Member Contributer RC36Rider Posted November 19, 2016 Member Contributer Share Posted November 19, 2016 1 hour ago, RhodeMoto said: I changed the spring in that measurement by 7%. Can we assume that the spring is now 7% lighter rate? Nope ! Here's the formula for calculating a coil spring rate. You changed both d (wire diameter) and D (mean coil diameter). Oh, yeah. It assumes round wire which is evidently no longer the case so have fun working it out. Link to comment Share on other sites More sharing options...
Member Contributer Dutchy Posted November 19, 2016 Member Contributer Share Posted November 19, 2016 Just flip a coin.......... Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted November 19, 2016 Member Contributer Share Posted November 19, 2016 After a lot of incredibly complex calculations, I reckon you have reduced spring rate by about 4%. Trust me on this, fellas. You would not understand such advanced maths anyway. Joke aside, if you give me the exact wire diameter, I can try and confirm that the above number is not too far off and explain how I calculated it.   Link to comment Share on other sites More sharing options...
RhodeMoto Posted November 20, 2016 Author Share Posted November 20, 2016 More a question of curiosity as I am going with it regardless. As mentioned the spring is no longer round so do not know if you can use standard formula,... By crude bathroom scale test; I had actually gotten 1.2kg before and now get 1kg,.. Both of these are questionable due to cheap scale and test equipment. But if the relative difference is any indication then they will be softer. Only makes sense as material is less. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted November 20, 2016 Member Contributer Share Posted November 20, 2016 Softer no doubt but by my estimate, you removed about 2% [Edit: 1.3% actually. Bad memory] of the material so I find your bathroom scale results very surprising. You are correct that changing the shape of the wire matters. I looked up the formula for rectangular wire and it is indeed different. Instead of d^4, it's width " height^3 and the 8 has to be changed to... something else that I haven't found yet so the correct factor for "out-of-round round" wire is anybody's guess.  Oh well, no big deal. Your springs now fit and you can actually proceed to test riding. Link to comment Share on other sites More sharing options...
RhodeMoto Posted November 28, 2016 Author Share Posted November 28, 2016 Reporting in with update. It lives! Finally together,.. after all the fork internal stuff - assembly was straight forward. Had some little stuff that slowed process. Sorting out cable, wire routing. Bleed front brakes as I had to loosen master. Clean contacts on switches. Rolled it out after dark and only did a few blocks. Late, no gear on, no plate,... To early for true report, but little brake dive. I am getting little sag and may have to adjust spacer. But it is only 19mm pre load??? Also did 120mm oil height using a 17 viscosity. Maybe would help to increase air space?` Keep in mind - I have only a short ride in damaged condition to compare to. Relative to that, this is major advancement! Thanks to all for information and moral support! Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted November 28, 2016 Member Contributer Share Posted November 28, 2016 8 hours ago, RhodeMoto said: Also did 120mm oil height using a 17 viscosity. Maybe would help to increase air space?` Oil height has very little effect on static sag (unless you have waaay too much which is not the case with 120 mm). Just to make sure: You did measure with fork leg fully collapsed and damper rod all the way down, right ? 8 hours ago, RhodeMoto said: I am getting little sag and may have to adjust spacer. But it is only 19mm pre load??? Considering your weight and the spring rate, 19 mm is probably too much already. I reckon RT calculate the rate for 35 mm sag @ 15 mm preload for the VFR. Put a zip tie around one fork leg and measure. There is really no other way to be sure.  The RT calculator gives 0.9 kg/mm for a 165# street rider on the '92-`93 and 1.0 for the '90-`91. Recommended preload is also different at 15 and 20 mm respectively. That seems a bit iffy to me. Edit: Didn't pay enough attention to the bike weight in # (metric person here. Sorry.). It's definitely wrong at 530# for the earlier bike vs 465# for the '92-'93. Link to comment Share on other sites More sharing options...
