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Old 6th March 2011, 12:07   #51
rovexCDTi
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Quote:
Originally Posted by Rincewind View Post

Don't rely on satnav's to give you accurate speedo readings as they're prone to delays and what not and it also depends on who's using the satellites too. If the military are mega busy, your sat navs will be affected!!
GPS satellites are passive, they cant be 'busy'. The only time they can be effected in that way is if they are being remotely reprogrammed or having diagnostics run on them and that is done individually, so as not to bring the system down. The effect on our GPS units at that time is extremely minimal, if there is even an effect.
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Old 6th March 2011, 16:51   #52
Keith
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Egremont that is a very impressive piece of work
Well done.

For most people with 18" wheels the speedo is fairly accurate <5% out as a rule but as the wheels get smaller the inaccuracy increases.

There is no option on T4 to calibrate the car by stating wheel or tyre size so your gadget would do the trick nicely
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Old 6th March 2011, 17:58   #53
rovexCDTi
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Checked my car today, its reading no more than 2 mph faster than actual at any speed. Quiite impressed really and i now know the limits when going past revenue generating devices.
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Old 6th March 2011, 18:42   #54
nicpy
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Smile speedo

I checked our car speedometer against a Sat Nav a while ago and found on average the speedo display to be 3mph faster than the sat nav, this is on a 2004 ZT. Watching the obd display on 7.3, which shows the same speeds as the speedometer. taking the obd to 7.4 and it agreed at all speeds with the sat nav, suggesting that on 7.4 that it pretty close to true speed. If you don`t trust your speedo or sat nav then use the kilometre (1/10) markers at the side of all of our motorways and time yourself over a set distance.
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Old 7th March 2011, 22:43   #55
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Quote:
Originally Posted by Keith View Post
Egremont that is a very impressive piece of work
Well done.

For most people with 18" wheels the speedo is fairly accurate <5% out as a rule but as the wheels get smaller the inaccuracy increases.

There is no option on T4 to calibrate the car by stating wheel or tyre size so your gadget would do the trick nicely
That's because the speedo is calibrated internally from the rest of the car and the pulses per km were different between 15 - 17" wheels and the 18" wheels were differnt and not in the T4 calibration.

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Old 7th March 2011, 22:54   #56
The Rover Man
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Quote:
Originally Posted by baggie9 View Post
I got stopped for speeding 46 in a 40 zone in my mgb in the 70s.The squad car that followed me said i was doing 46,my speedo was reading 40 because i was awre i was being followed.They gave me a ticket,my speedo was a new one.So i telephone Smiths who had my clock back and verified it.I went to court and got off with the charge, the police car speedo hadnt been calibrated.
Your post brings back a few memories for me. I was stopped about 21 years ago in my SD1 doing 93 mph average over 1 mile. I got my court summons, but got off the charge because my speedo was reading too low. I agreed to replace it, which I did, two years ago when it finally hit 100k and reset to 00000!
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