racerdave
^ Gone not forgotten ^
PVC pipe works well for the spacer.
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Minton Mod observations
- Thread starter Downeaster
- Start date
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- Tags
- how to suspension
jd750ace
Front Toward Enemy
Although specified by some to be tight wound on top, they can go either way.how high your forks extend on an unloaded bike means little. How much of the total travel is consumed with you on the bike, upright in riding position means a lot. This should only use about 30% of your total travel. If you had 5 inches of total travel, you would only want it to compress about 1.75
racerdave
^ Gone not forgotten ^
Thank's Twins. Damn CRS!
One way to check your forks for where they ride is to put a zip tie around your upper tube, not so tight it won't move, just snug enough so it stays where you put it. Push it down close to the dust shield.
Now go for a ride. After a few miles of riding the fork lower pushes the zip tie up. This gives you a good idea of how much the forks compress as you ride.
On mine the zip tie ended up about half way up the fork travel area.
If it only gets pushed up say 1/4 of the travel you have to much preload. If it gets pushed up to say 3/4 you need more preload.
This is just one easy way to get a course adjustment. Measuring the sag as described in most any suspension adjustment method will be much more precise.
Leo
Now go for a ride. After a few miles of riding the fork lower pushes the zip tie up. This gives you a good idea of how much the forks compress as you ride.
On mine the zip tie ended up about half way up the fork travel area.
If it only gets pushed up say 1/4 of the travel you have to much preload. If it gets pushed up to say 3/4 you need more preload.
This is just one easy way to get a course adjustment. Measuring the sag as described in most any suspension adjustment method will be much more precise.
Leo
It's a wonder to me that folks continue to rely on Joe Minton's old series on the XS650. Go ahead--stick a Shell #1 cam in that motor with stock valve springs, port, carb, pipe, and big bore that machine--then run it the way you've built it to run with an unwelded crank and see how long it takes the fly wheels to separate.
As jd has tried to tell you guys, there's no substitute for doing things right; and as Paul Thede is fond of saying, "The best you've ridden is the best you know." To get a badly needed clue about suspension tuning, go to http://www.totalcontroltraining.net/Suspension101eBook.pdf
As jd has tried to tell you guys, there's no substitute for doing things right; and as Paul Thede is fond of saying, "The best you've ridden is the best you know." To get a badly needed clue about suspension tuning, go to http://www.totalcontroltraining.net/Suspension101eBook.pdf
Ok Griz your argument against over powering the motors makes sense.
Pertaining to the front end mods are there any picking points for the improvements?
I know 5twins has found some in the hole sizing.
I'm not arguing against hopping up the motor, weekend, I'm just pointing out that it needs to be done right and that if you follow Minton's recommendations uncritically you'll wind up with a mess. 5twins has pointed out the errors in Minton's recipe for the forks, and I have nothing to add to his good job of correcting Minton's sloppy work.
As jd pointed out (and as both of discovered with our SV650's), even current damper rod forks tend to be undersprung and overdamped, and there's a reason for that. Dual rate springs are used in an effort to enable the forks to respond differently to different surface conditions, and excessive damping is applied to make the sloppy action more controllable. Emulator valves relieve damping on sharp, large bumps, and do a far better job of responding to the road surface. They also enable use of stiffer springs, improving control without loss of comfort or compliance.
I'm afraid that unless you want to roll the dice and resort to Chinese knockoffs (a bad idea both practically and ethically, IMO), the price tag for valves and a pair of correctly rated springs is close to $300. And that's wasted money unless you open the wallet for taller premium shocks. Performance isn't cheap.
As jd pointed out (and as both of discovered with our SV650's), even current damper rod forks tend to be undersprung and overdamped, and there's a reason for that. Dual rate springs are used in an effort to enable the forks to respond differently to different surface conditions, and excessive damping is applied to make the sloppy action more controllable. Emulator valves relieve damping on sharp, large bumps, and do a far better job of responding to the road surface. They also enable use of stiffer springs, improving control without loss of comfort or compliance.
I'm afraid that unless you want to roll the dice and resort to Chinese knockoffs (a bad idea both practically and ethically, IMO), the price tag for valves and a pair of correctly rated springs is close to $300. And that's wasted money unless you open the wallet for taller premium shocks. Performance isn't cheap.
racerdave
^ Gone not forgotten ^
I have 1.250 of sag from sitting on the bike, feet off the ground. I think that is in the ballpark with stock forks. I have installed Progressive springs that they spec for a XS650. # 11-1119. No spacer. Fork spring adjust set to position 3, from full soft. I forgot what weight oil I put in. The riding around the block I do does not give a true indication of bump absorption. Griz, I do wonder, do you expect to bottom the fork on slightly harder than normal stopping? My zip goes tight to the upper tree on a 30 mph stop.
