Member Contributer RC36Rider Posted November 15, 2015 Member Contributer Share Posted November 15, 2015 [...] All that being said, I am planning on slapping my ZX14 shock in there and giving it a try with and without the dogbone mod. Nothing like empirical data! The ZX-14 shock is also significantly shorter than stock (at least, the Öhlins model for the ZX-14 is). If I'm not mistaken, that will cause a very low ride height when combined with the stock linkage, won't it? That plus the spring rate does not sound auspicious to me but if you're willing to give it a try ... Still tend to believe that the dogbone mod is essential to a workable end result. I'm curious to see your results. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted November 15, 2015 Member Contributer Share Posted November 15, 2015 [...] WRT high link ratios: One person who seemed knowledgeable explained that shorter stokes at the shock means less tendency to froth the oil Honda has been moving away from these kinds of leverage ratios on the more recent CBRs. When Aprilia tweaked and refined their RSV Mille in 2001, they went from a 140 N/mm spring to 95 N/mm which I'm fairly sure means that they went from a VFR-like ratio with corresponding short stroke to a less extreme ratio. Not sure exactly why they did it but I'm sure that some very qualified people put in their best effort to improve on the bike and this was one of the things they elected to change. Edit: That's 95 N/mm, not 9.5 of course. Sorry. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted November 15, 2015 Member Contributer Share Posted November 15, 2015 I agree that a modification to the linkage, either triangle and/or dog bone, is essential if a shorter shock with lower spring rate is used without modifying the shock length and spring rate to achieve the correct ride height and suspension rate. The interaction, leverage, and travel ratios amplifies even minor changes to these linkages so precise measurements are needed. Nifty, have you measured the C-C distance on your modded dog bone? Link to comment Share on other sites More sharing options...
Waller Posted November 15, 2015 Share Posted November 15, 2015 WRT ride height, Nifty seemed to think it would be about 10mm lower than stock, and that his bike was 1 - 1.5 inches higher than stock with the bone mod. Am I wrong to think that I could order a longer spring or shim one and correct the burdened sag height? Of course that would mean that the suspension would top out 10mm sooner; it is hard to imagine that would be a problem. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted November 15, 2015 Member Contributer Share Posted November 15, 2015 WRT ride height, Nifty seemed to think it would be about 10mm lower than stock, and that his bike was 1 - 1.5 inches higher than stock with the bone mod. Am I wrong to think that I could order a longer spring or shim one and correct the burdened sag height? Of course that would mean that the suspension would top out 10mm sooner; it is hard to imagine that would be a problem. Longer spring won't make the shock physically longer, when unloaded it is already at it's internal max stroke. A longer spring would essentially add pre-load to the spring when installed but it wouldn't make it longer. The correct spring rate rather than longer spring length would be the way to correct the sag... I may have misunderstood your question, sorry if I did. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted November 15, 2015 Member Contributer Share Posted November 15, 2015 Not sure exactly. I just meant to make it clear that you will likely end up having to alter the dogbone which involves some welding. This is definitely not meant to stop anyone from trying but if welding up the dogbones is beyond what you are willing to do, you might end up with an expensive paper weight rather than a great cheap fix for your crummy, spent, old Showa. I also have never heard of anybody wanting to lower the rear end of an RC36 and make the steering geometry lazier than it already is. Unless you have very short legs and want to lower the whole bike. Nifty's current setup still raises the stock ride height significantly in spite of the shorter shock. Link to comment Share on other sites More sharing options...
