Kyle Racing Fork Revalve for 5th Gen

Went down to Kyle Racing today with my buddy Brian so that Dan Kyle could revalve the forks for the 5th Gen. Took about 2 hours for him to do the work, not counting interruptions from the phone ringing.

Overall verdict: Very good performance now from the forks. It matches the Ohlins rear for damping and control, and now the spring rate is correct.
The bike feels much better controlled and the handling is notably crisper, no dichotomoy of harshness on compression damping and softness with respect to springing. The bike also stops notably better because the front doesn't dive as much as before under braking. The increased fork spring preload means the front sits a bit higher than stock, so the bike understeers a bit more than before, but only by a skosh. I will have to drop the front in increments of 2 mms until I find that sweet spot of steering and stability. Probably only take between a 2-4 mm drop to get there.

One of the things Dan did was to polish the stock pistons flat with a diamond polishing slab. He had me do one and you could tell how the surface of the stock pistons were not flat; this will make the shims in the stack seal against the pistons better and work the way they were intended. We also polished up the main rod in the cartridge.

One thing that was disappointing was upon removing the forks, it was clear that the fork tubes had rust pitting on the tubes just under the lower fork bridge, probably from a lack of thorough cleaning of the bike by the original owner (thoroughly clean your fork tubes when you wash your bikes, guys!) This means we could not polish the fork tubes super smooth as they would rust more and risk cutting the seal. I have to order new fork tubes at some point in the near future and have Dan swap them in.

Photos to follow later; including pix of Dan checking shock springs on the shock dyno for linearity. Surprising how many springs from mfrs, including Ohlins are not linear. He showed us some shock dyno curves with some really crappy springs; springs that would never work right no matter what you did to setting.

There was a Hyperpro shock there with it's trademark purple spring. Dan said it was an okay shock, but not as good as an Ohlins in his opinion.

 

Puma, I really wish you would stop these modification. It is giving me a feeling of inadequacy...

Seriously, though; right on! Tuned suspension is a wonderous thing. As soon as I get to actually take an extended trip on my VFR and figure out if I am going to keep it, suspension will be the first thing on the list. In the meantime, I'll suffer with my jealousy.

For what it's worth (you know I can't help myself), and forgive me if you've already come across this info, linear wound coil springs typically follow a "20-60-20" curve. The first 20% of compression is unlinear/unpredictable, the next 60% is linear, and the last 20% is unlinear/unpredictable. This rule tends to hold true even with precision springs, so most designers will try to select a spring that they can use within those parameters in a critical design. Jeopardy, here I come... Not!

OK, end of unsolicited gearhead stuff. Have fun!

 

Hey PC; With all those suspension upgrades looks like no one will be able to keep up with you this spring. I have a few questions and comments about your forks. After I installed my Ohlins shock, I called the Ohlin tech guy to find out what he would recommend to do to the forks. He said a few things
must be done first. Take apart the forks and clean everything well. He also said that you must replace the fork seals and all the bushings. So I was wondering were the forks removed from the bike? If so what did the old fluid look like? Were the seals and bushings checked and replaced? I am asking you these questions because I want to send my forks out to Dan for a rebuild.
I did talk to Dan a few months back and he certainly knows his stuff,but I was wondering if he made the changes that the Ohlins guy spoke about.eddie

 

Lgn, we looked at dyno charts of a no. of springs, and while the good ones showed up curving upwards with respect to nonlinearity when nearing the full range of compression (that is when the spring had a lot of load on it), the good Ohlins springs did not have a nonlinear portion at the beginning as you describe above; they were almost perfectly flat from beginning to the end. In fact, Dan showed us a few that were perfectly flat across the entire range of compression (spring force).

Here Dan is putting my buddy Brian's spring for his Monster S4 in the dyno.



The dyno does it's work....compressing and releasing the spring in a programmable way...



The dyno trace of the spring's linearity...this is a good spring, it only goes nonliner at the very end of it's travel, and only slightly at that...



Here is a crap spring from another shock manufacturer...Dan says this spring will not work correctly regardless of what you do with respect to settings e.g. preload, damping rates; look at the nonlinearity. It's basically garbage...this is some of the dreck that people are getting when they buy aftermarket stuff.



