Vmax behaviour

[eein]

I'm just back from a two week driving holiday around central Europe. This gave me a chance to (legally) have a go to hit top speed on the autobahn. Managed to get to an indicated 157mph (253kmh).

Required a lot of focus and concentration at that speed... especially when a sudden torrential downpour started and I had to slow down … you can't hit the brakes in the wet at that speed!

I was surprised the car indicated 157mph, I thought it was electronically limited to 155 (250)? I guess the limiting must have some tolerance in it? I didn't feel it topping out or being limited, so maybe my limit has been removed?

Anyone else got experience at driving at vmax in a F01/02 and how it behaves? Any way to check for limited being removed, other that just driving that fast?

Iain

2012 F02 760Li SE

[helix402]

Your car is not delimited. Your speedo over reads. If you like you can add a digital speedo to your dash, where your data is displayed at the base of the cluster. This extra speedo can be added with Carly for BMW.

This can show real speed or “corrected” speed (overeading).

[Mike335i]

As above, I did 151mph 'corrected mph' in Germany a few years ago, which was closer to 160 on the dials.

[dcb]

Mike335i said:

As above, I did 151mph 'corrected mph' in Germany a few years ago, which was closer to 160 on the dials.

+1

GPS 155 mph is 160 mph in the dials in my 325.

Bit quick, but drama free really. No rattles, no drifting, no feeling
that the car is under any strain. About 5,000 rpm with the redline
somewhere north of 7,000 rpm.

Except for the Audi A3 flashing at me to get out of the way. That
was a bit irritating.

[Daaaveee]

Same on my E60 M5, 160mph on the dials, limited in 6th and 7th gear, 155mph GPS speed. Annoyingly my friends CLK55 AMG started pulling away!

[eein]

... sounds like I'll just have to take a trip back some time with a GPS speedometer!

[Pica-Pica]

So, an ‘I’ve maxed out on an autobahn’ boast.

You know full well that
a) your car is limited to 250km/hr
b) there is tolerance in all systems.

[Pica-Pica]

Technically, under UNECE regulation 39, the speedometer is tested for accuracy at 40 km/h, 80 km/h, and 120 km/h if VMax is greater than 150 km/h.

[bigdom]

eein said:

so maybe my limit has been removed?

If so, you weren't trying hard enough. You should have seen 190 mph on the dash.

[eein]

Are mobile phone GPS speedometers regarded accurate enough? I've used my phone quote a bit and it usually seems to be what I expect (a little more less than modern cars, lots less on older cars - my old mini used to indicate 110mph when my phone measured 82).

[Strudul]

helix402 said:

Your car is not delimited. Your speedo over reads.

All speedos over-read, but how does the ECU limit the top speed if not by the same value displayed?

[helix402]

Strudul said:

All speedos over-read, but how does the ECU limit the top speed if not by the same value displayed?

The DME/DDE limits the speed based on actual car speed usually sourced from a wheel speed sensor (via the DSC ecu). This is not the displayed speed.

[Strudul]

helix402 said:

The DME/DDE limits the speed based on actual car speed usually sourced from a wheel speed sensor (via the DSC ecu). This is not the displayed speed.

Whereas displayed speed is what? Calculated from rpm and gear?

[Solocle]

Sadly, my experience of Vmax is a woeful 101 mph GPS (Skoda Citigo). Although, it was downhill, with a quoted top speed of 99, so not all bad .
Observations: smooth as anything, 4000/6000 rpm.

[pjv997]

I’ve done a reasonable number of trips in different cars through Germany and whilst it is rude not to at least try one v-max when the opportunity arises, I most enjoy the ability to keep your foot stuck beyond 100 as you accelerate into a de-restricted stretch without having to worry about losing your licence.

It’s also uncanny how quickly you get attuned to cruising at 130, and interesting that the most common car that then overtakes is the A3 or A4 2.0 Diesel.

[helix402]

Strudul said:

Whereas displayed speed is what? Calculated from rpm and gear?

Displayed speed=actual x correction factor

For example, 155 x 1.05= 162.75

I think this calc will be done in BMW’s case by the instrument cluster (IKE).