Final drive cogs

[pear0]

DSCF2168 (1024x684).jpg

I am finishing up my 250 narrow case project and am wondering if the 15 front and 45 rear sprockets are appropriate for a casual use road bike. I don't have a speedometer or tach on the bike yet else I could work it out for myself. Thanks, TomA

[DewCatTea-Bob]

[quote= pear0 ...
" I am wondering if the 15 front and 45 rear sprockets are appropriate for a casual use road bike. "

____ That exact-same gearing is what was stock for the 1972 '250 ROAD' model,, and considering the 'style' of your bike, it's about as 'low' of gearing as you'd probably ever wish to be stuck with.
That 3.0:1 gearing on a 250 falls into the range that I'd refer-to as (higher ranged)- 'scrambler-type gearing',, and is not-only well suited for riding within city-limits, but also fairly good for jaunts between outer-city suburb/districts (satellited around a master-city).
__ However for also making somewhat extended 'country-rides' straight between spread-apart master-cities, (where most riding hours are still spent within city-limits),, I'd then much recommend a 16-tooth drive-sprocket (in place of your 15t) !
__ Yet still, if your riding-time is more-or-less equally split between city-riding & country-riding,, then a 17t.drive-sprocket ought-to be favored ! - (That's 250Monza-gearing -[45/17].)
And if most of your riding-time is done on country-roads out between city-limits, then you'd probably prefer a 18t.drive-sprocket. - (That's 250GT-gearing -[45/18].)
And if most-ALL of your riding-time is spent on rather long-term freeway-riding, then you'd no-doubt appreciate combining the 18t.sprocket with a 40~43t rear-sprocket ! - (That's 250Mark-3/Mark-III gearing.)
__ Conversely, if you intend to spend a slight-majority of your riding-time off-road,, you may then wish to consider rather installing 14t and/or 50t sprockets. - ([45/14 or 50/15]- That's mid-ranged 'scrambler-gearing', [as 50/14 is actual Scrambler-gearing].)
Or if rather a vast-majority & most-often spent off-road, then consider 55~60/14t sprockets. - (That's Motocross-gearing.)
____ If I-myself had been in-charge at Ducati during the time back when the 4-speed transmission was to-be replaced with a 5-speeder, I then would've had the 5-speed version designed rather with a WIDER-range of gear-ratios instead of the factory-chosen narrower*range that Ducati ended-up going with !!
(* Yes that's actually true,, the 4-speeder actually had a greater-difference between it's bottom & top gear-ratios, than does the 5-speeder !)
__ The 4-speed trans.ratios were set-apart reasonably enough, so I probably would've rather simply had the new 5th.gear-ratio set around 10% higher than the 4-speeder's top-gear. _ That way, ya then wouldn't have-to be torn-between decision-compromise of choosing sprocket-gearing that's mainly-optimized for either city-riding OR country-riding.
__ I believe that Ducati compromised their finally-chosen 5-speed transmission so as to be more suitable for their Scrambler-models (which more-so required a narrower-spread close-ratio transmission-set).


DUCATIly,
DCT-Bob

[pear0]

Thanks Bob that is exactly the kind of information I was seeking. I live in Montana and the bike is a 4 speed that was a scrambler. I will start looking for a taller ratio. Tom

[DewCatTea-Bob]

[quote= pear0 ...
" Thanks Bob that is exactly the kind of information I was seeking. "

____ You're welcome Tom !
__ Gearing is my third favorite subject on Duke-singles, and I might as well spread-out my experience, since I've had DUKEs of my-own geared with all those vary-same sprocket-ratios (and many other sprocket-combos as well !).



" the bike is a 4 speed that was a scrambler. "

____ Oh, I had just assumed it was a 5-speeder. _ PRETTY-nice conversion you've done to it !!
__ While ya can get-away with referring to it's past incarnation as a 'scrambler-type' of motorcycle,, Ducati had originally 'named' those off-road 250-models as the 'Motocross' version, (and all the Motocross-models are significantly different than Ducati's 1966 & newer 'Scrambler' models !).
It's transmission-ratios are the same as all the other 4-speed on-road/OHC.models,, and-so to get the gear-spread seemingly rather closer together, the Motocross-models were given lower sprocket-gearing of 55/14t, (which I deem to be at the very-bottom of the scrambler-type gearing-range, and quite close to being what I'd refer-to as 'off-road' gearing).
____ Now that I realize that your custom-Duke was a Motocross-model, I've become quite curious as to how you've altered the electrical-system to provide a more reasonable brake-light setup ! _ Or do you still have everything as stock, in that regard ?



" I will start looking for a taller ratio. "

____ Which sprocket-combo have you been most considering thus far ?
Since you're fortunate enough to have the 4-speed trans.version (with it's lower internal 1st.gear),, you thusly could still rather easily manage to get-by even during extended down-town/stop&go city-riding, whilst using even the highest sprocket-combo of 40/18t ! _ (So I'm thinking I'd suggest the 250GT-gearing -[45/18t] for you.)
__ I still have a large selection of new & used drive-sprockets, so if you inform me of what the lowest price you fine is, I'll then see about undercutting it for you.


Duke-Cheers,
-Bob

[pear0]

Brake light is still under development. I would like to use one of those inertia switches. but so far they come with a big ugly plate frame.
The bike came with a case protector that I will have to remove to put in a 17 or 18 sprocket. Which would be no problem.
I have a powerdynamo magneto generator but I did put a small battery in the system. I have found a 17 at Bevel heaven for $49 + which is a bit high me thinks.
Here is a link to a "before " picture. Tom


http://pic80.picturetrail.com:80/VOL212 ... 248666.jpg

[graeme]

Tom, you need to put a warning on the before picture.
I wish I could "un-see" the picture.

Graeme

[motoital]

Hello Tom, Nice bike you have there it looks clean and tidy. I do have a question for you thou. Did you use a different frame in the end? The before frame looks like a m1/m3 frame. It has the tool boxes for the Diana's. scramblers didn't have those other than the 200 motocross I think. I don't think that those had a horn mount thou. Your after photo is clean of all those. Did you shave your frame up? A lot of people assume it's a scr if it has case savers but I've seen road bikes with those too. I usually look at the intake port on the head.

[pear0]

Yes , Since it was not a restoration I took lots off the frame. Same frame as the before picture. Sold the tool boxes -- they bring good money for other goodies.

[Winter]

Fascinating stuff.

And if most-ALL of your riding-time is spent on rather long-term freeway-riding, then you'd no-doubt appreciate combining the 18t.sprocket with a 40~43t rear-sprocket ! - (That's 250Mark-3/Mark-III gearing.)

This begs the question: __And if most-ALL of my riding is going to be on a very long straight covered in salt in Utah running a stock 160, ......

I'll have to change the chain to a 428 since it looks not much more than a large bicycle chain...

Cheers,
Andrew