6" Lift w/ 33's
07-10-2018, 06:45 PM
#11
Renaissance Honky
Quick math says 4.88's would be good and feel kinda sporty. 2,300rpm @ 70
Edit: Checked the specs on a Kumho Road Venture in a 35x12.5x17" size. 608 rev/mile
General Grabber x3, same size: 594
Firestone Destination M/T2, same size, 603. Let's use the Kumho as a base.
608 rev/mile
60mph = 1 mile/minute
60mph = 608 RPM at the tire
x 4.88:1 gear ratio: 2,967.04 rpm driveshaft.
x0.7:1 OD ratio: 2,076 RPM @ the crank at 60mph
x (7/6) to get 70mph: 2423 @ 70 mph
If this was a 5.4, that would be about 2,070 rpm @70mph to get the same piston velocity. That's just a shade higher than what I see with my 3.55:1 gears and stock tires. It's not bad, but the top of 2nd gear is 80mph. If this is going to be more of a fun vehicle than a highway vehicle, you might want to look for a bigger number than the 4.88's. I cant say I have a problem with the gears in my truck, but I could see the appeal of 3.73 or 4.10's for towing or playing.
Short version: 4.88's would be better for your combo than 4.56's.
Edit: Checked the specs on a Kumho Road Venture in a 35x12.5x17" size. 608 rev/mile
General Grabber x3, same size: 594
Firestone Destination M/T2, same size, 603. Let's use the Kumho as a base.
608 rev/mile
60mph = 1 mile/minute
60mph = 608 RPM at the tire
x 4.88:1 gear ratio: 2,967.04 rpm driveshaft.
x0.7:1 OD ratio: 2,076 RPM @ the crank at 60mph
x (7/6) to get 70mph: 2423 @ 70 mph
If this was a 5.4, that would be about 2,070 rpm @70mph to get the same piston velocity. That's just a shade higher than what I see with my 3.55:1 gears and stock tires. It's not bad, but the top of 2nd gear is 80mph. If this is going to be more of a fun vehicle than a highway vehicle, you might want to look for a bigger number than the 4.88's. I cant say I have a problem with the gears in my truck, but I could see the appeal of 3.73 or 4.10's for towing or playing.
Short version: 4.88's would be better for your combo than 4.56's.
Last edited by Eric Kleven; 07-11-2018 at 03:53 PM.
07-11-2018, 02:16 PM
#12
Platinum Vendor
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07-11-2018, 03:53 PM
#13
Renaissance Honky
07-11-2018, 04:54 PM
#14
Member
Thread Starter
Thanks for the help! I don't wheel, it will be a daily with city, highway driving mostly. It will also be used for camping/over landing some as well. I think with a 4.6L, the 4.88's make sense as long as I'm not driving across states.
Downside is I do plan trips from OR to UT and CA and other areas, so highway would suck with the 4.88s right?? I'm planning on running Mickey Thompson Baja ATZ P3s after I lift.
Downside is I do plan trips from OR to UT and CA and other areas, so highway would suck with the 4.88s right?? I'm planning on running Mickey Thompson Baja ATZ P3s after I lift.
07-11-2018, 06:06 PM
#16
Renaissance Honky
Highway won't be bad at all. 2,400rpm on the 4.6 is pretty close to the piston speed of a 5.4 at 1,900-2,000. These engines don't have a problem with the RPM. The relationship between your exhaust and ears might be a different matter, however.
07-11-2018, 07:47 PM
#17
Member
Thread Starter
Alright well I'm not sure if you're a genius or what, but I'm sold on the 4.88's! Thanks for all the info, really appreciate it! Are you an engineer, or how do you know this stuff?
07-12-2018, 11:30 AM
#18
Senior Member
I had 33s when I first installed my 6" lift a month ago and they looked too small. 35s look just right. Im running the stock LS 3.55 gears but want to switch to 4.10. I have the 5.4 engine
07-12-2018, 11:32 AM
#19
Senior Member
From what Ive seen 4.88 is overkill unless youre going to run 40 inch tires or something similar in size. The formula i use is New Gear Ratio = [(new tire size/original tire size) x Original gear ratio]
07-12-2018, 12:48 PM
#20
Renaissance Honky
You'd be right on for the 5.4. 4.30's or 4.56's would work pretty good there.
Last edited by Eric Kleven; 07-12-2018 at 12:57 PM.