Gear ratio question - Dodge Diesel

Andrew k · 05-05-2005, 11:07 PM

From what I've heard 3.73 gears and 37" tires will put a six speed at around 1600rpm at 70mph. I do mostly empty highway miles so woudnt the 3.73s actually be better for me than 4.10s? I am not out so much for acceleration but definately don't want to lose speed pulling moutain passes. What do you guys think?

BigBlueDodge · 05-05-2005, 11:26 PM

1600 RPM's sound a little low to me. I run BFG 315/70/17 -> 34.4" tires and at 70 I get a hair under 1900 RPM's. I have 3.73 gears as well. With 37" I wouldn't think it would drop 300 RPM for just 2 inch diff. I'm guessing you will be around low 1800's for 37's at 70 MPH. For empty driving on highway, the 3.73 gears and big tires, the 3.73 gears will let your engine run at lower RPM and thus better MPG. Empty, I don't suspect you will lose any speed pulling mountain passes. Put a trailer with any sizable weight, and I'm willing to bet that you you are gonna need to drop a gear on mountain passes. Big tires look fantastic, but without regearing you are loosing torqe.

blown32 · 05-06-2005, 07:11 AM

I also have 315s and 3.73s. If I had it to do over I would go with the 4.10s

Empty is great, no down shifting and I can pull the passes faster than I can take the corners. But even with 8K enclosed car trailer it could use more gear and I only got 10.2 mpg on my last 250 mile tow at 65-70 mph.

05-05-2005, 11:26 PM	#2
BigBlueDodge Registered User Join Date: Mar 2005 Location: DFW, TX Posts: 331 My Photo Gallery My Classified Ads	1600 RPM's sound a little low to me. I run BFG 315/70/17 -> 34.4" tires and at 70 I get a hair under 1900 RPM's. I have 3.73 gears as well. With 37" I wouldn't think it would drop 300 RPM for just 2 inch diff. I'm guessing you will be around low 1800's for 37's at 70 MPH. For empty driving on highway, the 3.73 gears and big tires, the 3.73 gears will let your engine run at lower RPM and thus better MPG. Empty, I don't suspect you will lose any speed pulling mountain passes. Put a trailer with any sizable weight, and I'm willing to bet that you you are gonna need to drop a gear on mountain passes. Big tires look fantastic, but without regearing you are loosing torqe. __________________ BigBlueDodge SOLD - 2004.5 CTD QC 4x4 6sd (She will be missed) 2006 3500 Mega Cab SLT 4x4 Auto Inferno Red

05-06-2005, 07:11 AM	#3
blown32 Registered User Join Date: Aug 2004 Location: Cheyenne Wyoming Posts: 322 My Photo Gallery My Classified Ads	I also have 315s and 3.73s. If I had it to do over I would go with the 4.10s Empty is great, no down shifting and I can pull the passes faster than I can take the corners. But even with 8K enclosed car trailer it could use more gear and I only got 10.2 mpg on my last 250 mile tow at 65-70 mph. __________________ 2004.5 2500, 6 speed, 4x4, 3.73, LWB, HTT 62/65/13ss, AFE stainless exhaust manifold, 245/70/19.5s, Smarty POD, Banks high-ram, F&R MagTech covers, AEM dry-flow system, armothane rockers, 304 ss step bars (wife is 5'2"), Diamond Eye 5" to 4" duals, SRT10 piller and Autometer EGT, Boost gauge on steering colum, installed tow mirrors, spray coated Warn flares, flat bed, Curt 20K fifth wheel hitch, other do-dads, Powershot 2000 propane injection (still not installed, not sure I'm going to).

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