Setting the Sag....complete noob needing help

Babyhead_wipeout

Hello all, It's been a long time since my last visit but i'm back. Some of you may remember me as Saracen Fan.

I now have a new bike, a Boardman Comp 2011, it's white and has Suntour Epicon forks.

I need to set these forks up, I know I need to set the "sag" but i'm not entirely sure what that means or how to do it. I have a shock pump and even brought a £5 Aldis bike lift so I can start learning how to care for the old girl

So basically i'm asking for some advice on setting Sag......

....and while i'm here...I am setting up the gears which is going ok, but I cant get rid of front derailer rub on the outer edge of the chain when on the middle cog up front, only rubs when on smallest cog on cassette, any ideas? I have adjusted both limit screws all the way and it makes zero difference?

Ta.

supersonic

Sag is how much the forks compress under your weight when stood on the bike. 25% of full travel is a good starting point. If not 25% then find the air valve on the fork (probably atop the left leg), attach pump, increase/decrease pressure by 10psi, recheck sag.

Adjust cable tension, though some rub is inevitable. Park Tools site has a good guide.

nicklouse

Presuming the fork is an air fork add air to give the sag you want, 20-25% on an XC bike.

Chunkers1980

Set sag to 20ish percent of travel (how much the bike settles on the shock when in the attack position) and you don't actually 'need' the limit screws so it's a cable tension issue.

Babyhead_wipeout

Ok thanks, so if I put a couple of cable ties round the stanctions I can measure the sag, I have 100mm travel forks, so in theory I need them to sag 25mm, so the measurement from the fork top to the cable tie would be about 75mm?
If so I understand now.

As for the front mech, I just need to adjust the barrel adjuster? (Sram X5 all round) I have read the guide on here about setting up gears and I will probably start again, I know the limit screws are good as the chain never slips off or refuses to shift, I just get lots of ghost shifts and sluggish down shifts....so I guess tension issues?

cooldad

Put the cable tie at the bottom of the stanchion, then measure how far it has moved up after you get off the bike. Easier to do with two people, or a wall to lean on, as you don't want it compressing further as you get off.
You will also need to set the rebound damping. Compress the forks fully, and then lift the front end. You should just be able to get the wheel off the ground before the forks extend fully.
Then ride and fine tune.

chez_m356

Babyhead_wipeout wrote:

I have 100mm travel forks, so in theory I need them to sag 25mm, so the measurement from the fork top to the cable tie

the epicons on the boardman comp are 120mm travel http://www.boardmanbikes.com/mtb/ht_comp.html

bowden769

I should be getting my board man soon. How is she?

Babyhead_wipeout

Ah, thanks Chez_m356

bowden769, she's a beast! feels light and agile, well spec'd and solidly built. Once I have the gears and forks sorted she will be perfect.

bails87

You only need one cable tie btw, seeing as both sides of the fork move the same amount.

As for the gears, sounds like you're not too sure what you're doing and what adjuster does what. Start again and follow the park tools guide. Turning the limit screws will do absolutely nothing on the middle ring. And some rubbing can be expected at the extremes. In the middle ring and the smallest cog you could change up to the big ring at the front and change down a couple of gears to a bigger cog at the back. That would give you the same gear, tension the chain a bit better and stop the rub.

ElliesDad

I have the Boardman Comp HT and can confirm the forks are 120mm travel, as for the front mech you definately need to do more tweaking as I don't get any chain rub on the middle ring on any of the rear cogs. It took me quite a while to get the gears set up properly (still a relative noob myself) but just take your time and start from scatch using the many online quides. I found this video very helpful and features an SRAM mechanic:

http://www.youtube.com/watch?v=Zt0ZZm3jTlM

Babyhead_wipeout

Thanks, that video was great! While I was tinkering I noticed that when I was in top gear (smallest rear cog) on the shifter, it wasnt on the correct cog, the chain stayed on the second smallest cog even though the shifter was saying it was in top gear. I fixed this by taking the cable out the rear derailur and putting the chain on the smallest cog.
I loosened the barrel adjuster then reattched the cable. It now uses all the gears correcly however it still skips so I have more work to do.
I fixed the rubbing though lol

Babyhead_wipeout

Well after hours of adjustments the gears still aint right. Long story short I have noticed the rear mech cage appears to be bent :shock:

I had a fall and bent the mech hanger a few months ago, I replaced the hanger but it seems the mech copped the force too, from what I can see the lower jokey wheel is slightly twisted inwards towards the spokes.

So it seems I need a new rear mech The gears all work, its just shifting down the cassette (shifting to bigger cogs) seems tempermental.

What a bugger!