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4 Common Reasons Your MTB Shock is Losing Air

4 Common Reasons your shock is losing air

You’ll hear this a lot from MTB and eMTB riders: my shock (or fork) is losing air. Every time I check it it’s lower than I left it.

Well there are a few reasons that a functioning shock will show lower PSI.

Are you Pre-Charging your Pump?

The most common is not pre-charging the pump line prior threading the pump on and opening the Schrader valve.

This one is pretty easy to explain – the gauge is located at the end of a volume of hose. If you do not pre-charge that hose to approximately what you have in the shock when you open the Schrader valve to your air spring you increase the volume of the main chamber which will lower the overall PSI.

The smaller the suspension’s main chamber the more dramatic the PSI drop will be.

That’s why it’s a good idea to pre-charge your suspension pump. Thread the pump on until it makes a seal with the shock but hasn’t yet opened the valve.

Charge the pump to approximately what is in the main chamber.

Finish threading the pump onto the fork or shock. It will show a more accurate pressure of the main air spring as it doesn’t have the volume loss as a non-charged pump.

Like I mentioned this is the most common cause for “air loss” in suspension. It is seen in both the fork and rear shock.

Did You Cycle the Shock and Charge the Negative Air Chamber?

Another common cause for lower pressure, particularly in rear shocks, is setting the pressure and not charging the negative air chamber.

This is typically seen when large PSI jumps are made in the shock such as a brand new piece of equipment.

What does it look like? You set the pressure to the suggested PSI. You jump on the bike and go ride. Bike feels soft. You check the air and it’s dropped from the beginning of your pedal.

Unlike most forks, which usually charge the negative air chamber at full extension and thus see less of this, your rear shock most likely has an air divot to charge the negative chamber somewhere a bit into the stroke.

That means it takes a few compressions of the suspension to engage the negative air chamber. And once the piston allows the negative air chamber to fill it effectively drops the volume of the main chamber. Then when the shock extends and you check the PSI it will be lower.

It is a good practice to give a rear shock a few bounces during setup, especially when large PSI changes are made to ensure that the negative air chamber has charged and the shock will have the support you expect.

Does it Need Seals? Or Just Had Seals Installed?

It is actually more rare for a shock to be truly bleeding off PSI than for one of the above two to be the culprit on new suspension.

As the suspension ages seals may degrade and can be the cause of air loss. Suspension manufacturers have suggested service intervals based on hours of operation, but if your more aggressive on your equipment, such as a racer, you may find that shortening the service window keeps your bike running smoothly.

Some common causes of premature seal wear include dirt ingress, which is why it is so important to keep your stanchions as clean as you can before each ride. The less dirt the suspension pulls into the seals the less abuse on the seals, shafts, etc is incurred.

Occasionally a recently serviced fork or shock may ‘roll’ a seal or have been nicked during installation. Typically you’ll find this out when you’re setting back up for your ride or on your first ride. This is very rare on a professional level as the quality control of parts and service techniques eliminates the chance for most of this. But, there’s typically a handful of small to medium seals which make create an air-tight chamber and if one of them isn’t working you might have a slow leak.

Dirty or loose Schrader valves can cause air loss, although most shocks have a decently sealed cap these days.

Extreme temperature or altitude changes will effect your PSI and should be accommodated for. Check your sag before your chair lift day at altitude!

A less common cause, but it is out there: chemical degradation. Seal materials are susceptible to being attacked by other chemicals – so be aware of what comes in contact with your suspension.

A typical way to test for faulty seals is to set the shock at a test pressure, say 100psi, and allow it to sit overnight. Pre-charge a pump and check the pressure. A notable drop, ie more than might be expected from the pump increasing the main chamber volume, is likely worth an additional look.

Another test, although I must disclaim this one a bit, is to submerge the shock and watch for bubbles. I try to avoid this option as much as possible personally as I find it has to be a pretty decent leak for me it to be losing air visibly and can tend to be detected using the overnight pressure test. If it is leaking and pulls water in you’re going to have remove the water and any contaminated oil or grease since you don’t want water diluting or boiling in your suspension’s air chamber.

Very Rare PSI Loss Causes

The least common cause of air loss would be a crack or micro-crack in a casting. This can be a hard one to determine, particularly as it may require the shock to cycle and load up before the pressure rises enough to “open” the crack and vent air pressure.

Occasionally seals will have a similar end of service life where the air loss is occurring as the PSI increases, but, it’s fairly uncommon.

 

In conclusion, most of the air loss attributed to new or newly serviced product can be traced back to the pump increasing the volume, and thus lowering the pressure or in the case of rear shocks the negative air chamber charging.

If you’re using good practices with your setup and still noting air loss the next step is most likely to do a seal service, especially if the shock is near the service window or if its’ been used in extreme conditions.

If the new seals aren’t helping it’s probably worth digging a little deeper and possibly using a professional resource to help you locate the issue.

Local or ride in the South Orange County area? Come by and have our team service or tune your suspension. We are located at 21098 Bake Parkway #112 in Lake Forest near the corner of Bake and Trabuco.

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Factors of the Best E-Bike Suspension

Best e-bike suspension BMC AMP APS 1

Factors of the Best E-Bike Suspension

Suspension matters. OK, kind of obvious right? But let’s look at why your e-bike’s suspension design might be even more important than a pedal (or acoustic) option. The best e-bike suspension accounts for factors similar to a pedal option while adding some unique stresses as well.

There are as many suspension theories, and patents for them, and pretty much all market to be the be all end all right? Of course. But just like pedal bikes we can quickly narrow down the real deal from the fakers. Continue reading Factors of the Best E-Bike Suspension

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PreCharging a Suspension Pump – BikeCo Tips & Tricks

PreCharge Pump Blog Image

PreCharging a Suspension Pump – BikeCo Tips & Tricks

Let us show you how to precharge a suspension pump for the most accurate air suspension setup.

