Hi.

I just did quite a nice model for the front end then realized I had entered the wrong tyre size (185/60 13) but when I enter the correct size (205/60 13) it screws up the roll centre movement 🙁

When I change the size from 185 to 205 everything is fine as the aspect ratio is automatically changed to 54 but when I correct it to 60 that's when the roll centre movement becomes horrid.

However when I look at the tyre spec (Yoko A048) it gives the tyre size as 190/580R13 and the 205/60 13 is only used as a reference size so which dimensions should I enter?

This is the link to the model https://www.racingaspirations.com/mods/klw36qmn/

Basically I want to build a 750F so using my "logic" the best way to learn how ti do that is to 1st build a class B Sports special based loosely around the "standard" Locost book chassis. The "logic" behind this approach is that it will allow me to gain experience of altering the suspension geometry (from a know acceptable starting point) so that I can experience 1st hand what difference it makes to the car when it's on the track rather than on the laptop screen.

My plan is to correct any errors introduced to the front geometry by lowering the ride hight (chassis) to 80mm and improve it, if possible/necessary, and also to have an independent rear oooerr madam 🙂

At the moment I seem to have let myself become bogged down in roll centre migration instead of focusing on controlling castor change.

I changed the tyre size to 205/60-13 again and the report for the roll centre Y movement has gone wild again but I also downloaded the data and in excel it looks fine moving only 1mm with 2 degrees of roll and 5mm with 5 degrees of roll, so the problem may just be a glitch in the reporting software???

Since I mentioned caster control what would be a good camber change at say 5 degrees of roll?

And speaking of roll what amount should I be aiming for?

Those 2 questions are probably "how long is a piece of string" type questions but I'm just looking for a ball park type answer 🙂

Hmmm seems like I've fixed the tyre size issue but now my top arms appear to explode for the fun of it lol.

Anyway the new model is here http://racingasp.com/klw36qmn

I was talking about camber earlier...I read through my post several times to make sure I hadn't written caster by mistake and still managed to miss the typo lol.

That seems like a much better approach to solving the problem...start at the end (were I want the geometry to end up mid corner) and work back from there lol.

Where you say "(and with a bit of droop)" do you mean you aim to have around -2.5 degrees of camber of the outside wheel AND some droop of that wheel at the same time? I'd always imagined that the outside wheel would be in bump while cornering due to weight transfer or do jacking forces course droop? Basically I suppose I'm asking what attitude I should put the model in to simulate cornering movement of the wheel...roll with bump, roll with droop or just roll???