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Old 10th January 2005, 16:01   #1
DRC
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Question Speedo calibration

I have a technical problem with my new Petra, 18 days 1250kms???,
I believe the speedo and/or odo is not accurate

Feeling one: When i see an indicated speed of aroud 60km/h, i feel it may be more than 80, means speedo shows less ( i knew the old palios had this problem, any one know about petra, any other fellow petra owners can verify this for me?)
I really wanted to clarify this by driving along a know vehicle at a constant speed. So far couldn't do. will do it soon

Experiment one. Filled gas at reddy gas station (kumara park), reset trip, drove to jayanagar and back, trip showed 24kms. then drove to Madhugiri, I know its exactly 100 kms from bangalore (did not reset trip), and back. I expect the trip to show 224, I am surprised to see 192. thats 16% error!!!.

Sopke to Sundaram sevice , no use.

I thought the odo is all about fixed gear ratios. Can this be so wrong.??

help
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Old 10th January 2005, 18:39   #2
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Hey DRC even i had the same doubts with my Petra. The same feeling of speed being off with exactly those figures, displayed 60 feeling like 80. that is something that i have gotten used to now

The distance is something that even I had/ still have my doubts. actually should do a run with another non petra with stock tires to see how bad the error really is.

i have a suspicion that the error is about 10% since once someone gave me a drawn map which showed a confirmed distance of 10.5km and i got there in only 9.5km on the odo. btw, my odo reading would anyway be slightly off since the OD of my tyres is more than the stock tyres by about 7mm
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Old 10th January 2005, 18:50   #3
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Hi DRC,

Do you have the stock tires & wheels on your petra?

Is there a kinda grinding noise comming from in your instrument panel when you go at high speeds?

Sometimes what happens is.... or i should say all the times what happens is that these service centers disconnect the instrument display for the period before delivery, and before they deliver the car the connect it back. Sometimes they dont connect it too well......

I cant really remember... but im assuming the petra has a analog odometer?
Chances are its a slipping gear somewhere, ie if you have the correct diameter tires.

cya
R
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Old 10th January 2005, 18:52   #4
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Hey Rahul,

Do you have alloys on your petra as well? Would love to see pics if you do.... i dont think i have ever seen a petra/sienna with alloys! im sure a good set could give the car a whole new look!

let me know,
R
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Old 10th January 2005, 19:04   #5
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Do one thing, tell me what rpm the engine is running, in 3rd when your speedo is showing 60kmph. Or give me the speedo read at the closest round figure EG: 3000, 3500, 4000 rpm and so on. Maybe i'll be able to tell you how much error your speedo is showing.

Shan2nu

Last edited by Shan2nu : 10th January 2005 at 19:06.
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Old 10th January 2005, 19:05   #6
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Hey Rehaan, I havent put alloys on the Petra yet :-(

you should check out the the Aura website http://www.auraalloywheels.com/
they have a section called showroom, where you select your car and a set of wheels and they show you a picture of the car with that wheel. quite neat

btw, when i wanted to test drive the petra, the dealer folks gave me a car with a disconnected odo speedo cable!!! i realized they were trying to save mileage on a car that would later be bought by somebody else!!! sad that they resort to such cheap stunts instead of investing in a test drive car for the showroom
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Old 10th January 2005, 19:07   #7
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Are you running on the stock 175/65 R 14s? And is yours a Petrol or Diesel?

Shan2nu
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Old 10th January 2005, 19:12   #8
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Quote:
Do one thing, tell me what rpm the engine is running, in 3rd when your speedo is showing 60kmph. Or give me the speedo read at the closest round figure EG: 3000, 3500, 4000 rpm and so on. Maybe i'll be able to tell you how much error your speedo is showing.

Shan2nu
Shan2nu do you have a mapping table or something? will tell you the reading tomorrow morning...
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Old 10th January 2005, 19:41   #9
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Quote:
Shan2nu do you have a mapping table or something? will tell you the reading tomorrow morning...
Yeah i use the formula for that. Give me a speedo reading at any rpm in any gear and i'll tell you what true speed your should be doing.

Like i said round figures will be better.

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Old 11th January 2005, 12:02   #10
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i got a problem with my palios metre too
the speedometer just stops working and then so does the tripmeter
however whenever i send it to get it checked out, it works fine .
though the frequency has reduced now, it still happens but rarely
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Old 11th January 2005, 13:57   #11
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Quote:
Originally Posted by Rehaan
Hi DRC,

Do you have the stock tires & wheels on your petra?
R
Yea, I still have the stock rims and tyres,

Rahulmd, I agree with you, When I test drove I also got a black one with speedo disconnected (was that yours??), But I dont hear any grinding noise as such, may be disconnected at the driving end?!
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Old 11th January 2005, 14:14   #12
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And DRC, can you give me the gear ratios (1st to 5th), and the final drive ratio of the car. it'll be given in your car manual.

Shan2nu
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Old 11th January 2005, 14:28   #13
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havent got the gear ratios but i do 2700rpm at 60kmph in 3rd gear. will get you the gear ratios a little later.

after all this, would it be possible to share the calculations? :-)
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Old 11th January 2005, 14:42   #14
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Quote:
after all this, would it be possible to share the calculations? :-)
yeah sure. I think i've mentioned the formula in some other thread.

(engine rpm) / (gear ratio) / (final drive ratio) * (wheel circumference "in Inches") * (2.54) / (100000) * 60 = vehicle speed in kmph. That's the formula i use. You can use various permutations and combinations to findout, gear ratios, final drive ratios, wheel circumference, engine rpm at any given speed.

You can even come up with your own set of gear ratios that will help your vehicle stay within the power band at all times.

Shan2nu
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Old 11th January 2005, 14:51   #15
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Quote:
havent got the gear ratios but i do 2700rpm at 60kmph in 3rd gear
So your wheels (175/65 R14) should revolve at 546 rpm at 60kmph. Multiplying 546 by your final drive ratio will give me a figure. Dividing your engine rpm (2700) with that figure will give me your 3rd gear ratio (provided your speedo is accurate which it's never). So it's safer to know the ratios while calculating.

Shan2nu
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