forks bottoming out - help
 

have been out today and the cable tie I fitted is right at the bottom. I know its not sliding down, you can see where the slider is going to, I am just using all the travel!!

so how do I sort this? bike seems to ride well, and is super planted even on the bumpiest roads, but need to get some travel back, so is it up the preload, or stiffen compression, or both?

there is too much sag, so I will be upping the PL anyway, just want to know if I need to do more

thanks

Stop using the front brake :lol:

Stop trying to keep up with me :lol: :lol: :lol:

Get a slipper :D

Hope you had a good day and you've left enough tread on the tyres for Germany :)

cheeky...both of you :p constructive, helpful comments always welcome too ;)

set of diablo sc2's going on tuesday...1 qually session on a british ssport bike for a bargain price! cheap enough to chich away iof needed when we get back ;)

i dont think it would be of any surprise to suggest you may need bigger front springs.........but why not try a turn in on both the front pre load to see if that helps....

yep, thet'll be the first go, get the sag right. Then see how it goes from there. Trying to see how good I can get it before I spend money...as cash on mods means less cash on fuel!

yeah sorry me old mate.

Thing is though, when you're transferring a lot of weight through heavy braking, to stop the forks meeting the stops you'd have to firm up the springs/preload. Then this would have an adverse effect on the damping over bumps.
Not sure you can have it both ways so i reckon leave the springs in and firm up the preload a bit, and don't brake so much... braking only slows you down anyway!

at my speed I dont have to brake to much anyway ;) havent been too heavy on the brakes, no more than normal and not as if track riding

Adding preload to the spring will not stop it bottoming out, all it does is change the ride height and stops the initial high speed dip on the nose, the spring will still compress the same distance wether you preload it or not.

If the springs are the right weight for your given weight then decrease the air gap by adding more oil, but before doing any of the above, check that the sag is correct first.


Chris.

cheers, saw your other post...

I'm going to set teh sag right then dial in a couple of comp clicks see how that goes. Its a great bike to ride tho, the front end is spo planted I just want to ensure I dont do too much damage with my ham-fisted attempts at setup!!

So............he may need bigger springs........but try a little pre load first.......which may decrease the sag on the front to say 20mm.......:rolleyes: and achieve his aim..........or are we saying different things!!!!!!!!!

Preloading a progressive spring can make a difference as you should move the setting futher along the curve that relates to the spring rate.
But without changing springs you ideally need to increase the amount of travel available which is what preloading will do. putting it back up the curve leaving more to play with as the biggest factor is available travel

If you haven't got the correct springs for your weight and style of riding then forget about the ideal sag figure

By adding say 10mm of preload and therefore reducing sag you will have another 10mm of travel to help soak up the forces, if the average rate of a progressive spring is 0.75kg/mm that extra 10mm of preload will allow for 15kg of load to be applied before they bottom out.

If fork travel is 130mm and the ideal spring rate for you is 1kg/mm then with a static sag of 30mm it would take a load of 200kg to use up the remaining 100mm of travel.
If spring rate is 0.75kg/mm it only takes a load of 150kg to bottom out the forks, but if sag is only 20mm then it would take 165kg to use the 110mm trave and bottom the forks, not the ideal 200kg but closer to it

I agree Andy as you posted this while I was typing my reply above

:cool:

It is very easy to get mixed up on suspension, I know I do, but from what I have gleaned and put into practise over the past few years has helped me understand suspension better than before, but I still have a long way to go.

To answer the above, if it takes 100kg to fully compress a 100kg spring, no matter wether you preload the spring or add no preload, the spring will still fully compress. By adding preload all you are doing is stopping the spring moving for part of that 100kg pressure ie if you preload the spring by 25kg, it will not compress untill over 25kg has been put on it, after that it will compress at the same rate as it would have done if there was no preload on it.

The only way you can alter that is by changing the airgap or the spring weight.

The air gap only works for the last part of the forks compression, to little an air gap and the forks will feel as if they are bottoming out before they do and to much will allow the forks to bottom out.

Compression damping alters the speed the fork spring will compress, to much compression and the forks will feel harsh, to little and the forks will feel to soft.


As you can see it is like juggling 4 balls or more, they all have to work equaly or it all goes wrong.


Chris:burn:

Paul only has 2, that's why he has an 848 and not a 1098/1198 :lol:

I have some . . .
 

ohlins - 8.5nm and 9.5nm springs for sale - send me a pm or make me an offer - they need to goooooooooo!

khushy

The main thing about spring rate is that it is a measure of how much the spring is compressed by a given weight. which is why the amount of suspension travel is oh so important.