Many of our clients, and all of our racers, are looking to really dial in suspension. In order to accomplish this it is important to make minute adjustments to air pressure. This blog and video illustrate what’s happening in your air spring and why precharging a suspension pump is so important.

 

Continue reading PreCharging a Suspension Pump – BikeCo Tips & Tricks

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MotionIQ – the How of MTB Suspension Data Analytics

Motion Instruments MotionIQ Cody Kelley Setup

MotionIQ – the How of MTB Suspension Data Analytics

OK, you read the “why” about mountain bike suspension data acquisition (if you didn’t check out BikeCo Pro Rider Cody Kelley, Joe Binatena and Rob Pryzkucki from Motion Instruments discuss it here) let’s now look at the “how” of the Motion Instruments MotionIQ system.

Those who’ve read a lot of BikeCo’s content know I love formulas and data. Everything is just easier when you can minimize variables with facts. So suspension data acquisition would be right up my alley right? Well sort of. Continue reading MotionIQ – the How of MTB Suspension Data Analytics

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Suspension Testing with Cody Kelley and MotionIQ

Motion Instruments MotionIQ Cody Kelley

Suspension Testing with Cody Kelley and MotionIQ

Prior to EWS Northstar BikeCo Pro Rider Cody Kelley and Joe Binatena had a chance to work with our friends from Motion Instruments, a Suspension Data Analytics company.

We could write a thesis on it, but to keep it manageable we’re going to break it down into two semi-succinct parts… This section will cover some of the “why” then jump over to the “how”.

Continue reading Suspension Testing with Cody Kelley and MotionIQ

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Confidence with Compression: Adjusting your fork

7 15 19 Compression and Confidence

Confidence with Compression: Adjusting your fork

Confidence with Compression – sort of a vague title right? Am I gaining confidence on trail from compression? Am I confident adjusting my compression? Well, both.

The abridged back story: I had a chance to move further south. BikeCo’s website has been growing at a rate that I can now work remotely mostly and come up to the shop a couple times a week. Anyhow – for the first time since I started bikes I’m consistently riding trails I don’t know. This presents some really fun challenges particularly as I tend to ride solo most the time.

Now I didn’t move and decide I was one of our pro riders looking for the most ridiculous lines possible. Nor did I move and decide I was going to find every gravel trail to take my SB130 on. I’m riding the same basic level of trails but the unknown adds quite a bit to riding. Continue reading Confidence with Compression: Adjusting your fork

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New to MTB Buyer’s Guide – Wheel Size, Travel & Suspension

New to MTB Buyers Guide Wheel Size Travel Suspension

New to MTB Buyer’s Guide – Wheel Size, Travel & Suspension

Welcome to the second section of our New to MTB Buyer’s Guide. Missed the first? Jump back to it here. Ready to start looking at the actual components? Well here we go.

Let’s go over the key differences on a mountain bike setup.

New to MTB Buyer’s Guide – Wheel Size, Travel & Suspension

Wheel Size

Modern bikes feature 27.5″ or 29″ wheels. It used to be a world of “taller than X’ Y” you’re on this wheel…” Not anymore. Updates in bike geometry and design have produced bikes which cross over height, within reason.

Continue reading New to MTB Buyer’s Guide – Wheel Size, Travel & Suspension

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44mm vs 51mm Fork Offset

44mm vs 51mm Fork Offset

Many clients use our custom builders to quickly spec the parts they need for frame swap projects. That’s awesome. We’re glad to dial in everything from frame swaps, factory builds, semi to full custom bikes with our clients. We have had A LOT of clients ask about utilizing previous generation offset forks to their new bikes. Let’s take a look at the advantages of the lower offset forks, particularly the 29″ 44mm versus 51mm offset.

I guess let’s start at the end.

29″ bikes have reached an amazing level of performance. Modern 29’s pedal amazing while being much more behaved on the descends. We see smaller riders enjoying the current generation of big wheel offerings. Compare this with the days when Small 29’s weren’t even made because they scare riders out of the sport! Continue reading 44mm vs 51mm Fork Offset

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Front End Support – Fork Air, Volume & Compression

Front End Support – Fork Air, Volume & Compression

Between our BikeCo Pro Tune services as well as working with some of the fastest racers in MTB we get a lot of questions regarding suspension tuning. Modern forks offer more ways than ever to dial in your ride. Getting the right front end support with fork air, volume and compression improves tracking, ride quality, dive, and how your bike performs in the chunk.

Recently BikeCo Pro Rider Cody Kelley was in town working with Joe Binatena on the 2019 Alchemy Arktos 29. It was an interesting opportunity to sit down and listen to Cody and Joe discuss setup. Continue reading Front End Support – Fork Air, Volume & Compression

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Yeti Switch Infinity Review, Extended Ride

1 9 19 Yeti Switch Infinity Review Extended Ride

Yeti Switch Infinity Review, Extended Ride

After several weeks elusively riding Yeti it’s time for a Yeti Switch Infinity Review.

The current Yeti Switch Infinity suspension was a fairly radical departure from previous Yeti designs – but man they nailed it.

Early Switch Infinity

Yeti has used the SB (SuperBike) designation prior to the current Switch Infinity design. Earlier Switch Infinity pivoted the lower linkage through eccentric spacers and bearings. This involved large diameter bearings as well as a 2 piece “micro-switch” assembly. Visually it is quite similar to the Ibis Ripley – although it does a bit different thing based on patents, etc. Continue reading Yeti Switch Infinity Review, Extended Ride