Road bike questions

inkstom

New Member
Oct 13, 2008
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Austin, TX
You (respective posters) seem to be extremely knowledgeable about this topic so I would like to pick at your brains a little bit if I may.
Some of you may have already done this or currently still have the availability to do this so indulge me.

The only thing I hear is that this is possible on a 26" Mountain bike. I have little desire to be on a mountain bike so is it possible to do it on a 27" road bike? I do not see how anything would be impossible personally. It would still mount and the engine would run regardless. The chain and etc could be modified in length to fit.

Furthermore, after the engine is mounted and works properly on a bike, and the top speed is 30 MPH, whats not to get a smaller sprocket and change the gear ratio to increase speed. Granted the wear on the clutch would be greater as well as the rest. With higher gears chances are that the engine would need to be started or engaged at higher speeds in order to perform well within the functional range. Is the largest factor the safety factor? The lack of desire to go in excess of 30 MPH? Or is there something I have gotten wrong that inhibits the speed. Perhaps torque?

Please let me know. This has been waging war on my mind for the better part of a week now.

Thanks.
 

stude13

New Member
May 28, 2008
404
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north bend wa.
hi inkstrom and welcome; i think there would no problem with a motor on a 27". sure you can change gears. the question about speed has always been, how much money you want to invest. there are builds here using polini engines the other end might be a weedeater scrubber bike. the world is at your feet. mitch
 

Goat Herder

Gutter Rider
Apr 28, 2008
6,248
11
38
N.M.
Road bike will go faster on 44 tooth set up 30mph for sure.Down side tires less tolerant of stickers
[goat heads] less rubber to pad the bumps rims are easier to bend in my opinon. There are people using these and I never have heard them complain though.
 

shiloh0

New Member
Jun 28, 2008
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i thought about building a fast road bike but the frame doesnt look very tolerant of extra stress. also no front suspension. maybe a 700c commuter bike with straight bars would be a good option.
 

lennyharp

New Member
Jul 19, 2008
429
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Mesa Arizona
Road bikes are built to be lighter than cruisers and mountain bikes so the frames are generally weaker and this is not good when you stick a 10 pound 5 to 10 thousand rpm vibrating motor on the frame. Vibrations on to light a structure is bound to break it. Lets say you get a stronger than normal road frame the skinny tires absorb less shock and will flatspot easier and are less stable than the fatter tires used on most motorized bikes. The taller wheel is also weaker as there is more leverage at the longer distance from hub to tire. (basically is a longer lever and bends easier) You can use tandem rims and 48 spoke wheels to help here and a 37 mm tire will help with the too skinny problem. So basically you are creating extra problems to solve but they are solvable. I see no advantage to using a road bike except if it is all you have access to.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
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up north now
I built one with a road bike and it was the bee's knees fo'sho'!

The wheels and frames may look thin and weak, but I've never had one crack like my cruiser frame did.

The ultimate limiting factor of top speed on these chinese engine kits is wind resistance. They make about 2-3 horse power. Rolling resistance isn't that great, but wind resistance is squared for each addtional 10 mph.

That an if you rev one much beyond 7000 rpm, it will explode.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
A triangulated structure is stronger per pound than a bendy-twisty-curvy cruiser type frame any day.

Otherwise buildings and airplanes would be bendy-twisty-curvy.
 

lennyharp

New Member
Jul 19, 2008
429
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Mesa Arizona
I guess you got one of the thicker tubing road bike frames. Touring and cross bikes do use a heavy gage tube usually. Road bikes are made with lighter gage tubing and are generally not as strong as a heavier gage tubing bike even if it is a cantilever frame. Cruisers are the weaker design but use enough extra tube to make up for it usually. A diamond frame Mountain Bike is by far the strongest frame to use and that is what I have been saying since I joined the motorized bike forums. I have raced road bikes down mountain roads at 60 miles an hour, I have built bike frames from tube sets, so I know a little about this , and I would not recommend a road bike frame over a mountain bike or cruiser without solving the issues I pointed out. It is irresponsible to encourage someone to build a flimsy motorized bicycle in my opinion.
 

inkstom

New Member
Oct 13, 2008
22
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Austin, TX
Well darn, I was aware that road bikes were any more or less sturdy than others. In fact I would have thought it to have been the opposite, especially, with the carbon fiber bikes they have now. There is an article on "Harris Cyclery" that outlines all the different kinds of bikes and their strengths (haha punny) and weaknesses. As for the speed. I was thinking more like getting the bike to go 50+ so I could kind of maintain a little bit of speed on the highway. (Doesn't sound smart does it.) I work on one side of town and live on the other but travel time for me is always at the lowest traffic time.

