Rear NC Shock Measurements please?

[Just Plain Bill]

Would someone with an NC700X shock off the bike please supply me some reasonably accurate measurements? I'm not ready to remove mine just yet and I'm not confident of the accuracy of measurements I've tried to take with it on the bike. My goal is to find an inexpensive, fully adjustable sport bike shock to replace the NC unit and to do that I'll need the following dimensions of the NC shock:

1. Eye center to eye center length of the shock.
2. Outside diameter of the spring.
3. Free length of the spring (or length of the spring and approximate distance the adjusting collars have been threaded up).
4. Width of the upper mount (through which the mounting bolt goes)
5. Width of the lower mount (through which the mounting bolt goes)

I bought a CBR600 F4i shock for my first trial and have those measurements in case they're of any interest:

1. Eye to eye - 12"
2. OD of spring 3 5/16'
3. Free length of spring - between 5 1/2" - 6 1/2" (estimated)
4. Width of upper mount 1"
5. Width of lower mount 1 3/8"

The F4i shock seems to be a little shorter than the NC shock which shouldn't be a problem, but it has a hose for the remote reservoir sticking out one side of the upper part of the shock body. I expect that to complicate fitting it into the NC chassis.

My interest in the spring length is in case it's necessary to use the NC spring on the replacement shock body.

Bill

 

[L.B.S.]

Would someone with an NC700X shock off the bike please supply me some reasonably accurate measurements? I'm not ready to remove mine just yet and I'm not confident of the accuracy of measurements I've tried to take with it on the bike. My goal is to find an inexpensive, fully adjustable sport bike shock to replace the NC unit and to do that I'll need the following dimensions of the NC shock:

1. Eye center to eye center length of the shock.
2. Outside diameter of the spring.
3. Free length of the spring (or length of the spring and approximate distance the adjusting collars have been threaded up).
4. Width of the upper mount (through which the mounting bolt goes)
5. Width of the lower mount (through which the mounting bolt goes)

I bought a CBR600 F4i shock for my first trial and have those measurements in case they're of any interest:

1. Eye to eye - 12"
2. OD of spring 3 5/16'
3. Free length of spring - between 5 1/2" - 6 1/2" (estimated)
4. Width of upper mount 1"
5. Width of lower mount 1 3/8"

The F4i shock seems to be a little shorter than the NC shock which shouldn't be a problem, but it has a hose for the remote reservoir sticking out one side of the upper part of the shock body. I expect that to complicate fitting it into the NC chassis.

My interest in the spring length is in case it's necessary to use the NC spring on the replacement shock body.

Bill

Good on you for doing this legwork, Bill. It will be great to find out if potential donor shocks can be swapped over from other sources.

Since an F4i has a bit less travel than an NCX, I would also be curious to find out how much the linkage ratio differs between the two. Hopefully the actual shock travel isn't too different, and one can play with different link arm lengths to get it back to a similar lever arc, so you don't end up with an NCX with only the travel of a CBR.

 

[maxwellian]

I'm very interested in this endeavor.

been doing a bit of poking around in Ohlins' specs to find others with a similar length and stroke, then looking at the stock one they replace. Theirs has an eye to eye length of 312mm, stroke 56mm.

I'm down to pull my shock off this weekend if nobody has one handy.

 

[Antarius]

A GSXR1100 has a 312mm in length shock. FYI.

 

[maxwellian]

So, say a bike weighs the same, has the same shock stroke, but less wheel travel. As seems to apply to some of these sportbike shocks.

That means softer springs and damping, shorter efffective lever arm, right?

 

[Just Plain Bill]

Great stuff you guys -- you got me thinking. I took the F4i shock apart and used digital calipers to re-measure and added the spring wire diameter and stroke measurement, for good measure. Here's the new info for the F4i shock:

1. Eye center to eye center, length of the shock. 12 1/16" 306mm
2. Outside diameter of the spring. 3 5/16" 84mm
3. Free length of the spring 6" - 153mm.
4. Width of the upper mount spacer 1.12" 28.6mm
5. Width of the lower mount spacer 1.54" 39mm
6. Shock travel (stroke) 1.4" 35.6mm
7. Wire diameter of spring 0.49" 12.55mm

Next, and for the same amount of effort I probably could have taken the shock off the bike, I did what I could to take similar measurements of the NC shock:

1. Eye center to eye center length of the shock. 12 5/16" 315mm
2. Outside diameter of the spring. 3.125" 80mm (distance between linkage arms is 90mm).
3. Free length of the spring. At least 9.5" 240mm -still on the shock.
4. Width of the upper mount (through which the mounting bolt goes) ?
5. Width of the lower mount. 1.58" 40mm
6. Shock travel. 1.63" 41.5mm (used a telescope gauge - should be very close)
7. Spring wire diameter. 0.5" 12.80mm

If there's room for the remote reservoir hose, I believe the F4i shock should fit be generally compatible with the NCX.

