeds.
: Front end alignment. Check wheel alignment with triple clamps. If out of alignment, fork geometry will be incorrect and steering will suffer.
: Crash damage, check for proper frame geometry

Forks: Adjustment Locations

Rebound adjustment (if applicable) is located near the top of the fork.
Compression adjustment (if applicable) is located near the bottom of the fork.
Spring preload adjustment (if applicable) is generally hex style and located at the top of the fork.

Forks: Lack of Rebound

Symptoms:

: Forks are plush, but increasing speed causes loss of control and traction.
: The motorcycle wallows exiting the turn causing fading traction and loss of control.
: When taking a corner a speed, you experience front-end chatter, loss of traction and control.
: Aggressive input at speed lessons control and chassis attitude suffers.
: Front end fails to recover after aggressive input over bumpy surfaces.

Solution:
* Insufficient rebound. Increase rebound "gradually" until control and traction are optimized and chatter is gone.

Forks: Too Much Rebound

Symptoms:
: Front end feels locked up resulting in harsh ride.
: Suspension packs in and fails to return, giving a harsh ride.
Typically after the first bump, the bike will skip over subsequent bumps.
: With acceleration, the front end will tank slap or shake violently due to lack of front wheel tire contact.

Solution:
* Too much rebound. Decrease rebound "gradually" until control and traction are optimized.

Forks: Lack of Compression

Symptoms:
: Front-end dives severely, sometimes bottoming out over heavy bumps or during aggressive breaking
: Front feels soft or vague similar to lack of rebound.
: When bottoming, a clunk is heard. This is due to reaching the bottom of fork travel.

Solution:
* Insufficient compression. Increase "gradually" until control and traction are optimized.

Forks: Too Much Compression

Symptoms:
: Front end rides high through the corners, causing the bike to steer wide. It should ride in the middle of suspension travel.

Solution:
* Too much compression. Decrease compression "gradually" until bike neither bottoms or rides high.

: Front end chatters or shakes entering turns. This is due to incorrect oil height and/or too much low speed compression damping

Solution:
* First, verify that oil height is correct. If correct, then decrease compression "gradually" until chattering and shaking ceases.

: Bumps and ripples are felt directly in the triple clamps and through the chassis. This causes the front wheel to bounce over bumps.

Solution:
* Decrease compression "gradually" until control is regained.

: Ride is generally hard, and gets even harder when braking or entering turns.

Solution:* Decrease compression "gradually" until control is regained.

Shocks: Adjustment Locations

Rebound adjustment (if applicable) is located at the bottom of the shock.
Compression adjustment (if applicable) is located on the reservoir.
Spring prelude is located at the top of the shock.

Shock: Lack of Rebound

Symptoms:
: The ride will feel soft or vague and as speed increases, the rear end will want to wallow and/or weave over bumpy surfaces and traction suffers.
: Loss of traction will cause rear end to pogo or chatter due to shock returning too fast on exiting a corner.

Solution:
* Insufficient rebound: Increase rebound until wallowing and weaving disappears and control and traction are optimized.

Shock: Too Much Rebound

Symptoms:
: Ride is harsh, suspension control is limited and traction is lost.
: Rear end will pack in, forcing the bike wide in corners, due to rear squat. It will slow steering because front end is riding high.
: When rear end packs in, tires generally will overheat and will skip over bumps.
: When chopping throttle, rear end will tend to skip or hop on entries.

Solution:
* Too much rebound. Decrease rebound "gradually" until harsh ride is gone and traction is regained. Decrease rebound to keep rear end from packing.

Shock: Lack of Compression

Symptoms:
: The bike will not turn in entering a turn.
: With bottoming, control and traction are lost.
: With excessive rear end squat, when accelerating out of corners, the bike will tend to steer wide.

Solution:
* Insufficient compression. Increase compression "gradually" until traction and control is optimized and/or excessive rear end squat is gone.

Shock: Too Much Compression

Symptoms:
: Ride is harsh, but not as bad as too much rebound. As speed increases, so does harshness.
: There is very little rear end squat. This will cause loss of traction/sliding. Tire will overheat.
: Rear end will want to kick when going over medium to large bumps.

Solution:
* Too much compression. Decrease compression until harshness is gone.
Decrease compression until sliding stops and traction is regained.

Stock Tuning Limitations:

New motorcycles purchased from the dealership are generally set-up on the soft side, for a rider in the weight range of 140-165 lbs. If you are not in this range, you must retune the suspension for your weight within the internals of forks and shocks, the manufacturer puts valves with small venturis. This, along with shims, creates a damping curve. This works okay at slower speeds, but at higher speeds, when the suspension must react more quickly, the method cannot low enough oil, and you experience hydraulic lock. With hydraulic lock, there is no damping. The fork and/or shock cannot dampen correctly and handling suffers. The solution is to re-valve the active components for the proper damping curve. It does not matter what components you have, (Ohlins, Fox, KYB, Showa). If you can achieve the damping curve that is needed, it does not matter what brand name is on the component. Sometimes with stock components, when you turn the adjusters full in or out, you do not notice a difference. This is due to the fact that the manufacturer has put the damping curve in an area outside of your ideal range. After re-valving, the adjusters will be brought into play, and when you make an adjustment, you will be able to notice that they affect the way the way the fork or shock perform.

One of the problems with stock springs is, in most cases, it is of a progressive rate. This is to say, a spring at sag may be .85 kg per mm, and at 2.5 inches of travel, it may be 1.05 kg per mm, getting progressively stiffer. The ideal solution is to install a sprig with a straight rate, specific for your weight, and the weight of your motorcycle. In some cases, the factory installs a straight rate spring, but often the incorrect rate for your weight.

Dave W. Hodges
Circuit One Suspension

Remember to always make small adjustments, and keep notes! Sometimes more is not better and be patient. Suspension is an art/science.