Makeshift Frakenbike Dirt Jumper help

[pkovo]

I need help figuring out my best drivetrain option for this weirdo bike of mine.

Last year I franken-biked my old street trials bike into a makeshift DJ. Mostly so I could ride the BMX track when I take my daughter. Turns out, the bike works really well for this purpose, and i like it more than I expected. I'll probably move beyond practice an do a couple races this season. Why not, I'm at the trak riding anyway.

I rigged the bike with two rear cogs, one for trials and one for BMX, using an old derailleur and a short length of cable so I could switch gears just using the barrel adjuster. Well, this setup failed last weekend and sent me into the asphalt at the Port Jervis Pump track, so I’m looking for a more reliable setup.

Thinking I have a few options:

1. Setup single speed in a more reliable fashion, using a dedicated single speed tensioner out back instead of a derailleur? I don’t mind ditching the trials og all together.....I'm no Danny Mac after all. But not sure how reliable this is, and which tensioner(s) would be best in this case.
   
   
2. Set it up geared. Maybe I would be better off to just slap Zee der/shifter and a tight road cassette and call it good enough?
   
   
3. Buy a real DJ bike and continue my bike hoarding tendencies

Ok option 3 really isn’t an option as I don’t want to spend much $ on this BMX/Pump track avenue, at least not on myself. my daughters gear is a different story. However if anyone happens to have a Morpheus Vimana in size long, message me and we;ll talk

 

[Mountain Bike Mike]

#3 - and then ride it more

 

[stb222]

We are talking about a bike you appear to not ride that often and mentioned not spending money...so, throw on it whatever you have laying around. SS for lack of things to break but if you aren't ditching a ton, just throw whatever on it.

 

[pkovo]

We are talking about a bike you appear to not ride that often and mentioned not spending money...so, throw on it whatever you have laying around. SS for lack of things to break but if you aren't ditching a ton, just throw whatever on it.

Single speed would be my preference, and throwing it together with pieces on hand is what I did, but damn I went down hard when it threw the chain! I'm not sure the best way to set it up SS to reduce the likelihood of that happening again given it doesn't have sliding dropouts.

It might be ridiculous, but I thought about leaving it setup essentially the way it is, but fix the derailleur so it can't move....but use three cogs. The small one I need, an two bigger ones on either side. Essentially making it very difficult for the chain to come of at the rear since those bigger cogs will block it.

Also this way without needed to adjust between two cogs out back, I can make the chain supe tight

 

[stb222]

Single speed would be my preference, and throwing it together with pieces on hand is what I did, but damn I went down hard when it threw the chain! I'm not sure the best way to set it up SS to reduce the likelihood of that happening again given it doesn't have sliding dropouts.

It might be ridiculous, but I thought about leaving it setup essentially the way it is, but fix the derailleur so it can't move....but use three cogs. The small one I need, an two bigger ones on either side. Essentially making it very difficult for the chain to come of at the rear since those bigger cogs will block it.

Also this way without needed to adjust between two cogs out back, I can make the chain supe tight

Yes, dump the double cog thing or slam the adjustment screws so it can’t move (may need longer screws)

 

[pkovo]

Thanks, that's probably what I'll end up doing. I don't need gears, but if I had them and the chain jumped, my though is it would just grab the next cog instead of freewheeling.

Ironically, I didn't even need to pedal at Port Jervis, for the most part, but if I want to try for the first set of doubles I have to get 2-3 hard pedals in off the hill....which is what I was doing when I lost the chain.

As an aside, that place is sooo much fun! Sadly, lots of local kids with no helmets, which probably doesn't bode well for the track's future., but if I could ride that with any frequency, I would have to think it would help my mtb skills.....or I would just injur myself.

 

[mtbiker87]

I'd go SS myself. I've used both the Surly singulator, and the shimano Alfine tensioner on similar projects with good results. As an option, I have an older steel DJ frame with sliding drops I'd part with for a resonable price, or possible trade. Resonable being in $100 or so range.

 

[mtbiker87]

PJ is awesome ! But yeah, you need to get a run off the hill if going counter clockwise, as there is a bit of flat both before, and after that first berm, before you hit that first jump.

 

[pkovo]

Being a Surly guy, that's the first tensioner I was looking at.

let me know more about the frame. It can't hurt to consider all options Thing is, if it's newer, probably won't work. I'm running old gear that I like. Well really it's just the wheels I don't want to decommission, but they are non-disc so makes for limited options.

And that's exactly what I was trying to do....counterclockwise of the hill.

 

[gmb3]

I have a bag of old SS & tensioner bits sitting in my parts bin that i'll likely never use. You can have it. No guarantee there's a full solution in there, but you seem mechanically inclined and can probably figure something out. If you wanna go the geared route, i have a brand new LX 9-spd derailleur for $10 in this thread: https://www.mtbnj.com/forum/threads/5-friday-sale.39211/
PM me if any of this floats your boat.
I ran a 105 road derailleur and cassette back in the day for dirt jumping and dual slalom and it served me well.

 

[pkovo]

I have a bag of old SS & tensioner bits sitting in my parts bin that i'll likely never use. You can have it. No guarantee there's a full solution in there, but you seem mechanically inclined and can probably figure something out. If you wanna go the geared route, i have a brand new LX 9-spd derailleur for $10 in this thread: https://www.mtbnj.com/forum/threads/5-friday-sale.39211/
PM me if any of this floats your boat.
I ran a 105 road derailleur and cassette back in the day for dirt jumping and dual slalom and it served me well.

Man that super cool of you, thanks! I may just end up taking you up on that once I figure out what direction to go.

Curious, is there an advantage to using a road derailleur? Is it just he short cage? Pretty sure I have a couple old ones laying around. One is attached to a bike, but it hasn't been off it's hook in the garage in years.

I was thinking if I went the derailleur route I would need a clutch, but not sure there's anything clutched less than 10 speed, and using a lower speed setup would offer the advantage of a beefier chain.

 

[mtbiker87]

Only thing clutched in 9spd is Microshift or Box. Both are fairly new in coming to the market, so finding used probably not an option, though the Microshift stuff is pretty resonable new.

Think the biggest advantage to the road stuff is the tighter ratio, smaller cassette, and like you already mentioned, shorter cage.

 

[gmb3]

OK, let me know what you want to do. I think the road derailleur decision was a combo of cheap/compatible/short cage. I see what you're saying, clutch would be nice with all the jumping. Didn't have them back in the day but a chain tensioner kinda served that purpose.