Motion Ratio vs Wheel Travel

[SD]

I was hoping I could get some feedback from some of you on the relationship between motion ratio and wheel travel, and what you feel is ideal. I understand that rising motion ratios can cause undesirable oversteer/understeer effects from pitch movements during corner entry and exit. It seems like decreasing rates would be beneficial in corner entry/exit scenario, but that the response in bump and roll would not be adequate. As such I have decided to design towards as constant as possible, keeping in mind that rising rate would be better than decreasing rate.

I have been trying to finalize a new set of bellcrank plates to improve upon some that were done a few months ago. I have been using a combination of SolidWorks, Excel and Susprog3D to generate the graphs shown below.

On the graphs below, (-) corresponds to droop, while (+) corresponds to bump. Design is for 1.250"� droop, 1.75"� bump in which 0.5"� is the bump stop. I choose to do the analysis between 1.25"� droop and 1.5"� bump.

Graph 1 shows a sinusoidal type relationship, but if you look at the scale you can see that the wheel rate only changes by ~ 2.5 lb/in. My only concern with this relationship is its sensitivity to the inputs (coilover mount, bellcrank geometry), otherwise I feel it would act as a constant rate.

Graph 2 & 3 show rising rate motion ratios with graph 2 gaining ~ 6 lb/in and graph 3 gaining ~ 10 lb/in.

Any feedback would be greatly appreciated!

Graph 1


Graph 2


Graph 3

[SD]

I was hoping I could get some feedback from some of you on the relationship between motion ratio and wheel travel, and what you feel is ideal. I understand that rising motion ratios can cause undesirable oversteer/understeer effects from pitch movements during corner entry and exit. It seems like decreasing rates would be beneficial in corner entry/exit scenario, but that the response in bump and roll would not be adequate. As such I have decided to design towards as constant as possible, keeping in mind that rising rate would be better than decreasing rate.

I have been trying to finalize a new set of bellcrank plates to improve upon some that were done a few months ago. I have been using a combination of SolidWorks, Excel and Susprog3D to generate the graphs shown below.

On the graphs below, (-) corresponds to droop, while (+) corresponds to bump. Design is for 1.250"� droop, 1.75"� bump in which 0.5"� is the bump stop. I choose to do the analysis between 1.25"� droop and 1.5"� bump.

Graph 1 shows a sinusoidal type relationship, but if you look at the scale you can see that the wheel rate only changes by ~ 2.5 lb/in. My only concern with this relationship is its sensitivity to the inputs (coilover mount, bellcrank geometry), otherwise I feel it would act as a constant rate.

Graph 2 & 3 show rising rate motion ratios with graph 2 gaining ~ 6 lb/in and graph 3 gaining ~ 10 lb/in.

Any feedback would be greatly appreciated!

Graph 1


Graph 2


Graph 3

[FryGuy]

I would consider all of those linear. You can play around all day with bellcrank configurations in solidworks or whatever and still not be able to get anything perfectly linear. Those small wheel rate changes you have listed are probably not even enough for the driver to really feel it (maybe). Not to mention, even if you were able to get something completely linear, it won't nessecarily end up like that due to machining tolerences, hysteresis etc.

As far as the relationship between wheel rate and motion ratio you will find that you might need a dynamic motion ratio just in order to maintain a linear wheel rate depending on your suspension geometry. Wheel rate and motion ratios are tricky and highly dependent on geometry.