# What size Single Front Chainring?



## TehYoyo (Sep 16, 2012)

I'm thinking of building up a CX bike and 1 front ring seems like it'd be best.

What size should I get? I was thinking 39. I'll have 11-28 in the back.

Please don't try to persuade me against a single chainring. The first sentence should really read "I'm building a CX bike with 1 front ring."


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## jroden (Jun 15, 2004)

TehYoyo said:


> I'm thinking of building up a CX bike and 1 front ring seems like it'd be best.
> 
> What size should I get? I was thinking 39. I'll have 11-28 in the back.
> 
> Please don't try to persuade me against a single chainring. The first sentence should really read "I'm building a CX bike with 1 front ring."


There are a lot of riders who use a 42 or 44. You need to start with a gear calculator and figure out what sort of gear you need to get over the biggest hill you will ride then make your decision based on that. For normal cross courses for a strongish rider, a 44 x 28 is a very manageable gear for typical race courses. I'm fairly strong and rode a 42 for a number of seasons with a 12-25 or 27 and never wished for more.

The only issue that makes the single a pain is the chain falls off. The k-edge chain watchers seem like a good option, along with an outer chain guard. I have been known to just use a second chainting as the outer guard. For the budget minded, a third eye or jumpstop chain watcher is a good choice. A clutch rear der. and one of these new wide-narrow chainrings would be a cool option too.


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## krisdrum (Oct 29, 2007)

My set up is 38 x 11-26 usually. Certainly have never wished for more top end. A few times wished for a bit more low end, but I am much more of a spinner than grinder. The suggestion of starting with a gear calculator is a good one. If you already race, think through the courses you usually do and what gears you were in for different sections of the course. Calculate the gear inches you were in for those sections, then compare it to different 1X set-ups, varying ring and cassette.


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## vmaxx4 (Jul 19, 2011)

A narrow/wide chain ring works great. I have switched over all my mountain bikes to single ring. Even without the type 2 rear derail'r, they work very well.
As others have said, calculate your riding area speeds and if you are a "spinner"or a "grinder". I'm planning to run a 40. 

BikeCalc.com - Bicycle Gear Speed Chart


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## Dopamine (Jun 2, 2009)

I ran the single ring setup when I raced CX with a 42 up front and a 12-27 in back. 12-25 would be fine as well and this gearing is good as seemed to be the just right gearing for it would be faster to get off and run if you hit anything steep enough that this bogs down. Also there is a double bash-guard sandwich you can get from cyclocrossworld that keeps you from ever dropping a chain off the front, that is what I ran. Hmmmm, actually I can sell you my used double bash guard sandwich if you want, PM me if interested, I won't ask ludicrous price!


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## Dopamine (Jun 2, 2009)

This is what I'm talking about:
Thorne Products Wetzikon Aluminum Chainring Guard
Run two of those sandwiching the front ring, you need long chainring bolts as well to make it work, but you'll never ever drop a chain.


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## ozzybmx (Jun 23, 2013)

Wolftooth 42t CX chainrings are nice.


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## pretender (Sep 18, 2007)

Just like Groenendaal, 45 teeth.

Go big or go home.


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## seppo17 (Dec 7, 2008)

I think 40 or 42 are the popular choices. 

I run a double set up with 38/46 w/ 12-27. There are courses where I don't use the 46 and courses where I'm in the 46 the whole race.


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## Thom H (Aug 25, 2009)

38 or 42. Easy to get. I mount mine on the inside with a catcher on the outside and never have problems with the chain falling off. I ride a single speed a fair amount so the luxury of having a 26-28 instead of a 17or18 in back is a dream. If you need much lower gear than a 38/27 you can probably run faster in cross.
I do notice that gravel grinding I would rather go with a 34 or 36 as the long hills are tough, but that is a different sport, No? So my gravel grinder cross bike is set up with a 34/42 two ring front. Color me happy on that one.


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## scooterman (Apr 15, 2006)

im using a 40T up front with an 11-32 in the back. I could use a 11-28 for racing but i do ride my cx bike in the winter sometimes up very very steep and long dirt roads. I can't imagine anyone other than some very strong cat1-2 riders that could benefit from anything bigger than a 40x11 in a cx race. 40x11 is 26 mph @90 rpm with a 32c tire.


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## ozzybmx (Jun 23, 2013)

On the gravel grind, i use my CX mainly for that. Currently running a 11-32 cassette on the back with 38-46 double, going to go 42t wolftooth with an 11-36 cassette.

That way I lose nothing down low and only half a tooth in top gear... though I do gain a heavier rear cassette.


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## Erik_A (Sep 14, 2008)

Unless you are pro, 38t is plenty with an 11-28.


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## TehYoyo (Sep 16, 2012)

I'm going to run a 42 front with 11-27 in the back. That's still short cage so if worse comes to worst, I can switch to long cage and do something ridiculous like 11-32.


