Speedo under reading + ride comfort

[hairyguy4]

on my kzj70 my speedo massively under reads, running larger tyres (255 85 16) runs around 10 miles under actual speed getting a lot worse at higher speeds (70 mph is like 85+) surely it shouldn't be that bad with such a modest size increase?

Also a side question for the super knowledgeable Ben if he sees it lol, how does your 70 drive? Mine is rather harsh and jittery over bumps, I find myself driving over stuff rather fast to smooth it out, mainly from the back end, front end is decent enough though, rear springs are ome mediums and shocks are terrafirma landrover jobbies

 

[rob rule]

Brand new out of the box 70 series are normally around -4-5% under (speedo vs GPS). Larger diameter tyres normally reduce the Speedo to GPS difference ie. (305/70/16) are basically spot on. Obviously, oversize competition tires will further exaggerate the issue.

The % rate (over or under) should be relatively constant regardless of the speed -its a geared relationship.
ITO ride comfort -there are many variables here...tire choice/inflation pressure/load/ mechanical condition of suspension components and so on.. ((AFAICR OME med is +250kg so this could also be hindering you?))