The Firefly/PVD Serenity.

After designing the new titanium road and mountain bike dropouts for they guys at Firefly Bicycles in Boston, it was time for my payback. A nice titanium mountain bike. Of course, the design of the bike would be as specific as the dropout designs. I had a vision of exactly what I needed. The goal of the bike was to be a leggy, lean mountain bike for longer excursions on smoother trail. The bike also needed to be able to rail some real trail when the situation called. It should fit that bill nicely.

I’m going to test out the 38/26 & 11-34 gearing as it sits now. If that isn’t manageable (out of shape) I’ll swap out to a more trail oriented 36/24 & 11-32 gearing. We’ll see how that goes.

I’ve never had a bike so nicely crafted. The welding and detail are flawless. It just looks fantastic! Thanks so much!

Named after the Firefly class transport ship in the scifi epic of the same name. The Serenity.

The print showing the critical dimensions supplied to they guys at Firefly for making the bike. I get a little specific…

Note a few details:

* 30.9mm seat post - I wanted an option to add a dropper post when fully sorted late models are introduced. Now it’s the only 30.9mm posted Firefly.
* Future style FD routing – Front derailleur stops will be fazed out in the next few years. I’ll clean this up with a band clamp version when we see it.
* Great and proven Bay Area geometry. Low, slack, fast. All three. Weight set back for fast decending. Nice and flexy to hug the trail.
* Max tire clearance of 2.0″ - Running anything larger on a 700c wheel is just dumb. Kenda 1.95″ loaded.
* Cable routing for great function - PVD routing eliminates contaminates while keeping trail serviceability.
* Light, wide rims – What more could you ask for?
* Front end options – Squish or rigid. Fully sorted. This bike will be fun in the city with a carbon fork, leaner tires, and taller gearing. Smashingly good fun.

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I got down to finally replacing the Heavy Buffers Modified AR10 Buffer Spring on my AR-10. I’ve been having some cycling issues that have outlasted the break in period on the gun and I want to get that resolved. I had initially wanted to put a DPMS LR-308 Rifle Buffer Spring (#308-BS-10B) into the gun but they were out of stock at the suppliers I’ve been using until recently. It’s a lot nicer of a spring as it’s ends are properly flat instead of just chopped coil. The Heavy Buffers spring was mad of 0.070″ wire, 28 coils, and 290mm long. The DPMS spring is made of 0.080″ wire, 38 coils, and 323mm long. The action feels a lot better with the new spring.

An issue did come up though even after changing the spring… short-stroking.  This could have been a result of having the adjustable gas block too restricted but that was opened entirely and didn’t resolve the problem. This morning I went through the gun and found that using grease to lube the BCG had been a poor choice. As time has gone by the grease has caked and has slowed the movement of the BCG. I cleaned it up and lubed it with CLP. It’s far more free now. Hopefully this will solve the issue.

For additional insurance against friction I ordered up a POF-USA Roller Cam Pin .308 For AR/10 Piston Driven and Gas Impingement Rifles (PN# RCPA308). This may help reduce some of the drag during cycling. By letting the bolt cam roll instead of drag, considerable friction can be eliminated from the system. Let’s hope.

I also bought a Timney Trigger Tension Scale (8oz -10lbs). Using this on the AR-10 I measured 4 lbs exactly every time. Very very consistent, it has a Timney 4lb trigger installed. My Ruger 77/22 was letting go between 4.25 and 4.5lbs randomly. Ok, but not excellent.

On the theme of triggers, I ordered a new hammer spring for my Berretta 92FS. The trigger pull stock is very smooth and 5.5lbs. I swapped in a Wolff 28616 (16lb) spring for the stock 20lb spring. This reduced the trigger pull to 4lbs. Nice.

I changed the recoil spring in the Berretta as well. Since I shoot a lighter 115gr. round I should be able to smooth things a bit with a lighter spring. Replacing the stock 13lb spring with a Wolff 11lb (40611) spring was simple enough. The gun felt better than ever and I’ll be ordering a 9lb (40609) spring on my next order.

The best thing about all of this spring tuning is how cheap it is. Spring cost so little and the difference is really noticeable. Nice.

My new bike is going together. More on that later…

Working on PF30 for the first time is not going well. I’m a known BB92 guy. I know it’s the best way of doing things. The world, it seems, doesn’t agree with me. Thus, PF30 is taking over. Grrr…

The new bike has a PF30 BB with a width of 68mm. That’s a problem for a mountain bike. Mountain bikes with this setup should have a 73mm wide BB. The market has produced several shim kits to make up the difference. These don’t work the way I like with Shimano Hollowtech II cranks. Shimano likes a 96.5mm width at the crank faces for MTB, offset 2.5mm to the drive side. That means 2.5mm of shim on the non drive side and 5mm of shim on the drive from 68mm.

