Been digging deeper into understanding the suspension and tires (yes, the CamberTires, but lets not derail the thread). Focusing on figuring out scrub radius right now.

I understand the concept, but would like to know what the stock values are for reference. Has anyone posted the measurements of these?

Evo VIII/IX section seems to have much better discussion/information on suspension than the X

 

Our SAI is about 13.7* (assuming no camber plate, of course). That seems to match the official value for Evo 7-9s, which was 13.75*.

Scrub depends on offset and I don't know our scrub with the OE (+38) offset, so I can't help you there.

 

oh yeah, meant stock, just wanted SAI - rest is easy to calculate as all that changes with offset, plates, etc

thanks a TON though. this section is the only reason I visit evom anymore. back to theorycrafting

 

Note, also, that scrub is slightly altered (increased) when you flip the camber bolts, so it won't be the same same for all Xs running +38 wheels without camber plates. In other words, not all Xs that are obeying the FSM will have the same scrub. This is another reason that there isn't a spec value for scrub.

 

FSM?

are you saying its altered in another way besides the fact that it has more camber? because I do understand that more camber at the hub will push the wheel centerline point away from the SAI point (some call it the Dave Point). I was planning on finding stock values, then remodeling with different alignments to see how much it's changing

 

The angle of the steering axis is determined entirely by the end-points of the strut, which are the bushing in the upper shock mount and the ball-joint on the lower LCA. So that doesn't change when you tilt the hub on the knuckle, so where the steering axis hits the ground doesn't move, either. But where the tire hits the ground does move outward when you flip the bolt to get more camber, so the amount of scrub increases when you flip the bolt. Make sense?

 

right, we're saying the same thing (aren't we?)

maybe my post was confusing? as far as I know we just repeated after each other

anyway, thought it would be easy to figure out the scrub radius now that I know the SAI, but I'm stumped again...

wheel/tire centerline angle is 89 obviously, and SAI is 13.7 as you said...just lacking any relavant side lengths maybe I need more coffee

 

The missing piece of information is the distance between the steering axis and the hub-face at the height of the axle. You need that, too, to calculate scrub.

 

right, and really knowing any of the side lengths would get us there, but being imaginary geometry lines, it's not an easy measure

haven't had time to look at it lately with work, but maybe later

wondering if anyone out there measured this and just hasn't shared

 

There's a bunch of raw data that we should collect in a sticky. Maybe I'll ask a Mod to make a sticky thread for this.