RhodeMoto Posted November 28, 2016 Author Share Posted November 28, 2016 Oil level checked with tube collapsed, spring out, Rod in. Tube vertical. One thing I meant to check was if there is a definite stop when tube is at bottom. Seemed like it was just the bottom of tube sleaving over the aluminum cap at foot, and could possibly lead to error? I meant to check the exposed tube lengths to verify they were the same. Did work the tube and rod though several cycles and checked and rechecked, so hopefully good. I have to give pre load some thought. If we are changing from 19 to 15mm, that is only 4mm? At 1kg/mm spring rate that would only change 4kg,...... that is enough to to change sag? Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted November 28, 2016 Member Contributer Share Posted November 28, 2016 7 minutes ago, RhodeMoto said: I have to give pre load some thought. If we are changing from 19 to 15mm, that is only 4mm? At 1kg/mm spring rate that would only change 4kg,...... that is enough to to change sag? That will change sag by almost exactly 4 mm. Given the apparent error on the RT Website, i'd be inclined to go with the data for the '92-'93. So, if 0,9 springs at 15 mm preload give 35 mm of sag, you'd need 10 mm of preload on the 1.0 springs to get to the same 35 mm of sag. NB: That's an extra 4 kg * 2. Besides the fork springs do not carry all that much weight once you subtract the unsprung mass and take into account that they support only about 1/3 of your bodyweight. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted November 28, 2016 Member Contributer Share Posted November 28, 2016 40 minutes ago, RhodeMoto said: Seemed like it was just the bottom of tube sleaving over the aluminum cap at foot, and could possibly lead to error? Good point. I never paid much attention to the oil lock piece (the cap) but you're probably right that it can throw off your measurement. In principle, if you keep pressing down firmly, the fork leg should eventually compress all the way as its function is to create a large increase in damping force on the last few mm of travel so as to prevent hard bottoming. Link to comment Share on other sites More sharing options...
RhodeMoto Posted November 28, 2016 Author Share Posted November 28, 2016 Think I will let things settle in. Ride some and let things get happy. Then do some measuring. My guess is that I will need to cut spacers to have very minimal pre-load. In the meantime I have just checked my H2O sensor and with lead grounded I get full hot read. I was getting no reading when running bike, so this means dead sensor? Is it possible to get it out without major dismantle? Link to comment Share on other sites More sharing options...
RhodeMoto Posted December 2, 2016 Author Share Posted December 2, 2016 On 11/28/2016 at 9:06 AM, RC36Rider said: That will change sag by almost exactly 4 mm. Given the apparent error on the RT Website, i'd be inclined to go with the data for the '92-'93. So, if 0,9 springs at 15 mm preload give 35 mm of sag, you'd need 10 mm of preload on the 1.0 springs to get to the same 35 mm of sag. NB: That's an extra 4 kg * 2. Besides the fork springs do not carry all that much weight once you subtract the unsprung mass and take into account that they support only about 1/3 of your bodyweight. Bike has been out for a few miles. Front end feels solid - little brake dive. Wanted to get the forks worked in a bit and recheck sag. As checked I am getting 27mm rider sag at front and 43mm rear! For some reason I can not get my head around if the pre-load length relates directly to measured sag. So if length is cut by 10mm is the result a 10mm increase sag? Or does the fact that you are changing the initial force play a factor, and 10mm may affect actual by a greater or leaser amount. Anyone have a FOX rear shock or similar, and can tell me how to get access to pre-load ring? Battery box out? Looks like someone has resorted to a drift and has mashed up the notches. My water temp has responded to a connection cleaning and seems to be working! Very low on gauge after 30 minute run,... Link to comment Share on other sites More sharing options...
Member Contributer VFROZ Posted December 3, 2016 Member Contributer Share Posted December 3, 2016 Front is about right, rear could do with less. What is the static sag? Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted December 3, 2016 Member Contributer Share Posted December 3, 2016 10 hours ago, RhodeMoto said: For some reason I can not get my head around if the pre-load length relates directly to measured sag. It's not exact but it should be very close. - Force on spring = rate * total spring compression. - Total spring compression = sag + pre-load. As sag increases, there is also some weight transfer to the front, some increase in air spring force and a slight change to the rake angle which all affect the static equilibrium position but these are quite small so we just ignore them. Net result: Delta pre-load = Delta sag. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted December 3, 2016 Member Contributer Share Posted December 3, 2016 11 hours ago, RhodeMoto said: As checked I am getting 27mm rider sag at front and 43mm rear! Safe enough but the ballpark is more like F35-R30. At any rate, the rear riding lower than the front won't help with the 3G's already relatively lazy steering geometry. You'd certainly benefit from raising the rear closer to 35 mm. This should automatically cause the front sag to increase a bit. Or you could reduce front preload by 5 mm and measure again (on both ends). Link to comment Share on other sites More sharing options...
