SR Suntour forks — a guide

The SR Suntour fork range is very popular on new bikes. This article attempts to explain the differences.

Construction

Suntour forks are essentially consisted of four major parts:

The upper assembly:

The parts visible above are:

• the steerer tube, which at this point is either a straight 1 1/8" tube, or a tapered 1 1/2" to 1 1/8" tube. Suntour’s steerer tubes are made of an aluminium alloy (most forks beyond the cheap ones), carbon fibre (Axon Werx), or STKM (steel, on cheap forks). Straight forks can be adapted to fit a tapered frame, but not vice versa. In general a tapered fork should offer greater stiffness
• the crown. Cheaper forks use Suntour’s melt-forged alloy process. More expensive forks may use higher grade alloy (A6000/A7000), or hollow forging. Some Axon Werx forks use hollow carbon crowns. The available weight saving is fairly small from the crown.
• the stanchions. These are a major marketing point. Generally thicker stanchions means more stiffness. Suntour make 25.4mm, 28mm, 30mm, 32mm, 34mm, 35mm, 36mm, 38mm stanchions. Generally XC uses 30–34mm, trail uses 32–35mm, and 35mm-38mm are for enduro and downhill.
  A complicating factor is material choice. SR Suntour’s cheapest forks use chrome-plated steel (STKM), then nickel-plated steel (STKM), then A6000 alloy, then A7000 alloy. Alloy stanchions offer substantial weight savings over steel. Cheap steel stanchion forks with 34mm stanchions seem to be about marketing rather than performance

The lower case:

There is less to note here:

• The lower is either made of a magnesium alloy (over 90% magnesium), which is significantly lighter than aluminium, or on cheaper models, from aluminium.
• the lowest part of the lower is the q/r dropout or axle. Here you will find 9mm models, where you use a traditional quick release with the skewer from your bike wheels, 15mm or even 20mm (for downhill/enduro) models in either 100mm width or 110mm (boost), in which case you use Suntour’s axle. Suntour offer tool-less (threadless) axles, and tool types, which must match the lower. The toolless option is about 50 grams heavier, but Suntour do make a lighter titanium axle.

A damper cartridge

This is a major determinant of the performance of the fork. Suntour’s damper cartridges are nitrogen-sealed and cannot be opened, only replaced if they no longer function well. Better-quality forks contain better quality damping cartridges. For a given fork, there are often multiple damping cartridges available, which may perform differently, or have more adjustment options. Suntour uses a variety of different dampers, all of which are based on coil springs, though the spring is often inside the cartridge.

A spring insert

While one leg of the fork contains the damper assembly, the other contains the spring assembly. The spring assembly consists either of a metal coil or an air spring. The two work in the same way, but an air spring can be adjusted by simply reducing or increasing the amount of air in the spring according to your weight, while with coil forks there is a knob which turns to adjust the amount of initial compression in the spring according to your weight. Since air fork adjustment is done with a shock pump with pressure gauge, it’s easier to setup. There is however nothing wrong with coil springs, but they are perceived as low end. For coil forks SR Suntour sell replacement coils in different firmness grades.

XC forks

XCT/XCE

The XCT fork has gone through various modifications, ranging from awful to terrible.

In general there is a coil spring with pre-load adjustment on one side.

The damper side is empty in some old XCT forks. In forks without a suffix such as MLO, HLO), the damping construction is simpler using springs, rather than a cartridge.

The HLO cartridge found in some XCT forks is not likely to perform well as it is their cheapest option, and there is no rebound spring inside. Non-HLO forks will be even worse. HLO means ‘hydraulic lockout’. This feature is not particularly essential on forks.

In previous years, XCT was a 28mm steel stanchion fork. Now there is also a 30mm model. This is not really an upgrade, just marketing.

The XCE fork is essentially a 28mm XCT with damper spring (not damper cartridge).

XCM

The XCM fork is similar internally to the XCT. The main difference is the size of the stanchions, which historically were 30mm steel to XCT’s 28mm. Now there is also a XCM 32mm and even 34mm model to keep up with XCT’s size inflation

The XCM consists of three main variants:

• the no-suffix fork which doesn’t use a damping cartridge, but a second spring
• the HLO variant, which uses the same HLO cartridge found in XCM, which means similar performance
• the LO and RL variants, which have a better quality cartridge with rebound spring. LO means lockout and RL means remote lockout.

The HLO variant seems to be popular with OEMs, which is unfortunate as there’s not really a performance benefit over XCT HLO.

