Annoyed at speedo reading 5-6mph under actual. Pulled needle off speedo (it’s tight on there) carefully. Got my phone on Speedo drove at 40 pushed needle on and road tested to various speeds. Worked fine . Odometer will still be off I think

 

Yes it’s normal with bigger tires

 

Im running 265/75/16. I may go to a 33 in tire. Will re-gearing fix the speedo and odometer readings?

 

You are not regearing. You are putting the speedometer needle where it should read with a gps.

 

Re-gearing will not solve that issue Bignacio. Also you might have corrected the needle for a small speed range but it will still be off in other ranges.

 

no it wont. If the untouched speedo is out by 10mph from 10mph to 100mph relocating the needle to reflect the new speed will be maintained throughout. I’ve done it and it works

 

That's not how it works. Your speedo is thrown off because your tires are a certain percentage larger. If your tires are 10% larger, that throws your speedo off 10%. At 60 mph that would be 6 mph off. At 20 mph that would be 2 mph off. At 100 mph that would be 10 mpg off. Your speedo is still going to be off at other speeds than where you corrected it.

 

whatever you say........like you’ve done it

 

I mean it's just a simple math problem. I'm glad that it works for you but it is not a true solution across all speeds.

 

Pretty basic understanding of gear ratio and design will tell you that it only works At a certain speed, like others said, it is off by a percentage. You can say the world is flat all you want, but math really works. And yes re-gearing your differentials to match your tire size will 100% fix the problem the right way. Some vehicles you can buy a speedo cable reducing gear to compensate.