Posts tagged #Bike Fit

Bicycle Measurement

              You would think that the task of measuring a bike would be a very simple one but alas, as with most things in life, we have made it complex and ultimately very confusing. Over the years a few different ways of measuring frames, seat tube length specifically, have evolved. Sadly they have all become commonly used among the many frame manufactures out there, I have even dealt with manufacturers that have utilized 2 different methods of sizing within their range of bicycles. Needless to say this can get very confusing and needs to be kept in mind when purchasing a bike, especially when using an existing bikes measurement as the foundation for a new one. In my opinion buying a new bike in a size based solely on the fact that it is the size of the previous one is a bad way to go about things anyway but can be disastrous if the frames have been measured to different points.
 Today’s modern frames are designed very differently from the older, horizontal top tube, bikes of yesterday. The new geometry of compact frames with sloping top tubes are designed to have lots more visible seat post and can vary a lot from design to design so, again, sticking with the size of a previous one for the new and expecting it to fit like the old probably is not going to happen. Always get a new bike fit done on the bicycle style and design you are contemplating.
             The drawing below shows the various points that are used when quoting seat tube frame sizes. All have a starting point at the center of the bottom bracket but from there can be measured to the top of the top tube, the top of the seat tube itself or even to an imaginary line which represents the center of the top tube if it were a horizontal design
Click Image for full size.

There is actually another one that is only used by frame-builders when building custom frames and that is; to the center line of top tube where it will actually be. This is because we are building a bike to an individual’s body measurements and the tube dimensions are already factored in. We also work from center line dimensions when setting the frame jigs.

With all these methods you can see how varied the results can be. Looking at the frame in the picture you can see that there is quite a difference from   the shortest measurement to the longest on the same frame. I have always thought that the most important measurement on a production frame nowadays is the effective top tube length. When comparing a favorite frame to a possible new addition this is a good comparison measurement to start with, but again a proper fit is the way to go.

Posted on December 4, 2012 .

Re-Inventing the Wheel.

The bike business is a business like many others, ideas come and ideas go, some good some bad and many are just there to let people know that the company ain’t dead. Every once in a while an idea comes along and just kind of hangs in the periphery, just waiting for their time to come. One such idea is 650b wheels, not that the 650b wheel is a new idea, hell it’s not even an old idea it has been around for decades, but to mountain bike designers and riders it is relatively new. There are some people, and I myself am one, that contend that if we had designed mountain bikes from the ground up in the beginning instead of modifying road bikes and cruisers to go biking in the woods, we would probably have opted for 650b wheels right from the start, however modifying frames led us to the smaller 26 inch wheels that then became the mountain bike standard for so many years.
        A few years ago we made the quantum leap to the 700c wheel, more commonly referred to as the 29er, which has made a huge impact with off roaders. This has made it difficult for the 650b though. Going so long with one choice, the 26, then adding the 29er quite recently has meant some reluctance from mass manufactures to add yet another wheel size and different bike geometry to already swollen product lines. Luckily the fear of being left behind by the competition has won out and we are seeing many choices from frame companies along with tire and rim manufacturers for 650b. This is very good news. And here's why; Choices.
As mentioned before the industry standard 26inch wheel MTB has been around since the start of mountain biking, the 29er or 700c MTB wheel is a relative newcomer and the 650 b is the new kid in town. The important thing to keep in mind here though is to not disregard any of the old wheel sizes just because there is a new one. They all have their place when looking for a new bike.
During this bike season we have seen a lot of new customers, which is very nice, a lot of new MTB’ers have come through the door as well and a good deal of them have opted for the 29er. Now don't get me wrong a 29er is a fantastic machine but it is not for everybody.
Designing frames and frame geometry for big wheels is tough, sure anyone can build a bike to accept big wheels but getting the handling and feel dialed in is a very different matter and it is especially difficult getting it right on mid to small frame sizes. We have seen many, many riders lately that look like they have been swallowed whole by their bike and, while this arrangement is fine for a gentle trail ride, on a more MTB specific trail or good single-track it must be akin to riding a bull elephant with colic.
Before I carry on let me clarify what we actually mean when we talk about these different sizes. Below are the measurements, in millimeters across the wheel, bead to bead. The bead of a rim is about 3mm down from the top of the rim.

