The first thing we need to get straight in our heads is that the rolling chassis should be considered as a whole if we are to stand any chance of getting the overall plot right. Sure, you can fit the forks of your dreams but don't do it without considering the impact on everything else,

Then we need to ensure that the rolling chassis is actually doing what it should be doing. It is nothing more than a set of bearings and bushed that join tubes together, but it is only as good as the bearings, and only as strong as the tubes. A sobering thought is that while a badly maintained engine might stop at an inconvenient point, a badly maintained rolling chassis could kill you. Still, as long as it looks right, eh?

A rolling chassis, to get to the basics, is the frame and its ancillary equipment: forks, suspension, wheels, tyres and even handlebars and brakes, and the first thing you need to do it to make sure that this is set up correctly, so get out your book and make sure it is. You can get carried away with the idea that something needs tweaking because it doesn't perform well enough, but there is always a possibility that it would if it were set up properly. In reality, your book will not tell you much – unless you've got the full factory workshop manuals with full engineering tolerances – so we've got to use common sense, and we'll go through the sections stage-by-stage.

Forks:

Unless you've got a pair of balanced air forks, Springers or girder forks – which we'll deal with at another time – each fork leg operates independently of the other. Each comprises two primary parts: the stanchion, which is the chromed steel tube that bolts into your fork yokes, and the slider which is typically alloy and which slides up and down the stanchion, and which holds the front wheel spindle at the bottom. These are held apart by bearing surfaces, or fork bushes, which are replaceable when they wear out. With up-side-down forks, the stanchion and slider positions are inverted but otherwise the principles are the same. Each fork leg contains at least one spring and uses oil as both a lubricant and damping medium. Damping is a means of preventing a spring recoiling repeatedly until all the energy of the spring has dissipated.

Because each fork leg is independent, it would be able to move at a different rate to its matched partner were it not for the wheel spindle which keeps the bottom of the sliders together, and the strength of the spindle and its unions need to be strong to keep the spindle at right-angles to both sliders simultaneously. This, given the gyroscopic forces of the spinning front wheel, is asking an awful lot of your wheel spindle and it is not uncommon to find the fork sliders are also interconnected at, or around the front mudguard using a fork brace, and you will often see these incorporated into mudguard mounts to add the strength without upsetting the styling. A well-braced pair of sliders effectively forms a subassembly that works as a single entity, and this is a good thing.

The slider subassembly slots onto the stanchions, and is secured internally in one of a number of ways so that it doesn't fall off when (When? If!) you wheelie the bike.

Metal sliding on metal will wear one or other surface, so a sacrificial metal bush is fitted between the two surfaces because we don't want to have to replace the sliders of stanchions as they are expensive to produce. Bushes are made of a softer metal than either surface that they contact, so they wear first – in principle. Each fork leg will have two bushes: one that fits to the bottom of the fork stanchion and one that slots into the top of the fork slider. To aid the sliding, oil is used, and this oil needs to be kept inside the forks but allowed to flow freely across the bearing surfaces so oil-seals at the top the fork slider prevent the oil escaping, and crap entering.

If there were no damping in the forks, the slider would move up and down the stanchion with only the strength of the fork spring(s) to restrain it, which would be a bad thing. We want our forks to absorb the shocks of poorly maintained roads, and that is best done under tight control so we want to damp the movement of the slider on compression (when you hit the pothole) but mainly on the rebound (when the fork returns to its original position). This is the second role of the oil, and the reason why we use thicker oil here than in the engine – and indeed why there are different grades of oil. As the sliders move on the stanchions, the incompressible oil is transferred between the area where it's needed – inside the sliders, outside the stanchions, between the bushes – to the hollow tube of the stanchion via small holes drilled therein, and it is the size, location and number of these holes that determines how much oil can pass, how quickly and at which point of the suspension travel it is at. This provides the damping: bigger holes allow more oil to pass through more quickly and provide a suspension better suited to trail bikes, smaller holes give greater restriction and correspondingly stiffer suspension better suited for the road. The second factor would be to use a thicker or thinner oil, as the thinner oil would travel more easily though small holes than would thicker oil. This brings in another part of the equation, because we all know that heat will make oil thinner, and the action of pushing volumes of oil through small holes will warm the oil – this is what gives suspension fade on racing bikes, but they put their oil through much more punishing hoops that we ever will. Heat, anyway, is less of an issue on forks than on rear suspension units, as we can hold a lot of oil in the forks to absorb the heat, and because its got a good airflow.

