2nd Gen Non-Engine/Transmission Help- Wheel and Tire Brains needed

[#2_2nd_gen]

I really need help from tdr members. I apologize if this post is long, but I have been such a big CDT fan, I really want to get my issue fixed. This post is for real gear heads (and man I could use the help). Also, I have searched every post in the last 3 years for these answers, so any help would be great. I think I need direction. Let me give a little background.



I owned a ’97 CTD 4X4 5Sp with 3:54 gears LWB. It was perfectly geared for what I needed. It ran great, towed like a nut, ran good empty--- generally perfect. Did everything from horse trailer duty to mild / not so mild off roading, toy hauling, construction materials and extended cross country driving under no load. The sweet spot seemed to be 78 miles an hour with no load.



Then one day some excavator bought it from me on the street. It was a great deal for both of us. Mine had spent several winters in the mountains of Colorado and I drooled over a shinny 6 speed HO.



I now have taken delivery of a 2002 QC Short Box 6-speed with 4:10s. It seemed like a good way to go. The 6 speed has a taller drive number, so I made the call to go with the lower gears figuring some difference would be made up with the 6 gear, well the other would be made up in a larger tire. With only several thousand miles on it but here are my issues:



1. Its louder then heck going down the hightway compared to my 97. The engine is screaming for mercy and I fear that magical 78 MPH

2. My milage stinks (14 MPG indicated)



Here are my specific questions:

1. Will the truck mellow out with age

2. What tire size do I need to be at in order to have the same effective gearing as my ’97. The ’02 has a 6sp that is a . 6x final drive so it should act as a taller gear.

3. When I use the tire calculator on Randy’s Ring http://www.randysringandpinion.com/calc-tire.html

I come up that my stock tires are 31” calculated. However, when actually measure the tire it’s a 29”. I clearly understand that this has to do with the weight of the vehicle and the mounting. However, if I am figuring what tire to put on should I buy the calculated, indicated (sidewall) or measured (either loaded or unloaded) size.

4. It looks like the largest tire that I can fit (wihtout any hitting) is a 245/85/16 or 295/75-16. Is this true? Which has a larger diameter?

5. Many of you are going with the Rickson (or Alcoa?) 19. 5" wheels. If my only interest is tire size, would this get me anything. Sure- I know- I eat tires like breakfast cereal- too. So this does have some appeal.



Thanks again to all the TRD mebers fo your thelp.

 

[Ryan]

I think you need to consider new gears to replace the 4:10s. I f I remember correctly 6th gear on a 6spd and 5th gear on a 5spd are very close in ratios the big difference is there is an extra gear between 2nd and 6th on a 6spd. This is intended for quicker RPM build and to help keep the engine in the ideal torque range.

 

[RustyJC]

The NV4500 and NV5600 have almost the same 1st and "top" gear ratios as follows:



NV4500 1st - 5. 61:1

NV4500 5th - 0. 75:1



NV5600 1st - 5. 63:1

NV5600 6th - 0. 73:1



The primary benefit of the 6 speed is to tighten up the ratio splits (i. e. , to reduce the RPM change at each shift) between 1st and 6th gear for those of us who tow heavy. 6th isn't really any more of an OD than 5th on the 5 speed.



To get the effect of a 3. 54 gear, you would have to increase the diameter of your tires by a factor of 4. 10/3. 54 = 1. 1582. Therefore, if you have a 31" diameter tire now, you would need a 31" x 1. 1582 = 35. 9" tire to give you the equivalent of a 3. 54 axle ratio. This would, of course, require a speedometer/odometer correction as well.



Rusty

 

[#2_2nd_gen]

Thanks-- that was news I didnt really want, but will have to accept. I should just lean to the largest tire I can stuff under the body (without rubbing).

 

[Cooker]

The others have already offered some good advice. You will need to swap gears or go with a taller tire to achieve a lower RPM. I would try the tires first it is much less expensive.



The motor will mellow out a bit with the more miles you put on it. Your MPG's should also pick up a little bit, but with 4. 10 gears you should not expect the mileage you had with the 1997.



Best of luck with the new truck.

 

[#2_2nd_gen]

any idea on the tallest tire possible?

 

[GFoley]

A 255/85/16 will certianly fit. It is a bit taller than a 286/75/16. With either tire you'll drop in load rating from E to D. The 285 can carry more witght but not at the 80 psi that E rated tires give you.



If you have the wide factory aluminum wheels there should be no problems with mounting anything you have mentioned so far although I (personally) would not want to put a 245 on such a wide wheel. I liked the overall measurements on the BFG 295 tire but it is not stocked as widely as the 285 size is.



If you have the steel OEM wheels your dilema is different. Assuming they are the same 6. 5" width as my 99, only 3 tires are recommended for wheels this narrow. They are the 245/75, the 235/85, or the 255/85. A coule of posters have mounted the 285s on the OEM steel wheels without any excessive center wear problems.



Choices, choices:

Steel wheels - 3 tire choices

OEM aluminum - your call

or you could go all the way and get new wheels AND tires and chose both.



Hope this adds to the topic for you.



GLF

 

[BigUgly]

I've also seen Goodyear MT/Rs 305/70/16s on the stock 8" rims and it looked nice. One thing to remember if you intend to do any mild/moderate Offroading is to avoid the 19. 5s. It looks like I got the only 19. 5 that'll fit on these trucks with any decient tread, the Goodyear G124s..... which have been discontinued . Now, I can't seem to find ANY 19. 5s with a good AT/MT tread. It looks liek I may end up either going back to a smaller wheel , or a bigger one .

Josiah

 

[illflem]

Remember if you go with wider or more aggressive tires your mpgs may drop, you might not gain anything.

 

[TowPro]

I also think your mileage will go up some with age. I now have 10K miles on mine, but 90% of it is towing 10K lbs, so its well on its way to being broken in.



I started with an indicated 14mpg, now I am up to around an indicated 18. 5 mpg. This is at 65 with the cruse on the PA turnpike running empty.



But its not much different driving around the country.



many times I take my camper up to Hershey, then come home on saturday (empty) to work on my garage. I check it on the same 1. 5 hours of highway every time I do the trip.

 

[klenger]

The decision to change gears depends alot on how much high speed highway driving you do. I rarely drive my truck on the freeway for any distance empty. I am either in town empty, or on the highway towing the camper. For me, the 4. 10's work fine. I am not getting about 19 MPG around town and about 11 MPG towing. The other factor is do you have a 4WD or 2WD. A 4WD will cost double to switch gears. If you are doing it solely for fuel savings, I don't think you will ever get your money back doing the gear swap. My advice is to drive it more and see how it works out for you.