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Hi,
I was at Antur over the weekend on my Demo 8 with Coil Boxxers.
I've been there twice now and both times I've been pinch flatting the front. Looking at the travel marker on the forks I've still got about 2 inches of sanction left before the crown.
Is this right?
Am I using full travel? There was one time the rubber ring was right up against the crown, but I'm not 100% that happened while riding as it's not got that high again.
thing is, if the tyre compresses more easily than the fork you'll always get pinch flats.
It may not be about how much the fork is moving but about how much force needs to be put through it to get it to move.
Can you adjust high speed compression on these forks?
they've got
Damping: Motion Control IS (Integrated SpeedStack)
Adjustments: External low speed compression and rebound, Internal Pre-load
Obvious questions (But I'll ask anyway):
1- How much Stanchion is there between the lower crown and the seals?
2- Which spring do you have fitted? (and how much do you weigh?)
3- how much oil in either leg?
4- what (if anything) has been done to the damping on the fork? any dial twiddling or servicing?
5- what tyres/tubes/rims and pressures are you using?
measure the distance from travel marker to the seal, then you can see if you are getting close to full travel.
Surely if you're pinch flatting you need more pressure in your tyres regardless?
Measure the seals to crown length, should be 210mm or thereabouts. If it isnt that then move the legs up. Are they RC? Mine had a bumpstop thing inside which was just an elastomer and did nothing but limit the travel so I removed it. I still very rarely use full travel even with a standard spring. RS charts say I should be on a firm but I tried that and wasn't getting anything like full travel. Are you pinchflatting the front with dual ply tyres?
Medium spring,
I'm 12.5 stone
Onza ibex 2.4 tyre about 35 psi
Not done any fiddling with the forks (they're brand new)
I'll measure 200mm up the stanchion tonight. good/obvious idea! 🙂
Just looking for some fork tuning onfo on the net.
Weirdly when I'm pinch flatting, It's in weird places where I wouldn't expect it to happen.
Yep, I pinch flatted the front twice with dual ply tyres.
I managed to pinch flat both tyres on one run. 🙂
Maybe tubeless is the way to go?
Yep, RC Boxxers
These guys are right- since the height of the triple clamps varies depending on the bike, there's generally more stanchion on show than the forks can use.
Antur's generally a bit puncturey, not a problem I had but it's got a lot of wee square edges and it's fast. I'm just assuming it's an Ibex DH? What sort of pressures?
Yep Ibex dh tyres.
I'm running between 35 - 40 psi
Using some Specialized wheels off an Sx trail. Massive wide red rims. 🙂
You should be pinchflatting with that PSI. You could check you have the correct amount of oil in the forks , maybe get a lighter spring or even have the bushings resized.
A lot of ppl take an inch off the rubber dropstop.
Do the forks not come with the correct amount of oil new? (I've only had them a few months and ridden about 4 times)
Would 50 - 60 psi be better?
do they take a while to 'bed in'? ridden 4 times doesn't sound like much riding time?
You'd need to bung quite a bit of extra oil in to cause them to not achieve full travel, boxxers don't behave like LT single crown forks as they have that bit more internal volume...
12.5 stone you say, have you considered using a soft spring with some pre-load washers added, just to soften the fork a bit?
Oh and is the fork rebounding quickly, or are you finding it packs down a bit on steeps/bumpy rooty stuff?
That might explain things a bit if it's not extending sufficiently between successive hits then it may well be not working as intended...
35-40 PSI seems quite a lot of pressure to me on a DH bike given your weight, with or without tubes you shouldn't be finding it easy to pinch flat... I'm about a stone heavier and don't go above 30psi at either end, but YMMV of course.
I'll admit to generally preferring a softer fork and a softer tyre, but with relatively quick rebound to keep the tyre tracking the ground and gripping, but that's not to everyone's tastes and yes on bigger impacts or if really grunting on the pedals you will blow through your travel there's a limit to what compression damping can do IME...
12.5 stone would be pretty dang soft with a soft spring, I'm 10 stone on a medium/red. Might work for you but wouldn't for me.
I've checked the rota and it's my turn to be the dick- pinch flats are only really caused by 3 things- 1, too low pressure, 2, too delicate tyres and 3, riding into pointy things like an oaf. I've got the first 2 sorted on mine but still working on the third 😉