The ERGON grips will slide on easily because they are lock-on grips. On the end of each grip, the plastic bar end or metal clamp also clamps the grip onto the handlebar, keeping it in place and from rotating. If that part of the grip does not contact the handlebar it will come off.
This video shows how ERGON grips are installed
On some of our models, the factory grip is not as wide as the ERGONs, so you might have to loosen the brake and shifter to slide them inboard a tiny bit. See the image below:
If the ERGON grip is longer than the handlebar, then loosen the cap head bolt on the underside of the shifter with a 3mm allen wrench and the 4mm bolts for the brake lever.
Now you can slide those components inboard on the handlebar.
Loosen the clamping bolt on the ERGON grip, slide the grip on all the way, tap the end to ensure the handlebar and grip are flush to each other, and tighten the 4mm bolt on the underside of the clamp on the grip.
Now line up the shifter properly and tighten it down with a 3mm allen wrench. Then line up the brake lever and tighten it with a 4 mm allen wrench.