At first, I build it with a mechanical speed controller and no BEC, It was very very heavy, and almost impossible to drive on the track, it jumps like crazy and spin 180° at almost every turn.
This is how it was before: 4lb 15oz
Now the mods.
In stock form, the suspension is limited by the short rear shocks, I used the longer front shocks in the rear mounted on the rollbar.
In the frond I grinded the arm stoppers until I can use all the shock travel (on this picture, the left is modded, the right is stock)
As the rear roll bar is now supporting the shocks, I decided to reinforce it with an alloy rod betwen the roll bar and the rear motor housing.
To clear the rera shocks from the tire at full shock compresion, I had to widden the rear.
I made some axle with 5mm steel rod, and alloy wideners.
The widened rear:
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