Replacement Tyres from OEM Continentals

[Hillbilly]

Storm in a tea cup I reckon. If you are that worried that going a smidge above the recommended tyre then how do you even leave the house in the morning. Do you follow every speed limit all the time, do you have a burbly cat back that they could say is a power mod, have no flash tune loaded, wont go near aftermarket bushes or an alignment that pushes the angles a bit beyond what the factory suggested, have a non standard DV that would be classed as a power mod? Do you measure your tread depths and buy a whole set at only the whiff of a tread wear indicator coming up. Do you go above the recommended tyre pressures to give it a bit more side wall for spirited driving? An insurance company could probably pull you across the coals for all of those things if they were prepared to pull you up for going up an aspect ratio size up in a sensible tyre choice. If you are that worried about the repercussions of the tyre size suggested then I assume none of that other stuff I've mentioned is done to the car either. Each to there own but I say live life on the edge if that's the cliff we are talking about.

You are welcome to do what you like as are we.

The question was asked to prove what I said and the post above does that.
End of story.
What I do with my vehicles is my business but I prefer to keep them standard and legal .

If you want to push the boundaries feel free but dont critizise those who dont

[sambb]

Not criticizing. It comes down to where each person believes the boundaries to be. I don't fall on the side of needing a lawyer to read me every sub point for everything I do. I mean sometimes the nitty gritty fall on the other side - my 9N Polo for example. Stock tyres exaggerate the speedo. Everyone who has ones knows that. What are we to do - sue the government for 'time lost' for ADR'ing a car with an exaggerated speedo when all our trip times could have actually been a bit quicker if we'd run the gauntlet and deliberately gone a margin over 60kph OR take a deep breathe and a beer and go up an aspect ratio if we wanted so that our speedos are correct, and not be worried about the sky falling in if we do that. I can barely even find more than two decent stock sized tyres for my car anymore. They are being discontinued all the time and will be nil in a few years. The only other cars that run my size are the early minis. What would you have me do then - scrap the car when 205/45/16 is extinct lest I risk breaking a rule or heaven forbid change aspect ratio or even go to a 17in wheel on a completely non standard aspect ratio that shock horror was sold from the factory on the 6R which incidentally is more or less the same chassis as my car? Rules schmules - the police are not going to lock you up as a hoon for running a 45 vs a 40 conti/bridge/Mich/Goodyear on a 77TSi because its 4mm bigger rolling di mm. You don't truly believe that do you. Nor will the insurance company. If you are in a hoon car driving like a hoon...different matter, you'll maybe be treated accordingly. Perspective is all I'm saying.

[Hillbilly]

Not criticizing. It comes down to where each person believes the boundaries to be. I don't fall on the side of needing a lawyer to read me every sub point for everything I do. I mean sometimes the nitty gritty fall on the other side - my 9N Polo for example. Stock tyres exaggerate the speedo. Everyone who has ones knows that. What are we to do - sue the government for 'time lost' for ADR'ing a car with an exaggerated speedo when all our trip times could have actually been a bit quicker if we'd run the gauntlet and deliberately gone a margin over 60kph OR take a deep breathe and a beer and go up an aspect ratio if we wanted so that our speedos are correct, and not be worried about the sky falling in if we do that. I can barely even find more than two decent stock sized tyres for my car anymore. They are being discontinued all the time and will be nil in a few years. The only other cars that run my size are the early minis. What would you have me do then - scrap the car when 205/45/16 is extinct lest I risk breaking a rule or heaven forbid change aspect ratio or even go to a 17in wheel on a completely non standard aspect ratio that shock horror was sold from the factory on the 6R which incidentally is more or less the same chassis as my car? Rules schmules - the police are not going to lock you up as a hoon for running a 45 vs a 40 conti/bridge/Mich/Goodyear on a 77TSi because its 4mm bigger rolling di mm. You don't truly believe that do you. Nor will the insurance company. If you are in a hoon car driving like a hoon...different matter, you'll maybe be treated accordingly. Perspective is all I'm saying.

