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Recreational Cyclocross and Gravelbiking This has to be the most physically intense sport ever invented. It's high speed bicycle racing on a short off road course or riding the off pavement rides on gravel like :The Dirty Kanza". We also have a dedicated Racing forum for the Cyclocross Hard Core Racers.

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Old 08-25-14, 07:20 AM   #1
eulis
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sscx gear ratios?

afternoon all,
as I'm a newbie to the forum, I hope you can cut me some slack if I break any of the forum rules (I know the guys at lfgss are very uptight about theirs)
I have a surly steamroller in the making which I plan to use as a daily bike, but the occasional bit of cyclocross.
It's pretty much completely built (just waiting for the wheels to arrive) but as I've never ridden cx before, I'm unsure of the technicalities.
On my other bike I ride 50/15 in the notoriously hilly streets of Bristol, which is a ratio I like
I have a 38 tooth chainring up front which I would like to keep, especially as I have a very nice 14t fixed cog which I'll use most of the time.
the question is, what size freewheel should I use? I was thinking 18t might be nice, but I really can't be sure.
Any help is appreciated
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Old 08-25-14, 09:28 AM   #2
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I don't fully understand. You will be running the CX bike with a flip-flop fixed/free setup? You can't have a difference of more than 1 or 2 teeth between your fixed and free cogs, especially if you want to use your rear brake. So if you are already set on 38:14 for the fixed, the most you can get away with on the flip side is 15 or maybe 16.
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Old 08-25-14, 09:31 AM   #3
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I like 65" for gravel riding. The hills that do have me off and walking are still pretty tough and slow for the people with multiple gears.
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Old 08-25-14, 09:46 AM   #4
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When I race I have found 38x17 to be perfect for me but I would go for a little higher on the street. You will probably need to have 2 different chains with quick links to make the swap easier.
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Old 08-25-14, 09:48 AM   #5
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Come to the race prepared to change the gearing .. and get your dismount and running and remount practice in, if your gear is too high , run the hill..

50:15 is 3.333333:1 how about 2:1? 38:19?

White Dos freewheels pair 2 cogs together a few teeth difference ..
Use the same difference, say 19/17 & a 38/40 chain ring pair and the chain loop will stay same

17:40 the higher, 19:38 the lower.. a double flip freewheel hub would do too ..

Last edited by fietsbob; 08-25-14 at 10:04 AM.
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Old 08-25-14, 10:59 AM   #6
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When I race I have found 38x17 to be perfect for me but I would go for a little higher on the street. You will probably need to have 2 different chains with quick links to make the swap easier.
38x17 could work, how is it on the uphills?
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Old 08-25-14, 11:09 AM   #7
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It's fine for uphills.
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Old 08-25-14, 11:19 AM   #8
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think I'll go for that then and ride a 15t fixed cog on the back. I'll only be using it on roads to get me places slowly, so 2.5ish would be fine. There's some sprints coming up in september which it would be perfect for aswell! Thanks everyone for the help, it's made my life much easier
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Old 08-25-14, 01:09 PM   #9
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tight corners on CX courses wont go well on a fixie . but if this is just a street bike do as you wish .
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Old 08-25-14, 01:18 PM   #10
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It's nice to have options. I use 42x16 fixed for commuting, 43x15 fixed for winter road training, and 39x18 free for racing.
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Old 08-25-14, 01:46 PM   #11
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tight corners on CX courses wont go well on a fixie . but if this is just a street bike do as you wish .
I'll be riding freewheel on cyclocross, I'll use a flip flop hub so I can just switch them over
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Old 08-25-14, 01:56 PM   #12
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Gear selection for sscx is all about finding the balance between how much you're willing to mash and how much you're willing to spin. It's a personal choice, but it also depends on the courses you'll be racing.

Obviously your typical speeds will be a good bit lower on most cross courses than they would be on the street. You will also be accelerating from low speeds much more often. Most of the time, the limiting factor for your gear choice will be how much repeated accelerations wear you out rather than whether or not you can mash the gear up the steepest incline on the course. If the course you're racing on has any long straight stretches, you'll probably want to nudge your gearing up a bit.

I'm not nearly as strong as you. I ride a 47x18 gear on a road commute that has nothing more than gentle rolling hills. For CX races I drop down to a 38x18 gear, and if the course has any significant hills I stick to my geared bike. If you can ride 50x15 on hilly roads, then 38x17 may be at the low end of what you'd want.

Another factor to consider, however, is that small cogs are not as kind to your chain as big cogs and the bumps of off-road use make chain slip more likely. Anything smaller than 16T is kind of asking for trouble, though I suppose keeping a close eye on chain tension can mitigate this concern.
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Old 08-25-14, 01:59 PM   #13
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That answered flargle's question.

Just come prepared to change the gear after a couple trial laps of the course, as it's set up that day.

Last edited by fietsbob; 08-26-14 at 11:53 AM.
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Old 08-26-14, 04:19 AM   #14
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I'm not nearly as strong as you. I ride a 47x18 gear on a road commute that has nothing more than gentle rolling hills. For CX races I drop down to a 38x18 gear, and if the course has any significant hills I stick to my geared bike. If you can ride 50x15 on hilly roads, then 38x17 may be at the low end of what you'd want.

Another factor to consider, however, is that small cogs are not as kind to your chain as big cogs and the bumps of off-road use make chain slip more likely. Anything smaller than 16T is kind of asking for trouble, though I suppose keeping a close eye on chain tension can mitigate this concern.
very helpful andy thank you! Courses will most likely be quite hilly in places, so I was thinking a low ratio might be easier. 38x18 might be quite good, and I have a 16t fixed cog lying around which I could use for street riding. would also lower the chance of chain slip as you say, and if it's too small I can always chuck a 42t chainring up front
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Old 08-27-14, 10:23 AM   #15
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I think having a double-chainring setup is a great idea (thx fietsbob). The one trick would be getting your chainline good on both the free and fixed side. But you could have a pretty big jump in gear-inches between fixed and free and still keep the chainwrap the same, and therefore no need to adjust rear brake. That would be pretty slick.
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Old 08-27-14, 03:06 PM   #16
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White Ind has a setup like this called the Dingle.
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Old 08-28-14, 12:24 PM   #17
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I think having a double-chainring setup is a great idea (thx fietsbob). The one trick would be getting your chainline good on both the free and fixed side. But you could have a pretty big jump in gear-inches between fixed and free and still keep the chainwrap the same, and therefore no need to adjust rear brake. That would be pretty slick.
And if you had a device on board to switch between them while riding -- man, that would be the hot ticket.
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