General Question About Speedodmeter Being off? Anyone?

[NeedForSpeed]

My speedodmeter is off in my F-150.

I switched from 255\70\16 wheels & tires to 285\50\20

The new wheels and tires are bigger, maybe 2or 3 inches etc... taller.

How would this effect my speedometer?

Would it make it read faster or slower?

For example if I was doing 30 on my speedo, I'd really be doing..... 35 or 25? etc....

 

[Rearpl8tsinsite]

I believe a bigger tire takes longer to complete a revolution so officially your speedo will read less than what you are actually doing. By bigger I mean series and rim size not width. Your series is lower profile than before but your size went up 4 inches so I'd imagine your tires are taking longer to complete the revolution than your old tires which will cause your speedo to read less than actual. My guess is between 5-10 mph.

Correct me if I'm wrong.

 

[poopnut2]

I believe a bigger tire takes longer to complete a revolution so officially your speedo will read less than what you are actually doing. By bigger I mean series and rim size not width. Your series is lower profile than before but your size went up 4 inches so I'd imagine your tires are taking longer to complete the revolution than your old tires which will cause your speedo to read less than actual. My guess is between 5-10 mph.

Correct me if I'm wrong.

I'd correct you but you're right. :-D :beer:

 

[NeedForSpeed]

Which speedo gear to correct this?

ok thats what i was thinking, thanks for the input.

I recently got a ticket for going 9mph over the limit. 34 in a 25.

So my lawyer told me to gather up info on my speedometer being off.


Anyone know which speedo gear I would need to corect this?
Which speedometer gear for the tranny would I need? It's a 5speed.

97 F-150 4.6L w\ 5speed

 

[NeedForSpeed]

MORE COWBELL! :rockon: THE SONG NEEDS MORE COWBELL

lol i just looked at your picture and remembered that SNL episode.

ok back to the speedo question anyone?

 

[poopnut2]

I would post up on an F-150 forum. That's a tough question on which gear you need. Your truck comes stock with like 3.27's or 3.55's right? Maybe find a gear that would match up with 4.10's?

 

[Rearpl8tsinsite]

ok thats what i was thinking, thanks for the input.

I recently got a ticket for going 9mph over the limit. 34 in a 25.

So my lawyer told me to gather up info on my speedometer being off.

Can't help you with the gear size but you might want to check with auto club. They hold speedo tests every so often free of charge for members.

 

[NeedForSpeed]

who is auto club?

 

[Top_Fuel]

You don't need a new speedo gear. You just need to tell the PCM what tires are on your car...

http://www.hypertech.com/tiregear.html

 

[Rearpl8tsinsite]

You don't need a new speedo gear. You just need to tell the PCM what tires are on your car...

http://www.hypertech.com/tiregear.html

I was thinking about that but didn't know enough about F150's.


Auto club is AAA. Insurance and roadside assistance. Maybe thay don't exist in your state.

http://ww1.aaa.com/scripts/WebObjects.dll/ZipCode