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Acewell Speedo set up
wandr - 15/3/19 at 08:25 PM

Hi all, can anyone help me with set up of my digital speedometer, it's an acewell 3100 and I'm a bit baffled about how to get the tyre circumference right to enter into the Speedo itself, I have the instructions but they don't seem clear to me, tyre size is 195/60/13, I have IVA test in Southampton on weds 20th so any help much appreciated as it's the last thing to do before the test

HAL 1 - 15/3/19 at 08:41 PM

According to. ' willtheyfit.com ' they should be. 1772.5 mm
Or tyresize.com should give you an answer

Worth a try ?

Hal

SJ - 15/3/19 at 09:12 PM

Best bet is get a rough setting in there and on the way to the test check against a GPS speedo on your phone and adjust to over read by 5%.

1st question is where is your sensor?

Dingz - 15/3/19 at 11:32 PM

If all you need is the tyre circumference roll the car til the tyre valve is at the bottom, mark thr ‘road’, push the car forward for one tyre revolution and measure the distance travelled. This then assuming you’ve got the normal pressure in the tyre will give the true rolling circumference.

tims31 - 16/3/19 at 10:36 PM

Or a tape measure around the circumference

russbost - 18/3/19 at 08:53 AM

Take the circumference as given on the web (I found 1770mm) & increase that dimension by, say, 4%, in this case that would give you 1841; the speedo itself will be accurate to within 1%, so this will give you an over read of between 3 & 5% which is ideal, it must not be more than 10% & it is absolutely essential that it does not under read. eg, it's fine to have your speedo indicating 75mph when your actual speed is 70mph, it is NOT ok to have your speedo reading 69mph when you are doing 70

mcerd1 - 18/3/19 at 09:33 AM

quote:
Originally posted by Dingz
If all you need is the tyre circumference roll the car til the tyre valve is at the bottom, mark thr ‘road’, push the car forward for one tyre revolution and measure the distance travelled. This then assuming you’ve got the normal pressure in the tyre will give the true rolling circumference.


^^^ what he said - that'll give you decent measure of the actual effective rolling circumference

next best bet would be to check the tyre manufacturers data on the website (some of them list a rolling circumference or effective radius)



but for a quick estimate its as follows: (this is all most online calculators do anyway )

195/60/13 tyre used, but works for any size

nominal diameter of the rim in inches: 13" --> so 25.4 * 13" = 330.2mm (measured from where the bead of the tyre seats)

nominal width of the tyre in mm = 195
aspect ratio of the tyre = 60%

so the nominal height of the side wall from the rim is 60% of the width = 195*0.6 = 117mm

so the total diameter of the wheel = the rim + 2 * the sidewall height = 330.2 + 2*117 = 564.2mm
and Pi x this diameter give a circumference of = 1772.5mm

[Edited on 18/3/2019 by mcerd1]

russbost - 18/3/19 at 09:43 AM

Further to the above, whatever you do, do NOT use the exact figure of 1772.5 as the speedo will be "too accurate" - IVA inspectors want to see that additional margin of error, it is essential to increase that base figure by a minimum of 2% to ensure the speedo will always slightly over read

theduck - 18/3/19 at 10:40 AM

Also remember, if your pick up is on your propshaft, then you need to divide the tyre circumference by the diff ratio