Motorcycle Chassis and Suspension Specialists
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    Triumph   Sprint ST 1999    
           
       < Application: Sports / Rideday 100kg
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Comments / observations:
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    "Dear Peter ~ Thanks for getting my rear shock finished in time for this weekend - Haven't had a chance to ride it as yet but I'll let you know how it is soon. The front forks on my bike: I fitted a set of RaceTech valves, 1k.g. springs and 20 wt. oil 110 m.m. from the top of the legs and they feel much better but I have a few queries that I hope you can help me with ~ Couldn't get 20 wt oil so I had to mix 1 bottle of Harley Davidson "Heavy Duty" & 1 bottle of "Extra Heavy Duty" fork oil together - was told that the wts. were 16 & 22 which would average out as approx. 20 wt. when mixed together. First off the forks were far too hard and I've had to wind off 14 turns of preload, they feel much better (perfect on the track) but are still perhaps a bit hard and I don't think that I'm getting the full range of travel that I "think" I should have eg: The cable ties are 40 m.m. away from the bottom of the lower fork tree after a typical day's riding so I'm wondering if I should (a) Replace the oil with a known wt. (b) Take some oil out or (c) Something else you can suggest to me to try. Thanks again for the rebuild and excellent service."
 


"Following on from my previous email to you:

Had a good ride on the bike yesterday and the rear end is now very, very good and Iím happy with how it now feels and reacts. 

The bike feels very good in most road conditions (and I think it will be great on the track next Sunday at Broadford) but my impression is that the front is "chattering" across high speed bumps during cornering Ė I found myself running wide through a few corners but donít know if this was entirely due to the forks losing traction or me losing confidence when the front started to "chatter" Ė Itís fine on smooth and undulating corners but as soon as thereís some ripples or bumps it seems to "chatter" (for want of a better explanation)

Hope you can advise a fix for it Ö"
   
     
Glad to hear that the shock works well, here's why we have made our own (fork) damper tube valve system. The valve you have uses a spring which is linear in its rate increase; we use a shimstack like in shocks and cartridge fork which has a wheel speed sensing capacity. There is no bleed hole so we can control dive. The bleed and spring is fine for soft feel but hi - speed travel rates still mean harsh (chatter) and the return flow valve also will chatter which feels like fade.

There is three ways to fix, replace the valve with a Provalve $195, re-machine a new rebound system into your fork tubes $180 (you supply the fork tubes disassembled), replace the complete internals with a cartridge damping unit $650
Regards Peter
 
   
    "I canít afford to spend any more money on the suspension right now so can you suggest what I can do with the existing front end to at least alleviate the "chatter" problem such as fork oil wt and volume perhaps please."    
   
The problems are inherent with your current setup, if you use lighter oil... less rebound, heavier oil... too much rebound and worse chatter
Regards Peter
 
   
    "Whatís involved in me setting up your "Provalve" in regard to spacers, oil ,etc please."

(Provalve Installation Instructions and notes forwarded)