How far in advance can I renew my motorbike license in Chiang Mai before it expires?

Go and talk to your local Department of Land Transport office about their requirements for renewal.

Each office slightly differs on their requirements. For instance the office where I lived said it was fine to renew my temporary 2 year licence, one year ahead of expiry, directly to 5 year unrestricted licence.

That was handy way for me to formalize my motorcycle licence in an internationally recognized format. As in my home country I never had a motorcycle licence.

6 months before, 1 year after

Renew the license the day after it expire so your new license will last almost 6 years

You can also renew after it expires, I think up to a year after. I renewed recently a month later. I don’t ride a motorbike now but I didn’t want to lose it.

If it's temporary you need to wait until it expires usually. And depending on what visa you have at that time will determine whether you get another 2 years or a 5-year license.

Normally within 6 months of expiry .