# Bullet proof drivetrain. I need help!



## makomyday (Mar 24, 2010)

I have a stock heavy Specialized P2. The bike had 8 speeds, and I changed it to single speed, utilizing the stock front chainring, kept the stock chain, and used the 16tooth gear for the rear with spacers.
2 weeks ago the chain fell off while I was at full sprint, and I crashed very, very hard.

Here is my question about replacing parts. Which cranks, front chain ring, chain, rear gear should I get?

I am very gun shy of cranking down hard on the bike now due to breaking 3 bones, dislocated shoulder, concussion, etc from the last crash. 

How can I make it bullet proof?

Thanks!


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## PineTreeDJ (Oct 29, 2009)

Wow that sucks... I had that happen before but my wounds were not as severe

I think your main problem is that your chainline's off. That usually is the culprit with chains falling off. The other thing it could be is that your chain needs more tension, too much chain slap can cause the chain to derail.

To be safe though, get a new single speed chain and maybe make sure you are not missing any teeth on the chainring or cog


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## b-kul (Sep 20, 2009)

your main problem is the chain. get a ss chain and ss ring. make sure your chainline is good. new cranks wont do anything for your issues. neither will a new cog (unless it has teeth missing).


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## byknuts (Aug 9, 2008)

what happened with the old drivetrain?
double check all the parts, the chainring and cog need to be SS-specific, a ss-chain doesn't have ramped cutouts/shaping on the sideplates making it a bit stronger than normal ones (and there are some downright butch chains out there for SS use!)

did you have enough tension on the chain, was the chainline straight?


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## makomyday (Mar 24, 2010)

Chain line was straight. The bike is new. No worn parts. Chain was tight. I didn't know there were single speed specific chains like a bmx. I will check that route out.

I will get a new front ss chainring and chain. I just want to replace the cranks for piece of mind, what kind should I go for? I want to race bmx with it, and medium dirt jump/trails.

Thanks for everyones help.


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## PineTreeDJ (Oct 29, 2009)

makomyday said:


> Chain line was straight. The bike is new. No worn parts. Chain was tight. I didn't know there were single speed specific chains like a bmx. I will check that route out.
> 
> I will get a new front ss chainring and chain. I just want to replace the cranks for piece of mind, what kind should I go for? I want to race bmx with it, and medium dirt jump/trails.
> 
> Thanks for everyones help.


Depends on how tall you are and how you like the crank length you have now. I am 6'2" and have 175mm cranks. I feel they are too long for me so i am looking for some 170mm cranks. It is all personal preference and suitability. I used to ride with a 44" SS gearing but now am at 54" and loving it. Remember that every time you adjust something on your drive train, it will feel different than before so try and compensate before hand.

Personally I think your chainline was off, cause for the chain to pop off like that, it takes a bit of force. I hit some good size jumps and trails on a daily basis and have not yet had my chain pop off. The two times I have had it happen was when my chain broke and when my chainring was missing a tooth. SS specific hub won't fix the problem.


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## rdhfreethought (Aug 12, 2006)

The most bulletproof drivetrain is one with guides front and rear:
1. BMX chain/SS chain
2. SS/BMX chain rings 
3. The larger the ring, the better it holds a chain. So you can consider a larger rear cog, (and larger front chainring to get your gearing right)
4. Chain guide with bash guard for the front.
5. I like the Alfine chain tensioner for the rear. For a rear tensioner you need a derailleur pulley type tensioner, since it forces the chain THROUGH the plates. Avoid tensioners with a single pulley unless it is the 'pull up' type pulley that forces the chain between two guide plates. (remember the tensioner is not for tension--assuming you ride a hardtail--but to guide the chain)

Here is the best design (Alfine) and the worst design (Surly Singulator), in my opinion of course 

Multiple things will have to fail to get the chain off a setup like that.


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## makomyday (Mar 24, 2010)

The frame has horiz dropouts. Would I still need a tensioner like the pics above?


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## rdhfreethought (Aug 12, 2006)

Also, when you really crank on it, the BB flexes. Depending on how strong you are, it can be an inch or more. Mount a camera to the seat tube facing down, and you will see lots of flex, you did not know was there.

Not much you can do about that though (aside from stiffer frame)


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## rdhfreethought (Aug 12, 2006)

Has nothing to do with getting tension on the chain. It has to do with forcing the chain in a certain path.

Try this. Lay your frame its side, then push the chain below the chain stay. You see how much it flexes. If you push hard enough and turn the cranks, it will move the chain off the rings.

Now, if you try the same thing, with a chain guide at both ends, it will not come off.

