I appreciate everyone's help and advice! Let's try to be civilized here so nobody is deterred in the future from giving their advice. This kind of stuff really helps RWD newbs like myself out.

So I am for sure getting different tires, and definitely looking into better suspension. At the very minimum those two things will change but I still don't fully understand what I should be looking for in a set of coilovers honestly. Spring rate is something I could use some explaining on. There's a local set of Feal 441 suspension by me for sale but they are 9k front and rear, which is I want to say too stiff for my application. What should I aim for in regards to spring rate for a street car that mostly goes in a straight line?

It will most likely have to be custom made for your car.
No Off The Shelf stuff as I said before.

Yea I've actually reached out to quite a few companies and it seems nobody wants to tell me anymore than "we can definitely get you a custom drag setup for your car". I'm not just going to throw money at somebody and take their word, nobody is able to help explain to me what i'm buying and why so I can justify the benefits to my wallet. I will look at the suspension sub section but we both know it's all corner carvers on there. I'll probably get either the incorrect information or no information at all.

I'm surprised no one asked this yet.

What's your rear camber at? You mentioned being as low as you can go without rubbing, this in my eyes makes it seem like you're running at like -3* or more, which is only going to complicate the issue on rear end grip since you're losing tire contact at that point.

Suspension is a big one, especially if you're running on full soft you're losing any compression force which is what you really need for the shock to work and "push" the tire into the ground.

But like @CSG Mike mentioned, all of this is nothing unless you have better tires. Any shock with more compressive force is still going to make your current tires break loose.

Spring rate isn't derived off of ride quality, dampers and the ability to dampen those forces dictate ride quality

You need to get corner weights or at least front and rear weights to know optimal spring rate.

Rear camber is around -1 degree on both sides. I'm sure when it squats it might hit like -2 roughly. Maybe, worst case scenario -3 on a squat but since the car barely grips, i don't think it ever pushes the rear end that low because i would hear it rubbing.

Bingo :thumbsup:

The shock isn't as important here as your bump steer and stroke

55/45 f/r weight distribution is not so great to begin with for putting down decent power in a rear-drive car, even with a very short flat-4 engine. With a big long cast-iron turbo inline 6 mounted up front, it's surely worse, 57/43ish I'd guess? Not good... A 50/50 car would have 16% more static load on the rear wheels, and could load them up more under acceleration.

A big rear wing would help at speed, but in the lower gears you're not going to be putting much power down without adding mass to the rear of the car.

Honestly it's probably 60/40. There's a LOT more weight up front now.

I also don't know what camber i should be aiming for. Maybe like +1 ? or +2?

right now with your suspension and tire its probably not squatting much to change camber all that much, but once you get the tire and dial in the suspension that will change a lot.

your goal should be zero effective camber and toe in rear, with zero effective toe and maybe -.5 effective camber front with as much caster out front as will allow before wheel shaking/shimming for high speed stability. effective meaning while moving/squatting under load not static on an alignment rack.

This varies based on suspension setup and specific vehicle/setup etc..

but since this is also a street car a good at least starting alignment to shoot for on static rack would be

front -1 camber, 0 to 1/32 toe in per side, 5-7 degree caster (depends if/how much you can adjust, if it shakes/shimmys at speed you have too much caster)
Rear 0 camber 1/32 toe in per side

for a drag setup id probably run positive toe front and positive camber rear, but small compromises for street.

another method would be to jack up the front 2" and compress the rear 1" on the rack and shoot for 0 camber and toe all around. but again this gets more into drag car vs street car. as this will most likely mean you will be running positive camber rear and toe out front while static but be at 0 all around under load.

get the tire and dial in the suspension setup, then get the alignment, then finish tweaking the suspension settings.
If your planning on adding weight to the rear which I would recommend do that before getting vehicle weight to decide spring rate and before getting alignment.

Decide on what compromises you are willing to make and live with to get as close to your goal as possible.

