The Girvin Vector

From Harsh Reality to Perfect Performance

Jim Frost
September 18, 1996
Last modified September 23, 1996

Contents

Introduction

 Ahh, the Girvin Vector. There is probably no other fork out there whose riders have such a love/hate relationship. They love the precision, but when compared to most other forks on the market the adjective usually used to describe it is harsh. The fork's action is clearly best only on mid-sized hits, making it an effective cross-country suspension but without the comfort desired by most riders nor the response needed for downhill applications.

The harsh ride that most people complain about is not inherent in the fork, it's the result of abysmal tuning on the part of Girvin; as it comes from the factory the fork is quite simply overdamped to a fault. This behavior is fairly easy to correct and, once corrected, the Vector provides performance which is almost unparalleled in the industry. I'm here to tell you how to do it.

Getting at the Heart of the Matter (or: the easy way to remove the shock unit)

All of the techniques discussed here require you to remove the elastomer stack and ODS unit from your fork. The owner's manual tells you how to do it, but their technique requires removal of the shock pivot tube on the lower linkage, an onerous task.

There's a better way.

  1. Remove the wheel from the fork.
  2. Remove the two bolts attaching the upper linkage to the steerer collar with a 5mm allen wrench. Pull the upper linkage away from the collar, being careful to catch the pivot seals.
  3. Remove the pivot bolt holding the top of the shock from the steerer collar. At this point the fork legs and shock will be able to swing away from the bike.
  4. Using a 19mm or 3/4" cone wrench, loosen the lock nut at the bottom of the elastomer stack. This is a tight fit, but there is just enough room from the side of the fork to perform the task. Once you get the lock nut loose you can unscrew the whole unit by hand easily.
That's it. To put the unit back in follow the steps in reverse. Remember to put the upper link seals back in correctly -- the half-moon sections in the middle of the seal fit into the depressions on the steerer collar and positioned away from the linkage. They keep the seals in place while you push the linkage back into position.

The Cheap Way Out (or: upgrading without buying anything)

 The easiest and least expensive tuning improvement you can make is to the elastomer stack. The small elastomer has a 6.5mm spindle hole, compared to the 9mm hole on the larger. This is presumably to improve damping characteristics, something which should have been unnecessary with the advent of the ODS unit and which hurts small-impact performance considerably.

With an electric drill fitted with a 9mm bit, enlarge the hole in the small elastomer. This allows the elastomer to slide much more freely on the spindle and significantly improves small-impact performance. Because the elastomer deforms during the drilling it can take some effort to enlarge the hole enough; you can make the task a little easier by freezing the elastomer before you drill.

While you have the elastomers off you should liberally lubricate the spindle and elastomer holes. A dry lubricant such as BoShield is preferable, but waterproof grease works fine (although it will need to be reapplied several times).

Welcome to the Big Time (or: fixing the ODS unit)

Drilling out the elastomer improves small-bump performance, but curiously does nothing at all to midrange or big bump performance, which remain rather harsh.

This is due to overdamping by the ODS unit affecting the compression of the elastomer stack. The ODS unit comes filled with 30wt oil from Girvin, which is insanely heavy for their damper. Experimentation reveals that optimum damping is seen with weights ranging from 7.5wt to 15wt -- at least half the weight of stock, and as little as a quarter! For a mid-weight rider (150lbs or so) 10wt oil is very close to ideal; lighter riders may want to go a bit lighter, and heavier riders may want to go as high as 15wt. No one wants 30wt.

To change the oil in the ODS unit you must first open it up, as follows:

  1. Remove the elastomer stack, end plates, and elastomer spacer.
  2. Using a pin spanner (about $6 at your local bike shop) loosen the end cap on the ODS unit. This will be very difficult -- it's on very tight. I suggest putting a 5mm allen wrench through the pivot hole at the top of the ODS unit and placing that end of the unit (cap upward) in a vise, closing it just enough to hold the ODS unit from slipping. The allen wrench will keep the unit from turning within the vise, allowing you to put a lot of torque on the cap to loosen it.
  3. Remove the cap, exposing the seal.
  4. Pull the plunger and seal out of the ODS unit. The seal fits very tightly and is extremely difficult to remove by pulling with your hands. An easy way to do it is to replace the elastomer stack and use the preload adjuster to push the elastomer stack away from the seal. This will force the seal out of the ODS unit, along with the plunger. You could also substitute a properly sized piece of pipe for the elastomer stack between the stack endplates; this makes the extraction a little easier.
  5. Clean the oil off of the plunger and seal. Dump the oil in the unit and dry it out as best you can.
  6. Pour new oil into the ODS unit until the top of the oil is 44mm below the top of the ODS unit. This is the proper oil level; there will be some air trapped in the unit when it is reassembled.
  7. Insert the plunger back into the ODS unit and push the black seal into the unit. It will be a tight fit, but try to push it until the seal is flush with the top of the ODS unit. If you can't quite make it don't worry, the next step will finish the job.
  8. Put the ODS unit cap back on and screw it down snugly against the seal. Use the pin spanner to tighten it as much as possible.
  9. Put the elastomer stack, endplates, and separator plate back on the shock spindle and screw the lock nut on to hold the unit together.
  10. Reassemble the fork.
With lighter oil in the ODS unit you should find the fork much more responsive to larger hits.

