Alrighty then, you guys sound like you know what you are talking about .
From the wiki site, Amontons' Second Law: The force of friction is independent of the apparent area of contact.
So no matter the size of the contact area the amount of static friction is the same. ?
In other words, a kid on a little narrow sled will start sliding down a hill as easily as if he were on a big wide sled.

Those KX friction plates are like $18 apiece on Bikebandit. $18 x 7 = $126

Good info on the online clutch videos. I will look them up.

Thanks for the good info everybody, makes me glad I got out of bed today.
Dan

 

Dan,
Theoretically, yes. Provided the coefficient of friction is identical between the contact surface and the narrow and wide sled material. And "start sliding" is key for the static friction (starting to slide). Also, provided mass between both sleds & kid is the same. Sled on snow will throw in a curve ball as the narrow sled (or runners) will melt the snow easier and change the coefficient of friction.

Way back when dinosaurs roamed the earth, in college physics lab we conducted experiments with a piece of 2x4 on the skinny (2") edge and wide (4") edge on a plate, and measured the angle when the piece started to slide. It was different and slid at a lower angle on the skinny side, which theoretically was due to a different coefficient of friction and not on surface area. Then did the same thing with our physics books and noticed some slipped at lower angles than others (mine may have had some sticky dried beer on it).

 

Hmmm.
I just watched the RMATV vid Clutch Replacement Video | Rocky Mountain ATV, Inc.
It said the judder doesn't always go back in, depending on the kit. I put it in and don't remember the EBC kit saying one way or the other.

Any thoughts on that?

 

I'm wrong... read through some old notes for deriving friction coefficients, saw the variable A and assumed for area... not the case lol. Any this link is much more pertinent to motorcycles than wiki... indulge.

Friction (and contact patch size)

 

Just adding my experience here. My clutch started slipping after installing the 350BBK (Bill Blue). I checked the stack height and plate thicknesses and they were within spec. So as a 'cheap' fix, I bought the EBC springs.
https://fortnine.ca/en/ebc-csk-clutch-spring-set-csk144

They worked fine for about 3 months. But this week, my clutch started slipping again.

So I'm going to take the plunge with a full Barnett kit (although I seem to be the first?)

Kawasaki KLX250S (2006-2014) - Barnett Tool & Engineering

Yes, I know it's 2x the cost ($200 CAD vs. $100 for EBC DRC + Barnett springs) but it's got kevlar!

 

This was Just talked about on the ADVrider forum here:

Long term KLX250S review | Page 741 | Adventure Rider

Incase you weren't in on it, or haven't seen it. Good info.

 

Thanks Werloc.

I just read the posts on ADVrider. From the linked Youtube video, it would appear that my plates are 'contaminated' as I was using 100% synthetic oil. Bill Blue recommends Castrol Actevo (which is semi-synthetic), but I didn't make the switch until after installing the BBK.

So I'm back to needing new clutch friction plates... There seem to be two popular choices:
1) EBC DRC212 kit with Barnett springs
2) KX125 plates with the judder spring removed.

But I can't seem to find any reviews of the Barnett plates! They seem popular on other bikes, but nothing mentioned for the KLX250s.

So I guess I'm willing to be the guinea pig for the full Barnett clutch unless someone can tell me they are junk.

 

Not all full synthetic oils are problematic, just the ones that have friction modifiers. Something like Shell Rotella T6 is a full synthetic that works great in motorcycle applications.

 

I was using Mobil 1 Racing 4T in the summer and Amsoil in the winter. Both are "wet-clutch compatible" JASO MA/MA2 oils.

 

It's done. I'm now running the full Barnett kit: plates, friction plates, and springs.

First impressions are good. There is no judder added (which I've experienced in other 'performance' clutches).

Here's the stock clutch. Notice the top friction plate sits in separate grooves. This keeps the pack lifted up so it doesn't hit the bottom of the basket.


And here are the stock plates removed. Notice the dimpled surface on the plates.


Next we have the Barnett friction plates. These have much more area than stock as the pads are larger. Per instructions, i marinated these overnight in some delicious Castrol Actevo.


Here are the Barnett plates. Not too interesting. However, they lack the dimpled surface of the OEM plates. I wondered if this would reduce friction, as the surface is more rough on the OEM plates, or if it would increase friction, as less oil would be trapped between the friction plates and the metal plates.


And finally we have the likely culprit: springs. Well there's the problem! The EBC springs are noticeably thinner gauge wire than the Barnett springs. This results in fewer turns (EBC = 9 vs. Barnett = 8), and a stiffer spring. Also, the Barnett springs were 1mm taller.


I'll come back to this thread in 3 months or so with an update.