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Discussion Starter · #1 ·
Has any one used a single 42 tooth chainring and a 12/27 7 cog casette . I would like to do that to my cheapo sportek ridgerunner mountain bike. I read that many cyclocross riders like this setup for simplicity. My concern is top end speed. I wonder if it will be enough? Has any one used this setup in a race and if so what do you think about it? I won't ever be competing, on a race course but I do like blowing the doors off the cars on our small town streets.
I get really good exceleration and great shifting on the back using my 38 tooth front middle ring but I need a bit more top end. Thats why I picked a 42 tooth single. What do you guys think.
 

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If you really want speed, why not go for a road gearing.

I raced a 38 12/27 last year and got my butt kicked plenty, but it wasn't because of gearing. A 42x12 is pretty fast at higher rpm.

It is also a function of leg speed/cadence.
 

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Discussion Starter · #3 · (Edited)
Road gearing? I would have to learn about it first. My reasoning for the single gear is this. I want a mountain bike frame because (I have it in my head that it is stronger than a road bike frame. ( I like to jump off 8 inch side walks on to the road ) soooo... I think that the 26inch rims are stronger. Then I try to jump over small obstacles on trails, but can't, so my bike takes a pretty good beating. Quite often I'm not watching where I'm going, or I simply can't avoid smashing through a horrid sharp edged pot hole.... Stuff like that.

Then my bike has a 28/38/48 on the front. I never use the 28 tooth. I use the 38 tooth all the time. When I use the front 38 and back 12 I feel I have to pedal to fast at times and crave just a tiny bit more speed but it's not worth trying to shift to the big ring on the front and the big ring on the back for the time remaining for me to go fast. ( cheapo bike remember) Does that make sense?

any way since I don't use the 28 tooth or the 48 on the front it makes sense to me to get a bigger middle ring (42 tooth)and have just that. I can't take this setup for a test run before I buy the parts if I can even get them,so I have to guess or rely on your expertise. So thank you for your reply.
I also like the idea of the simplicity of one front ring.
 

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Pretty standard chainring set-ups these days for road are either 50/34 (compact) or 52/39 (traditional/standard). Those would be less effective if you take your bike off-road on anything more challenging than a smooth dirt path.
 

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I run a 39, 11/32 on my cross bike that is currently doing commuting duty. I do not have a problem holding 20-25mph on my commute.

with a 39 12 and a 90RPM cadence you should be able to get into the low 20's with a 42 12 you are in the mid 20s
 

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Gully and many other domestic pros have used and continue to use single 42s. Over the pond, guys are using up to 45s. It's becoming less common over there though as courses have gotten faster and faster. For all intents and purposes, those guys might as well be running 46 singles because they aren't in the small ring too often. Maybe for the Koppenbergcross or the Roubaix World Cup. They used to get more use in the Swiss races. But they will often still keep a spare bike (usually their third) with a single ring for really nasty days.

My point is that you likely won't be in need of top end speed with a 42/12.
 

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Discussion Starter · #7 ·
Thanks people. I will go with a 42 on the front then and then try some Kenda Kross plus tires. That should make a difference. Should be fun if nothing else.
 

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if your bike has 26 inch wheels and your objective is to zip around on flat streets, you should be able to run a 53 or larger front chainring if you have normal strength and fitness. The smaller wheels reduce the final drive ratio a bit.
 

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Discussion Starter · #9 ·
jroden said:
if your bike has 26 inch wheels and your objective is to zip around on flat streets, you should be able to run a 53 or larger front chainring if you have normal strength and fitness. The smaller wheels reduce the final drive ratio a bit.
I tried riding around using only my 48 front chain ring but had a hard time on some of the steeper areas or obstacles. (It felt like work)
But no....My objective is actually to have a bike that can adapt to whatever comes up in front of me with in reason of course. Be it flat roads or trails, city streets, side walks, curbs, hills or train bridges, gravel, pavement, dirt, grass, (hate mud..try to avoid) and woodland trails if they come up. Some times the riding surface and terrain switches from one to the other quickly and for only short stretches. Thus the need to shift rapidly. Every thing feels like a sprint. Believe me , there is a method to my madness. I try to improve my bike where ever I feel it could do better to suit where I ride. I didn't plan it this way...it's just how it worked out and I like it.
Unlike real Cyclocross riders, I hate getting off my bike once I'm on it and I hate mud.:eek: If I can't ride over it I just won't go that way or I'll ride around it.
 

