I have just posted in the maintenance and tips section describing rebuild work to the forks on my ’06 Sprint ST
. There is plenty of information scattered around the forum but it took a lot of searching before I made my final choices for upgrade. I’ve pulled the key points together in one place and posted here for anyone else who’s looking at suspension upgrade for their Sprint ST. Hopefully it’ll save you much of the searching and reading that I did – although you’ll soon have to search to find this post! This is not a list of everything that is available so, hopefully, others will add more.
First step in the process was to get the stock setup working properly. Last year I replaced the fork oil with fresh Bel-Ray 10W fork oil
and made sure it was set to the correct level. Then I adjusted preload to set front and rear sag
. I didn’t have any issues with bottoming or topping out so I stuck with my initial settings. I played around with the rear shock rebound adjustment to get a setting that felt right. With my suspension set that way I can find an acceptable setup for my weight (165 lbs = 75kg) but I know there's room for improvement. Money was not an obstacle but there has to be a limit. If I consider the market value of an ’06 Sprint then it doesn’t make sense to me to spend $2,000 on suspension.
Here are the options I considered:
This is the first step in the upgrade process. Changing the stock progressive springs for straight rate gets a unanimous thumbs up from those who’ve made this swap. At around $110 for a set of springs this is a cost-effective improvement. There a several sources including Race Tech
, Traxxion Dynamics
For a low cost upgrade changing springs and replacing the fork oil may be enough for some. Ideally damping should be altered to the match new springs and rider preferences. There are various ways to change damping:
Reconfigure Stock Showa Shim Stack
This old thread
contains some excellent information about the stock Showa damping. The OP is using his knowledge to work within a budget. Most of us do not have that experience so we’d have to turn to professionals at which point this may not be an attractive option.
Replace Stock Valves
For most of us replacing the stock compression and rebound valves will be easier, quicker and more cost effective. It does require some skill and at least a basic understanding of suspension. Those who don’t feel comfortable doing the work themselves can turn to professionals. Most popular choices for replacement valves are:
- Race Tech Gold Valves – Race Tech claim that their Gold Valves reduce the unnecessary harshness caused by the restrictive ports of the stock pistons. Race Tech Gold Valves come as a kit of parts that are assembled in place of the original Showa valves. The kits allow the compression and rebound valving to be configured to suit the rider. The stock Showa forks have no external damping adjustment but, if necessary, changes can be made by adjusting the shim stack. The current cost for Race Tech Gold Valves is $180 for compression and $170 for rebound valves.
- Traxxion Dynamics Axxion Valves - Traxxion makes similar claims about their Compression Valve & Rebound Axxion Valve being superior to the stock damping pistons. According to Traxxion’s website their valves are manufactured by Penske. I don’t have any experience with these but they look good in the website images and Traxxion certainly has a very good reputation. Reading the product details reveals that some Axxion Valve kits include shims to revalve the rebound side of your cartridge. Replacing the rebound valve is a better solution but if it’s possible to revalve the rebound portion the Sprint forks then those on a budget could find a cost saving. Current prices are $150 for compression and $176 for rebound valves.
Traxxion Dynamics AK-20 Axxion Cartridge Kit. This is a very sweet solution – but at a price. The AK-20 Axxion Cartridge Kit
is a complete replacement for the stock cartridge. At $1000 the kit is expensive but it does include springs and fork oil so that must be taken into consideration when comparing prices. Looking at the AK-20 cartridges it occurred to me that it wouldn’t be difficult to add external rebound damping adjustment to Sprint forks. That’s certainly something to ask about if you’re considering the AK-20 kit.
USD Fork Conversion
On this forum we have a superb thread covering all aspects of converting of a Sprint to USD fork setup
using TLS, Hayabusa or possibly GSXR forks. For those with the ability, resources and motivation going inverted is a great solution. The final result looks sharp and may well cost less than upgrading existing forks – particularly if you can sell your original forks. USD forks usually have external adjustment making fine tuning a bit easier but you still don’t have custom settings so further work may be required to tune the suspension. Depending on model and year of donor bike the original springs may be unsuitable for some riders. On some donor bikes the spring rates are the same as the stock springs in Sprint forks and may not work well for heavier riders. USD forks with custom springs and valving would have to be the ultimate suspension upgrade mod for a Sprint.
Improvements to the front forks are going to highlight any deficiencies at the rear. Options for the rear shock are:
- Rebuild Stock Rear Shock. The stock Showa rear shock will provide good results with a few simple mods. Older shocks will benefit from a rebuild with new seals, shaft bushing, oil and nitrogen recharge. Improvements to damping can be achieved by adding a Race Tech Gold Valve and Rebound Separator. Depending on rider weight the stock spring may be up to the task but heavier riders will likely require a new spring with preload spacer. Rebuilding the rear shock is not as straightforward as adding valves or cartridges to the front so most will opt to have the work done by someone else. A full rebuild including spring, preload spacer, Gold Valve and Rebound Separator, seals and nitrogen recharge will cost around $450. A $200 saving can be made if the Gold Valve and Rebound Separator upgrade is not included with further reduction if a new spring is not required.
- Replacement Shock. For those who prefer to put their money towards a new shock there are several options. Penske and Ohlins appear to be the most popular choices. A Penske Shock with correct spring is $625 with the option to add a remote reservoir for an additional $250. For the Sprint Ohlins specify their TR703 rear shock with a piggy-back reservoir and remote preload adjustment. A TR703 will set you back around $1,100. Shocks with a remote reservoir will need some thought about where the reservoir will be located. The usual locations are very close to the exhaust system – not good.
When considering suspension upgrades we have to make sure that existing components are in good condition. While upgrading the front suspension it is not necessary to completely dismantle the forks but it makes sense to do that to replace the seals. Bushings should also be replaced unless they are fairly new.
At the rear regular maintenance will ensure that wheel movement is not hampered by excess friction in the linkages. It is easy to ignore drag link and drop link bushings, sleeves and seals but these components should be cleaned, inspected and greased from time to time for the suspension to give its best. Swingarm movement should be checked too.