The stanchions, together with the yokes and steering stem form the second subassembly of the forks. Once you've got the two, or four pinch bolts holding your stanchions into your yokes, you have a significantly stronger union than you'll ever get with the sliders and spindle – providing they are bolted down tightly. The stanchions are largely responsible for the strength of the forks in terms of structural rigidity. Small bikes get away with spindly stanchions, but they give them less work to do, bigger bikes needs heavier items to cope with the weight and other forces. There are a few things to consider here:

• The longer the forks, the greater the potential for the stanchions to bend.
• Heavier gauge tubes are stronger.
• Larger diameter tubes are stronger.
• Larger diameter tubes have a bigger bearing surface.
• Bigger bearing surfaces dissipate loads better.

The last part of this section is the steering head – for it is here that the forks meet the frame. Any play here will cause strange handling behaviour and it needs to be checked regularly. Older bikes have steering head bearings comprising cup and cone races with free-range balls – a legacy of bicycle origins – but thankfully you're more likely to find or taper rollers on newer models but the same is true of both. Do NOT overtighten them to try and get rid of free play in the steering head or you'll damage the bearings.

Checking your forks.

Always refer to a good manual when doing anything at this level, and start off with a clean working area with a safe means of holding the bike upright, firmly with either wheel, or ideally both off the ground. A good workshop stand will be worth its weight in gold here.

It is also worth noting that while fork legs should be identical, you should not interchange parts between them as the wear rates might be different: easiest way to do this is to strip one leg at a time if you go that far.

With the forks assembled, you can check to see the state of the bushes by attempting to move the slider front-to-back in relation to the stanchion. This should be done with the forks fully extended, as it is then that the bushes are closest together and the wear is most apparent. Ideally, this should also be done with the front wheel out and any fork brace removed to make sure you are testing one fork leg at a time.

Drain both fork legs, and check the state of the oil coming out. If there is any trace of white in the oil, it means that the oil has emulsified with water and the forks need to be flushed to clear out any remaining water, or stripped for the same purpose. Water in fork oil is a problem in that water, unlike oil, can be compressed and so upsets the original calculations of the fork designers. If the fork oil is clean, throw it away and refill both fork legs with the right amount of the correct grade of oil.

If you have forks that are adjustable for preload, you need to check that the preloads are set the same for each fork. A spring preload is basically a means of raising or lowering the top of the fork stanchion on the inside, which is the top contact point of the fork spring, and serves to stiffen the spring slightly: if these are different, it is the same as having different springs in each fork legs, and a bad thing. Same with adjustable damping, which has the ability to restrict some of the oil transfer holes in the stanchion, thereby reducing the ability of the oil to pass quickly and stiffening the forks.

Fork springs are generally resilient, but take them out and have a look at them. If the coils of the springs get increasingly tighter at one end, you've got progressive springs which become increasingly stiffer as they are compressed: this is a good thing. Take both springs out and make sure they are both the same type, both the same length, and both installed the same way up … and that neither are broken. Broken springs are not common but it has happened. If there is any difference between them, those differences will conspire to prevent the forks working correctly. There are dimensions available to check the state of your springs against the original and if they are way out, replace them as a pair.

It seems obvious that no-one in their right mind would adjust forks independently of each other, but assume nothing. A mate of mine, building a seventies Triumph, found two different springs of different lengths in his forks. If you're not sure who last put the oil in, and if you didn't adjust the preload and damping, check it. It doesn't take long and it is small consolation that it was someone else's failure to do it properly when you're picking hedgerow out of your teeth.

