pauljm Posted August 30, 2009 Share Posted August 30, 2009 Just got back from Stockton beach where i caught nothing...2nd time beach fishing for me and the same result both times....anyway i have a 93 model jackaroo 4wd and i did the odometer test on the freeway and my odometer is 300m short over the 5kms. So when my speedo is showing 100km what speed am i actually doing? Call me stupid if u loke but maths was never my thing!I assume its out due to new wheels being put on it at some stage? Will have to check what they come out with originally....does anyone own a similar age jackaroo as this? This one has over 320000kms and goes ok however it has no torque at higher speeds and really struggles with the hills on the freeway...i am wondering if i was to rebuild the motor would i get much more power or were they always like this?Its a 3.2L isuzu petrol motor. Needless to say its a slow trip when i hook 2 tonne of boat and trailer to it........any help much appreciated. Link to comment Share on other sites More sharing options...
johnv Posted August 30, 2009 Share Posted August 30, 2009 definetly the wheels on the spedo is correct , but rebuilding motor doesn't give u more speed may be the izuzu is under powered. u might have to try and put a larger motor in possible from holden rodeo ute or upgrade to a newer ute john Link to comment Share on other sites More sharing options...
squizzytaylor Posted August 30, 2009 Share Posted August 30, 2009 6.38% under by my calcs so you are doing 106.38 kph when reading 100. I'm not that good at maths either so confirmation would be good. Geoff Link to comment Share on other sites More sharing options...
david88 Posted August 30, 2009 Share Posted August 30, 2009 106 km/h I may be wrong though that was just done quickly with a scrap of paper.. Link to comment Share on other sites More sharing options...
pauljm Posted August 30, 2009 Author Share Posted August 30, 2009 Thanks guys ......106! Now i know why i seemed to be overtaking a lot of cars on the way up there! Just cant remember what speed i was doing through the speed cameras.... Link to comment Share on other sites More sharing options...
hottyscotty Posted August 30, 2009 Share Posted August 30, 2009 if you get a fine, do a calibration test and you should be off scot free. but i would get it re-calibrated b4 a copper wants to be a d!ckhead Link to comment Share on other sites More sharing options...
robust Posted August 30, 2009 Share Posted August 30, 2009 MATHEMATICS!!!!!!!!!!!!!YUK, I'm getting a headache just thinking about it, sorry but i failed maths throughout my whole schooling life lol. Cheers Link to comment Share on other sites More sharing options...
jewieslayer Posted August 30, 2009 Share Posted August 30, 2009 Have u Changed the rims or tyres with a different size,Cause this will put it out Cheers Jewieslayer Link to comment Share on other sites More sharing options...
andrew399 Posted September 1, 2009 Share Posted September 1, 2009 Maybe i am just as bad as maths as i thought, but wouldnt it be 6% under 100km/h ie 94km/h? My only reasoning being that if the car says that it has travelled 5.3km when really it has only travelled 5 then when it says it is traveling 100kph it would also in reality be doing around 6% less than that?? Link to comment Share on other sites More sharing options...
david88 Posted September 1, 2009 Share Posted September 1, 2009 Maybe i am just as bad as maths as i thought, but wouldnt it be 6% under 100km/h ie 94km/h? My only reasoning being that if the car says that it has travelled 5.3km when really it has only travelled 5 then when it says it is traveling 100kph it would also in reality be doing around 6% less than that?? i did the odometer test on the freeway and my odometer is 300m short over the 5kms.. Link to comment Share on other sites More sharing options...
andrew399 Posted September 5, 2009 Share Posted September 5, 2009 (edited) haha thanks david88, maybe im even worse at english than maths!! Edited September 5, 2009 by dicko Link to comment Share on other sites More sharing options...
abecedarian Posted September 5, 2009 Share Posted September 5, 2009 (edited) Um, I think you have to factor in the time it took you to travel the 5km, not just what distance the odometer says. I say that because you could travel the 5km with your odometer saying you travelled 5.3km but you could've been doing 10km/hr the whole time... If you're sitting on 100km/hr according to your speedo all the way it should take you 3 minutes to cover 5km. 5 mins if you're doing 60km/hr, 4 mins at 80km/hr etc. Speed is a factor of time and distance whereas your odometer only measures distance... And although there's no guarantee that rebuilding your motor will make it pull up hills better, if it's done that many miles chances are it's worn a little. A rebuild may improve the efficiency of the motor (through better compression, tighter tolerances on bearing surfaces etc.) which may in turn increase the power output of a motor. All motors will over time lose power and a rebuild can help that. But it might be an expensive way to go about getting more power though... Edited September 5, 2009 by abecedarian Link to comment Share on other sites More sharing options...
