RT Lowering Pegs and Lean Angles

Just put some Suburban Machinery lowering pegs on the bike last week. I'm a fairly conservative rider but happened to lightly touch down the right peg feeler on one turn recently. One of the fun things about the Nav VI is that in its "My Motorcycle" / "Last Ride" app it gives the average and max left and right lean angle for the last ride.

For that ride, my max right lean was 41 degrees which corresponds to a lateral acceleration of approximately .87 g.

Being a retired mechanical engineer (my wife claims that's just a long-winded way of saying "nerd"), I decided to calculate how different this angle is from what the contact angle would be with the pegs at the stock height. Per Suburban Machinery's info and my own measurements the pegs are 1.25" lower than stock. Using that number I calculate the contact angle with the pegs at the stock height would be 51.5 degrees which would correspond to a lateral acceleration of 1.26 g.

Here are the nerdy disclaimers:

1. Contact angle in both cases will depend on how compressed the suspension is. Thus it will be affected by rider weight (I'm about 220 lb in geared-up riding configuration) and suspension adjustment (1 rider, "normal" in my case.)

2. The lateral acceleration I calculated is based on the vehicle/rider center of gravity being on the centerline of the bike. The rider hanging off or leaning out will change that a bit.

Ride safely & have fun!

stooie said:

Just put some Suburban Machinery lowering pegs on the bike last week. I'm a fairly conservative rider but happened to lightly touch down the right peg feeler on one turn recently. One of the fun things about the Nav VI is that in its "My Motorcycle" / "Last Ride" app it gives the average and max left and right lean angle for the last ride.

For that ride, my max right lean was 41 degrees which corresponds to a lateral acceleration of approximately .87 g.

Being a retired mechanical engineer (my wife claims that's just a long-winded way of saying "nerd"), I decided to calculate how different this angle is from what the contact angle would be with the pegs at the stock height. Per Suburban Machinery's info and my own measurements the pegs are 1.25" lower than stock. Using that number I calculate the contact angle with the pegs at the stock height would be 51.5 degrees which would correspond to a lateral acceleration of 1.26 g.

Here are the nerdy disclaimers:

1. Contact angle in both cases will depend on how compressed the suspension is. Thus it will be affected by rider weight (I'm about 220 lb in geared-up riding configuration) and suspension adjustment (1 rider, "normal" in my case.)

2. The lateral acceleration I calculated is based on the vehicle/rider center of gravity being on the centerline of the bike. The rider hanging off or leaning out will change that a bit.

Ride safely & have fun!

Click to expand...

Thank you for your post. I just purchased the lowering kit and worried about this very thing. My 02R1150RT had lowered pegs and I touched them too often. I don't know if the oilhead has different clearance then the Wethead but I'll find out soon. Today the Ilium brake pedal arrives so I'll be ready to install the lowering kit along with the brake pedal and make the shifter adjustment.

Jay

stooie said:

...Being a retired mechanical engineer...

Click to expand...

I prefer to tell people that I am a recovering engineer.

I also have the Suburban Machinery peg lowering bits. And I never achieve your target 41 degrees of lean... because my feet are so f%@# big that my boot toes touch first. That really catches my attention. If I put my toes on the pegs, then I can lean more, but I can't use the rear brake, which makes it challenging in other ways.

Maybe I need one of those Dan Gurney Recumbent motos!

Jay:

We're on the same page. After my first ride with the lowered pegs I ordered the same Illium adjustable brake pedal. We are getting them from the same manufacturing batch; mine arrives today, too.

Cap:

I never got tired of being an engineer. Alas for me, in mid-career I was "promoted" to be a low-level engineering manager. While managing was good from a financial standpoint, the most fun I had was in the early years working on helicopter rotor test stands, wind tunnels, etc. I never got tired of helicopters but by the time I retired I was REALLY tired of corporate America.

I feel your pain re; dragging the toes. When the peg scrapes, mild-mannered me has a thought bubble that goes "eek!". When the toe scrapes my thought bubble is more "What the #&*%!!!"

I would claim that any time one can, in any way, emulate the late, great Daniel Sexton Gurney it's a good idea to do so. Dan and I are similar in many ways; like Dan, I'm a bit taller than average and have a technical background. Practically the only things Dan had that I lack are great skill and great courage.

Very interesting...

I had the pegs on my RT, and touched them often enough to not really want them. I move to the inside of the bike, so I am thinking my lateral acceleration is a tad higher with the same bike lean angle.

jstrube said:

Very interesting...

I had the pegs on my RT, and touched them often enough to not really want them. I move to the inside of the bike, so I am thinking my lateral acceleration is a tad higher with the same bike lean angle.

Click to expand...

John:

You're dead on! Moving to the inside of the turn definitely helps the bike stay more upright for a given lateral acceleration (or alternately, gives more lateral acceleration for a given lean angle). That's why Rossi, et al do it.

