I see at summit racing that for a 2.4 cavy that have standard and .25mm undersized. For what reason would you use the undersized for? Does it enhance performance in some way???
When I step on the gas, I want people to think the world is coming to an end! - Homer J. Simpson
Undersized bearings are used when you have to turn the crank (remove material to make it even). The bearings then fill the space where the material removed from the crank used to be.

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better a delay than a disaster.