The boundary is what the ADR sets and it is 15mm max diameter larger in QLD MY Polo needs a tyre 40mm larger diameter to set the speedo correct at 100kph so I just ravel at 105 and Im happy. The ADR rule regarding speedos basically is that they can be up to 10kph fast at 100kph +4% but CANT read LESS than ACTUAL speed. So what do you do. I just live with it as its easier. Have tried adjusting using VCDS but it doesnt work on either car You can put a wider tyre on with similar diameter so dont see a a problem

[sambb]

The boundry is black and white in print, yes. If you want to just be 'right' then ok you can have it. But to say there's no common sense grey area in the real world ?????????? I think its agree to disagree time.

[Hillbilly]

The boundry is black and white in print, yes. If you want to just be 'right' then ok you can have it. But to say there's no common sense grey area in the real world ?????????? I think its agree to disagree time.

So working on your theory speed limits are just there to be ignored as well

[sambb]

sigh......the league of morons

[Hillbilly]

sigh......the league of morons

Of which you also are a member

[Sydneykid]

Here is the reply from QLD TMR which says you are wrong as the 4% DOES NOT APPLY TO DIAMETER

The limits of 15mm larger and 26mm smaller are documented within VSB14 – National Code of Practice for light vehicle modifications and applies to passenger cars of category MA.

The 4% rule that is documented within ADR23 applies only to width. The ADR"S are applicable nationwide


To understand the overall diameter tolerance allowed, you could use one of the many online tyre size calculators to understand the difference or refer to the Australian Tyre and Rim Guide for further information.

From the information you have provided, and using the ADR23 calculations to calculate, a tyre designation of 235/45/17 would have an overall diameter of 643.5mm.

Then how does he explain this;

6.1.5. Tyre outer-diameter specifications
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:
6.1.5.1. for sizes listed in Annex 5, and for tyres identified by the "tyre to rim fitment configuration" (see para. 3.1.10.) symbol "A", the nominal section height H is equal to:
H = 0.5 (D-d), for references see paragraph 6.1.2.
6.1.5.2. for other sizes, not listed in Annex 5, "H" and "d" are as defined in paragraph 6.1.2.1,

6.1.5.3. Coefficients "a" and "b" are respectively:
6.1.5.3.1. Coefficient "a" = 0.97
6.1.5.3.2. Coefficient "b" Radial, Run flat tyreDiagonal and Bias Belted
for ordinary
(road type) tyres 1.04 1.08
6.1.5.4. for snow tyres the overall diameter (Dmax) established in conformity with the above may be exceeded by 1 per cent.


Multiplying the "tyre outer diameter" by 1.04 gives the same result as adding 4%.


Cheers
Gary

[Sydneykid]

The limits of 15mm larger and 26mm smaller are documented within VSB14 – National Code of Practice for light vehicle modifications and applies to passenger cars of category MA.

VSB14 is a painful document but I thought you might be interested in this bit (which you may recall I did refer to in an earlier post);


4.1 REPLACEMENT TYRES ON STANDARD (OR MANUFACTURER’S OPTIONAL) RIMS
Some tyre sizes have become obsolete and are no longer available. Equivalent replacement tyres with different size designations may be fitted without specific certification under this Section.

Every passenger car manufactured after 1972 (ADR 24) is fitted with a tyre placard that contains information on original and optional tyres and rims for that vehicle model. A motor vehicle under 4.5 tonnes GVM which is required to comply with ADR 24 may be equipped with tyres other than those listed on the tyre placard provided that:
* the load rating of the tyres is not less than the lowest load rating listed on the tyre placard of the vehicle or equivalent variant of that model vehicle;
* the speed rating of the tyres fitted to a passenger vehicle is at least 180 km/h (S) when the tyre placard requires a higher speed rating than S;
* the speed rating of the tyres fitted to vehicles with special features for off-road use of at least 140 km/h N when the tyre placard requires a higher speed rating than N; and for all other vehicles a speed rating of at least 120 km/h.