Waller Posted November 15, 2015 Share Posted November 15, 2015 No, you understood. I think the shock length that is of great concern is when loaded. As you say, the unloaded shock length can't be changed, but by shimming the spring, or introducing a longer one, i think you can increase loaded ride height, even with the same pre-load. But I would bet my life on it yet, I have to think it though with the parts in my hands. I just did my mock up using admittedly imprecise measurements. The results: ....Drum Roll..... The stock link ratio is progressive, as suspected. More displacement of the tire yields a higher link ratio and therefore higher suspension rate shortening the bone 1" increases link ratio at all angles of displacement shortening the bone increases the progressive nature of the linkage in the range of motion I tested, the link ratio of the modded bone system starts at 1.2 times the stock ratio, and ends at 1.4 times the stock ratio. That means to me that the bone mod is in fact compensating for the softer ZX14 spring, and by the end of its stroke, it yields equivalent overall suspension rate. This may very well explain why it is working so well on Nifty's rough roads. RC 51 owners generally seek to reduce the progressive nature of their suspensions for the track, so this may not be so good for the track. Caveat: Again, measurements were not precise. I could use help on that. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted November 16, 2015 Member Contributer Share Posted November 16, 2015 ...! I was thinking about running a ZX14 front end too, glad to see someone doing it. When you get a sec, can you tell me the length of the forks? Thanks! . I'm traveling for work and I don't have my fork swap spreadsheet handy... it'll be a few days before I will have the numbers. Some easy reading on how the bike got to where it is... http://www.vfrdiscussion.com/forum/index.php/topic/80470-mail-order-rvf-800-some-assembly-required/page-1 Hey Nifty, sorry for the delay... my 2009 ZX14 forks are 745 mm from axle center to the top of the fork tube where the cap mounts. They are longer than most of the other USD options I have found except the RC51 at 755 mm. Hope this helps... we now return to your previous programming... Link to comment Share on other sites More sharing options...
downic71 Posted November 17, 2015 Share Posted November 17, 2015 Great thread - I'm following with interest. Just this week my '93 VFR started leaving small oily puddles on the floor just in-front of the rear wheel. I can see the oil dripping down from the shock area onto the rear of the collector box. I don't think there are any overflow pipes back there - so I figure the rear shock is leaking. Question for anyone who has removed a rear shock before - do you need to remove the exhaust collector box to gain access to the bottom of the shock/linkage. Or can it be done with it still in place? Thanks. Link to comment Share on other sites More sharing options...
750 Posted November 17, 2015 Share Posted November 17, 2015 Nah, Haynes says to remove rear wheel > battery box > undo bottom bolt > undo top bolt > lift shock up out of the frame. Reverse for install. Obviously this is with the bike and swing arm supported! Link to comment Share on other sites More sharing options...
Member Contributer RC51Nick Posted November 18, 2015 Member Contributer Share Posted November 18, 2015 Did I miss something but I can't find the video (if Nifty7Fifty put it up) that shows the modification to the shock linkage. There is one video on the first cpl. of pages that says it does not exist when I click on it. Am I the only one messed up or can someone direct me to a link showing that part of the conversion. Thanks. Link to comment Share on other sites More sharing options...
Waller Posted November 18, 2015 Share Posted November 18, 2015 Here is my attempt at a summary 1) With the dogbone mod, the zx14 mod : ~$100 gives a more progressive suspension rate varying from softer than stock up to stock rates unburdened height: slightly higher than stock height, depending on where you put the hole burdened height: similar to stock 2) XZ14 without the dogbone mod: ~$100 much softer suspension rate but with factory progression (softer at all postions) unburdened height 40mm lower, limits suspension travel down (assumes that shock fully extended is 10mm shorter than stock, which I read but have not measured) Burdened height: should sag lower than stock, increasing chance of bottoming out? 3) zx14 with replacement factory-rate spring and no dogbone mod: $200 factory suspension rate with factory progression unburdened height 40mm lower, limits suspension travel down (assumes that shock fully extended is 10mm shorter than stock, which I read but have not measured) Burdened eight: should be stock sag, if spring is shimmed 10mm at bottom or custom made 10mm longer Chance (small chance IMHO) that there may not be sufficient damping capability I think I am going to buy one of Daugherty's $420 929 modified shocks with custom springs for my weight. Only ~$200 more than option 3 above, without the reduced unburdened height and reduced extension capability. $300 more than option 1, without the increase in progressiveness, which is commonly thought to be undesirable on the track, many think undesirable on the street. Tried and true, and designed to complement modified forks. If I didn't ride on the track, I would try option 1. I would expect it to work well with older unmodified front forks, just as Nifty has reported. I would, however, install the shock without the spring, and run the rear suspension through the whole range of motion from bump stop to bump stop (or chassis interference)to make sure the shortened dogbone doesn't bind or have a singular point or over-center condition. Cheers. P.S. Option 3 seems appealing except that the reduced extension capability could cause the bike to lift the rear tire after a bump, which I imagine could lead to a highside when the tire comes back in contact. But this is beyond my knowledge, just a gut feeling. And it is getting more expensive. Link to comment Share on other sites More sharing options...
