Top Speed

I have a stock HT with a 32 rear sprocket and have been able to get 40+ miles per hour. My speedo is correct. How do I do it? It is by reducing drag, primarily aerodynamic. I am using a shimano front wheel with 16 spokes and a 700 x 23 tire. I also use a bmx chain and my frame is well aligned. The wheels roll perfectly, especially the front.

When I was doing my undergrad degree at Western Washington University, I took a vehicle design class given by Dr. Seal who was known for designing fuel economy cars that successfully competed worldwide with other cars, including those from MIT. Some things I learned:
weight is not a significant issue for top speed or fuel economy on level ground once the speed is established
lowering rolling resistance is especially important at lower speeds
frontal area is critical for reducing drag

I also have been a bicycle racer and coach, so I know how much those tight fitting clothes mean to speed. I once was riding down Mt. Rainier with sweats and a t shirt. Normally, I could go significantly faster than the cars and would pass them. This particular time I had to pull over so they could pass me.

One I ride the motorbicycle for speed, I make sure that I am not wearing a floppy jacket or baggy pants. I am considering putting on an old skinsuit just to test the difference; the same as used in Tour de France time trials.

I would like to see some of you experiment with reducing frontal area (less upright perhaps) and wearing less baggy clothing (OK, I do not expect spandex).
I love this forum and wish I had a great shop to do what some of you do (time would be nice too!)
 
Very good points, Douglas!
I'd like to see what improvement there is when a MAB uses a zip-closed dacron cover like they do on recumbent racers with a plastic windscreen.
...when I get a round tuit, my hedge trimmer will be on a home-built liteweight frame with no other purpose than running for top speed out the back road at Pozo Saloon.
I've got some dacron salvaged from advertising banners...
Best
rc
 
biknut said:
My 80cc has a 36T and will do a little over 35 mph, and I have a 50cc with a 40T and it will do about 30. These are top speeds though. A dependable cruising speed is about 5 mph less.
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I found out if I lay down on the 80 I can do 40 mph, but don't tell anyone because I'm a member of the 20 mph club.
 
biknut said:
I found out if I lay down on the 80 I can do 40 mph, but don't tell anyone because I'm a member of the 20 mph club.
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Yer fired! :p

LOL, I think I have a weak Huasheng. Maybe a Tuesday or Thursday one. It's rated for 2HP@6800RPM and the jackshaft on shift kit robs some power. At 30MPH my engine turns 6K RPM and I rarely make it there lol

Srsly, in a headwind, I'm lucky to do 23MPH at full throttle in 3rd gear. I can go 25 in 2nd gear! But I can't complain, I have zero engine problems other than a bad carb in one year! :D
 
My 48cc will run 31 to 32 on flats, has hit 35 down hill but way to many rpm's with the 44 tooth sprocket. But the 44 helps the little 48 climb hills.
 
Horses are horses. No matter the external upgrades you use, without changing the displacement they will only gallop so fast. Sure you can whip'em harder coming out the gate to try and get that .001th of a sec by using all kinds of aftermarket goodies, but in the sprint it's gonna come down to torque vs. speed ratio. That is determined solely by the diameter of the sprocket at your wheel. The larger it is the more torque you will have, as you decrease it in size the faster you can go. That is why a Jackshafted Bike will always win the race because you can adjust the ratio as needed. I mean there is no reason why you cant go 55mph on a tiny wheel sprocket except for the fact that it wouldn't have the torque to get movin off the line. so if you want top speed without playin catch up for the first half of the race get your gears an Jackshaft.
 
Let's see. Top speed of a HUMAN POWERED VEHICLE is about 81 mph. A lot less horsepower than a HT motor. I would guess my HT motor in the 81 would do what, a 100 mph? Not sure, but certainly a lot more then 81, so horses are horses does not really hold up well.
 
Doug do you have any idea how high a gear ratio those 81 MPH bikes are, the smallest gear on your mountain bike is their first gear and it takes them 5 miles on a flat road with no wind to get up to top speed.Plus they have carbon fiber bodies on them with almost no wind resistance and the bikes don't stand any more than a two feet high if that much and no more than 14 inches wide. And Humans are not RPM limited. These HT motors and cars have the same issue if you want to go faster get more HorsePower. Most people with a 44T sprocket can just barely reach 28MPH with the stock settings but when you upgrade engine parts exhaust etc, you can hit close 36MPH with a 44T sprocket. And wdpkr10 your right about the size of the wheel theory, but like I said HorsePower does matter and plays a HUGE part in how fast you can go with whatever size wheel and sprocket you have. I'm not trying to offend anybody I just the facts to be known.
 
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Humans are limited in their rpm. Much more than motors. Try to spin much past 150rpm. Most are spinning around 60 and time trialists actually do not spin all that fast.

The point here is that a HT motor has far more power than any human. Gearing is not such a big issue
 
douglasseattle said:
Humans are limited in their rpm. Much more than motors. Try to spin much past 150rpm. Most are spinning around 60 and time trialists actually do not spin all that fast.

The point here is that a HT motor has far more power than any human. Gearing is not such a big issue
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Actually, gearing is a huge issue. Those speed records are not practical. They are done simply for breaking records. This involves things such as special aerodynamic bikes and such.

Speaking of gearings and RPM, anytime someone claims 40mph on a HT with a 44t sprocket, I don't believe them. The engine would be spinning at 10k+ rpm. If someone mentions they used shift kits, smaller sprockets, balanced crankshafts, and better aerodynamics, I'll believe what they have to say. Otherwise, well, it's very easy for 28mph to feel like 40.
 
