I was in a bit of a hurry down the motorway the other day and I glanced at the speedo to see ~100MPH. I would have guessed it to be at about 4000RPM (2.0HDI 110) but it was just touching 3000RPM . Just wondering what you guys get and if my Pug revs low...
I'm normally a little over 3000 RPM at 70 MPH (mine's a 1.8 petrol)
2002 (D9) Peugeot 406 Coupe SE, 2.2 litre Petrol. Scarlet Red/Rouge Ecarlate/Rosso Scarlatto. Black Leather interior. SOLD
2008 (E60 LCI) BMW 525i M-Sport, 3.0 litre Petrol. Carbonschwarz Metallic. Black Dakota Leather and Myrtlewood interior.
Bugger, maybe my engine is revving high. It was only very recently - i.e. 3 weeks ago - given a full service (including brand new spark plugs, complete oil change, oil/fuel/air filter change, brake fluid top-up, new brake discs and pads, blah blah).
According to my TomTom, I'm actually only doing 63-65 when my speedo says I'm doing 70.
When I then accelerate until the TomTom says I'm doing 70, the speedo says I'm doing 75-ish. At that speed, the engine is revving at 3200RPM.
Without an accurate speedometer (I'm not trusting either the TomTom or the cars' speedo at this point), I'm guessing I'm actually doing around 70 because I've never been snapped by speedcams (never received a speeding ticket), and I am still being overtaken by blokes with German cars (that's all I'm ever overtaken by, is buggers in their Audis, BMWs and Mercedes-Benzes).
2002 (D9) Peugeot 406 Coupe SE, 2.2 litre Petrol. Scarlet Red/Rouge Ecarlate/Rosso Scarlatto. Black Leather interior. SOLD
2008 (E60 LCI) BMW 525i M-Sport, 3.0 litre Petrol. Carbonschwarz Metallic. Black Dakota Leather and Myrtlewood interior.
highlander wrote:According to my TomTom, I'm actually only doing 63-65 when my speedo says I'm doing 70.
At that speed, GPS devices are very accurate in terms of speed calculations as the large distance covered per time division substantially reduces the effects of GPS errors (due to atmospheric distortion, etc) on the calculations. Nearly all cars speedos over-read by 5-10% anyway.
<steve_earwig> I think this forum is more about keeping our cars going with minimal outlay than giving our cars more reason to go bang
Yep, I get pretty much the same, set my cruise at 76/77 on the speedo, TomTom shows 72/73, so I just ignore cameras etc. and haven't had a problem. This works out at about 2400 RPM
(I do reduce it a bit for the average speed jobbies though).
One question I have pondered. Do GPS systems give an accurate speed if you're not travelling in a straight line, or if you're on a steep hill?
2002 HDi 2.2 Exec Estate, (2008-12) (wonderful)
2003 HDi 2.2 6-speed Exec Estate (2012-19) (also a gem)
2009 Citroen C5 2.0 HDi VTR+ Estate (godawful heap)
2008 BMW E91 330i touring (great fun - murdered by a reversing SUV)
2007 BMW E91 325i touring (slower smoother quieter)
dogslife wrote:Do GPS systems give an accurate speed if you're not travelling in a straight line, or if you're on a steep hill?
Depends, and probably not.
Tomtom does appear to base its speed calculations on the path followed (not telling you how I know this ), but I can well imagine other brands (especially the cheap ones) would tell you're going a lot slower than you are because they just do a single 2-dimensional sum because it's much less computationally expensive
No in-car satnav systems I know of have elevation information, however since GPS does work using three dimensional co-ordinates, it's not unthinkable that some systems may take historical elevation data into account. I wouldn't count on it though. Simple way to test is to take one aboard a jet fighter and pull into a vertical climb... or you could drop one off the side of a tall building with a wireless camera strapped to it
<steve_earwig> I think this forum is more about keeping our cars going with minimal outlay than giving our cars more reason to go bang
dogslife wrote: Simple way to test is to take one aboard a jet fighter and pull into a vertical climb... or you could drop one off the side of a tall building with a wireless camera strapped to it
mjb wrote:Simple way to test is to take one aboard a jet fighter and pull into a vertical climb... or you could drop one off the side of a tall building with a wireless camera strapped to it
Mythbusters?
Did they do that? sweet!
<steve_earwig> I think this forum is more about keeping our cars going with minimal outlay than giving our cars more reason to go bang
and I glanced at the speedo to see ~100MPH. I would have guessed it to be at about 4000RPM (2.0HDI 110) but it was just touching 3000RPM 
. Just wondering what you guys get and if my Pug revs low...
)
), but I can well imagine other brands (especially the cheap ones) would tell you're going a lot slower than you are because they just do a single 2-dimensional sum because it's much less computationally expensive
