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Innacurate speedo, 2006 Legacy.


Aurai

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I have a BP5D GTB, completely factory, although my speedo overheads by about 10% give or take.

Is there a way to rectify this? Is it possible though the ecu, or other software fix?

I have seen speedo corrector kits about for other types of car but am unsure about the legality or the compatibility of these.

Anyone know about getting this sorted?

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 dbjury said:

The only stink thing is when your car says it\'s done 100,000k it\'s only done 90,000k. Jaycar has a new unit coming. It\'s ready to go and is ideal for this situation. Only problem is that not available yet. Looking April availability. It is in catalogue. By the way I have bp5 and my speedo reads about 107 when it\'s doin 100k. It\'s Anoying.

Sent from my slutty assistant...

Not entirely true, if it is a digital odometre then that is taken from the ECU, the speed and distance covered I have found on testing using OBD readers is way more accurate at the ECU, so i came to the conclusion that it is actually only in the speedo head itself.

I have tested this on 8 toyotas and 1 mercedes all have been about 10% out speed wise on speedo but pretty damn close on both speed and distance via ecu, this was checked using an APP on my phone and compared to GPS

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The thing is:- Normal tire wear from new to worn out is a 15%difference in speed reading to actual indicated.

So 10% is normal speedo error normally in most vehicles.. Now that leads to a discussion on:- . How The F** can you have a rule stating 4% as the margin before infringement.

True story!

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 soopersubaru said:

The thing is:- Normal tire wear from new to worn out is a 15%difference in speed reading to actual indicated.

So 10% is normal speedo error normally in most vehicles.. Now that leads to a discussion on:- . How The F** can you have a rule stating 4% as the margin before infringement.

True story!

And you can legally have a speedo that 10% out (wof standards)

so yes you could be driving at 100km/hr on your speedo but be pulled over for speeding

just one of those things

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Yeah I know the inaccuracy is normal, but it still irritates me, my last car was bang on and I liked knowing for sure how fast I was going, instead of me having to guess.

Id be interested to see if getting new tires sorts it.

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  • General Member

try the tool on this page for calculating rolling diameters and such

http://www.clubsub.org.nz/forum/index.php/topic,634.0.html

quick play suggests if you\'re on 215/45/17 you want to go up to 60 series to correct the speedo : that might look wack mind you (like balloooons)

or if you like new wheels try 225/50/18\'s ?

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I had customer with centre diff bind issue. Long story short. Two new rear tyres Circumference was 2030 metres. Worn tyres on the front Measured 2005 Metres. Two new front tyres sorted the bind issue. around 15% diff so at mid worn tires speedo should be at correct speed?.So your speedo will never be accurate A?..Or thereabouts.exactly. 10%? why worry?

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If really worried use a gps speedo maybe?

As said, it will always be slightly out. If you convert it bang on now with half worn tyres, changing to brand new will then make it read low. If it shows bang on with new tyres, itll gradually get further out. Got to pick a midpoint and much better having it read too high than thinking youre at 103 and actually being at 108 and getting a ticket.

For what its worth my altezza one was quite off, cranked the tyre pressure up to skidlols level and it got closer. The ecu derived speed as someone mentioned was also different to what the needle showed, needle was 3 or 4 kmh higher than the ecu output actually was too

Im guessing the effect of tyre wear would be more pronounced with bigger rolling diameter? Or less? Brain not working good

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 dbjury']

[quote name='dbjury said:

The only stink thing is when your car says it\'s done 100,000k it\'s only done 90,000k. Jaycar has a new unit coming. It\'s ready to go and is ideal for this situation. Only problem is that not available yet. Looking April availability. It is in catalogue. By the way I have bp5 and my speedo reads about 107 when it\'s doin 100k. It\'s Anoying.

Sent from my slutty assistant...

/quote]

Not entirely true, if it is a digital odometre then that is taken from the ECU, the speed and distance covered I have found on testing using OBD readers is way more accurate at the ECU, so i came to the conclusion that it is actually only in the speedo head itself.

I have tested this on 8 toyotas and 1 mercedes all have been about 10% out speed wise on speedo but pretty damn close on both speed and distance via ecu, this was checked using an APP on my phone and compared to GPS

I\'d like more info on your tests.

I have tested my speedo to the road markers 5k test marks that your see around the place (very accurate I hope) and my speedometer is out the same as the needle. My needle is also electronic operated and relies on the same signal as the speedometer so modifying this will fix it. In my case I have an equal odometer to needle read.

Appreciate your information. It is interesting to know.

Sent from my slutty assistant...

Pretty much exactly as it says, using Torque Pro on my phone with the OBD11 bluetooth adapter, I had the dials on the phone set to KM/hr (ecu) KM/hr (gps) distance (ecu) Distance (Gps) and compared that to the readings from the vehicle odo/speedo, the odo read about 1-2% difference( to be expected with tire wear and such) the speedo was 10% out. so i came to the conclusion that the speedo and odo either take speed/distance from different sources OR the speedo has a built is error.

I usually drive to my GPS on either my phone or my detector :)

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my 07 GT reads approx 7-10kph higher than the GPS speed reading (Garmin Nuvi). Your average GPS is apparently quite accurate with speedo readings. Originally I thought it was because I was running 225/40-18\'s (vs OEM 215/45-18s) as there\'s a slightly lower rolling diameter. But going back to OEM size didn\'t make a difference.

Further googling suggests that regulations in many countries define how accurate a car\'s speedo should be. In Aus the ADR stipulate that "the speedo must not indicate a speed less than the vehicle’s true speed or a speed greater than the vehicle’s true speed by an amount more than 10 percent plus 4 km/h. Significantly, this change means that speedos must always read \'safe\', meaning that the vehicle\'s true speed must not be higher than the speed indicated by the speedo." Apparently this aligns with rules set in Europe.

To further subjectively test the speedo accuracy I\'ve run through speed traps and past cops here in NSW at approx 120km indicated - 110km on GPS (on 110km highways) and had no tickets issued (thankfully!).

It is pretty stink that the speedo can\'t read true, or at least with the BP, a bit closer to true.

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Have the same annoyance on mine too. Aus spec Liberty that\'s about 10% out.

The thing that\'s been pissing me off though is when traveling along the roads with 110kph limits here the cruise control turns itself off when your doing more then an indicated 115 >:( and you can\'t turn it back on unless the cars been turned off and restarted.

It\'s frustrating why can\'t they just have them read what your actually doing from factory.

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It is because they are being over cautious as to being "sued" about the car going over speed to quickly.

I drive to my speedo BUT I double check it with the GPS on my radar detector/phone.

you can get an electronic speed adjuster that you may be able to fit to get your cruise to work better ( not sure if the cruise uses the speed sensor or ABS sensors for its speed)

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Have the same annoyance on mine too. Aus spec Liberty that\'s about 10% out.

Actually mine\'s an NZ spec Legacy GT. Shipped it over when I moved here for work. But doesn\'t surprise me that your speedo has the same tolerance of error. Your cruise control cutting out at 115km sucks - that seems pretty daft regardless of the speed limit, especially when the speedo\'s optimistic by 10%. My car doesn\'t have cruise though so I can\'t say if there\'s something wrong there.

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Can only imagine how many would be complaining if there speedo read lower tha actual road speed! Tickets eveywhere !

Which legally youd be able to put back on the manufacturer

OEM setting will allow a cushion for many varriances

- in tyres (ive seen 100mm rolling circumference difference in a 215/45 17 between different manufacturers)

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