In past articles about buying a bike we have often talked about how getting properly 'fitted' is one of the key stages of ensuring that you are buying the right bike for you (as opposed to someone who might be the same height...). What we didn't go through in any detail was how you get 'fitted', or which of the many fitting systems you should use - this article will try to address that question.

While getting fitted when you buy a bike is obviously important, you want the bike to be the right size, there are many more people out there riding bikes which they have never been properly fitted for or, and this is certainly true of triathletes, have modified in some way since they bought them. The Winter off-season is an ideal time to take stock of your bike fitting and to get any adjustments made before the really heavy training starts. It also allows you to re-set your bikes to their correct positions where you may have packed them in boxes for shipping, taken the seatpin out for cleaning, changed the saddle, and so on.

There are more fitting 'systems' than you might imagine. To start with, all the systems will start by taking physical measurements. These are generally based on height, inner leg length, arm length and chest width. Some of the measurements will use long bone length rather than inner leg but all the systems basically end up with a set of dimensions that relate to the positions of the joints on your skeleton. This is why height alone is not a valid sizing indicator, nor the old-fashioned 'standover' test - neither takes body proportion into account.

It's all about numbers

Once you have the numbers you can feed these into any of the fitting system. The traditional methods for frame sizing are based around a couple of simple formlae; the seat tube length measured from the centre of the bottom bracket to the centre of the top tube should be .65 of the inside leg measurement while the saddle height has been suggested as .833 of the inseam measurement (although modern clipless pedals need to have this reduced by a few millimetres. There are lots of interpretations of these formulae, a commonly-used one is the LeMond system which is named after Greg LeMond, the multiple Tour de France winner. (Note: although it's often referred to as the LeMond system it should be pointed out that he didn't invent it but, rather, popularised its use. The formulae have been around almost as long as the modern bicycle.

So, it's all just a few numbers and a calculator then; easy! Well, actually no - because just having the numbers isn't the whole story. Enter stage right systems like bikefitting.com's which have collated data from many thousands of bike bitting sessions and use these, together with their interpretations of the ratios to generate sizing for specific types of bike activity. Having access to tens of thousands of measurements also means that the results tend to become normalised - the more times you've had a go at creating the 'perfect' fit the better the chances that any one individual will end up with something that works. And, in general terms, also fits far better than using something like 'standover' or the salesperson's 'eye'. Indeed, the reason most bike shops use the bikefitting system is that it ensures that there are far fewer issues regarding customer's getting the wrong bike size in the first place.

At it's simplest level a bikefitting session will take about half an hour, can be conducted by pretty much anybody who has been through the training, and generates both frame and bike setup diagrams that the shop's mechanics can use to set up the bike - either 'out of the box' or as a custom build. The key thing for the shops is that, to a certain degree, it de-skills the task and so makes it quick and cheap, typically £35 for a standard fitting, while simultaneously reducing the risk. That's not to say that bike shops shouldn't have (or don't need) people who understand the principles behind the process - they do - but it does mean that not every member of staff needs to.

Unfortunately, there are two aspects that aren't catered for with systems like bikefitting; the first is the person who has measurements that are outside the range that is considered 'normal' and the second is that individuals may have preferences that the system cannot factor in. An example of the former might be a very tall (or very short) person or one who has disproportionately long arms (or legs) compared to their overall height. Any bike fit system which is based around normalised data will have problems with people who are outside the bell curve - and that can be up to 20% of the population.

The second aspect that isn't catered for is anything to do with personal preference. Some people can tolerate a much lower position at the front than others; a system based around normalised data will tend to always err on the side of caution. Equally, people with back trouble may need a more relaxed position to ensure that they can run off the bike without unnecessary stiffness. It is here that the skill of the human bike fitter comes into play, interpreting the results is just as important and measuring correctly in the first place.

The holistic approach

There are many other fitting systems on the market. One of the more commonly available is the one developed by Serotta, a custom frame builder in the USA. Cyclefit, based in London, are a highly regarded advocate of the system and, although they would obviously be delighted to sell you a custom Serotta, the system will produce useful information regardless of what brand of bike you ride. To get fully Serotta trained takes time and, as with all the top-end fitting systems, requires that you buy-in to their methodology. This has the advantage of ensuring that all the staff who do the measuring also understand, and can interpret, the resulting data while also eliminating any personal bias that the fitter may be bringing to the party.

Cyclefit are also the UK agents for BikeFit who are the suppliers of what used to be called Le Wedge. This is a plastic shim that can be fitted between the cleat and the shoe to offset any skeletal mis-alignment. This sort of trimming does actually work, Tri247's Editor has been using them for years to correct a knee problem.

In the States, and we believe that it will come over here soon to a very select few dealerships, Specialized have introduced a bikefitting system as part of their Body Geometry product line. Developed, we understand, as a project by Serotta and the highly respected Dr Andy Pruitt, the Director of the Boulder Center for Sports Medicine, it will be interesting to see if this addresses the tendency of the Serotta system to prescribe a shorter top tube and higher handlebar position than, say, the bikefitting system. Serotta's approach is an holistic one in that it takes the whole rider plus bike plus use into account when it generates a fit. However, just as the early bikefitting system tended to skew towards more flexible, aggressive positioning because that's where it got its initial data from, the Serotta system tends towards a more relaxed and comfortable position. Please note that we say 'tends' and not 'does' - the fit you get from any system should be as a result of your interaction with the fitter and is not just a 'cast in stone' set of numbers.