In special circumstances, the speed rating may be less than the ratings specified above if the speed rating of the tyre is more than the vehicle’s maximum speed. This will need to be confirmed with the Registration Authority.


You might also find the aspect ratio tolerance interesting (as that is specifically what we have been talking about (ie 45 versus 40).;

4.2.5 Tyre Aspect Ratio
Because of the different handling characteristics, the aspect ratio of tyres fitted to the front axle must not vary by more than 10 from the aspect ratio of tyres fitted to the rear axle (e.g. 175 65 R14 front and 205 45 R14 rear, has an aspect ratio difference of 20 and is not recommended, whereas 175 65 R14 front and 195 60 R14 rear has a difference of 5 and has similar handling characteristics).



The 15 mm larger and 25 mm smaller designations are mentioned in 4.2.4 but overruled by 4.2;

Note: Increases in tyre diameter are subject to compliance with all other requirements specified under this clause (Clause 4.2 Non-Standard Tyres and Rims)

FWIW I suspect that your source is deliberately being very obtuse, he's technically correct in saying that 4% isn't mentioned in the ADR in regards to the tyre diameter. But the tolerance is determined by multiplying the diameter by 1.04 (refer above). Last time I studied maths at university multiplying by 1.04 was the same as adding 4%.


Cheers
Gary

[Hillbilly]

VSB14 is a painful document but I thought you might be interested in this bit (which you may recall I did refer to in an earlier post);


4.1 REPLACEMENT TYRES ON STANDARD (OR MANUFACTURER’S OPTIONAL) RIMS
Some tyre sizes have become obsolete and are no longer available. Equivalent replacement tyres with different size designations may be fitted without specific certification under this Section.

Every passenger car manufactured after 1972 (ADR 24) is fitted with a tyre placard that contains information on original and optional tyres and rims for that vehicle model. A motor vehicle under 4.5 tonnes GVM which is required to comply with ADR 24 may be equipped with tyres other than those listed on the tyre placard provided that:
* the load rating of the tyres is not less than the lowest load rating listed on the tyre placard of the vehicle or equivalent variant of that model vehicle;
* the speed rating of the tyres fitted to a passenger vehicle is at least 180 km/h (S) when the tyre placard requires a higher speed rating than S;
* the speed rating of the tyres fitted to vehicles with special features for off-road use of at least 140 km/h N when the tyre placard requires a higher speed rating than N; and for all other vehicles a speed rating of at least 120 km/h.

In special circumstances, the speed rating may be less than the ratings specified above if the speed rating of the tyre is more than the vehicle’s maximum speed. This will need to be confirmed with the Registration Authority.


You might also find the aspect ratio tolerance interesting (as that is specifically what we have been talking about (ie 45 versus 40).;

4.2.5 Tyre Aspect Ratio
Because of the different handling characteristics, the aspect ratio of tyres fitted to the front axle must not vary by more than 10 from the aspect ratio of tyres fitted to the rear axle (e.g. 175 65 R14 front and 205 45 R14 rear, has an aspect ratio difference of 20 and is not recommended, whereas 175 65 R14 front and 195 60 R14 rear has a difference of 5 and has similar handling characteristics).



The 15 mm larger and 25 mm smaller designations are mentioned in 4.2.4 but overruled by 4.2;

Note: Increases in tyre diameter are subject to compliance with all other requirements specified under this clause (Clause 4.2 Non-Standard Tyres and Rims)

FWIW I suspect that your source is deliberately being very obtuse, he's technically correct in saying that 4% isn't mentioned in the ADR in regards to the tyre diameter. But the tolerance is determined by multiplying the diameter by 1.04 (refer above). Last time I studied maths at university multiplying by 1.04 was the same as adding 4%.


Cheers
Gary

Why dont you ring and tell him hes wrong then seeing you seem to be an expert on the subject.

I didnt go to university so have to rely on the legal documents and their interpretation by the people who have to enforce them
Im sure he will enjoy the conversation
His name is Adam