Ian
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Registered: 28th Aug 99
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quote:
Originally posted by bradfincham
how about a supra for example??
In that case, yes. Same system as the 106? If so then therefore same margin for error, unless Toyota are particular about that sort of thing. Legally all road cars can over-read by 10%, Supra, 106, whatever.
Don't also rule out the fact that someone driving at an indicated 126mph isn't really in a position to accurately compare the readouts from both devices having maintained a constant road speed. That may account for a few %.
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bradfincham
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as i said before, bad maths, just figured a quick way to sort it, roughly 15% difference then!
What the fuck is everyones problem, im just trying to find out more about how inaccurate my dials are etc and on higher powered cars!
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Ian
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quote:
Originally posted by Paul_J
I did not say, 'At the EXACT moment they clocked me at 101 mph, I saw 120 on my clocks / road angel / whatever!!!!'...
Exactly my point, its hardly a direct comparison.
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Paul_J
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It also is illegal for a manufacturer to produce a car that under reads! Say ... showing 10 mph when ACTUALLY doing 12 mph... Thus to be extra careful some manufacturers actually put in a couple of mph inaccuracy even when doing 5 mph!!! Thats why when your crawling in traffic (almost not moving) it shows 10 mph on the clocks. But as tyres expand (or you have big alloys etc) speedo's get more inacurate
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Dom
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Right....car clocks are inaccurate, dont take anything into account etc.
Stack dash are a lot more accurate, as the take in account tyre size, but i believe they work on a magnet sensor like that on mountain bike speedos.
GPS a lot lot more accurate - 1 to 1.5m accuracy
Military GPS...yup more accurate - 1-2ft accuracy.
Laser timing Gear, probably the best - probably cm's
hoped that has cleared things up 
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bradfincham
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It intrigues me as i always thought manifacturers used gps and this would be the same as the clocks, they would set it so they are the same?
so that way when you get caught speeding you can argue the clocks read differently!
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Jodi_the_g
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Nope could not argue as it would be an unroad worthy car if it was out my miles.
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Ian
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I'd dread to think Brad, are you using Corsa clocks and a Calibra gearbox? 
My GSi is well out as further to the factory tolerance the 40 profile tyres are small than the factory ones, which makes the error even worse.
Next airfield day we will so something properly scientific. I have logging gear here for a laptop and we can video etc., publish results as it is an ongoing question.
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Paul_J
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quote:
Originally posted by bradfincham
as i said before, bad maths, just figured a quick way to sort it, roughly 15% difference then!
What the fuck is everyones problem, im just trying to find out more about how inaccurate my dials are etc and on higher powered cars!
but what I'm saying mate... Is Firstly A) the speedo is not 15% inacurate all the time... Its like a sliding scale. Gets more inacurate the faster you go.
So at 50 mph I'm not saying it'll be 15% inaccurate, it'll be less.
It's generally as speeds get fast enough that make an effect against the tyres. If you've ever seen a Drag car do a burn out before going down the drag strip, watch as they spin their tyres up how much bigger they get in size!!!! ... imagine this as a measurement on the speedo and thus think about what effect it would make on the accuracy!
I'm also not saying all cars are 15% inacurate over 100 mph... yours may only be 10% or less, or more...
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*Donna*
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quote:
Originally posted by bradfincham
im just trying to find out more about how inaccurate my dials are etc and on higher powered cars!
The power of the car is irrelevant, for example, at 100mph (gps speed) a 1.6 corsa could give a speedo reading higher than thats of a scooby.
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bradfincham
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Cheers for that dom, yeh i know the stack uses a different sensor as we had a job to fit that.
But im just amazed at how different the speedo actually is!!
Cheers for clarifying that dom
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Ian
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quote:
Originally posted by Paul_J
as tyres expand (or you have big alloys etc) speedo's get more inacurate
Its actually the other way around, an under-reading error is reduced by larger wheels.
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Jodi_the_g
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quote:
Originally posted by Dom
GPS a lot lot more accurate - 1 to 1.5m accuracy
Military GPS...yup more accurate - 1-2ft accuracy.
hoped that has cleared things up
All GPS systems can are accurate to around 0.75 metres, though do them being used for targeters for weapons and home made bombs they contain software to enusre they are out, still making them practial but not as accurate to takle out a target.
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Paul_J
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quote:
Originally posted by bradfincham
It intrigues me as i always thought manifacturers used gps and this would be the same as the clocks, they would set it so they are the same?
so that way when you get caught speeding you can argue the clocks read differently!
