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I like rigid MTB.
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I'm planning to use 1x10 system for my cx.
What is the top speed that I can get for 38T front and 11T rear ?
 

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bipedal
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On a bike with 700Cx33 tires and a 40t CR and 11t cog I can push close to 30mph (at least downhill with a tailwind) :)
 

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Formerly of Kent
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I'm planning to use 1x10 system for my cx.
What is the top speed that I can get for 38T front and 11T rear ?
How much power can you produce? How fast can you pedal?

Those are the limiting factors.
 

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I'm planning to use 1x10 system for my cx.
What is the top speed that I can get for 38T front and 11T rear ?
Gear inches x .2973 will give you an estimate of your speed at 100 rpm.

Let's say your 'cross tires come out to 28" (estimating somewhere between regular road tires at 27" and mtb tires at 29", not exact but close enough for our purposes)

38x28/11 = 96.73 GI x .2973 = 28.75 mph @ 100 rpm. You can calculate your top speed based on you cadence from there. Every 10 rpm gets you 2.875 more or less speed.

Unless you plan on trying to climb a phone pole on your cross bike, I'd say use a 40t ring, maybe even a 42. 38x36 is a really, really low gear for a 'cross bike.
 

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Tighter. Cassette

Really no need for a big gap 11-36 on a cross bike think more like how would I ride on the road with this, plenty of people race a single ring and a 12-26 and a 38-42t front ring. I think you should be able to get to around 24 mph on the road with a 38/11. If you have a road bike with a standard crank you can just try going fast crossed up in the 39/11 and see how fast you can go. If your going to be ridding some big hills with a load on a rack then a 11-28 might be nice

Let's say your 'cross tires come out to 28" (estimating somewhere between regular road tires at 27" and mtb tires at 29", not exact but close enough for our purposes)

38x28/11 = 96.73 GI x .2973 = 28.75 mph @ 100 rpm. You can calculate your top speed based on you cadence from there. Every 10 rpm gets you 2.875 more or less speed.

Unless you plan on trying to climb a phone pole on your cross bike, I'd say use a 40t ring, maybe even a 42. 38x36 is a really, really low gear for a 'cross bike.[/QUOTE]
 

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I was a respectable cat3 last year (I'm faster this year already), with consistent low teen finishes in packs of 40 or so, - and several wins in c2 mtb a year ago spring. I ran a 1x9 38 11-32 with an older xtr rear derailluer, I adjusted the der stop to eliminate the 11 because of the chainline and I wasn't ever using the 11. Maybe cx is more hilly in my area, but I found those to be good gears and I like a more mtb style low gear for the short hard climbs (my knees are old, along with the rest of my body). I think a lot of guys who haven't raced cx imagine using the big ring and really going fast, but imo cx is pretty slow with lots of grass/mud and otherwise rough surfaces, more suitable to low gears than big gears. I think you would find the 38x32 low enough, and your derailleur could still be short enough to stay clear of a lot of the grass and crap that will get caught in the pulleys and break off your hanger.
 
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