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So what is the 42 replacing? The 38 or the 48? Shifting the gears to accommodate different terrain and conditions is why you aren't riding a single speed. Make us of that advantage. So I am confused why you want to possibly limit the "adaptable" machine you already have.
 

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Discussion Starter · #11 ·
krisdrum said:
So what is the 42 replacing? The 38 or the 48? Shifting the gears to accommodate different terrain and conditions is why you aren't riding a single speed. Make us of that advantage. So I am confused why you want to possibly limit the "adaptable" machine you already have.
"Why", you ask? Simplicity and the freedom that goes with it.
The gears would be dropped down from 21 badly and seldom used gears to 7 strategic gears tailored to suit my needs. The other 14 just complicates things and It would still accommodate my physical abilities, but in a cleaner crisper condensed package. I can't think of anything better than that.

I use the 38 the most but it comes up a tad short. The 48 ring is over kill and most of it never gets used.
So to simplify things I will kind of split the difference between the 38 and 48 on the front by replacing them with a 42.

A 42 on the front and 12/27 on the back with my 7 speed, indexed twist shifter should be lightening fast crisp and clean shifting and should be perfect for me . I would rather use 7 gears to the fullest than use 21 gears badly or never use most of them at all.

Slow front shifts, dropped chains, extra weight and gears, cable and shifter and derailleur would be eliminated along with the constant nagging decision of should I change front gears or shouldn't I.

If the 42 and 12/27 is a choice for some people who compete hard core there must be a reason. I wanted to know why.
 

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Ok, sorry, I lost that you were going from a triple to a 1x7 set-up with the 42 up front. I thought it was replacing one of the existing chainrings, not all of them. You'll probably want chainring guards for this set-up or something to keep the chain on the front ring. BBG makes nice ones in several different flavors, but there are tons of other options out there as well.

I'd also recommend being conscious of chainline when moving to this new set-up. Putting the single ring too inboard or outboard could cause some funky chain angles in certain rear cogs. Just something to think about and consider.
 

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Discussion Starter · #13 ·
krisdrum said:
Ok, sorry, I lost that you were going from a triple to a 1x7 set-up with the 42 up front. I thought it was replacing one of the existing chainrings, not all of them. You'll probably want chainring guards for this set-up or something to keep the chain on the front ring. BBG makes nice ones in several different flavors, but there are tons of other options out there as well.

I'd also recommend being conscious of chainline when moving to this new set-up. Putting the single ring too inboard or outboard could cause some funky chain angles in certain rear cogs. Just something to think about and consider.
No apology necessary. Yes I will definitely use a chain guide. I need to learn more about them and the types though, and the chain line is what I'm learning about now as we speak. Sheldon Brown has an excellent and helpful page on this topic.
http://www.sheldonbrown.com/chainline.html

My biggest set back right now is learning enough about the crank. It's not that old but they call it an old style Campagnolo. I know how to get it in and out no problem but I may have to order a longer one . I wonder if they are longer on just one end or are they longer on both ends? I have to make sure the 42 tooth gear is positioned out far enough to clear the bottom bar plus I have to worry about the chain line. I was told I have to order a whole crankset to get just one gear, because my bike is a cheapy and the spider is riveted onto the gears.
I was told that I can put a newer style cartridge type crank in but at what cost? . And then I still have to find out where to order one from.
Anyway...there is a steep learning curve. Not all cut and dried, that's for sure.
 
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