Getting To Know Your Tyres

[Dino 3]

I saw this on the e36coupe.com forum and thought I would share it with you all

 

It's a good read and very informative. No doubt there will be snippets of info we all know and some we don't know. Nonetheless it's all useful.

 

Thanks to Liquid off the e36coupe forum for the write up.

 

Getting to know your tyres

 

Tyres, without doubt, one of the most divisive subjects when it comes to replacement; either as part of their normal service life or because of modification.

 

They are without a doubt, a distress purchase for the motorist. We spend the life of the tyre, checking to see how they are wearing and if they're wearing evenly. Then, when they are almost worn out, we start looking for replacements. Psychologically, this makes you resent the replacement of them. We do not yet have the culture to be enthused about them.

By contrast, the biker scene is completely different. Most bikers like to try out as many tyres as possible, swapping and changing to suit their needs in search of the best balance for their bike. They will bore you all day long about tyres if you let them. If they appreciate the finer points of a tyres characteristics, why cant we?

 

The majority of drivers want the best tyres for budget prices. Whilst many manufacturers are now making much improved tyres in the budget sector, overall they are still deemed to be expensive, especially when you take into account the size of most alloy wheels these days.

A lot of this is down to knowledge. If tyres are treated as another internet search for your lunch hour, in order to find the lowest price every 12-18 months, then not much other thought is going to go into them. Certainly not any positive thought.

 

If we were all aware of what tyres do, how we can prolong their life and what different tyre types are capable of, then we just may have more interest.

 

With the winter settling in, I felt it was about time you guys should learn a few things about your tyres in order to save you money in the long run, and in some cases; possibly save your lives.

 

The basic anatomy of your tyre

 

Tyre technology has had to increase massively over the last decade, due to the introduction of ever faster, heavier and larger cars.

Modern tyres (since around 1968) are of a radial construction, as opposed to the old cross ply method that was prevalent in tyres of yester year. This means the steel belt structure of the tyre runs perpendicular (from one side to the other), with other circumferential layers, overlapping (dependant on manufacturer and application).

 

The tread belt assembly (outer casing) consists of the tread, joint less cap plies and steel cord belt plies (underneath the tread). These steel plies aid the directional stability of the tyre, especially at high speed.

The inner casing has a textile cord ply that keeps the tyre in shape under inflation, an inner liner (normally Butyl) to ensure an airtight bond and the sidewall and bead area.

The bead is especially important with modern cars fitted with low profile tyres. Strength here is very important in minimising any damage to the tyre structure and maintaining strength when cornering, especially under heavy loads at high speed.

 

Rubber is the largest constituent, making up some 41% of the tyre. Fillers such as silica, carbon and chalk represent around 30%. Re-inforcing materials (steel, nylon etc) are roughly 15%, oils and resins are 6%, chemicals for vulcanisation (manufacture) are 6% and chemicals to prevent antioxidisation and material fatigue are 2%

 

Asides from giving you grip and lateral stability when cornering, tyres also play a huge part in the suspension of your vehicle.

When manufacturers are developing their cars, then spend inordinate amounts of both time and money, ensuring they have the best match of tyre to a particular chassis. That doesnt mean all 3 series have the same tyres. As each model has a specific output of power, a tyre will be supplied to suit.

A good example of this is with the E46 M3. Continental provided a specific variant of their ContiSportContact 2 with the denotion M3. This was developed specifically for the needs of the car, as were the Michelin Cup tyres supplied for the CSL.

 

Anyone who has over/under inflated their tyres, will tell you what a big effect it can have on the handling of your car. With BMW, we are lucky enough to have one axle that drives and one axle that steers. This means we can really pinpoint the specific pressures at which our cars work best. ALWAYS adhere to the pressures stated in the handbook or the chart on your door shut for your specific tyre size.

As many of us choose aftermarket wheels, there will invariably be a lack of information, especially for the older generation cars that are running on much larger wheels than they did when standard.

Tyre manufacturers will have details of pressures for typical tyre sizes. This should be used as a cross reference guide with whatever information the vehicle manufacturer can give you. There will be two sets of pressure to adhere to: Unladen (driver) and laden (including passengers and/or load)

 

Issues with over inflation

 

Over inflated tyres can cause a few problems with your cars handling.

 

Tyres will have a smaller contact patch if they are over inflated. Even a difference as little as 4 psi can cause an imbalance and make the car skittish over and bumps and especially in corners. Obviously, this is more noticeable on the front tyres as your steering will feel vague and lighter than usual. At speed, your contact patch is reduced anyway. Make sure you regularly check your pressures!

