Making My Specialized Rockhopper Go FAST!

GoldenMotor.com

steiney

New Member
Mar 26, 2011
7
0
1
Gainesville, FL
Hello All!

Newfound motorized bicycle enthusiast here! I posted in the "Introductions" forum, but I thought I'd post more specifically in the Mountain Bike forum.

I have a Specialized Rockhopper that I want to make go really, really fast! So far, I have looked for complete engine mod kits, but the biggest I have found are 80cc, which translates to about 45 MPH max speed.

I would like to know if it is possible to put a 150cc engine on a bike, and if yes, where I would look to buy either a kit with that size engine, or the engine and a separate parts kit.

Thanks in advance!

steiney
 

skjjoe

Member
Mar 9, 2009
393
1
18
Boerne Texas
Buy a motorcycle if you want to go really fast. Bicycles where not made for those kind of speeds especially mountain bikes too squirrely
 

give me vtec

New Member
Jun 19, 2009
166
1
0
SoCal
Buy a motorcycle if you want to go really fast. Bicycles where not made for those kind of speeds especially mountain bikes too squirrely
I definitely agree... if you do however decide to put a large motor on a bicycle, you better match the power with sufficient supporting mods. ie.... larger brakes, spokes, wheels, etc.
 

steiney

New Member
Mar 26, 2011
7
0
1
Gainesville, FL
Yeah, I'm looking more for the kind of thing where you buy a kit with everything and just put together and enjoy. That would definitely be too much for me.

I'm thinking I might just go with the Grubee Skyhawk 80cc kit. It looks simple and the price is right.
 

max350

Active Member
Apr 10, 2010
322
55
28
Sweden, Örnsköldsvik
Hello All!

Newfound motorized bicycle enthusiast here! I posted in the "Introductions" forum, but I thought I'd post more specifically in the Mountain Bike forum.

I have a Specialized Rockhopper that I want to make go really, really fast! So far, I have looked for complete engine mod kits, but the biggest I have found are 80cc, which translates to about 45 MPH max speed.

I would like to know if it is possible to put a 150cc engine on a bike, and if yes, where I would look to buy either a kit with that size engine, or the engine and a separate parts kit.

Thanks in advance!

steiney
Thinking that maybe my next build will be a crazy build, using a two cylinder engine from a Yamaha RD125 !xct2
 

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bairdco

a guy who makes cool bikes
Aug 18, 2009
6,537
264
63
living the dream in southern california
if you want to buy a 66/80cc 2 stroke kit kit, expect a top speed of 30-35mph if you're lucky.

getting to 45mph isn't an easy chore. no simple bolt on mods will get you there, no matter what anyone tells you.

it's a combination of gearing, porting, and aftermarket parts and/or custom made parts.

there are very few bikes out there that can do 45+, and the ones that do ain't cheap, and they ain't easy.

the biggest factor in making a really fast bike isn't the engine, it's the bike itself. if you build it right, it can easily withstand the forces that more speed puts on it. if you don't build it right, you'll learn the hard way what 50mph feels like to your head...:)
 

steiney

New Member
Mar 26, 2011
7
0
1
Gainesville, FL
Thank you very much to everyone who posted in here. I really appreciate your help and thoughts/opinions! I will respond to everyone individually:

get a shift kit to go with it nothing like being able to shift through the gears
Forgive me, as I'm new to this specifically as well as engines/motors in general. What is a shift kit, and what does it do beyond the normal function of the engine or transmission? Does it make the gear shifting smoother?

Thinking that maybe my next build will be a crazy build, using a two cylinder engine from a Yamaha RD125 !
That sounds pretty awesome! I wish I knew how to do all that. I'm way too much of a beginner to try something like that.

I am wanting to build a 100 cc pocket bike motorbicycle. I think the right bike and you could put a lot of power to it it just depends on how it is built
True. I think I'd have to be going pretty fast for my Rockhopper to get squirrelly.

if you want to buy a 66/80cc 2 stroke kit kit, expect a top speed of 30-35mph if you're lucky.

getting to 45mph isn't an easy chore. no simple bolt on mods will get you there, no matter what anyone tells you.

it's a combination of gearing, porting, and aftermarket parts and/or custom made parts.

there are very few bikes out there that can do 45+, and the ones that do ain't cheap, and they ain't easy.

the biggest factor in making a really fast bike isn't the engine, it's the bike itself. if you build it right, it can easily withstand the forces that more speed puts on it. if you don't build it right, you'll learn the hard way what 50mph feels like to your head...
Well that's depressing! I'm still gonna by the Grubee kit and maybe a few mods. There's a dual boost bottle induction kit that seems to increase power somewhat (Dual Boost Bottle Induction Kit BikeBerry.com), and an expansion chamber I can add to the tailpipe for more power (Expansion Chamber BikeBerry.com).

-------------

If anyone has opinions on the add ons just listed, I would love to hear them.

I am planning on making the grubee kit purchase tomorrow morning. I want to give myself one more day to think the whole thing over.
 

timboellner

Member
Apr 1, 2009
435
0
16
Towson Maryland
If you want to go really fast buy a motorcycle.
Motorizing a bicycle is fun and ultimately a learning experience.
Going 30 mph on a bike feels like 50 mph in a car.
Bicycles aren't safe going really fast.
Most bikes aren't made to handle it.

There is plenty of fun to be had at 30 mph.

