top speed calculators

#21
Since torque converters can do a 1:1 gear ratio, is that equivalent to having the same number of teeth on each sprocket for a non torque converter setup? Therefore, when you have a torque converter and 19 in tires gearing has no effect on top speed? The calculator said 203 mph... Or is that not how it works?
 
#22
Since torque converters can do a 1:1 gear ratio, is that equivalent to having the same number of teeth on each sprocket for a non torque converter setup? Therefore, when you have a torque converter and 19 in tires gearing has no effect on top speed? The calculator said 203 mph... Or is that not how it works?
sorry to bring this back from the dead

the 1:1 happens at the engine and jackshaft input

using a baja warrior for example, stock it has 10 tooth at the engine, jackshaft input is 20 tooth, jackshaft output is 10 tooth, and axle has 50 tooth (for every 1 rotation at the axle, the engine turns 10 times). a torque converter when at 1:1 will act as if the jackshaft sprockets are the same or non existant. (for every 1 rotation at the axle, the engine now turns 5 times)

pretty much can double your top speed but not lose any low end torque like you would if you removed the jackshaft or made the sprockets on it the same.

correct me if im wrong as im new to :scooter: and all their greatness

a stock warrior at 3600 rpm is 20.35mph, with a 1:1 torque converter it would be 40.7 mph, TAVs can get .90:1 making the top speed around 45.2 mph
 
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#23
Seeing as though this thread was recently reserected, I'll add my 0.02 cents about buying a tach....
I recently purchased one of the cheap Chinese "knock off" tachs off of EBay for $ 20.00 that looks exactly like the one in Clyde's photo, My experience was that it is a piece of crap (You get what you pay for?) It would not program correctly as per the instructions and the rpm varied significantly (500+) even when holding the throttle constant. When I brought it to the attention of the distributor (T-Motorsports, Chino,CA) they immediately issued a full refund and also said "just keep the tach." I do not know if I got a lemon or if these are ALL junk. I do know that for the next tach I purchase I'll spring for the additional $$$ and buy either the (higher quality) "Tiny Tach" or a "Sendac".
 
#24
anyone ever use a $10 bell speedometer?

I programed my wheel in it with proportions (who knew i would actually USE those).. using the given dimensions (because its meant for bicycles not minibikes) and came out with like 1277 i think it was..

put the magnet on the wheel, had to use a fuel line between the sensor and the forks to get it to reach.

my bike is close- but not in running order right now so i cant test it yet. but i will post and let you know how accurate it is.

until then has anyone ever tried it?:shrug:
 
#25
I tried a bell bike speedo from wallmart didnt work for a motercycle with accelleration the readout was erratic so I returned it maby a mini bike accells slower it may work dont be suprised if it doesent.
 
#26
Here is the formula that I use for speed calculations. It is configured for minibikes with jackshafts but can be modified for just about any vehicle with tires and an engine.

(((RPM / S.R.) / J.R) X T.O.D) X .0029751 = MPH

RPM = engine revs. per min.

S.R. = sprocket ratio (big sprocket divided by little sprocket)

J.R. = jackshaft ratio (big sprocket divided by little sprocket)

T.O.D. = tire outside diameter in inches

MPH = miles per hour

.0029751 is the correction factor to get from RPMs to MPH.


Here is an example of how the formula can be modified for other vehicles. This is 1st gear in my GX200 powered MK8 Rokon:

(((((5000 / 8.0) / 2.0) / 3.0) / 1.23) X 25.0) X .0029751 = 6.3 MPH

RPM = engine revs. per min.

S.R. = sprocket ratio (72/9)

T.R. = transfer case ratio (64/32)

G.R. = 1st gear ratio (60/20)

C.R. = CVT ratio (Comet 20 w/ 7" driven)

T.O.D. = tire outside diameter (Titan 25X8-12)
 
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#27
I know this is an old thread, but I just have to say I agree with Michael on this one, buy a good quality tach right away, a Tiny Tach only costs $47 new. :shrug:
 
#30
Jackshaft Calculator with Sprocket Teeth, Tire Size, RPM and MPH

Strigoi,

This topic is interesting, and after reviewing the various calculators, wanted something more precise to visualize better, and be simple.

Put one together for jackshafts for my website, but interactive spreadsheets on a web page has a learning curve. Soon. It can be dressed up, for now its all about function.

You can download my jackshaft calculator spreadsheet and open it with Microsoft Excel from version 2003-on, use the free Open Office "Calc" program, or Google Docs.

Any good? Want one without the jackshaft? Mistakes? Wishes? Total crap?

Thanks for looking! :thumbsup:

Jon
 
#31
Any good? Want one without the jackshaft? Mistakes? Wishes? Total crap?

Thanks for looking! :thumbsup:

Jon
Jon, thanks for sharing that and putting the work into it. It's tedious computing a JS ratio, and even more tedious swapping sprockets around, hunting for the prefect ratio.

I'll be doing a two-speed clutch, double chain jack shaft project in the future. Your spreadsheet will help a lot. I downloaded it. :thumbsup:
 
#32
Jon, thanks for sharing that and putting the work into it. It's tedious computing a JS ratio, and even more tedious swapping sprockets around, hunting for the prefect ratio.