While the wheel is out, and the forks are dangling in space, it is a good time to check the steering head bearings so grab the bottom of the sliders (having first determined that the fork bushes are good) try to rock the whole fork assembly back and forwards relative to the frame. It goes without saying that you don't need brute force for this: too much force will drag the bike off whatever it's standing on and you'll be impaled by your fork leg. If you have excessive movement at the headstock, you need to tighten it up BUT it is first worth checking that you have completely free movement in the steering because if you have free play and tight spots on your steering, you're going to need new steering head bearings. Be aware, however, that tight steering can sometimes be a result of the massive array of cables and hydraulics that go the bars, and take that into account.

Frame:

This should ideally be a couple of triangles that are tacked together, triangulated further with a couple of identical triangles alongside them. Why? Because triangles are the simplest self-supporting shape. If you make a triangle out of a reasonably strong material and apply force to any point of the triangle, the shape will hold. Do the same with a square and you'll end up with a diamond without too much of a problem. So bicycles are great, and motorcycles are a compromise because the engine is too big to allow that to happen properly. Those folk running pre-WW1 bikes – and some hard-tail riders – can take delight in the purity of the form of their chassis, the rest of us can look on and marvel, but go out and use our bikes every day with little need of the skills of the chiropractor.

Thankfully, the science of frame building has moved on with the use of stronger tubing that allows enormous strength in the strangest shapes, but triangulation is still the panacea of the frame builders art.

The nicest thing about triangular frames is that they can be very light because of the intrinsic strength of the shape of the frame. The more you compromise that with swoopy curved tubes and supporting gussets to add strength, the more weight you add and weight is bad. There are all sorts of ways round this but if you're working with a stock chassis, you're best advised to leave it alone unless you know what you're doing, and just put lighter bits on it and reduce weight that way.

The niceties of frame design mean bog-all when checking that your own chassis is happy because it is already there and working. Frame checks are restricted to three areas really: has the bike been stacked and the frame twisted? Is the metal badly corroded? And how are the rubber-mounts, where fitted, holding up?

If your bike steers to one side or the other when riding hands-off, check its wheel alignment, or just cut your losses and get it professionally checked. If you can't ride the bike with your hands-off because it shakes its head like a puppy with a glove, get it professionally checked. If it's so bad that you can't comfortably steer with one hand, seek psychiatric help.

If there's a little surface rust on the frame, clean it up with a wire brush and wet-and-dry to get back to the metal, prime and respray it to prevent it getting worse. If you find, when you're wirebrushing it, that you can put your finger through the metal, talk to a professional frame builder who will tell you whether you can salvage it, or who can flog-you the custom frame you've always really wanted but couldn't justify. We're not in any way questioning the quality of the original items, here, but unless things are looked after, even the best stuff suffers.

In terms of rubber-mountings, if your engine bounces happily away in the frame, but perhaps in a more animated fashion than before, take it to a trusted Harley specialist and get them to give it the once over, or check the tolerances against a good manual.

Rear suspension, and the swinging-arm:

Since the evolution of the motorcycle from the simplicity of the rigid frame – which had little more to account for than the rear wheel alignment – a basic rear suspension system has done stirling service in almost every motorcycle since the fifties. There are exceptions, or course: there are always exceptions, and a notable one for us in this context would be the unexceptional plunger suspension fitted to sprung Indian chassis - and a great many British bikes of the period. Plungers have the advantage of the lines of the rigid frame beloved of chop builders, with a means of taking out the worst of the road bumps that you would have found then ... and unfortunately continue to find now. Plungers are small, self contained and undamped except by friction, and only then in some cases. They work independently of each other and have the same problems of forks in that the wheel tries to stay vertical while the chassis cants over round bends: they are a poor compromise. Harley's Softail design has all but killed off the custom plunger frame as it delivers the line without the compromise, and there's no shortage of manufacturers copying the Softail principle to hold just about any engine that you care to contemplate.

