Thanks Radmanfly, it confuses me as in Australia we dont talk inches, feet & miles anymore we have convereted to mm & kmh, anyway thanks for the saftey tips as I wouldnt try to do those rpms or speed, Im really building the bike for torque so I can pop monno's down the street & just for a laugh when I come up at the lights against 50cc scooters i want to scare them lol....
BMX Build
- Thread starter Brains
- Start date
Brains, let's test these gear ratios. Use an 8-tooth drive gear and 74-tooth sprocket, so you can make adjustments using 7t and 6t sprockets. With 8t, you have 9.25:1 gearing. Now create a jackshaft, using 36t sprocket on the hub and 16t on the jackshaft. Jackshaft ratio is 2.25:1. Multiply by 9.25 gets you 20.8:1. Using an online gear ratio calculator with 20" wheel gets you 64 kilometers/hour(40mph) at 14,000 rpm. With a 9t, speeds are 72kph(45mph) at 14,000 rpm.
For more low end, install 7t sprocket, which gets 10.57:1. Multiply with jackshaft 2.25 results in 23.78:1, and 56kph(35 mph). For even more low end, install 6t for gear ratio of 12.33:1. Multiply by 2.25 for 27.74:1 and speed of 48 kph(30mph).
All speeds at 14,000 rpm.
If someone can suggest an online calculator, Brains can work out more gear ratio combinations. It's good to start with 8t drive sprocket, because you can adjust up to 10t and down to 6t.
Good luck.
For more low end, install 7t sprocket, which gets 10.57:1. Multiply with jackshaft 2.25 results in 23.78:1, and 56kph(35 mph). For even more low end, install 6t for gear ratio of 12.33:1. Multiply by 2.25 for 27.74:1 and speed of 48 kph(30mph).
All speeds at 14,000 rpm.
If someone can suggest an online calculator, Brains can work out more gear ratio combinations. It's good to start with 8t drive sprocket, because you can adjust up to 10t and down to 6t.
Good luck.
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Thanks 5 - 7 Heaven, when I get home tonight Im going to suss out if I can get diffrent toothed sprokets as per your suggestion as I will be able to feel & see the diffrence in performance from swapping from one to another, I got heaps to do before I can give it a test drive, got what I need for the accelerator cable now & need to weld the brake carriers back as I cut them off as they were a bit to close for comfort in regards to the chain & still have to devise a chain tensioner as well, will post some more pics as I go along & just worked out that my camera takes video's, so will try this tonight & see how clear it comes out and if it does I will upload on you tube so you all can hear at least how it sounds, thanks a million all you have forwarded great material for me to become more understanding on how to calculate my gear ratio's as this takes a lot of the guess work out now, and should be able to be around the mark from the word go
jasonh
New Member
Wow, this is a nice build. You've got some skills Brains.
Can't wait to see this thing all buttoned up and working. Gonna be a monster. Would be pretty sweet to get one of those motors frame-mounted.
Just curious on your home made pipe bender you mentioned - any pics of the setup?
Can't wait to see this thing all buttoned up and working. Gonna be a monster. Would be pretty sweet to get one of those motors frame-mounted.
Just curious on your home made pipe bender you mentioned - any pics of the setup?
Thanks Jasonh, glad you like it so far, and your in luck you will see a build with this motor which will be frame mounted, I have an OCC stingray my dad got from a garage sale & its pretty rough in condition but its all their & original, as its got a 4 1/2 inch rear tyre this motor will work really well with the drive shaft offset it has & should rig up nicely & still retain its original working pedals as well, Im going to go a bit harder on this by putting NOS on it, should be a cracker of a build, I will start this one as soon as i finish this build which should be in about a week, so keep an eye out for the post
Ive finished basically this build apart from cleaning the frame up and then putting it into paint, putting it all back together neatly & hiding all the wires through the frame which i have already drilled the holes to feed them through.
Ive attached some of the latest pics, shows the chain tensioner I made up & a pic from the rear showing the chain offset and how its connected, had to machine out some of the rear frame legs to attain good chain clearance & then filled them back up with solid weld as I had to cut through the tube, this will ensure its retained its strength.
I have also taken off the original muffler I made & then re hashed an old exhaust I had to fit, it sounds a lot smoother now at idle but really performs a lot better through the rev range, I like it better
The test rides went really well & it pulls away with ease from a standing start with no help via the pedals so what ever (actually never used them to date), have done about 50 laps of my block & its sweet as, I must be doing around 60km/hr easy as thats the speed limit on local roads & Im passing cars, the look I get is unbelievable with the motorists, it has heaps in it still even at this speed, have not yet really pushed it to its maximum, but I still will try another carby set up I have on the weekend, it will be interesting to see what if any gains it makes, it feels really strong & secure when riding it
I have attached some pics for you all to see thus far
Ive attached some of the latest pics, shows the chain tensioner I made up & a pic from the rear showing the chain offset and how its connected, had to machine out some of the rear frame legs to attain good chain clearance & then filled them back up with solid weld as I had to cut through the tube, this will ensure its retained its strength.
I have also taken off the original muffler I made & then re hashed an old exhaust I had to fit, it sounds a lot smoother now at idle but really performs a lot better through the rev range, I like it better
The test rides went really well & it pulls away with ease from a standing start with no help via the pedals so what ever (actually never used them to date), have done about 50 laps of my block & its sweet as, I must be doing around 60km/hr easy as thats the speed limit on local roads & Im passing cars, the look I get is unbelievable with the motorists, it has heaps in it still even at this speed, have not yet really pushed it to its maximum, but I still will try another carby set up I have on the weekend, it will be interesting to see what if any gains it makes, it feels really strong & secure when riding it
I have attached some pics for you all to see thus far
Attachments
Great to see you both like it, Yeah I reckon I might have to put a red flashing light at the end of the tail pipe or keep clear when turning sign lol..., was going to make it shorter but I liked the look of it longer, to tell you the truth Radmanfly Ive been that shocked with which the bike pics up speed that I havn't even tried monnos yet, I'm to excited about the rush at the moment, I reckon that it will maintain it not a problem if I assist the front up and I could play with the throttle to keep it up there, but I reckon a larger rear sprocket like you said will do the job, its just that I don't know if I really want to try it this soon as until I get a hang of of it, as it comes on with such a bang and rush down low that I will need to put a wheel on the tail pipe like you said lol..., who knows if I paint it red it might get even faster
I decided to ride the bike to school this morning, so I can do more road tesing before I pull it down & get it ready for paint, and it seems to holding well, I reckon the extra wide sokes I used is doing its job with holding the rear weel together along with double walled rim, went up a 35 degree incline hill with ease, it seems though that at minimum throttle its cruising around 40km/hr, these little motors are defintley little Hiroshima Screamers, trying out a new carby on it tomorrow, will post pics of it compared to the one we have fitted already
Radmanfly
New Member
Double wall rim??
Yep its been an awesome bike to ride, heaps of fun & faster than I ever wanted, I have been asked how I made my throttle cable, so I will set out to take pics of step by step on how I did it so this might help other to do the same, double wall rim is simply instead of the the wall of the rim being single it is double, so it goes up and then around and back down again to form dual walls on either side with a hollow space between them, they are a standard rim you can purchase from any bicycle shop usually for serious off ride bikes which the rims take a real beating, the one issue I have had with doing some km on the bike now is that these motors drink flat out like a lizzard on hot summers day, its actually really amazing on how quick it gets to 60km, and its got heaps more pull if you want, I am using 6 tooth sprocket on the front and 76 on the rear at the moment
damonjackson_spl
New Member
he used a pocket bike chain and pocket bike sprocket, drill the pocket bike sprocket to the PCD of a rotor..
only problem is even if you find the biggest pocket bike sprocket you can find it is only good for max 20" wheels...
I have a reduction gearbox for my pocket bike engine and used standard 415 chain/sprocket (welded BMX 12t cog to pocket bike cog on gearbox) and mounted a 56tooth BMX chainwheel to 26" wheel, the gearing is okay, could do with a change thou..
only problem is even if you find the biggest pocket bike sprocket you can find it is only good for max 20" wheels...
I have a reduction gearbox for my pocket bike engine and used standard 415 chain/sprocket (welded BMX 12t cog to pocket bike cog on gearbox) and mounted a 56tooth BMX chainwheel to 26" wheel, the gearing is okay, could do with a change thou..