Then you have to look at what is going to use up your suspension travel and spring accordingly.
For road riding I would pick a shock with 65mm of travel over one with 60mm of travel any day, same goes for the front forks and a good match/balance between the two is also a factor as both wheels will encounter the same size of bumps at the same speed although the rear wheel normally has more mass so needs the shock to be sprung a bit stiffer so nowing your linkage ratio helps, although playing with the Nitrogen pressure in the shock can have a similar effect to playing with your front fork air gap.

the more travel you have the lighter spring you can use and the less force the rebound damping has to deal with

But as Paul is talking about his standard 848 forks and wanting to get more of the travel back I would try increasing the preload and worry more about remaining suspension travel followed by loaded sag and not worry about unloaded sag.

I have ridden a lot of miles with Paul, seen him ride my DD bike and know how hard he rides and if he keeps bottoming those forks it wont be long before he makes a dent in the scenery somewhere

Let's get it sorted then, we don't want that :(







:lol:

Do not confuse Fork travel with the overall travel of a progressive spring

A progressive spring could go from 0.6kg/mm to 1.2kg/mm over a distance of 180mm

So has an average spring rate of 0.9kg/mm

Lets assume the rate of change of the spring is linear (gets more complicated if its non linear)
Now if your fork only has 120mm of travel, without any pre-load the travel will use the 0.6kg/mm up to the 1.0kg/mm part of the spring, giving you an average of 0.8kg/mm, so softer than the spring average.
Now if you pre-load the spring by 30mm you end up using the 0.7kg/mm to 1.1kg/mm part of the spring giving you an average of 0.9kg/mm the same as the spring average.
Now if you pre-load the same spring by 60mm you use the part of the spring that is in the 0.8kg/mm to 1.2kg/mm giving an average spring rate of 1.0kg/mm resulting in stiffer than the total spring average.

up the preload then :D

job for Tuesday

Just like people did when they had bikes with twin rear shocks and wanted to carry a passenger, they just wound the stepped preload collar round a notch or two to stop the backend bottoming over the bumps

anyone know the std rate? just found the calculator on racetech and it says I should have 1.067kg springs, but only lists 1.0kg as max, so want to know the difference between that and standard as it says standard is 0.960 anyway!!

Only got info on the Ohlins FG5110 forks as fitted to the 1098S
1.0kg/mm springs, Fork Stroke/Travel 120mm

found a load of info here

http://old.racetech.com/evalving/Spr...pringType=Fork

http://www.ducati.ms/forums/showthread.php?t=55525

the 848 has a slightly ligher sping at .95

http://www.ducati.ms/forums/showthread.php?t=55525

Yep thats the one where I got the PDFs from when looking into the Setup on Dallas's 1098 following his get off at Silverstone,
Opinion is that they are sprung for riders weighing 72kg rider.

so if assuming a 50/50 Front/rear bias then 36kg on the front, roughly a 90kg rider would put another 9kg on the front and if the bike weighs 180kg wet it puts 90kg on the front so spring rates would need to be about 4% higher
and so on
Rider Spring
kg kg/mm
54 0.96
72 1.00
90 1.04
108 1.08
126 1.12

Its about 10 pies i think.......;) :D

I was going to tactfully suggest that since Paul is a 'big' lad he may need a stiffer spring-but I think you have already done that-just without the tact.....................:lol:

John

but looking at whats available, seems 1.0kg is all there is, and its not that much more than std so why spend the money?!

Yet they do up to 1.2kg/mm for the 996

http://www.motonekoparts.com/Race-Te...1-p-17992.html

I have seen them heavier before, and I think my sps ones were 1.1kg, just not listed for 848/1098

any 1098 rider wanna swap - they come std with 1.0kg!

Ohlins do a 08761-05
which is 1.05kg/mm

how easy to change them? any special tools needed?

Just the hammer you used to take the SPS apart :lol:

You need a tool to compress the preload spacer so that you can get in and undo the lock nut so that the fork tops can be unscrewed from the damper rod.
Best left to somebody that knows what they are doing and has the tools as the PDF also suggests a oillevel to get the correct air gap.
I bet there is a mechanic at Snells that could do it or Moo Rapido

The rest of the Ohlins info for the 848

http://www.ohlins.com/Product-search/?query=Ducati+848

whos moo rapido?? lol

never used them myself, but no some who will use no udder dealer


:lol:



:lol:

Stop milking it :lol: