Back to ba­sics: set­ting static sag

It de­fines how well any sus­pen­sion ad­just­ments work. It’s that im­por­tant

Practical Sportsbikes (UK) - - Inside - WORDS & PHO­TOG­RA­PHY ALAN SEE­LEY

SOME TIME in the 1990s, ad­justable sus­pen­sion on sports­bikes started to be­come the norm. Far be­yond the preload-only ad­justable shocks of pre­vi­ous decades, sud­denly we had the ca­pac­ity to fid­dle not only with spring preload fore and aft but also with the damp­ing too, com­pres­sion and re­bound now be­ing able to be ad­dressed sep­a­rately whereas be­fore, if it was found at all, it fell un­der the com­bined um­brella of ‘damp­ing’.

Some­times the dif­fer­ences that could be wrought from these set-ups were min­i­mal. In other cases it was of­ten eas­ily pos­si­ble to com­pletely ruin the han­dling through in­ept and ill-ad­vised fid­dling.

By the end of the 1990s how­ever, stock ad­justable sus­pen­sion was gen­er­ally pretty de­cent. For those who found stan­dard sus­pen­sion want­ing, a huge af­ter­mar­ket grew up with kits avail­able to re­spring, revalve and re­vive sports­bike sus­pen­sion.

Of­ten these made cheap mass-pro­duced sus­pen­sion com­po­nents work a lot bet­ter. They did of course take own­ers far be­yond the realms of the set­tings in their man­u­als. For the pur­poses of this fea­ture we will stick to what the var­i­ous ad­justers do so you can em­bark on your own ad­ven­tures in sus­pen­sion ad­just­ment. Start with stock set­ting, work in small in­cre­ments and re­mem­ber you can al­ways re­turn to stock.

To achieve best re­sults, sus­pen­sion com­po­nents should be ser­vices and in good work­ing con­di­tion.

Tools for the job

Steel rules or mea­sur­ing tape. Ca­ble tie. C-span­ner. Screw­driver(s). Span­ners.

1 Mea­sure up

First off we’ll look at rear static sag, that is how far down the sus­pen­sion’s to­tal stroke the bike sits at rest. You need to es­tab­lish two points to mea­sure be­tween – one on the swingarm and a fixed point on the bike. We’re go­ing from the top of the swingarm to the shock reser­voir.

2 Ask a friend

Get a mate to lift the bike up­right and bounce it up and down a cou­ple of times to set­tle the sus­pen­sion. Mea­sure at rest and with the rear end fully lifted. Note down the dif­fer­ence be­tween the two mea­sure­ments. Do it sev­eral times in case the bike isn’t set­tling in the same spot.

3 Rear preload

There’s a C-span­ner lurk­ing in there to loosen off the lock­ing ring to then move the ad­juster ring. To in­crease the amount of sag, less preload is re­quired. We’re aim­ing for a fig­ure be­tween 10mm and 12mm of rear static sag for the ZX-6R. We had to back the preload off to achieve this.

4 Front sag

A call to Dar­ren at MCT Sus­pen­sion sug­gested 26mm of static sag at the front. Butt a ca­ble tie against the fork seal with the bike at rest hav­ing first set­tled the sus­pen­sion then have your as­sis­tant lift the ’bars to fully ex­tend the forks and mea­sure be­tween seal and ca­ble tie.

5 Front preload

The ZX-6R’S front preload ad­justers re­quire a 17mm span­ner. Ad­just both legs evenly un­til the cor­rect amount of static sag is achieved. As at the rear, less preload means more sag. Adding preload does not make springs stiffer, it merely changes the mo­ment at which the spring com­presses.

6 Rear com­pres­sion

The ZX-6R’S shock has com­pres­sion damp­ing ad­just­ment on the re­mote reser­voir. Too lit­tle com­pres­sion damp­ing and the bike will be re­luc­tant to turn in and the rear will tend to squat. Too much and it will be harsh and kick off bumps while too lit­tle squat will lead to loss of trac­tion.

7 Rear re­bound

You’ll usu­ally find the rear re­bound ad­juster at the bot­tom of the shock. For il­lus­tra­tive pur­poses we’re show­ing the one on this old Yamaha shock. Lack of re­bound leads to wal­low­ing while too much re­bound damp­ing stops the rear re­cov­er­ing quickly enough forc­ing the bike wide in turns.

8 Front re­bound

The front re­bound ad­juster is con­cen­tric with the preload ad­juster. Too much re­bound causes a harsh ride to the point where the tyre strug­gles to main­tain con­tact with the road. Too lit­tle and the bike will wal­low and tend to run wide com­ing out of turns.

9 Front com­pres­sion

Too lit­tle front com­pres­sion damp­ing and the bike will tend to dive and may even bot­tom out. Too much com­pres­sion and the bike will again tend to run wide as it will sit too far up the stroke. Set your sus­pen­sion to the man­ual stock set­tings then make small tweaks to your taste.

Mind the paint with that steel rule, son

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