Speedometer survey at 2000 and 3000 RPM

[spitfire]

For all you 540/6 out there(and anyone else for that matter), what speeds do you attain at 2 and 3 grand in 6th gear. Tires are 235/45/17. I wonder if my speedometer is acurate. My result's are: 2000 gives 108 kms/hr and 3000 gives 155 kms/hr. I think they are high. Cheers.

[632 Regal]

thats cause you have a 2:93 rear gear, the 530 has a 3:15.

[Jay 535i]

Also remember that no car's speedo is 100% accurate.

[Interceptor]

Also remember that no car's speedo is 100% accurate.
Is there a certain percentage of inaccuracy or is it completely random? For examle, If I have stock tire size and everything is functioning properly, how much is the error rate accros the rpm band? Is it linear or...?

[Jon K]

Is there a certain percentage of inaccuracy or is it completely random? For examle, If I have stock tire size and everything is functioning properly, how much is the error rate accros the rpm band? Is it linear or...?


Most speedos are calibrated around 65mph. Above like 120mph I believe its something like 4 - 7% inaccurate or some crap. Although my friends STI was @ 165mph indicated and was at 164mph via GPS... wow.

[Jay 535i]

Is there a certain percentage of inaccuracy or is it completely random? For examle, If I have stock tire size and everything is functioning properly, how much is the error rate accros the rpm band? Is it linear or...?

It varies from one manufacturer to the next, and if you're running non-standard tires, that would have an effect, too. A 5-10% overestimation is about normal (i.e., if you speedo indicates 60 MPH your actual speed is proably around 54-57 MPH).

[Jon K]

It varies from one manufacturer to the next, and if you're running non-standard tires, that would have an effect, too. A 5-10% overestimation is about normal (i.e., if you speedo indicates 60 MPH your actual speed is proably around 54-57 MPH).


I forgot to mention that there IS a legality issue regarding if you speedometer should read inaccurately such that your actual speed is higher than your indicated speed, the manufacturer of the vehicle is supposedly required to recalibrate your vehicle.

[Qube]

I forgot to mention that there IS a legality issue regarding if you speedometer should read inaccurately such that your actual speed is higher than your indicated speed, the manufacturer of the vehicle is supposedly required to recalibrate your vehicle.

And they would do that even if you run non-standard size tires?

[Jon K]

And they would do that even if you run non-standard size tires?


Of course not.


But realistically, no one here should be running "non-standard" tires. For instance my car came with 205/65/15 tires. Factory optional sizes were up to 225/60/15 and thats considered a "standard" tire size for the vehicle. Then you could always get the optional alloys in 16" and run the 225/55/16 size. And likewise, as you go up and up in wheel diameter, your total tire/wheel package should stay similar in profile. I am now running 235/40/17 on the front and I believe that's within standard tire specification also. A non-standard size for the car might be if you run like 16's with 225/40/16's which would yield TONS of wheelwell-gap, but some people might do something (weird) like that. And that, would over course alter your speedometer readings.

[632 Regal]

my car at 65 on the speedo is 60 according to them radar machines...some sort of safety factor in out cars. There was a post about this last year and the consensis was that our cars were generally off by 5 mph. I also think you can adjust that in the OBC.

[uscharalph]

my car at 65 on the speedo is 60 according to them radar machines...some sort of safety factor in out cars. There was a post about this last year and the consensis was that our cars were generally off by 5 mph. I also think you can adjust that in the OBC.
Really? That's good. I always thought it was 5-10 mph higher, but never followed thru to check it out.

[baileydog]

My 540i/a with stock 225 x 15 shoes and stock rear end turns 3000rpm @ 160km....I checked that with the GPS.

Cheers...

[baileydog]

I checked out the difference between the OBC and the speedo in the dash with my new GPS up past 160km. The OBC was dead on...but the dash speedo was 3km low.

Cheers.

[Zeuk in Oz]

My '88 525i manual is 10% out.
I am doing 60 when the speedo shows 66.
Thats on standard 225/60/15 tyres.

[SharkmanBMW]

according to German law, they must be off by 7% (pretty sure it's 7) for safety reasons. That way no one will speed unknowingly