Questions about choosing sprocket sizes/final drive ratios

[wcorey]

I've come to the point of needing to get a sprocket set for my 450 R/T street/cafe conversion project, hopefully the last significant expenditure until relative completion.
Going with 428 as 530 is way overkill with the strength of modern chains these days.

I have a couple considerations, the main one is of course what is best for how I want the bike to behave. Motor is pretty much stock, just bigger carb and straight through exhaust. I do mostly twisty back road riding, tend to be hard on the throttle and prefer lower than stock gearing on other bikes I own for the hard drive out of the corners and such. But also hate running out of rpm's on the high speed sections and having to keep it unnecessarily wound up on the sometimes long drones to get to the twisties. What's the good compromise? I've heard of people preferring tall gearing on the 450's to take advantage of the torque while keeping rpm's down a little for increased engine longevity (yes I know they don't like to be lugged) but also hear of 17/38 gearing which seems somewhat extreme at 2.33/1. What to believe? I also tend to choose higher performance/lower longevity but that's slowly changing as I get older...

My other consideration is a design one. I've done a mono-shock rear suspension and have quite a bit of adjustment range for the rear ride height. One result of increasing rear ride height is obviously increased swing arm angle to where the chain gets very close to the swing arm pivot. I will put in a delrin slider but would still like as much clearance here as possible, bigger sprockets would help considerably. I've corresponded a bit with Nigel Lacey and he suggests just starting with the standard 2.66 ratio for street 450's, which puts me at 18/48 in the largest available size front. Is there anything significant to avoiding odd/odd or even/even tooth numbers as to increased wear? I could go to 18/47 and don't feel like a .05 ratio increase is going to change things that noticeably anyway.

I realize gearing is very subjective and dependent on many factors but I need to make some kind of informed decision and don't look forward to buying multiples of sprockets to try out. What does everyone else run and are you happy with it?


Bill

[DewCatTea-Bob]

" I've come to the point of needing to get a sprocket set for my 450 R/T street/cafe conversion project, "

____ Now you've brought-up one of my top-three favorite DUKE-subjects -(sprocket gearing/gear-ratios) ! _ So I'm going to have quite a bit to add here !
__ First to start-out, the 450R/T came-stock with 50/12t-gearing -(4.17), which was fine for off-road hill-climbing and such but, not much use for anything else other than just quick traffic-light to traffic-light / stop&go in-town city-driving type riding (with little chance of venturing much outside of in-town type speed-limits).
__ At the other (factory stock) extreme, the 450-Mk3 models came-stock with 32/12t-gearing -(2.67), which makes (w-c) 1st-gear on the high-side for in-town city-driving, but a fairly-good compromise for also including travel between cities.
Considering that a 450's Primary-Ratio is 2.11, this sprocket-ratio provides overall-gearing that's just about as high as that of a (very highly geared) stock 250Mach1's (which employs 40/18t x 2.5-P.Ratio) ! _ So that's fairly high gearing for a 450 !
__ The 450-Scrambler came-stock with 36/12 or 35/12t-gearing -(3.0; 2.92), and provided a fair compromise for both city & country riding, but certainly made long-jaunts between cities a fairly unpleasant experience due to the 450's vibration at constant 5th.gear cruising-speeds !
To cure that unpleasantness, I have chosen 30/14t-gearing -(2.14), but that required me to make my own rear-sprocket (from a #520 30t blank) and the sprocket-carrier had to have a relief-space machined into it so that the chain's inner-side plates didn't contact & ride on it ! _ This TOP (as high as possible with the lager chain size) gearing is not at all what Bill is looking for but, I-myself found this very-high gearing quite enjoyable for city to city cruising !
With gearing so high as this however, the employed camshaft has to be taken into consideration!_ Cuz if low-end torque-output isn't sufficient, top-gear becomes pretty-much useless (without a tail-wind or downhill-run) ! _ I learned that lesson when I then switched from a stock-Scrambler cyl.head (with mild cam) to a DESMO-head (with wild cam) ! _ As not only was any acceleration at any speed not noteworthy in 5th-gear, but even maintaining any speed reached with 4th-gear, was quite difficult !
__ For more close to the gearing which Bill is seeking, I once needed to search for the optimum gearing for running my 450D through the (National-Trails) 1/4-mile racetrack...
I never did get my 1/4-mile sprocket-gearing dialed-in to the exact over-all gear-ratio best needed for reaching top-RPM in 5th-gear right-at the finish-line, but the closest I did come to that desired optimum was with 50/17-gearing -(2.94, with #428-chain), which got me up to just under 98-MPH at the marker-line's speed-check point. _ Top-speed with that gearing was about 103-MPH. _ (With a 51 or 52t sprocket, I probably could've gotten my ET down to under 14.4 & slightly closer to 100-MPH (but doubt that speed could've been reached by the speed-check point).
__ So for what Bill seems to be looking for is a sprocket-ratio most likely somewhere between 2.8 & 3.0, I'm guessing,, but more certainly likely not any much lower than 3.1 since it seems that he doesn't wish to find his toe pressing for the next/(top) gear, while already in 5th, (whenever taking-it-easy doing just country-road cruising type riding).


