trikermutha
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Why work it destroy the air bag at 0 PSI??
Why work it destroy the air bag at 0 PSI??
The bag will flex & pinch in a way those air bags weren't ever designed to. And that's probably gonna apply even more if your standard suspension is also bottoming out! :shocked: When the first airbag on my RT was replaced, I was told to always make sure the bag was pressurised higher than the minimum air pressure of 5psi... :thumbup:
I am a simple man, so I use simple solutions. The way I figure it the rear fender tip of my bike runs about 15" above the ground with me and my normal cargo aboard. This is with the automatic system enabled, air bag at ±43 PSI, rear tire at 18 PSI. I've read that the OEM rear spring is in the mid 300 Lb/In range (also being a progressive spring), with the airbag taking up the slack. So if I can do it, and get a spring with the right force and pre-load, I figure I can get the bike to sit at the same spot or very slightly higher (to keep the air pump from cycling) with the air bag at 0 PSI (me and cargo aboard), but still have the air system available for a maximum loaded condition (2 up). I feel like the less the air pump has to do, the more reliable it will be (told you, I'm a simple man). I currently have a project in progress, I'll post it up if it works. For me, it's not about the ride height. I want to keep it normal. It's about minimizing the air pump usage while trying to maintain a decent ride quality.
Isn't the rear tire supposed to be around 28psi?
Isn't the rear tire supposed to be around 28psi?
I lost my compressor this spring, and this is my 2 cents on this system! It is a fine system when both parts are working the way there suppose to, and a piece of crap when not! The coil over shock that is not adjustable on the 2012rtl is basically there for a small amount of dampening factor, with a small soft spring that don't hold much of a load! The air bag is the item that holds the bulk of the load and gives your ride height! The bag has it's faults that if you ride a lot of dirt roads you may get some thing under the bag and get a leak, but the compressor has a check valve that plugs up and makes the pump run more than it should because it's always leaking down and pumping up! With out air in the bag you will be basically dead x if your hauling two people or carrying anything on the bike! I bypassed all the air system and hooked it direct from shrader to bag! I find that 55-80 psi is good for me and the wife, but what I plain on doing next year is get rid of that p,o,s, shock and get a good aftermarket adjustable shock and still use the bag as a overload as needed! This is one of those times when to much technology isn't good and why not keep it stupid simple! good luck with your science project, hope you find what your looking for
The Spyder rear suspension design is very basic and has no appreciable amount of rising rate via the suspension geometry.
Using a progressive wound coil spring adds some rising rate to the suspension but fails to add rising rate to the damping.
The air spring is inherently rising rate and this rate changes on extended volume to compressed volume ratios. Base pressure vs compressed pressure is important too.
I considered doing as you plan to but opted out. Simply 45 years of tuning moto suspension convinced me not to surrender any rising rate, regardless of how it is achieved.
In simplest terms, yes, you can install a correct sized with spring, and via adequate rate and preload obtain the setting you desire. Sadly, as the suspension compresses, there is a very good likelihood your spring rate will be insufficient as the suspension compresses.
Mr. PMK,
So I just finished the install, how do I tell if the spring rate is too low? Bottoming? I'm from the old Harley school, nerve damage and all, so I really don't know squat about good suspension and what to look for. How do I tell if the spring is overpowering the damping of the shock? Jouncing on bumps?
Mr. Mikey,
While I'm specifically setting mine up as a solo spring with air back up for 2 up riding, maybe a simple spring swap to a higher Lb/In rating would work for 2 up. Not sure how much spring the OEM rear shock can successfully dampen. I'm going to post the project with pics once I get the bugs ironed out and play test pilot. Stay tuned.
With my stock shock, I found that the rebound, or dampening sucked, I could grab the back of the bike on the ground with no air in the bag and bounce the back three, four times to the floor before the shock would wake up and start to work! It may be on it's way out or not I don't know, that's why I am going to put like a stage 2 Elka on board next year! Then I'll do basically what your doing!
So I took the Spyder for a test run, pretty happy with the result. Still working the bugs out, think I may have a tiny bit too much preload as I gained about 3/4" on the measurements taken at the rear fender. I'll back off the preload and take it out again until I get it right. Some pointers supplied by very helpful folks.
1. Went into the wayback search machine, actually found a TST for earlier versions of the RT series that say 10 PSI is the minimum pressure on the air system. I'll set my ride height to make that happen. (Thanks Mr Aawen)
2. The preload adjusters are so far up in the guts of the machine you will need something like the QA1 T115W spanner that fits on a 3/8" extension. Got one coming, will see if it fits. View attachment 175437
3. Running a 600 Lb/In Hyperco 9" free length spring because it was real cheap on EBay. Coil bind will never be an issue, so I recommend the 8" spring. With the sleeve setup I'm using I had to compress the 9" spring to get the upper retainers back on. Wouldn't be a problem with the 8" spring.
