Fork air gap

[Garnet]

I have a new 2012 NCS that I picked up a week ago. I have been busy adjusting everything to suit me.

The rear suspension sag seems spot on for me at 38mm or 32% of the 120mm travel. The front is a bit much at 45mm of 120, so I'm planning on adding a 7mm spacer under the fork cap and see where that puts me.

My concern is that I'm only getting 100mm of travel on the front. This has been checked by using a "zap strap" around the fork tube and measuring where it ends up after an exuberant ride. Normally reduced travel is caused by too small an air gap, or too much fluid in the forks. I have not felt any harsh bottoming, so I believe that the forks are bottoming on the air cushion, as they should.

Before I lower the level of fork oil, has anyone run into this problem, or should I be looking for another cause for the lack of travel?

 

[Deleted member 1183]

I will be interested to see the results of your testing etc. As these are budget forks it will always be difficult to improve on them. Rather than add spacers, a replacement progressive spring may be the way to go. However I do understand your thinking. My only adjustment so far has been to significantly increase the preload on the shock. After a ride out on rough roads yesterday, I now intend to increase the preload even more as there is too much sag.

 

[treybrad]

I'll be interested to follow along and see what others have found. I think Honda quote 6" travel, but some reviews have listed 5.4". I've had a zip tie on my forks since installing the Ricor valves a couple months back, and don't think I've ever seen more than 5" of travel total when I took the time to measure.

I measured more than that with the springs out of the tubes, sliding the fork bodies from full compression to extension (close to 6" I believe, but I'll have to find my notes to get that figure). That's the number I used to set my sag at 33%-ish, which means if I really only have 5" of travel, I'm closer to 40% sag. Never feel it bottoming harshly though.

trey

 

[jonnybegood]

I also have a zip tie on my fork tube to check travel. On my normal ride to work with out hard braking I only use 2 inches of travel even though I have a harsh ride over several cracks across the road. Under heavy braking I use 4.25 inches of travel. If Honda would have given us drain hole in the lower fork legs I think it would be easy to improve my ride with lighter oil and lower oil level.

 

[Garnet]

So I added a 9mm spacer to the top of the factory spacer today. My sag with rider is now 36mm which is 30% of the total travel of 120. I'm happy with that as I measured it without my gear on. BTW the race sag, (bike only) is 21mm. There us a rule of thumb formula that compares race sag and rider sag and tells you if you need if you need stiffer or lighter springs. I don't know it off the top of my head, so I'll find it and post it.

I reduced the fluid level by 10mm using my oil change sucker. Unfortunately I had no time for a test drive, so I'll keep you posted on the results.

 

[Garnet]

This article explains a bit about spring rates and sag: Peter Verdone Designs - Motorcycle Springs

In my case, I weigh 175 (w/o gear, as the measurements where taken) and the bike is 475. I'm guessing that the sprung weight of the bike to be 440 ish. So the total would be 615 and the bike is 71% of the load. Then bike sag (race sag or free sag) should be 71% of 36mm = 25.5mm. My readings for that number are 21mm, that would lead me believe that the spring rate is too soft for me. Since I'm after a smooth ride rather than ultimate track performance, I'm OK with that.

Now for a test ride tomorrow.

 

[Garnet]

After a quick test I still only have 100mm of travel.

Next I'll have to pull the springs and see if they have enough travel, but I can't see Honda putting in springs that would bind before full travel is reached, and I would have felt a solid thunk like that. I'm not too keen on removing much more fluid.

As to the above post, there is a flaw in my calculations as I am using total bike weight, not the front wheel weight. I have to sit and noodle a bit to come up with some better figures.

 

[dduelin]

It's hard to tune a damping rid fork. The air gap doesn't come into play until the last 30% or so of travel.......Honda had to balance compression damping against spring rate and seemed to use too much compression damping with springs a little too soft. I weigh 155 in street clothes and +/- 180 geared up and my rider sag is 40% but the forks don't use anywhere near full travel under any condition encountered in 20,xxx miles. I might address this with spacers about 6 mm longer, a mix of Honda fork oil about 7 wt, and lowering the stock 103 mm oil level by 10 or 15 %.

 

[maxwellian]

I'll chime in and say I'm very happy with my my Ricor cartridge emulators. Very easy install. I sucked the oil out, so no fork removal, no drilling. Just drop 'em in and change to 5W oil. Also adds the equivalent of I think ~10mm to the preload spacer.

 

[Garnet]

I managed a pretty good 200+ mile ride this past weekend. The only time I get to 100mm of travel is under hard braking, rough roads only yield about 90mm of travel.

