I'm a Vespa passionate. I love the geared ones mostly. Well... I have to admit that the new automatic (the GTS - LX is too small for me) are starting to get in my system like a season virus. But, enough of CVT!
I'm planing a overhaul to my old (original) PX engine. Along with the new top-end a new primary gearing is key to get the most welcome elasticity - hopefully - to the expected broader (and torquier) powerband.
To get an idea were the new gear relation would take me I've put together an excel file to find out which transmission is better to suit my needs...
Of course, one can't just throw any combination and expect it to work.
The longer relation needs a powerhouse that matches the additional torque required to roll at all regimes. I have to leave that "study" to whoever dare to dive in to this as each one as different needs, different spectations and - of course - different budgets...
You can download the excel file HERE.
It's 'protected', sort of. I would leave it that way.
This is not rocket science, I know, and can be done with minimum knowledge of excel and math but for those who don't want to bother and just play with the numbers here it is for you.
You just have to choose the primary relation and the tire perimeter (the speed depends on both). Then, just look for your model standard gearbox fixed ratios and see the speed you get at the listed engine RPM. Simple.
Hopefully, this will help you to decide where to put your money to get the desired speed. If you want more (which I discourage on 10" wheels) you only have two choices (can be combined):
- build a torquier engine (big bore top-end, bigger carb, new exhaust) and get a longer primary gear;
- build a screamer to take the RPM higher;
(or a compromise between these two)
Also, remember the pick two out of these three rule:
- cheap
- fast
- reliable
I hope this can be helpful to someone. Let me know if you find any error...
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