Archive for April, 2007

Comment on Wheels Tyre Test – April 2007

The Wheels tyre test in the April 07 issue is a credible effort to objectively test tyre performance, and the test has turned up some interesting and useful results.

This is a difficult thing to do, and car and tyre manufacturers go to exhaustive lengths to assess tyre performance and match it to a vehicle, usually on a test track or racing circuit hired for the day. The stakes are high for both car and tyre manufacturers, and usually they spend lots of research and development dollars to ensure they get the best result possible.

Both car and tyre manufacturers have well-developed test protocols established from many years experience of this type of testing. These test protocols must “square up to” the same issues that faced the Wheels crew in planning and executing the 2007 Tyre Test. Some of these issues are:

1. Controlling the test conditions

Variation in test conditions means the difference in results from successive test runs on different tyres isn’t solely due to the different performance of the two sets of tyres, and effectively renders the results useless. Significant variations in ambient temperature, track surface (surface roughness/texture, level of “contaminants” such as rubber dust, etc.), water depth for wet testing, degree of wear on test tyre treads, even wind speed – the list goes on and on, and all factors must be controlled or their effect minimised. The Wheels tyre test crew did a pretty reasonable job in this department.

For example, it isn’t possible to eliminate the effect of wear on a tyre tread, as some wear will occur during the course of the test. Rather the amount of wear must be minimised by limiting the number of test runs each individual tyre does, so that the wear is minimised and does not become a significant factor. The Wheels crew did this by using “objective” assessment methods for all the tests conducted. Using objective assessment methods means the number of test runs can be minimised, the amount of tread wear is minimised, and the length of time taken to complete any set of tests is minimised, meaning there is less chance of variation in weather conditions – which would cause variation in the tyre performance, and therefore unreliable test results.

2. Objective versus subjective assessment

Objective assessment simply means that some mechanical or electronic means are used to measure tyre performance – for example, measuring stopping distance, lap time, deceleration/acceleration – are all objective assessments. Objective assessment is regarded by development engineers as being more reliable and repeatable, but in the final analysis, does not provide test data on driver feel criteria, such as linearity and predictability in a tyre’s performance. Some tyre performance parameters, such as steering response or skid recovery, can only be tested subjectively – that is – rated by a test driver.

Subjective testing, means the test driver rates the tyre’s performance compared to the previous set of tyres, during multiple test runs on different sets of tyre types/brands. Subjective assessment is much more difficult to do well, and requires a much greater investment in time and money. With any realistic number of test tyre types, subjective assessment means a greater number of test runs must be done, as each set of tyres must ideally be compared with each other set of tyres, to enable the driver to make a direct comparison between each pair of tyre types (or brands).

For example to test 4 tyre types/brands A, B, C and D ideally requires a total of 8 test runs, and 2 runs on each tyre. The tyres would be tested in the following order:

A, B, C, D, A, C, B, D

With more sets of tyre types/brands to be tested, the number of test runs that must be done increases significantly. This often means that additional sets of each tyre type/brand must be used in the test, to limit the effect of tread wear on the test results.

As subjective testing relies on a driver’s assessment of a tyre’s performance, issues of driver preference, or bias, can also creep into the results. For this reason, more than one test driver is used, and the results pooled.

Tyre and car manufacturers rely on a combination of objective and subjective test methods, depending on what tyre performance parameter is being tested.

3. How can the test results be used?

Accurate and repeatable results are what we want from any test – otherwise we haven’t succeeded in sufficiently controlling the test conditions or there is some other basic problem with our test procedure.

The Wheels tyre test covered a number of very important tyre performance characteristics. The Wheels test crew went to considerable lengths to control or mitigate test variables, and obtained credible and useful results. But can these results be applied to my or your car?