 

Over inflation also causes wear in the middle of the tyres, As this area is where the bulk of your grip comes from, this is not good. This will cause your tyre to wear out much quicker. MOT testers are concerned with the middle portion of the tyre. This 75% represents the area on which they can and will fail you

 

Issues with under inflation

 

Under inflated tyres hold the same problems (albeit inversely) with the above

 

Under inflation will sap the strength from the sidewall structure of the tyre. This translates into sloppy overall handling, as well as following the shape and camber of the road to a higher degree.

 

When under inflated, the edge of the wheel has an increased propensity to chafe or bite into the butyl inner liner.

The corruption of the integrity of the liner will allow air to escape - into the tyre.

Normally, air will percolate into the sidewall, causing bulges etc. Although some natural condition of manufacture can cause a small protrusion from the sidewall, and egg, ball or finger shaped bulges indicate failure of one of the components and should be removed immediately (this is also a condition of impact damage).

 

Under inflated tyres can also overheat. The build up of pressure will cause the sidewall bulge to explode and cause irreparable damage. Those who went to the last Ring trip in August will remember the lorry tyre gave way in that traffic jam! Thats basically what happened to it.

 

Inflation pressures can change from axle to axle, but never from wheel to wheel. Make sure each axle pair is of the same pressure.

This should be checked every two weeks and before you undertake a long journey. Dont forget to check your spare (for those that are equipped). The spare should be inflated around 6 psi more than the standard tyre which is the recommendation for use in an emergency. Its better to have more air then not enough.

 

Valve caps are very important and are often overlooked. Not only do they protect the tyre valve from foreign object ingress, but they can maintain pressure if the valve were to fail.

 

Winter tyres

 

Although there is no real established market in the UK, they are now a consideration for more of us year on year.

A lot of you are now running winter wheels, in order save your tasty expensive rims from the inevitable onslaught of salt and grit that accompanies the winter months. Winter tyres may also be something to look at.

 

At 7 degrees, the rubber portion of tyres hardens considerably. This has a huge negative affect on road holding, before you even take into account what may be on the road surface. Winter tyres are specifically designed to negotiate ice and frozen surface due to their increased capability to resist the cold, as well as specific tread design that bites into the road surface, as opposed to riding over the top of it like your normal summer tyre.

Winter tyres are surprisingly effective in the summer months too, although it has been reported that you can have slightly increased road noise and fuel consumption.

 

Storing tyres

 

There are a few ways to store tyres, depending on their condition.

 

Tyres fitted to rims

 

Reduce the tyre pressure to around 15 psi. Either stack them on their side (on top of each other to form a stack) or hang them up by the rim

 

Tyres not fitted to rims.

 

Store these as they would stand naturally, on a piece of thick cardboard. Rotate them every month or so to avoid any flat spotting.

 

Make sure that any stored tyre is away from a heat source and any chemicals such as oil, paint, grease etc. Any residue that comes into contact with the tyre should be cleaned immediately, as it can cause increased degredation of the rubber constituents and/or react with the chemical structure of the tyre.

 

Get to know your tyres

 

Below are the common markings on tyres that will give you the information you need to look after them effectively. (All pictures are clickable thumbnails)

 

This represents the tyre size.

 

265 is the width of the tyre in mm. 40 is the aspect ratio (tyre height is 40% of the tyre width) and 17 is of course, the rim diameter.

 

 

This is the tyre size with both the load and speed indices. The number 96 is the load indices (see chart below) and the letter Y is the speed indices (see chart below) In this case, this tyre is cable of supporting 710kg of weight at a speed of 187mph

 

 

This is the DOT code. The first four characters represent the factory in which this tyre was made. The next few characters relates to the model and production run (this difers between manufacturers) The last 4 digits refers to the age of the tyre. The forst two represent the week in which it was made and the last two represent the year. In this case, the tyre was manufactured in week 5, 2006.

 

 

Orientation of the tyre. This shows that the tyre is directional and must be fitted in this way.

 

 

Tread wear indicators. This indicator in the tread groove underneath the red dot (Cheers J28 ) shows you the legal limit at a glance for quick reference. The problem with this indicator is that people can run the tyre down and wear the indicator away with the tyre. Because of this, there is a second indicator...

 

 

This is on the shoulder of the tyre. The top of the arrow marks the limit. There is no substitute for effective measuring though, so get yourself a depth gauge. They come in very handy.

 

 

Load and speed indices

 

I have only selected the measurements that would affect our cars. Obviously the results run in either direction for the liks of small passenger cars to big 4x4's. You should find all the information you need here.

