The Right Gear: Part Two

In my last post I thought a 33x19 gear might be the optimal gear for me at the Kettles. Today, I rode the 33x19 setup. My previous best time was 41:22 (41 minutes and 22 seconds) with a 34x19 gear. Today it was 40:10. Just the right gear lets you climb, accelerate and still have speed to cover the course in the least time. it pays to play around with various gears to find what is best for you. And just a slight change can make a difference.

Another aspect of single speeding is maintaining your momentum while minimizing your effort. With a little practice you can learn to take corners without losing much speed and to use just the effort needed to maintain your speed. Since each course is different the technique must be tweaked continually. The single speed really forces this on you as any loss of momentum is paid for with a lot of added effort.

Mike

Comparison: Singlespeed vs Geared

Last week I had ridden the singletrack at the Northern Kettles using a 9 speed (1x9) setup. Yesterday, I switched to a singlespeed setup using a 34x19 gear. I wanted to get a good comparison between the geared setup and the singlespeed. I also had data from last August when I had set my fastest times ever over the same trails.

The bottom line is that I was faster with the singlespeed. However, just being faster doesn't mean alot as course conditions can affect times dramatically. So I also compared the power readings from my PowerTap. Over the same trails, I averaged about 10 Watts more power with the singlespeed than with the geared bike. This is approximately the amount of power needed to pull the chain through the derailleur as measured on my bike about a month ago. I had measured 12 Watts as the power needed to pull the chain through the derailleur.

Because the power needed to pull the chain through the derailleur is not power that reaches the rear hub the PowerTap does not measure it as part of the power data. The PowerTap only measures power to the hub. If you can eliminate losses before the hub, then the power will pass on to the hub and be recorded by the PowerTap. In otherwords, that power is now available to move the bike instead of just pull the chain through the derailleur. More power should translate to quicker times and more speed.

When all the frictional losses are considered on a bike, a 1% increase in Power should translate to about 0.5% increase in speed. My overall power increase with the singlespeed was 8% while my speed increase was 4%. Excellent agreement.

Of course this is just one example and relates to just this course. The Kettles trails do not have big climbs although there are many very short uphill parts. I plan to do some more runs at the Kettles and try other areas also. I also want to try with a slight gearing change as I think I can do better with a 33x19 instead of the 34x19 gear.

As I collect more data I will give you more specifics.

Mike

Single Speed vs Derailleur Friction

Today I did an experiment to measure just how much additional friction is in a Derailleur as opposed to a single speed setup. An easy test shows that the derailleur has more friction. Take the pedals and spin them backwards in each setup. What you will find is that when connected to a derailleur the pedals stop quickly. In my case in about 1/2 a turn. Whereas in the single speed setup the pedals move easily, in my case more one turn.

I wanted a more quantitative measure of the difference than just the above observation. So I attached a weight to the pedals and measured the amount of weight needed to take the pedals from horizontal to vertical in 1/2 a second. What I found was that the derailleur took 4 times as much weight. This means that the power output needed to just turn the pedals is 4 times more for the derailleur than in the single speed setup.

Next I tried to determine the actual power needed. This was a very crude estimate but I came up with 16 Watts for the derailleur verses 4 Watts for the single speed. The difference of 12 Watts is power that is not going to moving the bike but is needed to just overcome drive train friction.

At the Iola race an additional 12 Watts of power for me would have translated to reducing my race time by two and a half minutes. That would have moved me from fifth to third in my age group.

All these measurements were crude but show that friction is the real enemy and a simple configuration such as a single speed can help lower it by a significant amount.

I want to improve my measurements to get a better estimate of the difference in power so stay tuned.

Mike

The Iola Race

Saturday I drove to Iola to pre-ride the course. I started with a 34x18 gear which was too big. I could not climb any of the four major climbs on the course. So I changed to a 34x19 gear. This made the climbing better but I could only do 1 of 4 climbs. Then I went to a 33x19 combination. This achieved 2 of 4 climbs. By that time I was too tired to try another lap.

Saturday evening, when I was back home, I changed to a 32x19 gear. Then Sunday morning I decided to just put my 1x9 geared setup back on the bike for the race. I felt that I needed some off-road single speed time before trying to race. Single speeding is more than just a bike, there is a definite technique to successful riding.

At the start of the race I was positioned at the front of my wave. The race started very fast and by the first climb I was in the middle of the wave. However, I started passing riders even on the first climb. At Iola you pass through the ski bowl twice each lap. The second pass consist of a fast descent followed by a quick, steep uphill. It is essential to hit the bottom of the hill as fast as you can to make good time to the top. On the first lap I descended at 31 mph. However, when I reached the bottom of the climb the course was filled with walking riders and no way around them. I had to skid to a halt and run my bike up the hill. After that the course was clear for the rest of the race and it was a "go as fast as you can" for the race.

At the end I finished 5th out of 9 in my age group (60+). I was 4 minutes from the winner of the age group. Each lap was faster than the previous lap which is a good sign. It was a good time and it was great to see everyone after a long winter. The one sad note was that the fastest rider in the 60+ age group, Wayne Fish, passed away over the winter. Wayne was a real competitor. I never beat him but always looked forward to trying to close the time gap each race. Wayne will be missed.

As to the single speed, I plan to get some off-road training rides in now that the trails are open and hopefully be really to try a race on the single speed next time.

Mike

What's All This White Stuff?

April 19th and it is snowing! I was hoping the trails might open this coming weekend; but, today it has snowed several inches and more is expected tonight. That means my first off road ride will probably be the pre-ride for the Iola race the following weekend.

My main concern is gearing. Since I don't have any experience choosing cogs for a race, it would have been nice to be able to ride some trails to get an idea about gear ratios. So what is my plan? Use a 52x11 gear and a cadence of 80, then all I have to do is miss the trees to win. What could possibly go wrong with that plan?

The really nice thing about single speeding is that you always have a good excuse. Humilliating defeat? "Well, I was on a single speed". Huge win? "And I was on a single speed". You always look good no matter what the outcome. No front, rear, middle suspension, 68 speed, $10,000 carbon marvel can do that for you.

Looking for the Sun,

Mike

Is a Single Speed Slower?

Each year I try to compare my training with where I was at the same time last year. In the past, I have used such things as time over a certain route or average speed for the same route. However, these are not a very good indicators as they are highly dependent on weather conditions.

Last year I purchased a CycleOps PowerTap hub for my MTB and now I can compare power over a ride, course, or part of a course such as a certain climb or sprint. So when I switched to a single speed I was very curious if the single speed was slower than a geared bike under various conditions.

So far I have only been able to compare various road rides, as here in Wisconsin the ground has not completely thawed and dried and so the trails are not yet open. Right now I am using a 2:1 gear ratio that seems to work well on the short but moderately steep hills in the area. This ratio gives me a top speed of about 20-21 mph before I "spin out" on flats and downhills.

So what is my overall finding so far? On the average I'm slightly faster on my single speed compared to my geared bike rides from last year. The average power output is slightly higher. That may mean I'm just in better condition than last year at this time, but it is interesting.

One worry I had about the single speed was in climbing, but when I compared specific climbs to the geared bike I have found that I'm just as fast on the single speed and have a similar power output. How about sprints? In a short sprint, 10 seconds, it appears that I am slightly faster on the single speed. On longer sprints I am slightly slower as I spin out after 10 seconds or so. It is encouraging and leads me to think I can compete with the geared bikes in my age group.

In a couple of weeks the trails should be open and I can test the single speed on single track, so keep checking back.

Mike