Slight update for anyone who cares

Kinja'd!!! "roflcopter" (roflroflroflcopter)
03/21/2014 at 01:14 • Filed to: None

Kinja'd!!!1 Kinja'd!!! 7

I posted about my car getting really funky after throwing wider tires on the back !!!error: Indecipherable SUB-paragraph formatting!!! and decided to stop by a place to check the alignment today, turns out things are a bit out of whack, but not to the extent that I'd think would be needed to cause the level of sketchiness my car exhibits at speed currently. Here's what the alignment is right now:

!!! UNKNOWN CONTENT TYPE !!!

Front: L R

Camber -1.1 -1.3

Cross Camber 0.2

Caster 6.0 6.5

Cross Caster -0.5

Toe 0.06 0.30

Total Toe 0.36

Rear: L R

Camber -0.3 -2.3

Cross Camber 1.9

Toe 0.19 0.29

Total Toe 0.47

All numbers are in degrees.

So from these numbers you can see that things have been slightly out of whack for a while now(which would explain my excessive inner tire wear on the rears) and I've been doing some research into what numbers I want to shoot for when realigning it and think I've decided on -1.4 camber up front, -0.9 rear, with about 6.0 degrees of caster and zero toe all the way around, I may add ~1/16 in total real toe if it's still floaty on the highway after that. I should have two more wide tires for up front in the next week or two as well which will square it back up but doing the alignment can't hurt after seeing those numbers...

And does anyone know why &'nbsp' doesn't work in Kinja anymore??


DISCUSSION (7)


Kinja'd!!! Racescort666 > roflcopter
03/21/2014 at 09:51

Kinja'd!!!1

Another thing that can mess with your handling is when you change your scrub radius by changing the offset on your wheels. Here's a decent blurb on scrub radius from H&R Springs.

Kinja'd!!!

It sounds like you had problems before but didn't really notice it. With wider tires and if your scrub radius changed, it's possible that these problems were merely exaggerated.

My recommendation: fix what you know is wrong (alignment) but keep in mind that doing different things with your wheels and tires will affect how your suspension controls your tires.


Kinja'd!!! roflcopter > Racescort666
03/21/2014 at 10:25

Kinja'd!!!1

Thanks for the really informative reply, and that is my plan, get the alignment numbers where I want them, then go ahead and order some wider tires for the front too so they'll be matched again, which in theory should take out pretty much any chance of it being weird, unless something is actually broken(which it's not).

I didn't really know what to expect deviating from stock, but my friend runs 245s the whole way around and has zero issues, although he is on larger 19 in wheels as well, and with a slightly different suspension setup. Only one way to figure out what works right?


Kinja'd!!! mrazekan > roflcopter
03/21/2014 at 10:45

Kinja'd!!!1

rEscort has a point, but as you stated, you put wider tires on the rear and not the front. I had a similar problem once. Do you have roads with grooves in them? In Portland, practically everyone that has them, throws on their studded tires the moment it is legal to do so. They don't take them off until they become illegal again. This leads to deep ruts in the road surface.

With wider tires in the back, or the front, it is likely that neither the inside edge or the outside edge of the contact patch of the rear tires line up with the front edges. Place this misalignment in a rut, and the lateral forces are different on the front and rear tire. If the front is higher up on the rut, where it is flatter, it will have a smaller side load than the rear tire which is slightly deeper in the rut.

At highway speeds, it does not take much steering input to get the car to respond. This small difference in lateral loads makes the car feel floaty. That is because sometimes the rear is steering and sometimes the front is. When I drove on non rutted, relatively flat sections of highway, newly paved areas, the float would go away. It also went away when I put the same size tires at the four corners.

I'm not saying this is exactly what is happening in your situation, but this was my experience with mismatched widths.

Cheers!


Kinja'd!!! roflcopter > mrazekan
03/21/2014 at 11:04

Kinja'd!!!0

That makes a lot of sense. Our roads aren't too rutted or anything but what you're describing does fit the symptoms. What you say about sometimes the rear is steering and sometimes the front is steering is EXACTLY what it feels like at highway speeds, and at lower speeds the steering is quite a bit lighter than it was previously, and I'd describe the turn-in as divey. The weird thing is that under hard throttle the car still feels planted. I guess we'll see how matching sizes and the alignment change things. Which do you guys think I should go for first?


Kinja'd!!! mrazekan > roflcopter
03/21/2014 at 15:08

Kinja'd!!!0

Sizes. It will take the floating feeling away from the car at highway speeds. After the tires you want are on, then do the alignment to spec. In general, as mentioned in your first thread, there is no need to change tire sizes unless you like the look, are working on correcting a handling problem, or have upgraded the brakes (1st) and increased the power (2nd) of the engine.

My SPG has 205 45 16 (not a common performance tire size) vs. the stock 195 60 15. I installed a set of front brakes from a 9000 and then boosted the output of the engine just past 200 HP (I think). The wider rubber had me spinning the tires much less than at the stock tune with the stock tires. The Quaife basically made wheel spin non existent. Time to add more go huh?


Kinja'd!!! roflcopter > mrazekan
03/21/2014 at 17:22

Kinja'd!!!0

While the decision for going bigger was partly based on looks(the stretched look of the 225s was gross), I also decided to do it because the car is going to start seeing more consistent AutoX use and the forums seem to agree that 245 is a good number on the rx8. We'll see if I can use them or not, with the 245s on the rear I no longer get the backend loose when shifting hard, so I guess that's a good thing.

I seem to remember reading a few different places that you can't really go with too much tire from a performance standpoint, as long as you fit your wheels to it and aren't dogging it in the slow sections.


Kinja'd!!! mrazekan > roflcopter
03/21/2014 at 20:02

Kinja'd!!!0

That's the kicker; you need to make sure it fits your wheels. The 205s on my 16s is the limit. One other thing to consider is rollover. By limiting the rubber, you can guarantee not to roll. If you have a high CG and more rubber on the road, you have new options. I don't think that will be a problem with the RX-8.

Cheers!