Each loading is per tyre. So a car that weighs 2000kg will need a minimum of 500kg per corner, a load index of 84.

 

Load Index

 

70 335kg 84 500kg 98 750kg

71 345kg 85 515kg 99 775kg

72 355kg 86 530kg 100 800kg

73 365kg 87 545kg 101 825kg

74 375kg 88 560kg 102 850kg

75 387kg 89 580kg 103 875kg

76 400kg 90 600kg 104 900kg

77 412kg 91 615kg 105 925kg

78 425kg 92 630kg 106 950kg

79 425kg 93 650kg 107 975kg

80 450kg 94 670kg 108 1000kg

81 462kg 95 690kg 109 1030kg

82 475kg 96 710kg 110 1060kg

83 487kg 97 730kg 111 1090kg

 

 

Speed index

 

The speed index is the maximum speed at which a tyre can carry the load mentioned in the table above.

 

R 106 mph

S 112 mph

T 118 mph

H 130 mph

V 150 mph

W 169 mph

Y 187 mph

ZR In excess of 150 mph (total limit to be measured by load indices)

 

 

 

Directional, rotational, asymmetric blah blah blah

 

There are a few categories in which tyres fall under. Directional tyres are very much a sport derivative tyre, favoured by many in the aftermarket scene.

 

Assymetric tyres are a good compromise between a standard tyre and a sport tyre. They retain some of the sport design as well as the more comfort orientated characteristics.

 

Standard rotational tyres are seldom seen in the aftermarket and are more suited to small standard passenger cars.

 

Here is a small list of the pros and cons of each tyre type

 

Directional

 

Pros

Aggressive V pattern design to aid cornering stability and increased speed

High aesthetic value given their design

 

Cons

 

Increased propensity to tramlining

Can only be fitted to one side of the car when rotating tyres

 

Assymetric

 

Pros

Great straight line road holding due to circumferential groove design

Low road noise

 

Cons

Compromised cornering abilities

 

Rotational

 

Pros

Can be swapped from position to position in order to prolong life

Fuel consumption efficient

 

Cons

Poor cornering ability

Boring looks.

 

Mixing tyres

 

The cardinal rule here is never mix tyres on the same axle. As you can see from my brief description above, different types of tyres have different properties, even if they are from the same manufacturer.

Mixed tyres will unbalance a car quite easily. Obviously it is impossible to surmise to what degree it will affect it; there are too many variables.

Asides from the handling implications, if you were to have an accident and it was noticed by an assessor/police etc, your insurance can be void as a result of it.

Porsche have a directive whereby a certain tyre must be fitted to their vehicles, or the warranty will be void. It's an important factor!

 

One thing I have experimented with and continue to experiment, is different tyres front and rear. As mentioned earlier, BMW's benefit from seperate drive and steer axles.

If you have access to tyres to try out, it's a worthwhiel exercise. Fine tuning tyres to your chassis can get more from your car. One big complaint is tramlining. Assymetric designs with circumferential grooves all but eliminate the effects of tramlining. You could use these on the front axle, whilst sticking to your favourite choice on the rear.

 

I am in no way saying you should do this. It is merely an option open to you and you should be aware of it. If you do your homewor and try some tyres out to match the balance out, it can be a very worthwhile endeavour.

I run Falken FK451's on the rear and Uniroyal Rainsport 1's on the front. It's been an interesting trial and they have suited the car really well together.

 

Tyre care

 

We all like to put on a bit of tyre black for a meet or a show. The truth is, most of these cleaners can actually protect the tyre. Keeping the tyre compound soft, will prevent cracking and crazing due to exposure to the elements. Think of it like moisturiser that you use for your skin.

Some are better than others at doing this. Take a cursory look at the product information the next time you pick up a bottle and compare it with the others available. Its a small thing, but all the small things add up.

 

Avoid going up kerbs. Sometimes its necessary as not all road and drives are perfect. If you do have to mount a kerb for any reason, try to make contact as squarely as possible. This will put the load across the entire tyre and will save the internal structure from most of the pressure than can cause breaks or kinks, as opposed to one corner if you drive up it at 45 degrees.

 

Do a visual check off all the tyres as part of your usual cleaning/maintenance regime. Stone trapping can lead to all sorts of issues. Shale is notorious for penetrating the tyre and causing a puncture. Even thorns from bushes have been known to cause punctures. Like many instances, an ounce of prevention is better than a pound of cure.

 

Inflation pressures are very important. The longer the tyre is kept at the correct pressure, the longer it will last and the better it will be at doing its job. Get yourself a pressure monitor/gauge and a tyre depth gauge (both can be had for a few pounds at most motor factors).

