Quote:
Originally Posted by Mojavemesa
The front suspension is definitely more compressed so I'll put in the ex500 fork springs. The ex500 people have specs on the rear springs and they say our spring is actually harder, makes sense since our swing arm is a touch longer. I'm going to swap to the shorter ex500 swing arm and play around with 250/500 spring combinations. Maybe use the 250 spring and the 500 shock and make a spacer so the preload adjuster functions the same. Way more power but I need to lighten this bike a lot now.
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Using the
RaceTech calculator, the stock PreGen fork springs (.44kg/mm) are good for about 25lb and the 500 springs (.585kg/mm) are good for about 110lb. With the extra weight from the engine, you want to go that much stiffer. Figuring +50lb for the engine and a rider weighing about 160lb, they suggest around a .75kg/mm spring. The 500 springs will definitely be better, but they may still be way too soft for you and the upgraded bike. The Gen1 has longer springs, so you do have more room to cut them down to stiffen them up (they're right around .70kg/mm when cut down to 17" long, which is the length of Gen2 springs).
The rear spring on the 500 is only 300lb/in compared to 440lb/in on the PreGen. It's not just a touch softer, it's a lot softer - it's only good for a ~120lb rider on the 500. The PreGen spring will fit on the 500 shock and the preload adjuster will get it down to the bench setting to match the 500's weight/suspension without any spacer, but it's about 1/8" from the end of the threads.
http://www.ex-500.com/index.php/topic,61377.0.html
How much difference is there in swingarm length between the two? The NewGen and Gen2 swingarms are the same length (when measured with standard tools, nothing super-accurate). I'm not sure how the Gen1 and Gen2 swingarm lengths compare.
The 500's swingarm is 7mm narrower than the NewGen's at the pivot point. If the PreGen frame is the same as the NewGen in that area (my understanding is that the NewGen stuff can be swapped onto a PreGen fairly easily, see
this thread), the 500 swingarm won't fit in the frame without narrowing it (which may cause problems with installing the bearings). The OD of the pivot sleeve and the ID of the needle bearings are the same between the Gen2 and NewGen, but the bolt and ID of the sleeve are different, so you have to reuse the one that matches your frame. The Gen1 also has a rear drum brake, so I'm not sure if there's anything missing from the swingarm related to mounting a disc brake.