Compact crank vs. new cassette?
07-25-08, 12:16 AM
#1
Member
Thread Starter
Join Date: May 2005
Posts: 39
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Compact crank vs. new cassette?
Speed at 80 RPM
50-34/12-25 53-39/12-25 53-39/12-27
50 34 53 39 53 39
12 26.1 17.7 12 27.6 20.3 12 27.6 20.3
13 24.1 16.4 13 25.5 18.8 13 25.5 18.8
14 22.3 15.2 14 23.7 17.4 14 23.7 17.4
15 20.8 14.2 15 22.1 16.3 15 22.1 16.3
17 18.4 12.5 17 19.5 14.3 17 19.5 14.3
19 16.5 11.2 19 17.4 12.8 19 17.4 12.8
21 14.9 10.1 21 15.8 11.6 21 15.8 11.6
23 13.6 9.2 23 14.4 10.6 24 13.8 10.2
25 12.5 8.5 25 13.3 9.8 27 12.3 9.0
Gain ratios
50-34/12-25 53-39/12-25 53-39/12-27
50 34 53 39 53 39
12 8.1 5.5 12 8.5 6.3 12 8.5 6.3
13 7.4 5.1 13 7.9 5.8 13 7.9 5.8
14 6.9 4.7 14 7.3 5.4 14 7.3 5.4
15 6.5 4.4 15 6.8 5 15 6.8 5
17 5.7 3.9 17 6 4.4 17 6 4.4
19 5.1 3.5 19 5.4 4 19 5.4 4
21 4.6 3.1 21 4.9 3.6 21 4.9 3.6
23 4.2 2.9 23 4.5 3.3 24 4.3 3.1
25 3.9 2.6 25 4.1 3.0 27 3.8 2.8
[/FONT]
So, it looks like I'll get nearly all of the benefits of the compact crank with the 12-27 cassette, at a fraction of the price. Am I missing something here that would make the compact a better choice?
Thanks,
MSC
Madison, WI[/FONT]
Last edited by MSC; 07-25-08 at 07:59 AM.
07-25-08, 01:43 AM
#3
Senior Member
It was an easier decision for me. My Biopace cranks was 52/42 and my cassette was already 12-27 (couldn't go bigger without a different dérailleur). My new SRAM Rival compact was 52/34 so I got a bigger jump (42 down to 34) for my money.
I'm very happy with the compact crank. Btw, Performance blows these out the door from time to time. The crank and new bottom bracket was less than $200 installed.
I'm very happy with the compact crank. Btw, Performance blows these out the door from time to time. The crank and new bottom bracket was less than $200 installed.
07-25-08, 04:25 AM
#4
Keep on climbing
Well, I can't read your table with the supplied formatting. Here's the rundown:
A 39/27 is about 7% lower then your current 39/25. So if you were churning along at 70rpm, you'll now have a bail-out gear that lets you spin along at about 75rpm.
A 34/25 is about 13% lower then your current 39/25. So if you were churning along at 70rpm, you'll now have a bail-out gear that lets you spin along at about 80rpm.
As you discovered through Sheldon's gear calculator... Compact's don't give you a whole lot of substantially different gears then standard doubles do. How much of a bailout gear do you really need?
A 39/27 is about 7% lower then your current 39/25. So if you were churning along at 70rpm, you'll now have a bail-out gear that lets you spin along at about 75rpm.
A 34/25 is about 13% lower then your current 39/25. So if you were churning along at 70rpm, you'll now have a bail-out gear that lets you spin along at about 80rpm.
As you discovered through Sheldon's gear calculator... Compact's don't give you a whole lot of substantially different gears then standard doubles do. How much of a bailout gear do you really need?
