alfa 147 jtd 16 v speedo accuracy - Alfa Romeo Forum
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alfa 147 jtd 16 v speedo accuracy

does anyone know how accurate my speedo will be?
bog standard tyres fitted by dealer before we bought it second hand and its done around 36k miles.
seen 138 a couple of times and downhill saw 141 (or has it all been a dream officer?)
never driven flat out for a few minutes to see if it will advance a few more mph but i was wondering if any gps owners or anyone in the know can tell me what the real speed is likely to be.
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Re: alfa 147 jtd 16 v speedo accuracy

I've seen 76 on GPS with my speedo indicating 80 which ties in with manufacturers erring on the safe side however I'm not sure how accurate measuring speed by GPS is as they are only accurate to 30 feet or M (can't remember which)
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Re: alfa 147 jtd 16 v speedo accuracy

Sounds like it's knackered. My speedo shows me doing 100 when I know I'm only doing 80. :S Lucklily under 50MPH its ok, but I do need to change it pretty damn soon.

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Re: alfa 147 jtd 16 v speedo accuracy

Most speeds seem to over read by about 10% as standard, so indicated 60mph is nearer to 55mph and therefor indicated 140mph is probably nearer 125mph. Could actually even be less as the error margin seems to increase as the speed increases.

I dunno about GPS stuff either. I have a GPS based speedometer gadget (also a built in speed camera database) and 30 mph on it feels really really slow, but by the time you get to it indicating 70mph it feels a lot faster than that. Maybe it all feels wrong as we have all spent so many years driving with speedos that read wrong/high and now the GPS is here and more accurate it feels wrong from our speed memory.

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Re: alfa 147 jtd 16 v speedo accuracy

On my 159 the GPS reads 77mph against 81 on the clock
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