An incomplete and mildly facetious list of possible solutions in increasing order of cost/complexity:

1. Turn down the boost until the tires can handle it. Numbers on paper are just bench racing when unusable.
2. Buy the stickiest streetable tires available, then return to option one and adjust accordingly.
3. Buy the stickiest tires available, follow step one and avoid rain.
4. Crank up the coil-overs in tribute to classic Detroit Muscle. Buy taller tires in accordance with option two, then follow option one. Examples: A 275/55-17 will add ~3" diameter (1.5" sidewall) over your 275/45-17 and will result in an effective rear gear ratio adjustment to 3.31:1 without actually changing the rear gear. 275/60-17 would add ~4.3" (2.15" sidewall) and result in a 3.19:1 effective rear gear ratio. Use a 275/45-19 or 275/50-19 (respectively) to get similar results with thinner sidewalls. The larger, heavier wheels should eat up some energy as well and further help reduce wheel spin.
5. Change out coil-overs and control arms. Work with a professional suspension tuner to choose/customize the optimal valve tuning, spring rates, and alignment required to modulate the forces being transmitted through your car by the ~384% increase in torque over stock. Return to options one and two to complete setup.
6. Change out the differential for one with a plethora of gearsets available. Keep original tire size. Follow earlier options as necessary.
7. Mini-tub. Retain a low vehicle ride height and stock external appearance while gaining clearance for taller and wider tires. Follow earlier steps as necessary.
8. Modify rear suspension design. Change out arms, angles, mounting points, etc. Target increases in areas like anti-squat to help drive the tires into to ground under power. Return to earlier steps as necessary.
9. Back-half the car. Install a solid axle with either ladder bar or 4-link suspension. Follow earlier steps as necessary. Enjoy all the straight line traction :party0030:. Avoid turns!

In all seriousness, it seems to me that although tires are "always the answer" there is reason to question your suspension. You say you have your coil-overs as low as possible. If I'm not mistaken, a 1" rear drop on our cars results in 2-2.5* negative camber and Flex Z specs say they drop as much as 3.4". I don't know what the resulting camber is when that low, but certainly more than -2*. I assume your drop isn't the full 3.4" because of your tire width and rubbing, but it seems quite probable that you have more camber than you're estimating unless you have adjustable arms and have had an alignment. Weight transfer and minimal dampening will still compress the rear and add additional negative camber without traction, just not as severely.

Your cheapest option is to turn down the boost and/or re-tune the boost curve and traction control to better manage the torque. This will be the safest option for any road condition regardless of which tires you choose.

A cursory web search indicates the lowest ratio gear the is300 differential housing will fit is 3.54:1 (possibly out of a Tacoma or gen3 Supra, not sure I didn't read that close). You could confirm this and possibly find a usable used gearset to swap in for a few hundred dollars. Reducing the gear ratio will help prevent over powering the tires, but this is not much of a change and probably not worth it if sticking with the is300 rear.


If your car was mine, I'd turn down the boost on the street and keep a high boost tune for use on drag radials (or wrinkle walls) at the strip or for use if I ever went to a drift track. Then again, if I wasn't intending to build a dedicated drag or drift car, I'd never put that kind of power in this platform. But that's just me and I no longer have the same immortality complex I had when I was younger.

Get creative and fit a bigger tire out back. It’s doable with adjustable suspension. Here is 305/35/18.

https://www.instagram.com/p/CKIB_Rqn...=1opc3ju3lgjp2

The mickey ss street comes in a 305/45r17 but I have a 9" wheel which is a bit small for that tire. Also, I think it would look kind of ugly poking out almost an inch. Being 5x100 makes things harder with wheel fitment and offsets.

I think i'm going to switch to some 275/40r17 mickey ss streets and see how it goes.

305/45/17 would be great but probably too tall for how wide it is being that it’s almost 28”. The 305/35/18 I’m running specs at 26.6” and I almost have to start working on the forward frame rail to get them under the fenders. I don’t know that you could get that 305/45/17 to really fit. I’m looking at a 28” slick for my drag pack but it would have to be on the narrow side.

There is plenty of room everywhere else. It’s the forward frame rail that is the problem when going to max width and diameter.

Btw I ran a Hoosier dr2 275/40/17 at the track and it worked great but on the street not so good. I don’t think the SS in that size will be much help to you either except maybe on a hot summer day.

https://www.instagram.com/p/CISEM8Un...=1k5bol12z5a12

Aside from all the other stuff, you need to get as much diameter back there as possible while still allowing all the suspension to work.