Too many inexperienced builders without much if any mechanical background want to jump right in and build something over the top.
It's a good way to get yourself hurt, or killed.
If the bike doesn't do you in, some aahole out on the road will accidently do it for you.

Do yourself a favor and hang out on the forum and invest your time learning about the hobby.

Your build will require a whole lot more than just slapping a motor on a bike.

The boost bottles are a waste of money by the way.
The debate has raged on for years here.

I hate to sound like a peter head but I speak the truth.

Tim
 

steiney

New Member
Mar 26, 2011
7
0
1
Gainesville, FL
timboeliner,

You don't sound like a "peter head" at all, and I appreciate your reply. I've already started to realize at least part of what you said. The more I think about it, 30 MPH is about as fast as I need to go for now. Especially considering I'm going to be taking that bad boy on off road bike trails. I think I can manage to get some decent air going 30. I was thinking about it, and I can get a good bit of air just by pedaling hard, and that's probably only going 15 to 20.

When you say "Your build will require a whole lot more than just slapping a motor on a bike", do you mean if I get crazy, or even with one of the Grubee kits? One benefit of going the kit route for me is that you just assemble it and ride. I plan to put it together with a friend, and neither of us know more than your average red-blooded American guy about automotive-type stuff.

So what's the deal with the boost bottles? I did a little googling and it seems like there's a lot more bad reviews than good.

Well anyway, thanks for your reply. I definitely plan to hang around here and wee what I can learn about putting engines on bikes.
 

poorboys bikes

Custom Bike Builder
Apr 18, 2010
46
0
0
wichita, ks
if you want to buy a 66/80cc 2 stroke kit kit, expect a top speed of 30-35mph if you're lucky.

getting to 45mph isn't an easy chore. no simple bolt on mods will get you there, no matter what anyone tells you.

it's a combination of gearing, porting, and aftermarket parts and/or custom made parts.

there are very few bikes out there that can do 45+, and the ones that do ain't cheap, and they ain't easy.

the biggest factor in making a really fast bike isn't the engine, it's the bike itself. if you build it right, it can easily withstand the forces that more speed puts on it. if you don't build it right, you'll learn the hard way what 50mph feels like to your head...:)
Great, atleast someone agrees with me, I get so much grief when i post that my felt goes 47-50mph!!! But thats because ive got ove 1500 in the bike, great wheels/tires, lots of aftermarket part from pirates and ampt. Plus the countless hours of building and rebuilding, port match/polishing, carb adjustments/ exhaust adjustments, finding the right gear ratio, finding the right fuel mixture/oil etc... And dont forget, these motors dont show there true potential til you have atleast 100 miles on 'em.... that is if you dont blow it up first!!!!
 

poorboys bikes

Custom Bike Builder
Apr 18, 2010
46
0
0
wichita, ks
This is a pic of my speed monster, its hard to believe these lil motors go so fast, but they do! just like people only using 10% of their brains, most of us only get 10% capability out of our motors due to lack of knowledge and know how/tools and such.
 

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bairdco

a guy who makes cool bikes
Aug 18, 2009
6,537
264
63
living the dream in southern california
this thread will link you to a 55mph+ bike: http://motorbicycling.com/f38/one-more-40s-colson-add-fleet-21037.html

the only proof i have are the multitudes of people who have seen it on the LA ride last month.

like i said, it ain't easy, and it ain't cheap.

my advice is to build your first bike with whatever you got. learn how it works and learn the basics. stay away from bolt-on products that claim to instantly boost your HP.

there's boost bottles and nitrous kits out there, and they're basically snake oil salesmans. it's the same as the exhaust tip and the spark plug you can buy for your car that advertise an extra "15-20 horsepower with increased gas mileage!!!"

it's b.s.

learning how the motor works and what you can do to it can turn a stock motor from a 25mph bike to a 35-40mph bike without spending any money on gimmicks. a dremel tool and some porting can do the same thing.

and i gotta repeat, just to drive it home, if you're gonna build a bike that goes fast, you need to concentrate on the bike, and not the powerplant. if you build a walmart bike that does 50mph, you're just gonna get to the hospital that much faster.
 

mbuna420

New Member
Oct 9, 2010
225
0
0
Oregon
Yep and well said from a few of ya no names as to not make any one of ya feel any more special than the others. In my opinion rock hoppers are pretty good bikes at least the older ones as I have no experience with the newer ones, and yes 30 feels insanely fast on a bicycle and not everyone should be going faster and if ya do it should be done right. My bike is getting there the setup is almost perfect now, a good rear wheal and fine tuning the motor is all that is left, thank goodness I have a little mechanical know how. This is my first two stroke and if I could get it to run right I would be happy we will see though I am taking it on it's second 50 mile ride today done a lot to it the last couple of days. The only reason I want to build a 100cc cag motor bike is so I can keep my self safer by keeping up with traffic a little easier and to get up hills a little better I am a 350 pounder so with out a jack shaft shift kit my motor just don't quit got enough umph and I think it will be cheaper to do a cag motor than it will be to make a whole china girl setup with the jack shaft race can and all. The only draw back to this decision is that I will have to fab my own mounts and the lack of tools will make it a little harder but I think I can getter done. Good luck man and let me tell ya it is nice being rid of the gas gobbler if we could only find a good sized diesel engine then we could be free of gas all together but I shouldn't get started on that because this long post will even get longer, peace out and again good luck this is the funnest hobby