[ChopperCharles]

So the RX4 comes with a 13T countershaft sprocket?
Well, you can buy the SG400 countershaft sprocket. It has 14 splines like the RX4, and it's got 14 teeth. It is a 520 sprocket, but that doesn't matter, it will still work fine with your 530 chain.

The SG400 also appears to use the same rear sprocket as the RX4, but also in 520. It has 40 teeth, where the RX4 has 44 stock. This should also swap. The 14T countershaft sprocket will get you 7.7% decrease in rpms. A 40T rear sprocket with a stock 13T countershaft will give you a 10% reduction in rpms.

The RX3 sprocket is 13 splines btw, which is why it won't fit.

Thanks for the link, I ordered the 13T 520 for my SG400. I want a bit more acceleration, it's geared for 112.5mph but can only pull 96-98mph in top gear.

Charles.