Rear Suspension Measurement: Fully Suspended? - Ducati Supersport 939 Forum
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post #1 of 25 (permalink) Old 10-29-2017, 12:33 AM Thread Starter
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Rear Suspension Measurement: Fully Suspended?

I'm in the process of tuning my suspension. I have a T-Rex triple tree stand that works perfectly to fully suspend the front (the pin size in the steering head is 27mm for anyone interested).

I have a trick to suspend the rear that involves reversing the pegs and (using my rear stand) lowering the bike pegs onto stands (see picture below of my Yamaha FZ-09).

But I thought that if someone else had measured the rear fully suspended, they could tell me the measurement (and where they measured to and from), and that would be close enough to save me the trouble.

So has anyone measured their rear fully suspended on an S model (with Ohlins shock)?

Thanks!

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post #2 of 25 (permalink) Old 10-29-2017, 01:55 AM
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sorry mate just looked through my paperwork and can't find where I wrote down the measurments. I have always tilted and balanced the bike on the kick stand and done it that way. Just quicker and easier but you do need someone to measure.
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post #3 of 25 (permalink) Old 10-29-2017, 01:16 PM Thread Starter
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sorry mate just looked through my paperwork and can't find where I wrote down the measurments. I have always tilted and balanced the bike on the kick stand and done it that way. Just quicker and easier but you do need someone to measure.
Thanks, Rhino! I hadn't thought of that kickstand trick.

I think that will do until I get motivated to reverse the pegs. It looks to be a little easier with Ducati, as the pegs have a cotter key. The Yamaha pins had to be drilled out and replaced.

I'm still interested in what others have measured, if anyone has done so.
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post #4 of 25 (permalink) Old 10-29-2017, 01:52 PM
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Just a word of caution, here. I’ve read reports where the mounting point on Ducati’s kickstand is sometimes in a thin area and an outright tear or bend is possible. Maybe not on our model, but on others, so the possibility is there. Just be coutious. The kickstand is not intended to support the full weight of the bike.
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post #5 of 25 (permalink) Old 10-29-2017, 03:23 PM Thread Starter
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The kickstand is not intended to support the full weight of the bike.
Good point.

I just tipped her up and measured with no incident. Don't want to tempt fate so will perform future measurements with stands under the pegs. Briefly tipping over on the side stand and then down gave me some idea of the suspended-to-ground compression, but since the bike's at nearly 45 degrees it's not accurate.

In stock form, it looks as if my front spring preload was a little low and the rear a little high. So too stiff at the rear and too loose at the front. I'm 175lb and 190lb with gear (I measure with gear).

I have the front down to 40mm, which is closer to where I want it. I usually go a bit firmer. But I'll ride it at 40 to see how I like it. 46mm to 40mm took only 1/2 turn, tightening the preload nut.

If I keep the front at 40, I'll set the rear at 44. That's around 30% of wheel travel.

The good news is that I won't need firmer springs. That's a pleasant surprise given that it's supposedly set up for a 145lb (65kg) rider.
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post #6 of 25 (permalink) Old 10-29-2017, 05:24 PM
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Originally Posted by Alley Oop View Post
Good point.

I just tipped her up and measured with no incident. Don't want to tempt fate so will perform future measurements with stands under the pegs. Briefly tipping over on the side stand and then down gave me some idea of the suspended-to-ground compression, but since the bike's at nearly 45 degrees it's not accurate.

In stock form, it looks as if my front spring preload was a little low and the rear a little high. So too stiff at the rear and too loose at the front. I'm 175lb and 190lb with gear (I measure with gear).

I have the front down to 40mm, which is closer to where I want it. I usually go a bit firmer. But I'll ride it at 40 to see how I like it. 46mm to 40mm took only 1/2 turn, tightening the preload nut.

If I keep the front at 40, I'll set the rear at 44. That's around 30% of wheel travel.

The good news is that I won't need firmer springs. That's a pleasant surprise given that it's supposedly set up for a 145lb (65kg) rider.
Yip when I set my suspension I found the same the front was low and the back was high. I sent quite some time going through the setup to suit me. (the whole journey is posted on here somewhere) in short I 1st levelled the bike front and back and it was Awesome till I started powering out of bends and then found that the bike rear was dipping and the front was lifting too much (making it unstable and slower as I was having to hold off the power to keep the front wheel on the ground) so ended up with settling for the front slightly lower in the front so she levels out on acceleration and now its perfect. Looks like you have it under control though.
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post #7 of 25 (permalink) Old 10-29-2017, 05:26 PM
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Originally Posted by se7en View Post
Just a word of caution, here. Iíve read reports where the mounting point on Ducatiís kickstand is sometimes in a thin area and an outright tear or bend is possible. Maybe not on our model, but on others, so the possibility is there. Just be coutious. The kickstand is not intended to support the full weight of the bike.
Good Point. I would defiantly not try and twist the bike with this mounting point.
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post #8 of 25 (permalink) Old 10-29-2017, 07:54 PM Thread Starter
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I can't edit my post anymore so want to add here that--after my preload addition (1/2 turn--I'm at 50mm front ride height not 40mm. So I must have botched a measurement. That means the 6mm per half turn may not be accurate.

Going to make another round of adjustments and measurements then report back.

Okay just did a full turn in (more preload) and only got 2mm less sag (manual says one turn gives 1mm).

So I went from 50mm to 48mm front sag. I'm not sure I have enough turns to get to 40mm.


Quote:
Originally Posted by Alley Oop View Post
Good point.

I just tipped her up and measured with no incident. Don't want to tempt fate so will perform future measurements with stands under the pegs. Briefly tipping over on the side stand and then down gave me some idea of the suspended-to-ground compression, but since the bike's at nearly 45 degrees it's not accurate.

In stock form, it looks as if my front spring preload was a little low and the rear a little high. So too stiff at the rear and too loose at the front. I'm 175lb and 190lb with gear (I measure with gear).

I have the front down to 40mm, which is closer to where I want it. I usually go a bit firmer. But I'll ride it at 40 to see how I like it. 46mm to 40mm took only 1/2 turn, tightening the preload nut.

If I keep the front at 40, I'll set the rear at 44. That's around 30% of wheel travel.

The good news is that I won't need firmer springs. That's a pleasant surprise given that it's supposedly set up for a 145lb (65kg) rider.
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post #9 of 25 (permalink) Old 10-29-2017, 08:55 PM
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Originally Posted by Alley Oop View Post
In stock form, it looks as if my front spring preload was a little low and the rear a little high. So too stiff at the rear and too loose at the front. I'm 175lb and 190lb with gear (I measure with gear).

I have the front down to 40mm, which is closer to where I want it. I usually go a bit firmer. But I'll ride it at 40 to see how I like it. 46mm to 40mm took only 1/2 turn, tightening the preload nut.

If I keep the front at 40, I'll set the rear at 44. That's around 30% of wheel travel.

The good news is that I won't need firmer springs. That's a pleasant surprise given that it's supposedly set up for a 145lb (65kg) rider.
Couple points, purely to help.....

Maybe just your terminology but preload (for all practical purposes) has no effect on the 'stiffness, firmness' of the fork or shock springs in a motorcycle. It only affects ride height, nothing else. Probably THE most misunderstood suspension adjustment on a motorcycle. So misunderstood even manufacturers often get it wrong in their Owners Manuals. The description of its purpose in your supersport Owners Manual is technical correct, but vague. It just says preload should be adjusted for load. That is correct, to maintain the appropriate ride height, depending on the load.

As long as the preload adjusters have sufficient range, a correct rider sag (weight of bike and rider) can be set with any spring weight. The spring weight may not be ideal, but a spot on rider sag can still be set. To help understand this point, you could set a correct rider sag with an appropriate length block of timber substituted for the spring. But the spring weigh of the block of timber is clearly unlikely to be ideal.

The usual 'rule of thumb' to evaluate spring rates is to compare the relationship between 'rider sag' and 'free sag' (amount the suspension compresses from fully extended just by the weight of the bike alone). If you have set a correct rider sag on an incorrect spring weigh, it will show up in the 'free sag' measurement. For example our extreme stiff spring, the block of wood, the 'free sag' will be excessive (being the exact same measurement as 'rider sag').
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Last edited by John; 10-29-2017 at 09:05 PM.
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post #10 of 25 (permalink) Old 10-30-2017, 02:38 AM
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To get rear fully unloaded, I ended up putting the bike on a baxley wheel chock and used a ladder and strapped the rear subframe with a ratchet strap (sorry no pics) and lifted the bike, while using a pit bull rear stand to keep it from wobbling.

I used tape (on the cowl) as a reference point and measured straight up from the axle. I got 582 mm free and 533 mm compressed (with me on board). I'm 170# with full gear. My rider sag was 49mm. Static sag was 23mm. Per the manual, total rear travel is 144mm. So I basically have 34% travel, same as with my fronts. I never needed to adjust the jam nuts .
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