Improving the breed

Feature article by Simon Bradley

 

Many, many years ago, dinosaurs roamed the earth, devouring all in their paths. These weren’t the ancient and vicious creatures of prehistoric times, though. Oh no, they were far more dangerous than that – faster, less predictable and more expensive to keep. They were the first breed of superbike, and among those who were skilled, brave or foolhardy enough to attempt to tame them there grew certain arcane traditions and rituals, often involving transplanting parts from other superbikes or adding parts made especially by the growing number of aftermarket suppliers. These rituals, which often went on late into the night accompanied by wild shouts of pain and frustration, acres of skinned knuckles and huge quantities of tobacco, nicotine and other consumables, all had the same goal. To reach nirvana. To achieve the impossible dream. To have a superbike that was actually manageable and wouldn’t spit the rider off and trample him at the earliest opportunity. And to make it faster and more reliable than its creators had managed with their billion yen development budgets. Gradually the modifications became more sophisticated, more in depth, until a hard core of enthusiasts with deeper pockets and bigger toolboxes than the others reached the pinnacle of their art, transplanting the throbbing heart of a superbike into a bespoke frame that handled better than anything they had ever imagined. And these hybrids, with their, um, functional appearance and their butch names like Magnum and Predator, ruled the roads.

But evolution is a funny thing, and survival of the fittest takes on a different meaning when your creations, despite your billion yen development budget, are being overshadowed by faster, lighter, better handling specials built by enthusiasts with no budget at all in sheds across the land. So the dinosaurs evolved. First of all the changes were small – a handling tweak here, a power hike there – but gradually the changes got more radical, more effective and more integrated until within a few years the dinosaurs were virtually extinct, wiped out by their adaptable, fast, light and above all user friendly progeny. And now, only about twenty years later, the wheel has turned full circle. Of the specialist frame builders there exists little trace. Most people now find that their superbike is far more capable straight out of the crate then they will ever be, and so any changes they make are purely cosmetic. But there are still some, perhaps misguided, perhaps foolhardy, who persist in trying to improve an already pretty fine product.

I am one of those people.

When the GSX-R 750 arrived on the market it was probably the first of the new breed of bikes, and as such bears a major proportion of the responsibility for killing the dinosaurs. The original, back in 1985, bears about as much resemblance to the current version as it did to its contempories back then, and from the rave reviews it has received, including some right here, you’d think that there isn’t much that could be improved. You’d be mistaken. Although it is a superlatively good bike in almost all areas, there are some things that still benefit from a bit of a tweak. Plus, of course, it’s nice to just personalise something a little…

Out of the box, the GSX-R produces something over 140bhp and weighs in at just 166kg. Performance is extremely respectable, with plenty of low end torque, a good healthy midrange and a great top end surge. But just about any bike that is sold for the road has a number of large troughs in the power curve. On the road they translate to flat spots – areas in the rev range where the bike just doesn’t pull as well as it might. This isn’t because the manufacturer is lazy. Far from it – they actually have to engineer these dips in. Emissions and noise testing requirements are totally arbitrary in that they say “at x rpm emissions will be less than this and the noise level will be below this” so bikes are made to comply with that. Often, especially when in pursuit of peak power further up the rev range, this means a little bit of fiddling around, and this inevitably results in a dip while things are calmed down enough to ensure that all the rules are satisfied. Ironically, when the rules were more relaxed it was more difficult to improve things yourself. Carburettors needed to be rejetted, needles needed adjusting and a whole sub-industry built up of arcane practitioners who could actually do this without turning your engine into scrap. But as requirements tightened up and more bikes came fitted with fuel injection, it became a relatively simple process to improve things enormously. There are a variety of devices on the market known generically as Power Commanders. In a nutshell they talk to the fuel injection computer and tell it to behave slightly differently. They can simply be used to clean up the fuelling through the rev range or they can be used to generate more power by simply putting more fuel through the engine. If that’s what you want then you’ll need to get more air in and more exhaust gas out, of course. There are several maps available for most bikes which will deliver the results you want fast, and everything you do is completely reversible, which is good news if you want to experiment with new settings.

Putting more fuel through won’t do any good if you can’t burn it, of course, and that means a better airflow. There are excellent high flow air filters which take care of that, and an added plus is that they last ages and so don’t need replacing at every service. Don’t be tempted to run without a air filter unless you have very deep pockets and can afford to regularly replace valves, pistons and injectors, all of which will be wrecked by grit and other detritus which will get dragged in.

