R_Cote Posted March 21, 2010 Share Posted March 21, 2010 Decided to start fiddling with my suspension again. A couple years back I did some fork valve surgury on my Y2K Viffer. Some of you might remember the topic of "Fork Valve Turbulance" and at one point it was a featured topic. Well I have since done 2 more revalves to the forks and the results don't seem to change much at all. I won't go into detail on the shimm stacks I tried but I am finally turning my attention to the back end. I know I need to increase the rear spring rate as I went up on the fork spring rate. I realize I'm chasing my tail with the valving as the front to rear is out of balance. I don't get much seat time so this is why it takes years for me to wrench on my bike and test it out. Free time is very elusive to me. I've been reading a lot on this forum about sag and spring rates and I feel I'm really starting to grasp the whole balance thing now. I want to purchase a heavier spring for my stock rear shock as purchasing an ohlins or penske seems to be out of my financial reach still. I stumbled accross this site ------> http://www.worldwidemetric.com/measurements.html and found it usefull for converting the metric to english. Thought you guys might find it usefull as well. I've always found that the kg's/mm difficult to follow and compare to the lbs./inch, as there is 25.4 mm's/inch. I wasn't really interested in lbs./inch when thinking in terms of mm's. Nuff said. I ran some Race Tech spring Rates and converted them as follows. Here is what I came up with. 15.3 kg/mm = 33.731 lbs./mm = 856.77 lbs./inch ----> stock spring on my Viffer. 16.1 kg/mm = 35.494 lbs./mm = 901.55 lbs./inch 16.96 kg/mm = 37.4 lbs/mm = 950 lbs/inch 17.8 kg/mm = 39.242 lbs./mm = 996.75 lbs/inch 19.6 kg/mm = 43.211 lbs./mm = 1097.56 lbs/inch Feel free if I have made any errors. I will be looking into getting a rr spring for the stock shock but not sure how high I will go. My static sag in the back is at only 6mm, with a rider sag of 34mm. My weight is 178lbs in street clothes. I need to go up but not sure how much I want to go. I have Sonic .90's up frt and the front seems to be over powering the rear. The front is a 22% increase over stock so I will most likely try to match the front's increase out back. Was wondering about the front stock rate as it is a progressively wound spring. It's rated at .74, but is that the begining rate or maximum rate? About the only thing the heavier springs up front accomplished for me is the elimination of brake dive and the badly cupping of my front tire. Was even entertaining the idea of running one .90 in one leg and a stock .74 in the other leg and keeping the rear stock. Any thoughts??? Link to comment Share on other sites More sharing options...
Member Contributer vfrcapn Posted March 21, 2010 Member Contributer Share Posted March 21, 2010 What's your preload setting with those rear sag figures? I would guess the 16.9 or 17.8 spring would be appropriate for your weight. When I was 185 I ran a 17kg spring on my Ohlins and was fairly happy with it. I wouldn't mix-match fork springs, the .90's sound about right. If you can wait a little the Ohlins/Penske/etc shocks pop up on eBay used for 1/3-1/2 retail. Link to comment Share on other sites More sharing options...
V4 Rosso Posted March 21, 2010 Share Posted March 21, 2010 I stumbled accross this site ------> http://www.worldwidemetric.com/measurements.html and found it usefull for converting the metric to english. Thought you guys might find it usefull as well. I've always found that the kg's/mm difficult to follow and compare to the lbs./inch, as there is 25.4 mm's/inch. I wasn't really interested in lbs./inch when thinking in terms of mm's. Nuff said. Number one rule of doing bike mods is to check VFRd first for info. The conversion chart can be found righ here :cheerleader: It's rated at .74, but is that the begining rate or maximum rate? It's the beginning low rate. Link to comment Share on other sites More sharing options...
R_Cote Posted March 21, 2010 Author Share Posted March 21, 2010 It's rated at .74, but is that the begining rate or maximum rate? It's the beginning low rate. So if .74 is the beginning rate then what is the ending rate? Was thinking of cutting the closely wound ends off the stock springs. Seems the lighter beginning rate is what messes up the sag numbers. Just the weight of the bike seems to compress (serious brake diving) the closely wound coils. Anyone know what the rate of the springs would be after cutting, without having to do a ton of measuring and mathamatics? Just curious. Link to comment Share on other sites More sharing options...
Baileyrock Posted March 21, 2010 Share Posted March 21, 2010 So if .74 is the beginning rate then what is the ending rate? Was thinking of cutting the closely wound ends off the stock springs. Seems the lighter beginning rate is what messes up the sag numbers. Just the weight of the bike seems to compress (serious brake diving) the closely wound coils. Anyone know what the rate of the springs would be after cutting, without having to do a ton of measuring and mathamatics? Just curious. HS had a thread on how to increase your fork spring rates buy cutting coils off to achieve certain rates and I know other suspension guys use the method too. Don't know if the thread still exists but try the search function. You can also add 10cc(to start) of fork oil to each leg to stiffen the overall rate a little and help with bottoming. 15 min job. :cheerleader: PS where have you been, haven't seen you post in a while. Link to comment Share on other sites More sharing options...
V4 Rosso Posted March 21, 2010 Share Posted March 21, 2010 :fing02: So if .74 is the beginning rate then what is the ending rate? Was thinking of cutting the closely wound ends off the stock springs. Seems the lighter beginning rate is what messes up the sag numbers. Just the weight of the bike seems to compress (serious brake diving) the closely wound coils. I don't know as I've never had my hands on one but expect it will be close to 1kg/mm. Link to comment Share on other sites More sharing options...
