engineerable tyre size rant

[ferrit]

well apparently Transport SA have no issues with my 31's on the lux- Just has to go out to regency park!

Except ive got 33's now... so I'll just talk to an engineer tomorrow and see what the go is for them!

[vt 98]

a mate up here in brizzie had 33's on his luxxie coppers pulled him up told him to take them off as the legal limit is actually just under a 31 but they let a 31 slide atleast they didn't give him a ticket hey

[mattsluxtruck]

My Maverick is a DX model which come factory fitted with the 7.50 / 16 split rims , which are real close to a 33" in rolling diameter. So does that mean by adding the 50mm allowed the 35's are actually legal?
I still have the tyre placard for the splits on the car and have used the argument successfully in the past , but Im thinking it might well be time to get them signed off now.

[Slunnie]

My Maverick is a DX model which come factory fitted with the 7.50 / 16 split rims , which are real close to a 33" in rolling diameter. So does that mean by adding the 50mm allowed the 35's are actually legal?
I still have the tyre placard for the splits on the car and have used the argument successfully in the past , but Im thinking it might well be time to get them signed off now.

7.50's should be about 31"

[Hulksta]

Yeah ive got both 31"s & 7.50/16s and they look to be the same height

[SWBMQCraig]

thought i would add my bit in here my mq patrol is listed in the "Australian tyre and rim association" handbook as having tyres that are 827mm tall as a stock option (32.55"), so that plus 50mm is 877mm and 35" tyres are listed as 883 mm in the same book.. so i am 6mm short of 35" tyres legally!!!

To me this is all bull anyway because you can have say 32" simex pedes that measure more like 33.8" or 35" anything (silverstone is notorious for this) that is only 34ish".. Clearly the "actual tyre diameter is the important measurment not the couple of numbers on the side!

On this note 34" tyres are legal (on my 4by at least), so why arnt there more available?? especially some radials!

Cheers,
Craig

[TWISTY]

On this note 34" tyres are legal (on my 4by at least), so why arnt there more available?? especially some radials!

Interco make the TrXus MT in a 34x12.5
http://www.intercotire.com/tires.php?id=11&g=1

[Athol]

Hey Athol , i was talking to you last week about the 4 inch lift and 35's on my nissan , is there any way in the near future you can engineer this setup? or do i have to take it to someone in shitney and pay $10,000 (which i dont have) for this new "brake test"

I've been a bit busy the last few weeks (eg went to Narellan, Mittagong and Bowral to inspect vehicles today).

I intend to put a submission to the RTA based on the highest ADR approved (fullly brake tested) GVM upgrade available on standard diameter tyres for patrols and landcruisers. Increasing the tyre diameter de-rates the brakes in the ratio of tyre diameters, so the GVM should be able to be the ADR approved increased rating multiplied by the original tyre diameter divided by the new tyre diameter. If the result of that calculation is greater than the original GVM of the vehicle, the brakes have already effectively been tested to exceed the original GVM with the increased diameter.

I suspect that the RTA will not accept that, but it's worth a try if it eliminates the need for an abridged brake test.

Athol

[craz3d]

Hey Athol , i was talking to you last week about the 4 inch lift and 35's on my nissan , is there any way in the near future you can engineer this setup? or do i have to take it to someone in shitney and pay $10,000 (which i dont have) for this new "brake test"

I've been a bit busy the last few weeks (eg went to Narellan, Mittagong and Bowral to inspect vehicles today).

I intend to put a submission to the RTA based on the highest ADR approved (fullly brake tested) GVM upgrade available on standard diameter tyres for patrols and landcruisers. Increasing the tyre diameter de-rates the brakes in the ratio of tyre diameters, so the GVM should be able to be the ADR approved increased rating multiplied by the original tyre diameter divided by the new tyre diameter. If the result of that calculation is greater than the original GVM of the vehicle, the brakes have already effectively been tested to exceed the original GVM with the increased diameter.

I suspect that the RTA will not accept that, but it's worth a try if it eliminates the need for an abridged brake test.

Athol

Kudos Athol, an engineer working for the team

[GUHOON]

Hey Athol , i was talking to you last week about the 4 inch lift and 35's on my nissan , is there any way in the near future you can engineer this setup? or do i have to take it to someone in shitney and pay $10,000 (which i dont have) for this new "brake test"

I've been a bit busy the last few weeks (eg went to Narellan, Mittagong and Bowral to inspect vehicles today).

