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Discussion Starter #1
well i assumed i had 3.73 gears, because one person did the math on here and it came out to that sooo well now i have a tuner and to my knowledge my car had the speedometer accurate before the tunes.

i told bama that i had 3.73 gears and 275/40/17 tires, but my speedo is off some.

this is me going 60mph or really really close in Fifth gear


to achieve this result i adjusted the stuff on the tuner before loading the tune
i set my wheels rotation per mile to 750 (a website calc told me 751 but i assume this isnt going to effect even 1mph in the long run)
and then i set my gear ratio to STOCK

now im not sure what the gears are, but 2k rpm in fifth going 60mph is not stock to my knowledge.

so what should i do next? maybe try to get my gear ratio to something lower than stock, like 3.00 gears or something to try to correct it?
 

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There's no way your on he stock gears doug 60 mph and your over 2k. The easiest way to find out is set your gear setup to stock on your tuner and have a friend pace you at 40mph if your speedo is at 40mph then that's your gear ratio. Repeat with the different options in the tuner until you find out what you have.

There's also the chalk test. Mark a line on your drive shaft and count the rotation of tire spins it takes before the driveshaft does one full rotation. If it take the tires 3.73 times to turn for one turn of the driveshaft then that's your gear ratio. Hope this helped!
 

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Discussion Starter #4
his is what i did...
okay so,
when im tuned to 3.73s my car says im going 40mph, however im going around 45mph
when im tuned to 4.10s my car says im going 40mph, however im going around 50mph
when im tuned to 3.55s my car says im going 40mph, however im going around 40mph
when im tuned to 3.55s my car says im going 60mph, however im going around 65mph

at 60mph (according to gps) in fifth gear im at around or very very close to 2k rpms
now according to that gear thread that would mean i have 4.10s

now my tires are 17inch rims 275/40/17 could this have to do with it...
i really want to know what gears are in my car, but i just dont think they are stock. but they could be maybe?
 

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Discussion Starter #5
^^ thats from my old thread, but every time i tune it to the other gears its off, but the closest i can get it to about right is stock gears.
and its perfectly accurate till i get up to about 50-55 mph
 

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Hmmm do the chalk test that I mentioned earlier and find out for certain what gears your running. After that tune it for that ratio and if its still off then its either a mechanical issue with your gauge or your tire size is off. I noticed you said you found the revolutions online, they may be wrong. Ask someone that's running the same size tires as you what they have it tuned to. May be kinda a pain in the ass I know, chasing a problem like this can be difficult sometimes.
 

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Also when I had my 4.10s put in it wasn't tuned at first, you said your speedometer is saying your going slower then you accually are? That's weird because when I changed gear sizes without tuning it, it said I was going faster then I accually was (ie. Gauge said 80 but I was going 65)
 

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You may have 4:10's or whatver you think you have...When you changed your gauges to those Steeda ones, are you POSITIVE you put the needle back on correctly? Mine's 6MPH off with 4:10's cause of the person who did my gauges...and I was too lazy to fix it yet.
 

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Ok I saw in the other thread that your tuner requires a millimeter conversion for tire size input. Here is what you do. Get a piece of chalk and a tape measure. Go outside and mark a line on your tire at the center point of your tire thats making contact with the ground,roll your car forwards or backwards until that line has made a complete revolution and is at the same point again facing the ground. Now use your tape meaure and measure both chalk marks on the concert. Take the inches and convert it to millimeters by multiplying it by 25.4. Next do the driveshaft rotation to come up with your correct gear ratio. Input that info into your tuner and the speedometer should be calibrated almost perfectly.
 

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You may have 4:10's or whatver you think you have...When you changed your gauges to those Steeda ones, are you POSITIVE you put the needle back on correctly? Mine's 6MPH off with 4:10's cause of the person who did my gauges...and I was too lazy to fix it yet.
I would almost put money on this being part of the problem.
 

