Suspension travel in the bump or rebound mode

[twr7cx]

I am currently reading through Tasmania's Light Vehicle Inspection Manual Version 8, June 2012, in regards to vehicle modifications and their legalities.

It states on p. 91:


The suspension travel in the bump or rebound mode must not be altered by more than one third of that measurement as specified by the original manufacturer.

Anyone know what would be meant by 'suspension travel in the bump or rebound mode'?

I know that the standard spacing between the top of the axels and the bump stops on the Discovery 2 is front 44.5mm and rear 61.5mm (on road height for the SLS rear model) or 71.5mm (coil spring rear). 1/3rd of these measurements is less than an inch, so I am assuming this therefore is not what is meant by 'bump or rebound mode'.

[Slunnie]

I'd be using a "to metal" measurement. The bumpstop will also compress and in many vehicle these are use as a part of he suspension to increase spring rate. Sounds like they were targeting lowered cars. You can lift a 4wd by any amount and still comply with this rule. Eg Les Richmond Automotives 4" kit.

[twr7cx]

Sounds like they were targeting lowered cars.

Hmmm... Cheers. That quote comes from p. 91 which is titled 'Appendix D: Lift Kits & Suspension Modifications', lowered suspension is covered in the Appendix C before it.

[Slunnie]

Do you have a link?

[twr7cx]

Do you have a link?

Sure do - http://www.aulro.com/afvb/modified-zone/168728-fyi-tasmanian-ais-inspection-manuals-details-legalities-roadworthy-modification.html

I am currently researching how far past the limits my vehicle is. Going to speak to some engineers about getting a compliance plate done for it (see what is involved, in particular cost wise which I think may be outrageous if a swerve test has to be done - I am hoping that some of the previous paperwork and engineer approvals by Les Richmond Automotive on their kits may help speed things along), otherwise I will cut out the guards and fit Les Richmond Automotive White Tiger flare kit (to stop the tyres rubbing and so I can space the wheels out), drop it back down to 2" suspension lift and fit smaller tyres at 31" diameter to comply without a engineered plate.

[Slunnie]

It's really not clear in quite a few areas in that doc. Is it bump/rebound from static ride height when full/empty or is it a maximum value. Suggested measurements from the bump stops, but this doesn't allow for bump stop compression. Not a well worded doc.

[twr7cx]

It's really not clear in quite a few areas in that doc. Is it bump/rebound from static ride height when full/empty or is it a maximum value. Suggested measurements from the bump stops, but this doesn't allow for bump stop compression. Not a well worded doc.

I agree. I have been reading through part of the Vehicle Standards Bulletin 14 (VSB 14) National Code of Practice for Light Vehicle Construction and Modification (NCOP) as well. It is much more technical, specific and accurate in it's wording.

The other thing not made clear in the document is whether there is a limit on total vehicle lift. The document talks about increasing the tyre diameter by 50mm and the suspension can be lifted by 50mm without issues, but I know in most other states they have a total lift limit of 50mm regardless of how it is achieved (body lift, suspension lift or tyre size increase or a combination of any of the three), but I can't see in that document anything relating to that...

[CJT]

In regards to your first question, when they talk about the 1/3 measurement you need to measure this with your lifted coils and standard shocks. I spoke to QLD Transport about the same sentence a few years ago as if you are replacing with longer travel shocks this does not apply. The information they provided was that above that these are measurements in relation to the factory wheel travel.

I believe that in a D2 when you calculate this out it is around 80mm increase in height allowed. Slunnie may be able to clarify that, I think he did all of those measurements when designing the Lovells coils a number of years ago.

If I remember correctly when I was researching all of this with QLD Transport and the new National Code of Practice, if you go to the full extent of the code and are able to have an engineer sign off and approve your modifications you can go to a total of 150mm lift.


This 150mm is made up of;

75mm suspension lift
50mm body lift
25mm lift from 50mm increase in tyre size.
I am pretty sure you have mentioned that you are using the LRA 4" lift which should fall under these guidelines given a 50mm suspension lift + 50mm suspension lowering in place of a body lift.

In discussions with my engineer and keeping in mind the NCOP that is why I chose to go with a 75mm spring lift, 32mm body lift (he advises me that this should be fine as long as he approves it before 1st April) and I have not really worried about the tyre size at this stage. I have 33x12.5 R18's which are slightly larger than standard but if it becomes an issue I will find some 31's to run on the standard alloys for around the city.

[CJT]

And to add to the information above, the NCOP states that any lift to a maximum of 50mm can be owner approved. Any lift beyond 50mm has to be engineer approved.

[Slunnie]

Back then the NSW rule was 1/3 metal to metal travel which for the D2 allowed about 70mm. This one bring 1/3 bump and 1/3 rebound is a weird one. I think the states can tighten up on the NCOP guides also which may be the case if they have their own rules and the NCOP..