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## scooterman (Apr 15, 2006)

TehYoyo said:


> I'm going to run a 42 front with 11-27 in the back. That's still short cage so if worse comes to worst, I can switch to long cage and do something ridiculous like 11-32.


Short cage MTB derailleurs do 32t fine.


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## Erik_A (Sep 14, 2008)

Pro Bike: Katie Compton's Trek Crockett Cyclocross Bike | Cyclocross Magazine ? Cyclocross News, Races, Bikes, Photos, Videos

https://wickwerks.com/single-front-chainring/


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## TehYoyo (Sep 16, 2012)

scooterman said:


> Short cage MTB derailleurs do 32t fine.


But short cage MTB derailleurs are weight-wise the same as long cage road derailleurs (without doing research on my part).


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## scooterman (Apr 15, 2006)

TehYoyo said:


> But short cage MTB derailleurs are weight-wise the same as long cage road derailleurs (without doing research on my part).


the Mtb derailleurs also have clutches in them. Do you use sram or shimano. If shimano you are stuck with a road derailleur pretty much. Sram 10 speed x9 x0 type2 etc work great with 10 or 11 speed sram levers.


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## mambo (Jul 29, 2012)

Didn't I read somewhere on the forum that real cyclists only use a 53?


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## bikerector (Oct 31, 2012)

Really depends on the courses in your area. For Michigan races and a 1x setup I would probably be a 38t front, maybe even a 36t. Rarely do I run out of gearing on the top end since I can spin pretty fast but it's nice to have those slow gears for climbs, sand pits, or mud slogs. Not very often do I hit much over 25mph in race which is easily done with a 38x11 at 90-ish rpms with a top sustained speed, for me, of about 30 mph at 110 rpms and top sprint speed of around 40 mph at 150 rpms.

If you can spin faster you can run smaller gears and still get the same overall speed range. Something racing sscx taught me since trying to hammer around on a tall gear is killer instead of spinning like mad everywhere. Really depends on your pedal style though, I know a lot of people feel comfortable mashing at 50 rpms up climbs on their ss mtb's.


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## 88 rex (Mar 18, 2008)

On the front I use a single 40t. 

On the rear I use a single 17t.


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## bikerector (Oct 31, 2012)

88 rex said:


> On the front I use a single 40t.
> 
> On the rear I use a single 17t.


More man than I. I run 40x18 for my sscx needs.


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## adam_mac84 (Sep 22, 2010)

scooterman said:


> the Mtb derailleurs also have clutches in them. Do you use sram or shimano. If shimano you are stuck with a road derailleur pretty much. Sram 10 speed x9 x0 type2 etc work great with 10 or 11 speed sram levers.


Have you tried this? Seems like some nice options to choose from, with the main difference with CX1 having a barrell adjuster. I can add that to the housing somewhere


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## scooterman (Apr 15, 2006)

yes, i have a super x disc with a X9 type2 RD short cage, force 22 shifter, 11-32 ultegra cassette 11spd, 40T wolftooth narrow wide. Works great. I havent raced it yet as i just set it up this spring/summer, but i've ridden it around about 150 miles.

I put in an inline barrel adjuster. I couldnt justify the expected price of a CX1 derailleur. I figured it would be close to xx1, xo1. I set this stuff up before CX1 came out. 

The x9 type 2 is about 80 grams more than the force derailleur. But the bike is 17 something pounds so its light enough. I'm much faster at racing cross when my chain doesnt fall off.


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## scooterman (Apr 15, 2006)

something to add to this. Changing a rear wheel on a disc brake/clutch derailleur bike sucks. It takes me probably about 6 seconds to change the rear wheel on a canti/normal derailluer bike. But probably a good 20 seconds on this setup. Just keep this in mind if you race and have pit wheels and not a pit bike.


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## adam_mac84 (Sep 22, 2010)

scooterman said:


> yes, i have a super x disc with a X9 type2 RD short cage, force 22 shifter, 11-32 ultegra cassette 11spd, 40T wolftooth narrow wide. Works great. I havent raced it yet as i just set it up this spring/summer, but i've ridden it around about 150 miles.
> 
> I put in an inline barrel adjuster. I couldnt justify the expected price of a CX1 derailleur. I figured it would be close to xx1, xo1. I set this stuff up before CX1 came out.
> 
> The x9 type 2 is about 80 grams more than the force derailleur. But the bike is 17 something pounds so its light enough. I'm much faster at racing cross when my chain doesnt fall off.



According to SRAM website. X9 type 2 is 250g, CX1 is 261

https://www.sram.com/sram/road/products/sram-force-cx1-rear-derailleur
https://www.sram.com/sram/mountain/products/sram-x9-type-2-10-speed-rear-derailleur


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