Track stuff from Finland

[petrolhead]

Originally Posted by engine-hear

Hello Petrolhead,

I would like to share some infos with you.

Front Fork Ninja 250 (all values in mm)
OEM Modified
FEGV* 0,0 15,0
*FEGV = Fork Emulator Gold Valve
Spring 420,5 420,5
Washer 1,5 1,5
Collar* 100,0 85,0
*Collar is what sharky_nrk calls 'spring preload spacer'
Sum 522,0 522,0
Preload 22,0 ~14,0 with 3 turns (to start with)
If you use Preload-Adjuster take them into account.

Do NOT use 15W Fork-Oil, use 10W or even lower.
Raise the Air gap until you think it's the best for you (start with recommendation)*
*When you put the FEGV into the fork it raises the oil-level by 29mm (measured)
DO NOT FORGET to drill the bigger holes into the damping rod!

Get the following product: https://www.hks-czech.de/produkte/hks-ggv
For: Elimination of the telescopic fork breakaway torque (this works absolute great!)

Lower the front by 10mm and raise the rear also by the 10mm, this makes the cornering easy. But, if you don't like it change the values like you want.

Sag setup (from my bike)
Front: 35mm
Rear: 27mm

My computer crashed 6 years ago, I think I could safe most of my data (but must search for it, since I didn't use them since then).
I have some documents also, but I think I need some posts, before I can insert them.

Thanks for this. I thought I might go back to slicker oil once I get emulators that actually fit.
The bike actually is lowered perhaps 1cm from the front and close to stock (high) setting in the rear. BTW, I keep my notes in a book in the track day tool box. Same thing with my E30.

[petrolhead]

I just spent an unreasonable amount of time bleeding the front brake/getting the softness out of it. I think I recognice the problem. With a solid caliper the pistons move only half of the distance of a floating caliper's pistons. Movement is so small, that pumping the lever doesn't really push them out. Tension of the piston seal pulls them back after applying brake. End solution was to push fluid with a 100ml syringe in to the caliper bleed and let it out from master cylinder bleed.
Once everything is set up the 16mm master cylinder is spot on for the 30/34 Brembo.

Book time for a car's brake fluid service is 30 minutes including bleeding the clutch. Yes european passenger vehicles mostly have 3 pedals. As they should.

[petrolhead]

At Alastaro racing circuit today for the first time ever
. On the first stint chain broke and I had no spare. 2 riding sets lost because of that, me dashing to the nearest (not near) parts store to get another one. Luckily no other damage due to that. Then some time lost due to red flags, lots happening there today. He kept pace with the lower middle group, all 600 or 1000 bikes with calm riders. Then moved to slow group in hope of less traffic. Lack of power shows there, his top speeds were 145ish. Fast bikes top 240km/h there. Reasonable amount of laps. I'll see about video later.
Four groups: fast, fast mid, slow mid, slow.

Edit, oh and I had said out loud the previous week that I should throw the chain in the metal bin and get a new one. Just as a matter of maintenance, no noticeable damage in it.
After six years of this hobby I got around to buying an approved "pit box carpet" whaddoyoucallthem. Allows me to handle fluids/refuel in pit box. Finland has seriously tight regs about ground water protection and green activists love nothing more than to spot and report violation on track. Real or imagined, noise or pollution.

[petrolhead]

Link to original page on YouTube.

[petrolhead]

On track photos ©Lumi Ollikainen.

[petrolhead]

I've been reading up on damping a bit. Am I thinking this correctly. If an emulator has a lot of preload on the top (compression) plate spring, that would make it very digressive? Then I've been playing with an idea of replacing the top plate and coil spring with a shim stack.

[sharky nrk]

That would be mostly accurate for the compression rates. The low speed ports will offer a particular curve that should be fairly restrictive with a relatively low cross sectional area for the orfices to pass the fluid through. Then the compression plate, once the spring is overcome by the additional force, will move upward opening the larger valve holes to allow for additional fluid flow with a damping curve that is far less restrictive. How digressive the overall curve is will depend on the number and size of the low speed orfice holes, and how much spring preload and what rate spring on the release valve.

[sharky nrk]

A shim stack may work in place of the "release valve" for even greater control of the damping curve but I am not sure the geoemetry of the "release valve" chamber would suit the flow around the shim stack well.

[petrolhead]

Originally Posted by sharky nrk

That would be mostly accurate for the compression rates. The low speed ports will offer a particular curve that should be fairly restrictive with a relatively low cross sectional area for the orfices to pass the fluid through. Then the compression plate, once the spring is overcome by the additional force, will move upward opening the larger valve holes to allow for additional fluid flow with a damping curve that is far less restrictive. How digressive the overall curve is will depend on the number and size of the low speed orfice holes, and how much spring preload and what rate spring on the release valve.

