What do you have to do to fit 39s or 40s?

6018 Views 15 Replies 11 Participants Last post by jeffmarion, Jan 20, 2009

RoCk-NeSs MoNsTeR

Discussion Starter · Jan 14, 2009

So I see that some of you are running 39s and 40s for tires. I'm thinking of running these myself but have some questions. How big of a lift are you running? What other mods have you done to fit your rubber? Any rubbing? Stock axles or aftermarket? If your running stock, how are they holding up? What kind of wheeling do you usually do?
Thanks for any info you can give me on this. :beer:

:beer:

1 - 16 of 16 Posts

WTF_LOL

· #2 · Jan 14, 2009

100dollar man removed his front drive shaft on the trail to run his 38's :thefinger:

:thefinger:

What axle are you running in front?

HAve not heard much of an issue on the rears. I think that size is too large for a d44 personally. I would say 60 to run that size. MAybe a very well built d44...

RoCk-NeSs MoNsTeR

Discussion Starter · #3 · Jan 14, 2009

WTF_LOL said:
100dollar man removed his front drive shaft on the trail to run his 38's

What axle are you running in front?

HAve not heard much of an issue on the rears. I think that size is too large for a d44 personally. I would say 60 to run that size. MAybe a very well built d44...

Stock Rubicon axles. Locked D44 F&R.

CONVICT

· #4 · Jan 14, 2009

Wheel it till you break it, then upgrade, if you break that, upgrade again.

rubirobv

· #5 · Jan 14, 2009 (Edited)

AZ Bulldog would be someone to ask. He's running 40s with a D30 on the front. I don't no the specifics of his build. He has a very nice looking rig.

He wheels alot and is surprised the axles have lasted over a year. He says the D60s are going in when they give out.

I'm guessing that he's not very hard on the throttle.

Broncojohn

· #6 · Jan 14, 2009

CONVICT said:
Wheel it till you break it, then upgrade, if you break that, upgrade again.

x2

:beer:

Jason

· #7 · Jan 14, 2009 (Edited)

I've got D60 axles front and rear and a 4 inch lift with 2" spacers (or 2 1/2" spacers...can't recall which). I'm also putting in longer shocks (Fox). I trimmed the inner fender wells and put Xenon fender flares on (not sure if doing those things helped with keeping it from rubbing or not).

I took the Jeep to Tellico to test it out and didn't have many problems with rubbing, but I was on 37" tires at the time. I haven't done any trail rides with the 40" tires yet.

VSDPV

· #8 · Jan 14, 2009

For 40" tires you need at least 6" of lift, aftermarket high clearance fenders, stubby front bumper, wheels with at most 4.5" of backspace, new CV driveshafts, 5.38 gears, chromoly axles shafts, reinforced Rubicon 44 axles (but D60 axles are preferred).

If you wheel hard, don't expect the D44 to last very long.

4ws.com

· #9 · Jan 19, 2009

To fit 40s...get some flat fenders (or modify [cut] your stock ones) and get a 4" or so lift. You'll probably have to do something with the bumpers if you still have the stock ones.

I wouldn't want to drive a JK with 40s and the stock engine. 37s were miserable enough, even with 5.13 gears.

suthernjeeper

· #10 · Jan 19, 2009

40s, well if u want a low COG u could always run stock ride height with a custom coilover suspension and take the plastice fenders off and trim a little. o and 60 axles with 5.38s :smokin:

:smokin:

jeffmarion

· #11 · Jan 20, 2009

I am planning on 40's (39.5" Iroks).

I am running a Poly 4.5" lift

I have already removed my fender flares and looks like I have enough clearance just with this. Will probably adjust bump stops if necessary, trim some sheetmetal, or install a 1" body lift.

I will install alloy shafts front and rear and run it till it breaks then upgrade.

RoCk-NeSs MoNsTeR

Discussion Starter · #12 · Jan 20, 2009

4ws.com said:
To fit 40s...get some flat fenders (or modify [cut] your stock ones) and get a 4" or so lift. You'll probably have to do something with the bumpers if you still have the stock ones.

I wouldn't want to drive a JK with 40s and the stock engine. 37s were miserable enough, even with 5.13 gears.

My current setup on the Rubicon is 4" TF lift, Mopar RC bumpers (front stubified, rear clearanced), cut the pinch weld, Xenon flat narrows and BFG MT/KM2 37's. think 39.5 IROKs will fit?

PhilD

· #13 · Jan 20, 2009

jeffmarion said:
I am planning on 40's (39.5" Iroks).

Those Iroks are pretty heavy at 99 lbs each, your axle shafts may not appreciate that weight when they break free and spin.

I am running a Poly 4.5" lift.

I have the same lift + 3/4" spacers and my 37's get hard into the wheels wells and Xenon fenders at times. I suspect you may have to run longer bump stops with 39.5's or 40's and rely more on droop, which isn't necessarily a bad thing.

My 37" KM2's will likely need replacing some time this year, and I'm in two minds whether to go with 37's again or step up to some 40's, but I'm pretty certain I'll be going with KM2's again.

PhilD

· #14 · Jan 20, 2009

WTF_LOL said:
I think that size is too large for a d44 personally. I would say 60 to run that size. MAybe a very well built d44...

I pretty much agree, I think 40's driven lightly will be okay with beefed up 44's, but if you drive hard then some 60's are likely in your near future.

WTF_LOL

· #15 · Jan 20, 2009

PhilD said:
Those Iroks are pretty heavy at 99 lbs each,

Yikes!

To put this into perspective, 99 lbs on those iroks as compared to KM2 37's at about 70ish. I would say eben though the biggest aspect is the leverage the weight plays a big part. I would go 60 to run those

jeffmarion

· #16 · Jan 20, 2009 (Edited)

PhilD said:
Those Iroks are pretty heavy at 99 lbs each, your axle shafts may not appreciate that weight when they break free and spin.

I have the same lift + 3/4" spacers and my 37's get hard into the wheels wells and Xenon fenders at times. I suspect you may have to run longer bump stops with 39.5's or 40's and rely more on droop, which isn't necessarily a bad thing.

My 37" KM2's will likely need replacing some time this year, and I'm in two minds whether to go with 37's again or step up to some 40's, but I'm pretty certain I'll be going with KM2's again.

Yeah I already looked into this. The 99lbs are for the Radials... I will be getting the bias ply. The Bias is 84 lbs. Thats only 3 lbs heavier than the 37-12.50 Irok radials I'm running now.

I know I will be on borrowed time, but like I said run it till it breaks then upgrade

As far as rubbing goes. I have not had any issues with mine rubbing at all with the poly 4.5 and the 37's and full factory flares

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