The rear spring on my new Penske is too light. I have it preloaded 21.4mm to give 30mm rider sag and about 3mm free sag. I understand that ideal preload is more like 15mm and free sag should be 5-10mm. That's what I'm shooting for. The current spring is rated at 500lbs and the application is an M695.
How much more spring do I need? In my quest to answer that question I came across an interesting post with some seemingly sensible math behind it. I want to avoid the trial and error approach to spring selection, and I don't trust online charts.
http://www.ducati.ms/forums/showthread.php?t=48737I collected the following data on my M695:
- Bike wt rear = 194lbs (measured by me)
- Rider wt = 180lbs
- % rider wt rear = 55% (measured by me)
- Unsprung wt rear = 40lbs (guess from linked post)
- Force from shock = 55lbs (measured in linked post)
- Linkage ratio = 2.71 (delta sag/delta shock travel, measured by me)
I ran some scenarios according to the calculations in the post, and it looks like I'd be good with about a 575lb or 600lb spring. That's consistent with a few reality checks from folks of similar weight who also know their actual sag numbers.
Anyone used this approach to help pick a spring?
BK