How-To: Bolt-On Suspension Mods

Out with the old, in with the new

What’s that you say Bunkie, your bike handles like a mattress but rides like a 2X4? You say it turns into the world’s fastest shopping cart at the first sign of a sweeping turn? You’re telling me it’s got limited ground clearance, wobbles like a drunk on Saturday night and telegraphs every little impact straight to your spine? Can’t say as I’m too surprised my friend, but at least you’re not alone.

Too many cruisers, particularly those in the intermediate price range, come equipped with less-than-stellar suspension. The springs tend to be inexpensive, straight-wound, single-rate units and the rear shocks, which are normally non-adjustable, are inclined toward damping rates that suit no one particularly well.

Ironically many riders find that even the pricier components fitted to upscale bikes don’t perform to their liking. And why should they? For the most part suspension systems are designed with a model rider in mind. Since it’s a good bet that your suspension criteria and that of the model are somewhat different it should come as no surprise that his suspension requirements and yours are going to be at odds.

In theory any suspension can be optimized with careful adjustment. If you’re running the OEM stuff this means playing with things like spring preload, and perhaps the front fork oil level and viscosity. More advanced systems may also incorporate some sort of externally adjustable damping adjustments; sorry to say these are less common than they should be.

But let’s be honest, more often than not when a rider’s suspension is off it’s because the spring rates are wrong and/or the damping inadequate. If the fundamental setup is off you can add preload and twist those screws till you’re blue in the face; in the end, the bike still won’t be right. When that’s the case, as it all too often is, modification of the offending components or their replacement may be the most practical solution.

What do I need?

Tool Kit:

While it’s certainly permissible to upgrade only the front or rear suspension (and if you’re on a limited budget that may be the only way you can afford to do things), it isn’t always a good long-term plan. Here’s why: In my experience, repairing a shortcoming at one end of the bike tends to aggravate problems at the other end. Besides, one of the prerequisites of suspension tuning is balance; that is, getting both the front and rear suspension to work in concert. So it doesn’t make a whole lot of sense to install a stiffer set of rear springs and shocks while leaving the sacked-out fork springs in place or vice-versa. Unless you’re an experienced suspension tuner trying to cure a clear-cut problem, my recommendation is to always upgrade both ends at the same time.

What you'll need to do this one:
1. Bike jack (if the bike has a centerstand you can use that and a small floor jack)
2. Common hand tools (wrenches and sockets sized to fit your bike's bolts, a hacksaw and measuring tape)
3. Torque wrench
4. Shop manual
5. Expendable supplies (rags, anti-seize or white lithium grease, and fork oil if a change is on the agenda)

OEM shocks, new suspension, how-to, suspension mods
Compare the skinny OEM shock on the left (ironically with a progressively wound spring) with the beefier unit supplied by Progressive Suspension.Photography by Mark Zimmerman

It’s a safe bet that replacing the lame or worn-out OEM fork springs and shocks with aftermarket items will substantially improve the handling of your average cruiser. The problem is, whose do you use?

Having tried most of the available aftermarket suspension products at one time or another I’d be hard pressed to state that any one is definitively better than the other, except under very specific conditions, especially where cruisers are concerned. That being the case I’d cruise a few of the chat rooms that cater to your bike and see what the other guys are using. The advantage here is that you’ll get some real-world feedback by riders who have racked up some miles on the stuff as opposed to a parts counterman who may be working on commission.

Once the new stuff is in your hot little hands, the rest of the job, as I’m so fond of saying, is something that anyone reading this can accomplish in the comfort of his own garage, so let’s take a step-by-step look at what it entails. In this instance we’ll be installing a set of Progressive Suspension’s progressively wound fork springs and matching 412 Cruiser shocks and springs, a combination that provides a lot of suspension bang for a very reasonable buck.

Along with the suspension components, the manufacturer will normally include any spacers or bushings required to mount the components, and, in the case of fork springs, spacers (these may need to be cut) to adjust preload. There should also be a set of instructions detailing proper installation techniques and adjustment procedures. Before you get in over your head, do yourself a favor—count up all the pieces and read through the instructions. It's going to be a real pain if something's missing or you don't understand the next step halfway through the project.