I just happen to have most of a bottle of 7 wt fork oil, so I'll take Dave's advice next. I certainly find that washboard like surfaces really overwhelm the forks, certainly too much comp. dampening. The only real solution will be some sort of new valving cartridge so that high and low speed damping can be adjusted seperatly, but those will have to wait till the next fiscal period.

In the mean time I will continue to experiment with little or no cost tweaks.

 

[Mike Cash]

Excuse an ignorant question here, but to measure full fork travel wouldn't you have to lift up on the front end? Doesn't the figure for fork travel include extension as well as compression? Or have you guys included extension in your measurements and I just missed it in the posts?

 

[treybrad]

Excuse an ignorant question here, but to measure full fork travel wouldn't you have to lift up on the front end? Doesn't the figure for fork travel include extension as well as compression? Or have you guys included extension in your measurements and I just missed it in the posts?

I put mine on the centerstand and rock it all the way back and get the front wheel off the ground. Then I gently rest it back down on the front tire, which doesn't compress the fork at all with the added weight of my top case/rack.

trey

 

[Garnet]

Since I had my fork caps off and the front end blocked up off the ground, I decided to check the actual fork travel, (not sure why I didn't do so before now). I only have 110mm of total travel on my NCS, the specs say 120. WTF? With that fact in hand 100mm of real world travel is correct as you don't want to use much more than 90% of travel in typical riding.

Turns out I didn't have that full a bottle of 7 wt so I sucked out about half stock fluid and topped up with the 7. Took it for a test ride, and I would like to think there was an improvement. I'm sure I'm just willing the results as it takes a long time for the new lighter oil to mix with the stock oil that is down in the internals of the forks.

I'm still miffed about the 110mm travel, I was robbed.

 

[dduelin]

I managed a pretty good 200+ mile ride this past weekend. The only time I get to 100mm of travel is under hard braking, rough roads only yield about 90mm of travel.

I just happen to have most of a bottle of 7 wt fork oil, so I'll take Dave's advice next. I certainly find that washboard like surfaces really overwhelm the forks, certainly too much comp. dampening. The only real solution will be some sort of new valving cartridge so that high and low speed damping can be adjusted seperatly, but those will have to wait till the next fiscal period.

In the mean time I will continue to experiment with little or no cost tweaks.

As you probably know, light oils like fork fluids do not measure well using SAE weight as a criteria. Some 7 wt oils act "thicker" than other brands' 10 wt oils when comparisons of viscosity indexes are used. The only reliable way to compare fork oil weight is to stay within a single brand and even that may not work within certain brands. The X comes with Honda SS 47 fluid which Honda says is 10 wt.
These links provide some real numbers to go by when looking to modify damping by going to a thinner or thicker oil. Unfortunately the links do not provide the numbers on SS 47. I'll probably try Honda SS-7 "5 wt" for a thinner oil and see where that leads.

Peter Verdone Designs - Low Speed Damping

http://www.qemsc.com.au/documents/suspensionoils.pdf

Edit to add info:

The Honda service manual states the front fork travel as 137 mm or 5.4". I have no reason to doubt that .... the most travel I ever noted was 132 mm and that was under threshold braking and I hit a small break in the pavement when the front tire was howling from impending lock up. That leaves 5 mm to bottoming out which would take extreme measures to do.

To start getting suspension sag measurements on the forks I jacked up the bike under the engine (on the center stand) to get the forks at full extension then measured the distance from the bottom of the lower triple clamp to the top edge of the fork wiper. This is a datum of 177 mm. The zip tie is slid all the way down against the wiper. Then I moved the bike gently off the center stand on it's wheels. The weight of the bike compresses the suspension and moves the zip tie up. I got the bike back up on the stand and measured the distance from the datum of the triple clamp to the tie - 132 mm. 177 minus 132 is 45 mm of free sag, or weight of bike alone on it's wheels.

With the help of my daughter to hold the fully gased-up bike upright I climbed on dressed in full gear. The bike is upright and resting full weight of bike and rider on the tires. This is rider or static sag.......weight of bike, rider, and cargo compressing the suspension. I gingerly get off the bike to not disturb the zip tie and measure the distance the zip tie moved up under weight of the bike with me on it. I did this several times to get an average figure of 122 mm. 177 minus 122 = 55 mm. The bike sagged 55 mm or 40% of total travel. Most suspension tuners use a target of 25 to 33% of travel as a target for rider sag on a bike with longer than normal suspension travel which the NC700X has. Mine is about 7% or 10 mm more than that. It doesn't need stiffer springs as it does not use all the available travel under all circumstances now but could use a longer preload spacer in the forks or the adjustable preload fork caps from the CB1100 to raise the ride height and reduce the rider sag to 45 mm but as the bike is already tall for me (29" inseam) I have held off messing around with the forks and raising the seat height. Even with 40% sag here is plenty of travel left for street riding which is 99% of what I do. The ideal goal is to have the bike operating in the middle 1/3rd of the available fork travel during normal riding and mine starts out a bit low (40% vs 33%) but does not bottom or top out. If I change to a thinner oil and lower the level 10-15% the forks would probably need the extra preload of a longer spacer to prevent bottoming.

