urbex Posted January 16, 2012 Report Share Posted January 16, 2012 Just a random question... What would make the speedometer/odometer be off? I've noticed that at highway speeds the speedo tends to be about 2mph off...and for every 100 miles of driving it reads 99 miles. Granted, it doesn't bother me enough to really fix it, but it's more out of curiosity. The speed sensor was replaced about a year ago so that's not it, and the tires are the stock size (for now). Can it just be that the cluster itself is inaccurate? Like I said, not that I'm really going to fix it, it's more of a learning thing...I just wondered why? Quote Link to comment Share on other sites More sharing options...
Mark 97 Cutlass Coupe Posted January 16, 2012 Report Share Posted January 16, 2012 Maybe someone took apart your cluster, and did not get the speedo needle back on correctly. My Cutlass is off almost 5mph at highway speeds and it is stock. Like you, to me it is not that big a deal. If it is, pull the cluster apart, and set the needle a little higher or lower than where is was sitting before. Quote Link to comment Share on other sites More sharing options...
urbex Posted January 16, 2012 Author Report Share Posted January 16, 2012 (edited) But would that also affect the odometer as well? I'm kinda wondering too, I may get a different tire size when I get tires for my new wheels. I was thinking maybe 215/65-16 or something along that. According to a calculator that if my speedo says 60, I'm going 61.5... Edited January 16, 2012 by urbex Quote Link to comment Share on other sites More sharing options...
slick Posted January 16, 2012 Report Share Posted January 16, 2012 Most vehicles are off by a few mph, especially over 50 mph. Quote Link to comment Share on other sites More sharing options...
urbex Posted January 16, 2012 Author Report Share Posted January 16, 2012 Oh are they? I guess I didn't know. I knew the HHR was off, but I do also have bigger tires on it than what was from factory. Quote Link to comment Share on other sites More sharing options...
Andrew Posted January 17, 2012 Report Share Posted January 17, 2012 factory analog gauges are always a bit off, and they almost always err on the side of caution. Quote Link to comment Share on other sites More sharing options...
WhatTheFehl Posted January 17, 2012 Report Share Posted January 17, 2012 Also, you should probably go with 225/60/16s for the new wheels, as that was the stock size from the factory that was optional for your car. Quote Link to comment Share on other sites More sharing options...
urbex Posted January 17, 2012 Author Report Share Posted January 17, 2012 Also, you should probably go with 225/60/16s for the new wheels, as that was the stock size from the factory that was optional for your car. That's probably what I would get, but I was toying with the idea of a different size to make the speedo accurate. Although I'll probably stick with the factory size...that's what I did on my HHR and I really didn't notice a difference much. Quote Link to comment Share on other sites More sharing options...
WhatTheFehl Posted January 17, 2012 Report Share Posted January 17, 2012 But a 215/65/16 and a 225/60/16 are for all intents and purpose the same overall diameter. Quote Link to comment Share on other sites More sharing options...
urbex Posted January 17, 2012 Author Report Share Posted January 17, 2012 Well I was just basing it on the calculator that showed it would be almost 2mph difference. Quote Link to comment Share on other sites More sharing options...
Crazy K Posted January 17, 2012 Report Share Posted January 17, 2012 I reprogrammed my GP after calculating that the odometer was off by about 5 miles for ever hundred I drove and that it was off by about 3 at 60mph. Once I had that 5% error, I multiplied the pulse per mile count by 1.05 and reprogrmmed the car. While I haven't done the odo crawl since, I have clocked the HUD against my GPS, and the numbers there are dead on. Now... as for the needle, it is two miles too slow at 60mph... but I never use it. LOL Quote Link to comment Share on other sites More sharing options...
dodgethis Posted January 17, 2012 Report Share Posted January 17, 2012 Well I was just basing it on the calculator that showed it would be almost 2mph difference. Urbex, I'll tell you what happend to me, I had swapped in a monte speedo cluster into my car, and while trying to keep the original mileage i had to take my old one apart and replace it into the new speedo cluster. My needle was off by 5mph too, bascially because I just took the needle off to get to the mileage cluster. What i did was i got on the highway with the plastic lens off, and while have my GPS reading out my speed, i just took the needle off and put it right where it should be. It's still about 1 to 2 mph off, but i feel thats close enough. Kinda dangerous what I did, but YMMV Quote Link to comment Share on other sites More sharing options...
Leo090 Posted January 17, 2012 Report Share Posted January 17, 2012 Urbex , I have a weird feeling that this speedometer issue is strangely connected to your hesitation issue. Ive noticed that under hot/humid condition whenever my car starts hesitating, surging, and all that nonsense our luminas try to pull, I find that my speedometer hesitates in reacting as well during this situation. But in general if you dont have a computerized speedometer, it sounds logical that it would be off by a bit Quote Link to comment Share on other sites More sharing options...
urbex Posted January 17, 2012 Author Report Share Posted January 17, 2012 Well my car hasn't been surging in months (probably because it's cold)... I won't say that isn't the case, but I would think there would be more of an error when it surges, which it's consistently off from what I've noticed. As for taking my cluster apart, I actually have a digital speedo I want to put in (waiting to figure out how the change the mileage so it's the same) so that won't help me. It does say that it's certified accurate though on the cluster, so I'm wondering if I put that one in if it'll be accurate? Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted January 19, 2012 Report Share Posted January 19, 2012 Most vehicles are off by a few mph, especially over 50 mph. truf. such is the nature of air-core needle drivers. I reprogrammed my GP after calculating that the odometer was off by about 5 miles for ever hundred I drove and that it was off by about 3 at 60mph. Once I had that 5% error, I multiplied the pulse per mile count by 1.05 and reprogrmmed the car.While I haven't done the odo crawl since, I have clocked the HUD against my GPS, and the numbers there are dead on. Now... as for the needle, it is two miles too slow at 60mph... but I never use it. LOL ken, your specific issue is caused by the "calibration resistors" on the PCB of the cluster. if your odometer is dead accurate, but the needle is reading wrong, then the cal resistors are to blame, since the PCM is sending out a proper signal, just that the cluster isn't displaying it properly. (waiting to figure out how the change the mileage so it's the same) so that won't help me. It does say that it's certified accurate though on the cluster, so I'm wondering if I put that one in if it'll be accurate? the digital ones are by definition, more accurate than the analogs since you don't have to deal with the potential inaccuracy of a guage. Quote Link to comment Share on other sites More sharing options...
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