I prefer any bearing configuration that gets the bearings as far apart as possible, thus my dislike for BB30/PF30. Of the adapters on the market, the Parlee unit is the only one to take advantage of increased bearing spacing. The problem is that these also don’t fix the MTB spacing issue. To get some of that off of the spindle, I made these little shims. 46mm ID x 49.25mm OD x 2.5mm. This way I only have to shim the spindle 2.5mm.

I don’t like this solution. I’m working on something else that’s pretty sweet but I figured that I could whip these up quick and get things rolling before investing in a final solution.

These parts were installed into the frame using Loctite 680 ’Slip Fit’ Retaining Compound. Adapters in PF30 shells that are made of aluminum are known to make some noise as they shift. I assume this is due to a greased interface. By using a retaining compound, I hope to create a structural buffer between the two parts and eliminated any shifting. We will see.

I finished working on the forks from my GSX-R750 K8 this Sunday. I was able to take a short ride on the bike that afternoon and a longer ride on the way to work this morning. The results are simply awesome. Not just in the functioning of the forks themselves but completing the whole bike and how that works now. I can honestly say that I am a few clicks away from being finished with the basic tuning of an incredible motorcycle.

I went back and put the OEM 50mm negative springs back into the dampers. This was the right thing to do as the 75mm springs were too long and I couldn’t acquire any 60mm springs. The 25mm springs were not the direction that I really should have gone and I had to undo that.

I also decided to use the Ohlins .95 kg/mm springs that I had. They are just a little softer than the OEM springs and will be better for street. They are 5mm shorter than stock resulting in 10mm of internal preload with the spacers that I cut. The external preload is set at 0mm and doesn’t need adjustment right now.

Correcting the forks length issue was done with some Traxxion Dynamics top caps with 20mm of extension from OEM. They look great with the black forks. More importantly they put the front end in the proper position.

The bike really holds a line now with the very slightest of over-steer. It is so much easier to ride, is super comfortable, and just as solid as a rock on even the most twisty and bumpy roads. Riding to work this morning on Bolinas/Fairfax Road and Route 1 north of San Francisco tested the bike in some of the most challenging conditions you can find anywhere. I was constantly tempted to go faster, push harder, and trust the bike more and more. It’s a great feeling when a bike is set up at this level. Really, I just need to get back in the groove of riding and get my flow back. It’s been a while since I really was in good riding shape. This upcoming weekend is going to be pretty fun!

One detail that will have to be resolved at some point, the rebound adjuster is set at just 1/3 of a turn out. That’s not very good for adjustment range. I may have to replace the ISO 16 oil with something thicker, like ISO 20. It’s just a small detail but worth working out next time I have the forks apart.

Valving. I didn’t make any internal valving adjustments to these forks. Given that the forks damping seems to work well enough and that it came stock with such a heavy spring, I decided that I would just leave things as they are. It may be that the rebound needle needs some reshaping or that an additional shim is needed on the rebound stack to give the fork some adjustment range. I’ll look into this later. I’m just happy to ride things as they are now.

Another detail is that the oil height (OEM 115mm) may be a bit too high. It’s a little early to tell and I’ll know more after this weekend but it does seem like there is room for improvement here.

I’ve got an amazing motorcycle. A 2008 GSX-R750! It’s pretty well modded and specifically put together for my needs and goals. I’ve done everything to it that I’ve wanted to except for one last detail, the fork.

Typically, tuning the fork of a motorcycle is one of the first things that I do, not the last. I was so impressed with this fork out of the box that I wanted to run it for a while and appreciate the great job that Showa did with it. That time has gone and it’s time to make it work far better. One major reason why this fork works so well, other than it being a magnificent example of Showa’s engineering, is that it is setup stock with quite a stiff spring. I’m used to Honda bikes that come with remarkably soft springs (7.5 N/mm!?!?). That’s pretty much unusable for anything but commuting. This bike has a 9.8 N/mm spring in it stock. WOW! That’s a racing spring. Anyway, it felt pretty good but there are two issues that really needed attention; length and oil lock.

The compression damping on this fork is pretty sweet as well. The main piston has valving for both high speed compression and rebound, the fork lowers have a blowoff valve and low speed compression adjustment. Pretty nice for a street bike. Things have changed so much in the last 10 years or so with sportbikes. From simple damper rod forks to external adjustments like on this cartridge fork. It’s good to be king.

