Suspension again!

[slartybartfarst]

Chad

Yea complete new tubes in alloy sounds. Dont forget you need the rear end lifted/sorted as well, otherwise Id be tempted to drop the legs through the clamps 10 to 20mm to keep the fork angle.

With this mod we seem to have the balance of ride height, squat, bump absorption, and dive so let me know your thoughts.

SBF

[Bfef]

Can I ask what the science bit is regarding this mod please? Not trying to be argumentitive just trying to understand!

If I read correctly the standard forks are too hard and too damped? Does this mean they don't compress very well when a bump is hit and they return to normal far too quick as the damping is too high?

Also, because of the spring and air gap a lot of travel is taken up just with the weight of the bike and rider?

So standard has very hard forks with no travel that damp far too aggresively? Have I read that bit right?

It seems to me as a layman that more "bounce" in the springs with less damping would soften the forks up quite a lot and stop the violent harshness at the bars when going over bumps.

I can see how using thinner oil would help the damping, I can also see that preloading the springs using longer spacers would help the static weight "sag".

But how does tensioning the springs help make them softer and more compliant? Or doesn't it and you are trying to control the rebound only?

I also don't understand the relationship between the springs and the air gap, is it to provide 3 levels of bounce? IE the springs have a tight coil and a lose coil (progressive?) and after they compress then the air gets compressed giving a 3rd "coil"?

Is it better to have less air and use the springs or the other way around?

Finally (!) is it possible to simulate a longer spacer by winding down the top (preload?) nuts further or are they limited because they won't screw into the top caps very far?

Many thanks, please enlighten me as I've just got to sort out the front end!!!

[Demansia]

Chad

Yea complete new tubes in alloy sounds. Dont forget you need the rear end lifted/sorted as well, otherwise Id be tempted to drop the legs through the clamps 10 to 20mm to keep the fork angle.

With this mod we seem to have the balance of ride height, squat, bump absorption, and dive so let me know your thoughts.

SBF

Cheers mate, i already have lift triangles in the back already & when the Falco shock arrives i should get another 10mm as well.

Chad

[bazzywazz]

The Falco shock and Bikefarm triangles jack up the rear to the max ! I had to " adjust " the lefthand exhaust with a hammer to clear the lower chain run ( just a little dent! )...

[Demansia]

The Falco shock and Bikefarm triangles jack up the rear to the max ! I had to " adjust " the lefthand exhaust with a hammer to clear the lower chain run ( just a little dent! )...

Bazz, i found that this happened with just the triangles & my ART pipes. I have mate that is an exhaust fitter & he sorted it for me.

Though it wont be a problem when he finally gets around to making me the set of custom "Laser GP" style pipes he still owes me for signwriting his racecar. These will hang off the right side of the bike similar to what vassilis67 did with his 650 & miss the chain all together

Chad

[weirdo]

I didn't fancy whacking my link pipe about, so i bought a honda crf chain roller off ebay (£7) and made a mounting bracket for it.
It's fastened to the lower exhaust mounting point. I thought it might need spring loading but all it needs is to just clear the pipe.

Certainly seems to be working ok.


BTW... When i rebuilt my forks, i only got 11mm of thread to go into the top nuts, even with the square "inner nuts" screwed as far down as they would go.

[Demansia]

I didn't fancy whacking my link pipe about, so i bought a honda crf chain roller off ebay (£7) and made a mounting bracket for it.
It's fastened to the lower exhaust mounting point. I thought it might need spring loading but all it needs is to just clear the pipe.

could you post a pic of this weirdo? 'im interested to see how you did it.

Chad

[weirdo]

Here it is. No need to spring load if you set the chain tension after fitting it. All it does is hold the chain off the pipe.


HURRAY !!! I DID THE PHOTO THING!! Thanks to Fausto for the idiot's guide

(dances from side to side) Go weirdo, go weirdo, go weirdo, etc....

[slartybartfarst]

Bfef

OK some explanation...I hope

1) Forks don't compress or return fast enough......so thinner oil hits both cases....(too be honest I think we can only detect they don't compress quick enough as the fork was so messed up)

2) The spring is too soft so the bike falls under its own weight to compresses the air, ok this is used as part of the springing but its used as the latter part as air force rises exponentially....so instead of transitioning from fairly liner spring to increasingly ramped up air the air rate is brought into play way too early in the initial suspension compression stroke as the fork is collapsed so making the fork seem harsh.