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Discussion Starter #12
i didnt do the gauges, and its only off at higher speeds, but when i correct it to 3.73s or 4.10s with my tuner, its off at lower speeds around 35-40mph
and looking at the rpms to mph it looks like i have 4.10s and not 3.73s :/ so i guess those are good gears
 

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Dunno, was just a suggestion lol. I'd try what Dales said, but I know GTs don't come with a Steeda gauge overlay unless you bought one, previous owner bought one, or you bought a GT with the whole Steeda makeover. That just stuck out to me, and I know it happens to be one of the biggest problems when people install LEDs or new reverse glows, etc. But anyways, do that chalk test and you'll know for sure man. Hope you figure it out.
 

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Discussion Starter #14
well when i find out for sure, if i set the tuner to that gear its still most likey going to be off though, since i set it to 3.55 3.73. 3.90 and 4.10 anyway how do i correct the needle.

and what else would cause it to be off only at higherspeeds, down low at city speeds, its accurate
 

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his is what i did...
okay so,
when im tuned to 3.73s my car says im going 40mph, however im going around 45mph
when im tuned to 4.10s my car says im going 40mph, however im going around 50mph
when im tuned to 3.55s my car says im going 40mph, however im going around 40mph
when im tuned to 3.55s my car says im going 60mph, however im going around 65mph

at 60mph (according to gps) in fifth gear im at around or very very close to 2k rpms
now according to that gear thread that would mean i have 4.10s

now my tires are 17inch rims 275/40/17 could this have to do with it...
i really want to know what gears are in my car, but i just dont think they are stock. but they could be maybe?
the revs per mile for 275/40-17s is the same as for the stock 245/45-17s--810 or so when on the car.

You said you set it to 750. Also, in the quoted message above, you say that at 60 in 5th, per the GPS, the engine is running around 2k. With 3.73s and the 275/40-17 tires you should be going 64 or so with 3.73s at 2k (here's my How Fast Can I Go in Each Gear? calculator).

However 810/750 = 1 .083; and 1.083 * 60 = 64.8 mph. Pretty close, reset the tire revs per mile to 810 and see what happen...
 

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Discussion Starter #16
the revs per mile for 275/40-17s is the same as for the stock 245/45-17s--810 or so when on the car.

You said you set it to 750. Also, in the quoted message above, you say that at 60 in 5th, per the GPS, the engine is running around 2k. With 3.73s and the 275/40-17 tires you should be going 64 or so with 3.73s at 2k (here's my How Fast Can I Go in Each Gear? calculator).

However 810/750 = 1 .083; and 1.083 * 60 = 64.8 mph. Pretty close, reset the tire revs per mile to 810 and see what happen...
Thanks i was looking at another fourm and found that calc. and saw 810.5 revs, how ever wouldnt that make my car speedometer read slower if i increase the tires, but then i could also change the gear ratio to 3.73 or 4.10 which everone it is
 

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Discussion Starter #17
i got it down to a 2mph error, when my car says im going 60mph im really going 58mph

but i set my tuner to 810 and then to 3.05 gears lol
 

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Thanks i was looking at another fourm and found that calc. and saw 810.5 revs, how ever wouldnt that make my car speedometer read slower if i increase the tires, but then i could also change the gear ratio to 3.73 or 4.10 which everone it is
You are correct--for some reason (maybe age, I just turned 64 today) my brain was looking at it from a reverse perspective--aka a "brain fart".

With the 275/40-17s, at 2k rpm, with 4.10s, and the tire revs/mile set to 810 you should be traveling close to 60 as shown below:



60 would actually be around 2050 rpm--with those settings for gears and revs/mile (4.10 and810), what does your speedometer read when you are at 2k rpm in 5th?
 

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Discussion Starter #19
right now its would read 62mph but its because i set my gear ratio to the one before 3.23s or what the stock is, i think its like 3.09s on the sct tuner or close maybe

this makes no since though
 
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