The stock length of this fork is too short for this bike and that is magnified when the rear ride height has been adjusted. Because of the short fork, the bike capsizes (over-steers) on corner entry. If you are used to a properly set up bike with neutral steering this can be quite an alarming struggle. It’s a known issue and many racers are forced to address it. Many people replace the top cap with a longer version that let’s them drop the fork in the clamps. This is simple and easy, but it’s also very expensive if you can even find the part for sale. I had tried this but they were out of stock. A cheaper way to do this on some bikes is to install a shorter negative spring since this bike is a long negative spring type fork. This is a $30 solution, but requires complete dis-assembly of the fork. That’s how it works for the 600cc bike. I decided to purchase some parts from Traxxion Dynamics to get this done, things got crossed up (wtf?!) and I ended up with short top out springs to swap out rather than the extended rebound valve base that they make for the 750. I don’t know what happened here as I had purchased the parts last year and only got to the fork now. I’m pretty pissed as I had made the assumption that this was all going right. Kinda pissed as I’ve put the time into the fork. At least I can test some other parameters.

The oil lock or bottoming valve is in place on the fork to provide the manufacturer and the consumer with a certain amount of protection in the case that a poorly setup fork is over taxed and wants to bottom (metal to metal). This is a good thing for the newb as they have this insurance. What’s the problem? Easy, this valve effects the last 34mm of travel on this fork. Once you have entered that region the fork works HORRIBLE. Imagine that! 40% of the compression travel is just the worst crap you can imagine offering very close to zero bump compliance. If you understand suspension tuning and how to use the bike properly, you can remove that valve opening up that 40% for as much traction and compliance as the rest of the forks range.

Here’s some of the information:

Leg weight – 3800 g.
Main spring – 265mm-9.8 N/mm
Negative spring – 50mm
Negative spring interact -95mm chrome
Measured oil height – 133mm (way off)
Oil – Showa SS-05 (ISO 15.7)
Bottoming valve function – last 34mm
Fork bottom – 2mm chrome

Original Setup,
w/max preload – 121mm chrome
w/min preload – 112mm chrome
Running – 15mm preload (max)
Preload spacer – 118mm
Low speed rebound – 1.5/3.5
Low speed compression – 3/4.5
High speed compression – 3/4.0

New Setup,
Traxxion Dynamics negative spring - 28mm
New preload spacer – 133mm
Oil – Red Line mix, ISO 16
OEM oil height – 115mm
w/min preload – 125mm chrome
Negative spring interact -120mm chrome

I’ll be refilling these forks with suspension fluid from Red Line Oil. I love the products from Red Line. They are fantastic. The suspension fluids that they make are of superior quality and really do make a difference when used in a system. Things just feel so much better using these oils. Another major reason is that Red Line offers five different viscosities to select and mix from providing a superb platform for any suspension tuner. Their range is both thinner and thicker than anything else out there. I’ll be mixing two oils to get the fluid for the forks. 79% LightWeight (ISO 18.4) and %21 ExtraLight (ISO 9.8) by volume. I’ve made a handy mixing chart that I use, here.

Cool! Blue and yellow make green. Make sure to mix well.

What did the shorter stiffer negative spring change from the longer softer one? Obviously, the interplay region in droop of course (0 to -35), but how does it change the ride height? In a way, not much. It mainly makes it easier to measure sag in a traditional way. Most of my gains in ride height are a result of the increased range from my preload spacer. Since the fork assembled with the new configuration resulted in just 3mm increased length, you can see what it did to the suppleness of the fork in droop. It’s pretty much garbage in comparison. Too stiff. Really, in the end, swapping out the negative springs was more of a downgrade to the fork and really the 15mm addition of internal preload was the change that raised the bike.

The graph below shows how the choice of negative spring changes the suspending force in the system. Note 0mm being JRA (just riding along ride height). 0 to 85mm is jounce and -35 to 0 is droop. Assuming that 979 N. are required to hold the bike up to the proper equalibriam position. When overly long negative springs are installed an additional 5.6mm of preload is required to get the bike up to the correct ride height thus shifting the curve up for the rest of the jounce region. Obviously, the use of negative springs is good for softening the wheel rate in droop when far less weight is on the wheel. This helps the tire track the road with even just slight weight on it rather than skipping off.

As a result of all of this, I’m going to order up the proper extention parts and put the long springs back in place when I do that install. 2 steps forward, one step back. Traxxion is sending me some longer caps and I’ve dug around and found some 75mm negative springs from a 2005 CBR600RR that I’ll put in to get even more juicy grip while on the gas. This may require softer main springs as 60mm is the longest negative spring that is good in this system.