" Going with 428 as 530 is way overkill with the strength of modern chains these days. "

____ I hope then that '#428' chain has indeed come a heck-of-a-lot advanced in wear-resistance since the days when I tried Regina-std.428 on my 450 ! _ Cuz that brand-new length of 428-chain really stretched-out after being used just a few-hundred (well lubed) miles of hard-running ! _ And considering the hard type of riding which you intend to do, I'd then suggest that you consider #520 instead.
Otherwise, so as to prevent your 428-chain from premature stretching & screwing-up your new-sprockets,, you'll have to buy at least two new chains and rotate them (from one to the other) every 500-miles, so as to not allow your sprockets to get worn-up before they otherwise would be (with the use of just one, sooner stretched-out chain) !
__ And I believe std.520-chain is not much different in weight than HD428, or ExHD428. _ So just something to be considered (for a stronger 450) !
If you do chose #428, then you should definitely keep your drive-sprocket as large as possible -(17 or 18t), cuz smaller-radius chain-paths wear-out the chain faster (and also eat-up a bit more power/fuel) !


" But also hate running out of rpm's on the high speed sections and having to keep it unnecessarily wound up on the sometimes long drones to get to the twisties. "
What's the good compromise? "

____ I'm afraid that there really isn't a "good" compromise...
__ When I first heard of the 5-speed transmission (then coming-out), I of course hoped & expected that it would have it's 1st.gear a little lower than the 4-speed's 1st, and it's 5th.gear a little higher than the 4-speed's 4th/top-gear ! _ However I was MUCH disappointed when I learned that not only was top-gear still the exact-same ratio, but also the new 1st.gear was actually HIGHER than the 4-speed's 1st.gear !!
And to make that poor situation even worse, when the WideCase-transmission came-out, it's 1st.gear was made even HIGHER ! - (Making the difference between 1st & 2nd even closer still.) _ I accepted that closer-ratio trans for the Scrambler-model but, I've ever since been upset with Ducati for squeezing-down the transmission ratios for the road-going models, (instead of further spreading them, between 1st & 5th)) !
__ But now here's another thought that many cycle.riders/(bikers) often don't even realize to fully consider...
While it's common-sense that lower-gearing indeed provides faster acceleration, that's only really true of your Duke's 1st.gear for getting-off-the-line with ! _ Once going & under-way, (with your non-peaky/wide power-range engine), a lowered over-all gear-ratio doesn't notably make ya go-faster ! _ Rather, ya mainly more so just go through your available gearing at a faster rate, until you've run out of gears to shift to. _ Now for a relatively peaky multi-cylinder engine, ya can really make use of a 6-speed (or more) close-ratio trans, so as to keep the revs more stationary nearer the engine's narrower peak-power RPM,, but that's not quite so the case with a big single (with it's relatively wide power-range). _ Thus for the 450, ya ought to actually prefer relatively higher-gearing, as each gear will then last longer as it revs-upward, thus keeping ya in it's power-range for longer spans,, and with it's extra-wide power-range, shifting-up to the next higher gear doesn't lead to any really big loss of power-advantage, (unlike with a peaky multi.cylinder).
Many bike-riders of course will still think otherwise but, that's mostly because they can FEEL the acceleration somewhat easier (with lower gearing) cuz the revs climb-up towards the peak-power point a bit quicker,, however, that peak-power peak also comes to it's end equally quicker, thus overall (for instance), climbing from 40 to 60 MPH is not actually notably quicker with lower overall-gearing than with higher overall-gearing. - (That of course with number of gears & their individual/internal ratios remaining the same, as is the case with Duc.singles.)
Therefore when choosing gearing for your big-single, ya ought shoot to error (off from what would be actually most-perfect), towards too-high rather than towards too-low, for a final-ratio.