In recent years a variety of exotic XCM forks boasting thru-axles, tapered head tubes, and boost spacing have appeared. Mostly these are something to be replaced as soon as possible for a better fork aftermarket. The 34mm boost models weigh around 3.4kg and the 32mm boost models 3.3kg, making these forks a good source of scrap metal for recycling. The older 30mm models are not so bad, at 2.8kg. Some of the 32mm and 34mm options have the LO-R damper, with adjustable rebound. This is a different cartridge from the XCR, though it is not clear if the performance differs.

XCR

XCR’s key upgrade over XCM was that it uses magnesium lowers. This makes the XCR fork around 600 grams lighter than the XCM. In 2014 the stanchions (which, remember, are still steel) were upsized from 30mm to 32mm, and the internal seals were improved compared to the earlier versions and to XCM/XCT (the same system is found in the XCM 34 only).

The XCR’s damping options are:

• LO/RL — the most basic damping cartridge for XCR
• LOR/RLR — this cartridge has an adjuster for the rebound spring

The XCR Air is almost identical to the XCR, but it has an air spring.

Tapered steerer XCRs tend to use alloy steerer tubes.

Raidon

In previous model years coil Raidons were available, now they are all air springs. The Raidon damping cartridge is aluminium whereas XCR and lower use steel cartridges. Only cartridges with adjustable rebound are available.

Like XCR, Raidon steerer tubes are alloy, while straight steerers are steel.

The Raidon stanchions are a big upgrade on lower forks, being alloy.

Raidon forks weigh in around 2.0kg, 32mm and 34mm options are available.

Epixon

In earlier model years Epixon had other names such as Epixon TR, Epixon XC, Epicon X1, Epicon X2, etc. Many of these forks were more advanced than the current Epixon. The current Epixon, referred to by Suntour as Epixon-9 because it serves the 9mm qr market, uses the same damper as in the Raidon.

Earlier versions shared Axon damping cartridges, which are higher quality.

The upgrade of Epixon over Raidon lies in the crown, which is alloy. Epixon uppers are the same as Axon. The Epixon saves around 150 grams, which might or might not be worth it, considering the lack of performance improvements.

Axon

The Axon offers better quality, more-durable cartridges. In addition, higher performance options are available. The full list of dampers:

• RLR/LOR — basic cartridge like a more durable Raidon/Epixon
• LORC/RLRC — adds low-speed compression adjustment
• PCS — more advanced cartridge with internal floating piston (IFP), and low-speed compression adjustment.

There are several versions of the Axon:

• Axon 32mm stanchion — non-PCS, around 1.7kg
• Axon 34mm stanchion — PCS, around 1.9kg
• Axon Elite 32mm and 34mm stanchion, PCS, hollow forged crown reduces weight to 1.6kg/1.7kg.
• Axon Werx 32mm — carbon fiber lowers save a mere 35 grams from Axon Elite 32mm
• Axon Werx F 32mm — hollow carbon crown brings weight down another 80 grams
• Axon Werx 34mm — it shares the hollow carbon crown of the Werx F, but goes back to magnesium lowers. Weight is 1.6kg. This is SR Suntour’s most advanced XC fork, featuring an air-negative spring, called ‘EQ’ or Equalizer.

Trekking forks

These are intended for roads and paths, with less travel.

M3010/CR7/CR8/CR85

These are SR Suntour’s v-brake forks, all built from cheap heavy materials.

Differences:

• CR7/M3010–25mm/25.4mm stanchions, no damping at all. Preload is not present on all models.
• CR8–28mm stanchions, non-designated models have no damping at all, MLO models have damping coil without rebound coil, HLO has basic damping cartridge,
• CR85 — ‘ebike’ model with 30mm stanchions. Either no damping, or rebound damper cartridge in type LO.

NEX, NVX

NEX (50/63mm)/NVX (63/75mm) are similar to XCT in terms of internals and materials. There are 30mm (e.g., the E25 for e-bikes) and 28mm stanchion variants.

Damping options:

• no suffix — some models empty, some models damping spring (no cartridge)
• HLO — most basic damping cartridge
• NLO— slightly less basic cartridge
• LO/RL — slighty less basic cartridge, with blow-out feature

NEX/NVX can be considered to correspond to the XCT & XCM product range.

Mobie A32

This is an e-bike fork. In terms of construction it’s similar to the XCM 32mm variant, however the travel is shorter.

There are only LO/NLO/RL cartridges, not the basic HLO or the spring.

NCX-D/NRX-D

The NCX-D (50/63mm) NRX-D (63/75mm) resembles XCR in that it gets the weight saving upgrade to magnesium lowers. Like the XCR there are both Air and Coil options.

As this is a 30mm trekking fork rather than a 32mm XC fork, it’s around 2kg for the NCX & 2.1kg for the NRX, rather than 2.4kg for the XCR.

Unlike the XCR there’s no adjustable rebound cartridge.