The current minimum legal tread depth, is 1.6mm. The safety organisation ROSPA advises to change your tyres when they reach 3mm, as braking distances; especially in the wet, are vastly reduced.

Some recent testing was done for a well known motoring magazine with identical cars. One wearing 3mm tyres, the other on 1.6mm tyres. They both broke from speeds of 70 mph. When the car that had 3mm had stopped, the other car was still doing 50mph. Just think about that for a minute

 

Obviously, a balance between economy and safety needs to be addressed. However, the majority of you that drive high powered variants of the BMW series, may want to think about changing your habits; given the time and money you invest in your car every year.

One suggestion I would make, is to swap out your tyres at 3mm and keep them as track tyres or to sell as track tyres.

Tyres with 3mm of tread will stand up to a few track days (surface and driving style permitting). This will afford you increased safety on the road and increased economy when it comes to having some fun. Seems like a pretty good compromise to me.

 

I hope this gives you a greater understanding of tyres, as opposed to the usual notion of ignoring them because theyre just black, round and not very exciting.

 

Thanks for reading

 

Liquid

[Richie-Van-GTi 71 2 Cars]

some useful info there, the picturtes showing wear indicators though, correct me if Im wrong but the first one is simply a mould point, the actual wear indicator is the raised part within the trench of the tread.

[Dino 3]

some useful info there, the picturtes showing wear indicators though, correct me if Im wrong but the first one is simply a mould point, the actual wear indicator is the raised part within the trench of the tread.

 

This indicator in the tread groove underneath the red dot

 

[Richie-Van-GTi 71 2 Cars]

teach me to half read whilst drinking miss artois

[Rob_the_Sparky 9]

I suspect the resaon bikers talk more about tyres is that they get through a hell of a lot of them. Givent he tyre life on a car you rarely get an opportunity to try several different types out.

[saveloy 8]

Jeeezus. Have you nothing to do this Christmas?

I have books with fewer words.

Incidentally, I have just bought a pair of Bridgestone RE 720's. I've not has a real chance of testing them, but they seem comparable the S - 03's they replaced. Possibly better actually.

[Dino 3]

Jeeezus. Have you nothing to do this Christmas?

I have books with fewer words.

Incidentally, I have just bought a pair of Bridgestone RE 720's. I've not has a real chance of testing them, but they seem comparable the S - 03's they replaced. Possibly better actually.

 

Jeeeeezus did you f***in read my post you moron? And yes I have lots do this Xmas. In fact you should have read when I posted this. I didnt write it someone else did, and even if I did write it I would be proud.

 

It would be nice for just once that you posted something constructive you Scotch drinking 36 yrd born again virgin. Oh and shave that awful beard off..........just caus you are going bald it doesnt mean you should compensate by growing offensive hairs on your chin

 

Oh and Merry Xmas

Edited December 24, 2006 by Dino

[Henry Yorke 269 3 Cars]

Oi you two kebab munchers (not the badly packed variety either!!) Cut it out, it is the season of goodwill and s*it!!

 

Useful stuff in there Dino, however it omits that if you put tyre shine onto a motorbike, it makes cornering interesting as I once found out after cleaning my brothers bike tyres when I had some spare on an applicator whilst doing the car!! He got a grazed knee

[saveloy 8]

Jeeeeezus did you f***in read my post you moron? And yes I have lots do this Xmas. In fact you should have read when I posted this. I didnt write it someone else did, and even if I did write it I would be proud.

 

It would be nice for just once that you posted something constructive you Scotch drinking 36 yrd born again virgin. Oh and shave that awful beard off..........just caus you are going bald it doesnt mean you should compensate by growing offensive hairs on your chin

 

Oh and Merry Xmas

 

 

My word, you really have outshone yourself there. I am almost lost for words.

Surprisingly for you perhaps, I did actually read the post this time, and no I did not think you wrote it.

As for the horrible rest, I'm seeing my mum soon. And I'm telling her what you wrote. Plus, I'm going to make some stuff up. So there.

 

A very merry Christmas to you too. And you Henry.

[tom_m 0]

this page is an outstanding resouce as far as tyres goes to:

 

http://www.chris-longhurst.com/carbibles/tyre_bible.html

[Dino 3]

this page is an outstanding resouce as far as tyres goes to:

 

http://www.chris-longhurst.com/carbibles/tyre_bible.html

 

Nice one Tom

[saveloy 8]

Re, what's with the apparent mid - life crises?

I can't honestly say I've noticed any character changes within your life.

Stop fretting - you're still a twat.