H.3 Rear

The stock shock suffers from several problems that can be rectified with a fully adjustable shock:

[Thx Selden Deemer]

H.3.1 Other shocks

H.3.1.1 CBR900RR

The CBR900RR shock is practically a direct bolt on to the Hawk GT. The upper mount will need some minor alterations and most of the time the Hawk's spring will replace the lower spring rate RR spring. A spacer ring approximately 1/2" thick is needed to compensate for the shorter Hawk spring on the 900RR shock body. A good starting point for a 150-pound rider is a spring length of approximately 142mm at full extension. This shock is fully adjustable. The 93-95 model increases rear ride height about 1" or 3cm while 96+ shocks do not.

Earlier 900RR shocks have a short hose to the remote reservoir, which makes it difficult to find a suitable mount location. Later models have a longer hose, and can be strapped to the right subframe rail, or a mount can be fabricated that bolts on to the wireframe guard on the right-hand footpeg assembly. If you retain the stock exhaust, you may want to fabricate a heat shield to block the considerable amount of heat that radiates from the "boom box;" otherwise the shock reservoir will get quite hot, which changes damping characteristics considerably. [Thx Kirk Roy and Selden Deemer]

H.3.1.1.1 CBR900RR/Hawk shock comparison

The 900RR shock must be modified to fit the Hawk. Following is a shock comparison showing the different dimensions and rates:

MeasurementHawk'93-'95 900RR'96+ 900RR
Overall length (center eye to eye)307mm320mm307mm
Travel (to rubber snubber)16mm31mm35mm
Spring Length
Free length154mmN/A175mm
Mounted (softest setting)145mm155mm163mm
Mounted (hardest setting)134mm146mm154mm
Spring Preload settings (travel)7 (10mm)7 (9mm)7 (10mm)
Spring I.D.
Large end61mm57.1mm57mm
Small end58mm50.8mm52mm
Mounting eye width
Top0.962"1.121"1.114"
Bottom1.537"1.536"1.535"
Force required to compress shock 10mm (without
spring & at softest C/R settings on 900RR shock)		38lb.N/A44lb.
Spring rate (based on measurements taken using
bathroom scale up to 300lb.		40lbs./mmN/A30lbs./mm

[Thx Jeff Gum]

H.3.1.1.2 CBR900RR Modification procedure

On both shocks the top mounting eye must be enlarged to 12mm and mounting eye narrowed (or frame widened). On 96 shocks the top hole can be offset milled approximately 0.025" to increase rear ride height slightly if desired. Conversely, the 95 and earlier shocks can also be offset milled in the other direction to reduce ride height some.

Spring Spacers: required to use Hawk spring on 900RR shocks (and maintain the OEM preload values). When installed with a combination of Hawk and RR spring seats: 95/earlier shock: 2.25" I.D./2.875" O.D. x 0.25" tall 96/later shock: 2.25" I.D./2.875" O.D. x 0.50" tall Using the Hawk spring seats in conjunction with the RR seats on the later RR shocks is a snap as they drop right on, with the spacer keeping the Hawk seat just off the RR lower seat enough before it interferes. However, on the earlier RR shocks the thicker/upper seat requires the ID be opened up around 0.005" so it will slide down over the shock body and rest against the preload adjuster. The lower seat needs to be opened up around 0.015" so it will slide down over the RR seat (that holds the spring retainers in place). In both cases, I installed the spacer between the RR and Hawk spring seats at the lower end of the shock as installed (spring retainer end). This positioning puts the narrower end of the spring at the top of the installed shock and gives the most clearance around the coolant reservoir, and using a combination of both Hawk and RR seats yields the best fit of the Hawk spring on the RR shock body.

Travel Limiter: A split type collar is required, because the end of the RR shock cannot be removed without discharging shock. It is mounted between the RR spring retainer plates and the rubber snubber. With the 95/earlier RR shocks, a travel limiter is not absolutely necessary as the compressed height nearly equals the OEM Hawk shock. I found, however, that using a limiter with my 95 shock allowed a much better chain adjustment (not as loose) since it must be set with the shock fully compressed. This is pretty easily done by installing the shock without the spring and lifting the rear up with a swingarm stand and adjusting the chain. It seems the small amount of swingarm movement that the travel limiter limits' (at the chain adjustment point) makes a pretty big difference in the slack chain' unloaded setting. Also, make sure to figure out a reference point at this time for future chain adjustments - without having to compress the shock all the way again.

