rich1833

I just got this car and thought to rpm's were alittle high for stock gear anyone know? 1998 trans am ls1 A4 with P245/50z/R16.

1st gear @ 2000rpm's=15mph
2nd gear @ 2000rpm's=25mph
3rd gear @ 2000rpm's=45mph
4th gear @ 2000rpm's=60mph

RPM WS6

iTrader: (3)

60mph in 4th gear @2000rpm with a 25.66" tire would be consistant with roughly a 3.73 gear.

Stock gear ratios were 2.73 or 3.23, neither of which should be anywhere near 2000rpm at 60mph with a stock tire height.

94 White T/A

Lookin like you have 3.73's

Lil_Wyvern

That's about right for my 2000 SS A4 with the 3.23, though I have the 275/40-17's on my car. At 60 I'm at 2000rpms (I know because of the Loudmouth 1 drone around those rpms). At 70mph I'm around 2400rpms.

I usually don't hot rod my car so it shifts around 2000rpms when driving normally, and those speeds you listed are correct.

RPM WS6

iTrader: (3)

Unless your OD or TCC isn't functioning, you're not actually at 2000rpm @60mph, nor 2400rpm @70mph with stock tire height (275/40/17 and 245/50/16 are the same effective height, 25.66 vs 25.65 inches) and 3.23 gears in 4th gear of the A4.

It's possibile that your tach or speedometer is off though.

Here is an excellent calculator that shows correct rpms for your setup:

http://www.f-body.org/gears/

4th gear at 2000rpm = 68mph with 3.23s and either stock tire size.

60mph = about 1775rpm in 4th gear with 3.23s and either stock tire size.

70mph = about 2100rpm in 4th gear with 3.23s and either stock tire size.

Lil_Wyvern

Nope. Everything is correct and works fine on my car. My friends 2001 Firehawk A4 is the same way.

RPM WS6

iTrader: (3)

Something is definitely not correct if you are actually seeing a true 2000rpm at 60mph with 275/40/17 tires and 3.23 gears in 4th under TCC lock-up. RPMs will be a bit higher if the torque converter is not locking, but that would indicate a problem because it should be locked at steady cruise in 4th at those speeds.

Fry_

Lil_Wyvern I'd bet $50 your tach is off, they're known for it. It looks like the OP got his info off his smart phone using the Torque app, I've done the same with my T/A, the tach reads 200 rpm high and the speedo is dead on. You could also use a good code reader/scan tool to read the live data stream to know you true rpm's. On a side note, if you get the shift light add on for Torque you can use 2 rubber bands to hold your phone it your rear view mirror at the drag strip, just set it so the hole screen changes from black to red it works perfect.

Grr

iTrader: (2)

LOL, I guess math is different where you live?? facts are facts guy 25.6" tire 3.23 gear at 2000rpm is 68mph. 2400 is 81mph the laws of nature dont change just for you

Lil_Wyvern

LOL. I'm not being mean or upset, but dude are you seriously trying to tell me what my car has just by some math number you run on a computer? My Camaro A4 rear end is the stock 3.23 WU8 package, 275/40-17, blah blah, etc. I bought it absolutely stock and it's always ran around 2000rpms at 60mph. I drive around 70-75mph on the interstate to around 2300-2400rpms (with torque converter locked) on my car cause those Loudmouth 1's quiet up around there. I had never changed out the rear end on my car as well as my buddy who has an A4 Firehawk and like my car, runs the same RPM's at those speed. Rich1833 was asking about his A4 rpm's/speed and my A4 Camaro and my buddy's A4 Firehawk runs exactly the same rpm's/speed.

The state I live in requires everything to work correctly. I know cause I sit there while they check everything for 30-40 minutes during the inspection. Nothing has changed on my car since I bought it, likewise on my buddy's car when he bought his brand new. But hey, if someone crawled under all three of our car's and swapped out all the rear-ends to a 3.73, I'm not going to complain.

RPM WS6

iTrader: (3)

I've had two A4 3.23 LS1 F-bodies with stock tire height. I bought both cars brand new. Neither one turned 2000rpm at 60mph. 60mph is a bit under 1800rpm with those gears and stock tires.

Math is math. 2000rpm = 68mph in 4th with a 4L60E + 3.23s and a 25.66" tire. Math can't lie. But your tach can certainly be off, many of them are.