All this extra fuel and air means more exhaust gasses, so they need to go as well. A good aftermarket exhaust will deal with that. Different bikes respond better to different systems, so it’s worth asking around before spending a lot of money on something that may not suit your needs. You should also think about just how noisy you want to be as this may effect your decision to get a road or race pipe. Of course, here I can only advocate road legal exhausts, despite the popularity of race pipes. Generally, the only thing you need to change is the end can as most modern bikes have otherwise very efficient systems. The only real benefit in changing the whole system is weight – you could save several kilos by replacing your standard steel exhaust with a titanium one, for example. The downside is the cost. A full system for the GSX-R retails at around £800 while the can was just £250. One last thing on exhausts. If your bikes has an exhaust power valve like a late Fireblade, R1 or GSX-R 1000 then you may well actually be worse off replacing the system. You will usually lose flexibility and mid range although you will gain a little top end power. I’d just go for a can on anything like that, personally.

On my bike you will find a Yoshimura Tri-Oval end can and some subtle changes to the injection mapping, courtesy of a Yoshimura fuel injection adjuster box. The end result is a small overall power hike, a minimal weight saving and a razor sharp throttle response from tickover right the way through to the red line. Which is nice.

All this power and performance is a bit of a double edged sword, though. More power means more speed which means you need to slow down more before you get round corners. If there is a weak spot on the current GSX-R, it is the brakes which, although adequate, aren’t really as spectacularly good as the rest of the bike. It’s probably a good idea, at this point, to take a step back and look at what makes your brakes, um, brake.

Assuming you have disc brakes, squeezing the lever or stepping on the pedal will push a piston into the master cylinder. This is full of fluid, some of which is pushed out of the other end. A rubber hose connects the master cylinder to the brake caliper which has a number of pistons in it. These pistons sit in slave cylinders which are also full of fluid. The fluid pushed down the pipe from the master cylinder goes into these slave cylinders and pushes the pistons out. In front of the pistons are the brake pads, which are pressed against the disc and slow the wheel down. But of course you knew all that.

The first way to improve your brakes is to remove anything that allows the hydraulic pressure to escape. As long as you have no leaks, the only thing that will allow pressure to ebb away is the rubber hose which can, and will, expand slightly as it is pressurised. The older the bike, the weaker the hose will be and the more it will expand. So fitting braided brake hoses is a good move. There are many commercial kits available, and there almost certainly is one that fits your bike. You should be aware that fitting braided hoses can take some “feel” out of the system, but you will notice a distinct improvement in your braking power.

If you feel as though you really need to up the ante, though, there are more extreme changes you can make. The first step is to replace the master cylinder. The braking power you have is produced, in simple terms, by the amount of fluid you displace from the master cylinder because that is what fills the slave cylinders. Logically, a bigger master cylinder will give more power, and to an extent that is indeed the case. Fitting a new master cylinder is not something you should do without a lot of thought, though, as you can easily ruin the braking feel of your bike and reduce your finely controlled brakes to a simple go/stop switch.

If that isn’t enough for you then the next option is to completely replace the front brakes. Companies like AP and Brembo are the best known suppliers of complete brake kits, although there are others available. This is not a cheap option and is not always even the most effective. But it certainly looks impressive and will almost never be a retrograde step. Again, there is almost certainly a kit available for your bike, either with or without replacement discs. It is not normally necessary to replace the master cylinder with kits like this.

You may have noticed that there is precious little available when it comes to improving the rear brake setup. Although I would be the last to dismiss the value of a back brake, when it come to serious retardation the front does the real work so that is where the real improvements can be made.

One last thing. Brake pads make an enormous difference. Not just how heavily worn they are, but what compound they are made from. It is rare in the extreme to find aftermarket pads that perform better than the original equipment items. Try, by all means, but be prepared for disappointment.

On my bike you will see a 42mm Brembo front master cylinder and braided hoses, linked to the original calipers and OE pads.

Now of course, back in prehistoric times, the aim of most home tuning was simply to make the bike handle well enough to be rideable. That is far from being an issue on the GSX-R. The handling is excellent, combining responsiveness and agility with a level of stability that would simply never have been possible just a few years ago. But that doesn’t mean it can’t be improved.

