On my DRZ400SM my feet wouldn't touch the ground and I kept tipping over when stopping. So I lowered it for more comfortable riding.
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If you lower your Grom you want it to be
BOTH front and rear to retain the fork angle. While making the angle more relaxed by only lowering the rear only makes the bike turn more slowly, making it steeper reduces trail which can be "death wobble" dangerous. On this bike I lowered it front and rear by sliding the forks up in the triple tree and adjustable lowering links on the rear. On the grom a shorter rear shock would lower the back, and I don't know about the forks, maybe shorter stiffer springs. Someone else here might know about that.