Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 1198 / 1098 / 848 > forks bottoming out - help

[chris.p]

Originally Posted by andyb

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....

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.

[bradders]

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!!

[skidlids]

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

[andyb]

Originally Posted by chris.p

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.

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

[skidlids]

Originally Posted by andyb

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

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

[andyb]

[chris.p]

Originally Posted by andyb

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

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

[Dementor]

Originally Posted by chris.p

As you can see it is like juggling 4 balls or more,


Chris

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