Twitchy/unstable in corners?

[.:ROBBO:.]

Some Background first.

Current set up- 2004 Demo 9. 2010 Boxxers(Bought second hand but recently serviced and im pretty sure all upgrades were done), Med spring, flat crown, Truvativ Holzfeller 50mm Direct Mount Stem and Pro Atherton Star Series 745mm/5*up/9*back/20mm rise bars.

Previously it was basicaly stock with 04 888s, stock Marz direct mount and Deity Twenty14 Bars 710mm/50mm rise.

Rear is a 6way swinger with a 500lb spring. I weigh 80ish KG.

I run the bars pretty much flat. Im almost convinced I have the forks tuned fairly well but im only going by what I've read in the manual and on the net. The current set up has lowered the front at least 50mm or more. Since going to this set up the bike is real twitchy/unstable cornering. Its way more noticable on a big sweeping corner if you touch the front at all. Its hard to explain but the bike just becomes really unsettled. And getting over the bars just makes it worse brakes or not. For those that know Kenilworth it was really noticable on the big RH sweeper comming out of the forest before the LH switch back down the bottom which is fairly washed out at the moment.

Before changing the set up the bike felt pretty much dialed. Except it was heavy up front. But definitely corned a lot better.

Have I gone to low in the front? Going by the pic the head angle looks to be a lot steeper but I have not measured it. Wrong choice of bars/stem? Or is it more likely my fork set up?

Dont bother replying if all your going to say is I should have bought Fox 40s. They both have their pros and cons.

Current set up-

Old set up but with different bars-

 

[T-Rex]

Do you think the front might be packing down on the long corners ie the rebound is too slow? If you have one problem corner it would be easy enough to test. Just do a run, push back up, turn the rebound speed up a few clicks, hit the corner again and see if it makes much difference.

Also, have you checked for basic stuff such as tyre pressures, no suspension components loose, etc?

 

[.:ROBBO:.]

Do you think the front might be packing down on the long corners ie the rebound is too slow? If you have one problem corner it would be easy enough to test. Just do a run, push back up, turn the rebound speed up a few clicks, hit the corner again and see if it makes much difference.

Also, have you checked for basic stuff such as tyre pressures, no suspension components loose, etc?

The more I think about it the more I think your right on the money. As the bike is also floating around a little through the high speed small bump sections. It also seams to get real low in the front on steaper rock gardens where the front end keeps having to drop down lots of steep faces.

Have checked all the basic stuff thanks.

Ill try a few things out at Illinbah this Sunday.

 

[patto_15]

Have you slowed down your rear rebound also? The bike comes twitchy if the rear end is too fast as it bounces through corners, instead of sitting and sticking in. I run my rear end pretty slow and my front end fast. Compression ramped up just a little.

 

[BUSHPIG]

I think your spring is a bit to heavy mate. I'm 76kg's kitted up and run a 300lb in a single pivot bike. no problems. This has increased my highspeed stability heaps! try getting a lighter spring.

 

[cluster]

I think your spring is a bit to heavy mate. I'm 76kg's kitted up and run a 300lb in a single pivot bike. no problems. This has increased my highspeed stability heaps! try getting a lighter spring.

I agree... either that or make the front end stiffer (get a stiffer spring for the fork, or turn up compression levels a little). Balanced suspension makes a huge difference; the frame should stay level when you bounce up and down whilst standing over the centre of the bike on flat ground, ie. the front end shouldn't dip like you say yours does in steeper rockgardens etc. A bit more high speed may also help in this regard, as rockgardens tend to be more leaning towards highspeed impact than small bumps - keeps the front end sitting up nicely towards the end of your travel.
EDIT: oops, my mind was playing tricks on me, i thought you had 40s (hence the "get a stiffer spring" comment). but same basics apply.

 

[pozzi]

If you've changed tire pressures that might have altered things. I run about 10 - 15psi on the front, helps alot especially on corner's like that one at kenilworth.

 

[Calvin M]

Another thing to try is sliding the fork legs down in the clamps to bring the front end up to where it used to be and it will also slacken the head angle. Do this and do some runs. Its good to have a low front end but not good to have to steep of a head angle.
The med spring in the fork sounds a little light for you to.

 

[.:ROBBO:.]

I had been thinking the rear spring was a little heavy. The bike comes stock with a Ti 450 and the guy I bought it off had it swapped for a 500. Why I dont know as he wouldn't have been any heavier than me. Although I can still use the full travel in the rear on big hits.

Rear is buzzing the seat right here-

 

[.:ROBBO:.]

Another thing to try is sliding the fork legs down in the clamps to bring the front end up to where it used to be and it will also slacken the head angle. Do this and do some runs. Its good to have a low front end but not good to have to steep of a head angle.
The med spring in the fork sounds a little light for you to.

I can't slide the legs down any further. Thay are all the way down now and that just gives me 205mm between the seals and the lower crown. And my steerer is to short to run the dropped crown on top as I need to run a spacer under the crown then or it hits the frame at full turn. My steerer was too short by 5mm when I fitted it. Its allready got a custom made extension and I dont want to run a longer one than is in there now.