Because the weight of the bike will load the suspension you’ll need some way to remove the tension. In some cases you can use the bike’s centerstand and a jack to support it. But with centerstands being in short supply these days a better bet is a dedicated bike jack. In any event it’ll need to be something capable of lifting the bike off its wheels, and stable enough to prevent it from nose-diving into the concrete while you wrestle with it.

OEM shocks, new suspension, how-to, suspension mods
Obviously you are going to want to remove the old stuff before you put on the new ones.Photography by Mark Zimmerman

Rear Shocks
Obviously we're going to begin by removing the old stuff. Since the new shocks are the exact length as the ones we're replacing, the correct procedure is to replace one side at a time. If the new shocks were shorter or longer than stock we'd need to remove both of the old shocks before installing the new.

Proving that even big-time magazine guys have bad days I ran into a hurdle when the stock shock bushing froze to its mount. A few naughty words and a Vise-Grip handshake managed to twist the offending bushing off the stud, a process I repeated three more times.

Since our Progressive 412 Cruiser Shocks come fully assembled, installation was as simple as selecting the correct bushing, greasing the snot out of it so it wouldn’t stick again and installing the new shocks. Don’t forget to install any required spacers or washers, and then position the shock in place, adjusting the offset as needed to prevent any clearance problems. Torque the retaining hardware and you’re done.

OEM shocks, new suspension, how-to, suspension mods
If a bushing freezes to its mount you may have to put in a little work. Don't worry, we hit the same problem.Photography by Mark Zimmerman
OEM shocks, new suspension, how-to, suspension mods
Don't forget to install any required spacers or washers.Photography by Mark Zimmerman
OEM shocks, new suspension, how-to, suspension mods
And position the rear shock in place and you're done.Photography by Mark Zimmerman

Front springs
Replacing the fork springs is slightly more involved. First consult your service manual; in some cases the handlebar will need to be removed before the springs can be withdrawn from the tubes. In other instances it may be easier to extract the tubes from the clamps altogether, particularly if you're combining this job with some other task, like changing the fork oil or installing some sort of damper modification kit. On that note I'll also tell you that it's far better to remove too many parts than it is to try and shortcut things by leaving something like the handlebar and cables attached and resting on the fuel tank where they'll get in your way and make a general nuisance of themselves while you manhandle the forks. If the bar is coming off, remove what you need to so it can be safely stowed on the shelf until it's ready to be re-installed and make sure that any easily damaged parts like the fuel tank or front fender are either removed or well protected from flying hardware.

OEM shocks, new suspension, how-to, suspension mods
The wimpy straight-wound stock spring is on the top, the progressively wound replacement on the bottom. Because the stock spring is so short an excessively long preload spacer (metal tube) is needed to take up the space.Photography by Mark Zimmerman
OEM shocks, new suspension, how-to, suspension mods
Before removing the fork caps, slacken the top clamp pinch bolts before removing the fork caps.Photography by Mark Zimmerman

Before removing the fork caps, slacken the top clamp pinch bolts. These bolts exert a clamping pressure on the caps as well as the tubes—if you forget to undo them, the caps may prove nearly impossible to remove.

Loosen both fork caps a few turns, even if the forks are coming off the bike (the clamps will secure the tubes far better than your average bench vise), then jack the bike up until the fork is fully extended. This will eliminate most preload, before removing the first cap. A word of warning: At the risk of seeming overly dramatic I should point out that spring tension may exert a considerable pressure on the cap, causing it to fly out of the tube as it reaches the last thread.

OEM shocks, new suspension, how-to, suspension mods
A layer of tape will prevent the wrench from marring the cap's finish.Photography by Mark Zimmerman

In addition to buggering the last few threads of the fork tube, large flying bolts can do a fair amount of damage to themselves, their surroundings or innocent bystanders. You’ll look silly walking around with a fork cap stuck in your forehead, and it’ll be expensive to repair the buggered-up threads, so be sure to maintain a bit of downward pressure on the bolt as you remove it. If you’re swapping the springs with the forks still attached to the bike, my suggestion is to remove and replace one spring at a time, finishing the first leg before proceeding to the next. That way if the jack fails or the bike is lowered onto its wheels for some reason the front end won’t collapse.

