Need Help on 900ss suspension set up - Ducati.ms - The Ultimate Ducati Forum
 
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post #1 of 5 (permalink) Old Dec 10th, 2018, 4:52 pm Thread Starter
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Need Help on 900ss suspension set up

I have a 900ss fe that was stolen and returned to me in truly scriptable condition, but the main frame seemed straight so it became a project bike. I cut off the rear of the frame and put on mounts for a 916 subframe.

Among a lot of stuff I put on an a new Ohlins TTX shock (upside down from a 2007 GSXR) had Ohlines valve it appropriately. I put 916 Tin forks sprung for my weight into IMA triples with adjustable offset.

Any info on the following as well as additional advice would be appreciated:

Shock length
Swing arm angle
fork protrusion above triple
steering head angle

Need to get closer, doesn't feel planted.

Thanks, Michael
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post #2 of 5 (permalink) Old Dec 10th, 2018, 8:11 pm
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Madness, not saying you can't get it work but it is already off the books.

Find the rake and trail you like best (on any bike but look for one that has a very close wheelbase distance to your bike -1410mm on most 900SS). Then look at the stock numbers for that bike and measure your bike to see how far off you are now from those sets of numbers with these alien parts.

If I told you 2.54 mm fork protrusion, Rake at 25 degrees with 104mm trail - is great for the street but not "twitchy enough" for the track, would that help? Those numbers are stock, and none of your parts were designed for those numbers, so,...

I have nothing to offer on the rear shock because there are too many variables but I don't see why you could not eventually dial it in though with some track time and careful measurements.

Start with the front setting your rake and trail to the numbers you prefer then get your sag height set properly on both ends and go riding. Beware different tires have a dramatic effect on what you are trying to do - especially if you go to race slicks so have that settled as a constant before you go changing stuff.

When you dial it in, don't be surprised it turns out to be like Jed Clampett's rifle from the Beverly Hillbillys - only you can shoot straight with it!

1991 900SS
1995 900SS SP #746

Last edited by RockAZ; Dec 10th, 2018 at 8:47 pm.
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post #3 of 5 (permalink) Old Dec 11th, 2018, 11:10 am
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Itís like pulling a live sharks teeth to get any constructive Input on a stock motorcycle, much less the version youíve come up with. Fellow Ducati riders will all start spouting gibberish about the mysterious setup of your suspension. I never had a motorcycle with adjustable suspension before buying a Ducati. Let me try to help. Try to set your new forks up like the originals as far as length from triple to axle. Set the damping to the base settings for the forks, not the bike. Measure the rear height vs stock and try to set it as close to stock height as you can with the adjustment available. Set rear damping to the recommendations of the bike it came from. That at least gives a starting point. Not a chance it will be close, but closer than you have now.

'96 Ducati SS900CR, '07 S4RS, '06 Busa, '77 Bonny,
'00 Superglide, '85 Sportster, '78 SR500
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post #4 of 5 (permalink) Old Dec 11th, 2018, 11:48 am
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Good info .

Any time you start making major modifications you end up somewhat on your own, your experiences becomes your data to determine if you are heading in the correct direction. Knowing where you are starting from is invaluable as you cannot make good choices of where to go if you do not know where you have been. Is your modified bike better than the bike not modified? what modifications did you make that made it better or worse and what did the change improve or degrade.

Lets take a few of your questions.

Quote:
Shock length
start with stock length and then you will modify length to get a swingarm angle or seat height you desire. You never mentioned what you were trying to do with the bike so a better result might be different then say I would be looking for based on the purpose of the bike.

Quote:
fork protrusion above triple
The stock forks are different length so you do not care so much about how much is above as much as how much as below when using different length forks. Again start with the axle center to tree distance of a properly set up fork. Different fork setup will give different results and you need to start with both forks being set up (race sag) first.

Quote:
steering head angle
Set again by everything else you do so be sure to pick your pieces carefully and it is easiest to start with oem settings.

Quote:
Need to get closer, doesn't feel planted.
You need to start by measuring what you have and then comparing it to known good units and then we might be able to help point you in some directions to improve what you have. Otherwise your best result will be getting the bike to a shop that specializes in building/modifying to get a better idea of what you are starting with and almost more importantly what you are looking for.
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post #5 of 5 (permalink) Old Dec 11th, 2018, 4:06 pm
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I have no idea what swing arm angle you ended up with, but while youíre looking at that pay attention to the change in chain free play through the arc of normal operation. You may need to change chain adjustment to assure you have proper slack as the swing arm moves. You also need to make sure the chain wonít grind the swing arm. Easier done with no shock installed, once you measure the arc.

'96 Ducati SS900CR, '07 S4RS, '06 Busa, '77 Bonny,
'00 Superglide, '85 Sportster, '78 SR500
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