yakfishing Posted September 5, 2009 Share Posted September 5, 2009 (edited) Um, I think you have to factor in the time it took you to travel the 5km, not just what distance the odometer says. I say that because you could travel the 5km with your odometer saying you travelled 5.3km but you could've been doing 10km/hr the whole time... If you're sitting on 100km/hr according to your speedo all the way it should take you 3 minutes to cover 5km. 5 mins if you're doing 60km/hr, 4 mins at 80km/hr etc. Speed is a factor of time and distance whereas your odometer only measures distance... I don't know how the mechanics of it works, but the speedo might well calculate it's reading from the odometer - ie distance/time. So if one's off, so is the other Edited September 5, 2009 by yakfishing Link to comment Share on other sites More sharing options...
david88 Posted September 6, 2009 Share Posted September 6, 2009 Um, I think you have to factor in the time it took you to travel the 5km, not just what distance the odometer says. I say that because you could travel the 5km with your odometer saying you travelled 5.3km but you could've been doing 10km/hr the whole time... Time is a constant (at these speeds). you dont need to worry about the time being off until you start approaching the speed of light, and if infact you are then I would really question how badly you need an engine rebuild... but really as said above, the speedo works by measuring the distance you travel per unit of time and multiplying it to kmph. the distance is the only thing that could be out. Link to comment Share on other sites More sharing options...
abecedarian Posted September 6, 2009 Share Posted September 6, 2009 Time is a constant (at these speeds). I'm not great at maths but that makes no sense whatsoever... From what I can remember of high school maths speed = distance / time. That being the case if the distance is set at 5km, then the time it takes ti travel that distance will change with changes in speed, making it a variable. If time was a constant then not only would the speed your traveling at only ever depend on how far you travelled, but it would take the same time to travel any distance whether it be 1km or 1000km, which isn't the case as far as I know... Anyway, that's semantics and not at all helpful to the situation. If it's a worry it's probably best to get the speedo calibrated properly. I wouldn't rely on using it as an excuse if you get a ticket because I've heard that might not be a valid excuse any more. Something about it being your responsibility to properly maintain your vehicle, and an accurate speedo would fall into category I'd think.... Link to comment Share on other sites More sharing options...
pauljm Posted September 6, 2009 Author Share Posted September 6, 2009 I'm not great at maths but that makes no sense whatsoever... From what I can remember of high school maths speed = distance / time. That being the case if the distance is set at 5km, then the time it takes ti travel that distance will change with changes in speed, making it a variable. If time was a constant then not only would the speed your traveling at only ever depend on how far you travelled, but it would take the same time to travel any distance whether it be 1km or 1000km, which isn't the case as far as I know... Anyway, that's semantics and not at all helpful to the situation. If it's a worry it's probably best to get the speedo calibrated properly. I wouldn't rely on using it as an excuse if you get a ticket because I've heard that might not be a valid excuse any more. Something about it being your responsibility to properly maintain your vehicle, and an accurate speedo would fall into category I'd think.... thanks for the responses but im tippin the first couple are right.....100 ks an hour = 106 .....there would be no reason to have an odometer check on the freeway if kms travelled didnt equate into kms an hour....thats the wholre reason for having it in the first place! as for the time it takes to travel a given distance... dunno what planet your on but if i took 5 hours to travel that same 5kms my odometer would be exactly the same! Unless i did it with the back wheels spinning which would have been fun! Link to comment Share on other sites More sharing options...
HawkesburyMarlin Posted September 6, 2009 Share Posted September 6, 2009 If you have a Navigator (or can borrow one), they often have a setting that will display your speed, I remember reading somewhere that the speed displayed is highly accurate. Link to comment Share on other sites More sharing options...
tide'n'knots Posted September 7, 2009 Share Posted September 7, 2009 multiply the distance by the time it took to travel divided by the speed of light and think of the first number you thought of then how fast is the fly buzzing around inside your car traveling at???? I failed maths too! pete. Link to comment Share on other sites More sharing options...
Mik Posted September 7, 2009 Share Posted September 7, 2009 100 / 5 (Distance measured) = 20 20 X 4.7 (What your speedo said you travelled) = 94 Therefore if you travelled a set distance of 100 kilometres your speedo would only read 94 kilometres Your speedo is 6klms/hr out at 100 When your speedo says your're doing 100klms/hr you are actually only doing 94klms/hr Or another way to check it: If you sat on exactly 100klms/hr for a measured distance of 100klms/ hr your actual distance travelled would still only be 94 kilometres. Therefore to reach 100kilometres in distance you will need to drive a little longer in time to reach it, thus your were not driving at 100 klms/hr Make sense? I'd be very surprised to see a speedo these days that is on the high side unless you seriously tamper with tyres. Manufacturers ere on the side of caution methinx. Link to comment Share on other sites More sharing options...
