Which is right?

[equate975]

I am trying to figure out if/how much my speedometer is off.

We paced it with another car and it seemed to be 1-1.5 miles off from his speedometer.

One thing I was playing with was the Average MPH, I would just hold down the reset button so it would update real time. It always shows me going 5mph slower than what the speedo says.

Which one is right?

I can live with it being off, I just would like to know by how much.

[blunttech]

I am trying to figure out if/how much my speedometer is off.

We paced it with another car and it seemed to be 1-1.5 miles off from his speedometer.

One thing I was playing with was the Average MPH, I would just hold down the reset button so it would update real time. It always shows me going 5mph slower than what the speedo says.

Which one is right?

I can live with it being off, I just would like to know by how much.

with that s52 im not certain the obc is accurate. i thought it was out of whack like the oh so important fuel economy gauge. can anyone confirm?
typically bmw speedos are off about 5mph anyway.

[azzkikr]

My e36 does the same thing. The computer reads about 5 mph less than the speedomoter. I normally check it when I am at one of those police radar things but neither are every the same. For me a difference of 1.5 mph wouldnt even bother me. The only thing that would matter is if the speedometer is fast then your milage would increase quicker than expected. If your off by 5mph at 50 that is a 10% increase.

[Jason89i]

I am trying to figure out if/how much my speedometer is off.
.

easy. if you have the obc, just use the timer and mile markers on the interstate. set cruse, use timer to figure out how many seconds it takes to go 1 mile. divide 3600 by the seconds. VIOLA......there's your exact speed.

if you want to be more accurate, take the number of seconds (round to the nearest tenth) it takes to go 2 miles. divide 7200 by the seconds.

cheers, jason

[Febi Guibo]

aren't BMW speedo's like, notoriously fast?

I think on my car, factoring in my somewhat undersized tires, I'm off by 6 mph or so, eg, showing 70, going 64-65...

maybe borrow somebody's G-tech?

[equate975]

with that s52 im not certain the obc is accurate. i thought it was out of whack like the oh so important fuel economy gauge. can anyone confirm?
typically bmw speedos are off about 5mph anyway.

I know my speedo and OBC were dead on when I had the s14, no question in my mind. Considering how I got pulled over going 90, and I got lasered at 90. The OBC and speedo would also line up perfectly.

I dont really care about the mileage, well auctually that would suck a bit for oil changes. I have 215k on her, and Im not selling it, so it dosnt bother me :)

[Ryan Stewart]

The MPH function is independent of the engine swap. They usually were optimistic with stock tire sizes. My new setup is 3% taller than stock and, according to my GPS its .6mph faster and according to radar on-point.

If you want to be certain get a GPS unit with WAAS and once it gets a 3D (differential) signal its going to be just about as accurate as anything.

[Beej '86 325es]

aren't BMW speedo's like, notoriously fast?

I think on my car, factoring in my somewhat undersized tires, I'm off by 6 mph or so, eg, showing 70, going 64-65...

maybe borrow somebody's G-tech?

yes. if i remember correctly from the days of BEN, the speedo is 4mph fast. BMW did this intentionally. The OBC is the accurate speed.