It turns out that the GVEs are not enough and you also need straight rate springs. Bought a pair of 0.9 Kg/mm.
I started reading quite a bit about suspension setup trying to understand the correct ingredients and how to use them.
This thread captures my measurements, experiments and results tuning the front suspension. I might eventually do the rear but there are not that many variables there.
MC garage suspension series: https://www.motorcyclistonline.com/maki ... technology
MC garage how to measure sag (read this to understand L, L1 and L2 mesurements): https://www.motorcyclistonline.com/moto ... -mc-garage
Race Tech Honda Shadow info: http://racetech.com/ProductSearch/12/Ho ... /1988-2007
Front suspension travel (FST): 150 mm (claimed) 140 mm (measured; I'm not sure I bottomed out so it might be close to 150 mm)
L = 219 mm (from fork wiper to lower fork clamp)
Suspension Theory Recommendations
- Rider sag should be 1/2 - 1/3 of the suspension travel.
- Free sag should be about 1/3 of rider sag (does this apply to cruisers ???).
Experiment #1: Stock suspension setup
Preload = 43 mm (measured this when I took off the OEM springs)
Free sag measurements
- FSL1 = 155 mm (Free Sag L1)
- FSL2 = 145 mm
- FS = L - (FSL1 + FSL2)/2 = 219 - 150 = 69 mm (Free Sag)
- RSL1 = 137 mm (Rider Sag L1)
- RSL2 = 129 mm
- RS = L - (RSL1 + RSL2)/2 = 219 - 133 = 86 mm (Rider Sag)
We can see that numbers are way out of line. Now, OEM springs are progressive so I'm not sure if same rules apply.
However we can see that rider sag (86 mm) already consumed more than half of the suspension travel so less remains for absorbing bumps. Also more likely we are getting closer to the higher spring rate because so much travel has already been taken by the rider sag.
Ride Quality (note that these are subjective)
- Plush Cadillac feel if no road irregularities are encountered.
- Small bumps are felt.
- Big square bumps are felt.
- More aggressive turns do not inspire confidence.
- Bike feels like it wants to fall into turns. Need to hold front wheel on the line.
- Deep dive when braking (how much ??? max 64 mm of travel left (150 - 86)).
- Releasing front brake at stops compresses the front suspension (it was either compress or release not 100% sure).
Experiment #2: Installed 0.9 Kg/mm straight rate springs
Preload = 15 mm (suggested by Race Tech)
Free sag measurements
- FSL1 = 192 mm (Free Sag L1)
- FSL2 = 184 mm
- FS = L - (FSL1 + FSL2)/2 = 219 - 188 = 31 mm (Free Sag)
- RSL1 = 180 mm (Rider Sag L1)
- RSL2 = 175 mm
- RS = L - (RSL1 + RSL2)/2 = 219 - 177.5 = 41.5 mm (Rider Sag)
We see that now rider sag is within range.
Free sag compared to rider sag is still out of line. That's why I wonder if this rule applies the same way to cruisers.
- Much improved front end feel.
- Front doesn't dive much under normal braking.
- Interestingly enough I don't feel the little hwy bumps as much as before. Sag with OEM setup might have brought the springs to the stiff end of their progressive rate.
- Front end is 44.5 mm (86 - 41.5) mm higher and as a result it affects steering. Will have to raise fork in triple tree to bring geometry to stock. Will do that once I install GVEs.
- When braking at stops front end bounces twice. Replacing oil should fix that (will do with GVEs install).
- Releasing front brake at stops doesn't change front end much.
- I can feel the back end bouncing over bumps. This is because the stock shocks which I believe to be really soft. Progressive 418s arrive today and will hopefully improve this.
- Front end is like on rails while in corners. Very reassuring feeling. A bit dangerous because it tempts you to push harder in corners ;-)
Experiment #3: Installed 1.0 Kg/mm straight rate springs
Preload = 12 mm
Free sag measurements
- FSL1 = 193 mm (Free Sag L1)
- FSL2 = 185 mm
- FS = L - (FSL1 + FSL2)/2 = 219 - 189 = 30 mm (Free Sag)
- RSL1 = 185 mm (Rider Sag L1)
- RSL2 = 180 mm
- RS = L - (RSL1 + RSL2)/2 = 219 - 182.5 = 36.5 mm (Rider Sag)
Rider sag (~24%) is at the lower limit of the recommended range (25% - 33%). Will try a lower preload tonight.
- HWY riding doesn't feel much different. Maybe the front is a bit stiffer.
- Front doesn't dive as much under braking.
- Will try twisties after work.
Experiment #4: Installed 1.0 Kg/mm straight rate springs
Preload = 5mm
I got the rider sag in the 42 mm range with 5 mm of preload. However my thinking is that springs might weaken a bit over time and with just 5 mm of preload I might end up with no preload on the springs down the line.
So I sent back the 1.0 kg/mm springs and I am currently running 0.9 kg/mm ones with 15 mm of preload. Also the 0.9 Kg/mm springs used more of the suspension travel than the 1.0 Kg/mm ones.
Experiment #5: Installed Race Tech Gold Valve Emulators with 0.9 Kg/mm straight rate springs
Preload = 15 mm (had to cut the spacers to adjust for the height of the GVEs)
I did not perform sag measurements since I expect them to be the same as in Experiment #2.
I did not replace fork seals since they did not leak.I did not replace fork seals since they did not leak.
GVE/Fork tuning parameters
- High speed compression dampening: blue springs (40 lbs) and 3 turns as recommended by Race Tech (I weigh 195 lbs)
- Low speed compression dampening: small plate with two holes
- Fork oil: 15 W Maxima (rebound dampening)
- Oil level: 160 mm (front end dive under braking ?)
- Wowwww !!! Mind blown !
- Bumps are mostly gone. To the point where I was looking for bumps in the hwy this morning to make sure I am not dreaming ;-) ...
- At times I thought that more engine vibration gets transmitted to the body than road irregularities.
- When braking at stops the second bounce is very small to non existent.
- Did I say wowwww ???
- Will try twisties later in the week.
It's gonna be worth your while for many miles to come. I've done most of the legwork for you so you have it easy ;-)