OK....
There is the standard R2, for a full description read Speedtech;s website. There is also the very limited Web Edition which has a heap of hop ups, is Orange and has the cells on the opposite side, and no you can't get one anymore
There is a Speedway PAL drive train upgrade that chages the motor mount and main drive shaft so that the shaft has a support in the middle too and the spur has less wobble. This fits the normal chassis.
Now there is the Xenon conversion and Speedway PAL conversion for the R2, both are similar, but the SPeedway PAL version has the cells swapped to the opposite side, slightly different cut out's on the main chassis and a slightly different top deck, aswell as on the A'spec version some extra wings to stiffen the chassis. Both conversions have a similar drive train to the Speedway PAL drive system, creating a wobble free spur, but the motor mount also screws into the top deck and has a removable rear section to the top deck for much easier spur gear access. The main chassis on both conversions is also 3mm instead of 2.5mm on the standard R2, but to keep the geometry the same the places where the bulkheads/motor mounts are located are machined down. The other big difference is the cells have been moved forward 5mm and the motor back a couple mm, this gives a little more steering and most say a nicer overall balance.
The R3 will do a lot of what the conversions do, cells further forward, motor mount attached to top deck and main chassis and supports the main drive shaft so the spur is wobble free. There are also a couple of things the conversions don't offer, like bulkheads that no longer need spacers for the shock tower mounting. There is no easy change spur gear though and the chassis is made of some new sort of graphite. The A-arms will be beefed up a little around the mounting points but they will be compatible with the R2.
Hope that makes things a little clearer. You may have noticed I mentioned spur wobble a lot, this was the main gripe with the kit spec R2. The kit shaft holders are plastic and tend to create a few problems with spurs stripping, especially with mod motors. A good start for fixing this is alloy shaft holders which makes things fine for stock and 19turn motors but you may still have problems with a hot mod motor. With the support in the center that the Speedway PAL drive system offers, it quickly became popular, now you have the option of either conversion kit too and of course the R3 comes as standard with the new motor mount that provides extra support for a wobble free spur.
I think I just sent myself to sleep
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