For the rest of us, there are swinging-arms, which is a significantly more simple assembly than the forks but no less important to the overall well-being of the bike. It's connected to the frame through a single spindle, supported by a bearing on each side and these should be checked periodically, according to the handbook, but it makes sense to do so every time you get the back wheel off the ground. What you're looking for is lateral – side-to-side – play and any is bad. The age and source of the frame will determine the bearings used – and their means of adjustment – but adjust it, if that what it needs or else replace the bearings if they're knackered. Knackered bearings make horrible grinding noises where road dirt has got into the races, and a lot of swing-arm bearings are not especially well sealed.

The swinging-arm itself is generally not a high tech device, but the shock absorber that controls it is. It works on the same principles as the forks, just on a smaller scale: preloads should be the same on both units, damping, if adjustable, should also be the same. The only difference between the forks and swinging-arm is that the rear wheel is held on both sides by a single piece of metal – the swinging-arm itself – and so should be less susceptible to the independence of the two shock absorbers. That doesn't mean that it can't be twisted – hence the trade in aftermarket triangulated swinging-arms. Softail owners are allowed to be smug at this point as the Softail swinging-arm is a much stronger item out of the box, and as the underslung shocks are mounted to a central point on the swinging-arm assembly it is less likely to twist. Non-softail owners can be equally smug as we haven't got the weight of the Softail swing-arm to keep under control.

Shock absorbers themselves are available in many flavours and styles, but until your bike is set up as it should be, there's no advantage in sticking a new pair of shocks on it because you may find your swinging-arm bearings are the root cause of your problems, or even the steering head. If, however, your shocks are leaking their damping oil you can either – depending on the type – get a seal kit, or cut your losses and buy a new pair. If you're buying new, adjustable damping is more important than pretty chrome.

If you're a spirited rider, you might want to consider a pair of shocks with remote reservoirs as these retain their damping characteristics for longer when giving them a hard time. As mentioned in the forks section, as oil moves about it'll get warmer, and as it gets warmer it'll get thinner and will move about more freely. Cooler oil can be maintained by a larger volume of oil to absorb the heat, and by keeping a percentage of it in a remote body away from the heat of the shock absorber unit itself.

Lastly, make sure that the rear wheel adjusters show that the rear wheel spindle is the same distance down each rear spindle slot. If it is not equal you will give the chain or belt a hard time, and the rear wheel will struggle to track the front – no matter how hard it tries. While you're there, it's worth checking that the chain or belt is correctly adjusted.

Wheels and tyres:

Okay, so the wheels are round and the tyres are pumped up. What's to check?

Wheel bearings are essential to the smooth running of your wheels and tight spots will cause excessive heat. Excessive heat will cause lubrication failure, which will cause further damage to your bearings. With your wheel off the ground, spin it slowly without letting go, and feel for roughness as it goes round. Be aware that brakes might be binding, but causes a different sensation, and that the drive belt or chain at the rear will also have an impact – chains especially.

Wheel balance is also important to prevent a light hammering sensation at either end. Balance is set when tyres are replaced by adding weights to the wheel rim or spoke nipple, ensuring that any imperfections in the tyre's weight distribution and the valve are countered. If you put your own tyres on, it is worth getting the wheels balanced afterwards. You can do this yourself, with access to the weights, but it's time consuming. To check your wheel is balanced, first make sure the wheel spins freely, and without the encumbrance of the brakes or final drive, then spin it a dozen times and mark the bottom of the tyre with chalk where it stops. If it always stops in the same place, the bottom of the wheel is heavier than the surrounding parts and it needs an appropriate weight adding directly opposite. If it always stops in a different place – which is actually unlikely – the balance is spot-on. If it tends to stop within a 90-degree section, it is slightly out but you'll probably not notice the difference. You can chase wheel balance for ever if you want perfect balance, so don't get too anal about it.

If you're running spoked wheels, check that the spokes are tight. It has be admitted that the gauge of spoke used on this sort of bike is unlikely to give problems but its worth keeping an eye on them as they get older. Tap each spoke with a spanner and compare the noise. A dull "clunk" suggests a loose spoke, while a higher-pitched "ting" will suggest an over-tight one.