It's an art as well as a science.

 

[Garnet]

My S came with what looks like the same red fork oil that my CBR125R had in it. It looks, feels and smells just like ATF, which usually has a cSt @ 40c of 35 which is very close to what Honda 10w is.

BTW the bit of 7wt I added was Maxima Racing Fork Fluid (125/150 7wt) rated at 26.7 cSt @ 40c. Unfortunatly I don't have an accurate measurement on what the blend is. I thinks I will just live with what I have till Race Tech's phone number works it's way to the top of the list. (They have already moved up several places.)

As for measuring travel, I had the bike blocked up like Dave explained above so the front wheel was just clear of the ground. Because I had the fork caps off, I simply lifted the front wheel up as far as it would go, then let it back down. I then measured from where my zip tie had stopped down to the fork seal.

 

[L.B.S.]

As for measuring travel, I had the bike blocked up like Dave explained above so the front wheel was just clear of the ground. Because I had the fork caps off, I simply lifted the front wheel up as far as it would go, then let it back down. I then measured from where my zip tie had stopped down to the fork seal.

Are you taking into account the rebound (or top out) spring at the bottom of the damper rod? It's about 12mm at least, free length. I wouldn't be at all surprised if the manufacturers counted that in their fork travel calculation specs. ie: "dry weight" "wet weight" "curb weight" etc., etc.

I don't think the weight of the wheel off the ground truly pulls the forks down 100% as far as they go, they are held up via the rebound spring a wee bit. If you secured the bike, and pulled down on the wheel, I am sure you could extend the forks another 10+ mm. (against spring tension)

 

[Garnet]

Are you taking into account the rebound (or top out) spring at the bottom of the damper rod? It's about 12mm at least, free length. I wouldn't be at all surprised if the manufacturers counted that in their fork travel calculation specs. ie: "dry weight" "wet weight" "curb weight" etc., etc.

I don't think the weight of the wheel off the ground truly pulls the forks down 100% as far as they go, they are held up via the rebound spring a wee bit. If you secured the bike, and pulled down on the wheel, I am sure you could extend the forks another 10+ mm. (against spring tension)

Good point, I never thought of that. But when I put the fork caps back on (springs preloaded) the forks did not extend further. I'll take a closer look, I never ran into this on my CBR.

 

[Antarius]

Garnet,

The bottom line is the damping rod style fork -- especially on one as thin as the NC's, is simply not capable of keeping up with a series of bumps in rapid succession. The rear shock isn't either, for that matter.

The only real true solution is, as you know, to go to a cartridge style fork that allows you to tune preload, compression and rebound independently of one another. Since you can't do that, you're going to be compromising somewhere the damping rod fork.

You will be able to soften or harden the ride up with a softer spring, less preload, a larger or smaller air gap, thinner or thicker oil, etc -- but you are still putting a bandaid on a broken arm. The reality is in all of those scenarios the fork is simply incapable of working as it should over a rough surface -- the fork isn't "quick enough" to follow the surface, and thus, skips or bottoms out. The wheel fails to follow the road smoothly. In any scenario with a damping rod suspension you will merely be suppressing that "feel," though the fork itself will still technically be operating improperly.

The same goes for the rear shock. The stock valving is just simply incapable of handling bumps in quick succession, the valving isn't fast enough to follow it -- so it stops working.. and like a bad strut on a car, this means you are now using the preload springrate as your means of rebound and compression. Needless to say, that's not ideal. Soften the preload a little so it's "softer" and you're more likely to bottom out, increase it, and you get a jarring ride because the valving isn't doing what it's supposed to (dampen) during the compression and rebound stroke.

Good on you for trying all you can before you toss in some emulators, or as some have some ricors or intimidators, or even a full cartridge kit -- but I think in the end you'll be doing exactly that.

I'm running the stock suspension -- which is just fine on a freeway, but horrible on a bumpy backroad when I want to do anything more than "cruise," due to the front end chatter -- until it's time to "service" it per the manual. Then emulators will go in the front and an Ohlins or similar length fully adjustable OEM shock will go on the back.

 

[Fuzzy]

All I can say is the gold valve emulators and Penske rear shock made a world of difference for me. If not perfect I am not intelligent enough to know it.

 

[Antarius]

All I can say is the gold valve emulators and Penske rear shock made a world of difference for me. If not perfect I am not intelligent enough to know it.

I bet is as close to perfect as we can reasonably get!