RPM/MPH Calculation

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Flameout

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Has anybody calculated the engine rpm ratio to the 10 tooth sprocket on the HT engines?
I don't want to "re-invent the wheel" if I not necessary. I could then use rear sprocket size
and wheel diameter to determine engine rpm from speed.

Thanks for any input.
 
Cabinfever1977 said:
that ratio calulator said i would do 132mph @ 7000rpms,lol.
i have a 44t sprocket with 26" wheels.
Click to expand...
7000 rpm = 30.0 mph in your case

The calculator worked fine for the guy above
and for myself
I have been calculating ratios for the EZ 4 stroke bike to
figure out rear belt sizes and it is invaluable

You entered the wrong figures so try again
Read the help file at the bottom

20 for drive gear for the bevel crank

82 for driven gear for the clutch gear

in one field
Click to expand...
then
10 for drive gear

44 for driven gear
Click to expand...

leave the other box at 1
 
looks like that even with a 25 in tire one only needs 7,500 rpms to get to 40mph with a 36 tooth sprocket !

i make 30-35 mph on the regular with a 44 and even came right up on 40 ! i think those super high rpm runs at 8,500 and 9,000 rpms are shorting the life of my motor lol

i like the power the 44 offers but i also like the speed ! if i regear shure i can get the speed i want with less rpms but i sacrafice hill climbing power ! well and gain engine life lol ! i say who cares ! if your china girl will rev out to 9,000 than let it ! just make shure to keep it well oiled ! 32:1 sounds right .... after all its only a china girl ! they cost a whole 100$ and even at 9,000 rpms it will last long enough for you to get your moneys worth !
 
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I usually take knot plus knot minus knot to figure things out.. you older guys and gals probably remember that from when Jethro became a banker on the Beverly Hillbillies and was asked how he balanced the books
now on subject. back when I had my gas bike the 44 was a little big and the 36 was to small, I had someone make me a 40t and it was the best of both worlds.
 
Northern Tools sells a tach/hour counter for around $45. Walmart sells multi function bicycle computers. Then you'd never have to guess again. Rpm and speed can vary on hills. Another good thing about the tach is it'll keep you from over reving going downhill.
 
Forbisher said:
7000 rpm = 30.0 mph in your case

The calculator worked fine for the guy above
and for myself
I have been calculating ratios for the EZ 4 stroke bike to
figure out rear belt sizes and it is invaluable

You entered the wrong figures so try again
Read the help file at the bottom


then


leave the other box at 1
Click to expand...
So what would the rpm be on a 26 I ch tire with 44 tooth sprocket running 38.8 mph
 
So by your calculations would you say 9,750 rpm would extrapolate to 50 mph with the same bike setup?

Many aspire to extrapolate to that speed with CG engines, lol. Many would say I'm a real dick as well, but I'm still having fun!

Rick C.
 
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Greg58 said:
Hey Rick if you’ll do the 9750 rpm I’ll watch.
Click to expand...

Greg speed really isn't my goal with the 66cc China girls so I run 48 t and 44t normally for daily, no pedal riding, but I do have two motors that will crack that 10,000 rpm mark with ease. One is a modified reed motor and the other a piston port which has been highly modified. The piston port has a twin brother which decided to part with it's rings a few years back at 12,000 plus. When it came up on pipe it felt like I'd shifted gears (using a tuned KTM expansion pipe) but while doing back to back to back runs of a half mile each at the airport it decided enough was too much. I felt really destructive that particular day. They do blow or don't last long when you push them past 8,000 rpm very long or very often. I test with a 48t sprocket to keep the speed down, rpm was my interest, but I was still zipping along pretty good that crisp fall morning.

I'm thinking of changing my 48t out for a 36t sprocket on my hybrid for a less busy motor between 30 mph and forty...at least I have a sprocket on order for it. I'm hoping it won't be too herky- jerky at 10 to 15 mph, but I'm not holding my breath. The piston port engine was never a daily rider & became almost un rideable at legal town speeds (under 25mph) even with a 48t sprocket, just too high strung. Since I use the electric hub for all my takeoffs I still won't have to pedal with the 36t sprocket, unless I want to, from dead starts such as at stop signs etc. The reed valve engine on the hybrid isn't anywhere near as high a tune as the piston port I described, but still the 36t may not work well enough for in town daily duty.

I'm aware anyone (me) can claim anything, when it comes to performance; so for those that doubt just have a good laugh at my expense and consider the tall tales of the Old guy as entertainment alone!

Still just having fun, Rick C.
 
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