HUD being retarded a bit.

[Sam_Well.13]

Hey Zilvians...
Noob here, so if this isnt the right section to post my problem please move.

Anways, I just recently picked up a S13 with a working HUD. As i was driving it home and following my wife i told her to take it easy and drive 65 mph which she said she was, as i was following her without gaining or loosing distance, my HUD reads im going 70 mph. So i pulled up next to her and coast.
Anyhow.. my problem is, is there anyway to correct this? Could it be my speed sensor on the transmission. im about 3-5 mph off. Sorry i tried searching here but people in here either have a working HUD, or not. Nothing similar to my problem. If you can direct me to the right place, i would thank you. :D

[Allmtoreg]

different sized wheels will cause this

[Sam_Well.13]

ic ic. ok. i have 17 on the car @ the moment. So is there a way i can reset and re-configure this to read right?

[!Zar!]

Nissan sells different pinion gears that goes onto the VSS.

[Oki180]

there should be a potentiometer on the back of the digi-speedo. You can adjust that to dial it in.

Here is a picture of the normal speedo See if your digi has something like this?

http://www.zeroyon.com/index/images/stories/tech/speedomod/pots.jpg

[Sam_Well.13]

too scared to open nd mess with it..lol.. its only off 3-5mph... so ill work with that.. thx fellas =]