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Regarding this mod, is going to a 55 tooth (55T) rear sprocket the only way to increase the reduction on the E-100?  What about the 9T front sprocket?  Is there anything smaller available such as 8T?  I am trying to get this scooter to work not just on pavement so I need as much reduction as possible, even if it means a drop in top speed of a few MPH.  Also, does the 55T sprocket with the 3 predrilled boltholes have a different bolt hole circle diameter than that of the 47T sprocket with the 4 predrilled boltholes or are they identical?   Thanks.

Is 55T the largest sprocket that will fit on the wheel?  What about the next size up which I think is 65T?  Will it fit on the E100 scooter?  What might happen if the sprocket is about the same diameter as the rear wheel?  Will it double as a soil aerator for my lawn?

E100 rear wheel is about 5.5 inches in diameter and even the 47 tooth sprocket hits the ground at about a 30 degree angle when tipped to the right so I decided not to put a large sprocket on the rear.  It is a shame they don't make smaller front sprockets that fit.   Oh well.

Update:  I changed my mind back and am going with a 62T rear sprocket.  The one I got does not have the correct size center hole so I have to first widen that to about 29mm (it is currently about 26mm).  Then I have to get the 4 holes drilled in the right place using the original 47T sprocket as a template.  Then I need a longer chain, I think about 10 links longer should do it (from 74 to 84 links).  I will have to remove the chain guard and warn any riders not to turn more than about 10 or 15 degrees during right turns but other than that, it seems it should work.  The sprocket is almost exactly 5 inches fromt tip to tip of opposing teeth

Does anyone know what type of drill bit I need to drill the 4 holes myself in the steel scooter sprocket?  Do I need 2 drill bits, a starter bit, then the final size bit the same size as I need the hole?  There is a Harbor Freight, Northern Tool, Lowe's and Home Depot close to where I live so who might have what I need?  I need to drill 2 sprockets so 8 holes total but 2 of those holes might only need widening a little so drill 6 holes and widen 2.  Thanks.

Regarding the chain link calculator link specified in a previous post here for this "thread", does that assume that the chain runs symmetrically?  An example would be imagine something like a small front sprocket and a large sprocket (such as 9T front and 50T rear).  Does that calculator assume the chain will run an equal amount upwards from horizontal (parallel to flat ground) and an equal amount down from horizontal?  This is not always the case and I suspect it is actually rarely the case.  Usually the chain has more "drop" than "rise" to meet the larger diameter of the rear sprocket.  So my main question is if the sprocket centers are not lined up horizontally, is this chain length calculator still accurate?  I know it has some problems cuz if I type in something ridiculous like 2000 tooth rear sprocket, it will tell me I need some super long chain but obviously a sprocket that large would bump into the front sprocket long before being 2000 teeth so the calculator has "bugs". 

The angle of the motor sprocket in relation to the wheel sprocket should have a small effect on required chain length.  Imagine that the top run of chain is level (parallel to the ground) and the bottom run of chain has a certain angle upwards (let's say 30 degrees for example).  Now imagine if the motor with the front sprocket was mounted up higher than previously (maybe as a mod to put a fan underneath the motor to better cool it).  Then we would have the top run of chain angled up and the bottom run of chain angled up more than before.  The chain length requirement either must increase (maybe a fraction of a link in some cases), of if there is a chain tensioner, it must pad out more chain to make up for the increased angles.  I think what you meant is if the sprocket centers are not lined up horizontally, the chain length wont change significantly, especially on scooters that have chain tensioners that can adjust for this.  It would have to be a radical change in sprocket centers to effect the required chain length and actual link or two.

I will be attempting to install a 7 front and 55 rear sprocket on a Razor E-100, to drop the top speed from about 10 MPH (16 KMH) to about 6.6 MPH (10.5 KMH).  This is to allow it to run better on hard dirt which is my application.  It is also because some young kids want to ride it and I feel better if it tops out at a lower speed.  The front sprocket is D bore but I think the D is too small do I may have to get a machinist to bore it to the proper diameters.  However, someone makes this sprocket so it leads me to believe it should fit as is on some scooter motor.  I wonder what motor that is that already accepts a 7 tooth D bore sprocket and if that motor could be mounted on the Razor E-100, thus saving having to pay a machinist to modify the sprocket for use on my existing "stock" motor.  Anyone know what motor this sprocket fits on?  I don't have it yet so I do not know the exact measurements but when I get it I will post the diameters of the D bore so maybe someone can match it up with a motor.  Thanks.