750 Posted November 18, 2015 Share Posted November 18, 2015 Waller, I'll never understand buying a 929 shock when you can buy something from Penske, Hyperpro or Maxton for similar money. Or are shocks way more expensive over there? Did I miss something but I can't find the video (if Nifty7Fifty put it up) that shows the modification to the shock linkage. There is one video on the first cpl. of pages that says it does not exist when I click on it. Am I the only one messed up or can someone direct me to a link showing that part of the conversion. Thanks. All his videos are here buddy https://www.youtube.com/channel/UC8jes9m4KqLh1pMfhPw8hiw Link to comment Share on other sites More sharing options...
Member Contributer Rice Posted November 18, 2015 Member Contributer Share Posted November 18, 2015 Waller, I'll never understand buying a 929 shock when you can buy something from Penske, Hyperpro or Maxton for similar money. Or are shocks way more expensive over there? 929 Shock with correct spring and matching shim stock for the rider - $420 Ohlins, Wilbers, Penske, Elka, etc... all about x2 as much. Link to comment Share on other sites More sharing options...
750 Posted November 18, 2015 Share Posted November 18, 2015 S'pose it's a bargain then! Link to comment Share on other sites More sharing options...
Nifty7Fifty Posted November 18, 2015 Author Share Posted November 18, 2015 https://youtu.be/4XWaChvjOOA Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted November 19, 2015 Member Contributer Share Posted November 19, 2015 ... Jamie Daugherty, a member here, may be able to tell you the dampening details of this KYB shock. Quick question, when you say the bike's height is close to the same after you cranked down the pre-load are you talking about static sag with just bike on its wheels or rider sag height with you in the saddle? Link to comment Share on other sites More sharing options...
Nifty7Fifty Posted November 19, 2015 Author Share Posted November 19, 2015 Quick question, when you say the bike's height is close to the same after you cranked down the pre-load are you talking about static sag with just bike on its wheels or rider sag height with you in the saddle? Rush, big thanks for posting your fork details, I'll be following your build to see how everything turns out! Static sag, wheels on ground, no rider, is roughly 1.5 - 2 inches over stock height. The sag with me on is very close to where it was with the original shock (I can tell by where my feet touch the ground). It's a touch lower, but I was surprised that the shock provided enough adjustment that allowed for a near exact pre-mod ride height, given the 15mm difference in shock length. I expected the zzr shock to net me a 1 inch over stock final height (with dogbone mod), which was my target. I can get that if I decrease the preload, but with the preload @ 80% loaded it's back up there. The center-to-center distance between the original and 2nd holes on the bone is 20mm. I advise anyone doing this mod to try 15mm center-to-center. I believe 15mm is gonna be the "magic number" for this swap, providing the best performance for this setup. 5mm shorter on that bone hole would have given me more room to play with the height. That's why I'm now recommending all those who do this swap to try it first without drilling the second hole for the bone... I think the results are gonna surprise alotta folks. And then the bone-mod is still an option for those wanting increased height or more spring. Now that's all relative to the ZZR shock however, the 20mm c2c bone hole will be much better suited for the BMW s1000rr rear shock, if/when I get around to playing with that. Link to comment Share on other sites More sharing options...
