| taygold |
 Posted: Fri Oct 28, 2011 8:08 am
 Subject: Ninja 250 front end swap (fork stiffness question) |
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I'm building a Virago 750 "cafe racer" and it just so happens the 250 ninja forks/ wheel slide right up in the triple! This is great because I cut the 19" monster front wheel down to a 16" which matches the rear. Anyway I'm trying to beef up my fork stiffness to support the extra weight of the virago (it weighs almost 200 lbs over the ninja) plus my own 150 lb (with gear) bum. I've read tons of threads and want to just throw out what I'm thinking of doing before actually cutting my springs.
the idea I'm getting is to cut down the stock springs by a few mm, say 10? and then make a PVC spacer that is 10mm longer than stock in order to keep my overall spring+ spacer length the same. Then probably add some 15W oil...Or would 20W maybe work better for this application? And I'm not too sure about the amount I'll want to cut?
This could also be looked at as though I were asking what I should do to my forks to support a 350 lb rider. And I'd like a rather stiff ride as I always hated how soft my old ninja was compared to the bigger sport bike I've owned.
thanks in advance for any advice! |
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| BrianM |
Posted: Fri Oct 28, 2011 8:38 am
Subject: Multi-prong question there... |
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First things first, getting the spring rate correct. While I am an advocate of cutting springs (when possible), it's not always possible. For instance, the stock spring rate is a whopping .44, and if you want a STIFF feel (why?, softer is faster) you'll need to get up to 1.00, or at the very minimum a .95. To obtain that, you would have to cut the spring in Half, at which point you're going to be running into coil-bind before you use all the suspension travel. This is a BAD THING. To get the Correct spring rate, you're either going to need to buy the right springs, or buy something that can be cut less than 1/3rd (free length greater than ~14 inches) it's total length. You do want whatever spring you put in to have a spacer that's the same length overall as stock.
Spring rate, of course, doesn't have anything to do with fork damping. So the same oil that you use with stock springs will work with beefy springs. Stick with 15wt oil.
The last thing you should consider, given the extra power and weight, is to add a fork brace. This will make the forks themselves more rigid, which means more precise handling through corners (less flex) ad better tracking under front brake. This is the company to call (only ones who make a fork brace for these forks as far as I know) ~ http://www.spec2.com/clips.html Just call to Verify that they do have a product that will work.
As you get it going, post up a photo or 6 |
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| taygold |
Posted: Fri Oct 28, 2011 1:00 pm
Subject: interesting points! |
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You are right- let me clarify what I meant by "stiff"- I was more referring to the "soggy" feel my old ninja had, tapping the front brake made the whole bike lurch forward etc. I don't really want a harsh ride that the 1.00 spring rate would produce (is this good logic?).
So just to stiffen the "preload" (is this a better word?) and help it from bottoming out in corner bumps with the extra weight and all -could I just cut a few inches off the springs and fab up new spacers to take up the slack and that will be enough?
What then, does heavier weight oil accomplish that I don't want?
Absolutely going to be making a brace for this puppy! good call. I'll probably just fab one up though out of aluminum block.
The project is going very well! I recently finished the tail & paint and wiring and motor build. Just need to finish this front end and re assemble the shaft/ rear end & make the under tail exhaust! Pics will be up shortly  |
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| BrianM |
Posted: Fri Oct 28, 2011 1:33 pm
Subject: upping preload is a great way to get awful results. |
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| taygold wrote: | | You are right- let me clarify what I meant by "stiff"- I was more referring to the "soggy" feel my old ninja had, tapping the front brake made the whole bike lurch forward etc. I don't really want a harsh ride that the 1.00 spring rate would produce (is this good logic?). |
Most of that is controlled by rider skill. I'm 250lbs, and riding hard on stock suspension doesn't lead to nose-dive with me. It's all in learning how to ride so to Avoid doing that (and I learned on an even more poorly suspended bike). a 1.00 spring would be what a 350lb person who's racing the 250 would want. A .95 spring would be what the same rider would want for street riding. Both would be on the firmer side, not the softer side. If you want firmer, just buy the right springs. You MIGHT get to the same front end feel on the Virago by cutting the springs as much as possible before running into coil-bind limiting suspension travel. You're never going to make it better though, the 200lb weight difference of the bike has guaranteed that.
