What's the smallest rear sprocket you can/used? *story time with pics*

Discussion in 'High Performance Bicycle Engine Tips and Motorized' started by Nate&Brandi, Feb 16, 2019.

  1. Nate&Brandi

    Nate&Brandi New Member

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    So I'll start by saying my bike is not stock by any means of the word I'll try to remember ever thing I have done: first off my engine is a pk80 race engine built by Fred over at CR machine with with that comes with a balanced crank, A generaly decent port job (I say this because he ports them for general use excellent port matching and A+ clean and professional) but there is some room for improvement depending on what your looking for so I put my little touches on it as well for a little more top end, I have a dio reed valve with a windowed a d modified piston, 21mm oko carb, all sits on a BBR TYPE gas tank frame 10 spoke mag rims, triple tree forks, 203mm disc brakes, oh forgot to mention a Fred head 6.5mm, and I run premium pump fuel mixed 50/50 with race fuel. I think that about covers the power train. But I had a 36t sprocket on and it was screaming so I decided to try a 30t for shirts and giggles and it's still screaming. I can't even go full throttle without red lining it. So I ordered a 26t this week to see what it will do. What is the smallest anyone has used with sucess?I WEIGHT 180 AND my bike just has so much power I know it can handle more. I mean as it is now I can take off from a dead stop with just the motor. It's CRAZY!!!!! THE LOCAL SHOP GUY where I live keeps asking me to let him see my ports and piston lol I won't just because the first bike I ever had I bought from him for 300 bucks was a pile of trash. The motor (older half breed)was good that's abut it I still have it on another bike. But it was on a Shwin frame and looked clean so I bought it on a whim. After I bought it noticed every bolt/ nut was stripped/double nutter both rims were bent, was missing 3 rag joint bolts well you get the picture, but that actually helped me discover how much I like working on them now because I had to completely overhaul that bike and it all started with a $50 huffy Cranbrook lol pics below of my first bike and my current bike 3 yrs and 3 builds later lol oh and it was laundry day hahaha. *pics were taken last year before last round of mods.
     

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  2. LR Jerry

    LR Jerry Active Member

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    Get these two things a cheap bicycle computer so you'll know how fast your going. Then get a small engine tachometer/hour counter.

    https://www.ebay.com/itm/Digital-Engine-Tach-Tachometer-Hour-Meter-Inductive-for-Motorcycle-Motor-YK/163426986591?hash=item260d01ea5f:m:mMePaQVzBxHokTkCNJC5U5A&LH_BIN=1

    Do you know the maximum safe RPM for your motor? Maximum horsepower is generally around 87-93% of maximum RPM. For example: 8000 RPM would be around 7000 RPM for max horsepower at 87.5%. With that knowledge you can then adjust your drive ratio to where it operates at max horsepower rpm. In other words it does no good to run a smaller sprocket if the strain on the engine won't allow it to turn but 6000 RPM but max horsepower is at 7000 RPM.

    That is the beauty of a shift kit you can adjust the drive ratio to run at max horsepower.
     
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  3. zing

    zing Member

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    Thank you Jerry It's a really good explanation when I can read it a 6 A M and get it :)
     

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