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Tire size/gearing questions

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07coupegt

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I am going to be installing a Tough Country 3" lift on my 1991 k5 in the next few days, but am not sure what size tires to buy. The truck has a 350tbi, 700r4, np241, and 3.08 gearing. I was going to buy 33" tires, but after doing some reading on the site, am not sure if they will work with my stock gearing. I don't want to change axles or gears. So will 33" tires work okay, what about 31". Right now the truck has 235/75R15 tires (aprox 28.5").
Thanks.
 
if you lift it you'll want bigger tires. If you get 33's you'll eventually want 35's. Re gear it. Its not that bad. plus you have overdrive. you'll be good.
 
Depends what you're doing with. I had 38s for 7 years and just put 33s on it cause my fullsize is retired from the trails. 308 is doable. I ran 38s and 273 gears on my first truck
 
Sure, it will work. Not like the truck will stop running or something. That gearing is far from optimum though and if you went with 33's and kept the gearing I would run with the transmission in D (drive) and keep it out of overdrive.

The quickest and cheapest solution would be to just find a set of axles with 3.73 gears and swap them in. This was the lowest factory gearing in 1/2 ton 10-bolts of this era that I am aware of. I know this is not the optimum gearing but you should be able to buy a complete set of axles pretty cheap and just slap them in.

Of course this isn't considering if you wanted to regear the current axles, which I would have a hard time spending the $$ on the 10-bolts. The next step is axle swaps.

I think 31's with a 3" lift would look pretty funny.
 
Yeah, I was kind of thinking that 31s would look too small with the lift. According to a calculator I found online, with stock tires and gearing, my truck is only running at 1500rpm at 60mph. With 33" tires, it would only be running at 1300rpm at 60mph and 1500rpm at 70mph. If I leave the truck in third, it will be running at 1800rpm at 60mph with 33" tires. Will the torque converter still lock up when the tranny is in 3rd? I don't want to swap axles, but it looks like it might be the best option.
 
I re-geared my 89 Burb from 3.42 to 4.11 and run 285/75R16's. It made a huge difference and it wasn't that hard to do! I bought the tools and it still came out tons cheaper!! You don't have to be a rocket scientist to do it, but being a jet engine mechanic helped! :D
 
It depends on what your wanting to do. If your gonna run a lot of trails and do some crawlin then you wanna swap to different axles. But I just ordered 4:56 gears for my 10 bolts. Im not gonna do much trail or crawlin but Im definatly plannin on some camping stuff and Ill prolly go down to Glamis or up to Pismo beach every now and then, just not planning on ringin it out offroad. Im going to drive mine everyday to work 40 minutes or so up and down a grade. All depends on your plans.
 
I ended up ordering a 2.5" skyjacker kit, and just got 32x11.5 bfg mud terrain km2s mounted. The truck drives good in the city, but I really need to gear it down. On the highway, if I am driving into the wind, I can't go over about 65mph, or the torque converter wants to unlock. If I drive in third it works fine, but the rpms are then a little higher than I would like. I have thought about swapping axles, but will most likely have the local 4x4 shop regear my current diffs instead, as the stock 10 bolts are more than enough for what I will be doing. My question is, what gears should I get? I am thinking 3.73 would be good, or should I get 4.10? I don't want it to be revving too high when cuising at 75, but I don't want it to be constantly shifting either. Being that it does alright with the 3.08s should 3.73s be low enough for it to stay in overdrive? if 3.73s will work, I may be able to find another set of 10 bolts to swap in instead of changing gears.
 
You could probably buy a pair of stock 3.73 gear 10-bolts for $200-$300 and bolt them in. I wouldn't be surprised if you got to $1,000 between parts and shop labor to regear your current axles.

With 32's and 3.08's you should only be running around 2,200 rpm at 65 mph in D which is just about right, and it's only a couple hundred rpm higher than you would run with 4.10's but using overdrive.

07coupegt said:
I ended up ordering a 2.5" skyjacker kit, and just got 32x11.5 bfg mud terrain km2s mounted. The truck drives good in the city, but I really need to gear it down. On the highway, if I am driving into the wind, I can't go over about 65mph, or the torque converter wants to unlock. If I drive in third it works fine, but the rpms are then a little higher than I would like. I have thought about swapping axles, but will most likely have the local 4x4 shop regear my current diffs instead, as the stock 10 bolts are more than enough for what I will be doing. My question is, what gears should I get? I am thinking 3.73 would be good, or should I get 4.10? I don't want it to be revving too high when cuising at 75, but I don't want it to be constantly shifting either. Being that it does alright with the 3.08s should 3.73s be low enough for it to stay in overdrive? if 3.73s will work, I may be able to find another set of 10 bolts to swap in instead of changing gears.
Click to expand...
 
I've got 32s and 4.10s now. I'm actually going to go with 4.56s when I drop in a dana 60 front (and I'll stay with the 32s).
 
My 87 has 3.42s and I'm running 31s with no lift and it seems to be about right. They look a little small but with no lift it's okay. I plan on swapping 3/4 ton axles with 4.10 gears, a 2in. lift and run 33s. I often tow a trailer with mine so I'm going for a little lower geared.
 
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