does any one know how to config them ?

They run off a cable so I don't think you can calibrate them as such, not sure. Are you on standard tyres?

Judging by the pic - i'd imagine your speedo is reading approx 10% over your actual speed.

Don't think you can do anything about it! The price you pay for changing your rolling radius!

You're guessing at 175/50s on a 13x7 then

You might be able to get a custom speedo drive made up

Probably be a good idea actually lol considering the amount of people in 175/50 13s.

my mk2f speedo reads 38mph @ 30 with standard steelies (4.5j -155-70s)and reads 35mph @ 30 with my bbs ra s (6j-175-55-15s) I'm guessing that this is a common problem with polos i general

hehe Kam explained why it happens to me but I forgot now. hopefully he'll remind me when he comes online :p

its because the circumference (sp) of the wheel has changed, got smaller, so one revoloution takes you less distance than the original wheel

so

more it takes more revoloutions to do the same speed but the speedo works of the wheel revs so it thinks youre going faster than you are

You can re-sit the needle but that would only add a fixed amount to everything, and as mentioned before it's a percentage of the speed so the actual amount out is different for any speed. I believe to calibrate it otherwise you'd have to strengthen/weaken the magnet that the cable turns in the back of the unit.

Personally I'm glad my speedo overreads as standard and my tyres are slightly smaller than standard, means even if I'm on the speed limit I'm almost certainly safe going through any speed cameras I may not have seen/mobile speed cameras.

Also who says GPS is 100% accurate if that's where you're getting the 'proper' speed from?

Just been looking at tyre prices and going for 175/60's over the standard 145/80's. Might not look as good as 50's but cheaper

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference

145/80-13 4.6in 11.1in 22.1in 69.5in 911 0.0%

165/55-13 3.6in 10.1in 20.1in 63.3in 1001 -9.0%

165/65-13 4.2in 10.7in 21.4in 67.4in 940 -3.1%

175/50-13 3.4in 9.9in 19.9in 62.5in 1014 -10.1%

175/60-13 4.1in 10.6in 21.3in 66.8in 948 -3.9%

185/60-13 4.4in 10.9in 21.7in 68.3in 928 -1.8%

185/70-13 5.1in 11.6in 23.2in 72.9in 869 4.8%

On the gps accuracy they are all accurate certainly more so than a polo speedo.

UK law requires a speedo to be accurate or 'fast' -0%, +10% at 30 mph

Nearly all GPS manufacturers quote 0.1 MPH accuracy on level ground, at constant speed and direction for several seconds and with a good sat lock. This applies to a cheap unit or an expensive gps survey unit at £25k only the later will no exactly where you are to within 20mm. Assuming a good path to the satellites they all use the same method of trilateration to calculate position.

Edited 9 July, 200719 yr by beemer

I've got the good old 155/70 13s and 145/80 13s to swap between and on the 145s my speedo is fairly accurate. It only starts to noticeably read under at 95 (driftbox) where its half way between 90 and 95.