R_Cote Posted March 21, 2010 Author Share Posted March 21, 2010 What's your preload setting with those rear sag figures? I would guess the 16.9 or 17.8 spring would be appropriate for your weight. When I was 185 I ran a 17kg spring on my Ohlins and was fairly happy with it. I wouldn't mix-match fork springs, the .90's sound about right. If you can wait a little the Ohlins/Penske/etc shocks pop up on eBay used for 1/3-1/2 retail. Rear preload is on #4 from the highest and with this the static = 7 mm and rider sag = 34mm. I adjusted the rear up to the 2nd form the highest ( meaning 1 more and the preload would be maxed) and this yielded me 4mm static and 26mm rider. I can't see going to the last adjustment as the numbers are getting further from ideal. Also don't notice much difference if any between these two adjustments. The front with the .90 springs has a static sag of 31mm and a rider sag of 45mm. I have 3 lines showing on the adjusters so I have it set pretty soft up front and still feel the front is overpowering the rear, if that's possible. Link to comment Share on other sites More sharing options...
Member Contributer vfrcapn Posted March 22, 2010 Member Contributer Share Posted March 22, 2010 What's your preload setting with those rear sag figures? I would guess the 16.9 or 17.8 spring would be appropriate for your weight. When I was 185 I ran a 17kg spring on my Ohlins and was fairly happy with it. I wouldn't mix-match fork springs, the .90's sound about right. If you can wait a little the Ohlins/Penske/etc shocks pop up on eBay used for 1/3-1/2 retail. Rear preload is on #4 from the highest and with this the static = 7 mm and rider sag = 34mm. I adjusted the rear up to the 2nd form the highest ( meaning 1 more and the preload would be maxed) and this yielded me 4mm static and 26mm rider. I can't see going to the last adjustment as the numbers are getting further from ideal. Also don't notice much difference if any between these two adjustments. The front with the .90 springs has a static sag of 31mm and a rider sag of 45mm. I have 3 lines showing on the adjusters so I have it set pretty soft up front and still feel the front is overpowering the rear, if that's possible. Ohlins recommends 10-20mm static and 25-40mm dynamic sag for the rear. So it sounds like a slightly stiffer spring would be appropriate for your weight to achieve the recommended static and dynamic sag. Backing off preload now will get your static sag ok but rider sag probably outside the range. With the Sonic springs did you cut new spacers, use the original ones or do they provide pre-cut spacers? Ohlins recommends 15-30mm static in the front, 35-50mm dynamic. Your spacers may be a little long on the front forks, that was my experience with the Racetech springs I bought. Link to comment Share on other sites More sharing options...
R_Cote Posted March 22, 2010 Author Share Posted March 22, 2010 What's your preload setting with those rear sag figures? I would guess the 16.9 or 17.8 spring would be appropriate for your weight. When I was 185 I ran a 17kg spring on my Ohlins and was fairly happy with it. I wouldn't mix-match fork springs, the .90's sound about right. If you can wait a little the Ohlins/Penske/etc shocks pop up on eBay used for 1/3-1/2 retail. Ohlins recommends 10-20mm static and 25-40mm dynamic sag for the rear. So it sounds like a slightly stiffer spring would be appropriate for your weight to achieve the recommended static and dynamic sag. Backing off preload now will get your static sag ok but rider sag probably outside the range. With the Sonic springs did you cut new spacers, use the original ones or do they provide pre-cut spacers? Ohlins recommends 15-30mm static in the front, 35-50mm dynamic. Your spacers may be a little long on the front forks, that was my experience with the Racetech springs I bought. Actually I made new spacers from the pvc pipe that was supplied with the springs. I made the spacer length to allow minimal preload with the adjusters full out. I figured with the correct spring rate this would be a good idea as it allows turning the adjusters in about midway to get the proper sag. It actually worked out that way. If I turn the preload in all the way I get too little sag and if I wind it out all the way I get too much sag. When in the middle the sag is good. Link to comment Share on other sites More sharing options...
Member Contributer vfrcapn Posted March 22, 2010 Member Contributer Share Posted March 22, 2010 Sounds like a good approach on the front spring spacers. So what negative handling affects are you experiencing that makes you feel it's unbalanced? Link to comment Share on other sites More sharing options...
R_Cote Posted March 22, 2010 Author Share Posted March 22, 2010 Sounds like a good approach on the front spring spacers. So what negative handling affects are you experiencing that makes you feel it's unbalanced? Negative affects. Front feels bouncy since I put the stiffer springs in. I went with 1.0 springs with tons of rebound damping added to the rebound stack. Then I went down to .90 springs and it still feels bouncy in the front. This is with the Race Tech recommended stack (lots of thick .15mm shims) with the heavier springs. I should describe the bouncyness as more like the front end is jarring my hands on small bumps, like smooth roller bumps. I can coast on level ground or down a hill and the small bumps feel like the forks are not giving, but they are, as I can see them moving. It soakes up pot holes really well and uses most of the travel. I thought it might be the low speed part of the stack on the compression valve but I really lightened that up, to no avail. So the fact that the forks are moving quite a bit and it still feels to stiff I thought I should address the rear spring as others on here suggest is a must. From what I have learned I totally agree the balance front to rear is quite a bit off. I believe the front is causing the rear to compress to easily as it is transfering energy to the rear. If a heavier rear spring does not cure this, then I am at a total loss and more confused than ever. Link to comment Share on other sites More sharing options...
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