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faffi

The big fork spring confusion

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faffi

My Dullville is way too softly sprung up front. I have not found the stock spring rate, but if the list of compatible models for aftermarket fork springs, it is about .6 kg/mm. Even the ST1100, 90 lb heavier than the Dullville and 200 lb above the MT07, only has .61 springs! And the old Suzuki Bandit 600 is listed to have just .45 springs, which sounds ridiculous, especially when I consider how silly soft the CB400SF was with .5 springs. And the SV650 that everybody complains about being way too soft? Spring rate between .69 and .71, depending on model.

 

In comparison, my former 2015 MT07 should have .87 springs (some say 2015s were inconsistent and many had softer springs - I wouldn't know). Consider that the Dullville and MT differ in weight by 110 lb, the MT being the lighter, the spring rates makes even less sense. Add to that the fact that even with more preload, for correct sag, and oil level at 125 mm, the MT would bottom its fork under maximum braking, it is no wonder that the Dullville does the same - before maximum braking (oil level at 110 mm).

 

Racetech recommend .95 fork springs for the ST1100 and .9 springs for the MT07 with a 190 lb rider. How does that make any sense? What am I missing? Where is the logic?

 

Anyway, I should probably get some .9 springs for my Dullville, despite me not being able to make any sense out of the various bikes and numbers. 

 

 

 

 

 

 

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RojoRacing

Type of riding makes a larger difference than pure weight.  Riding aggressively in the canyon on a sport bike is equal to 100lbs of weight over a casual cruiser riding down the coast.  Also suspension length could have a small factor but I doubt it.

 

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cornerslider

Most OEM springs are "progressive rate", meaning the more they are compressed, the more resistance is felt. They do this by adjusting he spacing between the coils over the length of the spring. This type of spring offers a relatively smooth ride in a wide variety of situations. I'm assuming that is why the manufactures use them- They can suit a wide variety of rider weights, and do an "okay" job doing so. I honestly don't know how the manufacturers give an accurate "weight" to a progressive spring"??? That being said, most aftermarket springs are "straight rate", meaning the resistance is the same no matter how far the spring is compressed. The spacing of the coils stays the same over the length of the spring. They are manufactured for a specific weight, for those  riders that want a more "dialed-in" suspension for "spirited" canyon carving, or track use.

 

I personally have straight rate Racetech springs (sprung for my weight) on my FZ-07, as I use it about 80% track. They do a MUCH better job for that purpose. I also have a Honda VTX1800, that is obviously a street only bike. I wouldn't even consider putting straight rate springs in it. Not worth the money- It does a great job with the OEM progressive rate springs. I even put aftermarket "Progressive" rear shocks on my VTX, and it rode much smoother after doing so. 

Edited by cornerslider

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twf

Stock FZ springs are straight rate, .875. 

Bikes used to come with pretty soft springs from factory. Than 20 or so years ago they started getting stiffer and stiffer. In some cases way to stiff for what we used to, like ninja 650 when it came out had 1.4 springs stock. On other hand some bikes work really good with stiff springs, I used 1.5 in my 09 R1.

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faffi

Did a test today: Static sag 35 mm with me on the bike. Sitting on the bike, pushing it off the centre stand, stopping with the front brake just as the rear wheel hits the ground, measured fork dive to 76 mm, or 3 inches. So that's how little it takes to compress the fork an additional 40 mm, or 1.5 inches.

 

So no doubt I do need stiffer springs. Those off a MT/FZ07 would likely work well, but probably not cost effective even used as a set of Racetech springs only cost a little over USD 100 with shipping to Norway.

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faffi
15 hours ago, RojoRacing said:

Type of riding makes a larger difference than pure weight.  Riding aggressively in the canyon on a sport bike is equal to 100lbs of weight over a casual cruiser riding down the coast.  Also suspension length could have a small factor but I doubt it.

 

Interesting!

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Kyuzo

I have a question regarding stock spring rates. Say I never will take my bike(FZ07) to the track and ride mostly streets- which entails quick stop and go up to around 60mphs and then back to O mph most of the time with an average speed around 40mph.  Throw in shitty pot holed roads. If I wanted less jarring in front could I actually go down a spring rate or two from my weight and add thicker oil? I have my zip tie on my fork and I rarely use more than 1/2 of the travel.  I have stock springs and 10wt oil btw, I weigh 155#'s w/o gear. Thanks

Edited by Kyuzo

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cornerslider
4 hours ago, Kyuzo said:

I have a question regarding stock spring rates. Say I never will take my bike(FZ07) to the track and ride mostly streets- which entails quick stop and go up to around 60mphs and then back to O mph most of the time with an average speed around 40mph.  Throw in shitty pot holed roads. If I wanted less jarring in front could I actually go down a spring rate or two from my weight and add thicker oil? I have my zip tie on my fork and I rarely use more than 1/2 of the travel.  I have stock springs and 10wt oil btw, I weigh 155#'s w/o gear. Thanks

I'm NOT the best suspension "tuner", but I think your on the right track.... It seems like some of that would work? Based on your zip-tie readings, you could probably go down in spring weight. My "best" suggestion would be to put in some Racetech "gold-valve fork emulators", as well as Racetech springs (for your weight). If you have the forks apart to do the springs anyway, it's a pretty cheap/easy mod to do- (I think they are like $169?) I would continue to use the 10wt oil though (regardless if you use emulators or not) . The emulators will do away with almost all of the "jarring", as well as the front-end "dive" when braking. If I had to choose between doing springs, or emulators.... For my money- I'd do the emulators first!!! 😀. IMHO- the FZ-07's front end is much worse than the rear suspension that a lot of folks complain about. You don't know how much your front-end is diving, until you make it STOP diving 😎.... Being that you're a #155 street rider, I think you would LOVE that set-up (even with a stock rear shock), and not break the bank doing so-

Edited by cornerslider

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faffi

For a smooth ride, try the DDC-valves instead together with 2.5W oil. The Racetech valves are more suited to track riding. YMMV.

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