" I've heard of people preferring tall gearing on the 450's to take advantage of the torque while keeping rpm's down a little for increased engine longevity "

____ It's actually not so much the "torque" itself as it is the 'wide-range' in which it's significant at/within.
And I suspect it has more to do with comfort than "longevity".


" but also hear of 17/38 gearing which seems somewhat extreme at 2.33/1. "

____ That is definitely high for a Duke with the 2.11 Primary-ratio, so perhaps that gearing/ratio was actually in reference for a 250 (with 60/24t primary).


" I also tend to choose higher performance/lower longevity but that's slowly changing as I get older... "

____ Then I'd much suspect that when you've finally sold-off all but one of your bikes, (with the assumption that your left-leg stays as usable as your starter-button thumb), your last remaining one will then be your 450, with (then) extra-high gearing.


" bigger sprockets would help considerably. "

____ Yes, and that will also of course increase chain-life !


" I've corresponded a bit with Nigel Lacey and he suggests just starting with the standard 2.66 ratio for street 450's, "

____ I'm thinking that you'd fine that to be a bit too high.


" which puts me at 18/48 in the largest available size front. "

____ A #428 18t will cause a #HD428 (or heavier) chain to make partial-contact & consequential wear between the chain & the internal-casing's alloy chain-guard.


" Is there anything significant to avoiding odd/odd or even/even tooth numbers as to increased wear? "

____ Interesting notion (which I-myself have also wondered about before)...
I suppose that if both sprockets had an 'even' number of teeth (and assuming your chain has an even-number of links), that then if one link-roller or one tooth developed a flaw, it could constantly rematch-up & poke-at the very-same roller/tooth match-up, and thus many times sooner possibly develop into an issue of sorts,, but otherwise seems an insignificant concern (with perfect sprockets). _ (That's a similar happenstance to what would happen if the calender-year had only 364-days, as then Jan.1st would ALWAYS match-up with Saturday -[from this year onward] !)


DUKE-Cheers,
-Bob

[wcorey]

Well Bob, I’m glad I’ve given you an outlet to expound upon a favorite subject and greatly appreciate the time and effort. As it seems you’ve covered the subject so extensively, I hope it doesn’t keep others from chiming in with more basic responses such as, ‘I went up/down a tooth up front on mine and love/hate it because…’.

While I wasn’t really expecting it, I was hopeful that there would be some obvious answer, everyone uses either this one or that type of thing. Not that it's an apples to apples comparison but back when my 996 was a current model, most (who really rode the things) found the stock gearing too tall and went at minimum down one in front and often up a few in back. Never heard of any instance of going taller than stock. I first went down one in front, not enough, down two in back, still not enough, then anther two and it was just right. On the other hand when I converted my ATK605 from dirt to supermoto, I guesstimated a rear sprocket size and have been perfectly happy with it. Not sure if I was lucky or just not that picky on that bike. On all my old Triumph twins I was never completely happy with any ratio, used to set one up high and another low and choose which one to use depending on where I was going.

I seem to be a little unclear as to what ratios you would suggest. Just to clarify, you're saying 2.8 to 3.1 but lean toward the 2.8 (or a bit higher) if anything?