No, Dave, my forks don't bottom on the brakes, landing from jumps, or under any other conditions. Here's what I'm running on my XS650 with 400 lbs. wet weight (with full fuel) and 150 lbs. of rider. Fork oil: Spectro 15W. Spring rate: .80 kg/mm. Valves: Race Tech, with blue preload springs set to 2 turns. Laden sag: 25 mm. at 14 mm. preload.
I'm not surprised that those springs bottom, but I am surprised that you're showing that little laden sag. You should check laden sag by first setting the zip tie in place with the front wheel hanging free. You also need to assume riding position with a helper holding the bike up while you get your feet on the pegs. Measure once with the front end settling from lift, once with the front end rising gently from slight compression, and average the two numbers; that will compensate for seal drag.
I'm not surprised that those springs bottom, but I am surprised that you're showing that little laden sag. You should check laden sag by first setting the zip tie in place with the front wheel hanging free. You also need to assume riding position with a helper holding the bike up while you get your feet on the pegs. Measure once with the front end settling from lift, once with the front end rising gently from slight compression, and average the two numbers; that will compensate for seal drag.
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racerdave
^ Gone not forgotten ^
From what I can find, these Progressive springs have pretty much the same rates as the oem did. Rach Techs site calculator wants near a 1.00kg spring for a 450 # bike and 250# rider.
That's about right. 1.0 kg/mm is approximately 56 lb/in. Stock springs run about .65 kg/mm in the heavy windings. Bear in mind that the Race Tech spring recommendation is for forks with emulators. The results would be pretty harsh in unmodified damper rod forks. If you're not installing emulators, a pair of the Mike's XS heavy duty dual rate springs with 50 lb/in rate in the heavy windings might give you better results.
racerdave
^ Gone not forgotten ^
Griz, I don't remember what I used for fork oil or the level. I think I may have used ATF and set it at the manuals level. Now what manual spec I used may also be variable. Maybe I need more oil? I don't want to spend any more real money yet, so give me your thought's, mainly towards the brake bottoming. I do still have the original oem springs. Cut a set of springs and run a longer spacer? Doesn't that raise the rate? A spacer with uncut springs, heavier oil {I know that's a cheap try}, or any combo using what I have worth trying?
jd750ace
Front Toward Enemy
Also, go with real fork oil. ATF is not formulated to retain a specific viscosity value, and will turn to a watery mess fast. Go with 15w, and being that you are around my size, go 20mm higher with the fluid level and see how you go from there. This reduces the air cush that takes place before the fluid going through the orfices gives good resistance. That's the cheapest course of action. Too much preload on those wimpy springs and you'll bind before max travel. I have 1.0 Race Tech springs and emulators in both the SV and the Road Star. Both bikes had .7 springs originally.
Yeah, that ATF thing was an oldschool cheap-bastard bandaid trick to get the fork seals to soften and stop weeping. It worked, but took on a life of its own as the 'hot tip'. Modern fork oils already have the seal conditioners, so the old ATF trick is 'passe', not recommended...
Amen, jd and TwoMany; there's no substitute for proper fork oil, and I can't name one bike shop in my area that doesn't stock Spectro. A quart of it costs no more than a quart of decent motorcycle engine oil and will last many seasons; why guys would be tempted to use anything else is a mystery to me.
Dave, I know you don't want to hear this, but at your weight those springs aren't going to cut it if you want a decent suspension, and neither are stock shocks and shock springs. Going high on oil level and/or viscosity slows down the damping action, and while that may avoid some brake dive, you probably won't like what it does for the rest of the ride. If you decide to use that work-around, bear in mind
that if you set the oil level too high you'll blow the seals.
Dave, I know you don't want to hear this, but at your weight those springs aren't going to cut it if you want a decent suspension, and neither are stock shocks and shock springs. Going high on oil level and/or viscosity slows down the damping action, and while that may avoid some brake dive, you probably won't like what it does for the rest of the ride. If you decide to use that work-around, bear in mind
that if you set the oil level too high you'll blow the seals.
