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33in tires and stock gearing?

89 jimmy

89 jimmy

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I have 89 gmc jimmy and still trying to decide whether i should go with 33,s or stick with 32,s. i have 2.5 in lift so would fit,but with stock gears are the 33,s going to burn up my tranny over time? mostly use for dd and little offroad. Will 33,s look ok with 2.5 lift? Trying to balance light trail ability with good looks and reliable dd. thx.
 
What gears do you have?

If you're really sure they're stock the VIN, build sheet (often in the glove box) and a tag on the diff cover will tell you.

Otherwise your best bet is to pull the cover and give us the numbers off of the ring gear.
 
by "stock" do you mean 3.42's? you won't burn up your tranny with that combo if you keep it out of overdrive till you're at highway speed and have a good cooler.......be a tad bit more sluggish though, like 3.08's and 31's.....i'm doing 3.73's with 33" soon. 4.10's are better yet for a DD imo though.

2.5" lift is perfect for 33's, i'd keep it on a 7" or 8" rim. 32 is nice too, make for a capable truck.

on the "plus" side is the 700R4 has a low first gear so you will feel a touch more power than say with a TH400. so these trucks usually do just fine with a bit higher gear, especially in city driving......
 
I run 33's with a 2.5 on my 89 with 3.73. I don't think a 1" difference will be all that noticable unless you have 3.08's, in which case your truck is already a bit doggy/

Mine had 3.08 and 32's when I bought it as a bone stock, garage kept, grocery getter. With 33's, it was hard enough to get it to go In to od, much less hold it.

Mine is a mild built (by comparison) mostly dd and I tow my bass boat long distances at times. The 33's/3.73 work well for me and what I do, but I agree there is an argument for 4.10's for this size tire on a dd.
 
I'm running 33's with the stock 3.73, and it works like a charm. I do stay out of OD unless I hit the interstate. I never tow 2000lbs or more in OD. I do have the heavy duty engine oil cooler, but not one for the tranny yet.
I would definitely recommend modifying your DRAC to adjust speedometer for the 33's. Mine was off by 12%, but is now only 0.5% off. Not sure about '89 but my '91 its tied to ABS, Cruise and who knows what else.
 
I doubt the average person will be able to feel the difference between a 32" and 33" tire (assuming we are talking an equivalent type....not a skinny 32" all season vs. super wide 33" Super Swamper SX or Bogger). Point being is the difference between a 32 and 33" tire isn't going to require a gear change.

Back in the days I had the following combinations:
32" BFG Muds and 3.73 gearing (when I bought the K5)
Swapped to 33" BFG mud with the 3.73's
Swapped to 4.10's with the 33's
Swapped to 35" MT/R's with the 4.10

To be honest I never could notice any "seat of the pants" difference in any of the above combinations.
 
You should be fine. I ran 35's with 3.08s in my 1009 with the diesel and it was still ok. The new truck I have with the 3.42s and 32s feels like a race car.
 
gt1009 said:
You should be fine. I ran 35's with 3.08s in my 1009 with the diesel and it was still ok. The new truck I have with the 3.42s and 32s feels like a race car.
Click to expand...


Yeah but a diesel and a th400 is a completely different animal than say a 305 and a 700r4
 
I have a 305sb, 700r4, sissy 10bolts w/ 3.08 gears. I have been abusing my rig for years with 33's.-NO PROBLEM!
I just switched to 35's but haven't changed my gears yet; now I'm a bit nervous.
I have been driving around the neighborhood & on the highway a little bit. The 1st,2nd,&3rd gears feel fine but OD is a little slow.
 
Altitude must have made a huge difference for me 33 and the 3.73 stock gears was ok in town, but I couldn't use OD unless I was over 75 on the interstate I was talked into 4.56 which are snappy as all get out but I think that 4.27 would have been best for me.
 
How do I tell what gears I have now? Are all 89 gmc jimmy the same from factory? I dont see anything on the rear diff that says or in the glovebox. I also have a tranny cooler rated to tow 10,000 lbs.(I dont tow near that just small fishing boat) and stock engine oil cooler so I guess I should be ok with the 33,s. I do however have to climb alot of hills.
 
glad to hear you have a tranny cooler and tow a light boat....towing is a completely different topic. you'll be towing in D not OD anyway, unless you build that 700R4.

jack the rear up under the pumpkin.....mark your driveshaft with chalk and spin the tire twice...count how many time the shaft spins.....divide the number by 2 and that'll get you close in figuring out the gear ratio. do you have 32's now? thoses trucks could have come with 3.08, 3.42 or 3.73 gearing.
 
shovelbill80 said:
see how many times the shaft spins......
Click to expand...

Highjack on: I spun mine ( I have a locker so I lifted both tires) and the d shaft had 3 1/4 revolutions. Is there a 3.23:1 ratio?- or do you think it's 3.08:1 with a backlash throwing me off a little bit? :dunno:

Highjack off
 
I don't understand how the tire size effects the results of the "lift & spin" test. One revolution of the tire would be the same weather it's on 33's or 35's.
For example, if I took my tires off , marked my break drum, then spin it around 1 revolution ; wouldn't I still get the same results?
 
pblaze725 said:
I don't understand how the tire size effects the results of the "lift & spin" test. One revolution of the tire would be the same weather it's on 33's or 35's.
For example, if I took my tires off , marked my break drum, then spin it around 1 revolution ; wouldn't I still get the same results?
Click to expand...

Correct...tire size doesn't matter in the test...the actual gear ratio does not change because of a larger tire.

But the effective ratio does change when in actual use though because of the larger circumference of the tire....
 
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