| Author |
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Cowboytutt
| | Posted on Sunday, July 18, 2010 - 10:48 pm: | 
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Thanks Phil. I'm no expert here at all, just sharing what worked for me. Please let me know how it works out for you. I didn't start working on mine until about 1K miles and here at 3200 I've pretty well got it sorted out but I have worn out the Pirelli rear tire. Figures! -Tutt |
Rodrob
| | Posted on Monday, July 19, 2010 - 12:21 am: |
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IMHO, there is a huge part of the equation missing from this discussion; Swing arm angle, which is at least as important as fork height, as they both interact and effect each other.
When you lower the fork tubes, you increase rake and trail. when you increase swingarm angle, you decrease rake and trail. Either can dramatically change the geometry and handling of the bike. This is critical to know because too little swing arm angle can have devastating effects on in turn and exit handling. You can increase swing arm angle directly 3 ways, increase spring rate, or preload, or shock length. IMHO 33mm of rear rider sag is too much (too little swingarm angle) for high performance handling on an 1125r. But if you want a cushier ride with that much sag, you must increase the swingarm angle so that you don't end up with a bike that squats, wiggles and wanders in the middle of and exiting turns. So how do you measure it? it's not easy to do directly, but you can measure the distance between the middle of both shock mounts since the angle is a function of that distance. I need to double check my measurements but I believe that I started at 325mm and ended at 335mm. That 10mm change made my bike handle like it's on rails. This adjustment was done after I set rear sag and preload by adjusting the length of the shock. By doing so, you will maintain your preload and sag, but get the ride height and therefor swingarm angle back to where it needs to be. |
Cowboytutt
| | Posted on Monday, July 19, 2010 - 06:18 pm: |
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Hi Rob. You are of course correct and if you raise rear ride height in any way you decrease rake and trail, conversly i.e. lowering the rear, the opposite.
The 1125's use a 21 degree steering angle with a scant 3.3" of trail. This is very aggressive when you consider the Yamaha R6 uses 24 degrees and 3.8"s of trail and its still considered one of the quickest handling 600's out there. For myself, I would not recommend changes that make the Buell's handling any quicker than it already is but it depends on the type and condition of the roads or race track you are on, I guess. And of course your personal preferences as to what inspires confidence and works best for you.
My friend and professional racer Chase McFarland runs an adjustable, chain drive conversion swingarm that is longer than stock and has an Ohlins steering damper so it seems that at least one racer is looking for more stability at track speeds.
Philp said in his original post that his bike felt stable in fast sweepers but was pretty bouncy in slow, tight turns. He is at the very light end of the weight scale for the spring rate and this may be part of the problem but hopefully we can help him out.
I just want to say again that I'm no expert on this subject and I've been struggling to find a way to make my bike handle well but also be stable for the bumpy roads I ride that will allow me to take advantage of the CR's amazing cornering clearance. My only intent was to share my personal experiences as to what has worked for me to help another. I very much appreciate your expertise and what others have to say on the subject. I do not think the the stock Buell shock is adjustable for shock length/ride height but it would sure be a nice feature to have.
Regards,
-Tutt |
Rodrob
| | Posted on Tuesday, July 20, 2010 - 08:59 am: |
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Tutt,
My post was not intended to be a criticism of your experience and techniques. If it came off that way, I apologize.
My intent was to point out that once one begins changing the geometry of the bike in one area, one must consider how it effects the others.
From Michael Richter at Erik Buell Racing - "What is the free length of the shock? I need the length from center to
center of the mount holes. Most likely around 325-328mm? It's pretty common
to raise the rear ride height of the bike, but it can quickly be overdone
and make the front feel vague."
Also - " The Buell chassis works differently than others out there. Do NOT listen to what
others say, especially numbers off any other brand/model of motorcycle."
I rechecked my numbers and I went from a shock length of 315 to 325.
I am no expert either, but I am learning fast on the track. Handling is a very personal experience. What is right for one may feel awful to the next. Keep up the good work and advise.
Cheers,
Rob |
Highlander51
| | Posted on Tuesday, July 20, 2010 - 10:39 am: |
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Rob,
I may be missing something here, but do you have the stock shock or a after market that is adjustable?
Also if some here recall there is a different front spring rate for the early 08's that is stiffer. I'm 200 lbs and not until I softened up the front did the bike start to work. This is street set up, tight canyon and uneven surface type stuff, not race track.
Mike |
Rodrob
| | Posted on Tuesday, July 20, 2010 - 12:02 pm: |
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I have the Ohlins TTX on the rear and the Showa Race Cartridge inserts from Erik Buell Racing. For what it's worth, I hated this setup when I first installed it. Now It's working much better for me, but I think I might have the Ohlins re-valved for the track.
I thought I was over sprung on the front and ordered lighter springs. But after running a zip tie on the fork tube, I found that under heavy braking and cornering, I was using 116mm of the 120mm travel available. Softer springs would bottom out, so I just had to get used to it.
I have to say that my bike is not that comfortable to ride until you start really laying it over, at which point the comfort comes from the reliability and predictability of the handling.
Are you sure that the stock shock has no length adjustment? |
Highlander51
| | Posted on Tuesday, July 20, 2010 - 12:37 pm: |
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Rob, I don't know if the stock is adjustable or not. I don't think so from looking at it. I live in the Valley also, so I'm sure we ride the areas, or do you just use your bike for the track?
Mike |
Rodrob
| | Posted on Tuesday, July 20, 2010 - 12:51 pm: |
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I try to do the Rockstore, Snake and Piuma - Stunt once a weekend to try and get my old ass in shape for the track. It's an uphill battle. Happy to hook up. |
Highlander51
| | Posted on Tuesday, July 20, 2010 - 01:00 pm: |
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Sounds good. I'll shoot you a PM later , I have to get going to work.
Mike |
Cowboytutt
| | Posted on Tuesday, July 20, 2010 - 10:41 pm: |
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Thanks for the sentiment Rob. I use top-of-the-line extra long Ohlins shocks on my HD Street Bob to improve ground clearance, ride quality and to quicken front end handling and they are truly a great shock. Very supple yet controlled.
Its fascinating to me that Erik Buell Racing would recommend raising rear ride height. I do think lowering the front forks flush in the clamps DID act as its supposed too IMHO.
But as I previously stated, I think I want to raise them half-way and split the difference. I think that will work best for me.
There may be a difference between track use on smooth pavement and bumpy rural roads.
I'll be meeting Chase McFarland at Laguna Seca I think, and Sean Higby for sure. I will ask them what they did to set up their bikes.
-Tutt |
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