Motion Ratio and LLTD Related Question

Hello HPA and friends! Finally I completed my first course here for suspension. Happy with all those knowledge shared by the team.

I just still have 2 question (actually 3), which still bugged me. Hope u guys can enlighten me.

1. Motion Ratio, here explained as Wheel to Spring (wheel/spring), means how much wheel is moved given spring movement distance, So USUALLY the number is >1 for some suspension. Meanwhile, for some outside forum knowledge, it's the other way around, which is spring movement given the wheel movement distance, which at some suspension type can give number <1. Is both correct? or one wrong one right? ,

1.b. so in related above question, I have Honda Fit GE8 that I use for autocross. it used divorced type of coilover, with shocks sit on uprights and spring on torsion bar. Usually what I found at forum, the rear motion ratio is 0.88 (some forum use Spring distance to pivot point vs wheel distance to pivot point). but If I use methode from HPA, normally the number will be the other way around, maybe around 1.13 ish.

2. for LLTD calculation sheet and the class. it says usually tune to 5% in front of static weight distribution as our baseline, for safe purpose. so in this theory, can I assume if lets say I wanna make my car to have more rotation, should I make the LLTD bias to rear?

Thanks!

Hi Andika, great questions here.

1. Working out your motion ratio gives you the ability to calculate the effective spring rate at the wheel (wheel rate). The calculations can be done in either direction, and inverted if needed to suit the lateral load transfer distribution sheet. 1.13 is the inverse of 0.88, so you can calculate your wheel rate by either dividing your spring rate by 1.13, or multiplying it by 0.88.

With the beam axle on the Fit, you will have close to a 1:1 rate in compression (over bumps) and 0.88/1.13 in roll (lateral).

2. Yes, that's correct. Increasing rear lateral load transfer will make the car rotate more (more oversteer).

As a side note, have you seen the work Honed Developments has been doing with the Honda Fit/Jazz chassis? They have been developing all kinds of products to make the GE8 chassis more suited to trackdays and racing. Here's the GE8 suspension recipe on the Honed blog: https://honeddevelopments.com/honda-fit-ge8-suspension-recipe/