Replacement Tyres from OEM Continentals

[sambb]

sigh......the league of morons

[Guest001]

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

[Guest001]

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

[Sydneykid]

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

More than happy to discuss it with him.

FWIW I'm occasionally called on as an expert witness, plus I also submit the odd technical paper on new and pending motor vehicle regulations. It has been my experience that the "enforcers" simply enforce what they have been trained to based on the interpretation of the regulations by their superiors and sometimes that interpretation, when tested, is legally incorrect. Albeit not that often, they are pretty good at their job, which you would expect as they do it every day. But occasionally they look at one reg and apply that in all circumstances when there are other regs that they should also consider.

For those that have been following, I still maintain my original position that a 215/45/17 tyre is 100% legal on a Polo Gti. As per 6.1.5 formula Dmax = d + (2H . b) where b = 1.04

Cheers
Gary

[brad]

True and to correct the speedo on our POLO which reads 106 at 100 it needs tyres that are 40 mm LARGER in diameter and therefore illegal
Eg tyres are 195/55/15 diameter 595mm

To get 6% correction they would have to be 195/65/15 which gives 6.3% difference diameter 635mm

I hope thats right but this says it is Custom wheels, rim tire packages Put big size in first

Don't ask me why the numbers don't add up but the speedo on the Octavia was out 10% at 100kph and I went from 632mm to 657mm (25mm difference) which is 4% difference in diameter and the speedo was dead accurate. Go figure.

[brad]

When I worked in the tyre industry and Australia actually made tyres 185 and 195 x 14 Goodyear Supersteels came out of the same mould as did a few others. They were close to the same height and width too.

At the multi-brand place I worked at you could line up 10 different brands of a 235/60r14 and they would vary by 30mm in diameter and 40mm in apparent width. A lot of the width difference was due to the shape of the transition profile from tread to sidewall. It was handy if somebody was scraping tyres due to being lowered and too much rim offset as you could plonk some Yokohamas (i think they were the small ones) on it and all the scraping was gone.

That was in the 1980s so i'm sure none of that happens anymore. ;-p

[Sydneykid]

Don't ask me why the numbers don't add up but the speedo on the Octavia was out 10% at 100kph and I went from 632mm to 657mm (25mm difference) which is 4% difference in diameter and the speedo was dead accurate. Go figure.

On old tyres, worn out but not quite illegal, there can be up to 5% difference in diameter compared to the same brand new tyres, with full tread depth. My Polo on brand new tyres did 100 kph (genuine, via the GPS data logger) at an indicated 105 kph. Over time they wore down and it got up to 109 kph (to do a genuine 100 kph). Put on a new pair of 45 series and it reads 100 kph at a genuine 100 kph. Obviously that will change as they wear, but won't get to the 9 kph difference that the 40 series ended up at.

We also experience diameter growth due to centrifugal force, on the race cars the wheel rpm and GPS speed traces differ at 60 kph to what they do at 270 kph. Plus different tyres grow at different rates, the cross ply tyres was use on the historic F2's grow faster than the radials we use on the F3.


Cheers
Gary