Hyperpro linear springs: what mm oil level does their 500 cc actually give?

[mr.millman]

Fork oil level with Hyperpro linear springs on an ST1300, anyone done this?

2003 ST1300A, 122k km. Fitting Hyperpro linear 9.5 N/mm springs (kit SL-HO13-SSA002) next week along with seals, dust covers and bushings.

Hyperpro's label says SAE 7.5 and 500 cc. Honda specs 638 cc and a 62 mm level with the stock spring. Their own instructions tell you to set a level in mm, but the label gives a volume, so there is no mm figure for this bike. I have asked Hyperpro and I am waiting for an answer.

What I have found here is that most people run 120 to 130 mm with aftermarket springs, since the high stock level is there to compensate for soft stock springs. One member said a single liter of Hyperpro fluid was just about right for both legs with Race Tech springs, which lines up with 500 per leg.

So, if you are running Hyperpro linear springs:

What mm level did 500 cc actually give you in a fully drained leg?
Did you stay at their figure or go your own way?

The springs measure 250 mm free length, same as the Honda spec of 249.6, so the stock spacer stays and preload is unchanged. I am planning on 550 cc measured out, then I will note the level in mm and keep that as my reference.

 

[dduelin]

Calculate the height of a cylinder with a volume of what ever volume in cc cubed you desire. You will need the ID of the fork tubes and the volume in cc to calculate.

Right cylinder
Solve for
volume




V
=
π

r
2

h

r Radius h Height

The volume of a cylinder is calculated using the formula V = π r² h, as explained by the Volume of a Cylinder Calculator.


Formula Components

• • V: Volume (cubic units like cm³ or m³)
  • π: Pi, approximately 3.14159
  • r: Radius of the circular base
  • h: Height (or length) of the cylinder
    AxFlow +2
    

How to Calculate

1. • Square the radius (r × r).
   • Multiply that result by Pi (π) to get the area of the circular base
     .
   • Multiply by the height (h) of the cylinder.
     YouTube·Math with Mr. J +1
     

Note: If you only know the diameter (d) instead of the radius, divide the diameter by 2 first (r = d / 2).
CK-12 Foundation


If you have specific measurements, tell me the radius (or diameter) and height, and I can help you calculate the exact volume.

 

[Larry Fine]

Don't you need to compensate for (subtract) the volume of the spring and other components?

 

[Igofar]

I ran 120mm oil height, and a 130mm spacer, with 7 weight oil.

 

[Larry Fine]

It's good to see you again, Larry.

 

[TerryS]

Calculate the height of a cylinder with a volume of what ever volume in cc cubed you desire. You will need the ID of the fork tubes and the volume in cc to calculate.

Right cylinder
Solve for
volume




V
=
π

r
2

h

r Radius h Height

The volume of a cylinder is calculated using the formula V = π r² h, as explained by the Volume of a Cylinder Calculator.


Formula Components

• • V: Volume (cubic units like cm³ or m³)
  • π: Pi, approximately 3.14159
  • r: Radius of the circular base
  • h: Height (or length) of the cylinder
    AxFlow +2

How to Calculate

1. • Square the radius (r × r).
   • Multiply that result by Pi (π) to get the area of the circular base
     .
   • Multiply by the height (h) of the cylinder.
     YouTube·Math with Mr. J +1

Note: If you only know the diameter (d) instead of the radius, divide the diameter by 2 first (r = d / 2).
CK-12 Foundation


If you have specific measurements, tell me the radius (or diameter) and height, and I can help you calculate the exact volume.

Not so fast there chief...the fork leg that you are filling also contains the damper cartridge: the tube, the base, the shims and valves and the damper rod. So you'd want to factor those into the volume as well. But I agree that you do not need to consider the spring as that is added after setting the oil height. I agree that for oil height, 130mm is about right with linear springs (and is what RaceTech recommended to me).

 

[PanRider1300]

I ran 120mm oil height, and a 130mm spacer, with 7 weight oil.

And you have the exact same springs?

 

[mr.millman]

Thanks all. I got an answer from another angle that fills the gap.

An ST1300 owner on Fb running the progressive Hyperpro kit asked Hyperpro directly and was told 160 mm. He poured about 500 ml per leg to get there. Since the level is set with the spring and spacer out, that volume to level relationship belongs to the fork and not the spring, so it should apply to my linear kit as well.

That gives two known points for this fork: Honda 638 cc at 62 mm, Hyperpro 500 cc at 160 mm. Roughly 1.4 cc per mm. My planned 550 cc should then land near 125 mm, which sits between Igofar's 120 and TerryS's 130.

Plan is to drain fully, leave the legs inverted overnight, pour 550, bleed the air, then measure the level and make both legs match.

I have also asked Hyperpro for their own mm figure and the viscosity of their SAE 7.5. I will post the answer here when it comes, since the linear kit labels seem to leave the level out.

 

[dduelin]

Not so fast there chief...the fork leg that you are filling also contains the damper cartridge: the tube, the base, the shims and valves and the damper rod. So you'd want to factor those into the volume as well. But I agree that you do not need to consider the spring as that is added after setting the oil height. I agree that for oil height, 130mm is about right with linear springs (and is what RaceTech recommended to me).

None of the fork internals less springs matter as they are already included in Honda's 62 mm stock level. By calculating the height of a cylinder with 638cc volume we know that produces a level of 62 mm. Scale down the cylinder's height in mm to produce a cylinder of 500cc. That difference in height added to 62 should be the new level. This may be just esoteric as the OP has settled on 550cc of fork oil then measure the level. I submit that that whatever level 550cc provides is just the starting point to tune the fork. After placing a zip tie on a fork leg and sliding it down to the leg's wiper boot it's time to take a spirited ride over a favorite road then a few threshold braking drills to see how much travel the fork is using. Zip tie is a poor mans data logger. If around 10 mm is left I would leave that oil level alone. We need 10 mm travel in reserve for emergency braking on rough pavement. If there is more than 10 mm then suck out a little oil to reduce effective spring rate at the very end of compression. Less than 10 mm add oil to increase effective spring rate. We can use the right angle cylinder formula to find the amount of cc needed to exactly adjust the level in mm.

Edit to add: Hyperpro sells only two springs for the ST1300 no matter what weight of rider(s), cargo, etc.. so tuning the air gap helps make up for the lack of choice in spring rate tailored to rider.

 

[mr.millman]

Got a reply from Hyperpro:

“
As our springs have a different volume and force we need a different Oil volume then standard.

The way we tested it that works best with this spring is to fill each leg with 500cc of oil.



With best regards,

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MERK​

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TYPE​

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FORK HYPERPRO NR​

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OEM NUMBER FRONT​

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FORK HYPERPRO OIL​

OILLEVEL​

FORK SPRING PRELOAD​

FORK STATIC SAG​

FORK COMPRESION​

FORK REBOUND​

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SL-HO13-SSA002

HONDA

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ST 1300 PAN EUROPEAN CBS/ABS LINEAR 9,5 N/mm

02-18

1243

51401-MCS-G01

SAE 7,5

500 CC

NOT ADJUSTABLE

25-30 MM

NOT ADJUSTABLE

NOT ADJUSTABLE

 

[dwalby]

The way we tested it that works best with this spring is to fill each leg with 500cc of oil.

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there is no "works best" setting when each rider's weight varies, and riding style varies.

that may not be a bad starting point, but experimentation is always worth the time to find what settings work best for you, including spring preload.