Yamaha SR500 & SR400 Forum

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PostPosted: Tue Mar 02, 2010 1:44 am 
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Hey Guys!

The engine is where I want it to be now so I'm moving onto the suspension.

I've got clipons on the bike mounted just below the top triple clamp and rearsets that probably aren't as "rear" as they should be but are a good compromise in comfort. Anyway, when coming into a corner and getting onto the brakes hard the front end dives a hell of a lot and I can feel the entire attitude of the bike shift towards the front. Other than that, the rebound etc seems fine.

I've also had an odd feeling like the rear of the bike doesn't have enough traction or a planted feel when coming out of corners hot - always downhill. At first I was thinking it was a problem with the rear shocks, but when I think of the front end dive thing it makes sense with the weight shifted forward there's no weight on the rear, hence the "light" feeling. I think I jumped the gun and bought some 2nd hand SR Ohlins from Japan. Interestingly, I don't think they have the rebound adjustment that the Ikons have.

So I guess I'll start with the front? I've got Ikon progressive springs and 15w oil in there at the moment. I haven't had a chance to measure static sag at the front end etc as yet but hopefully should have a chance soon. At the rear there is no static sag at all - so I might have to go some softer springs?

I'm on a bit of a budget as I've just picked up some second hand Ohlins from Japan. But is it worth doing myself or taking it to someone? People talk about suspension like it's some kind of black art... but I've been doing some reading on it lately and it doesn't seem all that complex - at least on an SR.

So... in a nutshell....

How do I stiffen the front end so it dives less under braking? What fork springs are you using?

Thanks in advance guys!


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PostPosted: Tue Mar 02, 2010 3:04 am 
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The first thing I would do would be simply to increase the amount of oil in the forks. Doing this decreases the volume of air above the oil so that it compresses quicker and therefore will stiffen the suspension sooner.

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PostPosted: Tue Mar 02, 2010 3:50 am 
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Alright, I shall do! It was around 200mm that came out before (I think) So how much more do you think would be a good idea?


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PostPosted: Tue Mar 02, 2010 4:12 am 
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Did you mean 200mm or 200ml?

Sounds like you need to first check then set the oil level by measuring its height. Once that's done you can adjust it in increments using a syringe. Saves pulling the forks out each time to measure the level.

No sag in the rear is not good. I have the same problem at the moment that's why I've got some Ikons coming from SOS Suspension next week (hopefully). Sean at SOS did mention that he'd expect to set sag at about 25% of travel, both ends. Didn't have time to discuss it in detail at the time but I'm assuming he meant rider sag.

That's a bit different to what I set the enduro bike up to but it's got about 300mm each end.

Rob

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PostPosted: Tue Mar 02, 2010 5:00 am 
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To be honest Robem, I completely forget. For some reason 200 rings a bell. But whatever came out, I measured in mm and put back in.

Let me know if you have any static sag in the new shocks. I've a funny feeling that a standard setup bike would be perfect with my Ikons, but there's virtually no weight on the backside of my bike. I might have to go with a softer spring, but I don't want the thing to be a boat!


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PostPosted: Tue Mar 02, 2010 7:30 am 
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Don't worry Marlon ,after a few years hitting it hard like you guys do ,the bike will sag all by itself with the 10-15 extra kgs that ends up on your butt(& I'm not talking about one of your rifles) :lol:
Getting married & having a few kids will do it too !
I'm with Ken on the more oil ,or some guys weld up one of the bleed holes(or even weld them all & redrill them smaller) Even a less viscosity oil .
Suspension is a field all in itself & as you said now that your engine is better in the goa dept now you need handling & woa.
What does Carl, Rick or Andy do for these problems ? Cheers Dave

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PostPosted: Tue Mar 02, 2010 7:55 am 
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How about the same amount but fork 20 weight?

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PostPosted: Tue Mar 02, 2010 7:57 am 
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Dave - I've still got a couple of years left in me yet, although my gut does seem to be catching up on me!

Staffy, i thought heavier weight oil mainly affected the rate of rebound. I'm probably wrong. :oops:

I've also noticed that Racetek sell gold valves and emulators for the SR as well. Oddly enough, it lists the SR500 and SR400 specifically on their site, with settings for each. Hmph. After a bit of googling Mike'sXS sell copies of these as well for around $50.00.

ha, there I go again, trying to throw money at the problem!


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PostPosted: Tue Mar 02, 2010 12:59 pm 
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Two adjustments can be made to forks with the fork oil. Oil level and viscosity.

The level determines the amount of air trapped above the oil. Remember that air is a TRUE progressive spring under compression. With less air volume at the top of the forks, The air's spring rate rises quicker for a given amount of fork compression. Air caps are nice but only act like a preload on a normal coil spring. The easiest way to adjust the oil level is to use a syringe attached to a tube with an adjustable clip to control the amount the tube reaches into the fork tube. Measurements here are linear (inches or millimeters) and not volumetric (ounces or milliliters).

Oil viscosity will have an effect on the forks dampening over the whole range of travel. Both compression and rebound. As the name would suggest, dampening controls the action of the spring (air or coil) but does not support the weight of the bike. That would be the springs function. The various holes top and bottom in the damper rod control the flow of the oil as well as any tapers on the OD of the damper rod as well as the ID of the damper rod.

Blocking off, enlarging or moving the location of damper rod holes and/or changing the damper rods various diameters both inside and outside is very model specific and best left to someone that thoroughly understands how forks work and knows what they want out of them.

Most people can get a very acceptable front fork action just playing with the coil spring, oil levels and viscosity.

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PostPosted: Wed Mar 03, 2010 12:22 pm 
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Blocking off, enlarging or moving the location of damper rod holes and/or changing the damper rods various diameters both inside and outside is very model specific and best left to someone that thoroughly understands how forks work and knows what they want out of them.

True enough I suppose, but...after remembering an obscure 'Minton' article regarding Yamaha XS650 mods, I followed his advise & blocked off two of the four holes (the upper ones) on both of my SR's damper rods, added 1 1/2" of preload spacers & made up some air caps. The difference over stock was dramatic. Brake induced dive was greatly reduced and the fork action over 'regular' road surfaces was much improved (no more porposising). I believe I was running 15wht. oil too.


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