Speedometer not reading correct mph?

[Deviousjet]

I SEARCHED FOR THIS AND FOUND NOTHING.... Now that I got that out of the way. I have an 89 coupe swapped over to Dual cam engine. It works great but Yesterday I was driving to albuquerque a 300 mile trip and noticed everyone was passing me. well my cousin was with me and he had a gps based speedo and it was registering my car was going 10 mph slower than what the digital speedo was saying. So today I drove next to my dad in his 2010 Honda Odyssey and confirmed that my car is registering 10 mph under I am only running 16 inch buddy club wheels with 215 40 16 Tires so that shouldn't be the reason that they are off. Any ideas? Maybe I need to replace the sensor that reads the mph? or is there a setting behind the speedo? This is a HUD car. Thanks for the help.

[Deviousjet]

bumpity bump bump bump

[g6civcx]

Stock size is 195/60-15. 215/40-16 is 5% smaller.

Use this calculator: Palo Alto Speedometer: Speedometer Calculator (http://www.paspeedo.com/calculator.htm)

Your speedo will be 5% too high because your tyre is smaller than stock.

[Deviousjet]

Dang Thank you. So I need to get bigger tires.

[Deviousjet]

Question though, Is there a multiplying factor the higher speed you go because I'm looking and that's only a difference of three mph what about the other 7? I"m pissed because I just got new tires so it's gonna be a while before I can replace them.

[g6civcx]

The odometer is not accurate.

[Pirate_Freder]

the other 7mph could be the speed sensor or the gauge cluster istelf. do you know for sure that the ring gear in the differential and all the gears in the transmission are stock?

BTW, cool to see another guy from NM. I'm from Roswell.

Fred

[sickstatus]

its ur tire/rim size. when i had 18s n switched to 15s, my speedometer was off by 5mph.

[Deviousjet]

To the dude from Roswell please check out crucesstreets.com that's a local site and alot of people from alamo, roswell etc. Anyways back to what sick status said. You said the change from 15's to 18's changed 5 mph. But I'm at ten and with a wheel and tire combo that's actually smaller than stock. I'm gonna put my new drift spares on they are 225 60 15's Hopefully That will help it. I'm gonna have to live with it for a while because I sure as hell don't feel like buying new expensive daily tires any time soon.

[Pirate_Freder]

you can always buy the rev speed meter by apex. that is of course if nothing is wrong with you car. it allows you to input a tire size correction value and displays the proper speed. or a dakota digital speed converter will change the reading of your stock speedometer for wtv you change(gears, tires).

I have joined crucesstreets but I haven't been active there. Just browsed around and nothing peaked my interest enough, I'll prob check it out again though when I am ready to go to some events in a month or so.

[bl3ujay07]

buy a gps or just drive 10 mph and be done with. My speedometer wouldnt work so i got myself a gps

[Deviousjet]

you can always buy the rev speed meter by apex. that is of course if nothing is wrong with you car. it allows you to input a tire size correction value and displays the proper speed. or a dakota digital speed converter will change the reading of your stock speedometer for wtv you change(gears, tires).

I have joined crucesstreets but I haven't been active there. Just browsed around and nothing peaked my interest enough, I'll prob check it out again though when I am ready to go to some events in a month or so.

It's kind of a slow thread but there's alot of 240's on that site. You may want to give it another look. The end of this month is the slidefest at Arroyo seco if you got some time feel free to check it out. That speed converter sounds interesting but I'm cheap,lol. I'll just go 10 over on my speedo until my rears wear out. Thanks for the help guys I'll put my drift tires on and see if that changes anything. Just haven't got to it yet.