Q: How to compare: double vs triple crankset

accelerator

I hope I'm using the correct terms but essentially I wanted to try and compare how much top end power transfer I would lose using the smaller double chainring Felt Trail Shot 2010 vs my current bike a triple chainring Mongoose Tyax Elite 2008. I appreciate the former is lighter by about 20% and has superior components which could result in more efficient power transmission but I just want to assume all other components equal for a second to get a worst case scenario.

So, is there a way I can calculate and say the top gear on the Felt could have up to as much resistance (or cadence transfer to the wheels, you know what I mean) as a certain gear on the larger chainring of the Mongoose using the below info?

Felt Trail Shot:
CRANKSET: Truvativ STYLO 2.2 AM Dual Ring with Bashguard, 2-Piece Crank Giga-X-Pipe External Bearing Design, 36/24T Cold-Forged AL-66, S=170mm; M-L=175mm
FREEWHEEL/CASSETTE: SRAM PG-950, 9-Speed Cassette, 11-32T

Mongoose Tyax Elite:
CRANKSET: Shimano FC-M311 42/32/22T
Freewheel: Shmano HG30 11-32t 8sp cassette

Worst comes to worst, I'll buy and test and return if no likey but I was interested in the information anyway, especially if I come up against similar crankset bikes with different ring sizes.

supersonic

It's simple ratios of the chainrings. A 44t is 10% higher geared than a 40t.

accelerator

EDIT: Totally revised post, hope someone doesn't reply before this edit goes through.

So, can I use the following formula:

1 crank turn @ 42 teeth turns an 11t cog 3.8 revolutions
Therefore:
crank ring teeth / rear cog teeth = ratio of wheel revolutions to crank revolution

So, the Felt at 2nd crank (36t) / 9th cog (11t) = 3.27
The Mongoose at 3rd crank (42t) / 8th cog (11t) = 3.8
The Mongoose at 3rd crank (42t) / 7th cog (1 from top @ 13t) = 3.23

I hope my Mongoose info is correct, got it from a site just selling the cassette

supersonic

Yes, as above, is just ratios.

Frodo1095

Use this website to work out gear ratios and gear inches, may give you a better idea.
http://www.sheldonbrown.com/gears/
I used it to compare my current 3 x 9 shimano XT set up vs a SRAM 2 x 10 set up I subsequently decided to go with on my new bike.
Gear ratios
XT 44/32/22 on 11/34 170mm crank vs SRAM 39/26 on 11/36 170mm crank
7.8
6.6 6.9
5.7 6.3
5.6 5.4
5.0 4.7
4.8 4.6
4.3 4.2
4.1 4.2
3.9
3.7 3.7
3.6 3.6
3.3
3.3 3.2
3.1 3.2
2.8
2.8 2.8
2.7 2.7
2.5
2.5 2.4
2.4 2.4
2.1 2.1
2.1 2.1
1.9
1.8 1.8
1.6 1.6
1.4 1.4
1.3

Gear inches
XT 44/33/22 on 11/13/15/17/20/23/26/30/34 with 170mm crank vs SRAM 39/26 on 11/12/14/16/18/21/24/28/32/36 with 170mm crank
103.8
87.8 92
76.1 84.3
75.5 72.3
67.1 63.2
63.9 61.3
57.1 56.2
55.3 56.2
51.9
49.6 48.2
48.8 48.2
43.9
43.9 42.2
41.5 42.2
38
38 37.5
36.1 36.1
33.6
33.6 32.1
31.9 31.6
28.5 28.1
27.7 28.1
24.8
24.4 24.1
21.9 21.1
19 18.7
16.8

As you can see I loose my very top and very bottom gears but still maintain a good spread of gears, and how often do you end up in your very top gear and if you are in your granny gear you are just about crawling anyhow so will still be slow going.

Finally settled on:
Gear inches
SRAM 26/39 on 12/13/15/17/19/21/24/28/32/36 with 170mm crank
84.3
77.8
67.4
59.5
56.2
53.2

51.9
48.2
45.0
42.2
39.7
36.1
35.5
32.1
31.6
28.1
28.1
24.1
21.1
18.7

Hope this helps