[mornview]

Greetings all,

First off, I'm sure this is such a basic question I was tempted to put it in the "Beginners" forum. I really do apologize for asking such a trivial question, but I can't figure this one out of my own (or with the aid of the "search" feature).

I'm turning an old Specialized Hard Rock into a single speed. I disassembled the three chain rings and then proceeded to mount the highest (48 tooth) chain ring as my single chain ring. Upon inspection, it looks like my chainring is WAAAY too close to the chain stay.

I should note that I had to remove the crank arm in order to lift off the smallest chainring. Incidentally, all of my experience working on cranks is with either one-piece or cottered-three pieces; this was actually my first time working on a square-tapered three-piece. Could I have somehow put the crank on too tightly? Or is it an issue with the chain-ring bolts? Or is it something else altogether that I am not seeing? Thanks in advance! Here are a few photos:

 

[finch2]

you've just put a ring meant for the outside into the middle position. If it doesn't rub on the chainstay then you should be OK to use it. Every bike is different to what size ring you can put there.

 

[Saul Lumikko]

You can't cause this by over-tightening the crank and it's not a chainring bolt issue either. It's just that the chainstays that accept wide tires have size limits for chainrings in the granny position, middle position and outer position.

What kind of gear ratio are you planning to use? Quite often SS MTBs have a 32-38 t chainring, which should fit the middle position nicely.

Another thing to consider is chainline: if you're mounting a SS cog with spacers to a regular cassette hub in the rear, you can easily move the chainline outboard and use the outer position (as it originally was) for the chainring.

My SS MTB has a 34 t chainring and I still use the outer position on the cranks, because this way I have the ability to flip the rear wheel, replace the brake rotor with a bolt-on cog and go fixed. The chainline remains unchanged.

 

[Awshucks]

I think its because you're running the outer ring. When I converted my old hardrock I used the 38t middle ring and got some 6mm chainring bolts. Since I was using it on single track even that was tough so I measured the bcd and got a 5 bolt 34t ring from surly. Good luck and post some pics when you're done. I myself JUST (like last month) converted my old spec hardrock. It's a blast

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[mornview]

You can't cause this by over-tightening the crank and it's not a chainring bolt issue either. It's just that the chainstays that accept wide tires have size limits for chainrings in the granny position, middle position and outer position.

What kind of gear ratio are you planning to use? Quite often SS MTBs have a 32-38 t chainring, which should fit the middle position nicely.

Another thing to consider is chainline: if you're mounting a SS cog with spacers to a regular cassette hub in the rear, you can easily move the chainline outboard and use the outer position (as it originally was) for the chainring.

My SS MTB has a 34 t chainring and I still use the outer position on the cranks, because this way I have the ability to flip the rear wheel, replace the brake rotor with a bolt-on cog and go fixed. The chainline remains unchanged.

You know, this was my intial guess; I just swear the large chainring had been on the inside of the spider before disassembly. Then again, I was so excited to get to work that I may not have been paying close attention.

I'm planning on running something around 48/16. The wheel I'm initially going to use with this set-up had a freewheel, so I have a single-speed freewheel in the mail. I realize this doesn't offer me as much flexibility in terms of chain line options (as a cassette would), and I've heard that having the chainring on the inside of the spider tends to produce better chainlines, so I guess I'll have to see what works for me when the freewheel arrives.

 

[mornview]

I think its because you're running the outer ring. When I converted my old hardrock I used the 38t middle ring and got some 6mm chainring bolts. Since I was using it on single track even that was tough so I measured the bcd and got a 5 bolt 34t ring from surly. Good luck and post some pics when you're done. I myself JUST (like last month) converted my old spec hardrock. It's a blast

Sent from my PC36100 using Tapatalk 2

What did you do for your rear wheel? Mine had an old Sun Tour freewheel. For as much research as I've done before starting this project (and believe me, I've done TONS), I still feel like it's going to be a complete gamble as to whether or not my chainline works or not. So I'm starting out by putting a new Shimano single speed freewheel on (I should have that in a few days). If that works, then I'm planning on trying to tackle the real reason I bought this bike - putting a Velosteel coaster brake hub (which I also need to buy) on there. I specifically sought out this frame because of it's horizontal dropouts (and it's low price). I figure the dropouts will increase my chances of success. But yeah, ultimately this project is going to be my winter bike for many, many winters to come.

 

[Awshucks]

I decided I wanted a free hub so I could use spacers to dial in the chain line better. I bought this: Dimension w/ Alex X2000 26" MTB Wheels > Components > Wheel Goods > Mountain Bike Wheels | Jenson USA Online Bike Shop except when I bought the wheel it was $34 not even on sale. I see they raised it to $44. At $34 it was a steal. And I bought a $20 gusset conversion kit.

here was my original post in case you want to see the steps of my conversion w/ pics. http://forums.mtbr.com/singlespeed/my-single-speed-story-898434.html

I suspect we're using the bikes for different purposes it sounds like you will be commuting on yours.

