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My Speedo Is Not Acurate..how Is Yours?

bluesky4me

By bluesky4me,
in Four Door Family & Wagoneers

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bluesky4me Community Regular

bluesky4me

Posted
Posted

Hi . After going through two diferent speed reading devices (one on the way to Geelong and the other on the Hume) It looks like my speed is not showing the correct KPH..And the most annoying part is.. I am going slower than I thought!!!...at 110 on the speedo the detector said I was doing 103. I hoped it was wrong but the second time (through a different one) made me think its probably right.

I would like to know if anyone else has found this. I dont like it ..even thought it will help prevent speeding fines.I am guessing it is a result of the after market wheels rather than a speedo fault. My tyres are 45/235/17

If this is a result of a larger overall diameter then some acceleration will also be lost.

I know its a minor issue but I would just like to get some thoughts.

Cheers.

Scott

Sydneykid Grand Master

Sydneykid

Posted
Posted
Hi . After going through two diferent speed reading devices (one on the way to Geelong and the other on the Hume) It looks like my speed is not showing the correct KPH..And the most annoying part is.. I am going slower than I thought!!!...at 110 on the speedo the detector said I was doing 103. I hoped it was wrong but the second time (through a different one) made me think its probably right.

I would like to know if anyone else has found this. I dont like it ..even thought it will help prevent speeding fines.I am guessing it is a result of the after market wheels rather than a speedo fault. My tyres are 45/235/17

If this is a result of a larger overall diameter then some acceleration will also be lost.

I know its a minor issue but I would just like to get some thoughts.

Cheers.

Scott

Standard new speedo is ~3-4% optimistic (shows higher speed than car is actually doing) with brand new tyres.

Bald tyres makes the speedo a further 4-5% optimistic.

So your 6% optimistic is pretty much right on the money.

Optimistic means lower gearing, hence faster accelerating, not that you would notice.

:laugh: cheers :)

66yostagea Grand Master

66yostagea

Posted
Posted

If you muckabout with wheel sizes and profiles, then you must look at the actual diameter of your rear wheels. You also have to take into account your ex gear box revs plus your diff ratio. You also have to consider whether the torque converter is "locked up".

I had a chat with Alex about this before, and there were various ex box ratios with final drive ratios.

You have to look at all these facets before you can ascertain whether your speedo is accurate or not.

And in this day and age of "revenue gathering" you have to know whether your speed is approaching the "Golden Point" mark.

I also believe, and a lot of multi-experienced drivers, will also believe, that you instinctively know, via the seat of your pants, exactly how FAST you are going.

If you get "done" its your fault! (wtf officer I was only going #*^++ kph) >_<>_<

oxford1327 Experienced

oxford1327

Posted
Posted

or you could buy a pivot speed meter and it will get rid of the fuel cutout at 180KPH and also is more accurate with a red digital readout. these little boxes work a treat as they also have a peak/hold function for trap speeds and 1/4 mile readouts too for strip runs if thats what you wanna look at.

from memory mine was around $125 plus install approx 3/4hr labour.

munchstagea Mentor

munchstagea

Posted
Posted

I went under the speed check on the Geelong/Melbourne road at 100 (speedo), got 96km/h on the radar, with a wheel/tyre combo that should be 1% bigger than standard I am pretty happy with that, I like to have a little margin between the limit and getting sent an invoice for not starring at my speedo all the time...

GoldZilla Grand Master

GoldZilla

Posted
Posted

Like SK said, it's super-rare to get a speedo that is dead-perfect accurate.

I believe that ADR's allow for up to 10% variance, which would cover tyre wear, inflation (how many people REALLY check their tyre pressures as often as they should?), etc.

A GPS device or some sort of regularly-calibrated dyno thing are probably the best two ways to get an accurate reading to check your speedo against.

  • 3 weeks later...
kralster Veteran

kralster

Posted
Posted

Thats why i never believe people who say that got their car up to 220 on the speedo, cos more than likely it's around the 200 mark.

Also need to take into account tyre expansion as they heat up.

R33stagea Rising Star

R33stagea

Posted
Posted

ive been booked 226 in a 90 zone.(R34 GTR)

had it up to 278 on the GPS then saw the nice man next to his white commondore and hit the brakes!!!! still 226 when he got me!!!!

very long 9 months walking!!!!!

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