There is a heap of info on the forum here about backspace v's Offset. basically, offset is measured from inner lip to inner lip, so a 7.5" rim is 7.5" from inner lip to inner lip. Howeevr backspace is measured from the outer lip. A 7.5" rim will actually be about 8.5" wide measured at the two outer lips. Check this website out http://www.rimsntires.com/specs.jsp
On a slightly different topic, it mentions that the wheels for the JK are 7.5" in width and have an offset of +44mm. Am I calculating this wrong or does that equate to a Backspace of 5.5"? For ages I had been under the impression the stock wheel BS was more like 6.25". If it is just 5.5" then that means going to a 5" BS after market rim would not exceed the 50mm allowable increase in track width... This is something that has kept me from getting a set of steelies for my JK for a while...
I just did a rough calc though so may be wrong...
7.5" = 187.5mm
centrepoint of rim = 93.75mm
+44mm offset = 137.75mm from inner edge of rim
137.75mm from inside of rim = 5.51" BS
The RTA data is not correct. A brand new JK will measure about 760mm from bottom lip of 17" rim to underside lip of flare, back and front on the left hand side. The right hand side will sit about 10 to 15mm lower so always use the LHS for measurements. Some will measure 755 and some 770mm, but most are 760mm. I measured mine when brand new, and have measured many others at the dealership just to make sure of my lift height when I had a warranty claim. They are all the same when new, give or take 10mm.
The stats for the 2 door JK com in at 525mm front and 563mm rear, measured from the centre of the wheels to the lip of the mudguard, for both Petrol and Diesel variants.
Mine, an 8 week 2000 km old 2 door with just installed mopar 2in springs comes in at 583 front and 572 rear. So the figures that the data sheets are based on seem to be quite strange. Means mine that sits pretty level is actually 47mm lifted front and only 9mm lifted rear! Go figure!!
Its interesting that many are 10 to 15mm lower on the right. I can understand this to account for the camber of the road etc, but mine was not. Mine were exact to the mm left to right with the stock springs?
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Cheers, Dave :)
2010 JK, then a 2015 KL Trailhawk, now a 2017 GC Trailhawk!
17x8 steel wheels with 5"BS will be fine on your truck up to but not over 35's...
With this back space you may get slight rubbing in the front and rear at full flex depending on lift and bump stop lengths...
The Ideal is 4.75 BS but they are hard to find...
4.5 is easy to find but you will need extended flares and you will be outside ADR if that means anything to you...
You will have no probs at all if just running 33's or should I say 11.5"or less wide tyres IE 285 to 305 max... 12.5"wide is where the rubbing will start.... thats most if not all 315's or 35's... and over...
On a slightly different topic, it mentions that the wheels for the JK are 7.5" in width and have an offset of +44mm. Am I calculating this wrong or does that equate to a Backspace of 5.5"? For ages I had been under the impression the stock wheel BS was more like 6.25". If it is just 5.5" then that means going to a 5" BS after market rim would not exceed the 50mm allowable increase in track width... This is something that has kept me from getting a set of steelies for my JK for a while...
I just did a rough calc though so may be wrong...
7.5" = 187.5mm
centrepoint of rim = 93.75mm
+44mm offset = 137.75mm from inner edge of rim
137.75mm from inside of rim = 5.51" BS
Is that the correct calculation?
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"Never get so busy making a living that you forget to make a life!"
2 Door Red Rock Renegade.
and if you look at most of the lift kits form the US all have bump stop mods which return them to standed in most cases.
not shore if im right but it is food for thought.
will look into it some more.
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back Space
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