If you're running alloy wheels, you're generally looking for any sort of crack forming.

Regardless of which wheel you're running, the lighter the wheel, the better: stock wheels are functional and cheap to produce and keep costs down, aftermarket wheels are expensive to produce but are lighter.

Tyres should be in good nick, with tread all the way round the circumference and across the section. If you spend all your time on motorways and dual carriageways, you'll wear the profile of the tyre flat and it'll behave erratically when crossing white lines or other imperfections. If this is the sort of riding that you do, get touring tyres which are designed to account for the tendency.

Make sure tyres are correctly inflated for the type of riding you're doing, and for the weight. It's worth knowing what the pressures should be for a variety of different circumstances.

One thing which only raised its head with the Year 2000 launch of both H-D's Deuce and Victory's SportCruiser, are the opportunities opened up by low profile tyres, and we predict that this will make its mark on the American bike market over the next few years.

We're all familiar with the 5.10x16 tyres that have been fitted to the backs of Harleys since the dawn of time. Big balloon tyres that are as high as they are wide, they are not renowned for their positive tracking of the road. The height of the tyre's sidewall can distort more than is good for it and this doesn't help roadholding.

What can you do?

If you're Harley-Davidson, you slap a bigger, seventeen-inch wheel into the Softail chassis and run a lower profile tyre on it. The increased radius of the wheel allows the reduction of the height in the tyre's sidewall thereby retaining the same static ground clearance. It also makes for a less distortable profile, and actually gives greater angles of lean over the original set-up, and a more lively ride. We would expect to see similar treatment given to the FXDX and T-Sport sooner rather than later. This does make life more complicated when buying tyres because we get into modern tyre sizing, and stuff like 160/70x17 as a tyre size, but that basically means 160mm wide with the height being 70% of the width, so 112mm high.

If you're Victory, you go that little bit further and slap a massive 180/55x17 into the V92SC, matched it to a low profile front … and then you grip it in a pair massive 50mm Marzocchi forks. As with the Deuce, the SportCruiser retains the same static ground clearance when compared to the standard cruiser.

Buells, being Sports bikes from the outset, have always been that way inclined with low-profile tyres front and rear with a massive 170/60x17 taking up the rear: yeah, okay so it's smaller than the Victory, but then so's the bike.

Brakes:

Anytime you check your brakes is a good time, because you put so much reliance on them, but what's it got to do with handling.

Short of the principles of maintaining a low unsprung weight, brakes wear and bind. For those who haven't read the Buell brochure, unsprung weight is basically the components of the bike that are on the road side of the suspension: wheels, brakes, fork sliders. The lighter those components are, basically, the easier it is for the suspension to keep the wheels in contact with the ground.

Worn brakes are just plain dangerous. If you're hammering down glorious roads – when the summer we're so overdue for finally arrives – you need them to be there for you when the local pony club materialises from behind the next bend. If you ain't got brakes, you ain't going to get the most out of what performance you've already got, so fix them.

If your brakes are binding, you're putting additional unnecessary pressures on the rest of your bike, and generating heat from the friction, which will further wear the brake pad. If one of a pair of twin disks is binding, the forks are not going to be at their best because there will be a slowing action working at one side of the forks. You will compensate for this, sometimes completely unknowingly, but it will ultimately lead to accelerated wear, and early failure.

Rolling Chassis Tweaking:

So you've got a rolling chassis that it properly set up as it should be. Now you can think about making it better, but at least you've got a basis for knowing what it's going to be an improvement on. There is still a massive range of opportunities to the frame builder borne of frame geometry and the like but to recap, the basic areas of consideration for quick results on a stock bike would be – in order of cost:

• Check the forks work properly, and are correctly set-up.
• Brace the forks.
• Fit progressive springs at the front and rear.
• Adjustable damping front and rear.
• Triangulated swinging-arm.
• Tyre and wheel selection.