I've been trying the Amp on my local off-road dirt track but it's been slow to bite the track and tend to spin out super easily while taking corners. Is that a tires problem (I have stock) and can anyone recommend better? The track is slightly dry/dusty but mostly packed dirt.
Also I've seen people recommend replacement bearings a lot and saying it makes things much better. Could someone explain better how? Thanks!
When trying to change the handling of your car, the first place to start is with tires. I recommend you give ProLine tires a look. The AMP MT (and the DB) are actually built on a Stadium Truck platform (they are virtually the same chassis as the Circuit ST) so you'll want to look at Stadium Truck tires.
The ProLine Holeshot tires will be a big step up. The biggest performance factor will be their softer rubber compound which will offer improved grip. I've also used JConcepts "Carvers" on the front with the ProLine Holeshot in the back on a dirt track that featured a mix of surface conditions-- loose crumbly, hardpack, dusty hardpack.
No one tire will be able to handle every surface equally well, but that's the whole reason behind outdoor dirt-- unpredictablility and the skill of the driver.
Put your car up on a block or stand so the wheels aren't touching the ground. Give the front wheels a spin. See how long they spin and if they make any noise. They they only turn around a few times or make grinding, hissing noises that means they are worn and should be replaced. Any drag or friction is resistance the motor has to overcome and is extra work.
Additionally, the bearing that came with the kit are typically really inexpensive--lower quality and unsealed. A new set of bearings from Avid or Fast Eddy will be of much higher quality and feature rubber seals to help prevent contamination by dirt/dust/water and thus give you better service life.
The bearings in your transmission are generally better protected than those in the spindle carriers/steering blocks/hub carriers so will likely be usable for much longer (but still likely to wear out and introduce wobble in the gear train).
Hot Racing and ecx make them. I took the rear aluminum hubs out of mine and went back to plastic. The aluminum was too stiff in the rear and prematurely toasting wheel bearings. I found the bearings to last twice as long with plastic because it flexes a little.