| taygold wrote: | | So just to stiffen the "preload" (is this a better word?) and help it from bottoming out in corner bumps with the extra weight and all -could I just cut a few inches off the springs and fab up new spacers to take up the slack and that will be enough? |
Preload is just that, it pre-loads the spring. Using round numbers for easy examples, if you have a 100lb per inch spring, that means it takes 100 pounds to compress it 1 inch, 200 for 2 inches, 300 for 3 inches, etc... If you pre-load that spring 1 inch, it will not move at all as you apply the first 100lbs of weight/force, but it still only takes 200lbs to move it 2 inches. The spring rate doesn't change just because you pre-load it. So you can make a spring not move when little force is applied (think expansion joints, potholes, etc...), but it'll still turn to a wet noodle the instant you brake or corner. Kinda backwards from what most riders SAY they want, a soft/comfortable/compliant ride that firms up when you start pushing harder.
| taygold wrote: | | What then, does heavier weight oil accomplish that I don't want? |
Oil weight controls 1 thing, damping. On the 250 forks, it controls Both rebound (the important one) and compression damping. Since the fork isn't changing, there's no reason to change the oil weight. Using 20wt oil will mean that the front forks feel "harsh" because the rebound can't extend the fork fully before the next bump. Ideal rebound damping means that if you push on the bars (with the front brake on) and then release to let it rebound, it should come up quickly and stop. If it comes up, then settles back down the oil is old or too light. If it slowly creeps up to a stop, the oil is too heavy.
This is all pretty standard stuff that hasn't changed for the past 40 years. |
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| taygold |
Posted: Fri Oct 28, 2011 5:52 pm
Subject: finally some answers |
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This is the info I've been searching for. So cutting the springs will only make it take more weight to begin compressing, but once reaching that point it will be the same "spring rate". -great...
I find it hard to believe that if you're riding your ninja hard braking into a corner it doesn't go a bit soft on you, no matter riding skill. The feeling of the 250 compared to my 636 is incomparable when riding under hard conditions. Just saying, it isn't mostly about the rider, it's more about the suspension; a good rider can just make a soft suspension perform better, but it will still be inferior.
Anyway, it sounds like there is no way to give the forks an improved feel without new springs. That's what you're getting at? I see now why heavier weight oil won't help. Not sure on oil level though? Maybe run a over stock level? And I guess it will be a good idea to just trim the springs a bit so they can hold up to the heavier weight of the bike. I'll have to wait on getting new springs...we'll see how she handles first. |
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| BrianM |
Posted: Fri Oct 28, 2011 5:59 pm
Subject: You've confused some things. |
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Preload beyond 10mm is not worth it as it doesn't CHANGE the spring rate
Cutting the springs changes the spring rate (what you need), you just can't cut the 250 springs short enough without running into other problems (clearance).
Oil level only affects the last couple of MM of suspension travel before the forks bottom out (hit a hydraulic lock, there's no contact of anything made). More oil might help if you find the bike bottoms out easily, go in 5mm (10cc) increments.
