How accurate are our/your odometers?

[yellowstang1994]

Hi guys, reason I am asking is I always thought my car gained more miles then what I really drove. I have the stock tires on it and everything. What really got me is. A run around the block near my house is exactly .54mi, however my car reads .90mi. So it's not very accurate. The guy that owned my car before me had 17in 03 cobra wheels on it. I wonder if that had anything to do with it?

 

[215what]

i think you have gears

 

[94-302-vert]

I bet if you drive speed limit on the highway people keep flying by you?

There are multiple ways to determine what gears you car has. But the best ways will be to jack up the car, rotate the back tires one revolution and cound how many times the D/S goes around, or pull the diff cover and count teeth and divide.

THen you can use what the factory speedo is reading to determine what gears were in the car originaly (by takeing ahigher speed RPM and MPH reading and knowing what gear you are in).

As for the tires, they are the same OD so that is not the problem.

Chris

 

[BlackVert]

you probably have gears. my odometer goes up faster that it should too.

what rpms are you turning at 70mph in 5th?

btw, nice avatar!

 

[yellowstang1994]

Thanks for the replies and comments on the avatar, lol. Man it's hard to beleive that my car would have gears in it, but I guess anything could be possible at this point. My friend that has a GN everytime he takes a ride in my car and I get on it, he asks me dude what the hell did you do to this thing lately to make it so quick? Maybee I do have gears. Blackvert, i'm going to drive tonight and see what rpms i'm at at 70 in 5th, I beleive it's 3grand or under but I want to make sure. And you guys are right, i'll be cruising at 80 and it seems like i'm just cruising with traffic.

 

[BlackVert]

if i remember correctly, stock gears put you at 2000 rpm at 70mph in 5th gear.

go with a friend who can set his on a known speed and see what your speed says.

 

[yellowstang1994]

Yep, looks like i'm turning 2,000rpms at 70mph in 5th gear, looks like I have the stockers. Thats what I figured from the get-go anyway.

 

[YellowGTS]

umm....I do have stock gears (2.73's) and in 5th gear, at 2k I'm running 80 mph.

OT- Well, that was before. Few days ago I had to put some used (but new) tires on the rear because mine were bald, um, I don't know why honestly. But anyhow, these tires are a little bit shorter, so it's like putting gears in the rear. I can smoke 2nd gear now! It feels so much faster and my speedo is off by like 4 or 5 mph. I need some 3.73's in this biotch!

Ok sorry for the excessive rambling, the point to the first part of this was that with 2.73's in 5th gear, you should be running close to 80 mph at 2k, not 70 mph.

 

[94-302-vert]

if you are doing an actual 70 mph when it says youare...

think about this:

If I put 44" tires on the back of my car for an indicated speed i will be going much faster, then if I put on 24" tires I will be going slower than indicated. But in both of these cases as I didn;t cahnge the relationship between engine RPM and where the car determiones speed (driveshaft RPM) both will say 70mph at 2k rpm....

Pace a friend, drive a known distance, coundt D/S rpm's, count teeth, etc. But it does sound like you need to change your speedo gear.

Chris

 

[GRGT1994]

Chris is right. You won't be able to tell anything by just looking at your RPM and speed. Those will read the same no matter what gears you have. Your actual speed will, of course, change with gears. But your speedo knows nothing of the gears in your rear end.

Jack the car up, then turn the other and count how many times the driveshaft turns for one complete revolution of the tire. A little less than 3 turns means you have 2.72 gears. Exactly 3 turns means you have 3.08 gears. Etc.

Or you could just run along side a friend on the highway at an agreed speed. That will at least confirm whether or not you have aftermarket gears.

 

[RIO5.0]

What was the queston??? I can't think straight looking at that avatar....