After their dubious experiences with the TL1000-S, Suzuki started fitting a steering damper to all their sportsbikes. A steering damper does exactly what you might expect from the name. It is a device that slows down steering responses to make a bike more stable. Some people swear by them, some swear at them. Everyone agrees that they have their place, but exactly where that place is remains a thorny point. Some of the finest handling bikes in recent times have them as standard – all Ducati superbikes and all current GSX-R Suzukis, for example – while others don’t allow them anywhere near their bikes, saying that a properly designed frame doesn’t need one. Personally, I believe that most bikes fitted with steering dampers at the factory are either doing it because it looks trick or because their company lawyers have had their fingers burnt before. Nonetheless, the GSX-R has one, and it does the job quite well. In fact, it does the job a little too well, making the steering a little heavy and lifeless at low speed and perhaps taking away some feedback as the pace increases. The standard damper is a mass produced item, of course, in non adjustable and sits below the bottom yoke inside the fairing. Replacing it with an adjustable damper means that 90% of the time I can ride with the damper turned right down so I get quick steering and loads of feedback, while when the going gets rough I can wind a bit more damping in to keep things under control.

There are lots of limitations on manufacturers when it comes to bolting things on their bikes, and suspension is often one of the first things to get compromised as a result. It may look great and it may well work OK, but it’s still built to the lowest cost that the factory could get away with. The GSX-R 750 is blessed with possibly the best standard forks fitted to any bike to leave Japan, which is a great start. Stripping and cleaning the internals before refilling them with top quality fork oil gets them working the way they were intended. I was astonished to see that my forks, even when the bike was just 6 months old, were gummed up at the bottom and several of the shims that were supposed to let oil flow past were stuck solidly together. After the cleanup it felt as though the front of the bike was completely new.

Standard rear shocks are often built down to a budget as well, and the GSX-R is no exception. Sadly there is officially little one can do about this, and replacing the shock with a better item is often the only real alternative. Sometimes you can get lucky, though. In this case we were able to repressurise the shock, which helped a lot as it was very low before, and we were able to machine a collar to fit a better quality spring. The result was a more compliant but better controlled rear end.

You can make significant changes to your bike’s handling without actually changing anything, though. It is easy enough to change the geometry of the bike to make it steer faster, for example, by dropping the forks a little through the yokes or by raising the rear ride height by adjusting the top shock mounting. It may be worth pointing out at this point that dropping the forks is actually a slightly misleading term as, in fact, the forks are actually raised in the yokes, which has the effect of dropping the front of the bike and steepening the steering head angle as a result. Compare the standard bike on the left here with mine above - look at how much more fork leg is showing above the yoke on mine.This makes the bike turn far more readily at the penalty of some loss of stability. Should you decide to do this you need to make sure that your front wheel won’t foul the radiator or fairing when you brake hard and you need to be aware that you have reduced your ground clearance by dropping the front and so you may find yourself scraping things that never touched before. You can achieve the same result by raising the back instead, with the added advantage that you are now gaining ground clearance instead of sacrificing it. The downside is hat you will probably have less scope for adjustment at the back and you will quickly find that your feet no longer reach the ground.

Of course, tyres play a vital role in handling as well. They are totally subjective, provided that they are the right fitment for the bike, as just how good a set of tyres is depends more than anything else on the rider’s perception and how confident they are. The Michelin Pilot Sports which came as standard were simply excellent, the Pirelli Diablos which are fitted now are at least as good. The GSX-R which we tested recently had Diablo Corsas, which were outstanding but completely shot after two weeks and one enthusiastic track day. Just don’t put a big rear tyre on if the handbook doesn’t require it – the extra unsprung weight will make it harder to turn and the reduced camber will make the bike understeer. Not a nice combination.

So, as far as refining the handling on my GSX-R 750 you will find a Sprint top mounted adjustable steering damper, forks filled with good oil and lowered a fair amount and a Tech 2000 spring fitted to a regassed standard rear shock. Tyres are Pirelli Diablos running standard pressures.

There are, of course, plenty of other things you can do to improve your bike or to make it more personal to you. For example, it still amazes me that some manufacturers supply bikes without rear huggers fitted. A hugger, in case you need it explaining, is a closely fitting mudguard that stops the back of your bike getting covered in all the crud that the wheel throws up. It’s particularly useful for prolonging the life of your suspension components as they no longer get pressure washed every time it rains.

Sportsbikes often benefit from slightly more protective screens, either “flip tops” or, more commonly, “double bubble” screens. Both do the same job – push more air over you rather than at you – and both will rob you of a little top end speed. You can get them tinted in most colours if you want to change the look of your bike as well.

There are so many other changes you can make, but there is one very useful thing to bear in mind.

The most tuneable part of your bike for speed, reliability, handling and safety is you, the rider. So before you throw another £1000 at an unobtanium exhaust system, why not consider spending a whole lot less on some training instead?

SB




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