26        559mm
650b    584mm
29er     622mm

As you can see the 650 falls about midway between the other two you will also note that the bead seat diameter of the 29er is the same as a standard road 700c so why do we call it a 29er when it is really only a modern 27inch road wheel. Well it is because some bright spark decided to measure the diameter outside to outside with a fully inflated mtb tire on, which gives you a measurement of roughly 29inches. Confused yet?
Anyway, back to the business at hand.  If you are a tallish or leggy person the big wheel option is definitely a choice for you. The frame size will be plenty to accommodate the extra clearance while still maintaining the ride characteristics of a good mtb. All the rules of bottom bracket height and head and seat tube angles still need to be obeyed and they can be with a mid to large frame size. However, if you are, shall we say a little vertically challenged, this is where problems arise. The rules of designing a bike to perform well for the rider tend to get thrown out the window and it all becomes about designing a small enough frame to at least reach the pedals on while the design is sacrificed to fit a big set of wheels. This really does not work. The cut off for a bike designed for the rider instead of the wheels generally falls somewhere around the 5’6” mark. There are exceptions for those with exceedingly long legs in relation to body height but generally speaking this is where sticking with the 26” wheels tends to be the better option.  Now though we have another option 650b.  This is where the slightly smaller size gives us, as frame designers, much more scope to still design the bike for the ultimate ride and handling but still giving the option of bigger wheels.
A Soma "B-Side" Built and ready to roll.
For those wanting to know more about the options available in the 650 or 29er range stop in or fire me an email. There are lots of choices. At the moment some of the best 650b frames tend to be from companies like Soma who offer the B-side. I expect some of the major names to start producing complete 650 bikes in the next year’s product line.
Posted on September 23, 2012 .

Aero-Bars. Making the Leap.

           Anyone who rides a road or Drop Bar bicycle regularly has, at one time or another, thought of bolting on a set of aero-bars. For some it is an idea born on a ride but dismissed before the brake pads have cooled. For others, it is tried and met with lackluster results and, for a few, a turning point in comfort and performance.
The following guidelines and advice is for those of you thinking of taking the aero plunge or who have a set of bars on their bike and are not sure how to set them up. Before we begin I will say that there are a couple of ways to approach aero set-up. For a' Time Trial' professional or specialist it is going to be very different from the way we fit and position bars for the casual or club rider. It is the latter that I shall concentrate on here.
Firstly, I often see bars that people have positioned after reading a magazine or following strict parameters used by Time Tail experts. Unless you are training exclusively for the TT discipline, do not set your bars this way. The aim should be for you to transition from drops to aero without a drastic change to your upper body position. One of the biggest problems is the elbow and hip height. This is often quoted in articles as a golden rule. It kinda' is if you're Bradley Wiggins however, for us mere mortals, it is not so important. If, after installing the bars and setting them up you find that your hips are in line with your elbows, then great. But, if your natural road bike position is comfortable in a higher front end do not change that to achieve a lineup of hips and elbows. You will lose more than you will gain.
        So where to start, well bar choice is important, there are hundreds of bars and designs on the market and all of them have their merits. But and it is a big but, most of them are not going to work for you and here is why; Adjustability. You need a bar with a wide range of adjustment and also, you still need to be able to ride using the drops and, I bet you like to ride the bar tops and hoods once in a while, that means the arm rests need to flip up when not in use. We like the profile Design bars for these reasons.
You will want to set the cups behind the handlebars and set the angles to comfortably cradle your forearms in their natural position, do not draw in your shoulders and arms to match the cups, this will restrict your airflow.
        The length of the aero-bars should be set so that when using them your head, neck and back position remain more or less the same as when you are in the drops. Lastly, try to set the angle of the extensions somewhat neutral. Bars that tilt up steeply from the elbow to the hands put unnecessary pressure on the spine and neck, keeping them level or even tilted down, will remove that issue.
The extensions on most bars will usually end up being just a little past the furthest point of you brake levers.0
Posted on August 13, 2012 .