3.73's or 4.10's for 315's?
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Joined: Aug 2004
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From: Little Elm, TX
3.73's or 4.10's for 315's?
Hi everyone, newby here with my first post….
I’m looking into getting my first Dodge CTD and I don’t want to make the wrong choice for the rear end gear. I’m not even sure I will ever go with the 315’s but I don’t want to lose this option before I drive it off the lot. If you were to buy a new 2500 4x4 6-speed and you planned on putting 315’s on it what gear would you go with? I won’t ever pull more than maybe 5000lbs and that wouldn’t be very often. Are the 3.73’s adequate? For a gasser I believe you should always get the lowest available gear ratio (especially with a 35 inch tire) to get the best performance but with a diesel there is so much more torque I don’t see that it would make much difference and would probably help with the mileage because of the lower RPM.
Thanks!
I’m looking into getting my first Dodge CTD and I don’t want to make the wrong choice for the rear end gear. I’m not even sure I will ever go with the 315’s but I don’t want to lose this option before I drive it off the lot. If you were to buy a new 2500 4x4 6-speed and you planned on putting 315’s on it what gear would you go with? I won’t ever pull more than maybe 5000lbs and that wouldn’t be very often. Are the 3.73’s adequate? For a gasser I believe you should always get the lowest available gear ratio (especially with a 35 inch tire) to get the best performance but with a diesel there is so much more torque I don’t see that it would make much difference and would probably help with the mileage because of the lower RPM.
Thanks!
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Joined: May 2004
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From: Caistor Centre, ON, Canada
Larger, heavier tires that are wider (more rolling resistance) almost never help mileage. It takes more power to get them rolling and more power to keep them rolling because the rolling resistance is considerably higher. That said, I think the lost mileage would be barely noticeable with 315's because of the CTD - but don't expect it to help. I think you could run either 3.73 or 4.10. If you were towing frequently with that tire I would go 4.10. No matter what, I would personally run 4.10's if I knew I was going to have 315 tires but if you are not running 315's, 4.10 would be a waste for your application - you just don't need them. There is no need for that gear unless you were intending on towing 10,000+lbs frequently or you wanted run a larger tire like a 315. Even then, many guys here will tell you they are happy with their 3.73's.
Just my .02
Just my .02
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I was in your shoes and opted for the 4.10's. In retrospect I should have gotten the 3.73's.
As you mentioned, our past experience with gas powered vehicles does not apply. The torque produced by this engine is awesome. My truck is a 6-speed with 315's. I live in very mountainous country, I still find myself reaching over to find 7th gear on a regular basis. On the other hand, from multple disussions on this board, milage seems to be much more dependant on speed than gear ratio for these vehicles. It doesn't seem to matter what ratio you run, there is a dramatic decline in milage as you compare 55 mph vs 65 mph vs 75 mph vs 85 mph. Others have been concerned regarding the effect to the engine with running 2500 rpm down the interstate all day. That's not really an issue. This same engine in marine applications routinely spins at 3,000 rpms day and night without ill effect.
As you mentioned, our past experience with gas powered vehicles does not apply. The torque produced by this engine is awesome. My truck is a 6-speed with 315's. I live in very mountainous country, I still find myself reaching over to find 7th gear on a regular basis. On the other hand, from multple disussions on this board, milage seems to be much more dependant on speed than gear ratio for these vehicles. It doesn't seem to matter what ratio you run, there is a dramatic decline in milage as you compare 55 mph vs 65 mph vs 75 mph vs 85 mph. Others have been concerned regarding the effect to the engine with running 2500 rpm down the interstate all day. That's not really an issue. This same engine in marine applications routinely spins at 3,000 rpms day and night without ill effect.
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Joined: Aug 2004
Posts: 196
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From: Saskatoon, SK
Get the 3.73's. 75 mph @ 2000 rpm with the 315's is a nice cruising speed. I have towed 8000 lbs with my truck and it has no problem towing in overdrive. If I towed anything significantly heavier I would just pull in 5th which is about 2300-2400 rpm @ 65mph. This will provide all the power you need, and 2400 rpm is still a reasonable cruising rpm.
Carl
Carl
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