All my builds are basically stock, all 80cc and all with 44 tooth sprockets...and I get to where I'm going, in one piece.
 
I meant to say that getting the correct gearing is not a factor. I have a 32 and could easily change the front to achieve a higher gear ratio.

The problem occurs when the motor does not have enough power to overcome the drag and most of it at higher speed is aerodynamic. Small improvements go a long way

Bicycle Speed (Velocity) And Power Calculator
Bike Calculator

Here some data for bicycle power requirements for pedaling:

typical fat tire back used for many motorized bikes with fat smooth tires, 157 pound rider, with 160 watts will achieve 14.5mph

same rider, racing bike, same conditions with 160 watts achieves 19.1 mph

same rider, triathlon bike, 160 watts achieves 20.2 mph

These are VERY SLOW speeds. As you go faster the power requirements sky rocket.

Check out the websites listed and play with the numbers and you will see what I am getting at.

Also, try entering a 500 pound rider compared to the 150 pound rider using 1000 watts riding on the hoods. The speed of the 500 pound rider slows down by about 1.5 mph (given same drag)
 
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This power to gear ratio applies to cars as well. For example, the bugatti veyron with 800HP can hit 200MPH, but in order to pass the wind resistance it needs that extra 500HP to get another 50MPH. The same goes with these HT engines. Here in town a cop clocked me doing 37MPH with a 44T tooth sprocket yes my engine did sound like a bomb waiting to burst but it still could have gone even faster if I would have pushed it more. Now with a 36T sprocket my engine purrs at 30MPH but I need very few upgrades to hit 36MPH easy but, for my bike atleast maybe with others bikes too, they will need all the upgrades they can get to hit 45MPH, also bringing in wheel diameter into play. Mine is 26"x2.00. I need to do more tuning on the Xchamber and I'll be able to hit 40MPH no problem. With all due respect to you guys who think HP is not that important for top speed, really look that up sometime about more HP needed to pass wind drag and such, you'll see what I'm talking about.
 
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29" genisis onyx aluminum frame with a z-80 slant head, port match and polish, bp7 plug, stock air cleaner,nt carb(stock jet, middle needle),custom full length exhaust with pocketbike expansion chamber, all gaskets sealed with indian head and carb sealed with non hardening rtv. 36t gear. bike is 60lbs full. and im 180lbs. 48mph sitting up. 52mph in full tuck board tracker position on a 72degree day.
 
atombomb232610 said:
29" genisis onyx aluminum frame with a z-80 slant head, port match and polish, bp7 plug, stock air cleaner,nt carb(stock jet, middle needle),custom full length exhaust with pocketbike expansion chamber, all gaskets sealed with indian head and carb sealed with non hardening rtv. 36t gear. bike is 60lbs full. and im 180lbs. 48mph sitting up. 52mph in full tuck board tracker position on a 72degree day.
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52MPH with a stock engine & a 36T driven......wow!

I have a 36T on a bike that has had several mods done to the engine with 26" wheels and it screams like it is coming apart at 38MPH.

Another bike I have has a 34T driven on a 26" wheel and it has hit 41mph sounds like it is coming apart at that speed, very high revs.... the engine has had everything smoothed up, port matched on both ends, port matched Manic intake, shaved head for much higher compression, and the upper wrist pin bearing has been replaced with a heavy duty one, good free flowing exhaust and well tuned NT carb with better K&N type air filter and 41MPH is tops on this 26" bike.

If you're really getting a GPS verified 52MPH out of that thing you really have a jewel of an engine there being able to pull those big 29-ers like that.

Wow...! Ride safe for sure.

Peace, map
 
Interesting topic. :).

And Texhun so you are saying that these engines do not have enough horsepower to get passed wind drag using lower sprockets with a very high speed?
 
I hate to even get involved. But I've built and sold over a dozen bikes. I've bought every kit out their. And i can honestly say the z -80 is the only engine kit i will ever buy again. This kit comes with a 41 tooth sprocket. On a Delmar frame stock muffler. 37mph on my tomtom gps.
I'm currently running a 36 tooth my cafe build. Stock NT carb pocket bike pipe set to hit at top end. This bike runs out of revs at 45 mph but still climbs up heavy grades at 25mph. If you know Providence RI I'm talking bought collage hill. The x-80 and z-80 kits from boy go fast are actually 68cc high compression engines. I tried a head from a pk-80 and also the manic head . The engine lost compression with both. sorry bought the semi incoherent rant It's past my bedtime. Any way this is all on un moded engines. But with port matching and a few tricks the z-80 is the beast of bike engines in my experience.
 
The HP is there but just can't be used because of all the restriction from the stock parts such as the cat muffler and sorry quality intake pipes and such.It's like you trying to run while being able to only breath through a straw that's how alot of these engines are. The Xchambers allows better breathing for the engine and then some, a better carb allows the engine to get the right fuel mixture without 4stroking, bogging, sputtering and so on, though some stock nt carbs are awesome but they lack the full potential for some engines. Listen guys I'm not trying to be annoying or rude I just want the facts out there, all you need is some research and 2 months worth of hours on these engines and you can understand what I'm talking about. I've had three of these engines and all were the same deal. Why do you think Bairdco can hit 62MPH on his bike with an HT engine, sure he's got like a 25T sprocket but still there's no way he could go that fast without upgrading for more power.
 
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biknut said:
I've always been curious about what the maximum RPM is for a China Girl motor. When either of mine get up to about 7000 they sound like they're about to blow, but they never do. I'm guessing a mushroom cloud of broken parts at about 8000 rpm.
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I have a raw motor that i spin to 8200 .
 
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