But again, if you're worried about the chain line toss the freewheel wheel and buy that dimension wheel and just buy spacers for the cassette hub so you can dial in the chain line better. (If you have your mind absolutely set on coaster brakes then I'm not sure as I'm just a pseudo-bike mechanic whose only done one conversion)

Also I don't know about your frame drop outs but mine had these little notches in them so when you placed the wheel it went to the same spot every time for shifting and braking reasons I guess. Some told me to cut that out and file it down to have a full horizontal drop out. I did it but I guess not good enough because literally after 4 days of filing and 2 dremel bits I could not get that sh*t ALL the way down to allow my wheel to go all the way back. It did go back some but not all the way. So if your drop outs do have those and you leave them you may be looking at a tensioner anyway depending on your gear ratio. At 34x18 my chain is tensioned.

 

[Saul Lumikko]

48/16 is crazy tall gearing for a mountain bike, even for a 26" with slicks on hard surfaces! Have you made some rides in this combo (if available) when you had gears to be sure you know what you're getting into? Just concerned about your knees is all.

If you have a threaded hub and put a freewheel on it, the middle position will be more likely to provide a straight chainline.

 

[mornview]

I decided I wanted a free hub so I could use spacers to dial in the chain line better. I bought this: Dimension w/ Alex X2000 26" MTB Wheels > Components > Wheel Goods > Mountain Bike Wheels | Jenson USA Online Bike Shop except when I bought the wheel it was $34 not even on sale. I see they raised it to $44. At $34 it was a steal. And I bought a $20 gusset conversion kit.

here was my original post in case you want to see the steps of my conversion w/ pics. http://forums.mtbr.com/singlespeed/my-single-speed-story-898434.html

I suspect we're using the bikes for different purposes it sounds like you will be commuting on yours.

But again, if you're worried about the chain line toss the freewheel wheel and buy that dimension wheel and just buy spacers for the cassette hub so you can dial in the chain line better. (If you have your mind absolutely set on coaster brakes then I'm not sure as I'm just a pseudo-bike mechanic whose only done one conversion)

Also I don't know about your frame drop outs but mine had these little notches in them so when you placed the wheel it went to the same spot every time for shifting and braking reasons I guess. Some told me to cut that out and file it down to have a full horizontal drop out. I did it but I guess not good enough because literally after 4 days of filing and 2 dremel bits I could not get that sh*t ALL the way down to allow my wheel to go all the way back. It did go back some but not all the way. So if your drop outs do have those and you leave them you may be looking at a tensioner anyway depending on your gear ratio. At 34x18 my chain is tensioned.

Thankfully my Hard Rock does not have those drop outs - that sounds like a pain.

And you're right - I'm definetely using mine for a different purpose than you, but all the same, thanks for all of the information. I'm still a little skeptical of the coaster brake working for me, so I'm glad to have options.

 

[mornview]

48/16 is crazy tall gearing for a mountain bike, even for a 26" with slicks on hard surfaces! Have you made some rides in this combo (if available) when you had gears to be sure you know what you're getting into? Just concerned about your knees is all.

If you have a threaded hub and put a freewheel on it, the middle position will be more likely to provide a straight chainline.

Well, I guess I should say from the outset that I pretty much only ride vintage bikes in the vein of the old Phillips and Raleigh three-speeds (except I'm riding the cheap one-speed knock-off brands, like Concord). They suit my needs perfectly and, frankly, if I could, that's all I would ride all year. The problem is, in Wisconsin I can't quite get by on such narrow tires during the winter (I just barely made it through my first one this year), and the frames of these bikes don't have enough clearance for something like a 26x2.00 tire. So my plan was to replicate everything about my vintage bikes (the upright seating, the high gear ratio, the coaster brake, the single speed drivetrain, etc.) on a mountain bike frame. Most of my vintage bikes have gear combinations somewhere around 46/18 or 46/16. I guess I didn't think the MTB geometery was going to make such a big difference, but if it is going to be a problem, I appreciate the heads up.

 

[Awshucks]

It may be the wheel size difference that will make it more challenging too. I'm guessing that hardrock is
26" and those vintage bikes are...what 27 1/4? The wheel difference is def. something to consider when thinking about gear ratios.

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[metrotuned]

Your chainring can be moved to the outside of the spider arms. It looks better, too. The chainring could also be too big, thus hitting the chainstay. Most MTB SS frames allow up to 36T max chainring, some even less! That's why you sometimes see a purposeful dimple where the chainring meets the chainstay. You can go down in chainring size, and down in cog size. You should also check out the gear inches and if you're happy with a particular combo, you can easily replicate it with different teeth chainring and cogs. Happy Singlespeeding!

This is hands down the best resource I have access to for gearing: https://www.facebook.com/notes/wos-...ain-gear-ratio-vs-gear-inches/372441806177987

 

[Awshucks]

Don't forget pics when it's done :thumbsup: