How much hp do I need?

reaching->c

New Member
Jan 15, 2009
7
0
0
malta
Hi, there this is my first thread and also my first attempt on try to build a motorized bike. I've got an average size CHEAP mountain which served me well during the past 5 years (and i use it a lot i.e. there's no way I'm walking anywhere..........I'm cycling to the spot) which I'd like to hook an engine too after restoring a bit. I have in mind to modify a frame to fit in a motor in it's middle. My objective is to reach 63 mph (I 'know it may be hard). I will also be building a gearbox of say 3 gears shifts to get the at most efficiency out of the engine. I ain't going to lower too much the gear ratio for more torque since I can pedal my way up thus having a gearbox aimed for speed. Now my 1st question is how much hp (or kWs if you prefer) do I approximately need and which motor to use (general purpose not those ****ing 49cc, "80cc" "engine"). I was thinking of a 6hp petrol/gasoline engine 4-stroke of about 2800rpm? What do you think and suggest anything i.e. suggesting and tips and warnings ANYTHING Thanks for reading!

edit: I noticed all of you are pointing that out so things i I didn't mention are:
1. The frame will be modified to fit the engine and also reinforced in it's weak points
2. I'm going to use some reinforced hydraulic rim brakes (the reason why not choosing disk brakes are mainly because they put to much stress on only one part of the rim which in cases can deform the rim itself. Rim brake disadvantages are that it can overheat the rim while going through long, long steep slopes but that is not my case and also i'm a bit of a hard driver (fast acceleration/deceleration) (Coaster brakes were a good option because 1. they aren't strong enough in my case and also not easy upgradeable and they need a lot of maintenance))
 
Last edited:

Clotho

Member
May 25, 2008
304
1
18
Would you attempt to pilot a raft made of pop bottles across the ocean? It has been done before so I won't tell you it is impossible. Raft across the Pacific.

What you are proposing has a great deal of risk associated with it that you should be aware of so you can make a balanced decision. It is not impossible but it is dangerous. Just like a soda bottle was never designed to be part of an ocean going raft your cheap old bicycle was never designed to go 60mph.

That being said it is possible to motorize your bike and get it to go pretty quick. 30mph with a stock motor may not sound that fast but it seems a great deal quicker when you are on it. Further tuning and modification can see even higher speeds with relative safety.

If after all this you still feel the need for greater speed then I think you should consider a motorcycle. They are properly designed for it and your chances of hurting yourself or others is much lower.
 

reaching->c

New Member
Jan 15, 2009
7
0
0
malta
To Clotho, I was ware of this from the beginning, I possess a motorcycle and it's pretty easy to reach 60mph on that but I'd like to reach 60mph on a bicycle (high modified)

As Bikeguy Joe pointed out it'll probably be somewhere near an 8hp.

Thanks for replying! (too all)

BTW I earlier mentions of building a gearbox of about 6 gears (2 low gear 4 high geared compares to the sprocket on the rear wheel) attached to the engine's shaft. Now I presume that would increase acceleration and also top speed. The 6 gears will be attaches one after the other very similar to rear derailleur. Then the chain will be passing around them and it will be hooked up to another gear in the gear box. A 'clutch system' will enable the chain to he lowered (and engaged to the derailleur or lifted up. Then basically to change gear the clutch will be engaged and the rear derailleur can be shifted across. Problem is would the gearbox overheat while going hard on the throttle? Would i need to enclose the gearbox and use some short of cooling system (oil).?
 
Last edited:

Dan

Staff
Staff member
May 25, 2008
12,775
106
48
55
Moosylvania
Sounds like it will be awesome Reaching. Please post pics when you get her done. What size drive chain will you be using?
 

reaching->c

New Member
Jan 15, 2009
7
0
0
malta
chain drive standard 50 or 60 (I'm still planing it our part by part i.e. Today I solved the problem of the gear shifter leaver: It'll be similar to a the brake leaver but attached the other way round. When it is squeezed the clutch is engaged and at that moment it can be turned up and down in steps to shift gears.) It'll be a lot of work since i have to do build/forge everything manual.
 

Dan

Staff
Staff member
May 25, 2008
12,775
106
48
55
Moosylvania
This really sounds fascinating. Can't wait to see what you build. There has been much discussion on doing what you have planned.
 

fm2200

New Member
Nov 16, 2008
258
1
0
new york city
I would not trust the bicycle frame for this over 50mph stuff. No matter how well you put this bike together there is a great risk that after a while, metal fatigue will happen and cause the frame to crack and break apart. Only a motorcycle or small scooter will be able to sustain these kinds of stressful related speeds. This may seem like a cheap way to get there in a hurry, but you will be seriously injured should the bike break apart, it's a real risk you'll be taking. fm2200 (by the way no mechanic no matter how smart he is can guage when metal has been fatigued or is at the breaking point).
 

reaching->c

New Member
Jan 15, 2009
7
0
0
malta
To anyone warning me,
I know of the dangers and inconveniences that can arise but what can i add:
1. Frame is 5 years old, and not ruined and there is not apparent metal fatigue.
When I mentioned that it was to be reinforced I meant reinforced so as to
Sustain the greater fatigue cause by the excessive speeds and engine
vibrations which it wasn't built for. When finished (a very long way to go)
frame will be as strong as that of a 125cc dirt bike but my engine is ~200cc
LOL if this thing succeeds it will be a motorcycle with pedals!

Yet another question: Considering the 200cc engine, the frame weight doubled and the much faster speeds shouldn't i change the wheels (rim and obviously tyre)?
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
236
63
up north now
Just the fact that you asked that question makes me think you should re=-think this whole thing.

But that's just me.
 

reaching->c

New Member
Jan 15, 2009
7
0
0
malta
Yeah Bikeguy Joe, you know what I'm gonna build a motorcycle .......................................with pedals really I just change the project's name. Fact is this thing all began when a few days ago I noticed my previous (not to say old) bicyle laying there on the garage floor and I though "**** that bike though cheap served me well for 5 of the most difficult years of my life" (not that I'm till young) so basically I just wanted to begin a project to 'recycle' and so whatever i'm gonna weld together it will gonna be around that frame.

BTW Yeah I need new rims and I'm thinking of getting them off a small old dirt bike. That way I'd also have drum brakes with aill be better than my hydraulic rim brakes.
 

Dan

Staff
Staff member
May 25, 2008
12,775
106
48
55
Moosylvania
Reaching, is just SOP to warn folks about the dangers of that much power on a bicycle. (Honestly I forgot to as I got lost in thought about your gearbox) Don't take it as discouragement in any way. Is just a very caring bunch here.

Really am looking forward to seeing your build
 

thatsdax

Member
Feb 22, 2008
869
1
16
www.thatsdax.com
I have hit almost 50mph on my Easy ride bike with a Titan XC 50. I was riding with both hands on the grips too. I did it going down a hill and only for a short burst to see how the Titan motor would handle the over speed. To my surprise, it did not bat an eye. Going almost 50mph on that bike was scary. I have not done it since. To go any faster would require a better bike. Not sure what better bike I would use.. But..You have to understand.. These are bicycles. And to go much over 40mph would get you in trouble here in USA with police. Most places, a bicycle going over 20mph will get you a ticket. 30 mph is nice.. 35-40 is great.. But.. Risk of death or serious injury increases exponentially beyond 40mph on a bicycle. Make sure you wear your full face helmet and leathers, shoulder protection, elbow pads, knee pads and every kind of pad you can think of if you wish to fly over 50 on your pedal bike.. And.. O yes.. You might want to carry a body bag along as well.. Enjoy the ride....
 

comfortableshoes

New Member
Jul 22, 2008
606
0
0
Beverly, MA USA
suicidal
Get a downhill bike made for extreme speeds. Most bikes are not made for those speeds.
I rode my MadWagon at 33mph on a smooth street and that was fun but I hit 31mph on a rough patch once and sweet j3sus that scared the **** out of me and I'm not exactly afraid of speed, rough road or riding a bike. I push my bike to some extremes and most of the time I'm happy cruising around at 20 mph or so.

I think what you'll need are some steel balls, 2 of 'em, and a change of underwear.

I hate to say this, but why not get a nice moped and modify it? Tomos makes some that look like motorcycles.
 

reaching->c

New Member
Jan 15, 2009
7
0
0
malta
I may be wrong but I think I already mentioned that I already have a motorcycle. This is more a project where the objective is to build it. I ain't going to use this bike as a cruiser or like everyday. And also I ain't afraid of reaching some speeds.
 

reaching->c

New Member
Jan 15, 2009
7
0
0
malta
I've got some bad news. My current occupation requires me to be on the move till about August-September so I don't have the time to build, test crash and trash my will be so awesome to drive bike. From a positive perspective I'll be earning some useful knowledge from this set of tasks and also I hope to bring back home some stuff to improve my biken my bike.