Spur gear used on sidewinders and anglewinders.
(Items that require replacement) can be replaced with just one wrench,
Adjusting the gear ratio is one of the relatively easy tuning methods.
Just to recap,
More gears → better acceleration (and braking)
Reduce the number of gears → Maximum speed up
It will be.
However, the gear ratio adjustment with the spur gear is fine adjustment (the change is not so large),
It feels like the final adjustments.
There are two types of spur gears: aluminum and plastic. 
The genuine specifications of major manufacturers are
slot.it, ScaleAuto, etc. are plastic, while NSR is aluminum.
Let's summarize the differences between aluminum and plastic (advantages and disadvantages).
●Advantages of plastic spur gears: Lightweight, (relatively) quiet, (slightly) cheaper
Advantages of aluminum spur gears: Durable (unbreakable)
- Good pickup
For me, the biggest difference is the pickup and durability.
Because of the difference in hardness, aluminum has better pickup (response),
I think you can really feel the difference in response even when comparing it with the same gear ratio.
This pickup not only affects the actual acceleration, but also changes the way you feel it, so it's a recommended part replacement for those who value feeling.
Gear ratios and feeling are largely a relative evaluation of "how much it has changed from before," so
I think it will be easier to choose if you have a set of staples in mind.
Also, since it's plastic, it may be inevitable in a sense,
Plastic spur gears will crack.
It would be fine if this only happened after I'd used it up to a certain extent, but
Older models (that have been assembled a long time ago) may crack even if they have not been driven much.
(Maybe the grease is seeping into the case?)
At one time, the NSR used plastic spur gears as standard equipment, but
It broke a lot, so I ended up switching back to aluminum spur gears.
(In the case of the NSR, there is a lot of play in the gears and the motor torque is strong, so the gears break when starting.)
It's best to adjust it to your own taste,
You also need to take into account the unique features of each manufacturer.