[maxtest]

I was looking for some 30" muddies for a sierra and a friend offered me his 31s so I got them they are pretty much brand new and on -40 offset rims. I am wondering what lift would be best I already have stronger extended shackles at home but not sure if that will add enough lift?

[Gwagensteve]

Longer shackles do nothing to fit larger tyres.

2" body lift
Bumpstop spacing
Guard cutting

Or some combination of all three mixed to suit.

This is covered roughly every week.

[DarkHorse]

That's a lot of offset. Bye bye turning circle...

[fordem]

Gwagensteve wrote:

Longer shackles do nothing to fit larger tyres.

Curiosity question here (I don't own anything with leaf springs), and I understand why longer shackles are not the best way to approach a lift - but - won't longer shackles put more clearance between the axle and the frame, which would also mean more clearance between the axle and the body, which is what you need to fit larger tires?

What am I missing?

[Gwagensteve]

They do, until you flex the suspension. Then the axle moves into the same spot it could before the longer shackles were fitted and the tyres still foul.

[christover1]

On my Sierra, I did a shackle lift and longer bumpstops to suit, before doing proper suspension and body lift.
It worked for 29's nicely, but I had done a full proper lift before 31's went on.

[Gwagensteve]

And the bumpstops are the key, not the shackles. Regardless of how it's achieved, fitting larger tyres is all about fitting them at full suspension flex, not at ride height - somehow the tyre has to be kept away from the chassis/body under all circumstances, not just stationary in the driveway.

It's why I (glibly, and slightly misleadingly) say suspension lift has nothing to do with fitting larger tyres. Suspension lift might be useful to fit bigger tyres, because it might allow sufficient compression travel to be retained after bumpstop spacing has been fitted. It's the bumpstop spacing that's clearing the tyres though, the suspension lift is there to tune ride characteristics, and how much compression travel required is dependent on user preference. Whether the tyres foul on the body or not isn't user preference. It's quite possible to run bumpstop spacing at stock ride height, if you are willing to have very limited compression wheel travel. For low speed work that's no problem at all.

Steve.

[Gwagensteve]

christover1 wrote:

On my Sierra, I did a shackle lift and longer bumpstops to suit, before doing proper suspension and body lift.
It worked for 29's nicely, but I had done a full proper lift before 31's went on.

I understand what you mean here by saying that shackles aren't a "proper lift" (and they aren't) but claiming you required a "proper lift" to clear 31's is a bit confusing - I think in your case, a combination of guard cutting, bumpstop spacing, and body lift was used to clear your 31's. The fact you also ran spring lift is secondary IMHO.

Steve.

PS I know I bang on about this ad infinitum , but it's such a commonly held belief that you can "slap some 2" springs and 31's on" and it's just not true. I think it's partially because the car looks about right on 2" springs and 31's, because 31's aren't all that big by "big car" standards, and if you don't flex the car up at all they "sort of" fit, especially with some of the insanely stiff aftermarket springs available. a 31" tyre is near enough a 20% increase in diameter. Nobody thinks they can put 2" springs in a cruiser and bolt 38's on, so I have no idea why people think you can do it with a sierra (for the same % tyre size increase)

[christover1]

I didn't mean I did a proper lift to fit 31's.
I meant I had already done a proper lift before fitting 31's.
So I can only speak for the 29's re shackle lift.
After proper lift my 31's fitted fine until offset change, then front inner guards needed trimmings.
(or I could have extended bumpstops more I suppose)