"Model" is an area open for debate. For Australia, "model" is defined by the document below. Basically, look at the compliance plates on both vehicles. If they have the EXACTLY same model listed, as far as the definition is concerned, they are the same model. I have had this debate with a senior person at Vicroads, he has taken another interpretation of "model", but cannot back it up with any documentation. It was only his personal interpretation. So we have agreed to disagree. My issue was that the Range Rover model (later referred to as a Range Rover Classic) was the same model by the definition and by the manufacturer from 1970 to 1995. Therefore I can put bits from a 1993 range onto a 1976 range. The person at Vicroads disagreed. But they have not wished to enforce their interpretation at this stage. So until proven otherwise, I am sticking with the definition set by the Federal Government.
What size tyres can I upgrade to with my BT-50
- Thread starter Patriot
- Start date
"Model" is an area open for debate. For Australia, "model" is defined by the document below. Basically, look at the compliance plates on both vehicles. If they have the EXACTLY same model listed, as far as the definition is concerned, they are the same model. I have had this debate with a senior person at Vicroads, he has taken another interpretation of "model", but cannot back it up with any documentation. It was only his personal interpretation. So we have agreed to disagree. My issue was that the Range Rover model (later referred to as a Range Rover Classic) was the same model by the definition and by the manufacturer from 1970 to 1995. Therefore I can put bits from a 1993 range onto a 1976 range. The person at Vicroads disagreed. But they have not wished to enforce their interpretation at this stage. So until proven otherwise, I am sticking with the definition set by the Federal Government.
They keep on changing the tolerances:
This appears the most recent, which allows 6% of off-road (special use) tyres.
3.5.6.2.1. The outer diameter of a tyre must not be outside the values Dmin and Dmax obtained from the following formulae:
Dmin = d + (2H . a)
Dmax = d + (2H . b)
where:
the coefficients "a" and "b" are:
coefficient "a" = 0.97
coefficient "b" = 1.04 for normal (road type) radial and 1.06 for Special tyres
for snow tyres the maximum overall diameter (Dmax) may be exceeded by 1%.
"Special use tyre" means a tyre intended for mixed use, both on and/or off road or for other special service duty;
So in regard to your specific question, the maximum actual diameter for a 285/75/16 is 33.9 inches. As you can go to 2 inches above that, you could just scrap in, without an engineers, a 36 inch with a little push of the rules. In NSW you are definitely allowed.
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All I am highlighting is that a manufacturer specifies a tyre size for a vehicle, it does not specify a tyre diameter. Most of the modification rules state that you can increase the diameter of the tyre by 50mm over that specified by the manufacturer. If you look up the specifications of individual tyres, the actual diameter varies across brands and tread patterns. So the question is, what is the diameter specified by the manufacturer so you can work out whether your new tyres meet the modification rules. By the relevant standards, the actually tyre diameter for a given tyre size can vary from x mm to y mm. Therefore you would meet the modification rules as long as your new tyre diameter is no more than y mm plus 50mm.
In NSW you are allowed a tyre that is 7% larger than that specified by the manufacturer without an engineers certificate. So on the example given, 7% is larger than 50mm and the 36 inch tyre would meet the requirements for self certification in NSW
My comments are more focused around how people read a single line in a states modification rules and believe that they know what is legal and what is not in that state.
For example, NSW modification rules (VSI 6) does not allow body lifts and only allows spring lifts if they do not raise the overall height of the vehicle more than 50mm. So can I legally fit in NSW a body lift of 50mm and also 50mm bigger tyres that would increase the height of the vehicle by a further 25mm. You would say NO if you only read VSI 6, but if you read their total rules, you are allowed to do the modification.
For a start, NSW clearly states that if your vehicle EITHER complies with VSB 14 or VSI 6, you car is legal in NSW. VSB 14 allows a 50mm body lift without an Engineers cert and therefore such a body lift is legal in NSW.
