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Discussion Starter #1 (Edited)
Today I decided to do some research on the whole 21" Tyre issue, as I'm interested in the Hartge 21" Wheels. First issue was, that there are not many 21" Tires available, and some questions have been raised as to whether the Continental ones, supplied by Hartge are within spec, this is important for insurances reasons in some jurisdictions. I decided to try and find out what the story is. So I contacted Hartge,Tirerack, a local supplier and get some specs from BMW's own publications. Please note all weights are in Kgs

So first I got BMW's specs (from published Specs and brochures)

Front Axle Max Load = 1090Kgs
Rear Axle Max Load = 1270Kgs

I asked Hartge what is the relationship between these numbers and the tyre spec they chose and they explained it

as : BMW's Axle Max Load/2 (divide by 2 for 2 wheels per Axel)

so using that formula we get

Load Index /Tyre load Front = 1090 /2 (divide by number of Tyres) = 545Kgs per Tyre

Load Index/ Tyre load Rear = 1270 /2 (2 Tyres) = 635Kgs per Tyre


So bases specs are Front 545Kgs, Rears 635Kgs

Now I was told (local source) that some "extra" is factored in for increased load on front wheels when breaking hard and on Rear Wheels when accelerating hard. But I cannot find any source, info , test or published explanation of what that "extra" is and how you figure out what it is ?

That leads to a grey area - of well how do you know a tyre is within spec ? I'll give you an example based on figures we know

Base Load Front = 545Kgs
BMW 19" Original Equipment Front Tyres Load =710Kgs
Hartge supplied Conti in 21" Tyres Load is 650Kgs

So without knowing how the "extra" is arrived at, just looking at base specs, then both tyres look more then up to the job , as the both are capable of dealing with more then 545Kgs. The question is , whether there is a pertinent/important reason t for BMW's choice of a 710 Kgs capable tyre ?

So faced with a Tyre and Wheel choice how can you verify that your chosen setup is within specification ?. Without knowing what "extra" I should add to the base 545Kgs spec how can I be sure I have a valid within spec tyre setup.

Btw I am ignoring the fact that some jurisdictions have a tyre placard in the car that purports to show the tyre spec,

Anyone got any ideas, or
disagree with the Hartge supplied base load calculation method ?
 

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m5-black said:
Today I decided to do some research on the whole 21" Tyre issue, as I'm interested in the Hartge 21" Wheels. First issue was, that there are not many 21" Tires available, and some questions have been raised as to whether the Continental ones, supplied by Hartge are within spec, this is important for insurances reasons in some jurisdictions. I decided to try and find out what the story is. So I contacted Hartge,Tirerack, a local supplier and get to some specs from BMW's own publications. Please note all weights are in Kgs

So first I got BMW's specs (from published Specs and brochures)

Front Axle Max Load = 1090Kgs
Rear Axle Max Load = 1270Kgs

I asked Hartge what the relationship between these numbers and the tyre spec they chose and they explained it

as BMW's Axle Max Load/2 (divide by 2 ofr 2 wheels per Axel)

so using that formula we get

Load Index /Tyre load Front = 1090 /2 (divide by number of Tyres) = 545Kgs per Tyre

Load Index/ Tyre load Read = 1270 /2 (2 Tyres) = 635Kgs per Tyre


So bases specs are Front 545Kgs, Rears 635Kgs

Now I was told (local source) that some "extra" is factored in for increased load on front wheels when breaking hard and on Rear Wheels when accelerating hard. But I cannot find any source, info , test or published explanation of what that "extra" is and how you figure out what it is

That leads to a grey area - of well how do you know a tyre is within spec. I'll give you an example based on figures we know

Base Load Front = 545Kgs
BMW 19" Original Equipment Front Tyres Load =710Kgs
Hartge supplied Conti in 21" Tyres Load is 650Kgs

So without knowing how the "extra" is arrived at, just looking at base specs, then both tyres look more then up to the job , as the both are capable of dealing with more then 545Kgs. The question is there any pertinent/important reason that we should know for BMW's choice of a 710 Kgs capable tyre

So faced with a Tyre and Wheel choice how can you verify that your chosen setup is within specification ?. Without knowing what "extra" I should add to the base 545Kgs spec how can I be sure I have a valid within spec tyre setup.