I don't know anything about the effects of the linkage geometry on axle travel but I did a simple calculation using the ratio between F4i (36.5mm) and NC (41.5mm) shock travel (86%) times 120mm NCX specs for axle travel and got 103mm as an approximation of rear axle travel if the F4i shock were used. It might not be accurate - I guess I'll have to put the shock on the bike without a spring and measure actual travel.

I don't use my NCX off road so if my calculation is accurate, giving up 17mm of travel (8.5mm up or down) wont be a problem.

If anyone needs measurements of photos of the F4i shock while it's apart, speak up now or forever hold your peace. At this point, I'm kind of encouraged and might stuff it in tomorrow.

Bill

 

[maxwellian]

Had some extra time today, so I pulled the shock. My measurements agree pretty closely with yours.

Eye to eye 312mm
Spring length 241
ID 51mm
Upper mount 28.6mm x M10
Lower mount 39.1mm x M10
Stroke 41mm (till the bumper starts to compress.)

 

[MZ5]

I understand worrying about travel and linkage ratio and spring and damping rates. Needn't we also consider the length of the swingarm? And perhaps the distance from the linkage-swingarm mount to the rear axle, and maybe from the swingarm pivot/mount to the linkage mount point? All these will impact nominal vs. effective spring rate.

 

[Craigmri]

Bill,

You rock bro! Your an NC pioneer!!! Cannot wait to hear the end results of your experimentation.

On my NC with all three Honda hard bags and myself(I weight about 195 lbs), I have my preload maxed out and I am BEARLY in sag spec. I hope that not only with this donor shock provide improved spring rate, but also improved damping and rebound capabilities.

 

[L.B.S.]

The same thoughts are echoing for me, MZ5, but then again, I am not quite up at the head of the class when it comes to sussing out on paper, the whole chain of events from theory to practice, so I bow out on the added complexities of calculating every possible variable. I know enough to stop when too much math is involved, har.


This is a nice little intro into various suspension designs and examples of their function, helpfully explained.

Motorcycle Suspension - Leverage and Linkages


At some point in experiments like this, I throw my hands up and just "see what happens", as my eyes glaze over with too much theory and not enough wrench turning, lol.

Often the result is: "Well, *that* didn't work, now did it!" unfortunately, heehee, but it is somehow more emotionally satisfying to poke at it with sticks instead of letting crummy laws of physics or what have you, scuttle the dream before even starting.

Kudos to all who are happily mucking about in this!

 

[maxwellian]

I understand worrying about travel and linkage ratio and spring and damping rates. Needn't we also consider the length of the swingarm? And perhaps the distance from the linkage-swingarm mount to the rear axle, and maybe from the swingarm pivot/mount to the linkage mount point? All these will impact nominal vs. effective spring rate.

Yes, but isn't it roughly equivalent to a simple lever with one end moving 150mm, and the other moving 40mm? Wouldn't those factors be more important in fine tuning than in spring rate difference between bikes with roughly the same weight distribution?

Racetech says the F4i shock's stock spring is 14.2kg/mm. No spec for our NC.

I tried putting a 20 pound (9 kg) sandbag on the spring just for kicks. I think it compressed more than a millimeter. I could probably whip up a test jig with a digital scale, plywood and allthread. If the f4i is way too stiff/soft, I'll measure mine.

 

[L.B.S.]

Yes, but isn't it roughly equivalent to a simple lever with one end moving 150mm, and the other moving 40mm? Wouldn't those factors would be more important in fine tuning than in spring rate difference between bikes with roughly the same weight distribution?

Racetech says the F4i shock's stock spring is 14.2kg/mm. No spec for our NC.

I tried putting a 20 pound (9 kg) sandbag on the spring just for kicks. I think it compressed more than a millimeter. I could probably whip up a test jig with a digital scale, plywood and allthread. If the f4i is way too stiff/soft, I'll measure mine.

