Douglas Ruby
Well-Known Member
- Region
- USA
- City
- Groton
Perhaps I am a bit dense, but the Specialized Turbo (in particular) as the lesser powered version of the family seems a bit over geared. It comes stock with an SRAM PG1030 11x32 cluster (11-12-13-15-17-19-22-25-28-32) and a 48T front sprocket.
Given that the 700x45c tires are effectively 28" tires, I used Sheldon Browns Gear Calculator and came up with stock gearing from 1st to 10th of 42", 48", 53.8", 61.1", 70.7", 79.1", 89.6", 103.4", 112", 122.2". At my normal cadence of 80 (typically 75-90) this equates to speeds from 10 mph to 29.1 mph. At a cadence of 90, the speed range is 11.2 mph to 32.7 mph. In my first 90 miles of riding I have NEVER been able to use 10th gear, and rarely have I gone above 8th. I believe that range and climbing ability are limited with this gearing because I am more likely to switch into Turbo or a higher level of ECO due to the gearing being too high. The ultra high 10th gear is of no practical use for me because it forces me below my normal cadence range at any speed I am likely to use save for a very long, steep descent at well over 30 mph.
Given that the max assisted speed is approx 26-28 mph, I decided that I wanted to be able to use all 10 speeds across the widest usable range, optimizing 10th gear for the maximum assisted speed (just over 26 mph) at 80 rpm. I then wanted to get the lowest possible 1st gear. I went to a SRAM PG1050 11x36 cluster (11-12-14-16-18-21-26-28-32-36) with a Vuelta 44T front sprocket from Nashbar. This gives gearing from 1st to 10th of: 34.2", 38.5", 44", 47.4", 58.7", 68.4", 77", 88", 102,7", 112". At a cadence of 80, the speed range is 8.1 mph to 26.7 mph. At a cadence of 90 rpm, the speed is 9.2 mph to 30 mph.
After installing the 44T front sprocket today I did a 14 mile ride, averaging 18.2 mph. The first 4 miles were at full TURBO (with some significant hilly sections). The 2nd half was either downhill or flat rail trail with just some uphill near the end. I used ECO 50% for most of the return trip except for a couple of hills near the end. While I never needed 1st gear, I found myself able to use 10th gear between 27 and 31 mph on descent and 8th and 9th gear for comfortable cruising in the 21 to 25 mph range using ECO 50% mode.
Most important to this change, is that the maximum assisted speed of around 26.7 mph now occurs in 10th gear instead of 8th gear and 1st gear is now 18.6% lower. Another view is that the ratio spread from the highest gear to my lowest gear is now 3.27 to 1 across 10 speeds versus the stock spread of 2.91 to 1. In fact, since 10th gear is NOT useable for me in stock form, the actual spread in stock gearing is 2.67 to 1 across 9 speeds. I consider this a 22% improvement in overall gearing useability.
Doug
Given that the 700x45c tires are effectively 28" tires, I used Sheldon Browns Gear Calculator and came up with stock gearing from 1st to 10th of 42", 48", 53.8", 61.1", 70.7", 79.1", 89.6", 103.4", 112", 122.2". At my normal cadence of 80 (typically 75-90) this equates to speeds from 10 mph to 29.1 mph. At a cadence of 90, the speed range is 11.2 mph to 32.7 mph. In my first 90 miles of riding I have NEVER been able to use 10th gear, and rarely have I gone above 8th. I believe that range and climbing ability are limited with this gearing because I am more likely to switch into Turbo or a higher level of ECO due to the gearing being too high. The ultra high 10th gear is of no practical use for me because it forces me below my normal cadence range at any speed I am likely to use save for a very long, steep descent at well over 30 mph.
Given that the max assisted speed is approx 26-28 mph, I decided that I wanted to be able to use all 10 speeds across the widest usable range, optimizing 10th gear for the maximum assisted speed (just over 26 mph) at 80 rpm. I then wanted to get the lowest possible 1st gear. I went to a SRAM PG1050 11x36 cluster (11-12-14-16-18-21-26-28-32-36) with a Vuelta 44T front sprocket from Nashbar. This gives gearing from 1st to 10th of: 34.2", 38.5", 44", 47.4", 58.7", 68.4", 77", 88", 102,7", 112". At a cadence of 80, the speed range is 8.1 mph to 26.7 mph. At a cadence of 90 rpm, the speed is 9.2 mph to 30 mph.
After installing the 44T front sprocket today I did a 14 mile ride, averaging 18.2 mph. The first 4 miles were at full TURBO (with some significant hilly sections). The 2nd half was either downhill or flat rail trail with just some uphill near the end. I used ECO 50% for most of the return trip except for a couple of hills near the end. While I never needed 1st gear, I found myself able to use 10th gear between 27 and 31 mph on descent and 8th and 9th gear for comfortable cruising in the 21 to 25 mph range using ECO 50% mode.
Most important to this change, is that the maximum assisted speed of around 26.7 mph now occurs in 10th gear instead of 8th gear and 1st gear is now 18.6% lower. Another view is that the ratio spread from the highest gear to my lowest gear is now 3.27 to 1 across 10 speeds versus the stock spread of 2.91 to 1. In fact, since 10th gear is NOT useable for me in stock form, the actual spread in stock gearing is 2.67 to 1 across 9 speeds. I consider this a 22% improvement in overall gearing useability.
Doug
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