RhodeMoto Posted December 3, 2016 Author Share Posted December 3, 2016 Static sag - 22-23mm front and rear. Feel I should check the nitrogen PSI in the rear before I play with the pre-load. Talked to FOX and they sent a set up but no specification on PSI? Heard reference to 300psi and that is to be used for ALL set ups and that this pressure is not related to shock compression, rebound, or any influence on spring rate assist or pre-load? Not sure if I am agreeing with this as I have schrader air valves on MY FZ600 fork caps and run 8psi with 15mm pre-load. If I drop the PSI it definitely lowers the sag and affects pre-load. If increased - bike lifts and seem to be firmer. Access to top of rear spring? - If battery holder is removed do you have clear access? Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted December 3, 2016 Member Contributer Share Posted December 3, 2016 10 minutes ago, RhodeMoto said: Static sag - 22-23mm front and rear. So Delta sag is about 20 mm at the back. Seems like the spring rate is fine but you need more preload. 14 minutes ago, RhodeMoto said: Feel I should check the nitrogen PSI in the rear before I play with the pre-load. Correct but you can't check nitrogen pressure accurately on a shock. Just filling the hose and gauge will cause a significant loss of pressure. 22 minutes ago, RhodeMoto said: Heard reference to 300psi and that is to be used for ALL set ups and that this pressure is not related to shock compression, rebound, or any influence on spring rate assist or pre-load? I have no data from FOX but Penske spec 300 PSI as MAX. My RT spec sheet for my 6G says 285. Nitrogen pressure does act almost like spring preload but that is not its purpose. The purpose is to prevent cavitation and not to assist the coil spring in any way. It just so happens that it unavoidably creates an extra spring force. The required pressure is probably almost completely independent of any other shock setup parameter hence the statement that it is not related. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted December 3, 2016 Member Contributer Share Posted December 3, 2016 Excerpt from Penske's PS-8975-STREET (Double Adjustable) - TECHNICAL MANUAL:, p.20: Warnings: Penske Racing Shocks never recommends running lower than 50 psi in our shocks depending on piston and shims being used. Lack of nitrogen pressure could result in “cavitation” which can result in loss of immediate damping and rider feel. We also do not recommend using pressure higher than 300 psi. This could result in stress fractures in main mounting components which may lead to seal or other failures. Always check with Penske Racing Shocks technicians on recommended pressures for your application and use. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted December 3, 2016 Member Contributer Share Posted December 3, 2016 BTW, in terms of force, nitrogen pressure is responsible for about 50-75# at the shock shaft (at full extension). At the wheel, that's about 20-30# on the VFR. Not huge but not trivial either. Link to comment Share on other sites More sharing options...
RhodeMoto Posted December 4, 2016 Author Share Posted December 4, 2016 )Using late night applied logic - I get that the 20-30lb at wheel equals a 20% change for a 170lb rider and equals a 5mm affective change Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted December 4, 2016 Member Contributer Share Posted December 4, 2016 7 hours ago, RhodeMoto said: [...] equals a 5mm affective change Yup ! Seems about right. I reckon complete loss of nitrogen pressure should cause a drop of 3-6 mm or thereabouts. NB: I don't have any hard data, just estimates but I am reasonably confident that they allow useful ballpark figures to be calculated. Link to comment Share on other sites More sharing options...
RhodeMoto Posted December 4, 2016 Author Share Posted December 4, 2016 So on ballpark figures,.... About the nitrogen charge. What figure to go for? Somewhere between 50 ad 300 seems rather a large spread. Frustrating I could not get a more diffinitive answer from FOX. And is this something a dealer can do or have heard going to welding gas supply Co. to charge? As the preload nut was already a bit mistreated I went with long screwdriver through frame opening and added some preload to rear. Now new symptom, I have a grab thing going on with front brakes. Rotors are clean, measure runout at +/- 0.005. If this was not moved for a long time is it possible the pads left some unseen deposit on rotor? I have a spare front rim (and rear) awaiting mount of new tires. The front has floating discs. Is this from later gen vfr? So swap of front will hopefully solve grab issue. Link to comment Share on other sites More sharing options...
Member Contributer VFROZ Posted December 4, 2016 Member Contributer Share Posted December 4, 2016 I asked this question to JD so I could check on my CBR929 modified shock. He advised it should have 190~200 PSI. I think you will need to go to a suspension shop for this. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted December 4, 2016 Member Contributer Share Posted December 4, 2016 1 hour ago, RhodeMoto said: The front has floating discs. Is this from later gen vfr? Definitely not stock but I think a 4G wheel with rotors will swap just fine. Period CBR6 probably also. 1 hour ago, RhodeMoto said: About the nitrogen charge. If you're positive that the shock has lost its nitrogen, i'd go for a full rebuild. There is probably something wrong with the seals or the Schräder valve core. Best to refresh the whole thing IMO. Should run you $100-150 or so. Otherwise, I'm not sure where to go for a straight recharge. I'd go for 250-285 purely because it's the safer option in the absence of hard data. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted December 4, 2016 Member Contributer Share Posted December 4, 2016 4 hours ago, RhodeMoto said: I have a grab thing going on with front brakes. Rotors are clean, measure runout at +/- 0.005. If this was not moved for a long time is it possible the pads left some unseen deposit on rotor? Hmmm! Drop the pads and examine for signs of contamination ? If that does not help, and since discs are clean and runout is OK, it's probably time for a caliper rebuild. Edit: Breakdown of things that could be wrong: - Partially seized pistons - Piston seals that are no longer pulling back as they should - Partially seized caliper sliding pins - Pad pins that have become grabby through corrosion or wear Link to comment Share on other sites More sharing options...
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