This is an apology to Lorri Lee Lown. I was wrong about something and insisted that I was right.

I argued that the increased friction caused by heavier riders and the increased drag due to their larger size overcame the increased gravitational pull compared to smaller lighter riders making the heavier slower. Doubts arose and I had to check my assumptions (based on experience). I was wrong enough that I couldn’t even push the numbers to fake it. I’m man enough to admit it. It doesn’t happen all the time. This time I was wrong.

This is a simple comparason, given similar parameters, a heavier bike and rider will go faster coasting down a hill than a lighter rider. The assumption is made that this is a road situation, straight ahead without any need for handling skills. It assumes that the tires are identical in every way and that the bikes have no internal (hub) friction.

This comparison is not applicable to offroad situation as the riders skills and tires will radically change the equation.

Using these variables,

Light rider mass – 160 lbs
Light bike mass – 16 lbs
Small rider frontal area – 0.40 m^2
Heavy rider mass – 190 lbs
Heavy bike mass – 18 lbs
Larger rider frontal area – 0.42 m^2

System Cd – 0.88
Air density – 1.225 kg/(m^3)
Gravity – 9.8 m/(s^2)
Tire rolling resistance – 0.004
Hill grade – 15% (8.53 degrees)

Here’s the equation for the aerodynamic drag forces:

Wikipedia

The gravitational pull is a vector component of the forces on the hill while the tire drag uses the normal component:

Wikipedia

Note that the when the pulling force of gravity crosses the resistive force of air, the velocity of the rider will fix. Obviously some real testing could make this a very useful graph.

The thing is, the lighter system is always really going to be faster in practice. It takes far less effort to quickly accelerate back up to speed after needed braking and the system is far easier to control as handling is needed. I would always give the benefit to the lighter rider over the heavier rider but in a simple coast in an idealized, yes, the heavier system wins.

Ask anybody that has studied physics about springs. They’ll tell you about Hooke’s Law, the linearity of coil springs, and brush them off as the most simple topic. They probably got great grades. Some of them probably got masters degrees or PhDs. The problem is is that they don’t know what they are talking about and are wrong. Ha!

Springs are awesome and so cool. For bicycle and motorcycle folk, they can mean the difference between a good/fast time and not so much. Other than tires, springs are the most important part of any suspension system and deserve considerable attention.

I’ve written so much in the past about springs, but I’m going to again. Why? Simple, I need content (Ha!) but also because we need constant reminders as to why springs need to always be put under a microscope.

Today, I’m talking about the most simple spring topic there is, rating them.

Rating springs is rarely done by most bicycle and motorcycle users. I understand that. There is some expensive equipment and some understanding needed for a tiny bit of information. What is really criminal though is how many  ‘experts’ don’t rate springs. This pisses me off as I’ve seen too many bikes just murdered by these people.

This week we sorted the springs out for Mary’s V-10c. She initially ordered her CCDB with a 300 lb/in spring. That was way off. We ordered a few more springs to test. I prefer to order any damper with a minimum of 3 springs. This gives me some range of tunign options to test with. Springs are extremely cheap and it is critical that you end up with the correct rate.

Here’s how the springs we got measured on my Longacre electronic coil spring tester;

It’s obvious that the springs don’t seem to be ending up where you would expect. We can see that graphically like this:

Bicycle industry springs are pretty bad as performance springs go. In motorsport, you would expect a spring to measure within 2% of the labeled value and behave linearly until past the designed stroke, they then tend to go wildly progressive. That’s not a big deal as long as the spring is not used in that range. After that, you then shop for the lightest spring. Honestly, I’ve rated a lot of motorsport springs and the vast majority of them will rate within 1% of their labeled rate. Öhlins tends to produce the finest springs in general when weight is factored in. Hyperco spring arn’t as light as Öhlins springs and sometimes don’t stay as linear as long, but they are priced a lot better and work very well.

Bicycle industry springs are really horrible in many ways. I’ll look at just two factors here.

* Accuracy: Fox promises to supply springs within 15% of their labeled value. You think that’s bad? Actually they often measure up to 25% off. You can expect that any bicycle spring you purchase will be about as bad. Why does this matter? Simply put, you can’t tune your suspension without measuring each spring you use (nobody does).  This is because of something called coil rate overlap. Assume two springs; a 400 lb/in labeled spring and a 450 lb/in labeled spring. The rider is looking for a stiffer spring. She swaps out the 400 for the 450 and the bike works worse. Why, imagine the 400 is actually 15% high and the 450 is 15% low. That means that she actually took out a 460 lb/in spring and replaced it with a 383 lb/in spring. This happens all the time, even if you go to Fox’s race support truck since they don’t bother to rate springs either. Fox also refuses to rate springs you order from them. Ugh! This is one of the #1 reasons why people get lost tuning suspension.