I must say I stand in awe of their cornering technique where they hang off the inside of the bike but then have it leaned over so far that they have to pull their knees and elbows in to keep them off the tarmac. All that keeps me from emulating them is the lack of athletisism, skill, talent, and, as our Spanish friends would say, the cojones.

Don't worry, be happy!

stooie said:

John:

You're dead on! Moving to the inside of the turn definitely helps the bike stay more upright for a given lateral acceleration (or alternately, gives more lateral acceleration for a given lean angle). That's why Rossi, et al do it.

I must say I stand in awe of their cornering technique where they hang off the inside of the bike but then have it leaned over so far that they have to pull their knees and elbows in to keep them off the tarmac. All that keeps me from emulating them is the lack of athletisism, skill, talent, and, as our Spanish friends would say, the cojones.

Don't worry, be happy!

Click to expand...

Unless you are on a track like they are with totally predictable road surface, you are probably smart to not emulate them.

stooie said:

Just put some Suburban Machinery lowering pegs on the bike last week. I'm a fairly conservative rider but happened to lightly touch down the right peg feeler on one turn recently. One of the fun things about the Nav VI is that in its "My Motorcycle" / "Last Ride" app it gives the average and max left and right lean angle for the last ride.

For that ride, my max right lean was 41 degrees which corresponds to a lateral acceleration of approximately .87 g.

Being a retired mechanical engineer (my wife claims that's just a long-winded way of saying "nerd"), I decided to calculate how different this angle is from what the contact angle would be with the pegs at the stock height. Per Suburban Machinery's info and my own measurements the pegs are 1.25" lower than stock. Using that number I calculate the contact angle with the pegs at the stock height would be 51.5 degrees which would correspond to a lateral acceleration of 1.26 g.

Here are the nerdy disclaimers:

1. Contact angle in both cases will depend on how compressed the suspension is. Thus it will be affected by rider weight (I'm about 220 lb in geared-up riding configuration) and suspension adjustment (1 rider, "normal" in my case.)

2. The lateral acceleration I calculated is based on the vehicle/rider center of gravity being on the centerline of the bike. The rider hanging off or leaning out will change that a bit.

Ride safely & have fun!

Click to expand...

Well, Nerd Math and Physics teacher here...wishing you had put the equations/computations you used to calculate these lean angles and gravitational vectors. I might be able to use them as samples in a class.

Wethead said:

Well, Nerd Math and Physics teacher here...wishing you had put the equations/computations you used to calculate these lean angles and gravitational vectors. I might be able to use them as samples in a class.

Click to expand...

Wethead: Nerdy I may be, but alas, I'm limited in ability to put equations and diagrams into this format.

It's really quite simple; maybe I can describe it to you. Visualize a vertical line representing the bike's centerline. At the height of the pegs add a horizontal line from the bike's centerline to the outside lower corner of the peg or peg feeler. Add a line from the bike's centerline at ground level to the peg feeler. This forms a right triangle with the hypotenuse being the line from the bike centerline to the peg. Lets all the horizontal line "side A" and the vertical line "side B".

Rotate the triangle so that the hypotenuse is level with the ground. The amount necessary to achieve this is how far the bike is leaning when the peg contacts the ground. Call this angle beta. Note that (90 degrees - beta) is the is the internal angle of the triangle between the hypotenuse and the bike's centerline. Lets call that internal angle "angle alpha".

Now we have a right triangle with a known interior angle alpha. If we knew the length of side A (distance from centerline to peg) then we'd have a right triangle with a known side length and opposite angle. To get the length of the line from the centerline to the peg feeler, I dropped a plumb bob (actually a nut on a string) from the outboard edge of each peg to the ground while the bike was on the center stand. The distance between divided by two is the length of side A.

Now comes the fun part: My Navigator VI told me what my max lean angle was. That's angle beta above and to repeat, interior triangle angle alpha = 90 - beta. Using trig:

Tan alpha = opposite / adjacent = side A / side B

Side B = Side A / Tan alpha

We now know everything about our triangle. We know sides A and B, the Pythagorean theorem allows us to calculate the the length of the hypotenuse, and we have interior angles of 90 degrees, alpha, and beta.

To calculate the lean angle for peg contact with the pegs at their original height, merely add 1.25 to the length of side B and redo the trig.

Let me know if I was clear. If not; PM me your email address and I'll send a pdf diagram that should make it more apparent.

I have to run now. I'll add a blurb later calculating the lateral force magnitude. It's really easy. Is similar to the the vector diagram of an airplane in a coordinated banked turn. Think of the lift vector perpendicular to the banked wing, a 1 g vertical vector which equal to the weight of the plane, and the resulting lateral acceration vector to close the triangle.

More later,