No 51, March 2007

Compact Cranks

By Lindsay Harvey

I recently swapped my Campagnolo Centaur front derailleur and 39/53 chain ring for a set of Centaur compact cranks with a 34/50 chain ring. My rear cog is a 13/29 so the new cranks give me some serious hill climbing ability.

The First Test

Adjustment of the compact cranks is slightly more difficult than for the standard cranks, and after 20 km around Centennial Park using the 20 possible combinations, it was back to Pedal Pushers/Cyclefit for some refinements. The main issue was that both chain rings were touching the front derailleur in the extreme positions. This issue was solved for the 34 chain ring but it is still an issue for the 50 chain ring on the 26 and 29 cogs at the rear. According to the Master mechanic this is usual for compact cranks and on the real test (see below) I didnŐt find it a problem as I didnŐt use that combination. You can also make slight adjustments to the position of the front derailleur using the ergo levers to help resolve this issue.

The Real Test

The route was St Leonards via Pacific Highway to Roseville Bridge, Terry Hills, Akuna Bay, West Head, Akuna Bay, Terry Hills, Mona Vale Road. Pacific Highway, St Leonards - a total distance of 99.6km with some serious hill climbing.

The first impression is that you use the larger chain ring more often. I thought there would be some reduction of top speed but I found that by increasing my cadence by from 90 to 110 rpm I did not loose any speed at the top end. In fact I probably should not have been using my 13 rear cog on the old 53 chain ring until I got to about 55- 60kmh as I found the combination of 50/13 quite comfortable at this speed. Any faster for me and I am going down a steep hill and I do peddle anyway. My first hill was the climb out of the Roseville Bridge and I noticed that I was using 34/24 for most of the way up and switched to 34/26 for the last 50 meters. This was easier compared to the standard cranks. My uphill cadence went from 70 to 80 and my hear rate was lower as there was less effort.

The second test of the hill climbing was coming out of Akuna Bay on the way to West Head and I found my self using the 34/24 combination and in places a bit lower again, so no real change from the 39/53 combination.

On this ride there are three hills that I struggle to maintain a 70 plus cadence: the second last hill just before West Head, the hill from the West Head Look Out to Resolute Picnic area and the hill from Illawong Bay to the Cottage Road Turn off. Of these three hills I find the Illawong Bay to Cottage Road intersection the hardest as thatŐs when I am starting to get tired after almost 70km of riding. The compact cranks allowed me to maintain 70 plus on all these climbs and I caught one of the riders of the group ahead who had a 40m start on me at the beginning of the climb. More importantly my heart rate was lower!

Using the momentum you gain from a down hill for as long as possible into the uphill makes climbing easier. Correct gear changing is essential if you want to get the best from the down hill momentum for the climb. On the slight rises I found that when you change from 50 to the 34 chain ring, it was necessary to drop one or two gears on the rear cog as well. It took a little bit of getting used to but did not seem to compromise forward momentum. If the uphill section coming off the downhill was steeper, I found the best combination was to change from 50/14 to 34/14. My cadence really picked up and it seemed to add acceleration to the climb.

The Summary

Being 56 years old and weighing in at 90kgs, the compact cranks allow me to go up the hills faster at a much better cadence. On the steep hills my cadence tends to drop to 60 (or less) even on the 39/29 combination but I can easily maintain 70 to 80 on the compact cranks. It is a strange feeling peddling at 70 plus up a steep hill when I have got used to a lower cadence. For me there was no loss of speed at the top end and there is a wonderful feeling of having the gears for very steep hills if required. These cranks worked very well for the Audax Alpine Classic.

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