I will mention this, I am by no means affluent when it comes to the complete inner workings of how this works but I have a pretty good idea. Although I have only seen pictures of the engine attached to bikes I grasp that the sprocket that runs the motor is attached to the other sprockets for the bike and a second chain is added: one for manual pedaling and the other for the motor (which is started without a starter or pull start by dropping the clutch with the bike moving.)

I could be wrong so correct me if I am but if another sprocket (smaller) was used instead of the sprocket that came with the kit, would that not increase the maximum potential speed of the a fore mentioned bike?

Like I mentioned further up, I am sure that would cause more stress on the clutch but is this at least at all feasible?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
Well darn, I was aware that road bikes were any more or less sturdy than others.

Don't use a bicycle to go 50 mph on a regular basis, no matter what frame you choose. Any frame you choose will be sufficient with a little dilligence of maintenance.

I will mention this, I am by no means affluent when it comes to the complete inner workings of how this works but I have a pretty good idea. Although I have only seen pictures of the engine attached to bikes I grasp that the sprocket that runs the motor is attached to the other sprockets for the bike and a second chain is added: one for manual pedaling and the other for the motor (which is started without a starter or pull start by dropping the clutch with the bike moving.)

The chain that comes with the kit goes from the engine to the back wheel. You pull in and lock the clutch to pedal the bike.

I could be wrong so correct me if I am but if another sprocket (smaller) was used instead of the sprocket that came with the kit, would that not increase the maximum potential speed of the a fore mentioned bike?

A smaller sprocket will get you a few more mph, but these engines don't have enough power/torque to pull you much faster than 40 mph, no matter what size sprocket you choose.

Like I mentioned further up, I am sure that would cause more stress on the clutch but is this at least at all feasible?
It will not really cause more stress on the clutch if used properly.
Does this help?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
I guess you got one of the thicker tubing road bike frames. Touring and cross bikes do use a heavy gage tube usually.
Yes, older, and heavier... Road bikes are made with lighter gage tubing and are generally not as strong as a heavier gage tubing bike even if it is a cantilever frame. Why then don't they configure road bikes with a cantilever frame? Cruisers are the weaker design but use enough extra tube to make up for it usually. A diamond frame Mountain Bike is by far the strongest frame to use and that is what I have been saying since I joined the motorized bike forums. You are correct sir! The BEST CHOICE. I have raced road bikes down mountain roads at 60 miles an hour, I have built bike frames from tube sets, so I know a little about this , and I would not recommend a road bike frame over a mountain bike or cruiser without solving the issues I pointed out. It is irresponsible to encourage someone to build a flimsy motorized bicycle in my opinion. You said it bub.
..........
 
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lennyharp

New Member
Jul 19, 2008
429
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Mesa Arizona
This may be info overload for the question asked but I wanted to bring this post over from another forum as it is pertinent info I gathered and use. I give some info on the better steel alloys and their thicknesses for mountain bike tubing. Most department store bikes in the past used mild steel so top be light were weak or with enough to be strong were heavy. Back in the 60's-80's people wanted to copy the European road racing bike looks and performance. To do this properly took a hand built frame with very light gage Columbus, or Reynolds tubing as a rule made from chromium molybdenum or Manganese molybdenum steel alloys respectively. Even then most people did not want to pay hand made prices so made exceptions to cut cost and at the same time lost quality. Above I see above a photo of a Huffy I believe, a mild steel spot welded frame that bike shops often get in a broken state often because they were this lower quality Department store bike. Now we are getting some horrendous department store bikes and others I have seen that are very good quality for the dollar. I just really trust the bike shops to generally have the good to excellent quality bikes. So any how with more than was asked for a short tutorial on frame quality and a plug for steel.

The advantage of oxy acetylene is that you can low temp braze. This is a very friendly way to build a bicycle frame. Cro moly 4130 steel tubing is the standard that has been best for bikes for a long time. Basically it is a spring steel that is very repairable and light weight and strong. At welding temperatures the 4130 steel crystallizes and becomes brittle and can lead to failures. If you can work a fillet on a joint you are working the heat below that critical temperature. That gives a good reason to get the tool you want.

Low temp rod is about 1600 F + and regular brazing rod is 1800 F + degree melting point. Welding is well over 2000 degrees. 1850 is the critical heat for 4130 chromium molybdenum steel. Welded steel just needs more thickness at the weld than is needed for the brazed joint. It is a trade off for double butted steel tubing as the added thickness is put there for modern welded frames.

I would not use the torch to cut this type of steel for the same heat reasons. I also hate wasting gas or in cutting you use a ton of Oxygen as that is what feeds the burning steel. I have tanks that are about 2 feet tall and there are 2 sizes larger. For Frame building this will last for at least 5 frames. I use a 00, 0 & 1 size tips for the majority of my work and these are all small tips by a welders standards. But I don't weld, I braze at low temperatures.