Unfortunately, the answer to this question is not simple, although some indication of an answer can be seen in the different rankings obtained for the two different tyre sizes used in the test. There were relative differences in the performance of the different brands in the two tyre sizes, when tested on two quite different vehicles. This is not at all surprising, when it is considered that most aspects of tyre performance on a vehicle are affected by interactions with the vehicle and it’s suspension, wheels and brakes. These interactions are complex, and often unpredictable without specialist engineering knowledge, which of course, is not readily available to the average tyre consumer. A further complication arises from the influence of the multitude of electronic vehicle performance aids that are becoming increasingly available on modern vehicles – such as ABS, EBD, EBA, ESP, etc, etc. These technologies can tend to mask or compensate for the differences between tyres.

4. How do you use this information for your own tyre purchase decision?

Which is the best tyre for you and your car? This is really two questions – the first being what tyre performance parameters are important to you – only you can answer – but Wheels’ comments are worth considering. The difference between “cheap” and quality high performance rubber as tested by Wheels in this test, can often be significant, and can be the difference between injury, or walking away from an accident or potential accident. The difference in cost between the “cheap” tyre might be recovered many times over, by the absence or reduction in damage to your car, or even worse, in injury to yourself.

The second question – what tyre works best on your car? By all means use the Wheels test as a guide. Another way is to check the CarbonBlack website for comments made by other drivers, who just may have commented on your vehicle and the tyres you may consider buying. While most consumers won’t have had the opportunity and the skills to really put their car and its tyres to the sort of test run by Wheels, they will have experience in the everyday conditions that may be just as relevant to your decision. The more comments you can aggregate and factor into your personal assessment and decision, the better informed you will be!

Allan Henry

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April 24, 2007 at 9:35 am 1 comment

Reading a Tyre’s Message

Tyres are a very tradeable commodity in today’s international trading world. Some countries use them to buy other currencies, and soon after a currency has been devalued, you will find tyres from there on your docks.

They are all made to similar technical, performance, and dimensional standards through a series of interlinked Tyre and Rim Association Standards world-wide. The major bodies are Tyre and Rim Association, U.S.A., Japan T & R, Australian T & R., and E.T.R.T.O. (Europe). So a Romanian made tyre fits a Peugot in Brazil- it’s no accident. These Standards cover the basics, but individual countries may require other information to be available to the tyre consumer. So manufacturers try to cover all the bases, by putting a veritable essay on the tyre sidewall some of which is relevant, some ( a lot), is not. For example, U.S.A. legislation requires performance information on tread wear, wet road/braking information. The ratings given are very high, the reason being that they are related to a bias ply tyre, which hasn’t been around as a passenger tyre now for over 20 years! Tyre technology improvements have made them meaningless.
So let’s stick to the basics of a tyre size code. Let’s take 195/75R15 92H as an example. Now I have to get a little bit technical, because measurements of a tyre are made under strictly controlled conditions, otherwise they too, would be meaningless.

195– dimensions in millimetres of the section width of the tyre (with raised lettering excluded), when mounted on a specified rim ( the measuring rim), inflated, stabilised for a period because they grow a little bit when inflated for the first time), and then measured at its widest point. The rim has to be specified, because section width increases with increasing rim width. Every young car enthusiast knows that!

75– the ratio of section width to section height. Section height is measured vertically from bead ledge to the crown of the inflated tyre.

R– The tyre is of radial construction. Nowadays, they nearly all are. If there is no “R”, then they are not Radials.

15– the nominal rim diameter. “Nominal” because it’s not exactly 15 inches, and how would you measure it on a taper anyway (see interference fit article). In fact to measure a rim accurately requires specialised equipment called a ball tape. Certain manufacturing tolerances are permitted, so each rim diameter and profile has its own ball tape measure, with the tolerances built in.

92. A code for the load in kilograms that the tyre can carry at a specified maximum pressure, in this case 630 kg. If for example, it was 96, this signifies that the tyre can carry a higher load, at a higher inflation pressure, so it has a stronger casing. The smallest code is 0 (zero), which carries 45 kg. That’s probably a wheel barrow tyre. The largest (so far) is 279, which carries 136 tonnes (136,000 kg), the size of which you have probably guessed as those giant machines that work in the mines.