Btw I am ignoring the fact that some jurisdictions have a tyre placard in the car that purports to show the tyre spec,

Anyone got any ideas, or a
disagree with the Hartge supplied base load calculation method ?
Well, here's my thinking:

BMW developed these tires with Conti specifically for the M5. Their load ratings are 710kg front, 775kg rear. They designed the tires with those load ratings for a reason - I imagine that was the spec that BMW gave them. Or possibly BMW gave Conti a spec, and they exceeded it. I don't know if you can ever figure that out though.

When substituting tires, I would not go with a lower load rating than the tires that were specifically designed for the car. I'm sure there is a safety factor built in, but I'd rather have that factor than not. When I talked to Tirerack, they said the same thing - they would not recommend lower load ratings than the OEM tire specs.
 

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Discussion Starter #3
Wolverine said:
Well, here's my thinking:

BMW developed these tires with Conti specifically for the M5. Their load ratings are 710kg front, 775kg rear. They designed the tires with those load ratings for a reason - I imagine that was the spec that BMW gave them. Or possibly BMW gave Conti a spec, and they exceeded it. I don't know if you can ever figure that out though.

When substituting tires, I would not go with a lower load rating than the tires that were specifically designed for the car. I'm sure there is a safety factor built in, but I'd rather have that factor than not. When I talked to Tirerack, they said the same thing - they would not recommend lower load ratings than the OEM tire specs.
Funny thing is that if you look on Tirerack you'll see that the non OE version of the tyre has an even higher load rating - higher by approx 199Lbs - which I find confusing.

I wish this tyre stuff was more transparent and straightforward.
 

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m5-black said:
Today I decided to do some research on the whole 21" Tyre issue, as I'm interested in the Hartge 21" Wheels. First issue was, that there are not many 21" Tires available, and some questions have been raised as to whether the Continental ones, supplied by Hartge are within spec, this is important for insurances reasons in some jurisdictions. I decided to try and find out what the story is. So I contacted Hartge,Tirerack, a local supplier and get some specs from BMW's own publications. Please note all weights are in Kgs

So first I got BMW's specs (from published Specs and brochures)

Front Axle Max Load = 1090Kgs
Rear Axle Max Load = 1270Kgs

I asked Hartge what is the relationship between these numbers and the tyre spec they chose and they explained it

as : BMW's Axle Max Load/2 (divide by 2 for 2 wheels per Axel)

so using that formula we get

Load Index /Tyre load Front = 1090 /2 (divide by number of Tyres) = 545Kgs per Tyre

Load Index/ Tyre load Rear = 1270 /2 (2 Tyres) = 635Kgs per Tyre


So bases specs are Front 545Kgs, Rears 635Kgs

Now I was told (local source) that some "extra" is factored in for increased load on front wheels when breaking hard and on Rear Wheels when accelerating hard. But I cannot find any source, info , test or published explanation of what that "extra" is and how you figure out what it is ?

That leads to a grey area - of well how do you know a tyre is within spec ? I'll give you an example based on figures we know

Base Load Front = 545Kgs
BMW 19" Original Equipment Front Tyres Load =710Kgs
Hartge supplied Conti in 21" Tyres Load is 650Kgs

So without knowing how the "extra" is arrived at, just looking at base specs, then both tyres look more then up to the job , as the both are capable of dealing with more then 545Kgs. The question is , whether there is a pertinent/important reason t for BMW's choice of a 710 Kgs capable tyre ?

So faced with a Tyre and Wheel choice how can you verify that your chosen setup is within specification ?. Without knowing what "extra" I should add to the base 545Kgs spec how can I be sure I have a valid within spec tyre setup.