Yea once the a new bike seems to have softened its springs its has very hard forks with no travel that damp far too aggressively.

Your right more "bounce" in the springs with less damping would soften the forks up quite a lot and stop the violent harshness at the bars when going over bumps.

Which is what we are doing here by using thinner oil and by getting the bike out of excessively compressing the air gap by making the more compliant steel springs take this initial load by pre compressing them ........the visual indication of this correct state is more extended forks.

You got to remember there are 2 spring mediums at work. 1 is the conventional spring (used for the little bumps) and the 2nd is the air which ramps up violently to stop the fork bottoming out.

Our point is the spring collapses to involve in the air part of the stroke in dealing with small bumps.........its not good at this!

To confuse the issue we are using progressive springs here, the principle is the weaker part compresses first then the stronger part comes into play however they are nothing compared to the effect of the air gap under compression so forget the progressive springs (we feel they are a red herring) wots needed is nice steel springs to deal with ripples in road then fast increasing air springing under compression to deal with that big road bump or heavy braking. Its a matter of the fork travelling a certain distance by metal spring before it starts to really pressurise the air nearer the end of its stroke.

So the perfect combination is metal spring then air.

The pre load nuts need to be wound against a stop (normally the underside face of the top nut)but there seems to be no reason you could nut put in a 20mm spacer on the top of the damper rod ) the damper rods would still screw in 13mm and you achieve the same effect.

DONT PANIC! (Hitch-hikers Guide) You will sort the front end if you pre load by 20,mm and use 5 weight oil @ quantity indicated.

[slartybartfarst]

Cool looking chain tensioner, yea my chain is on the exhaust a bit now. I tensioned it yesterday and it stays away from the exaust link pipes for my Carbon Brothers Cans 99 % of the time, I'll see if its sawing through! if so ill do this mod as the Rap rear end is so much better jacked up.....well lifted off the deck anyways.

[Ballacraine]

A very interesting and useful thread.

Thanks.

Nige.

[slartybartfarst]

High speed runs revealed the bike a bit flappy so forks dropped 10mm through clamps, this improves it no end and sacrafices little in ground clearance

To sum up on suspension mods to date

Both Rapters are now running:-

1) Spaced up front springs 20mm as per previous posts.
2) 5 weight fork oil to 100mm off top of compressed fork measured with all spacers in but no spring.
3) Forks dropped 10mm through clamps see pic.
4) Hagon progressive springs.
5) Rear triangles modded as previous pics to lift back end.

In addition my rap has a Hagon shocker wound with a fair bit of preload as per previous pics but we notice little difference to standard shock otherwise they are identical.

a) Spraying silicone on the leg sliding surfaces gives improved reaction indicating we may be at the level where the stiction of the sliders/seals is now showing. If we are down to that point its difficult to see where to go other than fork swap and that's not what this thread is about but there's no doubt there is merit in a pair of Ohlins.......Dream on!

b) Further experimentation will be 2.5 weight oil and maybe changing the air gap but for now both bikes are way way better so a little bit of getting to know this set up as a baseline is needed as so much has changed/improved.

[Demansia]

2) 10 weight fork oil to 100mm off top of compressed fork measured with all spacers in but no spring.

Hey Slarty,
in your original post you said that you used 5W oil? so are you using 10W?

Chad

[slartybartfarst]

Sorry mucked up it should be 5 weight I thought id corrected this

[Mighty Mariner]

How do you increase the pre load at the front?
Can it be done with the forks in situ?
When I undo the top cap it does not lift off do you have to compress the fork leg to expose the locknut underneath the cap?
I had feeling of too hard damping at the front on rough-ish surfaces so I increased the pre load on the rear shock as there was a lot of sag at the back, and took it out for a run and it improved the whole feel of the bike.
It's on a track day next month so want to get it reasonable at negotiating the bendy bits but I don't think the harshness at the front will be such an issue on the track I just want balance so I hope pre load at front will help and may be thinner oil?