Yes, your 636 suspension reacts better because it's CARTRIDGE FORKS, not damper rod. On the street, at legal speeds, a good rider will have no issue keeping up with (or leaving behind) an average or less than average rider no matter what bikes you assign them. Put the same rider on a bike with damper rod forks, then a bike with cartridge forks, that rider will tell you that the cartridge forks are better (they are). The reason I don't have brake dive, is because I ride sanely... you should read "The Pace" if you have any interest in keeping your drivers license and surviving to be an old rider. |
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| taygold |
Posted: Fri Oct 28, 2011 11:44 pm
Subject: been there done that...haha |
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Actually already learned the hard way so got that covered! got busted going down main street in my town at double the speed "racing" a viper on my 636...I was 18, only had my license for 2 years, and couldn't resist the teasing the viper gave me. Long story short- I would much rather obey laws than do community service again 
I don't plan on riding this virago project hard at all as it is mostly just a test of whether I can make the project a success. I wouldn't have even bothered messing with the forks at all except I got them completely disassembled and thought while they were apart I could make them hold up a bit better to the 500lb bike they'll be supporting.
To conclude then, what would be best is cut the springs by about 10mm, make a spacer to take up the slack, ride them & add 10cc of fork oil if I'm bottoming it out often? -call it a day. |
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| taygold |
Posted: Fri Oct 28, 2011 11:54 pm
Subject: here's an idea... |
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| Do people ever get short springs that have a higher spring rate, cut the stock springs and add in the short/ heavier springs instead of just putting a longer spacer in. Wouldn't this cause the progressive effect as there would be 2 levels of spring rates? But I suppose at that point you as mind as well just order a new set of progressive springs...But if you could get short/ heavy springs for half the price maybe it'd be worth it? |
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| taygold |
Posted: Sat Feb 04, 2012 12:09 pm
Subject: FINISHED! CHECK IT OUT! |
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Sorry I took so long to post pics, I finished it over a month ago...Just never got around to it. It was a wonderful success! I love the bike, such an attention getter.
by the way...how to do I upload more than one image??
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| taygold |
Posted: Sat Feb 04, 2012 12:11 pm
Subject: More pics |
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I'm gonna try photo bucket links...
hope those show up! |
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| taygold |
Posted: Sat Feb 04, 2012 12:17 pm
Subject: since the pics... |
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| These are a bit out of date, I painted and mounted the original ninja 250 front tire fender to match the bike. It was a nice finishing touch. Front does still feel a bit soft...probably won't both fixing it but if anyone knows of some old bikes that have the same diameter fork springs it would be much appreciated! |
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| Greenhorn |
Posted: Sun Feb 05, 2012 8:21 pm
Subject: Question about your headlights! |
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How mounts did you use for the headlights? Are those the stock 250 lights? I'm thinking about converting mine ex250 to a naked version.
Thank you! |
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| taygold |
Posted: Sun Feb 05, 2012 9:23 pm
Subject: about the headlight |
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| No it isn't a ninja headlight, It was a NOS (new old stock) that I found on eBay that originally was designed for the honda odyssey go cart made in the 80's. It is mounted via some headlight brackets I also got on eBay for around $15 shipped. All together I think that cost me around $40 to make. It was very easy to install, and I got to give it the retro look of a square headlight. |
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| Greenhorn |
Posted: Sun Feb 05, 2012 9:28 pm
Subject: Thank you! |
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| My fairings are in terrible shape and I'm trying to think of an affordable way to convert the bike into a naked. |
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| Bokonon |
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| carsnwomen91 |
Posted: Mon Feb 06, 2012 11:11 am
Subject: THIS IS SIIICK |
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you've made my dream caf? racer. It looks really good and its a vtwin!!! like a home made yamaha mt01... the 250 forks changed it a lot.