Btw I am ignoring the fact that some jurisdictions have a tyre placard in the car that purports to show the tyre spec,

Anyone got any ideas, or
disagree with the Hartge supplied base load calculation method ?
Hi Guys

Let me try and help here. I used to be in the alloy wheel business and was responsible for researching exactly this kind of thing when we started to look at new applications for our wheels.

The axle load rating that manufacturers give is the maximum including the extra amount that m5-black is querying.
The way manufacturers calculate this is by testing for maximum acceleration and braking, as well as lateral acceleration. You will also note that the rear axle load rating is higher than the front, when in reality the car is actually heavier at the front than the rear. The reason for this is to allow for all possibilities including towing something. So if the car was ever fitted with a tow bar then the additional weight has also been factored in.

If you add the load ratings that bmw give this gives a total weight of 2360kg's. Now we all know that an M5 does not weigh that much, the true weight I believe is sub 1800kg's.

M5-black you don’t have to worry about the extra weight for braking or accelerating as this has already been factored in.

As to the difference in load ratings of the standard 19" tyres and the 21" Conti's the explanation is most probably as follows, and this is based on my experience with dealing with conti for exactly this type of exercise:

The standard 19" tyre when built by the manufacturer already has an inbuilt strength and when conti then test to give a load rating these tests then conclude that the tyre in that particular size has a certain load rating. Most of this is based on carcass strength and construction. The OE tyres that have been developed for the M5 use this basic caucus and then the tyre is fine tuned by altering the type of compound and making alterations to sidewalls to match the dynamic requirements of the BMW engineers. Once this has been finalised the tyre is then retested and the final load rating is given. But it is fairly normal for tyres of this size and width to have this kind of load rating.

There is one factor that is also crucial to the load rating of the tyre that no one as yet has mentioned and that is the speed rating of the tyre.

For instance these tyres are Z rated, which means over 149mph, but as cars have got faster there has been three new additions that of W up to 168mph and Y which is up to 186mph. The other is (Y) in brackets which means that this tyre has normally been tested at over 186mph for its particular application.

Now it could be that the load rating of the OE tyres is 710kgs and it is Y rated, that means it will have that load rating up to 186mph. As the car exceeds this then the load rating also comes down, so it could be that by 205mph the tyre mat still have a load rating that is greater than BMW's load rating. I don’t recall this formula they used as speed increased, but I had these problems when I was developing a 20" wheel and Tyre for the Bentley GT Coupe.

I hope I have been of help.

One thing I could never understand, and this is aimed at the USA members, why is it in your country where people will sue you for something really trivial, do most of the industry have a blatant disregard for this type of safety on wheels and tyres. An example of this was when I was trying to develop the 20" wheel and tyre package for the Bentley and also the Aston Martin Vanquish I could not find the correct load rated and speed rated tyre. I could find the correct sizes but not the ratings that were required. I visit SEMA in LAsVegas that year and to my horror there were Bentley's running 22" wheels and tyres, where I know for a fact that the tyre did not have a load rating or speed rating anywhere close to what was required for that car to be safe!!!!! Absolutely mad.



So in short m5-blackk the Hartge wheel and tyre combo will be correct for the car. Hartge are a quality tuner and will have tested this.


Anyway I hope I have helped.

Thank you all for reading this far down.

:byee55amg
 

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Amjad Ali said:
For instance these tyres are Z rated, which means over 149mph, but as cars have got faster there has been three new additions that of W up to 168mph and Y which is up to 186mph. The other is (Y) in brackets which means that this tyre has normally been tested at over 186mph for its particular application.
Thank you for the explanation, one thing on my mind however.

How can the tyres under the M5 be Z rated when the limiter kicks in at 250km/h (155mph)? And BMW inidividual planning on offering a speed limiter removal so it can run upto 305km/h (189mph). I thought the conti's were rated to go upto 305km/h wouldn't that give it a Y rating and not a Z rating?

Since you seem to be fimiliar with these tyres and also fimiliar with the industry could you give us your opinion on the conti's? Things like comfort, noise level, grip, durability and such.
 

