A Bike Fitting with the GURU Bike Fit System

When cyclists think about getting a bike fitting they probably associate the process with buying a new bike. The sales person/bike shop owner/bike fitter does their own assessment on what size frame a person should be riding and then based on how sophisticated a system the bike shop uses, either sits that bike on a stationary trainer, sits you on bike fitting system that they manually adjust, or now in the second decade of the 21st century, they sit you on a fit system that moves and is controlled by a computer, while you ride it. The differences in these three methods are that now, finally, you can feel the changes in real time while you ride the “bike”, and this makes a big difference.

But back to my original premise that a bike fitting is probably associated with a “new” bike, here are a few reasons to get your current bike re-fit:

  • you’re changing your saddle type, the length of your crank arms, the shape or type of your handlebar, and/or adding aerobars to your bike
  • you’re returning to riding after a long layoff from injury or time away from training
  • you’re moving up to long course triathlon races or the opposite, moving down to shorter ones
  • you haven’t had a bike fit in 3+ years
  • you’re getting older and less flexible and it’s time to rethink the low and aggressive riding position you’ve been riding for a while

I decided that this off-season would be a good time to get myself re-fit on both my tri bike and road bike, principally because my road bike position hasn’t been checked in probably 10+ years and I know it’s out of whack AND I’m getting older and less flexible, damn it!

The local bike shop here in Santa Barbara that supports the SB Tri Club is Hazard’s Cyclesport, owned by Bruce Davis, and they have supported local triathletes for 20+ years and Bruce has been doing bike fitting for over 20 years himself. Last year Bruce acquired a GURU Bike Fit System, one of the new computer controlled bike fitting systems, and said he has done over 200 fittings already, wow! For a complete review and analysis of this system I direct you to Dan Empfield’s article at slowtwitch.com, so I don’t have to bore everyone with the details: GURU Fit System Bikehttp://www.slowtwitch.com/Bike_Fit/The_GURU_system_4136.html. The image is also from slowtwitch.com.

The basic steps you’ll go through are these:

  1. Your current bike setup is measured (saddle height over bottom bracket, saddle setback, drop from saddle to bars, reach from saddle to bars, and crank length), and then with you on the bike the angle of your knee at BDC (Bottom Dead Center), and at 90o after TDC the position of your knee relative to the pedal
  2. Then you are scanned by the fit system laser to get your basic dimensions (height, shoulder and hip width, leg and femur length, arm length). The system uses this information to help finding a bicycle frame that could be fit to your dimensions, and to pre-set the GURU fit bike into a baseline configuration
  3. If you’re buying a new bike, at this point you select a model and frame size from the GURU database (even brands not sold by your shop), to find the best match for your body type and size. Recommendations are also made for stem length and handlebar width. When doing a bike sizing fit (different from a complete bike fit), they can determine the rider’s preferred set up, then when the bike is being built match those dimensions so the rider is set up correctly from the start.
  4. The fit bike is then set up to either match what the GURU computer says it should be, or it’s overwritten by the bike fitter based on a conversation with you and your current set up, if this applies, or to the dimensions of your current bike
  5. This is the iterative step with you on the fit bike. The fitter moves between what your current set up is or the GURU determined set up, with you pedaling against a set resistance, as you adjust to the changes to see what feels and sounds the best. Based on whether the change is better, worse, or not noticeable, this is repeated until you come to a final configuration, the “after” configuration
  6. Once before and after settings have been established, you ride each setting on a “course” for a few minutes, while the fitter records the data at certain intervals, used as a comparison to see if there were any noticeable changes in performance, i.e., more power or efficiency. While watching the display on the screen you see the following three pieces of data: 1) A circular graph of how efficient you are at pedaling circles, 2) A bar graph showing the same thing, 3) A readout of your left versus right side, showing relative balance of power in percent and specific readings for each side. It shows how much power (in torque) is being applied to the left and right pedals, along with how balanced your body is at getting the power down. For example, you may show equal power to each pedal, but your right side may be working harder to achieve the same number as the left side. Could be from a leg length discrepancy, cleat placement, muscular imbalance, injury, etc.
  7. You test the bike and come back and repeats steps 4-6 to fine tune how it feels on the road

As hopefully everyone knows, changes to your bike position take a while for your body to adapt to. If you’re doing a re-fit and go out and ride, it may feel a bit foreign at the start, and might take more than a few hours in the saddle to get used to them. So what I’m saying is that don’t hop on your bike after a few adjustments and immediately decide that you don’t like it or that it isn’t working; old habits are ingrained in our body and mind, it just takes time. Of course if after a few rides you find yourself struggling to adapt, or your power output had dropped off, or you’re unable to hold your position for longer periods of time, go back to the shop and tweak the position some more, that’s part of the process and part of what you pay for.

For me, when this was all said and done I came away with a much better understanding of the process involved and the dynamics that have to be considered when setting up an athlete on their bike. Regardless of what kind of bike you ride, your riding habits, and your past performances, everyone could benefit from a bike fit on one of these new age tools, if for no other reason than to validate that the position and bike you are currently riding is suitable for you. In the best case you may find out that a few minor, or even major tweaks, can unleash more of the power in your legs to improve your bike splits, and then hopefully in turn your run.



Long Explanation of My Bike Fitting, For Those That Care…

I brought two bikes in for my fitting, a 2009 Cervelo P2 and my ’92 McMahon road bike, last fit maybe in 2002. I’ll focus on the P2 fitting for this discussion.

