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FORUM GODFATHER.....R.I.P. PAT
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Discussion Starter #1
Somebody at the DL650 Yahoo group wrote about the fairing being involved in high speed instability of our bikes. That lit a light inside my head. I'm copying my post on the subject here.

> At 01:56 PM 8/14/2009, Bryan Whitton wrote:
>>I have been building race bikes for decades and I have never seen a bike
>>become more stable by reducing the trail which sliding the fork tubes up
>>into the triple clamp does. As far as raising the back end. The effect on
>>the front end is the same; you are reducing the trail and making the
>>handling faster and/or less stable. If you lower the front and raise the
>>back you are making it even worse. This is why road race machines are
>>required to have fork dampers; they are basically unstable under certain
>>conditions. Steep rake and short trail numbers make them so.
>>
>>
>>Why would you expect the DL to become more stable by doing this?


I could have written exactly the same thing. All that is true and something we need to understand so I'm not trimming any of it. I like the idea of the fairing being involved. In fact, it may be the most important idea regarding V-Strom stability I've ever read and I've never seen it brought up before. I had a Yamaha XS1100E with a Vetter Windjammer that could lift the front end so much at speed that going much over 100mph would lose all steering input.

The talk about weight distribution needs to be addressed though. Raising and lowering the front with respect to the rear has very little effect on weight distribution. It has a big effect on rake, trail and the angle of attack of the fairing through the air. I recently went from 19mm lowering at both ends to 15mm down in front and stock in back. The former felt better than stock and the latter a lot better at normal road speeds.

I had my only crash involving injury in a quarter million miles of riding on a 2005 DL650 with stock suspension settings when it went into a tank slapper at an indicated 119mph. I've always attributed that to the aerodynamics and weight distribution of a tall windshield and three pieces of luggage. Now I'm thinking the fairing was also involved.

It appears the best way to set up our bikes for most conditions is the drop the front end 5-15mm with respect to the rear. Lowering the front seems to be one good way to do that. It also clamps the fork tubes lower to reduce front end flex. A fork brace will help too. Raising the rear won't do that but will change the fairing angle. Be aware that change of fairing angle that feels so nice at most of the speeds we ride will give the bike an even more unstable geometry at high speeds due to rake and trail reduction.

I've touted the benefits of a Scotts steering stabilizer ever since I put one on after that accident. I've also quit riding over 100mph. I used to do it once every long trip out west to see how fast the bike would go when on a straight run of Interstate with no cars or overpasses in sight. Some results were flying the front end of the Yamaha, breaking a rotor wire on a BMW R90S, breaking or loosening final drive fasteners in the same Beemer and crashing a V-Strom. It isn't worth the risk. Do lower the front a bit, DO add a Scotts and keep the speeds reasonable. Our bikes are not sport bikes. The frame and suspension are designed for handling rough surfaces without bottoming out, not for high speeds on pavement. The fairing is designed for upright rider protection, not for lowering the CD for a crouched rider.
 

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Nice read Pat, thanks for taking the time to post it. One question, with the front lower is the bike still neutral when accelerating in (or out of) a corner?
 

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FORUM GODFATHER.....R.I.P. PAT
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Discussion Starter #3
The steeper rake and shorter trail make the bike more agile at lower speeds but more unstable at higher speeds. You'll probably like the lower front for cornering.
 

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I want my bike as tall as possible so I have never lowered the forks (by raising then in the triples) but I have always thought such small changes results in small effect in handlinfg. I know the effects are real, just tiny.

Has anyone actually measured the difference in rake/trail by raising fork tubes 5-15mm? I'm no mathematical genius but it will make only a very tiny difference. I imagine you could feel the difference, but is it really a dramatic change?

I'd like to opine that the stock DL1000 is quite a competent handler right from the showroom, and is a bike able to change lines in a curve with the best of them. It may not win any roadrace championships, but it is an excellent handler in the real world, and strikes a good balance in being able to handle well in near every condition you are likely to find, this side of serious offroading.

I rub the edges off my tires every chance I get and the confidence level on my Vee is very high. I set it up for sport touring and use a KLR650 for severe trails. What a great combination of abilities--I feel like I've never been so well-mounted in my life. It gives me a new outlook on motorcycling. I think I am a more enthusiastic rider in my advanced age than when I was a kid.
 