Secondly, a body/spring lift is a different set of rules to tyre size increases. There is no limit on how much a tyre increase will increase the height of the car, only that it cannot be more than a 50mm increase in diameter (25mm increase in height of the car). So you can simply do the body or spring lift with standard size tyres on. As long as it does not increase the height of the car by more than 50mm, you can certify it yourself as being legal. Then you can go add bigger tyres on and certify them as being legal. Vicroads actually put the rules in layman terms and in their state regs (VSI 8), they state the overall limit of tyres and lifts is 75mm. That is, 25mm for the tyres and 50mm from a combination of spring and body lift.
So do not read a single line in a modification rule somewhere and think that is the limit, you have to look at the rules in total.
For example, NSW modification rules (VSI 6) does not allow body lifts and only allows spring lifts if they do not raise the overall height of the vehicle more than 50mm. So can I legally fit in NSW a body lift of 50mm and also 50mm bigger tyres that would increase the height of the vehicle by a further 25mm. You would say NO if you only read VSI 6, but if you read their total rules, you are allowed to do the modification.
For a start, NSW clearly states that if your vehicle EITHER complies with VSB 14 or VSI 6, you car is legal in NSW. VSB 14 allows a 50mm body lift without an Engineers cert and therefore such a body lift is legal in NSW.
Secondly, a body/spring lift is a different set of rules to tyre size increases. There is no limit on how much a tyre increase will increase the height of the car, only that it cannot be more than a 50mm increase in diameter (25mm increase in height of the car). So you can simply do the body or spring lift with standard size tyres on. As long as it does not increase the height of the car by more than 50mm, you can certify it yourself as being legal. Then you can go add bigger tyres on and certify them as being legal. Vicroads actually put the rules in layman terms and in their state regs (VSI 8), they state the overall limit of tyres and lifts is 75mm. That is, 25mm for the tyres and 50mm from a combination of spring and body lift.
So do not read a single line in a modification rule somewhere and think that is the limit, you have to look at the rules in total.
hiluxdriver
Well-Known Member
I have no idea why you try and make it so hard to understand.
From VSI#6
Replacement of tyres that change tyre overall diameter by more than 7% of the overall original diameter*.
* ’overall original diameter’ means the maximum outside diameter of the largest tyre specified by the vehicle’s original manufacturer as an option for the vehicle, as shown on the vehicle’s tyre placard.
Example requiring certification: • Replacing 215/65R17 (712 mm overall diameter) tyres with 265/65R17 (776 mm overall diameter) tyres, an increase in overall diameter of 64 mm, or 8%.
Example not requiring certification: • Replacing 215/65R17 (712 mm overall diameter) tyres with 235/65R17 (738 mm overall diameter) tyres, an increase in overall diameter of 26 mm, or 4%.
plod are not going to give a shit if the actual diameter does not match specifications. If it's bigger than 7% than expect a ticket.
ITS NOT THAT FLIPPING HARD
From VSI#6
Replacement of tyres that change tyre overall diameter by more than 7% of the overall original diameter*.
* ’overall original diameter’ means the maximum outside diameter of the largest tyre specified by the vehicle’s original manufacturer as an option for the vehicle, as shown on the vehicle’s tyre placard.
Example requiring certification: • Replacing 215/65R17 (712 mm overall diameter) tyres with 265/65R17 (776 mm overall diameter) tyres, an increase in overall diameter of 64 mm, or 8%.
Example not requiring certification: • Replacing 215/65R17 (712 mm overall diameter) tyres with 235/65R17 (738 mm overall diameter) tyres, an increase in overall diameter of 26 mm, or 4%.
plod are not going to give a shit if the actual diameter does not match specifications. If it's bigger than 7% than expect a ticket.