I intend to put a submission to the RTA based on the highest ADR approved (fullly brake tested) GVM upgrade available on standard diameter tyres for patrols and landcruisers. Increasing the tyre diameter de-rates the brakes in the ratio of tyre diameters, so the GVM should be able to be the ADR approved increased rating multiplied by the original tyre diameter divided by the new tyre diameter. If the result of that calculation is greater than the original GVM of the vehicle, the brakes have already effectively been tested to exceed the original GVM with the increased diameter.

I suspect that the RTA will not accept that, but it's worth a try if it eliminates the need for an abridged brake test.

Athol

Cheers mate , i knew i should of got off my arse and did something about it before this all came about
Keep us posted how you go and as soon as its sorted out ill come and give you some cash and get it all legit

[31zook]

Hey NIK, i rang an engineer about 31s, 50mm BL and 50mm springs and he chucked a tanty, saying he would not pass anything over 25mm in tyre or any BL of any sort. But Athol made it happen... Im going to try and use him in my next build...

Josh

[NIK]

Yep Athol does seem to be on our side instead of saying what we cant do his reading right into it to see HOW we can acheive what we want.
Thanks heaps
Nik

[Breaker Brother]

I've been a bit busy the last few weeks (eg went to Narellan, Mittagong and Bowral to inspect vehicles today).

I intend to put a submission to the RTA based on the highest ADR approved (fullly brake tested) GVM upgrade available on standard diameter tyres for patrols and landcruisers. Increasing the tyre diameter de-rates the brakes in the ratio of tyre diameters, so the GVM should be able to be the ADR approved increased rating multiplied by the original tyre diameter divided by the new tyre diameter. If the result of that calculation is greater than the original GVM of the vehicle, the brakes have already effectively been tested to exceed the original GVM with the increased diameter.

I suspect that the RTA will not accept that, but it's worth a try if it eliminates the need for an abridged brake test.

Athol

I assume this comes about because of the increased inertial force created by the larger tyres ?
in that situation, would a brake upgrade suffice, say on a hilux going to vented discs on the rear and a larger (25mm) disc on the front as they already have a 4 piston caliper ?

[DIRTY ROCK STAR]

Athol,

can you confirm, once a vehicle is engineered and rego'd etc.
then if the ADRs or other specs change. is the vehicle legal because it was done prior? or is this not the case?

Thanks

[joeblow]

Athol,

can you confirm, once a vehicle is engineered and rego'd etc.
then if the ADRs or other specs change. is the vehicle legal because it was done prior? or is this not the case?

Thanks

i think if this was the case there would be no hot rods on the road.

[nelpd96]

Guys,
Just to make this clear, a vehicle must always comply with the ADR's that were applicable at the time of manufacture. Engineering your vehicle is just a way of proving that the vehicle still meets those requirements.

When it comes to rims and tyres, you cannot engineer them. If you read the NCOP it will tell you what is allowed and what is not. As an engineer I cannot vertify anything with more than 50mm increase in track or more than 50% wider than the original tyre. The maximal allowable increase in rolling diameter is 50mm. A maximum of 150mm suspension lift is allowed as is a maximum of 50mm body lift.

Any engineer that tells you that he can do otherwise is bullshitting you and taking your money. If you get pulled over you haven't got a leg to stand on.

The above information was taken from the NCOP but all states apply the same regulations in this regard.

If you need any more information I am happy to help out.

Cheers
Paul

[-Scott-]

The above information was taken from the NCOP but all states apply the same regulations in this regard.

All states have legislated to adopt the NCOP?

[ferrit]

as far as im aware talking to an engineer a few weeks ago here in adelaide the NCOP's are just a piece of paper and not law here in SA.

[Athol]

I assume this comes about because of the increased inertial force created by the larger tyres ?
in that situation, would a brake upgrade suffice, say on a hilux going to vented discs on the rear and a larger (25mm) disc on the front as they already have a 4 piston caliper ?

