KNOW YOUR TYRES

They’re your last link to road or track, often defining the difference between knee down or tits up. No getting away from it, tyres are such crucial bits of kit. Mossy spoke to Bridgestone’s senior product manager Gary Hartshorne and gained a few tips and

FB: All tyres are the same, aren’t they?

GH: Not at all. Different materials such as steel, Kevlar and rayon are used in the construction of tyres. They have different weights, profiles, widths, overall diameters, compounds, constructions, speed and load ratings – all helping to give very different results in terms of performance and wear. Different types of tyres can behave very differently. Their performance has improved enormously even over the last few years thanks to major advances in technology.

FB: How important is it to fit the right type of tyre?

GH: It’s hugely important. Your safety depends on it. Fitting an inappropriate type or size of tyre, one not recommended or approved by a manufacturer, can seriously affect your safety. It can be crucial to make the right choice, and that’s not always easy. Even some single models of tyre from a manufacturer, carrying the same basic name on the sidewall, can differ subtly (or greatly) enough to give very markedly different performance and wear rates. An OE (original equipment) tyre of the ‘same type’ on a lightweight sportsbike can be very different to one fitted to a heavyweight sports tourer for instance, yet look about the same.

FB: Where’s the best place to get advice on tyre choice?

GH: Directly from a manufacturer is best. Manufacturers have a vast amount of experience and technical information. Most, like us at Bridgestone, have a dedicated website (www. bridgestone.co.uk) to help with enquiries. Using those will give you the most accurate information you need.

FB: How important are tyre pressures and how often should I check them?

GH: They’re very important. They dictate just how well a tyre performs. If it’s not right, the design of the tyre will be compromised. It’s built to perform at its best at a certain pressure. For example if it’s too low, it’ll overheat, and can wear unevenly and prematurely. With too high a pressure, the tyre won’t flex and deform correctly, reducing grip. They only need to be altered (lowered) for track use, but otherwise you should stick to the pressures recommended by the manufacturer for road riding – regardless of the way you’re going to use them on the road. Try to check them once a week and note any loss of pressure.

All tyres ‘leak’ and lose pressure through things like the rubber itself (tyres are porous), valves, and the tyre/rim seal.

The pressure is also there to support the weight of the bike, hence there’s a load index on the tyre. The recommended pressure and load indices work together so going too low will overload the carcass and could cause internal damage, damage none of us can see until it’s too late.

FB: Is it safe to mix different brands of tyres?

GH: There is an element of risk if you do, simply because not all combinations will have been tested and approved.

FB: What’s the advantage of multi-compound tyres?

GH: They allow a better balance of grip and mileage, allowing a longer ‘usable’ life.

FB: Can punctures be repaired?

GH: It depends entirely on the type of tyre. Tubeless tyres, designed to perform at very high speeds (such as Z-rated, safe to over 150mph tyres), shouldn’t be repaired. If you do, the integrity of their construction will be affected, and their subsequent safety compromised. They weren’t designed with a hole in them after all.

I would advise you not to repair any tyre. A tyre is about two metres in circumference so at 60mph the tyre will spin 800 times per mile. Do you really want to rely on a glued in rubber bung? The guidelines of British Standard BSau159f will help you understand more. ‘Get-youhome’ fixes such as plugs should only be used in an emergency, and only ridden on slowly for short distances. Running on very low pressures can run the risk of carcass damage.

FB: Why do you have to warm tyres up to get their best grip?

GH: With heat the tyre will become softer and mould more to the surface of the road, effectively offering a bigger contact patch.

FB: When is a tyre considered illegal?

GH: There are several reasons why a tyre can be deemed illegal. The most obvious is when it’s worn out, and if the tread depth is less than 1mm over 75% of the tyre then it will be viewed as illegal. If it has some structural damage, like a bulging sidewall for example, it can also lead to prosecution. Using a non DOT-approved tyre like a racing slick or wet, is seen as breaking the law too.

FB: What do all those markings on the side of tyres mean?

GH: In the case of a 180/55 ZR-17 rear tyre for example, the 180 figure refers to its width in millimetres, and the 55 its sidewall height expressed as a percentage (in this case 55%) of its width. The Z marking refers to its speed rating, the R its radial construction, and 17 its diameter in inches. Other markings signify things like being motorcycle-approved, any specific specification, and when it was made.

FB: What’s the best way to look after tyres?

GH: In use, keep the pressures correct and inspect the tyres regularly, checking visually for cuts and general damage. Do your best to avoid running over potholes and road debris. When the bike’s stored, try to keep the tyres warm and off the ground using paddock stands, or insulate them from the ground using some carpet.

If the tyres are in direct contact with the floor there’s a chance of the contact point becoming very cold, affecting the compound and making it brittle. Checking the pressures is important to stop the weight of the bike causing carcass damage to a deflated tyre.

FB: What goes into making a new tyre?

GH: Plenty. Typically there will be around two to three years of continuous and rigorous design, development and testing goes into getting a new tyre into production. A brief to make a tyre grippier, more durable and give better all-round performance than its predecessor is first drawn up.

Computer simulations then help to finalise the design of the first prototype which is then tested by riders virtually every day to perfect it via redesign and re-testing. Tyres are incredibly complex products that take vast amounts of effort to produce.

FB: How does racing influence road focused products?

GH: Grand Prix racing and road riding are clearly different, but the goals for producing the very best tyres for each of them are quite similar. We’ve certainly learned lots of technology from racing at the very highest level which we then include in our road tyres.

All-round performance and durability are key factors in race and road tyre production, and making a control tyre suitable for many different sorts of GP bikes and their riders has definitely helped us to benefit road riders. Without racing, we wouldn’t have been able to introduce new and advanced technologies as quickly as we have. Bridgestone is now back in world level racing in the Endurance World Championship. Endurance is a great test for road tyres as it provides more real world usage.

FB: Why are bike tyres so expensive?

GH: They’re not. Given the performance they offer, and the limited numbers they’re made in, their price can’t be seen as anything other than good value. Managing the performance of road-going superbikes like BMW’s S1000RR requires a very advanced product, as does making a tyre last on a tourer like a BMW R1200RT while still providing good grip. The market is very demanding these days.

And don’t forget the price of rubber for supercars like Ferrari and Porsche is extremely high. Those tyres are no more advanced or better-performing than the tyres you can buy for your bike.

FB: Will there be any radical new technologies on offer in the future?

GH: Features like airless tyres may well appear in the future. And as we discover new materials and technologies we’ll no doubt be able to make tyres grip more, yet last longer as they do.