As bike fitters, we are often lucky enough to have a myriad of tools available at our disposal to help riders achieve greater harmony between body and bike. Today we are going to demystify the bike fit jig.
As we know, and often reiterate, it’s not only a case of just having these tools that can make them beneficial, it’s also knowing when and how to use them appropriately that can be the difference between having a positive impact for a rider, or just confusing matters more than is necessary.
One of the most frequently used tools in our studio is our Purely Custom jig, or “fit-bike” as it is often referred to on our post fit reports.
Fitting on a jig can open up a whole world of possibilities that might not be possible if we were limited to using a bike that a rider has brought to a session, but it’s also important to note that fitting on a jig isn’t without its limitations as well.
Let’s get into it.
What is a Bike Fitting Jig?
To perhaps help you visualise things a little better, a jig is essentially a solid platform that will likely have two telescopic towers (one to attach a set of handlebars, the other a saddle) attached to it that can move on an X and Y axis in order to affect handlebar stack and reach, as well as saddle stack and reach.
In the middle of the platform is a central axle from which an adjustable crankset (facilitating changes to the crank length) chainring & pedals are attached and linked up to some sort of drivetrain device, often something that resembles a modified turbo trainer-esq contraption, in order to facilitate resistance when pedaling.
Bike fitting jigs have been around for a long time in various guises, and they are essentially a tool that allows the fitter and rider to explore things about a rider’s position and componentry quickly and easily.
The Pro’s of Using a Jig
Undoubtedly, there are a fair few positive’s to fitting on an adjustable jig. A jig can allow a fitter and rider to explore things that might otherwise be beyond the parameters of a current bike, both quickly and easily.
Take crank length for instance. Testing multiple different crank lengths on a regular bike would be horrendously time consuming and impractical (the exception being if you have a set of these beauties!) given the amount of different axle and bottom bracket standards that would need to be considered, not to mention chain line variances and the fact that it’s often the case that a change isn’t truly digested and appreciated until a previous position is returned to!
The same can be said for saddles. A fitting rig will often have a very fast and easy way to change a saddle, making objective feedback far clearer and faster for both fitter and rider. Saves a load of faffing with overly complicated saddle clamping systems!
It’s this speed of which such a variety of changes can be made that allows not only for almost instantaneous rider feedback to any given adjustment, but also to explore far for variables in a given timeframe.
Just one of the reasons the jig can be a very useful tool. The faster a positional change can be made, the clearer the difference between two positions might be.
Some of the newer, state of the art fitting jigs can now also mimic certain environments that a rider might find themselves in when out in the real world. For example, some jigs have incline and decline controls, allowing a rider to experience what a position / weight distribution / pedalling might feel like when climbing or descending on certain gradients.
This is particularly useful when fitting bikes for specific conditions, such as an XC Mountain Bike, or a specific hill climbing position for a road bike.
Fit Before You Buy.
Arguably the largest benefit to fitting with an adjustable jig is when fitting for a new bike.
Not being bound by any particular frame size or predetermined geometrical parameters or componentry, a fitter and rider can explore anything and everything in order to find the “ideal” bike environment.
Then recommend a bike accordingly based on these measurements, whether that be an off the shelf model or a custom made frame.
Perhaps you’re looking for a different style of bike, maybe you have a road bike already and are interested in a gravel bike?
Or perhaps you want a triathlon bike but don’t have any frame of reference for what a good tri bike position is?
This is becoming ever more important in an age where more and more bikes are sold directly to consumers, and more and more bikes are being sold with integrated proprietary componentry that has limited or no adjustability.
By being fitted on an adjustable bike fit jig before you commit to a purchase, you are arming yourself with knowledge from which you can make better buying decisions.
Knowing what bike frame shape, crank length, handlebar width, saddle etc is going to allow your body to move in the most comfortable and efficient way possible can save you a potentially very costly mistake down the line.
It is of course, up to the rider as to what they do with the information, but as the prices of bikes continue to rise, this can offer the piece of mind to purchase with confidence.
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Limitations
Fitting on a jig isn’t without its limitations, and it’s important to recognise this in order to get the most out of using one.
Bike Fit Jig Limitation 1
One of the biggest limitations of fitting using an adjustable jig sounds obvious, but it’s not an actual bike.
By this, I mean it doesn’t behave like an actual bike would when being ridden outside. Bike fit jigs are usually built on a broad platform, are very heavy and as a result, very stable.
There is little to no need for the rider to have to create their own stability in order to remain balanced when riding on a jig (or a turbo trainer for that matter, but that’s a story for another day) as the bike does the vast majority of it for you.
Often, positions on a bike fitting rig can be a bit “soft” as a result of riders not needing to create their own stability through their body in order to remain upright.
This means that we don’t know exactly how a position will actually feel out on the road until it is tested in that environment. How the rider creates stability and generates force on a jig compared to on a bike can sometimes be quite different.
This is why it is vitally important to have some adjustability in all areas of the bike, so that the position can be tweaked as required in order to create a balanced and stable position that also makes the bike handle well.
Bike Fit Jig Limitation 2
The second big limitation of fitting using an adjustable rig is the accurate transference of measurements from jig to bike.
It’s all well and good finding a great position on a bike fit jig, and a fitter documenting and presenting these measurements neatly in a report, but if they cannot be accurately implemented on a bike by a rider, mechanic or bike shop, then the position that is actually being ridden may not be the position that was intended and agreed upon by fitter and rider during the session.
Making sure that measurements are transferred as diligently and accurately as possible is paramount in achieving the desired result.
This is one of the reasons we offer a free follow up session with all of our full 4 hour fits – oftentimes it’s merely a case of resetting a measurement that hasn’t been implemented quite correctly that can greatly improve a riders experience on their bike.
Conclusion
So, armed with this knowledge, hopefully you can understand a little more about what a bike fit jig is and what it can offer us as fitters and riders, as well as understanding some of its potential limitations.
As with all tools, they must be used appropriately in the right scenario and with a clear view of what it is that needs to be achieved.
Whether that be fitting for a new bike, exploring components / positions beyond the physical parameters of an existing bike, or even just to facilitate faster positional changes within a given timeframe, knowing why you’re using a certain tool is often the first step in using it well.
Words by Mat (one ‘t’)
If you’ve made it to the end of this article, thank you and we hope it’s been useful for you.
If you have any questions about the right bike fit for you get in touch, we’re always an open door and there’s no such thing as a silly question: info@foundation.fit
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