Personal interpretation of the data can often be markedly different, a factor that always needs to be considered. One example of this is that in the early days of the bikefitting system, which was previously known as Bioracer for those who remember that far back..., the system typically used to put the handlebars about a centimetre lower than most people found them comfortable. In other words, the system was using data that was slighly biassed towards younger, more aggressive riders because that's the community that the data had been gathered from. As a result, mechanics assembling bikes from the data often used to add a 10cm spaced under the stem on the grounds that once you've cut a steerer tube there's no going back and so if the system was likely to be setting the bars too low they would compensate for that.

It hardly takes a rocket scientist to spot the obvious problem that's brewing here. Once the amount data in the system had been increased, the norms would tend to shift away from the more aggressive positioning and so the set-ups diagrams would start to get nearer to the position that the average rider would find comfortable. But, unless this is clearly recognised and understood by both the fitters and the mechanics then that extra 10mm spacer will still be added and the position will now tend towards the over-compensated! Critics of the system will claim this as being another weakness of a database driven system but, in reality, it's a small issue and it's one that fails 'safe' in that you can always remove a spacer and cut a steerer tube down. It's also 'safe' in that these changes will always tend towards the less extreme than the more extreme so there's less likelihood of being put into a radical position that the body just can't tolerate.

Taking the idea of rider involvement to possibly the ultimate degree is the fitting system used by another US custom bike fabricator; Seven. Not only do you have a full set of biometric data taken and interpreted to determine the frame geometry but you also have to complete an extensive questionnaire and they also conduct a phone interview with you to determine the ride characteristics that you are looking for. So, if you love, say, that Pinarello Prince ride quality and want a titanium bike setup with the same ride quality then that's what they'll do. For the knowledge-obsessed, it's apparently all about how they manipulate the tubing...

Get FISTed?

Dan Empfield, generally considered the father of the steep-angled triathlon frame and also the man behind the revered Slowtwitch website, has developed his own fitting system which goes by the rather odd name of FIST. There's a link in the table below to the explanation of how the system works but it's not dissimilar to the Serotta system in that it too is an holistic approach rather than just numbers from a database. Unlike the other mainstream systems, the FIST system is built around an understanding of triathlon, steep seat tube angles and the use of tribars which should mean that it would be a more appropriate system to use for setting up your tri or time trial bike. Unfortunately, so far as we know, there are no FIST certified fitters yet in the UK.

Going the other way entirely are the new breed of fitting systems which take their own measurements. There have been several demonstrations of such systems at trade bike shows over the past five years but essentially they all use some form of scanning system; lasers, light reflective dots on the joints, etc, to build a picture of your skeleton which then provides the raw data for analysis. What is interesting about these systems is that they also seems to be tending towards measuring on the bike rather than in isolation and can factor in the amount of power you are delivering while in that position.

And, to get back to where we started, that's what getting a bike that fits is all about: delivering power more efficiently. So, take a bit of time this winter to get yourself properly fitted to your bike or bikes. Factor in the types of races you are planning to do and the equipment that you will add to the bike like tribars or a new type of pedal or different length cranks and test yourself both before and after to see just how much power you can recover. We say 'recover' because a change to the bike fit isn't going to change the power output you have (well, not unless it's so badly set up that you really ought to have spotted the problem earlier) but rather let you utilise more of that power and so be more efficient.

In complete contrast to all of the above, there's a service James Parker used which we covered on the site a few months ago where you can video yourself on a turbo trainer and send the file off to be analysed. Back come some suggested changes and the cycle progresses until both parties feel that they have achieved the best compromise possible between fit, comfort and effective power delivery.

In conclusion

In summary, therefore, bike fitting is all about getting your position on the bike set up so that you are delivering the best possible power output while not compromising too much on comfort. For triathletes that will generally mean a different position to both regular road bike riders and to time trial - triathletes have to be able to run off the bike! The overall quality of your fit is as much about how the fitter interprets your needs as it is related to how well the fitting system generates its 'prescription'. However, what is certain is that getting fitted by any system is a much better starting point than being stuck with a bike that "suits you, sir".

The good news, relatively speaking, is that unless you really have been stitched up with the wrong frame size or geometry, most fitting issues can be resolved far cheaper than just giving up and buying a new bike. The cost of a fitting session, a new stem and some adjustments will be much less than buying a new frameset or even a complete bike. And now is the time to do it!

Oh, and while you are getting sorted out do remember to check your shoe fitting; lots of power gets lost through either badly fitting shoes or poorly set-up cleats on clipless pedals. You could even check your saddle fits properly; nowadays they come in different width fittings, both Specialized and Trek now offer a range of saddles that suit different 'sit bone' widths and this can make a radical difference to comfort and efficiency.

There are dozens of articles out there on bike fitting systems; here are a few that we think are worth reading if you want some more in-depth knowledge.

• Sheldon Brown's 'Revisionist theory'
• Bill Boston's Accufit system
• Peter White's 'How to fit a bicycle'
• Dan Empfield's FIST System
• Colorado Cyclists bikefitting article
• Edward Zimmerman's online bicycle size calculator