Quick Sprocket math check

[RUNMEDOWN]

I have been going over sprockets for the current build, (Auto-x with 200e lower (11 tooth front sprocket - Hi/Low sub trans)) According to the online calculators a 35 tooth rear would be near the stock set up (Within 5%) with the 11t front, but dropping to an 18' rear tire would require an additional change in the rear sprocket. So doing the math it looks like the stock 12t/40t with 22' tire of the stock 84' ATC200x would be equal to an 11t/28.6t/18' tire. but I have never run a rear sprocket that small (28 tooth?). I found a place to make whatever I need but does this sound right? Or factoring in that I am a big guy (6'3" 265lbs) should I gear up a bit (I am running a 10.25:1 piston at 66mm bore with bassani pipe, better cam, and big carb)? Maybe a 35T rear or even a 30?

[Jmoozy27]

I would run 12/40 with 20' tires and if it was too tall you could easily switch to an 11 tooth front. I fought with the gearing on my super x for months before I decided to switch to 12/40 from 13/42 then 14/42 then 12/42 then eventually switched from 250r axle to 1st gen x axle with stock gearing. I'm currently running 22" knobbies and I am satisfied with the results. So I think 20" light tire with 12/40 gear should be legit. Another set of rims with 18" tires would give you more options as well.

[RUNMEDOWN]

I am stuck with the 11 tooth front due to the sub-transmition, and I am building with 18" tires so I have to go by those parameters. I will use you ratios factoring in the tire difference to quantify my estimates. Thank you for the info
OK so assuming:
NS = New Sprocket
OS = Old Sprocket
NT = New Tire
OT = Old Tire
to find the correct new sprocket for a tire size would be NS = OS x NT/OT
and 1" of tire has 5% of change on rotation/gearing; (close enough for the 22" to 18" ratio)

stock 200x 12/40 gearing = .3
Stock 200e 11/47 gearing = .234
then auto-x with 11 front and 36rear = .305 (Very close to stock 200x)
factor in 4" tire drop (22"o 18" or 20%)means 11/36 would be off 20%
1 tooth on the front (Which I cant change) = 8% change and is the equivalent of 3 tooth on the rear (That is the assumption I need to check)
than by removing 6 teeth from the rear (Starting at the 36 to keep ratios correct) I would need to be at 30.
That seem wrong to me, can anyone see where I made an error in my calculations?
Factor in my ass is fat and likes to drag on the sand as I ride. Leaves a nice trail, my wife can always find me.
Found this so I can get close, just need to factor in the tire size difference
226021

[DohcBikes]

I am stuck with the 11 tooth front due to the sub-transmition, and I am building with 18" tires so I have to go by those parameters. I will use you ratios factoring in the tire difference to quantify my estimates. Thank you for the info
OK so assuming:
NS = New Sprocket
OS = Old Sprocket
NT = New Tire
OT = Old Tire
to find the correct new sprocket for a tire size would be NS = OS x NT/OT
and 1" of tire has 5% of change on rotation/gearing; (close enough for the 22" to 18" ratio)

stock 200x 12/40 gearing = .3
Stock 200e 11/47 gearing = .234
then auto-x with 11 front and 36rear = .305 (Very close to stock 200x)
factor in 4" tire drop (22"o 18" or 20%)means 11/36 would be off 20%
1 tooth on the front (Which I cant change) = 8% change and is the equivalent of 3 tooth on the rear (That is the assumption I need to check)
than by removing 6 teeth from the rear (Starting at the 36 to keep ratios correct) I would need to be at 30.
That seem wrong to me, can anyone see where I made an error in my calculations?
Factor in my ass is fat and likes to drag on the sand as I ride. Leaves a nice trail, my wife can always find me.
Found this so I can get close, just need to factor in the tire size difference
226021


Why do you think you are stuck with 11 tooth? Why 18"s on a trail trike? 18"s are tiny, for flat trackers that don't need clearance or suspension performance.
http://m.ebay.com/itm/270984468004