Typical base Zeb static sag?

[billium]

My 2023 Whyte E160 has a base Zeb with Debonair+ spring and 160mm of travel.
I am 65Kg and running at 70psi and a little concerned about the unladed fork length.

Lifting the fork by the crown until the wheel is off the ground, I measure 155mm of available fork travel - this seems ok given that there is going to be some residual negative chamber force but I am surprised that don't have the strength to extend it all the way to 160mm.
Letting the fork settle under the weight of the bike in a stand I measure only 140mm of available fork travel. Put another way, there is 12% static sag without any rider weight.

I did perform a lower leg service today and it did make the fork smoother but did not change the static sag or my inability to extend it all the way (at 70psi)

Are these numbers normal and if not what could be wrong?

 

[steve_sordy]

When you pumped it up for the first time, did you just go straight to 70psi? Some forks have a second chamber that needs pressurising as well. The fork needs deeply compressing during inflation to achieve this.

Best advice would be to go to the manufacturer's website and look up the fork to get the inflation advice.

Second best advice is to pump it up in stages, compressing the fork as deeply as possible 4-5 times after each inflation. I would suggest 20, 40, 60 psi stages before getting to your target.

You should do this with shocks as well, although the steps can be bigger.

 

[steve_sordy]

Also it could be lumps of grease, blocking one or more valve ports. I read about the following technique and tried it myself when I had a similar problem with a Fox 38.

Deflate the fork, turn the bike upside down, bars on to a soft and resilient surface (I use a garden kneeler).
Remove wheel, replace axle, put foot on bar, hands on axle, firm grip.

In line with the fork axis, wrench the lowers upwards with a very vigorous jerk. Repeat a few times.
You should hear some squelching and the fork may feel different after a few wrenches.

Put everything back and the right way up, inflate the fork in stages.

 

[billium]

The Zeb just has a dimple on the inside of the stanchion near to full extension that leaks air between positive and negative and I do hear a 'pft' as the air leaks through when changing the positive pressure and gently pumping the forks so it is not blocked.
I still wonder if this is normal because there is always about 10Kg of bike weight on the forks and the forks do fully extend if I add another 20psi .
I suppose the other possibility is that the damper is fighting being fully extended but to test that I would have to drain out the new oil I just put in that lower and I have not found any posts on such behaviour.

 

[steve_sordy]

Eventually I sent the Foz 38 to TF Tuned for a service. I mentioned its tendency to hide 10mm. They serviced it and said they could find nothing wrong with it. Back on the bike, 10mm stanchion hid itself again. 20psi more and it reappears. Must be the weight of the bike?

 

[CaptChip]

My 2023 Whyte E160 has a base Zeb with Debonair+ spring and 160mm of travel.
I am 65Kg and running at 70psi and a little concerned about the unladed fork length.

Lifting the fork by the crown until the wheel is off the ground, I measure 155mm of available fork travel - this seems ok given that there is going to be some residual negative chamber force but I am surprised that don't have the strength to extend it all the way to 160mm.
Letting the fork settle under the weight of the bike in a stand I measure only 140mm of available fork travel. Put another way, there is 12% static sag without any rider weight.

I did perform a lower leg service today and it did make the fork smoother but did not change the static sag or my inability to extend it all the way (at 70psi)

Are these numbers normal and if not what could be wrong?

The standard static sag on most forks is 25% of rated travel with the rider mounted in full riding gear

 

[billium]

Sure 25% with a rider but what should it be without a rider? With bike sitting in a wheel stand, at 90psi fork sag is zero but at 70psi it is 12% (just from the weight of the bike) which surprised me.

 

[steve_sordy]

Sure 25% with a rider but what should it be without a rider? With bike sitting in a wheel stand, at 90psi fork sag is zero but at 70psi it is 12% (just from the weight of the bike) which surprised me.

Don't get too preoccupied about the exact % sag. I can see you asking yourself "If 12% is there before I sit on it, what sag am I getting when it sags 30%? Am I in fact only getting 18%.....?"

It doesn't matter! If the bike is too soggy, then increase the psi in the fork and so forth. What is important is how it performs when you are riding it.

 

[bmwpowere36m3]

Sure 25% with a rider but what should it be without a rider? With bike sitting in a wheel stand, at 90psi fork sag is zero but at 70psi it is 12% (just from the weight of the bike) which surprised me.

Static sag isn't a metric with air forks... static and rider sag are used with coils and preload. Adjust for 20-25% rider sag as a starting point. Then add or remove air as desired to achieve riding characteristics desired.