Rear suspension for idiots and experts!

Rear Suspension set up and care

Following on from the fork guide Iíve done I thought Iíd do a similar for the rear shocks
Iíll break this down into set up and maintenance. Some of this info is fairly basic, but should cover most aspects / questions.


Rear Shocks

Shocks are broken down into air and coil, as in front forks, coil shocks use a coil spring for the suspension medium, and air shocks use compressed air. To adjust the shock for different rider weights with a coil shock you need to swap the coil spring for a heavier or lighter weight spring, for air shocks you need to add or remove pressure using a shock pump to adjust the springs performance.

Different resistance coils are available for most brands of shocks from the likes of TF Tuned; however the vast majority of bikes in the club come with air shocks so I will concentrate mostly on this.

Shock Stroke?

Rear shocks work slightly differently than front forks as the travel of the frame does not directly relate to the length of travel on the rear shock.

I.e. on forks a 140mm travel fork has a stroke length of 140mm. Rear shocks work differently most have a 2:1 or more stroke rate, so the amount the shock moves is not the same amount as the travel of the bike, using my Orange 5 as an example the bike has 140mm or rear travel, however the shock has a stroke of 51mm, so the 51mm of movement at the shock equates to 140mm travel at the rear of the bike.

To measure your shock stroke you need to measure the shaft at the base of the shock from the bottom of the rear can to the end of the smooth part of the shock. This gives you your shocks stroke length.

Setting Sag?

As we discussed sag on the forks guide, I am assuming you are aware what this is now. Again rear shocks are designed to run with between 25% Ė 33% of their travel as sag.
What does this mean? Well when you sit on the bike in your riding equipment and pack and adopt a normal riding position the suspension should compress under your weight by that amount.

As we have discussed shock stroke this is the critical measure to obtain rear shock sag, again using the Orange 5 example, the bike has a 51mm shock stroke and is designed to run around 33% sag, so 33% of 51mm (shock stroke) = 51/100 X 33 = 17mm. So to achieve a 33% sag rate, the shock sag measured along the shock shaft should be 17mm.

To set this lean the bike next to a wall, and whilst wearing your riding kit, get on the bike and assume a normal riding position, reach down and move the o-ring to the top of the shock then carefully get off the bike.

The distance the o-ring has moved from the top of the shock is the current sag, add or remove air pressure, are keep rechecking until you obtain the sag reading you require.

Once this is obtained you have correctly set the sag level for your bike and the movement at the shock will correlate to the correct sag amount at the rear wheel, i.e. in the Orange 5 example with 140mm travel, rear wheel sag will be 47mm.

Rebound

Most shocks have a form of rebound to adjust how fast they returns to full extension from compressing, so in laymanís terms how quickly it moves. On most rear shocks rebound is controlled by a nitrogen chamber housed within the rear shock mechanism.

This Nitrogen chamber is non home serviceable. Whereas on the front fork setting guide rebound was set very close to the fastest possible setting, on the rear shock a much slower rebound setting is required.

Adjust your rebound fully to the plus on the shock, it will return very slowly to its full length, now adjust fully the other way and the shock will return with lightening speed. Most shocks are adjusted best with 5-7 clicks positive from the lowest negative rebound setting.

This should mean the shock returns reasonably quickly but not so quick as to cause the rear of the bike to kick the rider from the saddle.

An easy way to test this is to ride the bike and land a drop heavily off a kerb or this like, the bike should suck up the hit, without providing kickback through the frame, if the frame and shock return in a controlled manner, you have set rebound correctly, if you have a kick back sensation from the suspension readjust your rebound settings.

Compression damping (what is this RP23 malarkey?)