* Precision: Specifically with regard to linearity. While it’s fine for a spring to go progressive after the range of the shock stroke (they all do), it’s bad if it happens prior to that. More important than that, the springs rate should be linear in that used range. This is pretty important stuff. Linkages are used to tune for rising or falling wheel rates not springs. There are progressive springs sold, but only a very few people have ever made much good use of them (the only situation I can even recall is Miguel DuHamel’s fork springs). Commercial progressively wound springs are generally a marketing one-size-fits-all solution sold to noobs. The next graph shows that these springs aren’t even linear in the usable range. They are progressive.

A note on the graph below. The graph of the rates look pretty wild but that shouldn’t be a distraction. The trend line is more important to focus on. Several factors contribute to the erratic behavior. The corse sample rate, the springs unwinding, and the accuracy of my measureing of travel and force. Regardless, the trend line resolves these elements.

Great! We have 4 progressive springs!! (dang!)

Here is a graph showing a few Ohlins motorsport springs that were dynamically rated on a Rohig shock dyno by Dan Kyle. Note that they are nice and liniar until they pass 40mm. That’s fine since they wont be used passed that range. Certainly there is a big difference between the behavior of these four springs. If the lowest one is the lightest, I’d choose that one.

Regarding my graph of the bicycle springs, you can see that all four of these springs start well below their labeled value and end up well above. This is even while removing the first 0.500″ of travel (known to be odd as the springs settle). This is pretty horrible but at least we now know what we have. They can be approximated as their mid stroke value, but still it’s a shame to do this.

At the end of the day, we will probably settle on using the 400#1 spring. She’s ridden this spring and has had good results with it. Also, as this spring approximates a true 400# spring, we can order a titanium spring now with more confidence that the behavior of the two springs will be similar. High end titanium springs will be far more accurately produced that commercial steel springs.

It’s happened again…

I joined up with the guys at Firefly Bicycles to get another dropout done. This time it’s for road bikes. Firefly makes a lot of extremely elegent and fast road bikes. The craftsmanship put into them is borderline obscene. The pride the owners of these bikes take is about the same. Any part added to one of these bikes has to be a home run, a field goal, and a slam dunk all rolled into one. Cool stuff.

The mountain bike disc dropout that we did recently was met with such acclaim that keeping the same theme and aesthetic on a new road dropout was irresistible. I’m pretty happy with the results. They look fantastic.

The pieces were machined by Richard DiFrancisco of Cantabrigian Mechanics. Richard does some incredible work and it’s a breath of fresh air having him in the bicycle industry. I’m hoping to do some more work with him in the future. He’s got some amazing capacity in his shop where he can do almost anything you could want.

Adapting a similar design philosophy to these dropouts was certainly a great challenge. The mountain drops had a lot more room to work with and a much greater mechanical need. Road dropouts are considerably smaller and weight is paramount… as is power transfer. A massive amount of drawing had to be done to fit the detail into the design and keep a similar relationship with the previous design. Some time was spent haggling some of the engineering details with Jamie. He wanted this, I wanted that but I think we both ended up happy with the compromises we made. It wasn’t just compromise though, there were quite a few developments and improvements added since the last dropout design. Subtle stuff, but that is where this game is won or lost. Details. I really had underestimated how much work would be involved. Some elements couldn’t be carried over but I believe that it’s a great result.

These are going to be some incredibly stiff and efficient units. I wish that I was close by so I could ride next to one of these bikes just to see how the light bounces off them during a ride.

I was at the Fontana City Nationals this weekend. A great venue and a great event.

Aaron Gwin was in the house during Saturday’s DH practice. I got to meet him and take some pictures. He’s a pretty low key guy. He didn’t race on Sunday.

The bike was essentially stock other than the obvious prototype Saint parts. The assumtion was that the real development bike is heald with TWR or out of sight. I was able to talk for a while with David ‘Monkey‘ Vasquez (Gwin’s mechanic). He was short and coy with some of his answers but it gave me a good idea of what was going on.

Gwin will be racing at Sea Otter this year. It will be nice to see the bike’s changes for Sea Otter as that is when the new Saint and Zee will be first shown. I’ve seen those parts privately and they are just awesome. Keep an eye out.

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This showed up on the interwebs. I can’t possibly imagine what’s coming…