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Amjad Ali said:
...So in short m5-blackk the Hartge wheel and tyre combo will be correct for the car. Hartge are a quality tuner and will have tested this...
I think this is a very dangerous and reckless recommendation. The only thing that is improtant IMO is whether his insurance company will compensate him for damage that occurs when he is on a tyre that does not conform to the manufacturers' specifications.

The tyre load rating spec for the M5 is clearly stated as 710 and 775kg - so if you are on a tyre that is load rated at less than that in some countries the car is deemed to be unroadworthy. The consequence of that is that insurance policies are void. Obviously it's still safe to drive but that is not the point from the point of who will be responsible for damage that occurs to the car or by the car.

If you are OK with driving your M5 without insurance, then you can put whatever rubber you want - but if you want to know that you're insured - just make one call and ask your insurer "if I have an accident in this car with these +2 wheels and tyres is my policy valid and hey say yes and give it to you in writing" then go for it.
 

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frylord said:
Thank you for the explanation, one thing on my mind however.

How can the tyres under the M5 be Z rated when the limiter kicks in at 250km/h (155mph)? And BMW inidividual planning on offering a speed limiter removal so it can run upto 305km/h (189mph). I thought the conti's were rated to go upto 305km/h wouldn't that give it a Y rating and not a Z rating?

Since you seem to be fimiliar with these tyres and also fimiliar with the industry could you give us your opinion on the conti's? Things like comfort, noise level, grip, durability and such.
The Y is an addition, so the tyre will probably have a ZY rating...
 

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frylord said:
Thank you for the explanation, one thing on my mind however.

How can the tyres under the M5 be Z rated when the limiter kicks in at 250km/h (155mph)? And BMW inidividual planning on offering a speed limiter removal so it can run upto 305km/h (189mph). I thought the conti's were rated to go upto 305km/h wouldn't that give it a Y rating and not a Z rating?

Since you seem to be fimiliar with these tyres and also fimiliar with the industry could you give us your opinion on the conti's? Things like comfort, noise level, grip, durability and such.
HI Fry as explained above the tyre is usually described as follows:

285 35 ZR19 98Y

This is the tyre width, aspect ratio and then the speed rating before the rim size. The 98Y is the load rating and additional speed rating.
As to the new limiter you have indeed made an interesting point. Can any members please post the exact tyre rating for me. If the car is going to run at 189mph then the tyre will have to be tested on the car for this. In this case it should end up with a (Y) rating. In brackets. This is exactly what Yokohama did with the Bentley tyre at 20". It has a (Y) rating meaing it has been tested on the car.

Many Thanks
 

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sydl said:
I think this is a very dangerous and reckless recommendation. The only thing that is improtant IMO is whether his insurance company will compensate him for damage that occurs when he is on a tyre that does not conform to the manufacturers' specifications.

The tyre load rating spec for the M5 is clearly stated as 710 and 775kg - so if you are on a tyre that is load rated at less than that in some countries the car is deemed to be unroadworthy. The consequence of that is that insurance policies are void. Obviously it's still safe to drive but that is not the point from the point of who will be responsible for damage that occurs to the car or by the car.

If you are OK with driving your M5 without insurance, then you can put whatever rubber you want - but if you want to know that you're insured - just make one call and ask your insurer "if I have an accident in this car with these +2 wheels and tyres is my policy valid and hey say yes and give it to you in writing" then go for it.
Sydl you make a very valid point. Yes you should only use rubber that is recommended by the insurance company. But you should also notify your insurance company that you will be using aftermarket wheels.
The reason I have recommended the Hartge package to m5-black is because it is by Hartge.
In Germany if you are going to fit any wheel or tyre on your car the package has to be TUV approved. Germany has the strictest rules and regulations anywhere in the world for wheels and tyres. If it is not TUV approved then not only is your car insurance invalid the car is not allowed on the road. TUV are the equivalent of the UK's Ministry of Transport. TUV testing is expensive and also very tough.
Hartge's package has TUV approval. The process for TUV approval is as follows:

From Memory
you have to supply approx 12 wheels. All bar 4 are destroyed in testing.
They then test for load rating, and they test until they physically break the wheel.
It is tested for corrosion and is subjected to corrosion tests.
Impact test where a predetermined weight is slammed into the wheel in a manner that represents the wheel hitting the kerb.
There are other tests but it’s too early and I have had no coffee yet.
The main part of the test however is making the tyre choice and fitting the complete package to the car in particular and road tested.