As for the 520 vs 428 debate, there does seem to be a general consensus in the singles community that a good 428 is plenty adequate for the 450’s, this from both racers and street riders. My 996 is also another basis I can use, it has been widely accepted for a long time now that 520 is fine for high output liter bikes. I’ve had an 8200lb tensile strength 520 chain on the 430lb, 130hp, 80ftlb, 996 for 20k mi and it’s still in good shape. While I’m sure there are other considerations beyond tensile strength, I believe the DID ER428NZ I have @ 5330lb tensile would be well within reason for the 450’s weight and power. I would guess that the original 530’s they came with were substantially less strong than that.

____ A #428 18t will cause a #HD428 (or heavier) chain to make partial-contact & consequential wear between the chain & the internal-casing's alloy chain-guard.

It could be that the newer chains have smaller outside dimensions, I’ve talked to a few people now who have used 18t extensively with no problem, Nigel said he once made up a 19t that barely fit but worked still. I hear if the chain goes excessively slack it can wear some grooves in the case but are relatively small and pose no real problem.

____ It's actually not so much the "torque" itself as it is the 'wide-range' in which it's significant at/within.

Torque would imply/be interchangeable with ‘wide range’ for most intents and purposes here…

____ I'm afraid that there really isn't a "good" compromise...

I often wondered why no one ever came out with a 6 speed where the first 5 were a nice close ratio and the 6th was a much taller ‘highway overdrive’ type gear. For that matter a ‘two speed’ rear hub would be even better in some ways. With the power available on the bigger bikes I guess it’s not all that needed, I recall a friend getting a new R1 a few years back and saying it would do 105mph in first gear.

____ Then I'd much suspect that when you've finally sold-off all but one of your bikes, (with the assumption that your left-leg stays as usable as your starter-button thumb), your last remaining one will then be your 450, with (then) extra-high gearing.

Odd as it would sound to some, I have at least a half doz bikes that I probably wouldn’t sell even if I couldn’t physically ride anymore. Assuming I don’t outlive them all, my friends will end up with them.



Bill

[DewCatTea-Bob]

" I seem to be a little unclear as to what ratios you would suggest. Just to clarify, you're saying 2.8 to 3.1 but lean toward the 2.8 (or a bit higher) if anything? "

____ Since you seemed like someone who likes lower gearing than myself, I left it up to you to choose to go as low as 3.1:1 but, I guess if you want to let me steer you towards an exact choice, then I suggest "50/18" (with 2nd-choice being 51/18), just like I have had on my own 450D. _ I had become content with that lower (than stock) gearing and left it that way since I then had my 750GT (with 32/16) for longer trips.


" As for the 520 vs 428 debate, there does seem to be a general consensus in the singles community that a good 428 is plenty adequate for the 450’s, this from both racers and street riders.
While I’m sure there are other considerations beyond tensile strength, I believe the DID ER428NZ I have @ 5330lb tensile would be well within reason for the 450’s weight and power. I would guess that the original 530’s they came with were substantially less strong than that. "

____ Strength ? _ I certainly never meant to imply that there may be any issue with the "strength" of any chain-size smaller than the stock #530, as I was always quite sure that even the weakest std.428-chain was up-to being 'strong' enough to handle any 450-DUKE's torque/power.
Rather, it's the 'size' of the parts which make-up the chain, that determines the rate of wear-down, thus allowing all the 'link-connections' to spread-apart and let the chain get "stretched-out" sooner,, (NOT the stretching of insufficiently-strong link-plates) !
And a so 'stretched-chain' is no-good for anything !
__ Larger sized chain has larger equivalent parts, which naturally hold-up relatively better against the forces which wear-out all the moving-parts.
So #428-chain is no-doubt certainly plenty strong enough, it just won't last as long, is-all !


" I’ve talked to a few people now who have used 18t extensively with no problem, Nigel said he once made up a 19t that barely fit but worked still. "

____ I'm doubting that it was always clear then that they all were only in reference to just the WideCase-motors, as the NarrowCase motor-cases indeed do-not have the same chain-clearance issue with such larger drive-sprockets !


" I hear if the chain goes excessively slack it can wear some grooves in the case but are relatively small and pose no real problem. "

____ Right, that's the issue I was referring to, but with a 18t & oversize #428-chain, it doesn't much matter if the slack is kept to a minimum, it still somehow comes into contact, (probably after a bit of 'stretch-wear').