Thanks for commenting. Thinking about it more, if one were to use shims.. maybe drill the compression side plate full of holes and stack shims on top of that. This is what I alwys do, trying to understand the system and maybe improve upon it by modification.
My thinking is that with an un preloaded shimstack the damping would be more linear or progressive.

Edit #2, now that I think of it. A stiffer spring with less preload a top the compression plate would be less digressive than a soft spring with more preload.

[engine-hear]

petrolhead,

I would like to give you some links to infos about the FEGV (if you have them already, just miss my comment)

https://racetech.com/ip-fegv-std-emulator/
https://racetech.com/ip-fegv-emulator-list/
https://racetech.com/emulator-tuning-guide/
https://www.fz07.org/thread/13473/my...lator-journey/
https://www.thumpertalk.com/forums/t...t-up-database/

[petrolhead]

Cat delete, minus 200g plus 0,01hp.

[petrolhead]

The welding won't be winning any prizes ar per. Two different materials with different wall thicknesses and small difference in OD.
I went through the welds with pressurerized air and patched as needed. And it fits the bike still, so good enough.

[engine-hear]

@petrolhead, when you want to do something amazing to the engine of your bike then install the 'Ignition Advance Kit - NOT designed (but usable) for 250!' - RTR-KAW-5-05
You find it here: http://www.factorypro.com/Prod_Pages/prodk14.html
(scroll down a little bit)
A description is also here: https://www.ninjette.org/forums/showthread.php?t=93996

[petrolhead]

Interesting mod that ^, thanks. People seem to report it works fine. Without comments, I'd be skeptical about moving the entire advance map by some degrees.

My solution for the exhaust mod was to tack the ends of it to a scrap metal frame, to hold it's form. This was again a zero cost mod I did in a hurry after work day so quick 'n dirty. By ear I couldn't notice a difference in exhaust noise.

[petrolhead]

Now I'm confused. The shim that sits a top the large spring is supposed to be the plate that opens in rebound, right? It's ten times softer than the narrow top spring. And rebound is supposed to do more damping than compression.
Edit.. I calculated the max cross sectional areas of flow, compression is ~1,41cm² and for rebound ~1,01cm². Still, I don't get it that the rebound side opens up with very little resistance.
Top plate has only one bleed, ~2,4mm diameter.

Edit 2. I miscalculated. Limiting factor in compression flow is the big shim's center hole, which is smaller than the one than the one that opens up in compression.
Edit 3, I measured rhe top springs to be ~6,5kg/cm.

[petrolhead]

One idea. Drill lot more holes in the top plate and put in a couple thin shims. Compression side would have more low/midspeed flow without affecting rebound. Would neccesitate a small additional bleed be drilled/filed sideways to the top plate. Absolutely no idea how that would work.

[sharky nrk]

these types of emulators are only for compression damping. the damper rods still control rebound. the rebound relief spring should be super soft to allow flow of oil back in to the chamber with very little resistance to flow.

you manange rebound in these types of fork setups with orfice size and oil weight and then adjust compression via the emulator. emulators primarily are a method to reduce the wallowing of damper rods due to slow compression movements and the harshness of compression hit on big bumps

[petrolhead]

Originally Posted by sharky nrk

these types of emulators are only for compression damping. the damper rods still control rebound. the rebound relief spring should be super soft to allow flow of oil back in to the chamber with very little resistance to flow.

you manange rebound in these types of fork setups with orfice size and oil weight and then adjust compression via the emulator. emulators primarily are a method to reduce the wallowing of damper rods due to slow compression movements and the harshness of compression hit on big bumps

In that case there'd be more damping in compression than in rebound which is kinda silly. I guess I could replace the lower soft spring with a stiffer one and limit it's range of opening.

[petrolhead]

I'm a bit lost, again. I don't understand the function of this hole. I've seen it called a rebound hole on some bikes but it doesn't compute. It's always open like the two bigger are, should allow similar flow to both directions?
Edit. The two damper rod holes are both about 5,2mm stock. The emulator's center oilway for compression flow is 12mm, minus 4mm bolt going thru it. That cross sectional area is exactly equal to two 8mm holes in damper rod.
Edit 2, nevermind. Damper rod goes thru a seal in the low end of inner tube. Holes are on different sides of that. Actually good thing to note. The height/placement of additional holes matters.

