Gear ratios etc

[tzsteve]

Im looking at lowering my top gear a touch & spotted a 48 tooth BGM gear , the dealer says i can use this with a standard tree this does not sound right to me
Any info would be helpful im currently running 22/47 from a 3 speed box modded to fit my 4 speed set up, not the 22/46 that is standard

[henri]

not seen a 48 tooth 4th , have used the 47 one with a standard tree ,i'll go have a nose ,what sites it on .H

[henri]

only 48 tooth i'm findings falc ,not much info on it either ,https://www.10pollici.com/en/homepage/classic-vespa/engine/gear-cogs/smallframe/4th-gear-48-teeth-falc-racing-for-4th-gear-z-19-20-vespa-50-90-125-et3-primavera-pk.2.1.111.gp.4629.uw , seems to be to go with the falc ultra short 4th tree .i know the crimaz 49 tooth can only go with the crimaz tree .H

[henri]

found the bgm 48 on scooter centre , according to them its combatible with a stock tree 22 tooth 4th gear on the tree .H

[tzsteve]

Thanks for the info folks much apreciated

[tzsteve]

henri thanks for the link to 10pollici.com i never know that there was such an array of gears to choose from looks like i will be buying from them

[henri]

Mar 29, 2022 9:17:05 GMT tzsteve said:

henri thanks for the link to 10pollici.com i never know that there was such an array of gears to choose from looks like i will be buying from them

10 pollici use to be my go to italian shop , mateo who runs it has a mutual friend , max on here . but post brexit his postage has a extra 50 euros customs handling charge ,use to be 29 euros now 79 euros . bit of a deal killer unless 2-3 group order an split postage between them .H

[jonnysnatchsniffer]

ive got a gear calculator on a hard drive somewhere that wayne miller made, it has lots and lots of variables, with drt gearsets, zirri and some others, it also has different tyre sizes, its pretty fucking good, you can see what the gearing will do with various changes and has a side by side jibbyjabba so you can view what you have then put in what you want, its handy as you see the gear overlap and will see that the gaps between gears will fall into the power when you change up, pm me yr email and ill send it to you

maybe one of the mods on here could do the same and put it in a sticky on the technical page

there are a few 1st gears that are taller, however i done things a bit different in that i used a 29/68 primary instead of the 27/69 that seem popular, i done this to give the clutch an slightly easier life, this with the drt F1 tree and 300x10 tyre make my final ratio the same as a standard prim/et3/pk 125 but with the benefit of a short 3rd and extra short 4th
it also raises the 1st gear

[tzsteve]

Thanks for the info,
I keep seeing links to waynes info but it always shows up as a dead link
Looks like ill be using the 28/69. With a tree going 10,14,16 18. And a 48 tooth on Fourth, im not racing or sprinting and the engine peaks at about 8000 so that should give me a true 60 in any condition . ( i think thats about 75 on the speedo)
I dont need to be doing much more around town , but getting to 60 rapidly will be ok the motor puts out 17 bhp so that will be enough ponies to do the job,
This will leave my modded box with the welded 22 and machined down 47 from a 3 speed box at 2% lower than standard waiting for a new motor, its nice in a low tune but not really what i want.

[jonnysnatchsniffer]

sent me yr email and ill send you the calculator, no link its exell, well done too

[tzsteve]

Hero mate

[tzsteve]

So i settled on 29/69. Pimaries 10,14,18,20 tree and a 48 fourth. At 8750 rpm (peak power is at this) i should get 60 in 3rd & 70 in 4th i guess my motor should pull that gearing ok

Postage and import was a killer

The gearing i had was just too high in 4th i had 29/69 with a near standard box great in the first three but never getting in to the power in 4th. I would have needed about 25 to 30 ponies to pull that gearing

[tzsteve]

Finally got the gearing as it should be,
now if im at 40 in third i can pop it into top and be in the power and able to accelerate at a reasonable rate.
Again henri thanks for the link.
And a thanks to mr. jonnysnatchsniffer for the info