Need some help figuring out the appropriate set-up.

For reference, OEM 19's have the following tire specs: 225/40/R19 front and 245/40/R19 rear

Currently I have OEM 19's with no drop or fender roll on 06 coupe sport suspension
Front: 19"x8" +30mm offset
Rear: 19"x8.5" +33mm offset
Tires: 245/35/19 front and 255/40/19 rear
spacers: 20mm front and 25mm rear

I am keeping the rear the same but replacing the front with 2 REAR oem 19's and will be dropping it about 1" all around on coilovers.
Front: 19"x8.5" +33mm offset
Rear: 19"x8.5" mm +33 offset
Tires: 255/35/19 front and 255/40/19 rear
spacers: ?? front and 25mm rear

So I'm gaining 1/2 an inch in rim width, but just 3mm of offset on the wheel itself, and adding a 10mm wider tire. And dropping 1".

Are my tire size choices correct to not mess with VDC?
What spacer should I use?
I have a rear camber kit but not a front...should I buy front camber arms or wait and see?

Thanks for any help.

 

You're going to run into VDC issues, there's a 3.71% difference and you want to stay under 3%. Just run a square setup of 255/35 all around, you'll actually be able to rotate tires too. With the 35/40 mix you'd end up raked, since you're running non-staggered wheels I'd say go with non-staggered tires too just to make your life easier.

Don't decide on spacers until you get the wheels mounted on the car, imo. Put them on first and then measure how much more flushness you want to achieve. You'll probably be pretty close to the fender with (deleted, I don't know, I can't think yet) but that's just a halfassed guess and I'm still working on coffee. Put the wheels on and grab a tape measure.

Rear camber kit's a good idea if you got the toe bolts with it, you may want them for your alignment. Front toe is very adjustable as is so no worries there, I wouldn't rush to get the front arms unless you find you need them, 1" isn't a lot of drop so you'll probably be OK but won't know until you get it on the alignment rack.

Since you're on coilovers you'll have the ability to drop it more down the road, if you think that's going to happen then you may as well grab all the camber correction items you can to be ready for that eventuality so you don't have to screw around too much when you do go lower. If you think you're going stay wtih the 1" drop disregard this portion.

 

hmmm were you using my old set-up in your calculator or the stock set-up for 19's of 225/40/R19 front and 245/40/R19 rear? I will edit my subject to include that info. I don't think i can run anything square that I could find when plugging in sizes.

 

No, I was using 255/35 and 255/40. I used the calculator on willtheyfit.com, take a look for a better idea.

 

okay i played with the calculator at willtheyfit.com
For reference, the OEM fitting for 19" Rays is 225/40/R19 the back is 245/40/R19. I am swapping out my OEM fronts and will be on 4 rear Rays: 19x8.5

Current Set-Up on 19x8.0 front and 19x8.5 rear:
Front: 245/35 = speedo error 1.30% circumference 2081.6 to 2054.9mm
Rear: 255/40 = speedo error -1.17% circ 2131.9 to 2157mm
net speedo error = 2.47%

Option 1:
Front: 255/35 speedo error = 0.23%
Compared to current tire this change yields +3.4mm of poke and 10mm inset
So this set-up will poke 3.4mm which is negligible with my current 20mm spacer
Rear: 255/40 speedo error = -1.17%.
net = 1.40%

Option 2: Square set-up
Front: 255/35 = speedo error 0.23% circ 2081.6 to 2076.9mm
Rear: 255/35 = speedo error 2.65% circ 2131.9 to 2076.9mm
net = 2.88%

Okay so instead of a staggered set-up it APPEARS that I can do 255/35 all around and not have a messed up VDC which will be advantageous because then I can rotate my tires and justify buying Michelin Pilot Super Sports since they are warrantied to last 30K miles if rotated.

 

Yes, you'll be good with the square set up. And for reference, when I came up with my 3.71% difference, I did so by comparing the 255/35/19 on 19x8.5+33 as the old tire vs. 255/40/19 on 8.5+33 as the new tire and it shows the speedo error between the two as -3.71%.

Your VDC will be fine if both the front and rear are within 3% of each other, it doesn't matter how far away from stock it is as long as the new front and the new rear aren't too far away from each other. VDC doesn't have anything set into it saying the wheels must rotate at a rate of X, it just compares the movement front to rear to make it's determination that everything is or isn't cool.

When the rear is rotating much faster or slower than the front (that magic 3%ish range) the VDC then think the car is sliding/slipping and tries to save you from yourself.

I bring this up because it looks like your using the speedo errors above to compare vs. stock and that's not necessary (handy info to have, but not directly related to VDC). On option two your "net = 2.88%" doesn't mean jack for VDC, as far as VDC is concerned they're perfectly equal and therefore just fine.

 

Why not run:

F: 225/45/19
R: 245/40/19

Difference of 0.8%

 

because that would be narrower (nearly stock) and i want wide tread. When I moved the fronts from 225 to 245 I really liked how the handling improved. The wider front made it grip a lot better rather than just plowing forward.

 

Yes, that's exactly what I was doing. So if I like meatier tires, I could run 255/40 square or 255/45 all around and it would make no difference?

 

^With VDC no. But a 45 series would probably have a negative effect on handling.

 

okay thanks guys, I guess now I'll need to figure out whether I want 35/40/45 for that part of the ratio with 255's.