The brake degradation due to tyre diameter is simple mechanics. The radius of the tyre can looked upon as a lever length between the axle and the ground. The longer the lever (bigger radius), the more torque you're applying to the brake. That means that, as the tyre diameter increases, the brake has to generate more torque (resistance) to achieve the same amount of braking force at the ground. This is also why it's common to fit lower ratio diffs to compensate for increased tyre diameter - otherwise, the engine struggles to push it along.

The RTA seem to be heading towards saying that any non-genuine brake combination for that model vehicle will require an abridged brake test if the vehicle is subject to a brake ADR (31, 35). That means, for example, that putting Patrol front and rear diffs under a Hilux could result in having to do an abridged brake test even on standard diameter tyres for the Patrol diffs. It's not what the current NSW rule book, the RTA Code of Practice for Light Vehicle Modifications (effective since 1994), says, but it seems to be where the RTA are heading.

Athol

[Hulksta]

Whats an abridged brake test involve? would it need to be done if putting GU diffs under a GQ patrol?

[Athol]

Just to make this clear, a vehicle must always comply with the ADR's that were applicable at the time of manufacture. Engineering your vehicle is just a way of proving that the vehicle still meets those requirements.

Yes, that's the underlying principle behind all of the rule books.

When it comes to rims and tyres, you cannot engineer them. If you read the NCOP it will tell you what is allowed and what is not. As an engineer I cannot vertify anything with more than 50mm increase in track or more than 50% wider than the original tyre. The maximal allowable increase in rolling diameter is 50mm. A maximum of 150mm suspension lift is allowed as is a maximum of 50mm body lift.

Those are the limits specified in the NCOP, and obviously only apply in the jurisdictions that have adopted the NCOP. The NSW RTA sent a letter to all signatories making it very clear that the NCOP has not been adopted and will be extensively revised before it is adopted. In the meantime, we continue using the RTA's Code of Practice for Light Vehicle Modification, which has been in use without revision since 1994.

The NSW rules specify different limits to the NCOP, and can be found in this information sheet:
http://www.rta.nsw.gov.au/registration/ ... 9_rev4.pdf

Any engineer that tells you that he can do otherwise is bullshitting you and taking your money. If you get pulled over you haven't got a leg to stand on.

If the engineer follows the rules applicable in the jurisdiction that the vehicle is to be registered, it's fine. If the engineer certifies something outside those rules, the paperwork is worthless.

I saw a photo today of a Pajero with 44" tyres, which was presented to a blue slip station complete with an engineering certificate. The RTA were not impressed, and I think that the engineer concerned might be in a little trouble...

The above information was taken from the NCOP but all states apply the same regulations in this regard.

All jurisdictions legislate that vehicles must continue to comply with the ADRs to which they were originally constructed, or a newer equivalent.

Details specified in a code of practice such as tyre diameter limits are an attempt to define limits that will comply, but are not a guarantee of compliance or that something exceeding those limits will necessarily fail the relevant ADRs. Something inside the defined limit might not comply with the ADR but will be deemed to do so without requiring testing unless the COP specifies that testing is required.

Athol

[Athol]

Whats an abridged brake test involve? would it need to be done if putting GU diffs under a GQ patrol?

From memory, the abridged test requires the vehicle to be loaded to GVM, then put through a series of brake tests like this (no guarantees that it's exactly right):
1. Instrument test - 100m/h normal stop, no distance or deceleration limit.
2. Disable one brake circuit. Complete 100km/h stop with a specified deceleration/distance. Re-enable those brakes.
3. Do (2) again for the other brake circuit.
4. Do (2) again for disabling the brake booster.
5. Normal 100km/h stop with specified deceleration/distance, which is more strict than the partial fail tests.
6. 10 consecutive "spike stops", each involving getting the vehicle to 50km/h, dropping into neutral and then applying over 835N pedal pressure (enough to lock it up on cold brakes), with specified deceleration/distance.
7. Repeat (5).

The vehicle has to stay within a specified lane width through the entire series of tests and the entire system must be fully servicable at the end of the test.

Disabling brakes cannot be done by clamping hoses because the clamps will leak under application pressure and retain pressure on release - in other words, the "disabled" brakes will apply but will not release. A plug has to be screwed into the master cylinder and a cap screwed over the line.

I wouldn't want to do those spike stops on a good set of tyres...

Athol

[Athol]

can you confirm, once a vehicle is engineered and rego'd etc.
then if the ADRs or other specs change. is the vehicle legal because it was done prior? or is this not the case?

