eforer

Hey guys, I'm hoping some of you track day hereos might have some insights in regards to my question:

I am in the market for new wheels and tires. I am thinking that I want to do something like the RPF1 in 9.5 width with 265 RT-615s. My concern is that adding all that mechanical grip will horrifically overwhelm the stock springs, dampers and sway bars. IE the car will want to transfer more weight than the suspension is really setup for. If I buy the wheels and tires, my car budget will be shot for awhile. Long term I am going to do something with the suspension, tentatively koni sport dampers with racing beat springs, sways and front end links. I wouldn't be able to that for some time, and I'm wondering if the car will be god awful with those tires on the stock suspension for the first few track days of the summer.

Thoughts?

Also, has anyone tried lowering the inboard mounting point of the upper suspension links to raise the roll centers? It might allow for a spring rate closer to stock while still transfering less weight. It will affect camber change too, but having not tracked the car and looked at a pyrometer, I can't say weather that would be good or bad. The reason I'm interested in this is because any lowering spring will cause both the upper and lower links to be more angled, placing the inboard point proportionaly lower relative to the outboard point. In terms of the geometry, the car will want to transfer more weight as the whole roll axis will be sitting lower. Even with the CG being lower it should still ultimately want to roll more (if the spring rates and damping remain unchanged) because the roll moment is the square of the distance between the RC an CG. It seems like when you go to some of the stiffer lowering springs, that the geometry is partially undoing the effects of the stiffer springs. This is just a thought based on experience with race car chassis setup, I have really no clue whats going on with the rx8 suspension.

CosmosMpower

I ran 255/40/17's on a 9.5" NT03+M for autocross and it was fine. The Falkens run really wide (wider than the RA1's I replaced them with). But yeah if you put that much sticky tire you'll have tons of body roll and it will probably drive like crap.

I upgraded to koni SA and MS springs (stiffest of the bunch) and it's fine for daily drive and great fun for autocross.

eforer

thats what I suspected. I'm not much of an auto-xer, but I do alot of road racing. This will be the first street car I've ever run on the track, so it should be an interesting experience. I want to keep it streetable, while still being competent on the track. Perhaps I should just slap 235s on the oe wheels if I'm leaving the suspension stock for the time being.

Red Devil

I drove the RPF1s with 275 Kumho MX tires all last summer, only other suspension upgrade were Whiteline Adjustable Sway Bars.

The sways alone did a pretty good job of keeping the body roll in check with the larger tires.

RoXanneBlack8

holy suspension geometry class batman! wow after reading that i now have a degree in mechanical engineering, whoa dude....

if ur gonna be ona road course then suspension would be my FIRST priority since mazda held back the most in that area more than anything else.....but since its ur car.....whatever man! have a blast haha!


245s would fit on the stock wheels, i was forced to mount them on a customers car a while back. total ***** to get on, but they will fit.....

i got 255/40 on my 18x8.5s and that was a lesson in wheel scratchin like u wouldnt believe....

put em on the stock wheels and get some suspension bits!!!!!! yay for grip!

LionZoo

I think the problem you're describing really depends on how much the roll center changes. Sadly the only way to find that out is to consult Mazda and i doubt they'll give the number and the geometry curves to you. Testing might solve your problem, but I agree that I too am worried about excessive lowering causing a higher tendency to roll.

eforer

We just need xy postions of the endpoints for the suspension links and the contact patch where it is inline with the face of the hub.

That reminds me of another question for the RX8 racing gods: Although it doesn't make as much of a difference on RWD cars, has anyone noticed differences resulting from the change in scrub radius when altering offsets and widths? I've never really played with that on any car as I've never had multiple sets of rims (too much $$ there).

Finally, since I'm asking all these questions. I might as well hit up the last one on my mind. How much caster does the rx8 have? Does it have any SAI as well? Can you reposition the upper wishbone on the car to change caster without major modification?

swoope

iTrader: (5)

you need to post this in the comp section!!!!!!

my head hurts, but learning is cool.....

https://www.rx8club.com/rx-8-racing-25/

the answers will make me drink again, but i will learn...

thx.

beers

eforer

Sorry, figured since it was regarding suspension stuff, it belonged here. I bet team has many of the answers I seek.