FORUM GODFATHER.....R.I.P. PAT
Join Date: Jan 2006
Location: Evanston IL USA
Epiphany about handling
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.