Wife's speedo off, reads 7mph fast from 45mph on up, change tire sizes?

[Larry Hampton]

I used the speedo app on my phone to get the difference. The original speedo in her car was jacked up, so I installed another one off a different car, but the 'new' speedo showed a lot higher milage than her original one, so I put her odometer in the 'new' speedo, but the speed is off quite a bit. From 45 on up is about 7 mph off, below that its around 5 mph off, obviously there is a 6 mph off range in there.

I pulled the speedo and jacked with the little silver arms but couldn't get it to really do anything different, it would change 1-2 mph.

So, with the thought of a taller tire causing the speedo to read slower, my idea is to get it closer with a cooler set of rims and tires. I want to stay with a more common tire size, dunno whether to go 15" or 16", 205-50-16 looks pretty close, wanted thoughts from the collective.

[GenevaDirt]

I used the speedo app on my phone to get the difference. The original speedo in her car was jacked up, so I installed another one off a different car, but the 'new' speedo showed a lot higher milage than her original one, so I put her odometer in the 'new' speedo, but the speed is off quite a bit. From 45 on up is about 7 mph off, below that its around 5 mph off, obviously there is a 6 mph off range in there.

I pulled the speedo and jacked with the little silver arms but couldn't get it to really do anything different, it would change 1-2 mph.

So, with the thought of a taller tire causing the speedo to read slower, my idea is to get it closer with a cooler set of rims and tires. I want to stay with a more common tire size, dunno whether to go 15" or 16", 205-50-16 looks pretty close, wanted thoughts from the collective.

what size tires are on the car now?

[Larry Hampton]

Kumho 155/80-12 same as everything else.

[GenevaDirt]

then I would say the speedo is messed up. No way with those tires should it be off that much or at all. !45/80 /12's is what was original back in the day...but with the 155/80/12's on every car I ever checked it on...it was spot on with the speedo and tripometer.

[DriverOne]

Re: Wife's speedo off, reads 7mph fast from 45mph on up, change tire sizes?

Larry, go 14" with 165/65 R14's.

[GenevaDirt]

Larry, go 14" with 165/65 R14's.

will not fix his speedo

[DriverOne]

Re: Wife's speedo off, reads 7mph fast from 45mph on up, change tire sizes?

Typo. 165/55R14

http://item.mobileweb.ebay.com/viewitem?itemId=221090128132

[GenevaDirt]

Typo. 165/55R14
http://item.mobileweb.ebay.com/viewi...d=221090128132

lol...still will not fix it. It is not right...if it is off with the tires he has on it then even if he puts tires on it that make it show right...he will still be going a different speed. Something is wrong with his speedo.

[FestYboy]

there's a clutch-like actuator that drives the needle for the speedo... if there has been any oil or other lube forced into that clutch, it'll drive the indicated speed up. but it'll be more linear (ie 5mph off at 20 and 10mph at 60 and 20 @ 90). it seems to me that there is a mechanical "clocking" issue that needs resolved. where does the needle sit at rest?

[Larry Hampton]

I know the speedo is off, but if it's on, and I put too big a tire it'll read slow. But now it's reading fast, so my thought is if I put a bigger tire on it to slow the speedo down close to correct.

I once tried to cut my bangs in college, the hair kept sweeping out in front of the scissors and my bangs curved down, so I thought if I slanted the scissors up, it would cut straight. I was wrong, I had 1/4" bangs after that.

As I said before, I tried another speedo and it wasn't right either. I've been wanting different wheels and tires and want the speedo closer, figured this might work. What am I missing.

[Larry Hampton]

there's a clutch-like actuator that drives the needle for the speedo... if there has been any oil or other lube forced into that clutch, it'll drive the indicated speed up. but it'll be more linear (ie 5mph off at 20 and 10mph at 60 and 20 @ 90). it seems to me that there is a mechanical "clocking" issue that needs resolved. where does the needle sit at rest?

0

[GenevaDirt]

I know the speedo is off, but if it's on, and I put too big a tire it'll read slow. But now it's reading fast, so my thought is if I put a bigger tire on it to slow the speedo down close to correct.

I once tried to cut my bangs in college, the hair kept sweeping out in front of the scissors and my bangs curved down, so I thought if I slanted the scissors up, it would cut straight. I was wrong, I had 1/4" bangs after that.

As I said before, I tried another speedo and it wasn't right either. I've been wanting different wheels and tires and want the speedo closer, figured this might work. What am I missing.

you will still be off with bugger tires...the speedo may seem right but you will actually be traveling further with bigger tires then what it is showing. I may not be thinking correctly but I do not think that you can fix it (and make it right) by putting different size tires on it.

[Larry Hampton]

Well, I pulled up a calculator, and it said if I put 205/50-16 on a speedo that was correct and ran 65, my speedo would read 58, so now with the stock tire and a bad speedo, I run 65 and the speedo reads 72, so if I put the bigger tires, it'll read close to right.

[Advancedynamix]

Larry, that makes sense to me too.

[Larry Hampton]

I know it's not the "right" way to fix it, but it does fit the needs I have with wanting a bigger, nicer tire combo for the wife's black GL. I'm trying to talk her into a BP swap as well. I'm looking at doing some trading for a '91 Protege auto.