The front suspenstion tuning thread

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The front suspenstion tuning thread

funkymonkey
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funkymonkey
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Joined: September 18th, 2017, 10:51 pm

July 5th, 2018, 2:56 am #1

A while ago I purchased the Race Tech Gold Valve Emulators (GVE) with the thought to install them on the T.

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

Invariants

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)
Rider sag measurements
  • RSL1 = 137 mm (Rider Sag L1)
  • RSL2 = 129 mm
  • RS = L - (RSL1 + RSL2)/2 = 219 - 133 = 86 mm (Rider Sag)
How does this measure up with suspension theory ?

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)
Rider sag measurements
  • RSL1 = 180 mm (Rider Sag L1)
  • RSL2 = 175 mm
  • RS = L - (RSL1 + RSL2)/2 = 219 - 177.5 = 41.5 mm (Rider Sag)
How does this measure up with suspension theory ?

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.

Ride Quality
  • 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 once. 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)
Rider sag measurements
  • RSL1 = 185 mm (Rider Sag L1)
  • RSL2 = 180 mm
  • RS = L - (RSL1 + RSL2)/2 = 219 - 182.5 = 36.5 mm (Rider Sag)
How does this measure up with suspension theory ?

Rider sag (~24%) is at the lower limit of the recommended range (25% - 33%). Will try a lower preload tonight.

Ride Quality
  • 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.
So far I'm impressed with the results. Hopefully GVE install and oil change will improve things further.
Last edited by funkymonkey on July 12th, 2018, 3:03 pm, edited 3 times in total.
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Cleve
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Cleve
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Joined: June 18th, 2009, 2:57 am

July 6th, 2018, 8:49 am #2

I'd think we need to allow for the heavier weight on the Cruisers. T is approx 30% heavier than the average sportbike, so maybe add 30% to free sag? Not sure about front/rear weight distribution vs a sportbike.

 I remember the straight rate springs in my 800 Vulcan had a lot of dive on braking, the Progressives really helped that one on ride and braking.

Smaller highway bumps - Are you checking fork alignment each time?  (or have you had them loosened yet?) A mis-alignment can make them bind or cause "stiction" where they don't move freely on the smaller bumps. 
(unfortunately, the MotionPro fork alignment tool is approx 1/2" too narrow for the T forks,,, Had to modify mine)

Low fluid levels will affect the bouncing at stops and the overall ride as the trapped air acts as a spring when compressed. Lower fluid=softer/bouncier ride. Switching to the thicker PVC spacers can have a minor effect re the air volume. raising or lowering fluid levels slightly can be used for fine-tuning...   but the valves need to always be covered. Are you low on fluid right now?

Don't the GVE's call for a thinner fluid also? Or am I thinking of these:

http://store.ricorshocks.com/harley_davidson_s/27.htm 
Cleve

Motorcycles: Bigger is NOT better, only bigger.
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funkymonkey
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funkymonkey
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Joined: September 18th, 2017, 10:51 pm

July 9th, 2018, 9:16 pm #3

Good point with the 30% extra free sag. So far I've only read in one place that free sag has to be 1/3 of rider sag. What I can say is that the springs feel good so I'll break that rule this time. I also have a set of 1.00 Kg/mm springs which I might try to see what numbers I get.

I didn't remove the forks to install the emulators and replace the oil yet. I have no idea how to check for fork alignment. I assume I'll just measure the distance in the triple tree.

Forks are probably low on fluid. Most likely fork oil has never been changed (just got the bike last year) so you can't expect much for a 20 yr old oil ;-) ...

RT recommends 15 W fork oil so I got 1L of Maxima fork oil. Hopefully I'll get to installing the emulators this week.

I also ordered a pair of Progressive 418-4812C shocks. They have rebound adjustability which is unusual for cruiser shocks.
I took a gamble since these are not listed as fitting the T but will see when they arrive. If they don't work I'm just out of $350 ;-) ...
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Cleve
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Cleve
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Joined: June 18th, 2009, 2:57 am

July 10th, 2018, 12:08 am #4

One vertical alignment method would be checked by seeing if the axle will slip in ok without any up/down pressure on the fork legs, The MotionPro gauge checks for parallel alignment, has 2 aluminum V's that you rest on the fork legs up high, then lock it in and move it to the lower area, see if the lower fork legs still sit perfectly in the v's. Pretty simple and easy to tell if they are bowed in or out even just slightly as the aluminum v's won't bottom out on both sides. works fine on narrower forks.
Honda says to align the fine groove in the axle with the "edge" of the left lower fork leg, tighten the axle clamp on that side, then torque the axle nut and then tighten the right clamp. Should work in theory...  Other manuals say to torque the axle, bounce the bike on the suspension several times to let it settle into place and then tighten the clamps. I'd think it would depend on the fork brace under the fender to be perfect doing it that way.  Heard another method is to bounce the front end several times, see if it stops at the exact same free sag spot each time. If there's any binding it may stop at different heights.

Old catalog, page 5 has some info on cruiser sag:
https://www.progressivesuspension.com/p ... atalog.pdf
Cleve

Motorcycles: Bigger is NOT better, only bigger.
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funkymonkey
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funkymonkey
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Joined: September 18th, 2017, 10:51 pm

July 10th, 2018, 10:43 pm #5

Thanks Cleve, I appreciate the input. Aligning the forks is the last piece of the puzzle (or is it ???) to help me install the RT GVEs. I plan to install them this week.

Now, I'd rather not buy any more tools for this job. I already spent $100+ on tools alone for this experiment ...

Thanks for the Progressive article. It still includes the 418 shocks that I ordered.
Oddly enough there is not much technical details about the internal construction of these shocks.
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Cleve
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Cleve
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Joined: June 18th, 2009, 2:57 am

July 11th, 2018, 6:29 pm #6

Are you replacing the seals? If so, might make a seal driver out of PVC fittings and a couple feet of PVC pipe from the hardware store. Take a seal with you...
Cleve

Motorcycles: Bigger is NOT better, only bigger.
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funkymonkey
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funkymonkey
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Joined: September 18th, 2017, 10:51 pm

July 11th, 2018, 8:43 pm #7

I have a full set of fork and dust seals as well bushings. I also bought a seal driver. It looks like I could have used PVC pipe. Will see if I can return the driver.

Honestly seals look OK and fork is not leaking so I am really tempted to leave them in place.
Obviously I won't know how bushings look like unless I disassemble the forks.

I read some post that suggest that you can take out the damping rod without disassembling the fork so this is what I plan on doing.
If there is a need I can always take everything apart at which point I'll replace both bushings and seals.
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