Compression damping or pro pedal, affects how active or reactive the shock is to suspension movement and hits through the frame and also assists with tuning out rider input (caused by peddling etc) most bikes come fitted with a derivative of the fox float series, (RP3 / RP23 etc) the setting of pro-pedal is engaged using the blue lockout lever. The shock has numerous settings:

● fully open (meaning shock most reactive) which is great for general single-track riding / descending

● pro-pedal 1 (shock slightly less active) great for general riding

● pro-pedal 2 (less active) hill climbing etc

● pro-pedal 3 (least active) long road sections etc

to adjust the settings have the shock fully open, lift the numbered dial and rotate the number to desired level push the blue dial back in, then operate the blue lever to put on the desired level of pro pedal. Pro pedal should always be adjusted with the bike unweighted, so do not alter between pro-pedal settings whilst riding but you can alternate between on or off with your current selected level.

Have a play with your pro-pedal as some bikes perform better in different settings, shocks come with different levels of tune to cope with different types of frame so all are not created equal. I tend to ride with the shock using predominantly pro-pedal 1 and fully open, but again experiment to find what works best for your setup.

Some bikes just have pro-pedal on or off setting meaning less adjustment is available, some have no pro-pedal at all meaning the shock is always full active.

Maintenance / Servicing

Cleaning

Rear Shocks are both expensive and exposed to all the filth we ride in and are subject to wear and tear. Sealing on rear shocks is very good, so dirt ingress is low, however in much the same fashion as front forks wear can occur so regular cleaning and occasional servicing is necessary.

To clean the rear shock, I normally spray the area with Muck Off / Fenwicks and agitate the area with a large cleaning or paint brush all around the shock and seal area. Then rinse and dry off, use a tea towel to get right around the seal area. Then spray the shaft with a silicon lube spray, (just a little) like fork juice etc, then compress the bike vigorously 20 times, this in conjunction with the spray will lift any dirt from the seals, you should see a small ring of dirt on the shock shaft, this will be dirt that was stuck under the seals, clean this off with a rag and you are done.

Servicing

Rear shocks have extremely complex internals with nitrogen charged chamber, however these tend to last well.
A basic and straightforward air can service, is easy to carry out and the parts are relatively inexpensive. The seal kit which fits all float series rear shocks is available from Mojo for £10 and is straightforward to do.
This involves replacing all internal dust and wiper seals and o-rings basic tools listed below are required.
I would recommend an air can service and seal change around every 12 months.

As many of you may or may not know I have the tools and the guides to service Fox, Rockshox, and Manitou rear shocks and am happy to service these for members for reasonable rates to cover materials and time taken, these rates are a fraction of what TF Tuned will charge and vary depending on the model of shock, pm me for more info.

Also I am more than happy to provide advice if you want to have a pop yourself.

Tools required
Allen keys (to remove shock from frame)
Strap wrench
Vice
A pick
Workshop cleaning towel
Grease
IPA (Iso Propyl Alcohol)
Float fluid (fox only)

If your shock develops more complex problems such as rapid loss of air pressure or problems with the rebound of the shock this will need sending away to Mojo / TF Tuned for attention.

Bushings

Shocks are fitted with a DU bushing in the eyelet of each end of the shock; these are a wearing part and need eventual replacement.
The mounting hard wear that connects the shock to the frame goes through these bushings so as they wear play develops in the rear shock / frame area.
Replacing the bushings is straight forward and inexpensive. It does require a special tool and a vice, but replacement bushes are inexpensive.

To test for wear in the bush stand at the rear of the bike and hold the rear wheel between your legs, hold the rear of the saddle and gently pull up and rock the frame, noticeable play will more than likely be worn shock bushes.

Again I can replace these for club members for a minimal charge.

Summary


1) Setting up and looking after your rear shock is no dark art and is both straight forward and saves heaps of money down the line.

2) Most manufacturersí websites contain a wealth of info on looking after your shock. A bit of research can yield great results.

3) Experiment with your setting and pressures and pro-pedal so you know how they feel, when you find your sweet spot, be sure to make a note of your pressures and rebound settings.

4) If you notice problems them looked at straight away, donít put it off.