If the vehicle complied with the regulations applicable at the time of certification and the applicable ADRs, it continues to be legal.

If it was certified but is subsequently found to not have complied when it was certified, it's a timebomb regardless of subsequent rule changes, and is likely to have later rules applied when it has to be re-certified after being defected.

The ADRs are not retrospective. A vehicle only has to meet the ADRs applicable to it or its components. If you fit a later engine, you have to meet that engine's pollution rule but the rest of the vehicle is generally only required to comply with its original year ADRs.

Athol

[Reddo]

with regards to oversized tire size, your going to have to options
legal options;

1) Stick the std tires on your 4wd and tow your tires to the play ground in a trailor, and or, such as the usa
2) Pull it on the back of a truck/trailor.

there is a third and thats just running them on the weekend and running the risk of being pulled over. I think you may be able to talk your way out of a defect with the police if your lucky, however, if you driving on them, and you hit someone and kill them, and the investigation finds you at fault, your insurance is right out the door, and your in trouble.

To me the debate on tire size just isnt worth it, id rather run skinnys to and from the track and have the overall height of the 4wd increased. + with the money you'd save on tire usage, its a possible option. But its a PITA and it has its down sides.

[nelpd96]

Athol,
I would have thought that you needed to do a lane change test on the larger diameter wheels as well, given the increase in the COG and unsprung mass in some cases. I realise that the lane change thing is really a subjective test but it couldn't hurt. Also I am thinking that you would have to conduct the abridged braking test because it will be very dependant on ventilation, brake fluid and pad contruction. I wouldn't think that the RTA would be happy with just saying that you have increased the brake daimeter by the same % and the wheel increase. Then there are the issues of continued compliance with ADR for the speedo etc.

I am sure that you have much more experience than me with regards to this but just my thoughts on the matter.

Cheers
Paul

[Athol]

I would have thought that you needed to do a lane change test on the larger diameter wheels as well, given the increase in the COG and unsprung mass in some cases. I realise that the lane change thing is really a subjective test but it couldn't hurt. Also I am thinking that you would have to conduct the abridged braking test because it will be very dependant on ventilation, brake fluid and pad contruction. I wouldn't think that the RTA would be happy with just saying that you have increased the brake daimeter by the same % and the wheel increase. Then there are the issues of continued compliance with ADR for the speedo etc.

There is a subjective requirement that the vehicle be safe and predictable in its handling, but the South Australian style swerve test is not required in NSW at present.

If you look at fully ADR approved GVM upgrade kits, they replace the suspension springs, dampers and leaf spring u-bolts, shackles and eye pins and some re-calibrate the rear brake proportioning valve using a pair of pressure gauges. The don't replace fluid or pads. A typical kit will take a 70 series Landcruiser from 3300kg to 3900kg. The original 265/70R16 tyres are 30.6" diameter. If you fitted 35" tyres, neglecting the fact that the overall energy to be dissipated is less for a lower GVM, the GVM at which the brake torques will be the same as for the upgrade will be 3900 * 30.6 / 35 = 3409kg, which is more than the OEM GVM of 3300kg.

The only potential argument against the 35" tyres would be if they were 15" rims, which could reduce brake cooling. The solution is to use 16" rims and tyres.

The speedo correction is the simplest part of the process. You either change the diff ratios to cancel out the tyre diameter change or you fit a correction unit in the speedo drive.

Athol

[bogged]

I saw a photo today of a Pajero with 44" tyres, which was presented to a blue slip station complete with an engineering certificate. The RTA were not impressed, and I think that the engineer concerned might be in a little trouble...

[MUD80D]

Ok so what about an 80# cruiser 95 model with the larger brakes running michelin xml 325/85/16 tires that are speed rated

[j-top paj]

i just hope this doesnt affect newer GUs fitting 35"s

or il have to keep my current GU for longer and stick a td42 in it (if thats allowed )

[DIRTY ROCK STAR]

I saw a photo today of a Pajero with 44" tyres, which was presented to a blue slip station complete with an engineering certificate. The RTA were not impressed, and I think that the engineer concerned might be in a little trouble...

was this local? newy?
just wondering if it was the black SWB that competed at tuff truck a couple of times.
surely nobody engineered 44s?