That's where I start to get curious, is how much is it really effected through the pivot arc, for progressiveness? Depending on a few quite minor changes, you could end up having a shock that is too harshly/quickly compressed in initial upstroke, followed by a not progressive enough leverage, that allows it to bottom out too quickly under big bumps.

Trying to combat this via lighter or heavier lb/in spring rates, and/or get mired in a compression and rebound damping yo-yo battle could prove frustrating if the basic premise was just a wee bit too far out of the ballpark.

I must have 1/2 a dozen springs rolling around underfoot from trying to get my CBR rates to a functional point, I am up several hundred lb/in beyond what I thought I needed, and it's *still* way under sprung...

 

[MZ5]

Yes, but isn't it roughly equivalent to a simple lever with one end moving 150mm, and the other moving 40mm?

That depends on the swingarm length of the donor bike vs the NC, doesn't it?
I don't know what the F4/F4i's swingarm length is, although an F4 was what I rode prior to this one. The point, though, is that if the length of that simple lever is doubled on the NCX vs the F4, that'll significantly impact whether a roughly equivalent spring rate is appropriate or not. Don't you think?

That's all I'm saying. I'm very glad for this pioneering work! I'm attempting to add useful considerations for those who _don't_ have a parts-donor bike just laying around.

 

[maxwellian]

I'm just thinking that the swingarm length is only the first input on the equation for the leverage ratio. Since it acts on a linkage, You could double the swingarm length, half the linkage length/ratio/whatever, and have things be roughly the same. It seems to me, a bike with the same weight on the back wheel, and the same ratio of wheel travel to shock stroke, should have to have roughly the same spring rate. Maybe there's something I'm missing, though.

 

[MZ5]

You mean from the factory? Maybe. Myself, I wouldn't expect Honda to use the same spring rate and linkage for a super-sport as for an 'adventure' bike, but they might. OTOH, I don't believe the two bikes in question have the same-length swingarms, nor the same relative positions of linkage attachment and axle. However, someone who still has an F4/F4i will have to measure things to know for sure.

I still think it's great to try to find donors for potentially more-sophisticated rear shocks.

 

[maxwellian]

The linkage difference may well cancel out the swingarm difference, is what I'm saying. If it didn't, the ratio of stroke to travel would be different. A sportbike is likely to have a stiffer spring, all else being equal. But, I think that we want a stiffer spring and variable compression damping, though.

 

[Just Plain Bill]

Thanks, I appreciate the validation.

Had some extra time today, so I pulled the shock. My measurements agree pretty closely with yours.

Eye to eye 312mm
Spring length 241
ID 51mm
Upper mount 28.6mm x M10
Lower mount 39.1mm x M10
Stroke 41mm (till the bumper starts to compress.)

 

[Just Plain Bill]

You might be right, but it's beyond my pay grade. But the CBR600 F4i weighs 370 pounds - about 130 pounds less than the NC700XD so if anything, the spring rate on the F4i is likely a little lower than the NCX.

Here's the thing: I was unable to adjust my stock shock to get less than 48mm of sag and compared to the front end (with preload adjusters) it was still harsh. If I can get the sag set within specs and fiddle with the dampening so those sharp edged bumps don't beat my butt, I'll be happy.

I'm just thinking that the swingarm length is only the first input on the equation for the leverage ratio. Since it acts on a linkage, You could double the swingarm length, half the linkage length/ratio/whatever, and have things be roughly the same. It seems to me, a bike with the same weight on the back wheel, and the same ratio of wheel travel to shock stroke, should have to have roughly the same spring rate. Maybe there's something I'm missing, though.

 

[Just Plain Bill]

Spent the evening installing the F4i shock in the NCX. It pretty much dropped right in. I had to loosen the dog bones and remove the bracket between the frame, shock and the swingarm (not identified by name in the NC700XD fiche but it uses four needle bearings #13) to make room while sliding the larger diameter of the F4i spring up to the top mount. The reservoir hose had to face the right side of the chassis to avoid hitting the chain. The hose was long enough to use a hose clamp to hold the reservoir to a frame tube.


http://nc700-forum.com/forum/attachment.php?attachmentid=9538&d=1382594196&thumb=1&stc=1


I've re-assembled the shock and tightened the suspension bolts. Still need to replace some of the parts I unnecessarily removed during the install. I will adjust preload and test ride the bike tomorrow and post results.

Bill

 

[maxwellian]

Awesome!

Wishing you luck.

I'm finding lots of almost good candidates, like the cbr1000rr, but those pesky hard-mounted reservoirs won't clear the tank.