4.10s INSTALLED!
5th Gear Member
Joined: Mar 2007
Posts: 3,925
From: Deep in the <3 of Tx
No it's not. My calculations (as I said) were done against the auto 5R55S which has an O/D (5th) of .75:1 ratio. Compare that to the 5-speed manual's .68:1 5th. This is why people say 3.73 for auto and 4.10 for manual. The math works out to be nearly the same between those two due to the auto having lower ratios.
5th Gear Member
Joined: Mar 2007
Posts: 3,925
From: Deep in the <3 of Tx
It should be 2873 rpm (since you have an auto
). Which makes sense b/c of my previous calculation was assuming a stock 27" tall tire (27.17 if you want to be exact).I was able to get 24.x MPG at 80 MPH a while back, which for me right now is 2456 RPM, and that was with my bama tune which seems to give me slightly worse MPG than my Brenspeed tune. So I guess if the tune is good, hitting 24 at your RPM (with the taller tire) makes more sense to me now.
2nd Gear Member
Joined: Nov 2008
Posts: 290
From: Las Vegas
Thread Starter
1st Gear Member
Joined: Oct 2007
Posts: 128
From: FL
I think I have lost 1-2 mpg on the interstate, but what I have noticed is that my around town driving has acutally improved my mpg. So kind of a trade off. 5th becomes a nice cruising gear for around town...so far I love them.....I would do it again in a heart beat....wish I had done this as my first mod.....
2nd Gear Member
Joined: Jan 2009
Posts: 245
From: North Carolina
What if you have a 20" rim. How does that change things betweem 373 and 410. The whole thing kinda confuses me. Some people say if you have 373 and a 20" rim then you would really have like a 355 rear. Somebody explain this to me please.
5th Gear Member
Joined: Mar 2007
Posts: 3,925
From: Deep in the <3 of Tx
It's not the diameter of the rim that matters, but the diameter of the tire. The stock diameter is 27.17". So the bigger the diameter you go, the effective rear ratio will become a smaller number.
Here's how you can calculate the RPM:
RPM = (1056 * MPH * TRANS_GEAR * REAR_RATIO) / TIRE_CIRCUMFERENCE
The stock tire circumference is about 85.36 (in this document I made, I have it as 85.34 for some reason. I guess I didn't use enough numbers for PI or something, lol).
1st Gear Member
Joined: Jun 2007
Posts: 132
From: OK
It doesn't matter what size rim you have. It goes off the height of the tire
here is a calculator the final gear ratio to type in for the auto is .71
http://www.csgnetwork.com/multirpmcalc.html
here is a calculator the final gear ratio to type in for the auto is .71
http://www.csgnetwork.com/multirpmcalc.html