Shocks

All you ever wanted to know about Motorcycle Shock Absorbers

This production comes to you courtesy of Rob Maytum and Performance Bikes (Sept 93') - most of the text (and witty bits) due solely to PB.....

All the following are based on the impressions on a CBR600 - a combination of riding time on the bike and testing on Maxton's Koni shock dyno. The shock dyno replicates furious shock activity, enough to overheat the stock shock in just 3 minutes. From this point on the damping deteriorates, providing less and less control of the damping as the oil thins out. This became the time to beat - if it could survive this then it was doing well.

Standard Showa - £447.04

The CBR600 like most Hondas (listen you VFR riders out there!) comes the the cheap and nasty Showa unit. In the trade it's rather unpleasently termed as an 'orifice' shock. This is no slur on its capabilities, rather an indiction of the way it works, i.e. repound damping is controlled by changing the size of an orifice, or hole, through which the damping oil passes. This tends to effect compression damping too : not ideal.

Compared with aftermarket shocks the standard unit lacks travel - the amount the damper squashes before it hits the bump rubber. On the CBR 600 you multiply this distance by 2.5 to get the wheel travel. A mere 30 mm of shock travel (75mm at the wheel), and a spring strong enough to support the White Helmets, doesn't help the CBR 600 in fast, bumpy corners. With the rebound adjustment set so there is actually some damping (full-in on mine) compression damping is badly effected giving a very firm , bouncy ride.

If you don't fancy splashing out £500 on a new shock Maxton (0928 740531) will modify and rebuild tyour original shock for a fraction of the cost.

Koni - £493.50

All Konis used to be self contained units; this new remote reservoir type is supposed to look after the slow-speed damping better. Like the Ohlins and Proflex, the Koni regulates high speed damping (long strokes or big bumps) with shim stacks. Where the shock only compresses a small distance, like over ripples and cat's eyes, the damper works normally.

The shock used actually belongs to dealer and racer Bob Jackson (05397 20580), and was specially built for the 93' TT. The TT is probably the closest type of racing to riding on the road , so pay attension this is the hot set-up.

A short spring (about 6 inches ont he stock shock) is more likly to go coil-bound at full compression. So Bob's Koni wears a comparitively light (540 lb) seven inch spring. The theory is simple; for mothers and fathers of bumps at very high speed you need a nice pliant spring and lots of travel. View the TT as a tarmac motorcross and you get the idea.

The Koni was the best fit; no slop at the mounting points and pleasingly effectiverose joints at the top and bottom. Beautiful. Like the Proflex, it came with just the right amount of hose to mount eh remote reservoir out of harms way on the rear subframe. Preload sadjustment is possible with the shock in place but altering compression damping means removing the shock and spring; with luck it's right first time. To get at the rebound screw you have to remove the sidepanel.

On the road the Knoi's softer spring made itself felt, but at somewhere as fast as Mallory or Donnington it may start to feel a bit soft. It made me wonder whether the Ohlins or Proflex, with a similar rated rear spring, would feel the same - this is definately the sort of spring rate you would be looking for for one-up use on the road. If you amke a habit of carrying passengers be prepared to compromise comfort for support.

Bob Jackson was second in the supersport using this shock. Perhaps even more amazing was winning man Jim Moodie's 118 mph lap on the standard item. Eeek. Does the man have no imagination?

Ohlins - £493.50

Fitting the Ohlins was a cinch. Part of the the reason was the lack of remote reservoir, the other a somewhat baggy fit needing fidding with shims to correct .... it's a bit of a surprise, really.

Also suprising was the lack of spherical bearings in the top and bottom eyes. Metallic bushes are a poor substitute for rose joints, giving a small degree of vertical play on compression and extension, putting unnecessary stress and strain on the nounting bolts. But they are more resistant to road grime.

Spring removal, as we discovered when we measured the rate, is not just a matter of unscrewing the preload rings with the provided C-spanner. You need a spring compressor to remove the bottom collets - either that or a vice-like grip. Preload adjustment is a bit involved. My road bike with all its wiring and bracketry, wouldn't allow the weilding of a C-spanner with the Ohlins in place. Setting up the static rear ride height (one of the first jobs fitting any shock) took much longer than expected.

