Mr.Sparks said:I was unaware that there was varied offset between models.
Mr.Sparks said:does that mean that all 850 ones are the same offset then?
Mr.Sparks said:Does anyone know if there a list of dimensions for Commando triple clamps/fork yokes? I was unaware that there was varied offset between models.
teeb said:750 #1 Top Offset 2.781” Bottom Offset 2.781” Difference 0.000”
750 #2 Top Offset 2.776” Bottom Offset 2.776” Difference 0.000”
850 #1 Top Offset 2.759” Bottom Offset 2.685” Difference 0.074”
0.074” over 5.75” gives about 0.74 degrees (5.75” is the aprox. spacing between bearings in fork bearing races and where the offset measurements were taken).
acotrel said:I have been thinking about what Ken said about when you increase the yoke offset, you increase the trail. And it sort of doesn't make sense to me. As you increase the offset, you move the axle forward, so the vertical line taken trough the axle to the ground moves forward. It usually intersects with the line taken through the steering head to the ground. So increasing the offset reduces the trail. In any case, on a good handling bike such as a Drixton Aermacchi, the steering head is very vertical, and a lot of yoke offset is used. If the rake is more horizontal such as on a Seeley or a Commando, that much offset creates a major problem. I think it is also possible that in some cases the vertical line taken through the axle and the line through the steering head might not intersect before they reach the ground.
If there is somebody on this forum who better knows the relationship between rake, trail and steering stability, would they please enlighten me ?
acotrel said:I have found that less offset when used with 27 degree rake, makes the steering quicker and more towards self-steering than stability. Are you saying that the effect is due to more OR less trail ? When I measure trail, I take a line down the side of the fork leg to the ground, and a vertical through the axle to the ground, then measure that distance. I then subtract the distance between the centre of the steering spindle to the line between the fork leg centres. So in effect increasing the offset decreases the trail. With the Seeley -the more offset, the more stable the bike becomes under brakes, so tipping into a corner is difficult. As you reduce the offset, the steering becomes quicker and the bike tightens it's line coming out of corners under acceleration, however under braking the bike feels less stiff when tipping in. In fact with my bike, all you do is put your mind where you want it to be. - Dangerous for beginners.
What I don't understand is the relationship or correlations between rake and trail and stability on various bikes. The Featherbed Manx has fairly short offset and a very steep head angle. I would have expected more offset. I know most of the replica Featherbed frames use 26 degree rake instead of the standard 24.5 and handle like Suzuki two-strokes when the normal offset is used.
acotrel said:When I reduced the offset on my Seeley, it moved towards self-steering. Perhaps when I did that I actually REDUCED the trail ?
acotrel said:Have you actually increased the trail on a bike and found it to become more stable ?