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FORUM GODFATHER.....R.I.P. PAT
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Discussion Starter #5
Lowering the front a bit is a very easy and free modification. Why don't you try it and see if you notice a difference. That's what counts. I tried it and it makes a noticeable difference to me. Just keep the speeds reasonable if you don't have a steering stabilizer.
 

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Cowboys aint easy to love
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Short version: Why did you choose 15mm to lower your front?

Long version: What was the method or criterion that caused you to select 15mm as the optimum change in front end height?

Followup question: Was your weight or physical profile a factor in your choice?
 

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Hi Pat,

Interesting comments! I have not doubt the fairing, in particular the part under the cowling/above the radiator has a detrimental effect at high speed stability. The part I mention looks like it is designed to provide lift at higher speeds. Has anyone tried a naked strom at speed?

As far as geometry: What is the rake and trail for a sport bike? What is it for a Dirt Bike? How does the Strom compare? With stock settings, how does stability compare at high speeds with the sport bike, trail bike and Stroms?

..Tom
 

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Stock numbers for a few Suzukis:

DL1000
Rake: 26.5 degrees
Trail: 110.6mm

DL650
Rake: 26.5 degrees
Trail: 110mm

GSX-R1000
Rake: 23.8 degrees
Trail: 98mm

Hayabusa
Rake: 24 degrees
Trail: 97 mm

Boulevard M109
Rake: 31.25 degrees
Trail: 111.76

Boulevard C50
Rake: 33.20 degrees
Trail: 141mm

Bandit 1250
Rake: 25.2 degrees
Trail: 104mm

SV650
Rake: 25.0 degrees
Trail: 100mm

DR650
Rake: 28 degrees
Trail: 105mm

DR-Z400
Rake: 27.4 degrees
Trail: 109mm
 

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Lowering the front a bit is a very easy and free modification. Why don't you try it and see if you notice a difference. That's what counts. I tried it and it makes a noticeable difference to me. Just keep the speeds reasonable if you don't have a steering stabilizer.

I always read your posts with interest, because you have so much knowledge about our bikes. I have appreciated your information and have learned a great deal from your posts. However my advice to MOST casual riders is leave the suspension alone. The bike is well set up for most riding conditions that the average rider will incur. Neither the Wee nor the Vee is designed to be ridden at 119 miles an hour. I feel very uncomfortable at speeds approaching 100 mph on my DL, it just does not feel stable.

My advice to anyone that wants to ride a bike at those speeds is buy a bike designed and set up for it. 100mph on a Gixxer or R1 is comfortable and predicitable, or any bike in that category. But I really don't feel that our suspension, brakes, frame etc. is designed for excessive speed. Maybe that type of speed for our bikes is asking too much without some major attention, and modification to the bike.

Safe riding.
 

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FORUM GODFATHER.....R.I.P. PAT
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Discussion Starter #10
I learned that lesson the hard way and am on the same page. Except for the bad habit I used to have of seeing how fast the bike could go one time on each long trip, I ride at the speed limit. It will be fine if I never do 100 again. Some readers here will continue to do high speeds though so I threw in the warning that anybody feeling the need at least have a steering stabilizer installed. At sensible speeds, I find dropping the front a good change. I believe Suzuki set up more rake and trail in the stock bike just to make things safer a 100mph or so. They also limited the top speed the Vee will go unrestricted to little more than the Wee can achieve. Our bikes are not designed for more speed than they can handle stock. They are set up as dual sports, not pure sport bikes with more aerodynamic fairings, crouched riding position and less suspension travel.
 

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random thoughts...shut me down

Rake is measured from the horizontal plane. From that I suggest that shortening the forks by 15mm only will accomplish this. By shortening the forks 15mm and lowering the the rear but however much coresponds to that to maintain a base line parallel to the original horizontal plane, rake and trail will remain constant but the bike's wheelbase will be shortened (I'm not aware of any adjustable lowering links, so it's more a case of lowering the rear and adjusting the front to match). Short bikes are pretty hyper though, see Buell.

Still awake? good. For a while I had 2 KLR's. One was stock height and one was lowered 2" fore and aft. The lowered bike was much, much more fun on the street (reason...see above even though I can't say I ever measured)...confirmed by random quanitative testing, ie.,hopping from one bike to the other.:rolleyes:

I remember reading a road test of a Yamaha RZ350 (years ago) and the comment was made that it was one of the easiest bikes you could ever drop. I don't remember the actual rake and trail, but I'm betting the rake was pretty steep and the trail was rather short...great stuff on the track.

