Rear Shock Air Pressure - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 14 (permalink) Old 05-03-2017, 09:42 AM Thread Starter
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Rear Shock Air Pressure

What sort of pressure shot be put in the rear shocks? I'd like it a bit firmer solo and definitely needs to be harder with a pillion to stop the mainstand grounding.

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post #2 of 14 (permalink) Old 05-03-2017, 10:32 AM
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The manual shows 0-43 psi.

Zero, or "atmospheric pressure for one rider of average build".

Add air with the bike on the centerstand.

The damper settings also increase firmness. I find the damper setting I like, then add air if needed. Think I settled on damper 3 and 8 psi, but would need to check to be sure. I never have a passenger.
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post #3 of 14 (permalink) Old 05-03-2017, 11:31 AM
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somewhere on this forum is a long thread with lots of opinions about this subject. I believe the most popular idea was about 10% of the normal operating weight, with out going over the 43psi limit. So, if you are 200# then you would put 20psi in it and have your dampers set to 2. Then if you had a passenger you would adjust your dampers to 4.

that's what i remember anyway. Of course this was suggested as a good starting point and you should adjust settings based on your preferences.
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post #4 of 14 (permalink) Old 05-03-2017, 12:35 PM
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Yes I wrote that and it was based on a conversation I had way back with a tech rep from Koni shocks. They were working on air assisted shocks...(not sure if they ever went to market) I asked how could one figure out how much air to put in, and they told me they found, through testing, that using a ten percent figure of the riders total weight in psi worked well. They only were testing with one rider, but said if you have a passenger or luggage to add that in too.

So if you weigh 210 pounds, you should add 21psi to each shock. Caution should be used filling the shocks, as the volume of each shock is so small it's very easy to overfill them. A hand pump is suggested over a hose from a gas station compresser. Also, many fittings lose air disconnecting them from the shock, so you might need to add a few pounds over to compensate for the loss.

The shocks on the Vulcan have no preload setting, and the dampening adjustment does little. If you can, replacing them with aftermarket items is definitely a good idea,especially if you are an "aggressive" rider.

(As well as adding Progressive fork springs and a fork brace.....)
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post #5 of 14 (permalink) Old 05-03-2017, 12:52 PM
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Quote:
Originally Posted by Knifemaker View Post
... the dampening adjustment does little. ......)
Actually, the dampening setting does a lot. I can back off one click and have the shocks bottom out on certain bumps. Go all the way to 5 and the rear is pretty dang stiff.

Now, if the air pressure is really high, one may not see as much change, but the dampening settings do change how the shock works by a noticeable amount.

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post #6 of 14 (permalink) Old 05-03-2017, 10:46 PM
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I like a firm feel, and ride with a passenger almost every weekend (our combined weight is a little over 400lbs). I've got the damping on 4 and keep the pressure about 35psi. Nice firm feel riding solo, and little to no bottoming out riding 2-up.

Knifemaker is dead on about the small volume of air in the shocks. I use a foot pump and go to 45psi (less than one full stroke of the pump), after disconnecting the fitting and checking with a pen-style gauge they are usually between 35-40psi. I've actually found that if I keep checking them, each use of the pen gauge will drop the pressure by 3-4psi - the volume of air is really that small...
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post #7 of 14 (permalink) Old 05-04-2017, 12:20 PM
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Quote:
Originally Posted by Spockster View Post
Actually, the dampening setting does a lot. I can back off one click and have the shocks bottom out on certain bumps. Go all the way to 5 and the rear is pretty dang stiff.

Now, if the air pressure is really high, one may not see as much change, but the dampening settings do change how the shock works by a noticeable amount.
I guess then it's more dependent on how much one preloads the springs. At 150 lbs I don't think I ever bottomed out my shocks.
I do know that older bikes I've sat on seemed to have weaker springs than mine, which was bought new. So perhaps if the shocks were more worn out, or if I weighed more I would have noticed a bigger difference in the dampening settings.
But before that happened I replaced them with a pair of Progressive 412's...
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post #8 of 14 (permalink) Old 05-04-2017, 02:37 PM
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I had been running a more firm setup, since I had a tendency to push a bit hard. After having huge problems with my back, I started looking for a softer setup. Just out riding one day and started clicking the damper adjustments. #1, bottomed out real easy. #2 was letting me bottom out quite a bit on those dips that catch you off guard. #3 worked, and then later I was able to fine tune that with air pressure.