When I mean particular car I mean that car, I used to make the same wheel for Mercedes and BMW but because one had a PCD of 112 and the other 120, it required separate tests.
The tyre load rating that you are mentioning as 710 and 775kg's would mean that the M5 would weigh 2970kg's, I don’t think that is correct.
Hartge's 21" package will have the TUV certificate not only for the wheels but also for the Car, because this is stated on the certificate.

TUV charge you for tyres, petrol used in the test, the hire of the car if need be. Everything has a charge. To give you an idea of this world, when you next complain about the price of your wheels consider this:

Design and CAD testing approx €100,000
Mould manufacture €60-75,000
TUV Testing €35,000

that’s before they even get to a point where they can sell a single wheel.

Now Sydl like I said I agree with you 100% and you are correct, but my recommendation is based on my knowledge of Hartge's TUV criteria. And it is on that basis that I have recommended this package.
 

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A very interesting & educational thread - thanks guys :cool2:
 

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Amjad Ali said:
...Now Sydl like I said I agree with you 100% and you are correct, but my recommendation is based on my knowledge of Hartge's TUV criteria. And it is on that basis that I have recommended this package.
I have no doubt that Hartge's engineering is up to scratch but there are countries that do not accept TUV or other standards except their own.

The issue of load rating is one that is incredibly specific. For example, there are some closed-road tarmac rallies in Australia run under FIA rules. The scrutineering requirement is that the cars be roadworthy. This is interpreted to mean that the cars run tyres rated by the manufacturer in their homologation papers. Essentially this means that the cars need to find R-compound (eg sticky competition rubber) that is road legal (ie no slicks) that meets the speed and the load rating of the manufacturer's car. So a Porsche GT3 or a Ferrari 360 for example, needs to find tyres at the OEM tyre's rating. It is easy for scrutineers to check this compliance because the tyre placard is stuck on the driver's door and the rating stated can be compared with what is stamped on the side of the tyre. If the two don't match, then the competitor has to get new tyres or the car can't compete.

This procedure is essentially the same when an insurance assessor investigates a damaged car. One of the first things they look for are non-standard aftermarket parts. Tyres, wheels, exhaust, engine modifications etc. And if they find anything that is non-standard they look at it with a microscope. If it doesn't comply then they would deny coverage. If you were the car's owner you would then turn to the company that sold you the parts (wheels etc.) that made your car unroadworthy and you would probably have a highly arguable case. Certainly in Australia you would find it very hard to buy a wheel and tyre package that was below the manufacturer's load rating from a shop because they have been told by their insurance company that the owner's of the shop would be personally liable for their customer's loss.

Wheels and tyres in particular, there have been many reported cases where if the tyres are greater or less than the original width and rolling radius by a certain %, the car is deemed to be unroadworthy. So if you go +1, then you have to match the new tyre's aspect ratio properly. Similarly, the new tyres must be the same load rating.

Of course, your country's insurance company and laws may be different, but given the international nature of insurers I would bet that they use similar procedures regardless of country.

If I were living in Europe and wanted to use the 21" wheels and tyres it would be very simple - just ring your insurer and DMV. And if you do, please post their response in this thread so we can be better informed of the situation in your country. What I have stated is the situation to the best of my knowledge in Australia.
 