H– A code for the speed capability of the tyre at specified load, temperature and pressure. In this case, it’s 210 km/h. The range of speed categories go from A1 (5 km/h) to A8 (40 km/h) for slow moving equipment. Then B to Z covers 50 to 300 km/h in 10 km/h steps, with 0 (Zero) omitted because it might get confused with O, and H out of sequence (because it was there first!) H comes after U, then follows V, Z, (same reason), W, and Y. X is omitted because the first radials (Michelin) were designated X, and this could breed confusion.
Z is different. ZR with no other speed category means the tyre has been designed to fit the performance of a particular high performance vehicle. They’re on your Ferrari or Lamborghini. ZR plus a speed category following, carries that speed category as defined e.g. 275/40ZR17 93W has a maximum speed of W (270 km/h)

Compare all the tyres at a particular size on CarbonBlack.com.au

April 20, 2007 at 9:41 am Leave a comment

Queensland Corvette Convention 2007

CarbonBlack checked out the Queensland Corvette Convention over the Easter weekend at Broadbeach in the Gold Coast. In a word…gorgeous….the men and their machines, the woman, the day, the weather. I spoke with Brent Carr of Mosman, NSW. Brent purchased his tired, tossed aside 1958 Corvette through a classified section of an auto magazine and has spent the last 13 years remodelling. And it shows.

Brent Carr of Mosman with his 1958 beauty!

April 16, 2007 at 8:53 am Leave a comment

Alignment of Tyres

A vehicle has to track straight on a road that is crowned, or sloped, or flat. The whole vehicle. On some of these huge road trains, their trailers seemingly have a track of their own, whipping from side to side. Yet the modern B-Doubles traveling the major highways, track quite well.

They bear the fruits of a lot of research into vehicle alignment. The whole set-up has been laser aligned to make the trailer track properly. The settings may be different for vehicles that travel the flat roads from the eastern States to W.A. ; or set so the trailer alignment counteracts the high crown of far N.Q. roads.

The Holden Kingswood, or any rear wheel drive car of that vintage, was not as critical in its alignment as the modern front wheel drive. The rear wheels thrust the car forward on the Kingswood, whereas the front wheels drag the car along in the FWD.

There are three major alignment factors- camber, castor, and toe in ( or out). All affect tyre wear and handling. The settings are decided by the car engineers. For example, a Commodore SS has more negative camber than a Commodore Executive, or the tolerances may be set to the maximum on one, the minimum on the other, to improve one aspect of handling.

But there is a fourth setting. The thrust line and its alignment to the drive are more critical in a front wheel drive. If one REAR wheel is out of alignment, it can make the whole car travel crabwise down the road. You see the car drifting off one way or the other, while the unconscious driver is constantly correcting his steering. Once you become aware of this, it’s amazing how many cars you see tracking like that. So if your car has been clipped over one rear wheel, the mountings have been disturbed, or the car repaired after a smash, ask for a “full four wheel alignment to the thrust line.”

If the front tyres on your car (which has had its alignment checked) still wear unevenly on the outside of one front tyre, and the inside of the other, look to the rear end to see what is making it travel crabwise.

April 13, 2007 at 9:43 am Leave a comment

Wheels Magazine 2007 tyre review.

If you’ve bought the April 2007 issue of “Wheels” magazine, you’ll be impressed with the amount of effort put into evaluating 2 popular tyres sold in the Australian market, the 235/45R18 on big sixes and V8’s, and the 205/55R16 sold on smaller sedans, and some sports cars. Three days of extensive testing showed the test results to be biased in favour of more expensive tyres, rather than cheap ones. Surprise! Surprise!

In tyres, as in many other manufactured articles, you get what you pay for, though I must admit the prices quoted for the tyres were the full retail, and no-one pays those, there’s just too much competition! Made me blanch a bit though!

So what distinguishes a cheap, poorly performing tyre from a good all-round tyre performer, such as the Dunlop Maxx, which handles, corners, grips in wet and dry, and responds to steering input. In a word, it’s “complexity”. What makes a tyre construction work is explained in the tyre technology section of this blog.