I found out the rear shocks had unequal air pressure, and both had a fair amount of water coming out when the air was bled off. Condensation would be my guess, we're going to have a 60 temperature swing this week. So maybe we need to change that winter air for summer air? May be a great place to be using nitrogen, from a regulated line of course.
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post #9 of 14 (permalink) Old 06-23-2017, 09:40 PM
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We could possibly have the crappiest roads in the world here in Illinois. When I go out for a ride on Route 20 bypass around Rockford, it seems that every 1/4 mile or so there is a saw cut across the road (probably because of pavement expansion and buckling). When they put the asphalt back into the saw cut it isn't level with the rest of the road. It's like having a speed bump every 1/4 mile or so. Took a ride last week and at 70 mph to keep up with traffic, it felt like the bike was taking a pounding and so was I. I'm beginning to think that this bike may not be ideal for long trips but I may be wrong. Now my mission is to find alternate routes for getting around, maybe on some secondary roads or back roads. Won't get me to where I am going very fast but at least it won't feel like someone is beating the tires with a baseball bat. So, today I purchased a bicycle pump with a built in pressure guage. Calculated the pressure needed in the shocks at 10% of my body weight. (I had checked the pressure earlier this week and got zero. Don't know if this was because there was no air in the shock or if it bled off when I put the gauge on there.) So I pumped it up to 25 psi and as I was pulling the air hose off the pressure dropped to 0. Finally I pumped it up to 35 psi and as I was taking the air hose off the needle showed that it slowly dropped to somewhere around 25 psi before totally dropping down to 0 once the air hose was completely off the valve stem. This makes me think that I probably have around 25 psi. This makes me think that possibly the best thing to do is pump it up to 43 psi as the manual calls for and then I will get somewhere in the neighborhood of 25-30 psi once the air hose is pulled off the stem. Anyone else have this problem to occur? I could calculate my required psi to the exact amount needed but if I can't pump and retain that pressure then it's all academic.

Any suggestions on getting an exact amount of air pressure will be greatly appreciated.
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post #10 of 14 (permalink) Old 06-24-2017, 07:12 AM Thread Starter
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We could possibly have the crappiest roads in the world here in Illinois. When I go out for a ride on Route 20 bypass around Rockford, it seems that every 1/4 mile or so there is a saw cut across the road (probably because of pavement expansion and buckling). When they put the asphalt back into the saw cut it isn't level with the rest of the road. It's like having a speed bump every 1/4 mile or so. Took a ride last week and at 70 mph to keep up with traffic, it felt like the bike was taking a pounding and so was I. I'm beginning to think that this bike may not be ideal for long trips but I may be wrong. Now my mission is to find alternate routes for getting around, maybe on some secondary roads or back roads. Won't get me to where I am going very fast but at least it won't feel like someone is beating the tires with a baseball bat. So, today I purchased a bicycle pump with a built in pressure guage. Calculated the pressure needed in the shocks at 10% of my body weight. (I had checked the pressure earlier this week and got zero. Don't know if this was because there was no air in the shock or if it bled off when I put the gauge on there.) So I pumped it up to 25 psi and as I was pulling the air hose off the pressure dropped to 0. Finally I pumped it up to 35 psi and as I was taking the air hose off the needle showed that it slowly dropped to somewhere around 25 psi before totally dropping down to 0 once the air hose was completely off the valve stem. This makes me think that I probably have around 25 psi. This makes me think that possibly the best thing to do is pump it up to 43 psi as the manual calls for and then I will get somewhere in the neighborhood of 25-30 psi once the air hose is pulled off the stem. Anyone else have this problem to occur? I could calculate my required psi to the exact amount needed but if I can't pump and retain that pressure then it's all academic.

Any suggestions on getting an exact amount of air pressure will be greatly appreciated.
You only think your roads are bad, you should see Northern Ireland!

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