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Spring rate and suspension setup.

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Sam.moz86 View Drop Down
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    Posted: 28 Jun 2020 at 08:06
Good morning you orrible lot. Wink

I'm after some suspension advice if anyone can help, it's not for my gen 2 though. 

Here goes, this may hurt your head for a Sunday morning. 

I'm converting a little RM85 to a supermoto pitbike and I need to order some custom springs. 

I weigh 94 kg, 104kg with all my kit. The bike weighs 69kg. I believe a 30mm sag is the ideal and 130mm of travel. I'm assuming travel is worked out by the gaps between the coil and the company making them will work this out. 

When calculating the required Spring rate do I combine all weights together 
So 173kg / 30mm = 5.76kg/mm
Is this correct? 

And how do you calculate spring rate for front forks? 

This is driving me potty and I don't want to order the wrong springs so I would really appreciate any help. 
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Pete 86 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pete 86 Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2020 at 09:07
Ok mate so 30mm rider sag is about in the middle so that's the right place to aim for.

1MM of preload on the front springs is usually around 1kg. 1 turn is usually 1mm/kg. Let's assume your bike is the same?.
So you need to pop the top off your forks and see how many MM the spring protrudes out of the forks.

Then you can see how many MM/KG the spring is pre-loaded to get the cap on.  
That number is your starting point.  "You can take that number off your full weight because you need the same amount of KG body weight to overcome that number.

You still with me?

Now you need to add preload to support the weight left over.
If you cant reach 30mm rider sag with the preload adjuster fully home then you can add the amount of pre load turns (mm/kg) to the amount already on the spring and then see what's left. Like before.

See how much sag you have left and take off in mm to 30mm.

Then you need to add the surpless mm to the preload number  you have And that number will will represent  mm or KG you need on your spring. Then you can play with your pre load either side of the centre point.Remember 1mm is 1kg.

That should give you the kg number you need for your body weight.

Make sense ??
Get your tape measure out and a pen and note book.

Try setting the bike to take your weight with what you have already.
When you have done that check the free sag (no) rider.  If it suspension topps out under its own weight then you need a stiffer spring. Too much pre load to !
If you have loads of free sag then a softer spring for the lighter weight.

That's all I have for you mateThumbs Up

My head is now fried, I'm going back to bedWacko
 
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Popparks View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Popparks Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2020 at 11:05
I was just about to reply to this then read Pete's post. That is exactly what I was about to say to the letter!!! 🤯
What Pete said👍£
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Pete 86 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pete 86 Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2020 at 12:41
Cheers popparks.  I thought I wasn't too far away. It's quite tricky to try and put it into words. Thumbs Up
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Sam.moz86 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sam.moz86 Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2020 at 19:49
Pete that's awesome cheers, the only sticky point for me is the bike is totally stripped down and the forks are stripped. 
Cracking write up first thing for a Sunday morning, you clearly didn't drink enough alcohol last night. LOL
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Pete 86 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pete 86 Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2020 at 19:53
 ahh, make it your last job.
You can pull the springs out with the forks and wheel bolted in.
I'll make up for the lack of pop toniteCool.
I'll deal with the consequences tmrw at workLOL

Just bare in mind that these procedures are for sport bikes eh.
Might not apply to your bike because it's an off roader and they have far more travel eh.
Proably have 60-80mm rider sag eh.
So a drastic spring change is proably req to met 30mm .
AND a good 10weight oil at least.
Or mix a 10 and 15 weight to make a 12.5w
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badapple View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote badapple Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2020 at 20:47
Hi sam where you been buddy?
I started out with nothing and I've still got most of it left
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Sam.moz86 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sam.moz86 Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2020 at 21:11
Hi Adam, 
Just been a little quiet lately and using Faceache a lot. Also lost my mojo with the bike. 
Spent a bit of cash on the Aprilia recently to try and re lite my fire, but it had other ideas and developed a misfire and splutter Angry

So another project came in to keep me busy. First time doing a complete strip down, re paint, freshly powder coated frame etc. Just the suspension that's giving me a headache. 

How's things? 
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badapple View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote badapple Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2020 at 22:47
Ah cool I only go on when I've got parts to sell sounds like a nice little project though. They can be a fickle beast at times that's for sure. All good here bud thanks for asking. I don't actually have an ape on the road anymore but have started breaking them since my missus killed mine long story. Just finishing off a gen1 trackbike that's for sale and I ride a 675 Daytona on the road and ZX6R on track. You still doing trackdays or is it pitbike racing only?
I started out with nothing and I've still got most of it left
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sam.moz86 Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 07:17
Sounds like you're keeping busy in the garage then. 

No TD's this year unfortunately hence the little pit bikes. Get the same buzz for a fraction of the cost. Huge grin factor. And if I can mail this little RM it'll be even better. LOL
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