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Overdrive ratio- 700r4?

F

Foy

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Raleigh, NC
Hi guys-
I'm thinking about putting some taller tires on my stock 1990 K1500 Suburban. It's a daily driver, not wheeled except for on the beach here in NC. The truck is running better than it has in a long time, and even with 182,000 miles on the 350, the cruising power/torque are great. I don't want to mess up the highway cruising by putting too tall of tires on it, so I want to be able to calculate the RPMs that she'd turn at 65 mph, after adjusting for the taller tires. What I'm missing is the locked-up final drive ratio of the 700r4's overdrive. Dad says he thinks it's a 20% gear, so 0.80/1.00. Is that correct?

By the way, I'm thinking of something like 32-33" tires, non-aggressive tread, something like 11 to 12 x 32 to 33, and they'll need to fit on my OEM Silverado alloy wheels.

Thanks for any help on the o/d ratio. I've got the RPM formula covered.

Cooper
 
Actually I believe it's .70, but an online search should also yield the gear ratios of the 700.

What gears are you running? Personally I wouldn't consider 33's on a truck with 3.42's and overdrive. You'd cruise 60 in 3rd gear.
 
Correct. .70 is the overdrive for a 700-R4. Also, with 3.42's I would not go bigger than a 32x11.50R15 Plus your wheels are only 7" wide. The 11.5" should be pretty much max on that wheel.

John
 
Stock tire on that truck is a 235/75R15. That's right around 29". For you to keep it in good cruising condition, don't go any bigger than 31". A 31x10.5 would really add the look you want without hurting crusing characteristics that much. I drive the exact same truck as you stated (90 K1500 suburban, 700R4, 3.42's - except for I'm running a 4" lift), and the 33's I have on there really mess with freeway driving.
 
[ QUOTE ]
Plus your wheels are only 7" wide.

[/ QUOTE ]

I thought it was finalized that all 1/2 ton 4wd trucks had 15x8's, while the 15x7's were only on the 2wd variants?
 
Same as Heavy4x4, I too have a '90 'Burb with the 3.42's....I took the 31's off beforereally using them, and went with some 32's I had laying around....I didn't even use the OD even on the highway, it just wasn't a happy combination....

Now with 4 inches of lift and 35's I am swapping to 4.56's to get back some driveability....I say 31's.....
 
I must go with a 10" rim then, I don't like how the 12.5 wide tire sits on the 8" rim......
 
I've ran 33's with the 3.42 gearing and 3.73 gearing. In my K5. I wouldn't do it in a Sub though. I was always a dog on the hills with both gearsets and how much more does a Sub weigh more than a K5? Definately think about moving another gearset up.
 
I have a set of the stock aluminum wheels from that era. I am 99% sure they are 7" wide, but I'll double check tomorrow. If I'm wrong, please disregard my commments above. /forums/images/graemlins/ignore.gif /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

John
 
wheel width thread

Only one I could find. But from other threads, looks like AL wheels were 15x7, steel 4wd were 15x8. 2wd must have been 15x7, and there is even reference to 15x6, but it didn't appear that was confirmed.
 
I have 3.42's and 33's on my Jimmy. Its a little doggy on hills. I can cruise 75-80 on the interstate and only turn 2200 RPM in OD. Is that bad? It doesnt ever come out of OD by itself in the mountains but it is always coming out of lockup so I can keep the speed up on hills. Sometimes I pull it out of OD so I can get up the hill quicker. So is there anything to be concerned about with my gear/tire combo?
 
Not if you are happy with it, just put in and watch the trans temp gauge....

My driving is mostly in town and two lane, I want to get back some performance....
 
I did mean the AL were 7". I checked and there 7". The steelies are 8" for sure /forums/images/graemlins/thumb.gif

John
 
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