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sydl said:
If I were living in Europe and wanted to use the 21" wheels and tyres it would be very simple - just ring your insurer and DMV. And if you do, please post their response in this thread so we can be better informed of the situation in your country. What I have stated is the situation to the best of my knowledge in Australia.
Hi Sydl

Like I said I agree with you 100%. Yes you should inform your insurance company right from the offset. I understand the point you make regarding the racing to FIA rules, and its for those reasons dor instance the M3 CSL comes with the tyres it does.

As to the situation in Australia, I am all to aware of it. My dealer there was Bob Jane's T-Marts and the problems I used to get where I would have to change offsets for a particular fitment, even though everywhere else in the world it was never as a problem, used to cause me nightmares. We spoke about this when I was there last year.

Sydl if you think Australia is bad dont even go there with Switzerland!!!!!

I think this is a subjective thing but you are 100% correct, I would always recommend that you check with your innsurance company before changing ANY part on your car not just wheels and tyres.

I believe there is a member there already with the 21" wheels and tyres.

I would not have any issues with my insurance company, they would probably use it to rip me off for some more money the bas$%rds buy thats about it in the UK.

Have a good one Sydl.
 

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Amjad Ali said:
...Sydl if you think Australia is bad dont even go there with Switzerland!!!!!
Really? Strict there too? Does that mean that a TUV approved wheel/tyre combo like Hartge would not be legal in Switzerland?

I think the reason why it's got so bad in the last few years is due to a lot of the performance turbo cars (WRX, Evos) having aftermarket turbos, wheels, tyres, exhausts, pop-off valves and god knows what else added to the cars. These cars then have accidents and the insurers look for an escape clause.
 

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sydl said:
Really? Strict there too? Does that mean that a TUV approved wheel/tyre combo like Hartge would not be legal in Switzerland?

I think the reason why it's got so bad in the last few years is due to a lot of the performance turbo cars (WRX, Evos) having aftermarket turbos, wheels, tyres, exhausts, pop-off valves and god knows what else added to the cars. These cars then have accidents and the insurers look for an escape clause.
In Switzerland they have no problem with TUV, but a lot of manufacturers including my old company would change offsets to improve looks and handling. In Switzerland there is minimal deviation from the original offset and width of the wheels.
We used to make a 9 x20" wheel for the Bentley GT with a 16mm ofset for the rear and 31mm off sett for the front. The original was 9 x19 with an offset of 41mm. The fronts were JUST legal but the backs we could not use. So for there I used to have to ship ET31 wheels. Used to screw my stock up something stupid!!!!
 

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The Hartge tyres are made for the load for the M5. Anything else would be totally lunacu from Hartge to sell to the public. I will reply with a detailed post below.

sydl said:
I think this is a very dangerous and reckless recommendation. The only thing that is improtant IMO is whether his insurance company will compensate him for damage that occurs when he is on a tyre that does not conform to the manufacturers' specifications.

The tyre load rating spec for the M5 is clearly stated as 710 and 775kg - so if you are on a tyre that is load rated at less than that in some countries the car is deemed to be unroadworthy. The consequence of that is that insurance policies are void. Obviously it's still safe to drive but that is not the point from the point of who will be responsible for damage that occurs to the car or by the car.

If you are OK with driving your M5 without insurance, then you can put whatever rubber you want - but if you want to know that you're insured - just make one call and ask your insurer "if I have an accident in this car with these +2 wheels and tyres is my policy valid and hey say yes and give it to you in writing" then go for it.
 

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I talked to Hartge today, Volker one of the responsible technicians. I'll try to explain below. I should read more into definition of load index but a summary is below.

Load index is decided by formerly ETRTO (European Tyre and Rim Technical Orginazation), it is now under well known ISO (International Organazation for Standardization). Load index is just another way of saying load in kilograms [kg] per wheel. For example:

Load index Load [kg]
96 710 kg
95 690 kg
94 670 kg


The ISO decides the width and load index for every tyre size. A tyre manufacturer can specify "Usual" or "Extra load" for the particluar tyre he choose. Extra load you add 4 to this index.