95/earlier shocks: I installed 2 concentric split collars. The inner one is aluminum and sold by McMaster-Carr - «"ID x 1-1/8"OD x 13/32" high (PN: 6436K71). Open the ID first to 17/32", then open all but about 1/8" up to 14mm (this provides a good fit around the threaded *and* smooth parts of the shock shaft), then taper the screw heads so they don't protrude out so much. Due to the way the collar is manufactured, you need to install some shims between the collar halves during machining to keep the outside diameter as close as possible to 1-1/8". The outer collar is a Grainger (another industrial supply house) item made of Delrin, 1-1/8"ID x 1-7/8"OD x «" thick (PN: 1F578). Use a dremel to relieve the ID in a couple of spots for the inner collar screw heads and taper the outer collar screws for added clearance for the RR spring seat/retainer. Mount the collars so that the inner collar is flush against the shaft locking nut, and the outer collar sits flush against the spring retainer plates (temporarily installed) - which should get the bottoms of both collars close to flush where they will rest against the rubber snubber. Note the relative positions of the collars to each other when relieving the outer one for the inner collar's screw heads as the reliefs will be closer to one side. Then, get a 1" rubber washer from a plumbing supply store, open the ID to fit around the shock shaft, slit one side then fit/super-glue it into the counterbore in the rubber snubber, making that surface flat. This spacer combo results in providing OEM Hawk shock travel on the RR shock, has good strength with the aluminum inner collar yet provides full support for the snubber with the Delrin outer collar. Remember, if you adjust the chain as described and the travel limiter *fails* - the chain then becomes your travel limiter, with possibly disastrous and definitely expensive results!

96/later shocks: The limiter thickness works out to be 0.730" (between the snubber and the spring retainer plates for OEM travel) on this shock. For custom builders, make the spacer 1.8" outside diameter x 0.730" long with a 0.125" high x 1.0" diameter boss sticking out one end (in addition to the 0.730" length). This fits into the rubber snubber. Counterbore the other end about 0.130" deep x 1.0" diameter to clear the locking nut on the shock shaft and allow the spacer to sit flat against the retaining plates. The inner through hole is 14mm, which is snugged down against the shock shaft by gradually sanding the spacer halves against a flat plate and checking the fit until it's tight. This design will provide full support of the rubber snubber and a solid register between shaft/snubber/retainer plates. Alternately, a nylon split collar from McMaster-Carr can be used, PN: 60485K65 (about $8). It is 1-3/8"OD, 9/16" wide with «" bore. The bore needs to be enlarged to 17/32" and all but 1/8" to 14mm (like the 95 shock), and again a rubber washer is used to flatten out the counterbore in the snubber. With the 9/16" thickness, together with 0.130" (counterbore made in the custom collar to clear the shock locking nut) you have 0.692", which is just 0.038" shy of the 0.730" needed - close enough. This collar will register directly against the shaft locking nut instead of the spring retainer plates. I selected this collar due to it's small shaft size and relatively large OD. It would be preferable to find an equivalent in aluminum, but they only come in smaller OD's and I feel it's better to have as much support against the rubber snubber as possible. There may also be some combination of concentric collars that can be used here, but I couldn't find any pairs that yielded the required (9/16" minimum) thickness. McMaster-Carr's catalog is available on-line @ www.mcmaster.com; Grainger @ www.grainger.com - though I think Grainger only sells to businesses/wholesale.

To add a few more details: Despite measuring the spring rates with a bathroom scale and makeshift contraption on my drill press (on the 96 and stock springs), they're pretty close to information others have gathered on the list As others have found, with the 95RR shock installed my kickstand was now too short (I'd removed the center stand long ago). I added about 1-3/4" to the length by cutting it about «" above the foot, grinding the stub ends down to a more rounded cross section and having a piece of slightly flattened' thick wall tubing welded in. This disables the little rubber safety pad normally on the end, BTW; so I just cut it off as well. I also fitted a polyethylene chain slider (behind the kickstand mount) from Doug Napier, replacing the rubber OEM one. This seems to improve the chain overslack' condition when the suspension is unloaded and should wear much better than the stock slider. It is, however, quite a bit noisier than the OEM slider, especially during deceleration. At any rate, I don't know if Doug is even making these up anymore. Another possible solution is a primary chain slider for a Harley Davidson big twin. I've seen one of these rigged' onto a Hawk in place of the stock slider and I think it would work very well if you can figure out how to mount it up properly. Let me know if you have any questions, I'll be glad to help you out with any additional info./comments/observations/(opinions?) I have.

