Best gearing for '78 900SS w/ 40PHM's with stock rims/tires?

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hulagun
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Best gearing for '78 900SS w/ 40PHM's with stock rims/tires?

Post by hulagun » Sat Apr 03, 2004 11:54 am

I'm getting ready to install a new chain and sprockets, and want to make sure my bike is geared right. I use it for street riding with occasional track forays. It has 15/36 right now (same as stock) and seems fine as-is. I might try a 38 rear for a little more grunt around the hills of SF (not that it needs it).

What are others (with similar bikes and riding styles) running for sprocket gearing?
ivan thelin
san francisco
1954 MV Agusta 175 Sport
1967 Motobi 125 Sport
1975 Ducati 750 GT
1978 Ducati 900 SS

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BevHevSteve
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gearing on my bike

Post by BevHevSteve » Sun Apr 04, 2004 4:32 pm

Hey Ivan,

I run 16/39 which I think is PERFECT, we ride similar on the same roads... I would recommend the same for you. I would go to a 16 for less sharp chain wrap so your chain will last longer, also I KNOW you have room for the 16 tooth and an Xring, I run the DID ERV 530 on mine. I think it would be a mistake to go with a 15/38. I feel like any larger on the rear on my bike and i would have to limit any freeway jaunts to slow lane travel..... We are running pretty high revvs at 70 MPH as it is. Check out the gear chart below.

15/36 = 2.40
15/38 = 2.53
16/39 = 2.44
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Bob Hartmann
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Post by Bob Hartmann » Wed Apr 21, 2004 8:52 am

I'm going to do this from memory, but I think 15/38 was stock, (although the factory manual gave two different combinations - that didn't add up to the same ratio - as stock). My '78 SS arrived with 16/35 when I bought it 12 years ago - which was so long I don't think 5th gear ever got used below 80mph.

The MHRs of the day were geared 'longer' than SS's in an attempt at higher top speeds. Together with a bit more weight from the fiberglass they must have been relatively sluggish around town.

Never mind. I'm now on 16/38, which is terrific. Agree about the larger front sprocket. The bike's very, very happy with this setup. It suits the long-legged nature of the motor while allowing a good amount of pickup. For my taste, anything shorter really would be aiming at short-distance acceleration.

Only engine performance mods, btw, are VeeTwo cams - halfway between stock and Imola. Smooth across the range.

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Robert Hartmann
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Nico Georgeoglou
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best gearing for '78 900SS w/40 PHM, stock rim/tires.

Post by Nico Georgeoglou » Thu Apr 22, 2004 4:55 am

Hi Robert,

You are right that MHR were longer geared than 40 PHM 900SS, but the main reason that Ducati decided so, were the ever stricter legislations of the times towards noise reduction. In fact SS derived 900 MHR were slower in acceleration terms than 900SS exactly because they were overgeared. What you were missing from overgearing, you were gaining from more effective aerodynamics at higher speeds though. The horsepower was adequate to have all this huge frontal fairing surface able to penetrate the air at fair speeds and I can still see on my '83 example 200 kph. However the engine noise reverberating in the inner fairing surfaces is almost unbearable even under a modern full face helmet. For long highway hauls you need earplugs, even more so if you keep your head low, half protected behind the windscreen. With standard gearing you need to wound the 900MHR engine over 5000 rpm in order not to feel that you are riding below torque. But between 5000 and 7000 rpm in 5th, the bike keeps a nice stamina and is heading like an arrow. MHR is also much more comfortable at these speeds thanks to this heavy full fairing as you say. 900SS might be accelerating faster, but you fight to stay on the bike at higher speeds.

Ride safely

Nico

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