Grr

iTrader: (2)

not ******* you dude, but seriously

SOMEBODY DIG UP EINSTEIN THIS GUY JUST PROVED THAT MATH IS WRONG

it is what it is, you CANNOT disprove simple math, regardless of what you "beleive"

Lil_Wyvern

I'll have it checked out during the next inspection. This state always hooks up my Camaro and my Odyssey (don't diss the minivan. LOL!) to them little machines always required me to hold my car at certain up to 4500RPM's to check for emissions and whatever it said on the tach was the same on the machine. What I don't understand is why my buddy's car and mine do the same thing (I've driven his many times and vice versa) and Rich1833's car is at the same speed/rpms. Quincidence? I don't know, but could be many things. I'm just going by what I've seen on both our cars and answering Rich1833's question.

Grr, I know your not ******* me, but I've been on some of the little sites that you plug in the math and some sites come out way off, especially the "guestimated quarter mile times" or "horsepower on to wheels" on cars. Maybe it's correct, but it could also be off. I've fooled around on a few with my old T-bird a while back and it said my car had a 3.55 rear gear when I actually had a 3.08. Just an FYI!

JDEP162

i thought the exact same thing when i bought mine (98Z, a4, 3.23), but i used a scan gauge, and the tach was off, runs right around 1780-1800 at 60mph, and the dash tach says 2000rpm. long story short dash tachs arent 100% accurate on 15 year old cars.

Snake_Skinner

iTrader: (12)

So i hear are tach's are off all the time, do they usually read higher or lower than what the rpm actually is? By looking at you'alls posts it looks to be higher, so is it always higher?

ajwoodtransport

Just to keep the arguement lively....some tire manufacturers measure their width diffrently, and therefore the aspect ratio and tire rpm's won't match some online gear/road speed caculators. It's best to go the tire manufacturers website and actually see what they say for their specific tire revolutions....and then go back to the online caculators to throw in the numbers. Also tire wear will throw off everything...although that's probably a pretty minor thing with the little amount of tread that's on most sport tires. In the trucking world, you set your odometer based on all the different info like that and periodicaly adjust as the tire wears.....that way you are not paying anymore then nessasary for road taxes such as IFTA, IRP, and various other individual state taxes. Also, in the life a semi truck...your miles may be off several tens of thousands of miles which can influence if you are still in warranty and also resale value. Having said all that, I'd agree that the road speed caculators with general inputs will get you close enough to determine what gears you have. Let the bashing begin...LOL.

AmDWs6

get a officer to track your speed's & get done with it lol.

RPM WS6

iTrader: (3)

This is definitely not the case with non-regroovable, Z-rated passenger tires for a car such as an F-body. Overall diameter will never change enough due to normal wear alone to make an 8mph difference in tach/speedo readings within the service life of a tire. Manufacturing differences between brands will also not be enough to create such a discrepency. For example:

Stock tire height for 4th gen V8 F-body: 25.66" or 25.65"

With that tire height, and 3.23 gears, and the OD ratio of a 4L60E transmission, you end up with 68mph at 2000rpm.

If you were to reduce the tire height to 24.66", and keep everything else the same, you'd then be going 65mph at 2000rpm. That's still not even close to an 8mph difference, and this would require a tire that has lost one full inch of diameter over a 275/40/17 or 245/50/16 tire - something that is not possible within the normal service life of a Z-rated passenger tire, and not within the range that would be allowable for a brand new tire to have ever been designated as a 275/40/17 or 245/50/16.

In other words, there is no way to see a true 2000rpm at 60mph with stock tire size, 3.23 gears, and a 4L60E with functioning lock-up and OD. I'm not calling anyone a liar or crazy about what they're seeing on their tach, but I AM calling the tach wrong if it shows data that is simply not possible.

ajwoodtransport

I hear ya, I'm just having a Cliff Clavin moment. "Ahhhh, in Colonial days the swelling of the wood spokes would offset carriage height and cause the horses to...blah, blah, blah".

sawblade99Z

iTrader: (1)

Not trying to hijack, but I recall reading somewhere that if you hold the car in 3rd at 75 mph, the rpms will tell you which gears you have. 2730, 3230, 3730, 4100 rpms and so on. I tried it and mine read ~2730 rpms per my tach and backed up by my Scan Gauge, which is dead on for my 2.73s. Assuming stock tire size, does this method always work?