# I really need bigger tires (RPM)

Discussion in '1982-Present GM Diesel' started by Pookster, Apr 5, 2004.

1. ### Pookster1/2 ton status

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So, I plopped my calculations in:

Fifth gear: 0.73 x T-case high: 1 x Differential: 4.10 = Final Drive: 2.99

Tire size:245/75 16 (supposd to be like a 30" tire, mine measured 29")

So, to keep the optimal fuel band of 1900-2100 RPM, I would have to drive at... 55mph?? UNBEARABLE considering most of my highway driving is a minimum 65 and a max of 75.

so, I have to find a 33" outer for optimal flexibility at 65-70mph, and a 35" outer for optimal flexibility at 75mph.

I think I'll stick with the 33" outers for now.

Since the consensus is 285x75 for my 16" rim (unless someone knows something slightly bigger that is widely avaliable).

I shouldnt have a fitment problem, since Im replacing my fenders with fiberglass with a 3" flare.

Any other thoughts? Any brands? The kumho's look pretty affordable. The other choices would be the walmart liberator. (looks like a firestone??).

2. ### tRustyK5Big meanieStaff MemberSuper ModeratorGMOTM WinnerAuthor

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Measure the circumference of the tire and divide by 3.141. Use that as the true height of the tire. Theoretical height should be 30.46" or 95.67" circumference.

At any rate, if they're a little worn and work out to a true 30" using the circumference your rpm's would be:

60 mph...2011 rpm
65 mph...2179 rpm
70 mph...2346 rpm
75 mph...2514 rpm

With a 285-75R16 your theoretical true height should be 32.83". Assuming it's actually a little smaller we'll use 32.5".

60 mph...1856 rpm
65 mph...2011 rpm
70 mph...2166 rpm
75 mph...2320 rpm

I've been looking at the MT Baja MTX radial which seems reasonably priced even in the ~35" size. Also has a mild enough tread pattern it should be quiet and have decent longevity.

Rene

3. ### Pookster1/2 ton status

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This truck will most likely never see off road duty other than a fire road to a camp site. I dont even mind a highway ribbed tire.

4. ### Pookster1/2 ton status

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Did some research- the 285 75 16's they sell at walmart are the LIBERATORS- are made by either Michelin or bf goodrich.

so i will probably go with those.

5. ### imiceman441 ton status

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[ QUOTE ]
Did some research- the 285 75 16's they sell at walmart are the LIBERATORS- are made by either Michelin or bf goodrich.

so i will probably go with those.

[/ QUOTE ]

You can also go with 305/70/16 for a 32.9" tire
Or if you want bigger 315/75/16 for a 34.5" tire
or if you want skinnier tires 255/85/16 for 33.6" tire

I was doing a search for the same reason, for my crewcab tow vehicle.
I want tall thin highway or mild dirt road tires.

6. ### Pookster1/2 ton status

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Looks like the other three listed are a little rarer to find- I wanted to keep the tires as common as possible. Looks like the 285/75 is the same one used on the f250'. Which means in a pinch, I can go borrow a set of tires/wheels from any f250/f350. /forums/images/graemlins/smile.gif

7. ### arveetek1/2 ton status

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I just finished replacing my tires. I went from the worn out 29" (30 when new) 245/75/R16 tires to new 31" 265/75/R16. They're BG Goodrich Long Trail T/A tires I got from Sam's. They're the same brand and style I had before, and I got nearly 60,000 miles out of those tires. I really like them. Somewhat aggressive tread but no noise.

I decreased my rpms a little as well. I find this new tire size to be the best with 4.10 gears for everyday use....some towing, mostly highway driving. Cruises down the road at 75 mph and gets me 19 mpg. Haven't checked the mileage since getting the new tires.

Casey

8. ### 76_Cheyenne1/2 ton status

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Will 285/75/16 fit on a stock 98 2500? I currently have 265/75/16. Also looking for a little less rpm at cruising speed.

9. ### Pookster1/2 ton status

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From my understanding, yes.

10. ### arveetek1/2 ton status

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Yes, I think so. I think that's about as large as you can go without any lifts/body mods.

Casey

11. ### Diesel Dan1/2 ton status

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They'll fit, but might rub on turns in the front. Work with a guy who has 285/75-16s on stock wheels on his '99 K2500 crewcab.

Another option would be 255/85R-16s, same height but about 1" narrower.

12. ### ugly_blazer1/2 ton status

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[ QUOTE ]
Will 285/75/16 fit on a stock 98 2500? I currently have 265/75/16. Also looking for a little less rpm at cruising speed.

[/ QUOTE ]

A friend of mine has 285/75/16 BFG Mud Terrains on his Z71. He cranked the torsion bars and put an add-a-leaf in the rear. They fit fine without the small lift though, he needed add-a-leafs to pull a trailer and raised the front to match.

13. ### Pookster1/2 ton status

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Someone had stated in another post not to go bigger than 33" overall diameter- that going bigger would cause more wear on front end components-

But to my understand, these components are virtually identical on the H2- which come stock with 35" equavalents.

So... wacha all think about that?

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