• Any numbered stem, ie (37, 25, 35, 45) etc. has the bearings mounted to the chair (caster barrel).
• Any lettered stem, ie (KR, XF, ZR, Z2) etc. has the bearings in the fork of the wheelchair.
• IM = 1/2” no stem, MT = 12mm no stem.
• With any Uni-Tines, all above and below applies, except there is no Pivot Pin

Speed wobble, also known as Flutter, is caused by conflicting forces the wheel experiences as it rolls. Horizontal torque related to rotational inertia pulls the wheels inward, while frictional forces pull against that, causing a resonant frequency that leads to oscillation at the caster stem axis.

• Frog Legs forks absorb bumps and vibrations that may trigger flutter, and their suspension helps keep both front wheels in constant contact with the ground on uneven surfaces.
• Frog Legs forks do not experience flutter more than standard rigid forks.

Advice to Prevent Flutter

1. Ensure the caster fork bearings are perpendicular to the ground (e.g., check for bent frames or stems).
2. Ensure tension on the caster fork bearings by tightening the nut/bolt at the top of the caster housing until the caster flips around and stops after 1 to 1.5 full revolutions. Check for worn-out bearings and use waterproof bearings with friction in the seals.
3. Use balanced, high-quality wheels to avoid creating a pseudo vibration that matches the fork's resonant frequency.

99.9% of all issues with the wheels are bearing-related.

• Remove the wheel and clean out the spacers, axles, and bearings.
• Reinstall the axle back into the wheel and fork, then tighten.
• If the issue persists, replace the bearings (608RS) with an 8mm inside diameter 3/5”. If the wheels don’t fit a manufacturer's fork/axle, they may need an R6 wheel with a bigger diameter axle (3/8”).

• Tilted Fork: One fork is tilted back slightly. Above where the fork meets the chair's frame, there are two camber adjustment washers with grooves/teeth. If someone installs Frog Legs forks, they may not reinstall these washers correctly, affecting camber alignment.

• Floating: One fork touches the ground while the other does not. Chair frames can bend/flex, causing this issue. Solution: Send extra stem bolt washers (part number 101-60z) to lower the fork that is not touching the ground. This also applies to Quickie chairs.
• Stem Bolts Don’t Fit: Stem bolts fit standard caster barrel housing bearings, but sometimes the bearings are a different size, preventing the stem bolt from fitting. Solution: Get a photo of the bearing inside the housing. If the stem bolt sticks out, it’s too long, and a shorter one is needed. Measure the amount protruding and calculate the required length.
• Too Much Vibration: Polymer bushings may be old or worn out. Solution: Send new bushings.
• Wheels Don’t Fit: The person may have a narrow fork and need a narrower wheel.
• For any bearing, axle/pivot pin, screw, or other parts that need replacement, always advise replacing the same parts on the other fork for longevity.