shimp

On my 2004 Silverado RCSB, 5 speed 4.8, changed from this:

235/70/16 (28.95in)

to this:

275/55/20 (31.90in)

Basically 3" more tire/wheel. My gear is 3.42, with 5 speed manual. This change raised my truck up 3" and made it too long through the gears... Speedo is 10.2% off, need to recalibrate with HPTuners, I can handle that, but I want to know what gear I should choose if I decide to change.

Would 3.73 be okay? Or if I wanted similar performance to what I had with the smaller tires and 3.42, would I need to go to 4.10? Which would you do and why? I am not really after 1/4 mile speed, but I would like to 3-4 shift at 95-100mph. Is there a calculator online somewhere I can use to figure that up? Note with the 3.42 and the smaller tires, the 3-4 shift @ 5900rpm was at 100-101mph if I remember right, now it's at like 112mph or more on GPS, not real sure, need to recal the speedo and check it all out.

Thanks!

shimp

hmm, if 3rd in NV3500 is 1.40:1, rear ratio is 4.10, tire size is 31.90 inches, then it looks like I will be popping 5900rpm @ 97.58mph in 3rd, shift to 4th, will pop 5900rpm @ 136.6.

Does that look correct (I suck at math..)

ALSO, looks like 1st:

Was (with small tires) with 3.42 shift at 5900 1st, was 37mph
With big tires, 4.10, 5900 shift will be at just under 34mph (help 60 foot times how much?)

2nd Gear shift:

Was 5900 @ around 64mph with small tires and 3.42
Will be around 59mph @ 5900 rpm (help 1/4 mile times?)




Thanks!

Mort

To maintain what you had your need to change your gears about 10% or the same you changed your tire diameter.

(31.9-28.95)/28.95*100 = 10.19%

3.42 + 10.19% = 3.77

So 3.73 gears will get you very close to what you had and my guess is most people here will tell you to go to 4.10 if you are going to bother to change. That will up your towing capacity and get you off the line a little quicker. It will also up your cruise rpm a little and should give you a little better throttle response. Depending on how you drive it may not hurt your MPG too much.

trever1t

iTrader: (14)

Do the 4.10s
I wish I had
you will too

shimp

Yeah, after doing the math, the 4.10's look really nice...

I drive the crap out of my truck, never worry much about fuel economy. If I was worried about that I would have bought a V-6...

Thanks for the encouragement to go 4.10. When the time comes to change, that is what I will be going with.