Speedo Error

My 2006 Defender 110 is showing about a 14% error on the speedo, for example 55mph is only 48mph according to Google maps - I have checked Google maps against my DIsco speedo and they match, so definitely a speedo error on the 110. Tyre sizes are 225/80/R16. I think the recommended size for alloys is 235/85/R16. Would that correct the speedo error?

Probably get close, those tires are on the small side for a 110 and likely look a bit silly.

There are 5 different "cogs" from which one can be chosen to match the wheel / differential combination.
With a bit of research you might find one to match your combination.