[Ths Jeff Gum]

A similar write up of this by Jeff with pictures is available at: www.WILDnKRAZED.com/Go9/R_SHOCK/index.html

H.3.1.2 Fox

Fox Racing sells a remote reservoir shock for the Hawk, with separate compression and rebound damping adjustments, and spring preload adjustment. The shock is available with two different springs, their 840 spring and their 950 spring and is rebuildable. One lister had Fox lengthen the reservoir hose for easier mounting.

H.3.1.3 Ohlins

Ohlins, like Fox, sells a remote reservoir shock that is adjustable for both rebound and compression damping. The unit is said to be slightly more expensive than the Fox shock, and offers adjustable spring preload.

H.3.1.4 Progressive

Progressive Suspension offers two rear shocks for the Hawk, the first being their #415 series with a remote reservoir. This shock has a progressively wound spring, and adjustable compression and rebound damping, as well as a threaded spring preload adjuster. Their second offering is their 420 series shock with internal reservoir, adjustable rebound damping, and spring preload adjustment.

H.3.1.5 Penske

Penke Racing Shocks makes their good, albeit expensive, shock for the Hawk, style 8900. The Penske unit allows for ride height adjustment and twenty-five "clicks" of rebound adjustment. The shock is ordered with one of three available remote compression adjusters: the 8981 offers six compression settings and is considered the "base" model; the 8986 offers ten compression settings and the 8987 offers thirty "clicks" of low-speed compression adjustment and twenty-four "clicks" of high-speed adjustment. The fancier the compression adjuster, the heftier the price tag. A nice attribute of this is that you can buy a base shock, then upgrade when needed. Penske ships the Hawk shock with a stout 1100 in/lb spring. Penske shock are owner rebuildable and revlavable if you're so inclined. [Thx Tim Krone]

H.3.2 Adjusting rear suspension

H.3.2.1 Setting sag Per Race Tech

  1. Extend the suspension completely by getting the wheel off the ground. It helps to have a few friends around. On bikes with sidestands the bike can usually be carefully rocked up on the stand to unload the suspension. Most race stands will not work because the suspension will still be loaded by resting on the swingarm rather than the wheel. Measure the distance from the axle vertically to some point on the chassis. Mark this reference point because you'll need to refer to it again. This measurement is L1. If the measurement is not exactly vertical the sag numbers will be inaccurate (too low).
  2. Take the bike off the stand and put the rider on board in riding position. Have a third person balance the bike from the front. If accuracy is important to you, you must take friction of the linkage into account. This is where our procedure is different: We take two additional measurements. First, push down on the rear end about 25mm (1") and let it extend very slowly.

    Where it stops, measure the distance between the axle and the mark on chassis again. If there were no drag in the linkage the bike would come up a little further. It's important that you do not bounce! This measurement is L2.

  3. Have your assistant lift up on the rear of the bike about 25mm and let it down very slowly. Where it stops, measure it. If there were no drag it would drop a little further. Remember, don't bounce! This measurement it L3.
  4. The spring sag is in the middle of these two measurements. In fact, if there were no drag in the linkage, L2 and L3 would be the samH. To get the actual sag figure you find the midpoint by averaging the two numbers and subtracting them from the fully extended measurement L1: static spring sag = L1 -[(L2 + L3) / 2].
  5. Adjust the preload with whatever method applies to your bike. Spring collars are common, and some benefit from the use of special tools. In a pinch you can use a blunt chisel to unlock the collars and turn the main adjusting collar. If you have too much sag you need more preload; if you have too little sag you need less preload. For road race bikes, rear sag is typically 25 to 30mm. Street riders usually use 30 to 35mm. Bikes set up for the track are compromise when ridden on the street. The firmer settings commonly used on the tract are generally not recommended (or desirable) for roadwork.

H.3.2.2 Compression damping

Dialing in proper settings for compression and rebound damping requires a great deal of experimentation and time. Be patient and take notes after every change. Start at full soft, but do not adjust until you have found a satisfactory setting for rebound damping, then try increasing compression at eighth turn intervals until the ride becomes harsh, then back off an eighth turn. Too much compression damping yields a harsh ride and the faster you go the worse it gets. This, in turn, will lead to traction problems over rough surfaces. [Thx Selden Deemer]

H.3.2.3 Rebound damping

Start at full soft, and increase at quarter turn intervals until the ride starts to become harsh, then back off a quarter turn. Shocks heat up under use, so settings that are appropriate with a cold shock may need to be increased on extended rides or in hot weather. On the other hand, settings that work well when the shock is good and hot will be harsh for short rides in cool weather. [Thx Selden Deemer]