Need some info on using H2 wheels/tires

[rat4go]

Folks,

I've stumbled on a new set of H2 wheels/tires (315/70-17) for a good price, and I'm in need of tires, so now I'm thinking.

I've read as many of the posts I could find with the search, but still have questions, so here goes...

I have an '03 GMC 4x4 Crew S/B. What do I need to do to make these 315's fit? Best I can tell, I need to trim the front facia a bit, and maybe lift the front of the truck a couple inches.

I've read that I can accomplish the lift via the torsion bars, but the ride will suffer. I've looked at the Cognito kit, but by the time I add that to the price of the wheels/tires, I coulda replaced my 285s on stock wheels and been money ahead.

What about the rear? Any mods required? 2" lift blocks?

I'm not willing to do this half a$$ed, but I have to keep the cost down or it'll never fly past the wife (seems she still remembers my new hunting rifle/scope and a few other recent purchaces :-( )

Any input would be appreciated!

Thanks!


Rich

[FJ40INTOW]

Have you considered other factors other than clearance? The taller tires will change your final drive ratio causing all the shift points to change for the Allison. For your final ratio to stay near the same you will need to go with 4.10 ring and pinions. Just my $0.02 worth. What says the list? FWIW I also bought the some H2 wheels without the tires. I bought 265-70R-17 E ATX Michelins. I have 48K miles on them and they look good enough to make it through the winter.

[rat4go]

Yep, I've considered the impact of the taller tires and I am all set there - just need to understand what it takes to make 'em fit correctly before I end up with tires I can't use!

Rich

[Buck]

The bigger tires didn't impact driveability to much. The truck tracks better, runs lower RPM's, more ground clearance and looks a lot better than the OEM "pizza cutters".

Check out my pics ;)
You can do this mod without the Cognito leveling kit. It does have some benefits but you will need green keys to clear those tires. H2 wheels have 5.5" backspace. It would be best to stay with the stock upper control arms(not Cognito leveling kit) with H2 wheels because of clearance issues. I needed to use the 1/4" wheel spacers but don't like them (wheels not hub centric)and may go with 5.125" backspace wheels next summer (Weld EVO)

Definately you will need:
1. Cognito idler/pitman arm supports
2. Green Torsion bar keys
3. New shocks highly recommended ;)

[rat4go]

Thanks for the reply! I understand the 'definately needed' parts list.

What drove you to the 1/4" wheel spacers? Inboard clearance to sway bar or susp components?

Any issues with fender/wheel well clearance? I understand I'll need to trim the lower rear edge of the stock facia as that part just touches my 285's right now.

Does it ride harsher with just greenkeys and no geometry changes or is that the basis for the shock recommendations?

Thanks again!

Rich

[Buck]

Originally posted by rat4go:


What drove you to the 1/4" wheel spacers? Inboard clearance to sway bar or susp components?

Any issues with fender/wheel well clearance? I understand I'll need to trim the lower rear edge of the stock facia as that part just touches my 285's right now.

Does it ride harsher with just greenkeys and no geometry changes or is that the basis for the shock recommendations?

Thanks again!

Rich 1/4" wheel spacers are part of the Cognito leveling kit. They are in the kit so you can still run factory wheel with the kit. The portion of the upper control arm (UCA) that houses the ball joint is very close to the wheel (where the balancing weights go) with high offset wheels. The last I knew they recommended a max 4.5" backspace wheels with their kit.

You are right about the air dam trimming. I also trimmed some steel away from the rear fender. That is not needed but I wanted to have front mud flaps and wheel offroad a little and didn't want any chance of rubbing ;)
I also moved the windshield washer reservoir ahead a bit as things were to close for my liking. Remove the driver side battery. There is a number of bolts holding the battery tray in place I found where the reservoir was bolted to the tray and removed that bolt only. Then I gently pushed the reservoir ahead and marked the hole location with a marker. Then I removed the tray and drilled a new hole.

The ride is stiffer, but not harsh by any means. There is also more unsprung weight with the bigger wheels/tires! With the green keys you are nearing bumpsteer because of the increased tie-rod angles. I only raised mine about 3/4" more than what the max OEM torsion keys would allow. CV angles are also increased. I am more concerned with the tie-rods than the CV angles. Bottom line the stock shocks are JUNK! Ride is noticeably better with the YELLOW Bilsteins.

For the rear end, mine sits level as is. I put air bags on the rear to hold it 1-1.5" higher in the rear when empty. That way you don't have to mess with blocks and longer shocks and all that garbage. When I tow the gooseneck I make the truck level with the air bags.