Is it overkill? Yes. But worth avoiding the same disaster, and you can ride without worrying again.


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## makomyday (Mar 24, 2010)

rdhfreethought said:


> Has nothing to do with getting tension on the chain. It has to do with forcing the chain in a certain path.
> 
> Try this. Lay your frame its side, then push the chain below the chain stay. You see how much it flexes. If you push hard enough and turn the cranks, it will move the chain off the rings.
> 
> ...


Thank you! I have unbelievable anxiety now when I attempt to crank down hard. I am going to get a bunch of parts today, and maybe ride the track tomorrow, depending on how my ribs, shoulder, knee, ankle are feeling. This old body isn't healing to fast.


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## ZenkiS14 (Aug 25, 2008)

If i were you, I'd run a set of 48spline Profile cranks, or Deity's with a proper BMX sprocket, and proper single speed rear cog. 

On my personal STP, I run a set of Saint cranks with E.13 Guidering sprocket, and a Surly single speed cog in the rear with a Shadow Conspiracy Half-link Pintle chain. 

Depending on what size cog I decide to ride, I will also use my Rennen tensioner, never had a drop. And I feel my drivetrain is actually bullet proof.


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## makomyday (Mar 24, 2010)

ZenkiS14 said:


> If i were you, I'd run a set of 48spline Profile cranks, or Deity's with a proper BMX sprocket, and proper single speed rear cog.
> 
> On my personal STP, I run a set of Saint cranks with E.13 Guidering sprocket, and a Surly single speed cog in the rear with a Shadow Conspiracy Half-link Pintle chain.
> 
> Depending on what size cog I decide to ride, I will also use my Rennen tensioner, never had a drop. And I feel my drivetrain is actually bullet proof.


Thanks Zen!


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## ZenkiS14 (Aug 25, 2008)

With horizontel dropouts, you should be able to run nice 48spline BMX cranks, with nice Single Speed cog and front BMX sprocket. 

Run a BMX-style chain-tugger in the rear dropout. You wont ever drop a chain, and it will feel solid as hell. 

Stay away from chain tensioners, especially spring adjusted ones. You have horizontel dropouts so that you dont need a tensioner.


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## Air Junkie (May 11, 2010)

ZenkiS14 said:


> With horizontel dropouts, you should be able to run nice 48spline BMX cranks, with nice Single Speed cog and front BMX sprocket.
> 
> Run a BMX-style chain-tugger in the rear dropout. You wont ever drop a chain, and it will feel solid as hell.
> 
> Stay away from chain tensioners, especially spring adjusted ones. You have horizontel dropouts so that you dont need a tensioner.


True, a chain "tugger" (BMX riders call 'em chain tensioners, but I guess that gets confusing) makes it easier to dial in the perfect tension, which is all too important. But it still doesn't make your drivetrain "bomb proof".

I had a friend who I used to race with on the BMX track. One day he was in a sprint race with someone just in the street when his chain fell off. He flew over the handlebars, cracked his head open and died.

That was on a BMX bike. I guess what I'm saying is, always make sure your drivetrain is in good condition, no matter what setup, but especially for single speeds because if your chain slips on a multi-speed it just goes to the next gear!

I don't mean to scare anyone, just where a helmet.


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## makomyday (Mar 24, 2010)

Wow.
Well I'm not dead, just very sore still after 3.5 weeks. Sleeping is still very difficult.

I am just going to buy a new bike that is made for single speed and sell this death machine.



Air Junkie said:


> True, a chain "tugger" (BMX riders call 'em chain tensioners, but I guess that gets confusing) makes it easier to dial in the perfect tension, which is all too important. But it still doesn't make your drivetrain "bomb proof".
> 
> I had a friend who I used to race with on the BMX track. One day he was in a sprint race with someone just in the street when his chain fell off. He flew over the handlebars, cracked his head open and died.
> 
> ...


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## boostin (Apr 21, 2008)

yea man I went through this a couple years ago. I didn't know that multi geared chains and cogs are designed to skip between gears, but it makes sense. When you try to run them ss even if its aligned they have a tendancy to pop off under tension. 

It hurts so much


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## rdhfreethought (Aug 12, 2006)

makomyday said:


> Wow.
> Well I'm not dead, just very sore still after 3.5 weeks. Sleeping is still very difficult.
> 
> I am just going to buy a new bike that is made for single speed and sell this death machine.


Any hardtail with horizontal dropouts is "MADE for singlespeed". A singlespeed specific bike will not offer anything better than your P2.