But if this is the issue then I really have no choice. When I bought the forks there wasn't a single replacement steerer available in Aus.

Ive got the heavy spring so can give that a go on Sunday as well. It only takes 2 min to change.

 

[cluster]

hmm... i know it's different frame geo and everything, but i ride an 08 demo 8 and am running a 450lb manitou Ti on the rear, feels perfect (for me anyway)... and i weigh about 65 to 67 kitted up. so you might actually need a stiffer spring for your weight???
Good point about the tire pressure though whoever said that, that can also make a big difference to the overall feel of the bike.

 

[.:ROBBO:.]

If you've changed tire pressures that might have altered things. I run about 10 - 15psi on the front, helps alot especially on corner's like that one at kenilworth.

I haven't changed tyre pressures at all. Although i run around 23 in the front and 28 in the rear. Maybe these are to high but its how I've allways run so shouldn't be whats causing an issue thats only just started.

Lots of Ideas anyway. Thanks to the guys that have taken the time to reply. If anyone else has any ideas im all ears.

 

[sprocket]

i was under the impression the the springs in forks and shocks was to get the right sag..? and the way to get it to run better was to just muck around with compression/rebound adjustments..

as said before just try riding a corner that its really noticable on a few times and making small adjustments with your compression and rebound.. not major changes as u might loose track of where ur base settings were.
I have just gotten back on the bike after 10 months and had a similar issue with the 2010 boxxers i had, ended up running 4 clicks more of both high and low speed compression and then had to slow down the rear rebound in my 1st shock (in own a 2stage) to match what the front was doing to get a better balance

 

[.:ROBBO:.]

I was also under the impression that choosing the right spring was all about sag.

My Sag is spot on in the front with the medium. And from memory when I first bought the bike the rear was correct as well. As I said it was pretty much dialed with the old set up just heavy.

What made me notice the bike wasnt right to start with was when a mate who has allways been way slower on our local DH trail could all of a sudden get away or catch me through the corners and rough stuff. It just took me to ride somewhere different with a big sweeper to make me realise where it feels so wrong.

I imagine its going to be in the Comp and Rebound set up as Ive only set it up by what the book says.

 

[T-Rex]

I think your spring is a bit to heavy mate. I'm 76kg's kitted up and run a 300lb in a single pivot bike. no problems. This has increased my highspeed stability heaps! try getting a lighter spring.

You can't directly compare a single pivot spring rate to a multi pivot spring rate. Single pivots typically have a much lighter spring rate due to different leverage ratios.

Robbo, run your weight and setup through this spring calculator to see if you are roughly right with your spring rate. As you say above, you can start with getting your sag right, and that will give you a rough guide.

http://tftuned.com/info/spring_calculator.aspx

 

[l +Jarrod+ l]

Get a lighter spring. Other wise the frame is to old for the way the forks are set up so low. New frame.

 

[Calvin M]

I can't slide the legs down any further. Thay are all the way down now and that just gives me 205mm between the seals and the lower crown. And my steerer is to short to run the dropped crown on top as I need to run a spacer under the crown then or it hits the frame at full turn. My steerer was too short by 5mm when I fitted it. Its allready got a custom made extension and I dont want to run a longer one than is in there now.

But if this is the issue then I really have no choice. When I bought the forks there wasn't a single replacement steerer available in Aus.

Ive got the heavy spring so can give that a go on Sunday as well. It only takes 2 min to change.

Ok I thought you had a drop crown on it by the picture but it is your dump stops that I could see.

How does the head angle look compared to other DH bikes that you can line it up beside. To give you a idear weather it is steeper then most other DH rigs.
Do you know that angle it had from new? Think they were 66 which is very steep compared to most new DH bikes. So now with a lower front end it would be steeper again.

 

[PirateKing]

Hey RUFF,

What rate spring is your rear? Do the demo9's run 2.75" or 3" stroke shocks? Either way give I'll send you a message tomorrow with what rates I have on my bikes if you want to borrow them on sunday and give them a go, if they are different to yours.

(bender4865 @ OL)

 

[chris95]

I haven't changed tyre pressures at all. Although i run around 23 in the front and 28 in the rear. Maybe these are to high but its how I've allways run so shouldn't be whats causing an issue thats only just started.

Lots of Ideas anyway. Thanks to the guys that have taken the time to reply. If anyone else has any ideas im all ears.

thats a preety good pressure, i would go any lower than that otherwise you will be dinging your rims on the hard hits

 

[.:ROBBO:.]

Ok I thought you had a drop crown on it by the picture but it is your dump stops that I could see.

How does the head angle look compared to other DH bikes that you can line it up beside. To give you a idear weather it is steeper then most other DH rigs.
Do you know that angle it had from new? Think they were 66 which is very steep compared to most new DH bikes. So now with a lower front end it would be steeper again.

From stock they are at 66*.

Ive got a '07 Big Hit as well. The Big hit should be at 66* as well. Here are a couple of shots comparing the two.

I guess I really need to get the drop crown on there. This means buying a new steerer.

Although while I was taking these pics I did notice the rebound is a little slow. Took 3 clicks to make it feel about right. Its possible its been moved while shuttling or binning it as it fairly easy to move being on the bottom.