4. If looking at doing this type thing I recommend taking a bunch of measurements multiple times and document them so you can determine a mean average before ever taking anything apart.
5. I started with 1" of preload, backed it down to .750". Closing in on the right ride height. (Many Thanks to Mr. spyderyderjim who helped tremendously and actually provided usable information). If I get too small on the preload I may have to go down to a 550 Lb/In spring.
As an aside, on my first test pilot run, I finally got to meet the Nanny. Crowded the RTL into a short radius turn way too hard, braked way to much towards the apex, and rolled in way too much throttle on the exit. Both front wheels were screaming, but it wasn't until the right front wheel lifted that the Nanny reacted calmly and benignly. She gently lifted throttle for about 1/4 second, and as soon as the wheel touched down again reapplied the throttle back to full. Nice! Mine seems to have a very forgiving calibration. Baja Ron sway bar and Vredestein tires allow much more turning force.
So initial thoughts are the 600 Lb/In spring seems very slightly firmer than the OEM spring and air bag with 42 PSI in it. Preload adjustment may help with this. I am looking to keep the cushy touring ride of the RTL. I did notice the current setup seems to have a more coupled feel between front and rear, before the change the rear seemed at times to be more squishy than the front, and felt disconnected and vague. As expected the new linear setup doesn't handle the tiny stutter bums was well as the progressive bag and spring setup, but it's not uncomfortable or non-compliant, just linear. I can hardly tell the difference in ride, so I'm happy. I'll post up the information when I'm sure the project is good.
Good write up and entirely as expected. Yes, added rate will not settle as well on small stutters compared to the progressiveness of the sir spring.
In regards to damping, the oem shock is capable of controlling your spring rate. You must reconsider your data. The spring you purchased provides force X at full droop, provides force Y at static sag, and force Z at full compression.
Oem is the sum of the coil spring force and air spring force. The air spring is variable via the compressor. However, since you are measuring ride height at a given dimension, also known as static sag, the force of your spring (rate and preload) is equal to the oem of spring rate, preload and air pressure. In simple terms, static sag for each is equal net force to hold the rear end up.
Because your new setup is far more linear than oem, it will store more net force at full droop. Additionally, as the suspension begins to compress, your spring force increases essentially in a linear manner. The oem air spring will increase progressively. The oem progressive spring increases force progressively, combined they provide a greater peak force to prevent bottoming out.
What I suspect you did notice was less initial squat, pretty typical when removing a progressive setup and converting to linesr. Sadly though, typically, linear setups are less desirable from mid stroke to full compression. Assuming the Spyder employs a 30% of available travel as sag, there is not much margin until the machine blows through the stroke.
If anything, the linear spring should require added compression damping to help hold the bike up in the mid stroke.
Regardless, all the best with it. You might want to purchase a few springs and test. 1” of preload seems to be a lot. I suspect if that preload could be 3/8” or less, the static sag could dial in, the ride would be more supple and the firmer spring rate would not blow through the stroke as easily.
Also, with added rear grip, you may find a need to increase front grip, either via tires, tire pressures, or returning to a small diameter swaybar.
Maybe I missed this, but why are you trying to mostly remove the usefulness of the air bag system?
Air bags themselves have been very reliable for years - they're used in semi-trucks and are capable of very high weight capacities if designed properly. I understand the compressors and solenoid valves can/do fail but those can be remedied w/ higher quality components.
A lot of fine vocabulary there, but I don't understand where you read into my post that I need increased front grip. The bike would never corner as it does now with the OEM sway bar or tires. With the current car tires and Baja Ron sway bar it will pull a substantial amount more G force in the turns. I'm not a racer, so I don't have all that fine verbiage, but this thing handles like it's on rails now. The tire lifting didn't affect the line, and seemed pretty benign other than the amount of lateral G's. Now that I know where the Nanny resides, I'll probably never meet her again. Way above my comfort threshold, but a man must find the envelope.
As far as "blowing through the stroke", maybe I'm crass but I really can't tell much difference. The bike runs smooth and true, without much difference in ride quality. It doesn't pitch or jounce, and the ride is supple. Meaning the forces are in equilibrium. So as far as it goes, the only concern now is will it bottom? I gave it a pretty rough ride, and didn't notice any clunking going over the bumps.