Bicycle frame - Wikipedia, is a great start for information on the Bicycle frame. You are right to add some thickness to a standard bicycle frame to get more strength for a motored bike. If you are to use 4130 below is a table from Nova Cycles Supply for one of their Mountain bike tube sets.

DIA(MM) WALL(MM) LENGTH(MM)
DT 31.7 0.8/0.5/0.8 650
TT 28.6 0.8/0.5/0.8 600
ST 28.6 1.2/0.6/0.9 520
CS 24 0.9 425
SS 16 0.6 560
HT 36 1.1 200

For example the DT is the down tube from head tube to bottom bracket is the largest tube and takes the most stress in standard bicycle riding. It is less than 1 milllimeter on each end and only .5 mm for most of it's length.
1 millimeter = 0.0393700787 inch
This should give you an idea of the great strength the Cro Moly tubing has, and why a mountain bike can weigh 25 to 30 pounds and still be strong. If you double the wall thickness you would be overbuilding for a motored bike with say a 5 hp 20 lb motor. Brazing works great with .049 inch or even .065 inch wall thickness tubing. Welding works great too but for my money I would braze a well mitered tube with a filit radius that holds and is very repairable. Mike Rother has a great article on old Schwinns and filit brazing.
 

saetta

New Member
Jul 29, 2008
156
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Central Missouri
I favored using a cruiser style bike over my other existing bikes because of the strong frame that it offered. I did not see the need for having multiple speeds since the single speed is enough to get me going until starting the engine.
 

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inkstom

New Member
Oct 13, 2008
22
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0
Austin, TX
Holy moley, those are amazingly detailed and qualitative responses. Thanks you all so very much. The reason I was thinking about going that fast is because I know at times with or without the motor there will be times that the availability to go that fast with all the hills and stuff around.
topography austin, tx - Google Maps
Here is a topographical map of the area that I live in if you're at all interested, but that was the main concern: getting uphill. Generally in my experience if you can get going that fast then you would have no trouble on the steeper areas/terrain. Furthermore a road bike seemed more suitable for doing those speeds and I am more comfortable with a road bike at those speeds. I am glad that y'all made it abundantly clear that that is not acceptable.

Well, I have a 26" mountain bike and I bought a kit online today. So we will see what becomes of me and this project. I think I am going to stick a sprocket with fewer teeth to give it a little more speed (despite the evil looks). And lennyharp I am going to remember what you wrote the next time I go looking for a bike. I am walking everywhere now so hopefully this will be a little more time efficient in relation to time spent traveling :D. This has been a dream of mine for the longest time, I had no idea there was a whole community devoted entirely to this otherwise I would have been here a whole lot sooner.

80cc Motorized Bicycle Engine Kit Bike Berry
This is the kit I bought today so hopefully this is going to be sufficient enough to propel the bike into action. I have access to a machine shop and a friend that welds so as far as the little idiosyncrasies that will occur, I plan to prevail :). Those questions were railing my mind and I am glad that they were answered appropriately to the best of everyone's knowledge.
Cheers
-T
 

lennyharp

New Member
Jul 19, 2008
429
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Mesa Arizona


The bike can be built up with what ever componets you want. I was so comfortable using road bars that I used them to race and commute on a mountain bike once. That may not work too well with the motor and clutch controls but inventive minds invent ways... I do know that down hill mountain bike racers use an 8 - 10 degree bent back bar with a 2 to 4 inch rise and may hit 60 mph on fire road decents. Any thing that is used by serious down hillers; spokes, rims, brakes, tires, bars, frames and forks; should be strong enough for a motorized bike.

Your motor choice looks good but I don't know the seller. His site looks good so go for it. Or go check out the page that lists most sellers ... http://motorbicycling.com/f3/find-dealer-review-1730.html
The motor needs to be installed solid and broken in gently for 100 to 200 miles.
Here is a link to some great info on that aspect...
http://motorbicycling.com/f30/bicycle-motor-preperation-care-354.html
Use your welder buddy as needed as he will see a lot of ways to make it mount solidly and can really help out. Have fun and make sure you can stop better than you can go. Austin would be a nice place to ride.
 

Motormac

New Member
Sep 23, 2008
108
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Ontario Canada
Question for Goat Herder,and or Lennyharp, Is a 115 volt home hobby type stick welder good for doing bike frames? Or do I need a wire feed mig welder?I dont want anything expensive as it would not get used that often and would be for general around the home use as well.
 

lennyharp

New Member
Jul 19, 2008
429
1
0
Mesa Arizona
it will do but I explained my preference above for oxy acetylene torch to keep heats low for the work. Tig welding would be second choice and then mig and last stick for me. Mild steel is less sensitive to over heating but takes twice the thickness for the same amount of strength. That is the material I would use with your mig or stick home setup.and save a lot of expense for materials.