Read what I said above... It's against the law for the manufacturers to release a car that under reads (says a speed on the speedo lower than what the car is actually doing!) - thus why run the risk of making it 100% accurate and thus it could possibly go either way a few percent... when they can put it out say 3/4% when stationary... then (natural physics) it gets more inacurate as it gets faster.
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bradfincham
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yep tigra clocks and astra geabox!!
Which i know will be different, i was under the impression that indicated 135 mph on my car was the actual speed give or take few mph for clocks and 17's!
yes ian i would be very interested to see that, as doing motorsport we dont touch this till year 2, so its all pretty new to me know!
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Ian
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quote:
Originally posted by bradfincham
i always thought manifacturers used gps and this would be the same as the clocks, they would set it so they are the same?
I think its more than they can't than they don't.
Plus it it was spot on and you change the tyres, it under-reads. If its over and you do the same, it just gets closer to normal.
Its illegal on one side and not so bad on the other, so they stay on the not so bad.
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*Donna*
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quote:
Originally posted by Paul_J
quote:
Originally posted by bradfincham
It intrigues me as i always thought manifacturers used gps and this would be the same as the clocks, they would set it so they are the same?
so that way when you get caught speeding you can argue the clocks read differently!
Read what I said above... It's against the law for the manufacturers to release a car that under reads (says a speed on the speedo lower than what the car is actually doing!) - thus why run the risk of making it 100% accurate and thus it could possibly go either way a few percent... when they can put it out say 3/4% when stationary... then (natural physics) it gets more inacurate as it gets faster.
quote:
Originally posted by *Donna*
Clocks typically over read, the faster you go, usually the more they over read. Its against the law for them to under read. I would say no car speedo is accurate, however, a Road Angel is. 
I said this on page 3 
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Paul_J
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quote:
Originally posted by Ian
quote:
Originally posted by Paul_J
as tyres expand (or you have big alloys etc) speedo's get more inacurate
Its actually the other way around, an under-reading error is reduced by larger wheels.
I didn't say which way it went more inacurate 
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Dom
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quote:
Originally posted by Jodi_the_g
quote:
Originally posted by Dom
GPS a lot lot more accurate - 1 to 1.5m accuracy
Military GPS...yup more accurate - 1-2ft accuracy.
hoped that has cleared things up
All GPS systems can are accurate to around 0.75 metres, though do them being used for targeters for weapons and home made bombs they contain software to enusre they are out, still making them practial but not as accurate to takle out a target.
i know that mate, but military have it alot better than 0.75m meters, its more like 0.3m (ie: length of a ruler). But yes, they adjust it on commericial GPS to around 1-2meters to stop it being used for bombs and stuff like you said
But also, the more sats you have linked the better the accuracy is - plus i know that the US military have some of there own sats up that do GPS stuff
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bradfincham
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yeh thats what i did, i travelled at 30,40,60,70 mph next to my mum in her st170 and there was no difference whatsoever,
red corsa was a different story!
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Ian
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Sorry to all those who replied to the original post and whose replies are now lost - Paul deleted the thread while I was in the middle of moving posts over to the split thread.
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Paul_J
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quote:
Originally posted by bradfincham
yeh thats what i did, i travelled at 30,40,60,70 mph next to my mum in her st170 and there was no difference whatsoever,
red corsa was a different story!
but you see... This is why everyone assumes their speedo's arn't inacurate... Your both doing the same speeds, your speedo's are going equally inaccurate
Mate, next time we meet up - I'll put my road angel in your car and we'll go for a spin - You may be lucky and some how have a calibrated 100% accurate speedo? If not it may be interesting to see what speed's your actually doing - either way, will be a learning experience.
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bradfincham
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yeh, certainly would be!
I would invest in one but i simply dont drive the car enough to make it worthwhile!
Astra is geared to reach 135 mph, so if my clocks read that does that mean the astra readings are inaccurate or my clocks are or there both right?? ha ha
questions questions questions
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Paul_J
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The problem is - knowing your true speed some times makes it easier to speed. Since most people would believe say 80-85 mph on a motorway to be an acceptable speed.
But then, when most people are doing 80 mph they are only doing 75 mph in reality ... So when they're doing 90 mph on clocks they're only doing 83 mph.
And thus, you take it to 85 mph on the road angel and think 'oh well I'm only doing 85 mph' - but on a normal speedo you'd be doing 93ish which you'd feel like your speeding with.
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bradfincham
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i would be too worried to trust the road angel and go through cameras when the clocks read over the legal 10% + 2 mph limit
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