Cornering a Vincent

[davidd]

Recently in the Greg Brillus Racer thread there has been some discussion of cornering. Style is a personal thing, but so is how you set up your bike. I found that road racers tend to not want to drag anything on the bike because it tends to disturb the handling rather than improve it. Of course, with street bikes you have to make some compromises that you probably would not make on the track.

I wanted to check the racers clearance. I took the springs out of the suspension, front and rear. This gave me the "worst case" scenario.

I lowered it to the side with a chain hoist and I tied the front end to the band saw to keep the wheel from flopping. I got 45 degrees on the digital level.

This is the view down there. The silver peg is the foot peg. The one further back is for the track stand.

I mocked up an exhaust pipe to see where it would fit and it did not. You have to run a high pipe or a pipe under the center line of the engine. It is nearly impossible to run under the engine because there is a catch pan requirement and there is a silencer requirement. There is just not enough room under there.

This shows how close the 2" pipe runs. Where do you go to clear the shifter?

Finally, it is good to be able to shift even if this is the worst case scenario. I am rotating the shifter down.

The other side is a little more straight forward. Surprisingly, it is tighter even though I narrowed up the primary case.

It doesn't touch, but it is close. I did "high side" once and primary cover was scratched in that area, but it is not a great concern when cornering.

I came to realize that the pegs should never touch down unless you crash. Nor should anything else in my opinion. I found this pretty easy to do in the shop and I learned a great deal by being able to visualize what might be going on.

David

 

[Bill Thomas]

I am no good on bends !, Not Brave, When I built my L/ning rep, 2" pipes, Side by side !, I just put the bike on it's Right side, And thought there is no way anything will touch down.
First race, First bend, Redgate at Donnington Scrape scrape !!, Those pipes looked so good and sounded super, But they had to go. Cheers Bill.

 

[bmetcalf]

So, this is out?

(By the way, if you were wondering, that's not me. It's Stan Hailwood's son.)

 

[vibrac]

Of course static tests assume the track is level, here is Ben finding out its not! Occasionaly he also found the Burman box changing automatically on some corners as well ...

 

[druridge]

Recently in the Greg Brillus Racer thread there has been some discussion of cornering. Style is a personal thing, but so is how you set up your bike. I found that road racers tend to not want to drag anything on the bike because it tends to disturb the handling rather than improve it. Of course, with street bikes you have to make some compromises that you probably would not make on the track.

I wanted to check the racers clearance. I took the springs out of the suspension, front and rear. This gave me the "worst case" scenario.
View attachment 19828
I lowered it to the side with a chain hoist and I tied the front end to the band saw to keep the wheel from flopping. I got 45 degrees on the digital level.
View attachment 19830
This is the view down there. The silver peg is the foot peg. The one further back is for the track stand.
View attachment 19831
I mocked up an exhaust pipe to see where it would fit and it did not. You have to run a high pipe or a pipe under the center line of the engine. It is nearly impossible to run under the engine because there is a catch pan requirement and there is a silencer requirement. There is just not enough room under there.
View attachment 19829
This shows how close the 2" pipe runs. Where do you go to clear the shifter?
View attachment 19832
Finally, it is good to be able to shift even if this is the worst case scenario. I am rotating the shifter down.

The other side is a little more straight forward. Surprisingly, it is tighter even though I narrowed up the primary case.
View attachment 19833
It doesn't touch, but it is close. I did "high side" once and primary cover was scratched in that area, but it is not a great concern when cornering.

I came to realize that the pegs should never touch down unless you crash. Nor should anything else in my opinion. I found this pretty easy to do in the shop and I learned a great deal by being able to visualize what might be going on.

David

Very impressive David (& informative).
I was involved in testing the potential tilt angles of an Army Landrover (Defender type) at an RAF site. We had it over to 45 degrees on a tilting pad before we got it to the balance point where we could move it by hand to rubber cushions on the left & right.
Shown static in your photos it seems an incredible angle of lean.

 

[davidd]

Those photos show some of the problems. If you are grinding through to your polished nails then there is a serious ergonomics problem. The rider doesn't always get a choice. But, you would hate to find you crashed because you chose to ride the bike in a way that lifted the tires off the track.

As Tim's photo shows, often in a race you try something and you hope it will work out. If there is good clearance for not just the track, but that occasion where you might come too close to the curb, you are all set. I remember running a low straight pipe the first time I raced Daytona with the Grey Flash (19" wheels). We entered the track just before the Horseshoe. I went gingerly into the Horseshoe and the pipe began to lift the wheels. A quick change of lines remedied it, but it made it difficult to concentrate on learning the track.

Early days at Summit Point, WV. The first time around I touched the knee to the placement, but the puck was in the wrong place and it was not very comfortable touching down with just the thickness of the leather. You can see that the knee would touch down if further out because I have moved off the center of the seat. This allows the bike to go round the corner with a little less lean. More importantly, if you have misjudged the apex and you are running out of pavement you can keep turning in and not run off the track. Alternatively, if you are straight up and down on the bike in the corner and you have to turn tighter you can hike to the inside and you should be OK. I thought that being able to do these things might come in handy.

