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Old 01-26-09, 08:45 PM   #1
jgedwa
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Smaller wheel on rear of MTB:pedal strike?

I find myself in possession of a nice little 24" (507mm) rear wheel. The Doctor Frankenbike wants to see if I can make it work on a spare frame I have. It has discs, so brake reach is not a problem. The only issue I can anticipate is pedal strike.

So, at its lowest point, how low of a pedal can I get away with? For street use and maybe some light trail.

I have also been eyeballing my 29er Karate Monkey to see if I can make a 49er (copyright, 2009, Jim) out of it. For weirdness sake it has its appeal, but I don't think it will work.

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Old 01-26-09, 09:30 PM   #2
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Are you going to use the 24" rear wheel with a standard 26" front? That will have an impact on the bikes geometry giving the effect a shallower headtube angle. Using it with a 29" front will make the change even more extreme.
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Old 01-26-09, 09:34 PM   #3
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Just playing around with it.

Yes, still with a 26" front. I know it will mess with the geometry; I just want to try it out for kicks, assuming the pedals don't hit.

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Old 01-26-09, 09:41 PM   #4
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9cm tarmac to center of pedal spindle is as low as I like to go, even though I've seen some lower lowriders. I'd like to see how freeky the 49er looks, however... kinda SWB chopper, I'm thinking...

got any 160mm cranksets?
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Old 01-26-09, 09:55 PM   #5
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I think I will have 9cm down there on the KM; I might just have to try out the 49er idea. Remember you heard it here first!

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Old 01-26-09, 10:39 PM   #6
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I find myself in possession of a nice little 24" (507mm) rear wheel. The Doctor Frankenbike wants to see if I can make it work on a spare frame I have. It has discs, so brake reach is not a problem. The only issue I can anticipate is pedal strike.

So, at its lowest point, how low of a pedal can I get away with? For street use and maybe some light trail.

I have also been eyeballing my 29er Karate Monkey to see if I can make a 49er (copyright, 2009, Jim) out of it. For weirdness sake it has its appeal, but I don't think it will work.

jim
The locals around here do this all the time with their North Shore bikes. It helps with the crazy steeps. Pedal strike probably won't be much of an issue, but you will find that your BB height is more like a road bike's than a mountain bike's.
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Old 01-27-09, 12:37 PM   #7
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Going from 26" to 24" in the rear will lower the rear axle by (559-507)/2 (assuming same tire width on both) which is 2.6cm. The bottom bracket will not be lower by that full amount, however. Using a wheelbase of 105cm and chainstays of 42cm, the BB will be approximately (105-42)/105 * 2.6cm = 1.6cm lower. Lowering the rear axle by 2.6cm will also slacken your head angle by about 1.4 degrees.

For the "49er", the rear axle would be lowered by (622-507)/2 which is 5.8cm, which would lower the BB by about 3.5cm and slacken the head angle by about 3.2 degrees.
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Old 01-27-09, 12:41 PM   #8
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I think C-dale even made a few hardtails stock like this some years back, no?
+1 on the little cranks...
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Old 01-27-09, 04:27 PM   #9
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Going from 26" to 24" in the rear will lower the rear axle by (559-507)/2 (assuming same tire width on both) which is 2.6cm. The bottom bracket will not be lower by that full amount, however. Using a wheelbase of 105cm and chainstays of 42cm, the BB will be approximately (105-42)/105 * 2.6cm = 1.6cm lower. Lowering the rear axle by 2.6cm will also slacken your head angle by about 1.4 degrees.

For the "49er", the rear axle would be lowered by (622-507)/2 which is 5.8cm, which would lower the BB by about 3.5cm and slacken the head angle by about 3.2 degrees.
Many thanks. What you did with your head, I did with my eyes and a ruler. Got more or less the same results. On one frame I am considering running this experiment on, that leaves the pedal spindle just at 9cm above the ground. By eye, it looks pretty low. I am just curious how low people go with that measurement.

jim
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Old 01-27-09, 05:21 PM   #10
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Just playing around with it.

Yes, still with a 26" front. I know it will mess with the geometry; I just want to try it out for kicks, assuming the pedals don't hit.
I'm thinking that it must too cold and snowy in Carlisle to ride. That's one seriously goofy winter project!
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Old 01-27-09, 06:40 PM   #11
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Never too cold to break out the ol' 49er! Either I, or my remaining estate, will report back results soon.

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Old 01-27-09, 07:08 PM   #12
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Its dark and very snowy, so I couldn't really run it through its paces, but the monster does live!

I give you the 49er Karate Monkey!

Sorry for the lousy camera phone pic.

jim
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Old 01-27-09, 09:16 PM   #13
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That rear derailleur cage angle hurts to look at!
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Old 01-27-09, 09:33 PM   #14
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That rear derailleur cage angle hurts to look at!
It is in the laregst rear cog, so it is stretched pretty tight. But not overly, I think. In the smallest cog it points straight down. And even in the largest cog the chain still bends around each jockey wheel.

You think its too tight? I am more of a fixed-gear or SS or IGH guy, so I am open to criticism on it.

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Old 01-29-09, 12:22 PM   #15
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cannondale used to make a trials bike with a 24"rear wheel i believe, that was back in the mid 80's so i could be misrembering
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Old 01-29-09, 08:39 PM   #16
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49er! Sweet. I thought I was the only one who came up with this type of crazy idea. My guess is that it will climb like a goat, but suck on the flats and down hills. Let us know how it rides...
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Old 01-29-09, 09:04 PM   #17
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Due to weather, I have managed to put about two miles on it on the roads around my house.

I would say, so far, that it rides better than I would have guessed. And I knew it would drop the gearing down alot, but I really did not anticipate how low it would be.

Hopefully, I will get more of a chance this weekend.

jim
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