Step 1

As Bruce did the last fitting on my P2, he is familiar with my riding and riding style, and as a longtime friend also knows my history of low back (psoas and glutes) issues. We discussed the focus on the fitting, more on comfort and the ability to ride long without pain, versus a lower and possibly faster position. The tradeoff here is the more aggressive riding position that the athlete may or may not be able to maintain for the duration of the ride, which might compromise their ability to get off the bike and run effectively, versus a slighter less aero position that the athlete can ride all day, albeit maybe a bit slower, but which then allows them to run faster. As I’ve moved down in distance to the sprint and Olympic races for the foreseeable future, I could go either way, but I’m still riding long on weekends so I suggested we focus on comfort over outright speed.

Bruce immediately recognized that my seat height was a bit low, if still within reasonable boundaries, but something to look at, and that from the side I was riding with a flat back in the aero position, but kind of stretched out, possibly contributing to my low back tightness. He also noted that my seat was tilted back a little more than he would prescribe which by rotating my hips backward could also be contributing to my back issues.

Step 2

In your bare feet you stand still so the GURU system can scan in your dimensions, which as I said, helps it determine the correct frame model and size; not all frames are created equal by all companies. Some favor a longer top tube, good for those with longer femurs (like me), while others compensate by relying on a standard length top tube with the use of longer stems. Each of these paradigms has pluses and minuses, so all the information gathered helps the computer search the database for the optimum frame for your specific dimensions. The database is extensive, but it only gives suggestions. The fitter will discuss the findings with the rider to come up with the best bike/position for that rider.

In the past this was all done by eyeball and not to say that bike shops would fit you to a bike that really didn’t fit, but without a full range of bikes and sizes in their shop at the time, you might find yourself up or down one size compared to the “ideal” sized frame, out of convenience.

Step 3

As I was getting a re-fit on an existing bike, I skipped this step, but I can always go back with the data provided by the GURU Fit System, which is emailed to you, and take it to any shop and they could use it to spec out a bike for me. As Bruce also mentioned, if you happen to be on the road and are renting a bike, you can also provide this info to the rental company to help them set the bike up to your preference, mimicking the feel of your bike at home.

Step 4

What the fit determined was my ideal set up, as compared to my current set up, wasn’t too far off, and Bruce’s observation that my seat was a bit low was one of the things it too noticed. We started out with the fit bike set up to mimic my current set up with a minor change to my seat angle. Bruce dropped the nose of the saddle surmising that the seat had slipped over time, so he wanted to reset it to a normal angle.

Step 5

Starting with my seat position we went up and forward, a standard adjustment when raising the seat, and I immediately felt my low back relax. With my saddle nose already pointed down a few degrees I’m really feeling how the changes might help my back.

Then he focused on the front end, bringing the aerobars back and up, resulting in a more upright, and yes slightly less aero position, but my neck, shoulders, and low back were all feeling more relaxed, and while pedaling I felt more comfortable while spinning.

One note here, during this step the resistance you are pedaling against is set so that you are spinning at your nominal cadence, as seen by a display on the big screen in front of you. I am more of a spinner when I’m riding in the aerobars and time-trialing, so I was dialed in at 93-95 RPM for the test.

Once we had finished tweaking these settings, Bruce saved them and then we played around with switching back and forth from the original settings to the new ones. Again, this is where in the old days you would have to stop and get off the bike/bike-fit machine, while the fitter removed parts and replaced them and/or adjusted them. Then you’d get back on and try and make a determination if the new position was better, worse, or that there was no difference.

Now you are riding the bike and without stopping it readjusts itself to the other setting so you can feel in real-time the affect the changes make, good, bad or indifferent. I think this is where these new systems shine and where your money will be well spent.

Step 6

Moving on to riding the “bike” with my new settings on a set course, in this case a short flat section to establish baseline readings and then a slight incline, I’m watching the screen, seeing that I’m spinning nice round circles with pretty equal balance from left to right. I’m not putting out much power, as I’m in the flats, waiting for the hill. At two minutes Bruce takes a snapshot of my results, then a minute later, now up on the hill. We repeat this test after a break with my old configuration, and then after a cool down spin we sit and discuss the results.

All things being equal, there wasn’t much difference in the results, albeit that my power was actually higher in the original position at the second snapshot. I said that I think I pushed more on the second round, already familiar with the drill, and Bruce opined that muscle memory, your body and mind being used to a certain position, takes a while to erase and replace with the sensations of a new position, so my results were in line with what he has seen before. The real test would be out on the streets and how it all felt then.

Step 7

This will be a work in progress as I start riding the bike with these new settings. I’m looking forward to longer rides to see how my back and upper body feel after pushing hard, and oddly enough for the first brick run of the upcoming New Year to see if in fact my back does feel better and if this translates into my legs feeling better off the bike, allowing me to run faster. I have a history of leg cramps early on the run, so charging out of T2 is not something I tend to do because of this, easing the speed on as my body adjusts to the pounding of the run.

Bike #2, the McMahon

A final thought on the second bike fitting I had with my road bike. This bike is a titanium framed ’92 McMahon, size 59cm, which is one size larger than I would be fitted on today. It started life with a Shimano 105 groupo from my ’89 Diamondback Master TG, which morphed over time into an Ultegra groupo, and then finally a brand new 9-speed Dura Ace kit. That whole set up moved over to a ’02 Griffen tri bike, and the frame sat unused until that group was upgraded to a 10-speed, where I then returned the 9-speed parts to it.

Finally today that drive train has given up the ghost so I’m upgrading it while moving my old 10-speed parts that have been sitting in a drawer since I upgraded my Cervelo, which replace my Griffen in ’09, to Ui2 electronic shifting. The actual bike fitting revealed my seat was actually in a much better position than my TT bike, but that my handlebars were way too far away and down, which I suspected. I’m a proponent of riding a road bike in the off season to change things up, and it turns out that I keep this bike in my office so that my weekday rides are always on the road bike and weekend rides on my P2.

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