A Match Made In Heaven (or: metal springs save the day)

 Manufacturers switched from air/oil forks to elastomer sprung forks for several reasons: Elastomer forks didn't need seals, so there was little stiction and small-bump compliance was considerably better than air/oil; Elastomers have their own damping so no oil was needed; Elastomers are very inexpensive, allowing them to produce forks much more cheaply and profitably.

Unfortunately there are several serious problems with elastomers:

It's long been known that metal springs have excellent spring characteristics -- linear response rates, temperature insensitivity, and excellent small-bump response in particular. The problem with using springs has been the rebound; they bounce back as hard as they were compressed, causing a vicious kickback. Steel springs absolutely require external damping.

Once oil dampers were being included in elastomer shocks there were no practical reasons why metal springs couldn't be used in place of elastomers. While the suspension fork manufacturers stuck with elastomers, it's likely that they did so primarily because they already had significant investments in that technology. Aftermarket suppliers such as Mountain Speed and others picked up where the manufacturers left off, offering drop-in replacements such as Speed Springs which improve small bump compliance significantly and increase effective travel through their linear response rates.

Metal springs correct several deficiencies in the stock elastomer setup of the Girvin Vector. Since they have no contact with the damper spindle there is no friction to induce stiction, so small-bump performance is dramatically enhanced. In theory the linear spring rate should improve effective travel too: the stock configuration offers a mere 1.75" of real travel versus the claimed 2.5"; while this is good enough for cross-country use, it is considerably less than the real-world travel offered by most cross-country telescoping forks on the market.

My first exposure to a steel spring replacement on the Vector was with a friend's fork; he had replaced the elastomers with a 200lb Noleen spring from the rear of an Azonics T-1 full-suspension bike. While this upgrade worked very well compared to the stock elastomers, it had three deficiencies compared to upgrades such as the Mountain Speed SpeedPro spring kit (pictured above):

Unfortunately simply switching to a steel spring does little to affect the fork action on anything but small hits even though the spring should provide significant improvements on larger hits. As with the elastomer setup this is the result of overdamping by the ODS unit. In order to realize the full potential of the fork you must perform the ODS oil change described earlier. Once this is done, midrange hits are absorbed with the same effectiveness as small hits (they very nearly disappear) and the added half-inch or so of travel is easily noticed on larger hits.

To date steel springs such as the SpeedPro in combination with lighter oil in the ODS unit offer the best possible configuration for the Girvin Vector. These two changes provide excellent response throughout the entire fork travel, making it both more comfortable in cross-country applications and a very usable downhill fork for hardtails and short-travel full-suspension bicycles. The only detriment to the upgrade is added weight -- the 3.3lb weight of the stock Vector bulks out to approximately 3.6lbs. In practice, however, the weight goes unnoticed compared to the dramatic improvement in the fork's effectiveness.

What Girvin Is Doing

Now that you've learned what's wrong with the Vector and some techniques to fix it, you are probably asking yourself why Girvin hasn't made these changes themselves. After all, it could hardly have escaped their notice that the fork action is not particularly smooth, and they had ample time to play with oil weights and elastomer configurations during research and testing.

I wish I knew. The tuning changes described in the early part of the article were obvious even to someone like myself with limited engineering education and experience, and customers such as myself have repeatedly attempted to discuss the tuning of their forks with them but have received little if any response.

Early peeks at the 1997 Vector lineup indicate that the feedback has not gone unnoticed, however. Girvin will be using a lighter weight oil in their elastomer-equipped ODS units, which should significantly improve their performance. In addition, Girvin will be offering Vectors equipped with Noleen coil-over shocks rather than elastomers, so it will no longer be necessary to use aftermarket springs to see optimum performance from your Vector.

The NR-1 shock Girvin will be using is already available as an upgrade. Unfortunately this unit offers no advantages over a tuned ODS unit with the SpeedPro spring, and costs nearly three times as much.

1997 may well prove to be the year where Girvin gets their shock right; but current Vector owners can have that same performance now.

Legalese

Tuning tips are the result of experimentation by the author and others without support or feedback by Girvin/ProFlex. Any or all such modifications may affect your fork's warrantee. The author specifically disclaims any liability for damage, either direct or indirect, resulting from the modifications described herein.