The ergonomics of this bike caused the leg to be in a strange position. I had only 11" from the seat to the peg. This is why the puck was in the wrong place and the legs were tucked under too much. I added 4" to the seat height. You can see the G50 poking down and it is the closest item to the ground. It is a center line straight pipe, before the rules required a silencer and oil catch pan.

I should mention that the wheels in all of the above were 18". I ran 19" on the Flash, but I really wanted 18" wheels for the improved handling and braking.

This is the Flash with 19" wheels and a center line straight pipe. It is hard to se withe the shadow, but the even though there is more ground clearance, the pipe is quite close. It gets quite busy under there when you have to add a silencer and a catch pan.

As a result of all the fooling around, the above position became sort of a standard for me. Clubman bars to lower me a bit, both feet on the balls of the foot. This seems necessary if you inclined at all to shift your weight around. Nothing touches and nothing to get trapped.

David

 

[davidd]

I have to mention that I tried moving the feet back and raising the seat. After I crashed and replaced the bars with new Clubmans, I encountered a horrible handling problem. I chased it for nearly two years and could not get rid of it. I was unable to change lines in a corner and as a result I had to be careful about selecting the line when going in. This slowed me down considerably. Some competitors even complained that they could not pass me because I was hogging the line. As the person in front, I was not too concerned with the complaint, but I had tried almost everything and could not get back to the good handling.

Finally, I went to stock bars with the idea of starting over. The handling of the bike changed completely. It would move anywhere I wanted it in a corner and it reduced my lap times enormously.

This is a shot of the first race with the stock bars that restored the good handling. The second race with the stock bars I was feeling very good and the riders who were giving me a hard time were nowhere fast enough to complain. So, it helped us all.

I mention this because the problem took me by surprise. Sometimes if you get an odd response you have to go back to basics and this was it. I often say "Start with the stock bars and move on from there." If you feel the handling going away, go back to stock.

David

 

[greg brillus]

Hi there David, All good points........I would add that perhaps what seems a problem to us does not seem an issue to others........ I too found the clubman bars shifted my weight too far forward which unloaded the back wheel and caused it wanting to slide somewhat, but Phil has found he is pushing the bike hard and causing the front to slide more than the rear. He is keen to try lower forward slung bars like the set up on the Flash at Phillip Island recently, and I was unsure about this due to the lesser room afforded by the coilover up front, so perhaps he might try the clubmans and see what he thinks. I'm now trying to get my head around handling improvements to the slimline Featherbed set up that I have bought unto myself...............Cheers.............Greg.

 

[davidd]

Greg,

I certainly wish that I knew more about this particular problem. Your experience was an important factor in confirming that there was a possible problem with the handle bar ergonomics on Girdraulics. I think the best news is that stock bars seem to cure any problems that might be caused by experimentation. If you think you have a problem it is great to go back to a basic set up that works. I mentioned this problem to Patrick after the IOM race that Bruno ran in 2015. He may have designed his bars with that in mind. I did not want him to waste time like I did trying to figure out an odd and obscure problem that was difficult to pin down.

I felt that the problem I was experiencing was not due to the weight on the front end specifically, but the weight on the bars. It disappeared when I could hold the bars loosely with no weight on the grips, which was supplied by the stock bars. Any excess weight on the grips and it was like steering with an overly tight damper, it was hard to settle on a line and when you did it was hard to change it again. This appeared to me like it was just an oddity of having the bars behind the turning center of the forks, maybe. I felt that I was never able to locate the problem, only the cure.

I did check the weight balance of the bike loaded with me as the rider in full gear. I think it is good to know how much weight is actually on the front and rear wheels with the rider in the riding position. I found that I crowded the tank and that put the weight further forward. I noticed when I lengthened the seat I did not crowd the tank as much, even though I did not feel uncomfortable crowding the tank. It is pretty easy to do in the shop with an old spring scale. Run the front onto the scale and assume the riding position. Do the same with the rear. It is good to have a few hands to help. It can give you a base line if you like what you have. When you change bars, seat or pegs you can weigh yourself again and test your results to the base line.

Phil is very good and he will probably want to experiment with tire compounds to make sure he has the sliding on the front down to something that he is comfortable with. I am not sure I mentioned this before, but the Comet racers seem to respond incredibly well to the lower profile tires. Carleton mentioned this to me again this past weekend. He found a big gain when he swapped to 80's. It was not as obvious to me because I was fighting with this handling problem mentioned above. When I solved that my lap times lowered by a huge amount and I was overjoyed with the handling.

David

 

[vibrac]

If you look at the picture of my avitar you can see back then I was using 'Ace Bars' I suppose they suited me or I would have changed them earlier, except that notch on the battered numberplate reminds me I had already thrown it down the road the week before at another meeting and that was at a slowish corner......