Here's another thing to throw in. I sugest that either the Vee or the Wee can tollerate a certain degree of reduction of rake and trail due to the 19" front wheel. I went from a sport bike to a Vee and was immediately impressed by how planted (and how easily corrected) the bike felt in fast long sweepers.

And for my final scientific blah blah, I should add that from day one I have set the forks on my Wee as high as I can, that being where they contact the handle bars. Stock height in the rear. I like it that way.
 

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Also note

Rake, trail, and handling are moving targets. When you twist the grip the front suspension extends, the read squats, and your rake and trail change. When braking hard, the reverse occurs. In other words, the attitude of the bike in relation to the ground changes the suspension stats. Of course, rake and trail don't tell the whole story. If your frame or forks are a bit willowy (like ours) then some additional stabilizing will be required. I don't frequently top 90, and then only for brief periods, so dropping the front suspension and raising the preload give a bit better response, and since I don't go fast enough to wake up the frame/fairing gremlins that's OK.
 

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I agree that the fairing has a lot to do with things. I've always said this after I discovered a huge updraft that comes from the fairing. Just ride at speed in a t-shirt and see what happens. The t-shirt will be around your neck, that's what. Everyone is rightfully concerned about the buffeting around the windscreen, but I think the updraft effect is more important for high speed stability, more than rider comfort.
 

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Anyone wanna buy a wind tunnel and get that super cool paint used to calculate airflow?
 

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Safety First

Thanks for the advice. Anything safety related is most welcome. Spending my summer on crutches after a Wee wreck has taken a lot of fun out of it.
 

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There's no question about the fairing having a huge effect on handling.....we used to equate it to putting a barn door on top of your handlebars and trying to dive it into a corner. You can feel the difference quite easily and it takes a lot more rider input.

I raised my forks as much as an inch and a quarter and the effect was dramatic. Where it used to get squirrelly at 90, now it was getting even more unstable at 75! Increasing rake will net you high-speed stability at the cost of handling. The moving target is the compromise of stability with handling.....something that seems rather elusive with the combination of a 19" hoop, a second rate frame and just ok quality components. I had bikes back in the 70's (that I didn't race) that handled much better but they also didn't track very well at high speeds. Right now, my forks are up 5/8" and my rear preload jacked to the max...makes it tough to reach the ground since I'm only 6' tall but it handles it's best with that setup. I also have a fork brace, .95# springs and a Give 265 windshield. Ever since I got the bike it's felt as though there was some kind of disconnect somewhere in the frame...like it was acting like a hinge. I don't know if it's the offset of the rear wheel or in the swing arm but it's always been there. Maybe one day I'll rip it all apart and see if I can find the gremlin.

jeff
 

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I raised my fork tubes 1/2" and found that in aggressive cornering, the bike was falling into corners too fast, and causing me to clip the apex. Raising the tubes back to stock fixed this. I think too many people get into analysis paralysis by reading the internet and adjusting the bikes without understanding what their bikes are doing below them. Its all about what feels right to make you corner faster and more confidently.
 

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I raised my fork tubes 1/2" and found that in aggressive cornering, the bike was falling into corners too fast, and causing me to clip the apex. Raising the tubes back to stock fixed this. I think too many people get into analysis paralysis by reading the internet and adjusting the bikes without understanding what their bikes are doing below them. Its all about what feels right to make you corner faster and more confidently.
I originally lowered the font of the bike/raised the forks about half an inch to help me with the way the bike and I reacted to being in the wake turbulence of trucks. It helped me greatly there and (to me) improved the handling and turn-in tremendously.

This is an example of different strokes for different folks.. one man's too-fast turn in is another's great improvement in handling!

..Tom
 

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I just had another epiphany

I think there's a relationship between fork length and Jeff Kushner's avatar.
 

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ST1300

riders often talk about instability at 120mph. A friend of mine experimented on the Autobahn and found that if you lowered the windshield to the lowest setting (electric adjustment), stability returned and he topped out just over 130mph.

My view is that a fairing/windshield that works well below 100 mph will tend to unload the front at 100+. Luggage at the rear will also. So, I think all of GWs points are well taken. If I were intending to do 100+ I would set the bike up there and take what I got at lower speeds. Actually, for 100+ I'd buy a good crotch rocket.

I had mine at 106 (actual) with the big JCW topbox and what I later found to be a rear tire with low pressure. The bike felt fine, but that's just not my thing. Racetrack stuff really. My world is below 100.
 
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