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219 vs 35 for gear ratios
What actually decides lap time is whether the engine is in the right part of the powerband at the road speeds that matter. That is a tooth-count ratio problem. Pitch does not belong in that calculation.
The usual mistake is trying to clone a 35 pair onto 219. A 219 setup that shares the same numerical ratio still has different sprocket diameters and a lighter chain, so it does not necessarily pull the same way. When you switch, do you take the nearest 219 combination that hits the calculated ratio, or do you expect to run it slightly different for that reason?
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nearest ratio first then treat it like a new setup not a clone
16/56 on 35 is 3.50. on 219 thats 15/53 (3.53) or 15/52 (3.47). start there. dont go looking for a 16/56 in 219 just cuz the numbers look the same
pitch doesnt go in the ratio math. rear divided by front is still the ratio. what changes is the parts around it
a 219 15t is way smaller than a 35 16t. the rear that keeps 3.5 is smaller too and the chain is lighter. same number on paper, less spinning weight, wont pull the same even if the calc says 3.50
if your trying to keep the same size driver you had on 35 you add teeth on the 219 front. thats clearance / wrap, not hitting 3.5
what i do
1. pick the 219 pair that lands on the old ratio
2. keep half tooth gears around that so you can move a little
3. check chain line and the clutch, smaller 219 driver changes how it loads
4. watch the watch and exit rpm. falls on the straight go taller, wont come off the corner go shorter
expect to live a tooth either side of the old number. thats normal. mistake is forcing the old 16/56 onto 219 and calling it the same kart
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The quantity that actually sets engine rpm against axle rpm is the pitch-diameter ratio, not the tooth-count quotient. A sprocket's pitch diameter is P / sin(180°/N), so the reduction is sin(180°/N_drive) / sin(180°/N_axle), which sits close to N_axle / N_drive and diverges more when either sprocket is small. Chain pitch P cancels, which means a given pair of tooth counts has the same kinematic ratio on #219 as on #35. Pairs that only share the same N_axle / N_drive still differ slightly because the sine term depends on the absolute counts.
When you switch, choose the #219 pair with the nearest pitch-diameter ratio rather than the nearest tooth-count ratio. Chain mass can change inertia and losses enough to affect acceleration, but it does not change how road speed maps to engine rpm.
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