The TR-HSI fork is a coil NCX-D with HLO damper. It is built for hydraulic rim brakes, and is very heavy as a result.

NCX-E/NRX-E/NRX-S

The NCX/NRX-E is a slightly upgraded-D with alloy stanchions. This saves around 300 grams versus the -D.

The NRX-S uses slightly higher grade stanchions

This is the equivalent of a Raidon XC fork.

Mobie25/45

These are two ‘ebike’ forks. The Mobie25 has 32mm stanchions and the Mobie45 has 34mm stanchions.

The Mobie25 is effectively a short-travel Raidon, while the Mobie45 is a short-travel Aion (trail fork), i.e. they are similar quality but Mobie45 has bigger stanchions.

Both have air and coil options.

Trail forks

SR Suntour’s trail forks start about the Raidon level.

The line-up is:

• Zeron 35 (stanchion size) is the lowest-end, however as a new design it has adjustable air volume. The damper is Raidon/Epixon class, with adjustable damping and optional adjustable compression. Coil option exists.
• Aion 34 contains a higher quality damper (Axon class). It’s lighter than the Zeron.
• Aion 35 has the PCS damper, and the adjustable air volume
• Auron 34 has the PCS cartridge, hollow crown and titanium axle is supplied. There is also a model with both high and low-speed compression adjustment. It saves 100 grams over the Aion 34.
• Auron 35 is completely identical to the Aion 35 but with titanium axle and the option of buying with the high & low-speed compression-adjustment on the damper. From 2021 model year, Auron 35 gets the EQ air negative spring system.

Note that in general the 35mm models are boost and the 34mm models are not — the 35mm is a newer model, but the 34mm is still sold.

Durolux (All-mountain/enduro)

The Durolux fork receives regular updates. Like most high end forks you find magnesium lowers & aluminium uppers. 2016 was the first iteration of the current model with increase in stanchion size to 36mm, the PCS IFP cartridge, and the new R2C2 damper with both low- & high-speed compression and rebound adjustments. Travel is adjustable from 160–180mm for or 150–170mm. The R2C2 damper was upgraded in 2018.

The damper options are RC (rebound & compression), RC2 (rebound & low & high-speed compression), R2C2. It weighs around 2.2kg.

For 2020 Durolux was updated to ‘Durolux EQ’ with the air negative spring.

Rux (Downhill)

The Rux was originally (2007) a moderately priced coil jump fork. For 2013 it was changed to be a dual-crown downhill fork with 200mm travel, 38mm stanchions, air spring, rebound and low & high-speed compression adjustment (RC2).

From 2016 it was upgraded with the PCS IFP cartridge, and an optional R2C2 model with both low & high-speed rebound adjustment. The 2018 model is the most recent upgrade with lighter lowers & improved R2C2 & PCS cartridge.

Rear shocks

As SR Suntour is mostly specced on cheap MTBs they have not produced as many rear shocks.

XC-Pro/Epicon/Epixon/Raidon

The XC-Pro was introduced 2006. For 2008 it was renamed Epicon. In 2009 the Epicon was renamed to Raidon and the new Epicon given higher maximum air pressure (300 psi rather than 200psi). From 2015 the Epicon was renamed Epixon, and in 2016 discontinued, leaving Raidon as the entry-level.

The types:

• Raidon-LO, lockout, fixed rebound, no compression damping adjust
• Raidon-R (before 2012 -DA), no lockout, fixed rebound, compression adjust
• Epicon-DA (from 2012 -R), no lockout, adjustable rebound, compression adjust
• Epicon-LOD (from 2012 -LOR), lockout, adjustable rebound, compression adjust
• Epicon-AM-LODP (2011) (from 2012 LORP) — non-adjustable platform damping added, stopping the shock from moving under normal smooth pedalling to LOD
• Epicon-RC2 (2012) (from 2013 RC)- both low & high speed compression adjust

The weight of the Raidon is around 295g and the Epicon slightly less.

Durolux/Duair/Edge

The Durolux was introduced in 2011 with the key design feature of a dual chamber air cartridge. It was replaced by the Duair (same chassis, new damper, adjustable air volume using spacers). The Duair was replaced by the Edge in 2019.

Types:

• R — adjustable rebound
• LO-R/R8 — lock-out/80% lockout, adjustable rebound
• RLR/RLR8 -remote lock-out/80% lockout, adjustable rebound
• RCA/RC — adjustable compression, adjustable rebound

The weight is around 300g.

Triair

SR Suntour introduced the Triair 3CR piggyback shock in 2018.

It has 3 compression modes (trail, climb and downhill), with separate high-speed and low-speed rebound, and adjustable low-speed rebound.

The weight is around 400g.