Lockup clutch spring pressures

Jeff, If you are running 1150 primary gearing then around 220lbs of launch pressure and a maximum of 1.5 to 2 grams of weight on three fingers with the other 3 no added weight at all. This should get you started.

If you are running the popular 750 primary ratio then start at 280lbs of spring pressure and about 3.5 grams of weight on 3 fingers only.

This should be a good baseline to get you started.

   I meant the actual total static spring pressure provided by the 6 clutch springs.

That and the weight added to the arms for the lockup.

I just dont want to spend the first weeks of the season stumbling for a baseline clutch setup. I can then make changes as I figure out what the bike wants.

I have set these things up before but never on the big tire.

I appreciate the help.

 

Also, it does have the 1100/1150 ratio.

The bike/rider will weigh about 610 lbs.

Edited by Fasthouse

 

 If I am planning on running nitrous, will I need more spring pressure/weight?

 I just see a lot of lockup bikes that "slam" at the starting line. Its like they have a ton of spring pressure.  Some even bog real bad.

If your going to have that tight a clutch why bother with the lockup at all?

Or am I missing something?

Edited by Fasthouse

Originally posted by Fasthouse   If your going to have that tight a clutch why bother with the lockup at all?

I agree, You can get just about any clutch to lock up with stiff enough springs. The point of a lock up is to be able to lock up the clutch with softer springs so you wont bog or break the back tire loose on the launch.

... Some tires / suspension require a hit that almost bogs the engine. For thirty maybe thirtyfive years I and many crew guys have been hearing riders / drivers say "it did not feel like my best ET / sixty foot". This is because as the clutch snaps that last little bit of inertia out of the spinning crank mass it gives the tire the best "plant". I did not figure this out till about "87 when I was able to put incremental time slips together with data, but knew somewhat what the driver was saying since "74. The "feeling" is that the engine is too low and feels like it is taking forever to climb out; as opposed to somewhat driving through the tire and or clutch.

 

  Yea, Thats all I am looking for is a baseline.

On the smalltire I just used stock springs and one washer on each arm.

 But that was a street tire and we were using the tire a little. I always wanted to go softer on the spring setting and play with the weight.

The S/C bike I ride now has a slider. Great for short times, great for consistancy,

not so great for reaction times.

With the new Bike I want to try a lockup.

Bill, I might want to take you up on those springs.

Keep the advice coming guys, I am learning a lot!

Figured I may as well add my 2 cents to all these lockup posts.  I did a search and was amazed at how many times this is talked about. 

I have two MRE types.  I use it on an old GS with little luck so far, so take this info for what its worth which may be nothing.  Also, my math may be wrong.....

I started by measuring three sets of springs. 
APE Red, 60 lbs @ 1"
GS head spings (i think), 43 lbs @ 1"
Schnitz Yellow, 41 lbs @ 1"

Weighed the weights.
Stainless nut with nylon insert 3.5622 grams
Bolt 6.0652 grams
Washer was 1.1044 grams
I tossed out the weight of the arms and used it for some saftey factor.

Taking some rough numbers off the lockup, the center of the hub to the center of the weights is about 2".   The center of the arm to the center of the weights is about 0.9".  The length of the arm to where it hits the button is about 0.5".

I use the 1100 gears, so the crank has 49 teeth and the basket has 87.

With this you can calculate the force added to the pack from the weights.
Just convert the grams and inches to pounds and feet and use:

(Engine RPM * (basket teeth / crank teeth))^2  * 0.000341 * (weight of washers + nut + bolt) * the distance of the weights to center of hub * lever ratio of arm.

^2 is squared
0.000341 is the coefficient of centrifugal force


So, if its not spinning there is no weight. 

In my case, using 4 washers on each arm is about the following:

500 RPM = 1.2 lbs
1000 RPM  = 5.0 lbs
2000 RPM = 20 lbs
4000 RPM = 79 lbs
8000 RPM = 317 lbs
9000 RPM = 401 lbs

So, If you used three APE red springs thats 3 * 60 lbs or 180.  This is added to the
centrifugal force.   In my case that would be more than 600 lbs of force (remember I did not add the arm weight)

The problems I have had are finding a good balance.  I use an air clutch lever and have played with slowing down the release rate to help dampen the shock, but still give me high enough static pressure to do a burn-out in third. 

One thing that does make a lot of sense to me is that the track prep is key.  How the pros figure it out is far beyond me.

Originally posted by geek (Engine RPM * (basket teeth / crank teeth))^2  * 0.000341 * (weight of washers + nut + bolt) * the distance of the weights to center of hub * lever ratio of arm.

Need to multiply the weight by the number of arms, in my case 6.  Then you should get the same numbers.

I had often thought about sticking a tape recorder on a bike but not to listen to it.    Those new MP3 recorders could be mounted to the frame real easy.   Not sure how it would help with clutch tuneing.

A few people asked about the program so I am making it available for free.  I cleaned it up a bit.  Still no great features. 

dickey.intell-a-sys.com/turbo/lockup.exe

The program is built using LabView 6.1i.  You will need to download the LabView runtime engine in order to run it. 

http://digital.ni.com/softlib.nsf/websearch/57F2E10F3CD9306B 86256B4100683DE1?opendocument&node=132070_US

Lots of good discussion regarding static spring pressure and lockup weight, but no talk whatsoever about the counter-weight springs. I think jackinzoar was referring to this in one of his posts.

So what springs do you use for the counter-weights? Maybe the term "counter-weight springs" is wrong, I dunno. What I mean is the weight under the lockup fingers. The MTC lockup I have has 6 fingers. Came with 5# springs on 3 of them and 7# springs on the other 3.

Turned out to be all wrong for my app. I run about 324 pounds of static spring pressure and *lots* of weight on all 6 fingers. The counter-weight spring selection was critical for my application.

--jack