FORK BUSHING CLEARANCE EXPLAINED
Sirris forks are engineered for maximum oil flow around the bushings to ensure ultimate performance.
Read below to learn how this works.
You can feel the fork's engineered bushing clearance when the bike is stationary. This clearance is intentional and disappears during riding as oil flows through the fork and lubricates the bushings.
Too little clearance can cause binding and poor lubrication, while too much reduces steering precision.
HOW IT WORKS:
There is an oil port in the stanchion that supplies oil between the inner and outer tubes. When the bike is stationary, this port will circulate oil back into the fork leg and some bushing clearance may be noticed as the oil drains from the top bushing area to the bottom of the fork.
Forks from WP, KYB and Showa typically have a higher static oil level around the upper bushing than Sirris, making the bushing clearance less noticeable.
While riding, all performance suspension brands maintain very similar lubrication of the bushings. The overall bushing clearance can be measured with a special rig, and the differences between all performance manufacturers are very similar. If the numbers are studied in detail, Sirris tend to run the bushing clearance slightly lower than some competitors. Still, the difference between the performance suspension manufacturers is so small that parts are in many cases interchangeable. Every fork built by Sirris has overall bushing clearance measured and documented at the end of the production line as a part of our quality control.
Some competitors place the oil ports differently to reduce how this clearance can be felt, balancing attributes like performance and durability differently compared to Sirris. During normal riding, oil continuously lubricates the bushings, so play or noise should not be present unless the bushing clearance exceeds our specification from excessive wear.
Manufacturers that position this oil port higher, or even remove it, likely intend to make the bushing clearance less noticeable rather than offering a performance benefit.
STATIC BATH OIL LEVEL
Why it feels different on a stand (or rocking motion with front brake on) vs. riding:
When the bike is on a stand, oil inside the fork settles toward the bottom, making the bushing clearance easier to feel by hand.
BATH OIL IN MOTION
When riding, oil is distributed throughout the fork and fully lubricates the bushings, creating a smooth sliding interface allowing the bushings to slide as designed. In this state, the fork performs as intended and the bushing clearance is not noticeable.
This picture shows oil flow shortly after riding. Oil is pooling on top of the bushing and is flowing towards the lower port.
BUSHING COVERAGE
During normal riding, oil continuously lubricates the upper and lower bushings to ensure smooth operation under the highest loads.
BUSHING GAP: An in-depth look
Sirris forks use PTFE-coated steel bushings with very tightly controlled clearance between the inner and outer tubes.
This small amount of clearance is critical to performance. Under riding conditions, the fork is subjected to significant loads and slight flex (elastic deformation). The designed clearance between the bushings and sliding surfaces prevents the fork from binding in these situations, allowing it to move freely and track smoothly over terrain. This design follows proven practices from high-performance combustion motorcycles and uses the same suppliers trusted by leading manufacturers.
If the clearance was tighter, the fork would feel harsher and less compliant under load. Using tighter-fitting polymer bushings (common in bicycles) would also reduce both durability and performance in demanding conditions.
Bushing lifespan — Sirris bushings are designed for durability and typically last around 100 hours of riding before excessive wear develops. Actual lifespan will vary depending on riding conditions and severity of use.
Keep in mind that bushing wear must be significant before it can be felt while riding. The slight play you feel on a stand is a normal part of a high-performance fork design.
Before replacing bushings, be sure to check for other possible sources of movement so you don’t end up chasing the wrong problem.
BUSHING SERVICE
Bushing service should be scheduled at 90 hours. Hit the button for more information on service intervals.
Important: Don’t confuse normal clearance with other issues
It’s common for riders to notice this small amount of fork bushing clearance on a stand and assume it’s related to a different sensation while riding. In many cases, the real issue comes from elsewhere on the bike, such as:
Loose or worn steering bearings
Loose or worn head set bearings are very common on small and mid-size emotos and are usually felt as clicking or knocking from the front end of the bike. This can felt when riding and standing still.