OEM shocks, new suspension, how-to, suspension mods
Raising your bike up on the jack will help eliminate most of the preload. Also, protect your bike from flying parts with a towel.Photography by Mark Zimmerman

Extract the old spring slowly so you don’t splash fork oil all over the place, and replace it with the new one. Since the new springs are progressively wound, the coils are tighter at one end than the other, and the spring doesn’t care which way it’s installed, so my preference is to position the close-wound end at the bottom because it reduces spring noise. Conversely, some manuals specify installing the springs in the opposite direction, to reduce unsprung weight. From a practical standpoint it won’t matter which way they are installed so don’t sweat the small stuff.

Follow the instructions and cut the preload spacer (if one is required) to the correct length. Make every effort to cut the spacer as squarely as possible, and make certain the ends are deburred and cleaned to prevent chips of PVC from clogging up your forks. In the unlikely event that no preload spacer measurements are provided, the rough rule of thumb is that the spring or the spring and spacer should be flush or slightly above the top of the fork tube when the tube is fully extended.

Install the spacer and any required washers. Lubricate the threads of the fork cap and the cap O-rings with a dab of white grease, anti-seize compound or fork oil.

OEM shocks, new suspension, how-to, suspension mods
This went in tight coils first.Photography by Mark Zimmerman

Reinstalling the caps can be tricky, especially if you’re fighting a much stiffer spring and lots of preload. Since the tubes and caps typically employ a fine thread it’s easy to cross-thread the cap, an event sure to ruin anyone’s day. Make certain the cap engages the fork thread squarely, and that the cap threads in with only moderate pressure. if it feels likes it’s binding, stop, remove the cap and examine the threads before continuing. If there is evidence of cross-threading, remove the preload spacer and thread the cap in by hand a few times to straighten out the threads. As with any critical fastener, all final tightening should be done with a torque wrench. Once the caps are tight, torque the pinch bolts, then proceed with reassembling the rest of the bike.

OEM shocks, new suspension, how-to, suspension mods
Measure twice, cut once—the hose clamp helps keep the cut straight.Photography by Mark Zimmerman
OEM shocks, new suspension, how-to, suspension mods
Lube up the fork cap with white grease, anti-seize compound, or fork oil.Photography by Mark Zimmerman

Last word
Like they say, results may vary. It'd be foolish to think that every single rider who bolts on an aftermarket shock is going to be ecstatic with the results. Some of you'd complain if you were hung with a fresh rope. But at the very least your suspension upgrades should provide a solid starting point for further improvement. Don't be afraid to try tweaking the set-up until the bike behaves the way you want it to. Remember, you ride the bike—it's never supposed to be the other way around.

OEM shocks, new suspension, how-to, suspension mods
Tighten the caps and finish up reassembling the rest of the bike and you are on your way.Photography by Mark Zimmerman

Torque Tip
Occasionally you may need to torque something to spec using a tool that extends the length of the torque wrench. The problem is that such an extension increases the amount of torque you're applying to the fastener for a given reading on the wrench's dial. To avoid overtorquing the fastener you'll need to reduce the applied torque. Here's the simple formula for figuring it all out:

  1. Measure the torque wrench length from the center of the hex drive to the center of the handle. This is dimension A.

  2. Measure the length of the extension from the center of its hex, or jaws, to the center of the torque wrench's square drive. We'll call this dimension B.

  3. Next we need to know two things: First is the desired torque we'd like to apply to the fastener—we'll call this T. Next we need to know what the torque wrench should be reading when the fastener is at the correct torque—this we'll call CT or corrected torque.

CT=(A x T)/(A + B)

Here’s the formula: First, multiply the torque wrench’s length by the amount of torque desired. Divide that sum by the torque wrench length added to the length of the extension. The result is the corrected torque. Let’s assume the wrench is 12” long, the extension 6” and we want 30 ft.-lbs. applied to the fastener. All we need to do is plug in the numbers to see what our torque wrench should read: 12 (length of wrench “A”) X 30 (torque desired “T”) = 360 12 (length of wrench “A”) + 6 (length of extension “B”) = 18, and 360 divided by 18 = 20 (CT). So in this case, when the torque wrench reads 20 ft.-lbs., 30 ft.-lbs. of torque is actually being applied to the fastener.