my speedo is off
10-19-2010, 12:43 PM
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my speedo is off i just bought the car, its a 02 z28 with 100k miles on it. when i was driving back in the hwy, i drove right next to my gf in the other car, i noticed at the speedo i was running 60 mph which didnt feel right so i called her and asked her what speed she's running at, and she says 75
so my speedometer is off around 15 mph, i bought the car from a dealer, so i've no idea what kind of gears it has.
my question is, would a higher ratio gearing mess up the speedometer reading? such speedo reads 60 when it's supposed to be 75?
thank you for your help
Ray
so my speedometer is off around 15 mph, i bought the car from a dealer, so i've no idea what kind of gears it has.
my question is, would a higher ratio gearing mess up the speedometer reading? such speedo reads 60 when it's supposed to be 75?
thank you for your help
Ray
10-19-2010, 02:32 PM
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no. a lower gear ration would make that happen, like say if the car came in with 4.11s and they put 3.42s back in it. What are your rpm's at "60"? Is your car an A4 or M6??
10-19-2010, 03:29 PM
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The car probably had 4.11 before since I bought it from a dealer I've no idea what gear it is/was in. Its m6, I was cruising on 6th gear, 60 mph was around 2.5g
10-19-2010, 05:06 PM
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okay i ran all this assuming you had the stock 275/40/17, the stock 0.5:1 6th gear, and were infact in 6th
Okay, mathmatically, you would need to have a 5.13 ring and pinion to be going (technically 74) 75mph at 2500 in a 0.5:1 6th gear. To get your speedo to show 60 mph while spinning 2500rpms your car would have to think it had literally a 6.30 ring and pinion. I dont even think they make a gearset that high for a 10bolt (assuming it has the stock rear end).
something is very fucked in your car my friend. honestly that sound alot like stock gearing driving in 4th. Im in no way shape or form calling you an idiot, but your 100% sure you were in 6th correct? like i said not trying to start a war, ive done it before too, but damn something is fucked if you were really in 6th
to do your own research, go to www,f-body.org/gears/
you need to figure out something quick man, who knows how long your car ws driven like that, you could have A TON more miles on it than you actually do
Okay, mathmatically, you would need to have a 5.13 ring and pinion to be going (technically 74) 75mph at 2500 in a 0.5:1 6th gear. To get your speedo to show 60 mph while spinning 2500rpms your car would have to think it had literally a 6.30 ring and pinion. I dont even think they make a gearset that high for a 10bolt (assuming it has the stock rear end).
something is very fucked in your car my friend. honestly that sound alot like stock gearing driving in 4th. Im in no way shape or form calling you an idiot, but your 100% sure you were in 6th correct? like i said not trying to start a war, ive done it before too, but damn something is fucked if you were really in 6th
to do your own research, go to www,f-body.org/gears/
you need to figure out something quick man, who knows how long your car ws driven like that, you could have A TON more miles on it than you actually do
10-19-2010, 08:22 PM
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Tires are 245 all around, I'll do my research and report back here, the car's in the shop now, getting checked for every little things, everything on the car is solid though, carfax's clean too.
10-21-2010, 03:09 AM
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the 245/45 and the 275/40 are the same size (25.6blahblahblah inches) so something is off. You could/have the shop pull the diff cover and count ring teeth and see whats up, or if they have a tech2/scanner have them check and see what the r/p ration is set to
10-25-2010, 09:19 PM
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ok i was wrong with the rpm on 6th gear, just got the car back from the shop today, 60 mph on 6th gear is around 1600 rpm..the speedo still off by at least 13 mph i'm scratching my head now..
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10-26-2010, 12:55 AM
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Your car had 4.11's in it and now has either a 3.42 or a 3.23 in it. 1600 for 60 is right on for a M6 car with 4.11's, and 1600 rpm on a 3.42 is 71mph, on a 3.23 it's 76 mph. Your speedo will be off by a certain percentage, not a specific mph.
Pop the cover and count the teeth, or just reprogram it. You can't take your speed based on doing the same speed as another car and going off their speedo. There are tolerances everywhere.
Pop the cover and count the teeth, or just reprogram it. You can't take your speed based on doing the same speed as another car and going off their speedo. There are tolerances everywhere.
10-26-2010, 03:21 AM
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Your car had 4.11's in it and now has either a 3.42 or a 3.23 in it. 1600 for 60 is right on for a M6 car with 4.11's, and 1600 rpm on a 3.42 is 71mph, on a 3.23 it's 76 mph. Your speedo will be off by a certain percentage, not a specific mph.
Pop the cover and count the teeth, or just reprogram it. You can't take your speed based on doing the same speed as another car and going off their speedo. There are tolerances everywhere.
Pop the cover and count the teeth, or just reprogram it. You can't take your speed based on doing the same speed as another car and going off their speedo. There are tolerances everywhere.
