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i have a Cannondale Hooligan I on which I plan to remove the Shimano Nexus 3spd IGH and replace it with a derailleur gear system. This bike has ETRTO 406 aka 20 inch wheels.

I want to use an 11 speed XTR M9000 medium cage RD

My question is: what is the maximum number of teeth I can have on the cassette? I see there is a 11-46 or 11-42 and 11-40.

The question isn't about the capacity of the derailleur but about whether there will be enough clearance between the derailleur and the ground.

thanks!

Argenti Apparatus
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turnipforge
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  • Does the bike's frame have any way to mount a derailleur? – Andrew Henle Jul 23 '19 at 16:47
  • You'll have to come up with a method to mount a derailleur, the Hooligan frame does not have a hanger. I also thought the rear hub spacing would be too narrow for a 11 speed hub, but the Nexus 3 speed hubs with a disc rotor are 135mm (see here) – Argenti Apparatus Jul 23 '19 at 17:26
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    There appears to be a hooligan 2 that uses the same frame and does use a derailleur. You will still have to procure a derailleur hanger, perhaps your cannondale LBS will be able to help with that. FWIW, the Hooligan 2 uses a 9spd cassette. Your LBS, being familiar with possibly both bikes may be able to offer insight on the clearance. – renesis Jul 23 '19 at 18:07

1 Answers1

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Rough estimate of distance of tip of derailleur cage from axle center:

I assume top pulley wheel is just touching sprocket, and pulley centers lie on a radius line from wheel axle center.

The radius through chain pin centers of a sprocket is approximated by n * s / 2 pi. n is number of teeth, s is chain pitch: 12.75mm in this case (see here).

Add say 5mm to pin center radius to get approximate total radius of sprocket.

40 teeth: 86mm

42 teeth: 90mm

46 teeth: 98mm

XTR RD-M9000 derailleurs have 11 tooth pulleys (I think)

11 teeth: 27mm

The distance of the tip of the lower pulley wheel from the wheel axle center is sprocket radius + (2 * pulley radius) + cage pulley center to pulley center distance.

Guessing the pulley center to pulley center distance is 80mm:

40 teeth: 220mm

42 teeth: 224mm

46 teeth: 232mm

How much clearance between the axle center and road do you have? An ETRTO 406 rim is obviously 203mm radius, plus say 25mm tire depth for a 35mm wide tire: 228mm.

There are plenty of 20" wheel folding bikes with derailleurs available, but I assume these use ~30 tooth largest sprockets. Browsing through google images of folding bikes I see their derailleur cages are very close to the ground anyway.

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