Most "singlespeed" frames are designed for wannabe roadies to ride XC trails. That would likely make a P2 rider cry. To keep a chain from breaking use a stronger chain (i.e. BMX/Singlespeed chain). To keep it from falling off, use a non-ramped chanring and cog, and use a chainguide from and rear (as I noted above).

Just about everyone will say a chainguide on an urban/DJ bike is overkill. And they are right, but if you want the MOST bombproof drivetrain, running something like what Zenki is running will FORCE the chain to stay on the cogs....it has nowhere else to go. It could only come off by breaking it.


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## Air Junkie (May 11, 2010)

rdhfreethought said:


> Any hardtail with horizontal dropouts is "MADE for singlespeed". A singlespeed specific bike will not offer anything better than your P2.
> 
> Most "singlespeed" frames are designed for wannabe roadies to ride XC trails. That would likely make a P2 rider cry. To keep a chain from breaking use a stronger chain (i.e. BMX/Singlespeed chain). To keep it from falling off, use a non-ramped chanring and cog, and use a chainguide from and rear (as I noted above).
> 
> Just about everyone will say a chainguide on an urban/DJ bike is overkill. And they are right, but if you want the MOST bombproof drivetrain, running something like what Zenki is running will FORCE the chain to stay on the cogs....it has nowhere else to go. It could only come off by breaking it.


true.

And to make now that the only thing that could cause another crash due to the drivetrain is if the chain breakes. So to eliminate that from ever happening, get a half link chain.


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## ZenkiS14 (Aug 25, 2008)

Check out my build.

This is a bomb proof drivetrain. Never dropped a chain, ever.

http://zenkis14.pinkbike.com/album/My-2007-Giant-STP-Frost-Green/


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## ducktape (May 21, 2007)

If you're saying that you've used the 16T cog off the cassette than that is possibly your issue. Get a SS type cog without ramps and pins and hopefully you won't have a recurrence.


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## ZenkiS14 (Aug 25, 2008)

You need single speed parts for a single speed to be drop free. 

Get a profile or Surly Single Speed Cog, a real legit Single Speed BMX chain (710SL or Half-link if needed), and a real single speed front chainring. Either e.13 or a BMX one.


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## XSL_WiLL (Nov 2, 2004)

You don't need a chainguide with horizontal dropouts (and what the hell is a rear chainguide?). If the chainline is good, the chain tension is good, and the cogs are straight cut and not bent, the chain will not drop.


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## BMeX (Jun 16, 2010)

XSL_WiLL said:


> You don't need a chainguide with horizontal dropouts (and what the hell is a rear chainguide?)..


http://www.petracycles.co.uk/produc...urrency=USD&products_id=18418&source=googleus

SS horizontal drop out rear chain guide


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## sittingduck (Apr 26, 2005)

ducktape said:


> If you're saying that you've used the 16T cog off the cassette than that is possibly your issue. Get a SS type cog without ramps and pins and hopefully you won't have a recurrence.


 BINGO! That's it right there, combined with the 8 speed chain, a recipe for disaster. As you unfortunately found out. I hope you heal up fast, sounds brutal.

Get a good, strong SS chain, an SS rear cog, and some BMX cranks. (Or at least a good, single speed front ring)

I run KMC 410H chains, and replace them OFTEN, because I worry about breaking one. No worries about dropping them though....
NO CHAINGUIDES are necessary with horizontal drops!


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## Demo-9 (Mar 24, 2006)

Wow. Sorry to hear that.....

This is what you need:

1. 1/8" BMX chain
2. 1/8" chainring and cog

Converting the P2 to a single speed while using the same cranks, chainring, cog and chain spells disaster - especially if you are a strong sprinter. You need the strength of a wider chain and the added benefit of BMX specific chainring/cog. Simply using a 16t cog from the cassette is not enough IMO.

You said in your 1st post the chain fell off. That is why you should always run 1/8" BMX set-up for SS. This virtually eliminates the chain from falling off. It is wider, has much more surface area and the chainring/cog always have a wider/thicker base to them to keep the chain from popping off. 

I recommend you get a set of BMX cranks, chainring, Surly cog and a KMC BMX chain. ALso 1/2 link chains are the worst thing ever invented. They constantly stretch and require constant maintenance to maintain a tight chain. If you need a 1/2 link to shorten the chain length, use ONE FRIGGIN LINK! A full 1/2 link chain is heavy and useless.

Also most important is proper chainline. You can dial in the perfect line with BMX cranks and cog spacers. Lastly, you do not need a tensioner. Good luck and heal up.


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