Hi Zers. I am currently have two questions regarding the tire width and suspension geometry. I am still doing the research, while I wish to have your track experience to help me understand more.

Background: I don’t care the looking at all. All I care about are the grip and cost. I currently have Nitto NT555 245/275 -40R18 for autocross only and plan to track the car this year (No track experience). I want to buy an used 18” rims and Nitto NT01 tires (I don’t know why, just addict to Nitto, used to consider NT05, but really want to have experience on the R-compound Tires).

Question 1 – I may go for the OEM Track rims, however the rim width is 8” front & 8.5” rear. It is impossible to hold 245/275 which is my preference setup. So the most possible setup will be 225/245 or 235/245. Is there a big affect to lost grip for running narrow (compare with 245/275) compound tires? What other factors I didn’t catch can be impacted with two setups?

Question 2 – NT01 only offers 225/40-18, 235/40-18 and 245/40-18. If I pick 225/245, the Rim center height will be lowered 11.25mm Front & 12.25mm rear compared with OEM setup. But from a suspension geometry standpoint, if I lower the car, for example, 1” F&R, is it better to have smaller wheels to make upper & lower control arms within the good range of incline angles? (Camber/Toe will not be considered since it can be easily adjusted)

Any of your advice will be appreciated!

 

First of all, look into 17's if possible. Something 17x9 to 17x10 with 275/40-17 front and rear would be a great start. if your dead set on 18's , look into 18x9.5 all around, 18x10 all around or 18x9.5 and 18x10.5 combo. We will discuss tire sizing for 18's later, depending on what you decide.

Tires, you want to learn on street tires, you want to burn thru 3 to 5 sets of street tires before you step up to an R comp. In the long run you will be a much faster driver. comps mask mistakes, it will take longer for you to properly learn how to drive. if you must start on Nitto, the NT05 is the tire for you.

Geometry, im lost on what your trying to ask. I will say that lowering your car an inch will destroy the front geometry, than with proper tie rods (SPL) you can lower the car about 1.25 before the geometry goes to crap. The rear can be lowered around 1.25 to 1.5 before you screw it up. This is suspension lowering, nothing to do with shorter tires, they don't effect the suspension.

 

Terra, Thanks so much for the prompt response! I came up with more after reading your reply, wish you don't mind to advise my following questions.
Rims:
- I’ve heard high profile tires are more flexible and may delay the steering response? But for myself, I don't think I would feel the difference, so I am wondering why you recommend 17”?
- Nissan designed staggered wheel on our Z must be a reason, so why would you recommend all around and what’s the advantage to run all around than staggered? Only because of the contact patch?

Tires:
- This is really a good point for me to do more researches on the tires vs driving experience/skill. I will appreciate if you could recommend some tires that I can start with.

Geometry:
- I bought a KW V3 2 months ago. It’s not been installed yet since I’d like to learn more about how to tune it prior to do any stupid move. I can understand how tie rods helps the lower control arm when lowering a car, but in terms of the lowered range, what would be proper in front?

 

Ive run 17's and 18's , I only run 18's now because the Hankook RS3 is not available in wide 17 inch sizes. My car run in the street class for time attack and the RS3's are one of the fastest tires. I can't even tell the difference in sidewall between the two, but can easily tell the difference in sidewall between different brands of tires. (Also look at the sidewall of an F1 car ) no rubber bands there.

The stagger is probably there for a few reasons, quickness in steering, induced understeer and looks. I have run staggered on the track and non stagger. The Z in an understeering pig, square is so much better. Then non stagger can also be rotated if you run a compromised street alignment, track alignment seems to wear pretty even.

Hit the track, get some autocross and trackdays in before you swap to your coilovers. The tie rods have nothing to do with your lower control arm, its all about tie rod angle. You want your tie rod paralell to the ground, you can lower the car much before you have the tie rod angled. Same with your control arms, you want them level to the ground, that is why the Z can not be lowered much before geometry gets screwed.

My car in example is lowered around 20mm up front, with SPL tie rod ends installed, and about 40mm in the back with Sikky raised subframe bushings. My suspension performs very well. The other thing, the lower you go, the less suspension travel you have. The less travel you have the easier it is to bottom out. When you bottom out, it is simple to lose traction, loss of traction kills lap times.

 

Then run a square setup. If you have 8" or 8.5" wheels run 245s all around. 9" wide wheels run 275s all around. 10" wide wheels run 285s all around.

 

The staggered setup is for insurance and safety reasons. Most manufactures dial in understeer because it scrubs off more speed and easier to regain control. It is also the slowest way around a corner for those exact same reasons.

 

Thanks guys!!
I got tight up on last weekend and didn’t really have a chance to do much research. By googling, people just mentioned square setup will reduce understeering, but no one explain why? So with the proper suspension setup, 245/275 vs 245/245, the staggered 245/275 will have more understeering?? (pls correct me if I am wrong, the under/oversteering mainly affected by slip angle & weight, and slip angle depends on the contact patch and all other suspension parameters, which being said, with the similar setup, it would be all about the tire width?)