BMW M chosed "Regular" because of the 19' dimension and their choise of combination of comfort and sport. More exactly 96 for fron wheels and 99 for rear wheels. So if it existed, a front wheel to the M5 in "Extra load" would have load index 100. However as seen above there is no need for that since the wheels could carry the M5 without problems.

Important fact is: you cannot change load index more than "Extra load" (+4).

Load index is a result function of various variables with the most important ones are air volume and tyre structure. Air volume on a 21' is less than on a 19' since the inner radius is larger of the tyre with almost remained outer radius of the tyre as we calcuted here.

Consequently a larger wheel must have a lower load index since it has less volume of air.

Hartge have worked with Continental to develop these tyres and this dimension is available from Continental (Hartge partner), Michelin and Pirelli. Hartge wheels are "Extra load" and in this dimension it is the only tyre available (they are not available in "Regular").

Maximun load M5 front wheels: 545 kg. Hartge have 650 kg
Maximum load M5 rear wheels: 635 kg. Hartge have 710 kg

Also, as a "advanced course" Hartge can prove that their tyre is OK for 320 km/h and BMW M5 standard are approved for 310 km/h. This was hard to understand over the phone but I assume their calculations are correct, and that goes in line with BMW M own limiter at 305 km/h.

Definition: Load on tyre: axle load / 2.

Further facts:

The Hartge wheel weight a bit more due it's increased size (of course) and also the design of the spokes. The spokes could have been hollow but this would have lead to a much higher price.
 

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Gustav said:
I talked to Hartge today, Volker one of the responsible technicians. I'll try to explain below.
Gustav, this is very interesting, thanks for taking the trouble to talk to Hartge but the obvious question is:
Q. Why aren't the 21" tyres just designated with a load rating of 96 for the front and 99 for the rear if that is what they are? For the front for example, why is it necessary for Continental to say it is "92 XL" (which Hartge and not Continental told you is equivalent to 96)? Either it is 96 or it isn't. The Continental web site just says: "XL - Extra Load (designates specially reinforced tyres)" - it doesn't say that it is +4.
http://www.conti-online.com/generat...ps/tipps/what_is_written_on_your_tyre_en.html

The point is whether you want to have the argument with the authorities and insurance company. The will just look at the load rating, and *not* the load rating + the "XL" because they are just not interested in what the "XL" means.

Is it possible for you/someone to call your insurance company and ask them whether they are happy to insure an M5 with 92 XL when BMW wants 96 and see what they say on this topic?

Anyone want to ring Continental in Germany?
 

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Gustav

Many thanks for taking the time to calll Hartge.

:M5thumbs:
 

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Thing is, it is ISO that decides load rating for the tyre, not Continental. That is what that organasation purpose is as far as tyre ratings if I understood it correctly.

sydl said:
Gustav, this is very interesting, thanks for taking the trouble to talk to Hartge but the obvious question is:
Q. Why aren't the 21" tyres just designated with a load rating of 96 for the front and 99 for the rear if that is what they are? For the front for example, why is it necessary for Continental to say it is "92 XL" (which Hartge and not Continental told you is equivalent to 96)? Either it is 96 or it isn't. The Continental web site just says: "XL - Extra Load (designates specially reinforced tyres)" - it doesn't say that it is +4.
http://www.conti-online.com/generator/www/de/en/continental/automobile/themes/tyretips/tipps/what_is_written_on_your_tyre_en.html

The point is whether you want to have the argument with the authorities and insurance company. The will just look at the load rating, and *not* the load rating + the "XL" because they are just not interested in what the "XL" means.

Is it possible for you/someone to call your insurance company and ask them whether they are happy to insure an M5 with 92 XL when BMW wants 96 and see what they say on this topic?

Anyone want to ring Continental in Germany?
 

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my insurance company (BMW Original Insurance Sweden) had a simple enough answer over the phone.

If the tire/wheel combination passes the "Besiktning" or MOT equivelant in the UK - it is allowed to be a valid upgrade with the insurers at no extra costs.
 
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