And it comes at a price.

Sure, you could be critical that they only did two timed runs, maybe three if the deviation was too great, but the (skilled) test drivers must have been slightly stir crazy, and even more skilled, or even more tired, at the end of three day’s testing. So some deviation from standard must be expected. Nethertheless, good tyres all rated within 1-2% of each other, whereas poorer quality tyres fell down in one or more important aspects.

To search, compare and buy tyres online, we recommend CarbonBlack, it’s free, it’s fast and it’s easy. You just have to tell CarbonBlack about your car and current tyres and tyre dealers located in your area will bid to offer you the tyres you need, at the right price!

April 7, 2007 at 7:47 am Leave a comment

Daring raid nets $31,000 worth of tyres

I just found this article reporting the tyre theft that happened in Sydney West near Homebush.

Quite funny because I had written in a previous article that tyres are a form of international currency, since they are all made to the same technical standards worldwide.

However, the thieves who took off with a container load of tyres, read currency, in Sydney will find that they are quite bulky, and hard to conceal, even in their container. If they are truck tyres, probably Bridgestones, they will find a market, but where do they get them fitted?

Reminds me of the time that 165-13 tyres were disappearing from a huge warehouse, and no-one knew how. Why only 165-13? Turned out they fitted exactly into a 44 gallon (200 litre) rubbish drum , in fact so neatly that the rubbish (on top) could be emptied out without dislodging the tyres underneath. Didn’t shift much rubbish though, only netted nine months gaol!

April 4, 2007 at 9:49 am Leave a comment

Tyre Tread Wear

TYRES WEAR OUT. “Isn’t that great!” say the tyre dealers. ”Need some new tyres already, and gee, do they cost a lot”, says the motorist. Of course the tyre companies do make a tyre that never wears out. It’s called the “spare wheel” (Joke.)

Tyres wear out because they grip the road, by developing friction. Friction is a study in itself, but without it, you would get nowhere- no acceleration, no braking, no steering. This all occurs where the tyre meets the road. The less movement of the rubber under the footprint, the less the tyre wears- called a steel radial tyre. The less heavy braking, or fast cornering you do, the less the tyre wears. The reason- in order to develop friction, the tyre must slip to develop grip. In order to corner, the tyre surface must distort at the contact patch by slipping. This is happening all the time. When your tyres chirp as you accelerate, or squeal as you brake violently, you are only hearing what goes on all the time.

The A.B.S. braking systems on modern cars pick the point of maximum grip, which is just before the tyre starts to skid, to optimise their brake performance. A.B.S. systems are calibrated to pick this point of maximum grip. They “let go” just before the tyre starts to slide, pulsing far more rapidly, on and off, than even a skilled motorist could do, to maintain maximum braking power. So realise that it is not the brakes that stop the car, it’s the tyre grip. If there is no grip available, like on ice, then you have trouble going anywhere at all!

Due to excessive movement of the tread rubber, the bias ply tyre, which was the normal tyre 30 years ago, reached its engineering limit. It couldn’t go much faster, got too hot, wore fast, and distorted at high speed. Michelin invented and marketed the steel belt radial in 1948, patented its method of construction, and the world’s tyre engineers had to wait till the patents expired. An interim radial tyre, called the Pirelli Cinturato, was developed in this period, which didn’t infringe the patents. At one stage, 44 tyre companies around the world were making tyres of that design.

You were doing well to get 25000 kilometres out of a set of bias ply tyres, and with steel belt radials, this has doubled. Putting steel belts on a radial casing allowed the tyre to develop it’s cornering power at a lower slip angle, so it didn’t wear as fast. Incidentally did you know that hooning around roundabouts can wear your tyres up to eight times faster than straight ahead running?

However, the first radials were down on wet road holding, being skinny by today’s standards. In other words good tread wear and good grip proved dificult to combine in the one tyre. It still is.

April 2, 2007 at 1:28 pm 1 comment