[Harry BarnOwl]

Hi,

Recently got my fox 40 back from having the bushings replaced and a service, but I really can't get them to feel right. I had a few runs yesterday and changed one setting at a time, and while things improved they still didn't feel as good as they have before (it's about this time I wish I'd take a note of the settings before I sent them off!).

The main things about the ride that bug me are the front wheel being completely unpredictable under repeated harsh hits. I sessioned a particularly harsh rock garden with a lot of holes and it felt like a point-and-hope-for-the-best affair, and I felt like a passenger on the bike. I figured this is probably a rebound side issue, so I went from about 5 clicks of rebound to 10, however it still suffered from the same issue although to a lesser extent. I had a play around with the compression settings and this didn't help either.

The other main issue was just a lack of front wheel grip, particularly on the exits of berms. I hit a particularly harsh berm which gives a big compression, and the front wheel grip was noticeably bad on the exit.

So has anyone got any tips apart from keep changing things click by click? I weigh 85 kg (~190lbs) and have a green spring so I'm within the right weight range for the spring (I'm not running much preload either) and the sag seems spot on. I like a reasonably firm but predictable fork that sits relatively high in the travel and doesn't feel wallowy.

Any help appreciated.

 

[Udi]

Keep in mind that bushing replacement results in some break-in time before sliding performance is optimum. That could easily explain why they don't feel as good as they did before, give it 5-10 solid days of riding before worrying too much.

Poor front wheel grip on corner exit suggests you either need to get over the front more, or the fork is sitting too high / head angle too slack. It's generally something I deal with in trade for a bike that works better elsewhere, but a little more rebound damping might help to stop it springing back too soon (which you've already tried). More compression damping can reduce the initial dive under hard cornering which will result in a more predictable exit, but don't forget that the rear end affects all this too - eg. excessive rear dive / sag will reduce forward weight bias and slacken head angle, decreasing front traction.

Keep in mind that getting significant compression damping from the stock pre-11 damper requires fairly firm adjuster settings, generally HS at about 3/4 of range or more, and LS at 1/2 of range or more. But I'd make sure the fork is running smoothly and completely broken in before stressing over adjustments.

 

[Harry BarnOwl]

Thanks for that, I didn't think about the break in time. Do you think it really makes that big a difference? I'm just curious.

Funnily enough, I recently slid the stanchions up in the crowns, lowering the headtube and steepening the head angle - I was thinking of reversing this a little bit and dropping my bars lower down as it seems my riding position has changed a bit since I clipped in...I was under the impression that I was over the front too much as I've been going over the bars a lot more recently when I bin it.

It's interesting you mention how the rear plays into this, as I was actually going to mention that on that particular high speed berm that the whole bike felt...squirelly. It's like at the bottom of the stroke the whole bike would rather go sideways than straight out. If it helps at all, I'm riding a Sunday with a vivid 5.1 (450 lb spring - maybe too light?) out back. I also set up the shock at the same time (recently came back from a rebuild too), but I felt like I got the shock to feel pretty spot on, although it's interesting what you say about rear dive as I couldn't decide between 3 clicks of compression and 1 click of compression on my shock. I also cranked up the end stroke rebound a bit as it felt a bit too kicky for my liking.

I'll keep riding her in and experiment with the compression settings at both extremes. I'll also lower my bar height a bit just to experiment.

On a side note, can you recommend any good literature on suspension and damping characteristics, particularly for bikes? I'm a physics undergraduate and my final year project is modelling suspension to show suspension in bikes leads to a more stable chassis (I'm using a quarter car model that I've coded up in Matlab) and this stuff really interests me, and you're clearly well read on the subject.

 

[Steve M]

Who was your 40 serviced by? If it's done by a FOX distributor it's not uncommon for them to update the valving to the current spec either, which means you may now have substantially more compression damping in your fork than you're used to. As Udi said, it also takes a bit of time for new bushings to break in, so even if the valving has remained the same, you may have some extra friction (particularly when the fork is changing direction, ie the moment between compression and rebound) that is affecting things.

At 85kg on a Sunday, a 450lbs/in spring is a little on the stiff side. Is this the same spring you were using prior to your rebuilds?

 

[buckoW]

What kind of tire pressure are you running. It almost sounds like the tire is too hard.

Steve might be right about the updated valving. Therefore, you are riding higher in the travel due to more compression damping and your weight/suspension is no longer balanced like you had it/liked it before. Sometimes, when testing new valving in a 40 I need to bring down my static front end height because it is running higher dynamically.

 

[Harry BarnOwl]

Steve M
Who was your 40 serviced by? If it's done by a FOX distributor it's not uncommon for them to update the valving to the current spec either, which means you may now have substantially more compression damping in your fork than you're used to. As Udi said, it also takes a bit of time for new bushings to break in, so even if the valving has remained the same, you may have some extra friction (particularly when the fork is changing direction, ie the moment between compression and rebound) that is affecting things.

At 85kg on a Sunday, a 450lbs/in spring is a little on the stiff side. Is this the same spring you were using prior to your rebuilds?

I'll call J Tech and ask them about the valving. The added friction from new bushes makes a lot of sense regarding how it feels in general. The spring is the same one I've had for years, the markings have actually rubbed off. It may well be a 400 rather than a 450 come to think of it.

buckoW
What kind of tire pressure are you running. It almost sounds like the tire is too hard.

Steve might be right about the updated valving. Therefore, you are riding higher in the travel due to more compression damping and your weight/suspension is no longer balanced like you had it/liked it before. Sometimes, when testing new valving in a 40 I need to bring down my static front end height because it is running higher dynamically.

Same tyre pressure as usual, somewhere between 25 and 30. Or, on my scientifically approved squeezing-with-fingers method, it's moderately squidgy.

You may well be right, I want to play around with my bar height anyway so I'll have a crack with it tomorrow and see what's what.

Thank you everyone for taking the time to reply.

 

[Harry BarnOwl]

Thought I'd follow up on this.

Had another days riding on them, set the rebound to 5 clicks, LSC to 8 clicks and HSC to 5 clicks. Had the HSC at 8 clicks but it felt like the front wheel was getting away from me in the rock gardens - turned it down to 5 and it felt spot on.

I also moved the crowns up a bit more to raise the front end, which made the bike feel a lot more balanced.

Feels absolutely perfect now. Jumps and pumps when I want it to, keeps the chassis stable relative to the shock, soaks up all the really rough stuff. Cheers for the advice.