I'll be doing a two-speed clutch, double chain jack shaft project in the future. Your spreadsheet will help a lot. I downloaded it. :thumbsup:
Thanks for checking it out Dave! A while back I illustrated how the 2-speed clutch setups operate, and OMB members added knowledge of the differences:

FAIRBANKS

COMET

Finished the other two calculators, here are all 3 links for downloading:

No Jackshaft

2-Speed Jackshaft

with Jackshaft




If you do not have Excel or wish to use these online, you can open and play with these spreadsheets using ZOHO:

No Jackshaft

2-Speed Jackshaft

with Jackshaft


Jon
 
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#33
That's why I couldn't use Clyde as my username , I'm not the only one!
Another Jack-shaft gear ratio with tire size calculator = Rawge's Mini Chopper Information Site - Jackshafts

Tachometers?
GO TO ebay, or Amazon.com ... type in "tachometer hour meter" in their search. For about $15 USD there are cheap induction models flooding the market now (12/2010). They need NO other wiring hook-up (or power supply) other than its own single wirewrap to your spark plug.

A single wire from tach wraps 3-4 times around the spark plug wire and senses the electrical pulse. It will work on many 2 stroke and 4 strokes (it's programmable per how many spark plug firings per revolution). Has an Hour Meter on it too.
Cheap, and Chinese, it will only last as long as it's lithium battery works (they say about 4 years, probably less)
They look like this EXAMPLE:

This is just an example I pulled from some Amazon sellers page Amazon.com: Digital Hour Meter and Tachometer with Maintenance Settings: Automotive
 
#35
I have a 6.5 HP engine and was testing this out. Sure doesn't seem right. I would have thought it was going to be higher MPH. I am trying to work out the right gear ratio for the bike. Any suggestions?

Diameter in Inches - 12
Engine RPM -3600
Teeth on Axle -60
Teeth on Clutch - 13
MPH - 28
 
#36
The calculations in the spreadsheet are simple, precise math. The formulas are visible, and textbook.

A spreadsheet does not accommodate real-world variables. For example, perhaps the rear tire expands 3/4 of an inch at full speed. That decreases the final gear ratio to produce a bit more top speed, getting you almost 30 MPH. Maybe the tire is a little taller than 12".

If the engine is actually turns 4000 RPM you are at almost 33 MPH. That's 5 MPH different than the calculations.

If you drop that rear sprocket to 45 teeth, you are between 37 and 44 MPH depending on variables like exact tire diameter and RPM.

Go for 35 teeth and you likely run out of torque to get above a calculated 48 to 56+ MPH.
 
#37
Go for 35 teeth and you likely run out of torque to get above a calculated 48 to 56+ MPH.
Jon, that is indeed the missing variable. Torque. Once you really think about this, computing for speed seems useless. It's a mini bike. It will never run like a Kawasaki 125 dual sport will, not anywhere. If you want to go fast, get a used 1996 Hyundai. :laugh:

The only aspect I care about is if the bike has the torque commensurate with the gearing to accelerate and maintain governed or desired RPM. Speed is secondary.

If you're building a drag bike, speed is still secondary. It is torque, gearing, and how they interact with the clutch and drive system to maintain the power curve under acceleration until the mass is overcome by inertia. That's the way I look at it anyway.
 
#38
Dave,

Funny you mention torque. Someone described horsepower as controlling how fast you hit the wall, and torque how far you pass through it.

A Hyundai! LOL :laugh:

MY Buell X1 Lightning is a torquey machine: it lacks the horsepower and upper RPM of Asian and Italian bikes, but man it will holeshot you ahead of nearly anything off the line. It will accelerate like crazy to 50 yet never go past 6,500 RPM, while a crotch rocket is screaming past double that at the same speed.

Similarly, a belt drive torque converter (in snowmobile terms, a clutch) gears the revs to extract maximum torque. I have a GC160 Honda with a Comet TAV-2 geared to stay at or below 3,600 RPM where it makes the most torque. Fast? No Sir. It will run as fast as the torque it makes. It pulls harder than plain gears though, while remaining quieter, easy to ride, and reliable for putting around.

Hope your summer on the lake is off to a good start!
 
#39
Hope your summer on the lake is off to a good start!
So far, so good Jon! Good definition of torque vs horsepower! Another one is that 330 HP Peterbuilt semi that pulls 80,000 pounds up and down the highway, vs. that 375 HP SS Chevelle that doesn't.

I brought a hot rod Harley to Japan and rode it there a few years. I'd kill them stop light to stop light with the thing. They all thought my Harley was way more powerful than their 1100 cc tricked out rice burners. Heck no, they had 50 more horsepower, and like you said, another 5000 RPM to play with. However, the next stop light prevented them from realizing that. :thumbsup:
 

Motra

Active Member
#40
Jon, that is indeed the missing variable. Torque. Once you really think about this, computing for speed seems useless. It's a mini bike. It will never run like a Kawasaki 125 dual sport will, not anywhere. If you want to go fast, get a used 1996 Hyundai. :laugh:

The only aspect I care about is if the bike has the torque commensurate with the gearing to accelerate and maintain governed or desired RPM. Speed is secondary.

If you're building a drag bike, speed is still secondary. It is torque, gearing, and how they interact with the clutch and drive system to maintain the power curve under acceleration until the mass is overcome by inertia. That's the way I look at it anyway.
I've tried posting this info several times and nobody really seems to care. It doesn't matter what your top speed is if you can't get to it. Brisk acceleration is very desirable too so if you gear for 55 MPH and don't have the power to get there very fast, you have a pretty boring ride and an overworked clutch.

My spreadsheets give torque figures and take into effect the size of the drive wheel to get the actual thrust being applied to the ground, and the vehicle speed at which the maximum torque is being applied. I did this because I'm into Tote-Gotes where torque is king and top speed secondary. The spreadsheets don't account for drive train losses or tractive forces, that's above my pay grade.



 

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