Start by making sure the head set is tight according to manufacturer specifications. You should not feel any play between the head tube and the triple clamp when applying alternating load. If your head set is firm with no play, it can still generate noise from worn bearings.
Sirris aftermarket forks come with the lower bearing race included. If there is wear to the outer race installed in the frame, the bearings won’t mate properly. A common symptom is clicking or popping during use. If outer race is worn, replace with a new outer race.
Loose axle
Follow manufacturer instructions specific to Sirris forks or Sirris assembly instructions when installing the front axle. It is important to torque the pinch bolts to spec to avoid movement between the axle and the drop out. If you are using an aftermarket axle, make sure the diameter of the axle is the same as the OEM axle or the Sirris axle you are replacing.
Loose or worn wheel bearings
Some bikes have undersized wheel bearings for the application. Remove the wheel from the bike and rotate the wheel bearings with your finger. They should rotate smoothly without tugging, noise or play. Also make sure the wheel spacers mates correctly with both the wheel and the drop outs.
Battery or component movement
Many electric bikes have battery movement or start having battery movement from wear or simply that you are going faster after upgrading your suspension. Battery movement is generally both heard and felt as a dull thump when going fast in rough sections, when landing after a jump or any abrupt movement of the bike. There are multiple solutions, most common are to add a pneumatic wedge or an additional battery strap.
Motor tugging
Some Emotos get a tugging feel from rotating the motor when the bike is moved back and forth. This tugging can be surprisingly hard to identify. If you lock the rear brake, or remove the chain, the motor tugging will go away.
Brake Pads or Rotors
Brakes can generate noise that can be hard to track down. If your brakes have anti-rattle springs/clips, make sure they are present and installed correctly. If you apply the brakes while rocking the motorcycle back and forth, both movement of the pads in the caliper and floating discs can generate both noise and play. If the brakes have a floating caliper, make sure the bushings don’t have play and that they are lubricated.
Front Disc Guards
If you have a front disc guard that clamps on the front axle, make sure it mates correctly on all interfaces. If the disc guard prevents the drop out and wheel axle to mate correctly, it might generate play in the system.
FAQ
DETAILED ANSWERS TO COMMON QUESTIONS:
Why does my new (or low-mileage) fork seem to make noise or feel loose when riding?
If you notice knocking while riding, first check for other common sources of movement:
- Battery movement (e-bikes)
- Loose or worn headset bearings
- Headset cups moving in the frame
- Loose or incorrectly installed front axle
- Worn front wheel bearings
- Brake pad or floating rotor movement when the front brake is applied
These issues are often mistaken for fork bushing clearance.
How do I know if there is too much play?
If bushing play due to wear can be felt when riding, it's time to schedule your fork service.
If you feel "play or knocking" while riding a new or low mileage fork it is very unlikely related to fork bushings as this is checked during the manufacturing process.
A precise measurement requires specialized equipment. The simplest check is to ride the bike.
Why doesn't the fork always keep the bushings submerged in oil?
The bath oil level is carefully tuned for performance and durability. Too much oil can reduce performance and damage seals. Like an engine, the fork relies on continuous oil circulation—not simply a high oil level—to provide lubrication and maintain a protective oil film.
Why does one fork leg feel looser than the other?
Small manufacturing tolerances across all components can create slight differences in perceived play between fork legs. During riding, the circulating oil fills these clearances, making the difference effectively disappear.
My other bikes don't do this. Why?
Most performance suspension forks use similar bushing designs, but manufacturers use different oil flow strategies. Some designs minimize perceived play when the bike is stationary by reducing oil flow to the bushings. Sirris prioritizes continuous lubrication, durability, and on-trail performance, even if that means slight bushing clearance may be noticeable when the bike is not being ridden.
My fork has play and want to have it checked. How do I have it checked?
Sirris can check your fork with equipment needed to measure fork play to make sure the components are within tolerance. If all parts are within production tolerances and overall play is in spec labor, oil and shipping will be charged. If we find any parts outside specifications, labor, oil and shipping is covered by Sirris within Sirris warranty terms. Worn or damaged parts are not covered by warranty.
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