[petrolhead]

Originally Posted by sharky nrk

these types of emulators are only for compression damping. the damper rods still control rebound. the rebound relief spring should be super soft to allow flow of oil back in to the chamber with very little resistance to flow.

you manange rebound in these types of fork setups with orfice size and oil weight and then adjust compression via the emulator. emulators primarily are a method to reduce the wallowing of damper rods due to slow compression movements and the harshness of compression hit on big bumps

While commenting on this I hadn t realized how rebound damping works in these. Apparently the seal at the bottom of inner tube acts as a check valve, allowing the underside of piston to fill up but the oil only exits thru the small hole when the space becomes smaller in rebound.
Edit. Drilled the two existing damper rod holes to 7,85mm. That's almost 2,28 times the original area of flow and 85% of what the emulator can flow. Apparently my 7,5 drill bit does a 7,85 hole.

[petrolhead]

YSS310 emulator is 0,4mm bigger than the tube internal diameter (~30,6mm). Also the lower part is 24mm whereas the piston's "cup" is only 23 where it's supposed to sit. So it takes some grinding to make them fit. The parts that would just drop in are YSS290. It baffles me that they advertise 33,5mm parts as a fit. Apparently the Race Tech emulator for 250R has 29mm OD. I'm making do with these. They might not be the last solution that these forks see.

[petrolhead]

I've been trying to calculate the force of the "air spring" in the forks. There's so many variables that I'm probably missing something, I got some wild numbers as result. I'll have to fill up a fork and take maeasurements I guess. I thought if I had data points with couple different oil levels I could use that as a spring tuning tool.
Another thing I thought about.. with a higher oil level the average pressure is higher. Common sense says it should lessen oil cavitation / foaming .

[Mohawk]

Air operates on Boyles law, if you halve the volume you double the pressure. So if you have a 100mm air gap at 1bar atmospheric pressure & you compress forks 50mm you will have 2bar pressure, compress another 25mm (half the volume) you will have 4bar etc for every halving of the volume. So you can calculate air gap to pressure ratios based on firk travel.

Re cavitation or aeration, on a damper rod fork, fit a top hat in the spring bottom so oil ejected during compression hits it say 25mm up the centre of the spring & is deflected sideways which still in the oil column, thus it never sprays into the air gap & avoids foaming. Bare on mind that as the fork reaches full compression the gaps between spring coils compress & will reduce the sideways flow this increasing compression damping in extreme cases.

[engine-hear]

Hello Jarno,

something more to read...

https://www.peterverdone.com/suspension-nerds/

https://www.peterverdone.com/archive/damping.htm

There's many more.

[petrolhead]

Originally Posted by Mohawk

Air operates on Boyles law, if you halve the volume you double the pressure. So if you have a 100mm air gap at 1bar atmospheric pressure & you compress forks 50mm you will have 2bar pressure, compress another 25mm (half the volume) you will have 4bar etc for every halving of the volume. So you can calculate air gap to pressure ratios based on firk travel.

Re cavitation or aeration, on a damper rod fork, fit a top hat in the spring bottom so oil ejected during compression hits it say 25mm up the centre of the spring & is deflected sideways which still in the oil column, thus it never sprays into the air gap & avoids foaming. Bare on mind that as the fork reaches full compression the gaps between spring coils compress & will reduce the sideways flow this increasing compression damping in extreme cases.

Thanks for your comment.
Yes that's how gas pressure works. My difficulty was to calculate the initial air volume. 108mm oil level fully compresed doesn't translate to oil level 108+X when de compressed by X mm. My measurement was that with 108mm compressed, 113mm of extension drops the level by 149mm. I guess that's down to inner tube wall thickness also having a volume. I'm not looking to make this an exact tool, I want to find out a ball park figure how much force I add by raising the level by say 5mm. Having a guesstimate might save a couple of trials and errors. One could make an Excel about this, might be handy.
Coming from the world of cars, I think that a medium/soft coil spring combined to a meaningful amount of air spring might be good. Soft spring gives compliance and allows the suspension to do what it's supposed to. A steeply progressive air spring then limits max dive.

-Jarno

Edit: with the emulators oil flows pretty muh sideways from under a 16mm top plate. Spring ID is ~20,5mm so area of flow between them is about 1,25cm², more than enough in worst case scenario. But that's actually something to consider because I'd toyed with the idea of having shims on top of the plate.

[petrolhead]

Originally Posted by engine-hear

Hello Jarno,

something more to read...

https://www.peterverdone.com/suspension-nerds/

https://www.peterverdone.com/archive/damping.htm

There's many more.

Hi
Feel free to dump any and all links here. And thanks.

Edit. I did the calculation with stock 108mm oil level. At 7cm of compression the air spring is only ¼ of the coil spring force. At 9cm it's half of coil springs, in effect ⅓ of the total. Raising the level to 100mm does very little change til ¾ of suspension travel is used up, then ramps up very quickly. If the air volume was larger with an initial pressure the force would be more linear and meaningful sooner in fork travel.

Link to original page on YouTube.