DerekD Posted September 8, 2009 Share Posted September 8, 2009 (edited) I just want to make sure that I understand the facts first. If I read your statement correctly then: You travelled a set distance of 5000m. When you completed it your odometer stated you had covered 4700m (i.e. 300m short). If this is the case then: When your odometer reads 5000m you have covered an actual distance of 5319m. (5000m / 4700m x 5000m = 5319m) Or to put it non mathamatical terms. The odometer is linked to the revolutions and diameter of the wheel but in this case each revolution of the wheel takes you a little bit further than it should have been calibrated for. This will affect the speed of the car in a similar way. The speedometer is using the same distance data and (assuming the timing function is working properly) while you may read 100km per hour because each revolution of the wheel is taking you a little further than it was calibrated for you are actually going further and thus faster than you think. How much? The correction factor is: 5319m (actual distance) / 5000m (distance on odometer) = 1.0638 Thus 100km per hour on spedometer = 100km per hour x 1.0638 = 106.38 km per hour actual. So at 100km per hour on the dial you are speeding. One possible cause of this problem is that at some stage someone put some larger diameter wheels on the car than it came with originally. Edited September 8, 2009 by DerekD Link to comment Share on other sites More sharing options...
Mik Posted September 8, 2009 Share Posted September 8, 2009 (edited) Ahhhh I was wondering when someone would spot my obvious & deliberate mistake........... Ok ok I got is ass about didneye. Is there a prize for the correct answer? Derek I reckon you should go halvies with me seeing as I helped prompt you into action.....So I'll have 33% of whatever the prize is eh! Edited September 8, 2009 by Boofhead Link to comment Share on other sites More sharing options...
Mik Posted September 8, 2009 Share Posted September 8, 2009 So anyway, I actually worked out my blunder today whilst driving. (Seriously, I did it all by meself) But I came up with a few interesting facts. We have several (5) GPS units, 4 are identical & one is the same make but a different model. They all calculate the same in a vehicle travelling at 100 k/hr (Actually one read 101 but all others were exactly 100k/hr. Now, these units tell me that my speedo is exactly 8 k/hr slower than what the GPS reads. IE when the vehicle speedo reads 100k/hr the GPS says 92. However, the trip metre in the GPS reads different to the odometre by only 4.08 per 100 kilometres. Here's my calcs. Vehicle odometre reads 0 to 25.0 kilometres. GPS odometre reads 0 to 23.98 kilometres. 25 kilometres was the longest test I did but I also did several over a 5 kilometre distance & the vehicle odometre said 5 kilometres while the GPS read 4.8 kilometres So how is this right? My odometre is out by 4.08 but my speedo is out by 8? What's the go there, I would have thought they would be the same? Sorry if I hijacked this post Link to comment Share on other sites More sharing options...
DerekD Posted September 8, 2009 Share Posted September 8, 2009 Hi Boofhead, I took the theoretical route and made the assumption that the timer in the spedometer was working correctly which was the best that I could do at the time. You wondered why your test results were out. The velocity (speed) is a function of distance divided by time. I explained why the distance could be out which explains the problem with the odometer. The other variable time is probably a result of the timer in the instrumentation being not quite as precise as you would like. I suspect they don't have quartz movement or an atomic clock in the spedometer. I must say that I am impressed that you took the time to test out a theory and then reported your findings. You have the makings of a scientist. Whereas I am only an engineer (would you have guessed?). For Payatz to test it properly he would need to also time the trip with a reliable stopwatch and then have the velocity consistent through the trip. 60km per hour would be a good speed (1 km each minute, thus 5km = five minutes). Alternatively he could do as you did and use a GPS and skip the whole calculations business. Derek Link to comment Share on other sites More sharing options...
DerekD Posted September 9, 2009 Share Posted September 9, 2009 Hi again Boofhead, There is another reason for the odometer distance to be out from the GPS information. The odometer measures the distance your wheels travel whereas the GPS may take a best fit approach. To explain further, when Payatz did the test distance if he swerved from side to side his car may have travelled more distance than the point to point distance of the test trip. When you did your test I suspect it was not a dead straight road. The GPS may take a location say every 2 seconds and it may join the dots in a straight line and work out the distance. The small diferences may add up over time. When commercial GPS units came out I understand there was a deliberate error included in them so that they could not be used for military purposes. Depending on how big these tolerances are these days the total of the deliberate errors could add up. Having said that I would still trust a GPS over the instumentation in the car. Regards, Derek Link to comment Share on other sites More sharing options...
Mik Posted September 9, 2009 Share Posted September 9, 2009 I must say that I am impressed that you took the time to test out a theory and then reported your findings. You have the makings of a scientist. If failed math & science Derek, but I do admit to a slight penchant of geek in me. If it flashes & makes noises generally its got my attention. Might explain why I have so many bloody gawdy rattling lures eh! Oh, no wait, thats coz I'm addicted to fishing. Whereas I am only an engineer (would you have guessed?). Derek Geeze mate I was just starting to like you too! Actually you answered the odometre / speedo discrepency with the info you sent me from Wikipedia. Seems that the needle & the odometre or "Trip" metre are independantly driven by the cable, thus they could vary between each other. I still can't get over the fact that its all done with magnets, I thought it was supposed to be smoke & mirrors. Link to comment Share on other sites More sharing options...
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