Lift and Tyres of your JK

[JasperJ]

Originally Posted by jktom

The 30% rule says something like you can only increase your ride height by 30% of wheel travel, and wheel travel is measured at rest between the bumpstops, it does not mention asking the manufacturer for the specifications. From memory a new JK has about 60mm space in the front between the two bump stops, so that leaves room for a 20mm lift. There has been much debate on how to measure wheel travel, such as jacking the car up, and let it down to full droop, take that measurment, then use 30% of that, which would probaby (at a guess) allow 3 to 4" of lift. But it has been stated by QT that you measure between the bumpstops at rest.

That's actually incorrect. The document he was referring to should have been the AIS INFORMATION SHEET No. 18 FITTING OF BODY LIFT KITS AND SUSPENSION HEIGHT MODIFICATIONS TO MOTOR VEHICLES, you can find it here to read yourself. http://www.transport.qld.gov.au/reso...3d_feb2004.pdf
It may have been someone's interpretation of the document but it in fact says:

"Suspension height modifications carried out in accordance with good engineering practice will be considered acceptable where the suspension travel in the bump or rebound mode is not altered by more than one-third of that measurement as specified by the original manufacturer. A vehicle modification application will not be required."


The only way to measure bump to rebound height is to jack the vehicle until the front wheels hang at full rebound. The distance between the pads and the bumpstops is the bump stop height. on the JK Wrangler 1/3 this is approximately 66 mm. Whoever quoted that to you cannot read or does not know what bump and rebound are in suspension terms.

Jas

[budgie]

hi guys,i am trying to get my head around the rim sizing with back space.I am looking at the 97 series rock crawler rims and jeep conection lists them as 17x8 with 4.75 back spacing.will these hang out side the guard with 285/75/17 on them.

[Gravel]

Originally Posted by budgie

hi guys,i am trying to get my head around the rim sizing with back space.I am looking at the 97 series rock crawler rims and jeep conection lists them as 17x8 with 4.75 back spacing.will these hang out side the guard with 285/75/17 on them.

No you should be fine...

[wranglertj]

yep budgie you should be O.K But you can always measure to find out.
You are pushing your rim out an extra 1.5inchs. Going to a 33 wont make a massive difference going from a 32 in width

[SeaComms]

Originally Posted by JasperJ

"Suspension height modifications carried out in accordance with good engineering practice will be considered acceptable where the suspension travel in the bump or rebound mode is not altered by more than one-third of that measurement as specified by the original manufacturer. A vehicle modification application will not be required."


The only way to measure bump to rebound height is to jack the vehicle until the front wheels hang at full rebound. The distance between the pads and the bumpstops is the bump stop height. on the JK Wrangler 1/3 this is approximately 66 mm. Whoever quoted that to you cannot read or does not know what bump and rebound are in suspension terms.

Jas

Just weighing in to this debate, I have just read and re-read this article and I will have to disagree with you. In my interpretation (yes, interpretation as I believe it) is it means no more than 33% change in the distance of the stock axle position at rest to bump stop and/or stock position to rebound. Not a 33% change in the total distance from bump to rebound. It doesnt mention moving the bump stop, but I believe this would defeat the purpose of the ruling as it is aimed at not affecting the suspension geometry too far. This plays back to 'interpretation' as written by jktom.

Since I have already stuck in the lifted springs I dont know the original figures, but since I did wheel to arch measurements before and after all I need to know now is full rebound distance then I can recalculate the original axle to bump and axle to rebound, then can compare this to the 2inch spring lifted position.

In my case keeping the orignal shocks and bump stops, I have not altered the total bump to rebound distance at all, but I have increased the travel to bump stop by 60mm and reduced the travel to rebound 60mm. For this to be within specs I would have required minimum 240mm travel each way at stock. I would take a guess that this is well over the 1/3 original distances, but will measure it all out and document it on the weekend.

[chrgd xr]

Budgie , Ive got that wheel and tyre combination and they will stick out past the guards but not by much.

[jktom]

There are many interpretations here, hence why I have never suggested I am right - others are wrong. I was not trying to turn this into a debate, just passing on some research?? There are also several documents looking at modifications, some of which have changed over the last few years as well. I had this point clarified by QT and they referred to the the distance betweem the two bump stops while at rest, not the total wheel travel, but hey, i have seem different interpretations from different people within QLD transport as well. AT also refer a lot of interpretation to ADR's and the Trade practices in relation to modifications as they are unable to make a decision. But hey, i think if we stay at around the 50mm mark, which is acceptable in most areas, and also acceptable by Jeep in most cases, i think we should be fine.
PS. I read another document about geometry which stated something about altering the original geometry. i could interpret this to say that a high steer kit is legal as it corrects geometry, providing it is ADR compliant. Its strange that of MOPAR released a OEm version of the Rancho drop brackets, they would be legal, but the Rancho ones would not???