Sorry, I cannot find the camber/toe database for Track/AutoX if there already had one (I know there is suspension database with huge helpful information). So if you would like to give your own setup as the reference for us beginners to better familiar our Z, that will be very helpful and appreciated! The followings are all I can image as the main factors can affect the camber/toe setup or the overall suspension setup you love the best.
-Coilover spring rates
-Damper rates (if adjustable)
-Sway bar (% stiffness over the OEM)
-Lowered inch
-Tire size
-Camber
-Toe
-Anything else?
-The preference of understeering or oversteering

Sorry for asking too much, I read the general knowledge from the books and online, and wish to learn more specific knowledge on the Z prior to build it (I current have all suspension parts(except bushing and tie rod), brakes and LSD sitting in my garage).

 

Seting are different from car to car, tires, track etc etc. There are many posts about basic settings, just do some reading in this section. Understeer can be tunes out with suspension, but this is done by removing traction from the rear, who do you want to do that, just add equal traction up front and fine tune with suspension.

BTW start reading here http://farnorthracing.com/autocross_secrets.html , some will be over your head, but read the whole thing. Mostly for autocross, but a lot of it transfers over to the road course too.

 

His suggestions on frequencies is poo for a RWD car. 2.2/2.5 on a street tire Z will be a drift mobile.

 

Yup, thats why i went with basically Nismo T2 rates , with a frequency of 2.1 front and 2.08 rear. About to step the rear up slightly, just one Kg more rate. My car plows high and low speed and i don't like the feeling of stiffening the rear sway from anything but the softest setting on the Hotchkiss bar.



OP, as you can see, everyone is different, we all have different setups. The only base setup i will give you is -3 front camber -2 rear and DO NOT SLAM YOUR CAR!!!!

 

Yup, I know everyone has their own setup & preference, I don’t mean to copy anyone’s. I just want to understand and learn your feeling on your setup, which can guide me or at least narrow down the options for my start. I will say to feel the bad setup also important, but the life doesn’t allow me to spend too much time and money on my passion, so I have to try to learn things quick and right

 

My frequencies are on the soft side for my tire size/compound, but I run about 2.35 F/R.

 

I would recommend going with oem wheels in oem tire sizing and something less grippy, just to get acquainted with the Z at the track. Enjoy the setup the nissan engineers developed a little while before tweaking.

 

Set up with what you have for springs, set it up 20mm lowered up front , 30mm lowered rear, -2.5 to -3 front camber and -2 to -2.3 rear camber. Dampers, set to what KW recomends and work from there. Dampers are not simple to set up, but i suggest starting soft and slowly work up if needed.

 

Just curious, when you guys tried the different cambers, toes. Did you go to shop to do alignment and cost you around $100 every time? I know there are DIY tools can measure camber, is that useful?

 

I agree. That is why I use stock suspension, just wider summer tires to run autoX last year. The car was understeering, slow cornering (with open diff). I didn’t drive too hard since the brakes were so weak, however I did spin out some times, I guess it mostly because of cold tires, improper pressure and less experience.

 

http://www.speedwaymotors.com/Longac...FYpDMgod5lAAnQ toe plates, i use 2x 3 foot levels at home. I really need to spend the $60 and make my life easier.

There are also camber guages available. All kinds of stuff available. I have done full alignment at home , i don't like to. Typically i bring mine in 2x a year for a touch up.

Alignment shops, many have warrenty, 3 year and lifetime plans. I paid $130 for a 3 year setup. Make sure you find a shop that will do custom specs, make sure you do not abuse it. Some of the other track guys screwed it up in Vegas. They would bring the car in on friday before a trackday, then monday to go back to street specs, do that once a month and they turn their back on the community. My car ony goes on the rack 1 to 2 times a year, 2 years now they seem pretty cool with me. Also i had to go to a different store when i changed bumpers, be prepared.

BTW SPL front upper arms are the easy way to adjust camber. They use shims, once you figure out things, changes are simple.

The rear , no matter what you have is a pain, even on a rack. I try not to mess with the rear unless really needed.

 

This is not my commute car, I only drive it less than 1k per year on the street. so I will not worry about driving -2.5 camber on the street. SPL UCA is too expensive… wish I can find someone sell an used for around $300~other than the easier tune, Kinetix & SPC seems good as well.
BTW, thanks for the farnorthracing link, that is a good one

 

Kinetix would be the arm then, do not get SPC if you want to make adjustments

 

Need advice again, after searching around, I cannot find the proper answer that how much the difference is running 245 square vs 275 square in terms of the handling.
I will buy the rims anyway, so I'd like to go for the right one. Maybe 245 would be the good start?