After that dialing in didn't take too long. With a bit of grunting, and some snake like contortions of the wrist, both the rebound and compression dampers can be reached with the bodywork intact. Beware of any 'helpful' friens sitting on the bike while your fingers are between the linkages.

On the road the Ohlins felt a little softer than stock. Gone was the bounciness when it was powered out of corners. Hitting a bloated cats' eye at 90 used to induce a nasty boinginess (technical term) - the more banked over you were at the time the worse it was. Deliberately hitting the same cats' seye with the Ohlins on failed to replicate this behaviour. The same can be said of the Proflex and Koni.

Drive out of corners was the biggest difference; no more pogoing as the power was fed on. This was more noticable on the road where you find those undulating bumps on the outside of a corner .... or at Mallory three days after the truck GP. The Ohlins high speed damping coped with these conditions far better than the O/E unit againlike the Proflex and Koni.

It's a much better shock than the standard unit; you only have to see the range of damping adjustment on the shock dyno to see the proof. The rest of the proof is in the improved ride and roadholding, but a softer spring would be better still.

Proflex - £470.00

The Dutch-made Proflex is widely used in Supersport racing, largely because it's fractionally cheaper than most other available. Fitting was fairly straightforward but the top bush need drilling out before the bolt could be pushed through the eye: tiresome if your lock-up is miles from a source of electricty.

The next problem is finding a home for the remote reservoir bottle and rubber hose. You get two big jubilee clips but no spacers to mount a round bottle to a round frame. We made our own out of neoprene.

Altering preload or compression damping is easier with the rear mudguard out - a pain when you're setting up, but not a problem when it's done. Spring preload is altered with the providied tool, which looks rather like a dot punch. Fitting into holes on the springs threaded collar, it's less likely to rip your knucles apart than a C-spanner.

Rebound damping is adjusted by a flat headed screw on the remote reservoir bottle. I have to remove the left ahnd sidepanel to get at mine, but when it's set up you should never change it again unless you change tyre brands or developsigns of annorexia or obesity.

While the Proflex was markedly better than the standard shock I couldn't distinguish between it and, say, the Ohlins. The dyno spotted a few differences, and several race speed laps of a track might confirm this. On the road the Profelx felt as good as the Ohlins or the Koni, giving my kidneys a much easier time yet still feeling taut when the bike flicked hard from right to left, or hit a bump mid-corner.

Quadrant - £198

(Quadrant info removed - company thought to've gone bust)

Conclusion

Suspension is like food, sex and architecture. Some like it one way, some the other. Jim Moodie obviously doesn't need to change anything, but his 93' CBR's shock is infinately superior to the one on my 91'. He wouldn't have done 118 mph on my shock for sure.

Unless I was going racing I'd have trouble spending £490 on a Koni, or for that matter £470 on an Ohlins or Prolex with a softer spring. For road riding you have the following options:

  1. Let someone revalve the standard shock, perhaps with a softer rear spring.
  2. Buy a Proflex with a soft spring and spend the £23.50 you've saved over the Koni on riotous living.
  3. Leave it as it is, put up with a bit of bounciness and buy some new leathers instead.
  4. When you're finally sick of the standard unit, buy the Quadrant.

I must admit, even after being spoilt by the luxury of new shocks, I've plumped for option 3. Except that I didn't buy any new Leathers because I'm a tight old scrote.


Mark Forsyth

Well there you have it folks - everything you ever wanted to know about shocks but were afraid to ask .... One very long typing session later!!

My friend whose just ahs his shock (VFR) rebuilt with new seals and oil (specialist job as it's a cut and weld thing as the stock units are 'non-rebuildable') hasn't taken it out and tried it yet so I don't know how good it is (He's running around on his CX500 rat bike which he dispatched on - I'm not saying it's scary, but the brake hoses are so old you can pull the front brake right back to the bar!!!) - Anyway he paid £30 for the privalige, but only because they misquoted him over the phone (jammy git) - the normal price is around £80 - I'll let you know how things go when he's riding it again if anyone is interested.

Ah well time to go, best wishes to all

Robin Maytum

BTW. I've just found out I can type at a massive 20 wpm