did u change the frame or did you keep the stock frame and just add that custom high tail piece |
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| carsnwomen91 |
Posted: Mon Feb 06, 2012 11:18 am
Subject: spring rate |
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| can't you get aftermarket springs? racetech and sonic springs sell ones for the 250. They have a calculator to determing which spring is best for you but you got 250 forks on a different bike so you might have to add the weight difference between between both bikes and your weight. |
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| taygold |
Posted: Mon Feb 06, 2012 1:26 pm
Subject: what I would do |
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| If it were my 250, I would probably sell the fairings on eBay or CL and take that money to buy a good looking headlight bucket, bracket, and vapor gauge speedo/ tach. They are about $100 but very slick and work well. |
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| taygold |
Posted: Mon Feb 06, 2012 1:29 pm
Subject: thanks! |
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| We share a similar dream then because that was my goal too, I've always wanted a V-twin powered cafe racer! The Virago is an awesome starting place because the sub frame is completely bolt-on so I didn't have to change the frame at all. I simply un bolted the low cruiser original sub and fabricated a new one with Low's angle iron and some sheet metal I had kicking around. The entire seat area is 100% unique but the best part is that it is also 100% reversible. |
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| taygold |
Posted: Mon Feb 06, 2012 1:32 pm
Subject: exactly right |
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| You're right about the springs available but I am scared from reviews I've read that they are no good. People say they go progress too softly at first and then become too hard too fast. Or that they quality isn't up to par. I would like some feed back from people who have some after market springs if anyone out there has an opinion. Basically with my 135lb self, plus the extra bike weight, it's as though these forks were carrying a 500lb person on a stock 250 ninja...just for reference. |
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| Bokonon |
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| taygold |
Posted: Mon Feb 06, 2012 8:22 pm
Subject: perfect! |
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| Thanks that's exactly what I was looking for. So with race tech I can get a set of .95kg for $125 before shipping (hardest they supply). Sonic springs however, has 1.00kg springs for only $80 before S&H. Is this a no brainer or is there some incredible quality difference I should be aware of? Also, just for reference the calculator says I would ideally have a 1.172 spring rate for my purpose. |
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| taygold |
Posted: Mon Feb 06, 2012 8:26 pm
Subject: one more thing |
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| Okay I re-calculated that since a virago weighs about 520lbs wet, that plus me would only be 650lbs. When I calculated that weight it came up with an ideal rate of .948. So I can go with the .95 from either brand. Sonic springs is over $40 cheaper. I feel like this is what I'll do. If anyone knows something I've over looked speak now! |
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| Bokonon |
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| jkv45 |
Posted: Wed Feb 08, 2012 10:05 am
Subject: +1 on Sonic Springs |
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| Rich at Sonic Springs is a great guy and will get exactly you what you need at a decent price. He works with a lot of racers, and the spring quality is top-notch. |
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| taygold |
Posted: Wed Feb 08, 2012 3:36 pm
Subject: good to hear |
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| Cool because I ordered a set of .95 from SS and I am hopeful they will make the front end on this build feel complete! |
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| taygold |
Posted: Fri Feb 10, 2012 10:47 am
Subject: update on springs! |
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They arrived yesterday (extremely fast shipping!) and I promptly installed them and gave the bike a test run. WOW did it make a difference! totally different beast, it feels much more stable now, and sits higher in the front which is nice. I'm very pleased and would definitely recommend them to anyone.
NEXT UP!: speedo. Anyone know the gear ratio for the speedo on a ninja 250? (2:1, 60:1, 1:1, etc) there are several different variations, I'll probably just end up hooking the speedo cable up and visually checking it. |
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| Bokonon |
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| nate7723 |
Posted: Sat Feb 11, 2012 6:04 am
Subject: There was some discussion about this a year ago |
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Here's the link, and a relevant quote
http://forums.ninja250.org/posting.php?mode=topicreview&t=84153&tro=1
| Quote: |
FrugalNinja250
Posted: 21 Feb 2011 09:46
Here's what I came up with:
The speedometer hub gear ratio is 23:9; For every 23 turns of the front wheel the speedo cable turns 9 times.
The first gear set inside the speedo head has a ratio of 10:1; for every 10 turns of the speedo cable the cross shaft spins 1 time.
The second gear set has a ratio of 16:1, so every 16 turns of the cross shaft turns the longitudinal shaft 1 time.
The last gear set ratio is 14:1; every 14 rotations of the longitudinal shaft turns the 10ths wheel of the odometer 1 time.
If you do the math, the overall ratio between the wheel and odometer is (14*16*10*9)/23, or ~876.5:1.
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