Waller Posted November 19, 2015 Share Posted November 19, 2015 I just realized two things. One is that I had a screwed up notion of how pre-load would affect sag. Thanks for the info on that Nifty. The second thing I noticed is that my zx14 spring is tapered. The ID at the top is smaller than the ID at the bottom. I don't know if that means anything about rate or progressive rate. Also I wonder if it makes it harder to fit a replacement. BTW - When I guessed that the suspension rate would be soft without the dogbone mod, I should have specified that I was talking static suspension rate, not dynamic. The ride could firm based on the damping, as opposed to the spring rate. Link to comment Share on other sites More sharing options...
Member Contributer RC36Rider Posted November 19, 2015 Member Contributer Share Posted November 19, 2015 The second thing I noticed is that my zx14 spring is tapered. The ID at the top is smaller than the ID at the bottom. I don't know if that means anything about rate or progressive rate. Also I wonder if it makes it harder to fit a replacement. Race Tech mention the need for an adapter collar in order to fit their non-tapered spring to the stock shock. Tapered springs are progressive according to this: Peter Verdone's test of a CBR 600 RR shock spring: http://www.peterverdone.com/archive/600RRshock.html http://www.acxesspring.com/linear-spring-rate.html Link to comment Share on other sites More sharing options...
Nifty7Fifty Posted November 19, 2015 Author Share Posted November 19, 2015 I just realized two things. One is that I had a screwed up notion of how pre-load would affect sag. Thanks for the info on that Nifty. The second thing I noticed is that my zx14 spring is tapered. The ID at the top is smaller than the ID at the bottom. I don't know if that means anything about rate or progressive rate. Also I wonder if it makes it harder to fit a replacement. The second thing I noticed is that my zx14 spring is tapered. The ID at the top is smaller than the ID at the bottom. I don't know if that means anything about rate or progressive rate. Also I wonder if it makes it harder to fit a replacement. Race Tech mention the need for an adapter collar in order to fit their non-tapered spring to the stock shock. Tapered springs are progressive according to this: Peter Verdone's test of a CBR 600 RR shock spring: http://www.peterverdone.com/archive/600RRshock.html http://www.acxesspring.com/linear-spring-rate.html Awesome info guys, Thank you for posting!!! This confirms my assertion that the spring is progressive and explains why the rear end stiffens-up consistently with tightening the preload.. Just as Waller observed, spring has a slight taper to it. There are a few different styles of progressive springs. Someone posted a pic of only one style, and mistakenly assumed that's how all progressive springs should look. That's the problem with doing quick internet searches rather than real work. Volkswagen, for example, uses progressive springs that look exactly like linear springs. Spring technology has indeed advanced in recent years. Yes, a 10 kg/mm spring is still a 10kg/mm spring, but the materials used to make the springs have revolutionized the industry. The newer materials react better, and stay true far longer than older springs. Your older 16 kg/mm spring might be functioning at 13kg/mm or less, due to years of use. Most newer springs retain their correct rate and characteristics for the life of the bike. Link to comment Share on other sites More sharing options...
downic71 Posted November 22, 2015 Share Posted November 22, 2015 Nah, Haynes says to remove rear wheel > battery box > undo bottom bolt > undo top bolt > lift shock up out of the frame. Reverse for install. Obviously this is with the bike and swing arm supported! Thanks John - this will be my big winter project! I just picked-up a ZX14 shock from ebay with 12K miles on for $50 US shipped to my door! It was a bit dirty - when it arrived. 20 minutes of scrubbing Came out looking really good I guess I'm committed now! Link to comment Share on other sites More sharing options...
Nifty7Fifty Posted November 23, 2015 Author Share Posted November 23, 2015 Link to comment Share on other sites More sharing options...
slovcan Posted November 23, 2015 Share Posted November 23, 2015 Thanks Bill. So, how did it feel to you with the new settings? Are they final? It did look good. There seemed to be less suspension travel used than in the first video you did (bearing in mind the different test route). That's down to the extra pre-load and compression, I'd say. Do you still advocate trying the stock dogbone hole with these settings after this test ride? Cheers, Glenn Link to comment Share on other sites More sharing options...
Member Contributer Switchblade Posted November 23, 2015 Member Contributer Share Posted November 23, 2015 What exhaust ? You mean no exhaust, it sounds good ! Rear shock is awesome . Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.