How speed limited is "100 speed limited"

Been taking a few tows off Aus Post trucks of late. They have the "100
speed limited" stickers on the back of the trailer, but the prime mover
seems to sit on 110kmh.
Or there's a reason I haven't copped a speeding ticket yet ...
- sanbar

 

I'm generalising from experience with the speed limiters on our bus
fleet, but a couple of observations might be relevant.

1. Car (and bike) manufacturers set thier speedos to deliberately read
low so they don't end up getting sued by irate motorists (and riders)
who go "but I was sitting on 100kph) (if they set them to 100 then due
to manufacturing tolereances some would read high and some low).

2. Truck (and bus) manufacturers don't do this.

3. Truck (and bus) speedos are generally of higher accuracy.

4. There is a nominal 3 kph 'tolerance' for speed cameras.

5. Many speed limiters only adjust in 5 kph increments.


When you add all this together...

Car (and bike) speedo's generally read 100kph and 95(or thereabouts),
add say 3 kph for the inflexible adjustment on the limiter (no one sets
them to 98, they all choose 103).

That means that a car will see the truck sitting on 103 as doing 108 (as
bugger all close to 110 as possible)... and then come into the news
group and say "these trucks are doing 110" when in fact they really aren't.

Of course at this point most car drivers will scream "MY CAR SPEEDO IS
ACCURATE YOU @#$%#@!!!", but I'm hoping most bike riders are above that


G-S

 

More people have GPS on their bikes and in their cars.

So it bollocks to say that everybody is relying purely their speedo.

I personally use a stopwatch when i'm out riding. 60k = 1km in 60 sec. 120 =
1km in 30 sec, etc.

Its a very good way to while away the hours doing arithmatic.

You just have to be careful to keep your eyes on the road while operating
the stropwatch ( almost hit a dog once).

GB.

 

MY BIKE SPEEDO IS ACCURATE YOU @#$%#@!

Seriously, though. While mapping a navigation ride earlier this year,
the BMW (R.I.P) showed something like 212.4 km, while the GPS showed 212
km. I had similar results when mapping the economy rally.

Haven't tried the FJR yet.

---
Cheers

PeterC [aka MildThing]
'81 Suzuki GS450-s (gone on to better and brighter things - I hope)
'87 BMW K100RT (write-off)
'81 Yamaha Virago (XV) 750H (work in progress)
'01 Yamaha FJR1300

www.dmcsc.org.au
http://eladesom.com.au/ulysses/
# 37181

 

First off you almost definitely have 2 different errors on your speedo
and on your odo

Generally bike and car speedos read 5-10 % high. That is the speedo is
saying 110 kph when actually you are doing 100 kph.
The exception is prestige cars (BMW, Lexus) that seem to read with 2%
of true.

You odo will have a different error and on bikes I have found that
they are normally with 3% (plus or minus).

The manufacturers seem to be covering there own arse for speeding but
want to be reasonably accurate on the odo for servicing purposes.

 

That's your odometer. They're generally pretty good. The speedo
is driven from the same cable, but it's not (except for electronic
ones) as accurate.

Unless you mean 212km/h, in which case no wonder it's RIP!

Most of the "100 speed limited" trucks seem to sit on 100 +- 3
according to my GPS. I've been overtaken by a couple doing
perhaps 120 though, I wonder what the lurk is.

-----sharks

 

they have bigger tyres than when the speed limiter was fitted

 

As an Aus Post driver I can state that unless there is a malfunction
in the speed limiter system of the prime mover that they are accurate.
The linehaul Volvo's are maintained very well and the drivers have
their own big brother id tags to register who is behind the wheel.
They will gather speed on downhill runs but if they go over a preset
limit questions get asked as to what happened.
I'm pretty sure the vehicles have real time gps monitoring and have
heard from other drivers going over speed humps or out of driveways to
roughly of getting phone calls asking if they have crashed or not.

The MAN's we own have excellent speed limiters and seem to be set a
little slower than the Volvo's. The MAN's aren't as sophisticated yet
in the monitoring but will be eventually I've been told.

If you have any doubts about Post vehilces just ring the customer
service number with veh reg, location, date and time of day and they
will check it out.
I know this from being asked 20 question a couple of times when some
nong has done something silly and had a sook.
Hope that helps.

anon AP driver

 

The work Camry was similar, about 1% optomistic.

cheers,

(remove the nospam bit for email)

Bill_h

 

you pull a fuse out

another trick ive heard of is you nail it down a hill, mass of the truck
will put it well over 110kph, you then keep the power on, the speed limit
only kicks in at 100-110, somehow the limiter cant handle the higher speed,
if you slow down you will loose it, but if you keep the power on, you will
maintain that speed.

i see trucks every day fly past at 140kph, which is awfulyl fast for 100kph
speed limited b double.

 

No... and I never said that.
I said the ones saying "all these trucks are sitting on 110kph" are
wrong, and explained one possible method why they might be wrong.

There are of course some trucks breaking the limits, and the regs, but
that wasn't what was said...

The testing results I quoted are from GPS enabled vehicle logging
systems. The accuracy of which I assume you understand


G-S

 

Your car is a performance spec vehicle nev... I wouldn't be surprised if
that was deliberate (as is the under specing of the taxi and mums ones


G-S

 

None of this means that what I am saying is untrue... if the tolerance
of the car speedo's is about 5%. Thefore assuming they are aiming at
about 95kph for 100kph the normal spread will be from 90 to 100 at 100.

Just means yours was (luckily) at the top end...


G-S

 

Of course there are people rorting the system, and it isn't really that
hard, but I find it a bit hard to believe that Aust Post make a habit of
this *grin*

They are hardly "Tip Over Transport" or "The Dodgy Brothers"


G-S

 

Quite possibly, and the analogue speedo on the Sprint *IS* quite
optimistic - closer to 10%.

cheers,

(remove the nospam bit for email)

Bill_h

 

Ahhh be careful, just because the odometer is accurate, doesn't mean the
speedo is.

In the cages I usually compare the odo with those 5km stretches they
mark on the highway, never had one that differed by more than 100m. When
you set the cruise control then clock the elapsed time to cover the
distance, the speedo almost always reads between 5 and 7km out (in the
cars I've owned), at around 100 or 110. I've never tested at
significantly lower or higher speeds so I can't comment as to whether
it's a linear error or a percentage error.

JL

 

ex-police RT?

the first ex-cop one I had, had a sticker on the speedo from an instrument
repair place where they had the speedo calibrated for accurate gauging of
speeds of road users. My other BMWs have read about 10% fast.

The TDM has a BC800 computer calibrated to the 5km test areas on the
freeway.

Al

 

K100 is electronic, no cable.

Al

 

Hmmm. I'd always assumed that, because they feed off the same mechanism,
that their accuracy would be similar.

---
Cheers

PeterC [aka MildThing]
'81 Suzuki GS450-s (gone on to better and brighter things - I hope)
'87 BMW K100RT (write-off)
'81 Yamaha Virago (XV) 750H (work in progress)
'01 Yamaha FJR1300

www.dmcsc.org.au
http://eladesom.com.au/ulysses/
# 37181

 

I don't know. The log book and receipts would indicate not, but I
noticed that it was previously painted white (now red). It certainly had
spare toggle switches on the dash which could've been for lights and
sirens etc.
---
Cheers

PeterC [aka MildThing]
'81 Suzuki GS450-s (gone on to better and brighter things - I hope)
'87 BMW K100RT (write-off)
'81 Yamaha Virago (XV) 750H (work in progress)
'01 Yamaha FJR1300

www.dmcsc.org.au
http://eladesom.com.au/ulysses/
# 37181