Hummer H3 38in Tires??

[Acer4LO]

Alright guys in a bit interesting situation and I need some pointers. I know this is an age old question, but I have some specific questions for this thread. Anyway I came across this really amazing deal for a wheel and tire combo, I am talking more than half price and these things are basically new. I think the reason why this set is so cheap is because of the bolt pattern. Obviously it is 6x5.5, so no jeeps and this setup is made for a trail rig not a mudder. Where the problem begins however is that they are 38 inches. Yes I know not the greatest idea, but I really want to do it anyway because it is my dream setup and this opportunity is way too good to pass up. One of the questions that I have this is about the gear ratio. I have an Alpha, so 4.10 gears. I did a calculation to determine the new gear ratio I would need and it is 4.72. Here is my math to double check:

4.10 (Alpha Gear Ratio) X 38in (New Size) / 33in (Stock Adv Package Size) = 4.72


From what I know the stock axles can only go up to 4.56 correct? If I were to upgrade to this gear ratio to 4.56 would I be okay or will I have shifting problems and will it suck at crawling? (Assuming I update the PCM) If I were to do this am I just asking for trouble from literally everything under the truck like the driveline, steering, and axles? Do note that I have the rancho, outfitter tire rods, and mayhem metal works steering rack clamp so that may help a bit. I already looked it up and each tire is pretty heavy at around 100lbs without the wheel. My tires are about 55lbs each now. Another question, if you guys advise against this, should I get them to use it later when I do a SAS? Or at that point should I be looking at some beefier 8 bolt axles like 06H3?

If anyone can help it would be appreciated!

 

[06 H3]

Personally the work needed to go from 4.10 to 4.56 is a lot for one ratio step lower (higher numerically.) so I’m not sure it’s worth the expense. The 10 bolt should be ok with 38s and I say that because the front diff will go before the 10 bolt.

Another reason I’m against 4.56 is a smaller pinion then 4.10s. That AAM will need all the help it can get so the bigger the pinion the better.

4low will be fine. That factory adventure package 4:1 will still be a great low range with 38s.

On road is may be sluggish. Do a tune, firm up the shifts.

Offroad: the bigger tie rods and steering rack clamp should help but you would be a guinea pig on seeing if those upgrades will make it last.
The bigger problem is the front diff.

I’m a believer in wheel it till she blows! Then upgrade

 

[Acer4LO]

Thanks for the help!! The front is a concern… I do have the cast iron axle even though it is an early 2008 model (Not sure I mentioned that before). Previous owner blew his aluminum diff pulling out cars out of the snow. Took it to the dealer and got a new one. Lol he kept it and included it when I got the truck. But yeah the biggest worry have if the front axle possibly cracking or the diff blowing up. Have you ever seen or heard of a H3 cast iron diff getting destroyed beyond repair? I know that would be one heck of an expensive fix to replace since they are pretty rare and Schwarttzy is already looking for one. Would realistically have to start a SAS project if that were to happen. Also I won’t really get to test the limits of this setup until the Rubicon this summer. I do go wheeling quite a bit, but we don’t have anything out here like you do you California.

 

[amrg]

You will be slow with 38s. Don't forget to take into account the weight of the tires/wheels. Those will play a huge roll on how big an impact you have with driveability.

If you want power, put a 6.0 or get an LSA supercharger on the 5.3 and with 4.10s you should be good.

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[4speedfunk]

4.56 is the limit for the stock AAM-7.6. I know several guys running re-geared Alphas with 35”s and they all seem to like it. 38” is a lot of tire for 4.56s and the trans will probably hunt between 3rd and 4th on the highway. Mileage and manners will suffer.

As for the cast iron diff...it is certainly better than the alum version but it’s not the golden egg. It doesn’t offer any more strength in terms of the ring & pinion. It simply fixes the flexing issues that the aluminum case has. Yes...I have seen blown-up cast iron versions. You can still get most parts from GM or AAM. Front e-locker parts are hard to find and Eaton no longer sells them. Instead you’ll have to deal with GM. You can convert an alum to cast iron by simply replacing the casting...everything bolts up the same. Definitely upgrade the outboard diff bushings to urethane to match the Rancho crossmember bushing. Those drop brackets need all the help you can give them.

Expect shorter hub, ball joint, and A-arm bushing life. You might also need to upgrade the shocks to handle the extra weight of the 38”s, as they may want to oscillate on washboard surfaces.

 

[Acer4LO]

Alright after going back and forth I decided to go for the 38s. Here is the setup:

38x13.50Rx18 Toyo M/T Tires on 18in TrailReady Baja Style Aluminum Beadlocks, Slim Ring (18 X 9, 6x5.5 Lug) Full Set of 5. Tires Have less than 2k on them, so brand new. Main reason I got these was because of the killer deal, way too good to pass up. Also motivates me to start doing some larger projects. Here are a few pics. I am going bolt them on next week to test them out. Few noob questions, how do I / what is the best way to update the PCM and tune up the shifts on the transmission so I can make this rig road worthy? I won't be running the current rig setup for too long. In the next year or two I looking to start a SAS, SOA, and truss the rear 10bolt (Like the SAS Aussie Rig).

 

[Mb30sdl]

Looking good


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[Acer4LO]

Looking good


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Yep! Going to test mount them this weekend. I won't be doing much with these tires yet until I do some more mods.

Things to add:
- Put on Mayhem metal works steering clamp
- New shocks
- Tune trans / PCM
- Add rear shackle lift
- Possibly do a SOA

 

[rsm688]

My H3 Alpha is on 37s with factory gears and runs fine. Outfitter Designs is working on a Dana 44 IFS front axle replacement and then you can gear it as low as you want. I'm going to get it and regear front and rear when they release it.

Definitely need upgraded steering rack mount, make sure you have 16mm tie rod ends, I would use the Siberian poly front control arm bushings. Scorpworks upgraded diff bushings. That will really help solidify the front end with all that extra weight. I am currently in the middle of installing all the above on mine plus new MOOG upper control arms and lower ball joints, new hubs, new OEM steering rack with 16mm tie rods, Bilstein shocks (for a 4" lifted chevy Silverado they fit the H3 with rancho lift because the rancho shocks suck lol). I also am putting in some new torsion bars just to have a fully fresh and brand new front end that's tighter and tougher than from the factory. Adding an add a leaf to my rear rancho springs (which luckily have not sagged even a drop). I'm gonna SOA the rear end eventually and I have the Predator ECM tune on my H3 (came with it but I would use PCM of NC as they did a great job on my other H3)

 

[cwedge411]

Im guess 2 months later and no pics he didnt get it to fit?

 

[Acer4LO]

Im guess 2 months later and no pics he didnt get it to fit?

Nope I got them. I haven't put them on, just tested them. Still need to do some things before putting them on.

Check out my build thread for all pics: http://www.hummer4x4offroad.com/for...73-Acer4LO-s-2008-Alpha-H3-Build-Thread/page4