The short version
- A go kart wheel bearing is one of two completely different jobs, and mixing them up is the usual mistake.
- Front spindle bearings sit inside the wheel hub. Live axle bearings sit in hangers bolted to the frame.
- Sizes are simple and standard. 5/8 inch spindles and 1 inch or 1 1/4 inch live axles cover most karts.
- Choose double lip rubber seals over metal shields, because dirt is what kills them.
Karts are refreshingly honest machines. There is no press work, no staked nut and no hub unit costing three figures, just plain catalog bearings you can buy anywhere.
The only real skill is knowing which of the two positions you are working on.
The two positions
The front wheels turn on stub spindles, with a pair of small bearings inside each wheel hub carrying the kart’s weight.
The rear is a live axle, meaning one solid shaft turning with both wheels. It is supported by bearings in hangers on the frame, not inside the wheels.
So a noise from the back is usually an axle bearing in a hanger, and a wobbling front wheel is a spindle bearing.
The general idea of a live axle is on the axle bearing page.
Sizes you will actually meet
| Position | Bore | Typical part |
|---|---|---|
| Front spindle | 5/8 in | 99502H, 1 3/8 in outside diameter |
| Front spindle, some karts | 3/4 in | Flanged ball bearing |
| Live axle, off road kart | 1 in | Flanged bearing with flangettes |
| Live axle, larger kart | 1 1/4 in | Flanged bearing with flangettes |
| Racing kart axle | Metric, 30 to 50 mm | Sealed deep groove, held in cassettes |
The 99502H is worth memorizing. It measures 5/8 by 1 3/8 by 7/16 inch and crosses to 6202 5/8 and 6202 10, so you can find it under several names.
Cross referencing is on the cross reference page.
The flangette, which confuses people
A live axle bearing usually has a spherical outer surface, so it can self align slightly within its housing.
Two stamped steel flangettes clamp around it and bolt to the axle hanger. They are what hold it, not a press fit.
Because the outer can pivot a little, small misalignment between the two hangers is tolerated. Large misalignment is not, and it wears both bearings quickly.
Sealed or shielded
A shielded bearing has a metal disc close to the inner race but not touching it. Dust walks straight past it.
A 2RS bearing has contact rubber lips on both sides. It costs a little more and lasts far longer in dirt.
On a track kart the extra drag of contact seals matters and shields are sometimes chosen deliberately. On anything that sees dirt, take the seals.
Why a go kart wheel bearing fails
- Dirt and water, which is the leading cause and the reason seals matter.
- Side load from hard cornering on a kart with no suspension to absorb it.
- Hanger misalignment, which forces the two axle bearings to fight each other.
- Overtightened flangettes, which pinch the outer and destroy the internal clearance.
- Impact fitting, where hammering on the inner race dents the raceways before the kart ever moves.
Pushing on the inner race sends the entire fitting force through the balls onto the outer race.
That leaves small dents that become noise within hours of running.
The same rule on cars is on the fitting page.
Fitting and alignment
Slide the new bearing onto a clean axle, checking for grooves where the old one sat. A worn axle will never hold a new bearing tight.
Bolt one hanger down, fit the axle through both, then snug the second hanger with the axle turning. Let the bearings find their own position before you tighten fully.
Spin it by hand afterwards. It should turn freely with no notchiness and no binding at any point in the revolution.
Greasing
Sealed bearings arrive filled and should be left alone. There is nothing useful you can add.
Some off road karts use a greasable hub instead, and those follow ordinary practice with a marine grade grease if they get wet.
Grease types are on the grease types page and the wet case is on the marine grease page.
A golf cart looks similar and is not, since it mixes both designs. That is on the page about cart front and rear bearings.
Common questions
What size is a go kart wheel bearing?
Front spindles are usually 5/8 inch, taking a 99502H. Live axles are commonly 1 inch or 1 1/4 inch.
What does 99502H cross to?
It is the same bearing as 6202 5/8 and 6202 10, measuring 5/8 by 1 3/8 by 7/16 inch.
What are flangettes?
Stamped steel halves that clamp around a spherical outer bearing and bolt to the axle hanger. They hold the bearing without a press fit.
Sealed or shielded bearings?
Sealed, on anything that sees dirt. Rubber lips keep out what a metal shield lets straight through.
Why does my new axle bearing sound rough already?
Usually it was driven in by the inner race, or the two hangers are misaligned and loading it sideways.
Do I grease a go kart wheel bearing?
Not a sealed one. Greasable hubs on some off road karts are the exception.
How tight should the flangette bolts be?
Snug, with the axle turning as you tighten. Overtightening pinches the outer race and kills the clearance inside.