" Torque would imply/be interchangeable with ‘wide range’ for most intents and purposes here… "

____ Perhaps so but, many also use the term -("torque") to specifically refer to
"low-end power" ! - Meaning how strong power-output is only below mid-range RPM.


" I often wondered why no one ever came out with a 6 speed where the first 5 were a nice close ratio and the 6th was a much taller ‘highway overdrive’ type gear. "

____ I sure agree ! _ I think that's what Ducati should've done when they had the possibility to do so when they created the w-c motor-cases which could accept such !
Anyhow, I believe Honda did indeed incorporate that great idea back in the '80s, for their then new V4 models.


" I have at least a half doz bikes that I probably wouldn’t sell even if I couldn’t physically ride anymore. "

____ That unfortunately happens to be my very own circumstances, for well over a decade now.


____ Come-on all you other 450-Dukers, PLEASE let us know what the sprocket-sizes are on YOUR 450, and also let Bill (& the rest of us) know how ya like your 450's resulting final-ratio, (or rather 'speed to RPM', if-you-will) !


Hopeful-Cheers,
-Bob



UPDATE !! - I was deeper-thinking about my old-great 450-days (back in the '70s), and recalled something which I had previously not correctly/fully recalled concerning a (incorrect)-fact stated within my previous-post above ! ...
And that error/oversight is that I had forgotten that for the 1/4-mile racetrack, I'd switch the 18t (which I'd otherwise always leave matched with the 50t), with a 17t drive-sprocket ! _ Otherwise all else I had stated was correct, and I've now corrected that error in my post !
Sorry about that !
DCT-B

[Rick]

I've found working back from what I want as a result is the best solution to gearing. For example, how fast do I want to be going at redline in top gear. I don't have technical info on a RT450, but using the narrowcase 250 specs will demonstrate what I do.
The primary- crankshaft/clutch- ration is 2.5/1 (24tooth/60tooth) and 5th gear is 1/0.988 (31tooth/30tooth)- 5th is a slight overdrive.
The Avon website gives a AM26 Roadrider 90/90/18" tire diameter as 619mm.
Calculating the rear wheel revolutions/mile and the crankshaft/transmission ration gives the 'fixed' values, then you calculate how chain sprocket rations affect the speed. So, if I put the RT450 12/50 sprockets on a bike with the 250 clutch and transmission ratios, 8000rpm at the crankshaft would give me 57.5mph, probably not what you want.
Trial and error is a terrible way to solve a problem, a few minutes with a calculator will save lots of time.
Someday I'll put this into a spreadsheet so I don't need to figure it out every time.

[machten]

Does this help?....

http://www.gearingcommander.com/

I know it doesnt have duc singles in the database, but you can enter your own data, save them and use them later. I can't vouch for the accuracy.

Kev

[Rick]

Certainly does, their calculator gives 57.6mph @8000rpm.
Thanks for the link.




Rick

[machten]

Glad it helped. It gives some good info. Reason for the accuracy disclainer is that the GT 750 database gearing is incorrect (from memory it was primary drive). I keep my own copy which I load up. The calcs all seem fine from what I've used it for. (but I still wish i had it in spreadsheet!!!)

Kev

[Rick]

Kev,
There are at least 2 different primary/clutch gear ratios in the GT750, but you probably knew that.
Rick

[machten]

Hi Rick,

I'm aware that there are two primary gearings on 750 roundcases that i know of. My understanding was the the lower gearing was used on the Sports and (i think) Green frames, the higher on GT's. I'm not aware of GT's having anything other than one designated primary drive gearing.

I have both a Sport and a GT. Right now I have the GT clutch drive in the Sport, used mostely for country riding - cruising at circa 100km/h at 4000rpm on 90 height Avons and 36 tooth sprocket whereas the GT which i use more for city riding would be about 5000rpm at 100km/h on 100 height tyres using the Sport's drive. The GT is using a 38 tooth sprocket. Quite a difference!

Kev