ITS NOT THAT FLIPPING HARD
phs
Well-Known Member
The numbering on a tyre placard specifies what OD it is. Thow many brands can vary that's not an issue for a tyre placard as its not a brand of tyre but a bunch of numbers that relate to a size .
if a size on a placard specifies 285/75r16 it relates specifically to the mathematical size for those numbers . In this case = 32.8" that is clean cut
When changing tyre size you could argue your specific tyres that have 35x12.5r17 on there sidewall only measure 34.4" OD what ever I DONT know if that would fly none the less with 285/75r16 your starting at 32.8" not what some one may think those numbers will work out too.
so in VICTORIA you can only go anothe 1.968" bigger which is 34.79"
I am awear all states vary that's why I stated it for VIC as patriots 4wd is registered in Victoria.
if a size on a placard specifies 285/75r16 it relates specifically to the mathematical size for those numbers . In this case = 32.8" that is clean cut
When changing tyre size you could argue your specific tyres that have 35x12.5r17 on there sidewall only measure 34.4" OD what ever I DONT know if that would fly none the less with 285/75r16 your starting at 32.8" not what some one may think those numbers will work out too.
so in VICTORIA you can only go anothe 1.968" bigger which is 34.79"
I am awear all states vary that's why I stated it for VIC as patriots 4wd is registered in Victoria.
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phs
Well-Known Member
Please correct me if I'm wrong but last time I checked in Victoria
it's 75mm
50mm suspension or body ect. And 25mm tyres
Which is 50mm bigger tyre OD TO achieve 25mm lift
You have got it in one. That is, the maximum outside diameter for the tyre size specified by the manufacturer. So now what is the maximum diameter for a 215/65R17?
phs
Well-Known Member
And I'm out don't think it can be explain any more
All the best working it out .
hiluxdriver
Well-Known Member
If you want to take the definition of tyre sizes being listed by others, it is a good conservative approach and you will not put on too large tyres using those interpretations. For those of us that want to run the largest tyres with out an engineers certificate, then I have informed you how far you can go.
I cannot explain it any further and refuse to get into further debates with people who just want to stir things up.
I cannot explain it any further and refuse to get into further debates with people who just want to stir things up.
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hiluxdriver
Well-Known Member
phs
Well-Known Member
You can't just add 50mm to the width and expect that keeping the same multiplying profile ( 75 ) will be ok it's not
It's 50mm to your total Tyre OD
315x75r16 are not 35s either more 34.6"
Going from a 265/75r16 to a 315/75r16 would be a 75mm OD Increase about 9.3%
I love how scare tactics keep on coming into these conversations. Have you heard of anyone being booked for tyres where the tyre size indicates that they are up to 3 inches bigger than standard. I haven't. The cops go after the guys with obviously larger tyres, not the ones that may or may not be slightly over.
I have been running tyres that are between 50mm and 75mm above standard (if you take the mathematical calculation) for decades. I have been pulled over by cops a number of times and the tyres have never raised an eyebrow
phs
Well-Known Member
hiluxdriver
Well-Known Member
So you spend sooooo much time on here trying to correct people and make sure the laws are clear for us all I assume, to then clearly say you break the law and imply that it's ok to do so? But I am using scare tactics? I'll block you now before I say something that I'll regret.
When have I said that I have broken the law?
My tyres have always been legal and always will be.
I only indicated that, based on YOUR calculation, they were bigger than 50mm. I have NEVER said that my tyres were illegal. I just went out and measured them, they are more than 5mm less than the current ADRs and well within limits for the ADRs in place at the time of manufacture.
The reason that I used the 50mm to 75mm range is that below 50mm on your calculation, it is clearly legal. Above 75mm and it is most likely illegal. In between these, you have to start looking at the actual regs and measuring tyres, which the cops would not want to do. So between 50mm and 75mm it may be legal or may not be, you would have to do the actual calculations.
You post things and then try to argue against what you post. This just shows to me that you want to argue.
You posted that it was 50mm greater than the MAXIMUM diameter of the LARGEST tyre size. Why do you think that they used these words? Why didn't they just say the largest diameter listed by the manufacturer. They didn't because they only specify a tyre size rather than a diameter. Then why didn't they just state it was 50mm from the diameter of the largest tyre size, why did they add MAXIMUM diameter of that tyre size. It is clear that they know that there is a range of diameters that fit within a certain tyre size and not that there is only one as you claim.
But even though you posted this definition, you continue to argue that there is one and only diameter for each tyre size and you have to use your calculation when working out whether you meet the requirements or not.
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