Springs ready to go on customer's shocks. All shocks that you buy from Dan are matched for your weight. Certain springs for certain bikes (longer, lighter spring rate springs) are typically excellent in their accuracry of spring rate with respect to linearity AND reproducibility from spring to spring and lot to lot of wire, and do not need to be measured. All the ones you see with paper rolled up in them have been individually tested and have quantitative data on their performance.



Unfortunately for us, Honda has tended to use suspension linkage designs that require short, high rate springs...which are not so reproducible in their accuracy and linearity. So, in applications like these, Dan tests every one, and sends bad ones back to Ohlins. Where else can you buy a shock at a discount and get customer service that will ensure that when needed, your individual spring gets tested with quantitative data that it is accurate and linear with respect to spring rate? Impressive stuff indeed.

 

Eddie, we did not remove the fork tubes because they had rust spots, and I am going to replace the tubes at some point in the near future, so we did not dissemble the tubes from the sliders. We only pulled the cartridges and revalved those. Typically though, you do not need to replace Honda bushings...even Max McAllister of Traxxion Dynamics says this.

We did clean everything throughly, and then revalved the cartridge. The oil was dirty and Dan refilled with 5wt instead of 10 wt using the new shim stacks.

Forks draining...


Dan using the diamond hone to flatten the pistons...


Dan swapping out a shock spring...


Newly reconstructed shim stacks...

 

Thanks, Puma! I really like the tech stuff... looks like I know who to call when/if it's time for suspenders. I'll look for his website after I finish posting this.

I wanted to send you the link I had for the spring info, but most of my old bookmarks went away with my recent hard drive death. It was an "Engineering Note" sort of thing that covered generalities that I dug up when I was doing some RaceTech emulator mods. I do have to say that the Ohlins chart is mighty impressive. I think the crap spring, or one of its relatives, may have been one I have on a shock I no longer use...

 

Nice write up Steven I'll just ask as I haven't searched nor looked very hard, but whats Dans web site? physical address? okay what about a phone number? I just might like Dan to look at what I have, more than one opinion is a good thing. I tell ya with this write up he just might get a shit load from here arriving at is door. Good job.
Question ,what about your fork springs? did you stay with the stock ones? I know from past experiences Honda puts in way to soft a spring from the start, and no matter how hard you try with fluid and the like, the springs are to soft. whats your take on this as I'm sure others would like to know. onward ho.

 

Lgn, if I recall correctly, the crap spring came from another manufacturer. This does not mean that Ohlins does not make bad springs from time to time...they do. Dan says that if a few springs from a particular build are good, then the rest usually are. Ohlins probably buys steel wire in large rolls, pulls them off and winds them into springs. My guess is that when springs are not so good, it is a reflection of the quality of, or variances in, steel provided by the OEM supplier to Ohlins. The key point is that Dan, with his extensive experience, knows which ones to test and which ones he typically does not have to test.

And as you point out, it's hard to argue with quantative data...

 

Jay,
Here is Dan's web site: http://www.kyleusa.com/

It has his street address and phone no. on the front page.

To answer your question, no, removed the stock springs and replaced them with linear ones appropriate for my weight. You are right, the stock springs are waayyy too soft. Dan then revalved the cartridge work better...the design is based on an F4 design that Dan developed from a racing application. It's the same basic design for a number of bikes, including the RC51, CBR929, 954, F4, F4i and VFRs. The very newest bikes (e.g. 600RRs and 1000RRs), he recommends using an Ohlins 25mm cartridge kit.

 

Non-linearity is a trait of all springs. This is apparent at the ends of travel, free length on one end and solid height at the other. Springs have residual stress from being coiled which interferes near the free length. At the other end, due to production variances you'll never have all the coils touch at the same time. As coils begin to bind the rate spikes rapidly. This is why you are not supposed to use a spring within 10% of either end. I have a spreadsheet that I use to determine if the spring is over stressed but it also shows me a graph of the operating range and flags if it's outside the 80% zone. Spring manufacturers never check the rate of a spring on the extreme ends, though it looks like Dan does.

Springs are crude devices but require a lot of science to understand fully. I'm not sure that I agree with Dan's comments about a non-linear spring "not work correctly". I think all aftermarket shocks come with springs that are good enough for 99.9% of us.