|Fixed Gear Newb -- Questions||toonces|
Dec 24, 2002 9:23 PM
|I'm going to put together an old MTB frame and rigid fork for use as a fixed gear bike. I dont' have a wheelet yet so I'm wondering what my options are for hubs. I read that flipflop hubs will work, but won't using a fixed gear unthread the cog or is there a lockring of somesort? If I can use a normal SS rear wheel, that would ease the build process.
Also, what gearing should be used? I'm planning on slapping on a 175 mm crank I have lying around and using it's 42t big ring. For general road use on slightly hilly terrain, what should I be pushing? I'm no beefy-legged road monster so I'd like something a bit easier. Keep in mind that I'll be using 26-inch wheels since it's an old MTB frame.
Appreciate any info.
Dec 25, 2002 4:52 AM
|Regarding flip/flop hubs, one side this threading for a cog and uses a lockring, the other side just has standard threading for a freewheel. I'm using a 42 x 16 which is fine for flat north Texas. You might want to go 42 x 17 or 18 for hilly terrain.|
|Gear ratio conversions for 26" MTB wheels||Tig|
Dec 25, 2002 10:30 AM
|Thanks to Sheldon Brown's gear calcuator http://www.sheldonbrown.com/gears/index.html we can calculate Dave's and my favorite road ratio (about 69 gear inches) for MTB wheels. A 700c wheel using a 42 x 16 gear combination for 69 gear inches equals about a 42 x 15 with MTB wheels (26" x 1.5" tires). For Dave's hilly terrain recommendations, you would use a 16 or 17 cog to get nearly the same gear ratio.
For more useful info, check out these sites:
http://www.63xc.com/ -Check out the How To pages.
|Gear ratio conversions for 26" MTB wheels||fixedgearhead|
Dec 25, 2002 3:00 PM
|I may have to defer to those that ride 26" wheels, which I don't, but I was under the impression that 26" wheels were not as efficient as 700cm wheels when it came to transmitting power to the pavement all other things being equal. There is also the factor of wider tires having more rolling resistance too. Unless slicks of some kind are used, that would neccessitate a higher gear inch or ratio. I can't tell you how I came to that conclusion. I just seem to remember reading it somewhere. I think it was in a discussion forum by various builders of touring bikes as to the wisdom of 26" V 700cm for efficiency, when it comes to maintaining a constant rate of speed between the two bikes. Again I don't know and can't quote the source so I may stand corrected. One thing that I do know about is the use of 175mm cranks. Unless you have a very, very high bottom bracket you are in danger of setting yourself up for pedal strike and all the complications and hazards that entails. You probably are planing on using the crank arms that were in use when the bike was used as a mountain bike, as an economy measure, One thing you don't want to happen is for the peddle to come into contact with the ground when you are going around a corner. "Remember you can't coast thru corners." Set the bike up with pedals and shoes that you will use with the bike, as envisioned, and lean the bike over until the edge of the pedal/shoe touches the ground. That is the amount of lean you will be able to do, period. Imagine the fun you will have when that pedal strikes the ground as you are going 20mph into a turn and the rear wheel, or front wheel, lifts off the ground after the pedle strikes the ground. I would suggest that you look for 165mm length crank arms to use. Maybe at the most 170mm if your bottom bracket is high. Just one more thing to think about as you contemplate the conversion. Sometimes you have to spend some more money that you didn't think about to accomplish your goals.
Dec 25, 2002 3:59 PM
|You're right on about how knobbies have a greater rolling resistance than smooth slicks. Smaller diameter wheels also have more rolling resistance then larger ones. I don't know if a wider tire has more rolling resistance from the width alone (aerodynamics not factored in), but I've heard the associated lower pressure increases rolling resistance. The rolling resistance difference between 23 and 25 mm tires is so little for us mortals, it isn't worth worrying about. I'd go with the more comfortable, lower pressure wider tire for everyday use. With a fixed gear we can't do much bunny-hopping over holes and cracks, so the wider, slightly taller tires are good for taking the extra abuse without pinch flatting.
Little differences like this can add up, but one of them alone usually isn't even noticeable to the rider. The rolling resistance difference between a larger diameter slick 700c, 23 or 25 mm width tire vs a 26" knobby MTB tire has got to be huge. Make that MTB tire a 1.25" slick, and it makes for a nice improvement. I used to commute to work on a MTB and when I changed to 1.25" slicks, the average speed from the same effort went up by a good 3 to 4 MPH.
You're right about the dangers of pedal ground clearance using 175 mm cranks. MTB's have higher bottom brackets, so that helps a little. They use 175's for greater power for climbing. I still don't know if they would be safe or not with a fixed MTB on the road...
|re: Fixed Gear Newb -- Questions||fixedgearhead|
Dec 25, 2002 5:54 AM
|I would also suggest that you use a fixed/free hub. Suzue makes one as do other higher priced mfgrs. To keep it simple use your 42 chainring and17tooth fixed gear cog and lockring on the fixed side and 18 tooth freewheel, the largest 3/32 size available, on the other side. That will allow you to get home with an easier peddle if you tire yourself out on the ride. After awhile you may even dispense with the freewheel side. If you think that might be an option you should concider a fixed/fixed hub That would allow you to thread a freewheel on the off side in place of the fixed gear cog and when you want to, you can replace it with a fixed gear cog and lockring. That gives you three options for use:fixed /fixed and fixed/freewheel. If finances are not an issue,(when are they ever not) I would highly reccomend a Phil Wood fixed/fixed hub. They are available in various spacings to suit your needs. They are absolutely bulletproof and can be rebuilt by the Mfgr. for a nominal fee after 30,000-50,000 miles of use.. I use them on all my bikes and have never had a problem with them as other people on this board will attest. They are the benchmark of the industry. Pricy but worth it in my opinion. I would caution you to avoid the absolute cheapest fixed/free hubs as they have many reported problems from various people that post to this board. I have not used the various conversion options that are available. They may work and they are sure to be less expensive so that may be a way to go if money is a concern. Just try to balance the options that you give yourself against the money you will be spending. You will probably be upgrading to something more expensive anyway later after the bug gets implanted in your psyche. It has for everybody that tries it. Welcome to the revolution.
|re: Fixed Gear Newb -- Questions||anita handle|
Jan 4, 2003 9:36 PM
|here kitty kitty kitty. hehe.|
|re: Fixed Gear Newb -- Questions||toonces|
Jan 5, 2003 9:03 PM
|Dude, stop stalking me. And for pete's sake, get yerself a handle already :p|| |