(NA) more tire or less bind

[ckcadavona]

I've been contemplating future ideas for my 240 and I would like to get NRR's opinion. How much tire is enough or too much for a NA(180whpmax) 240? Would the use of urethane vs spherical/metal bearings/bushings justify the use of a smaller tire considering the hp potential of a NA KA? Also take into account the advantage of running smaller lighter wheel tire combo vs loss of grip.

15x7-rim
225, 245, 275(probably wont fit)- R compound tire
spherical bearings

or

17x9-rim
255, 265, 275- R compound tire
urethane bushings

[McCoy]

The first question would be, is this a car that your wanting to compete with in Solo/Solo II? I only ask because there are certain rules that you'll need to comply to for tires and suspension components.

Jason R. won solo II Nats in STS with a lightweight 17x7.5" Volk wheel and a shaved 225/45/17 RE-01R's.

Of course PJ was able to do pretty well with his larger wheel/tire setup when he was NA.

[ckcadavona]

DSP/ITS...possibly TT?

I know the sphericals have to be pressed into the stock arms/uprights etc. I didn't see any tire restrictions with the exception of using a 15x7 wheel in ITS and DOT approval.

Thinking back to when I installed my bushings...I don't think some of the stock arms will be capable of running spherical bearings but I'm not sure.

[veilside180sx]

You'd need at least a 15x9 to run the 275/35/15 Hoosier on.

[ecugrad]

I am in the same boat here and vote for mo' tire/urethane

I have just never heard anyone complain about too much grip.

[racepar1]

I think 255 is about the max you really wanna run with that much power, maybe 275. If you go bigger it will scrub too much speed in higher speed sweepers or carousel turns. Last time I was at big willow I was going flat out through turn 2 (80mph looooooonnnnnnnnggggggggg carousel type turn). The tire scrub from my 255 azenis was holding me back. I would imagine that if I upped my tires to say 275's it would probably actually slow me down there, of course I would gain elsewhere. I plan on switching to 255/40/17 nt01's for my next set and upping it to 275's on the set after that just to test this issue.

[spool_sample]

Look more at tire diameter, especially for auto-x.

Some people value the gearing changes more than the grip that one tire might provide over another (i.e. STX, where the WRXs run 235s, even though the rules allow 245s).

[Def]

Agreed with tire diameter. I hated how long the gears were with 275/40-17s.


I really never felt any difference between 275's and 235's with respect to grip. As long as you aren't overheating the tires I think you're fine as long as you're in the general ballpark(235-275 width). Gearing changes will get you more speed than being able to pull 0.003 G's more, and the narrower tires actually get up to temp on a lighter car on track.

[jmauld]

I run the 285/30/18s on my ~155hp S14. I can definitely feel a difference in the drivers's seat between these tires and the 225/15's that I used to run.
- More grip
- Reduce steering response (heavier tire/wheel combo)
- Power is not as responsive (weight & diameter)

However, even with the two negatives above and the fact that these tires are 3yrs old, they still seem to work very well, for me.

I plan on trying out the 275/15s next. If I can find a rim to put them on. My tire guy kicked me out the door when I asked him if he would try squeezing them on my 15x8 Kosei's. :)

[Def]

Changing the spring rate and slipangle a tire operates at will change how they "feel." Plus compound changes will make more of a difference wrt lateral grip than geometry, along those lines getting the tread in the right temp region will be the biggest benefit.

Using what you have is way better than tossing on super wide rubber and expecting something magical will happen. Look at a current Koni Challenge car - the tire is nothing exotic, but they will blow away a club racer with similar power and much wider tires on the same chassis because they spend time optimizing their setup.

[Wiisass]

If it's a track car, what Def said about temps is key. If it's an autox car, those guys just seem to put on the widest tire they can with a good cold coeff of friction and go for it.

So for a track car, you don't want too big of a tire because you won't be able to get it up to temp and you don't want too small of a tire because you will overheat it. So get something in that range with a good compound and you will be fine. It would be awesome if we could get tire curves for some of this stuff and then you could see what effect width has on lateral force, but I doubt that would ever happen.

Is the sphericals vs. poly bushings just to save money? Or for a class? Or for what? Good sphericals would be the way to go for everything. Poly would be fine if you need it to keep the car in a competive class or whatever. I don't like rubber/poly because they add some hysteresis, spring rate and damping into the suspension when they shouldn't. It's hard to account for them and they aren't letting the shock/spring do the job that they're supposed to be doing.

And after that it all comes down to tuning. You need to set up the car to use whatever tires you choose. Remember, tires are the most important part of a suspension and the suspension needs to be set up around the tires. If you aren't optimizing the tire, you are wasting your time. So dial in the alignment based on what the tire likes, set the dampers based on tire spring rate, etc. And don't forget to pick the correct sized tire for the rim that you have or are going to use. I still think that running too wide of a tire on a skinner wheel is a bad idea. Follow manufacturer's specs at least, but trying to squeeze a really wide tire on some stock wheels is not a good idea in regards to at least cornering stiffness of the tire. People seem to do it with alright results and sometimes you may have to do it, but I doubt that people are gaining much, if anything, versus running a better matched wheel/tire setup.

[Def]

I agree. I think sticking towards the high end of the tire's suggested wheel size always produces better results than sticking towards the low end(i.e. a 255/40-17 on a 17x10" wheel vs. a 295/35-17, or even a 275/40-17). You end up with a sidewall geometry that is much better suited to resisting side loading, and the transition to different slip angles seems much less abrupt. I agree that super wide tires like a 275/40-17 on a 17x9" are very counterproductive, and you end up with about the same rolling tread width on the ground as a smaller tire, but horrible sidewall geometry.

One thing that does really freak out less skilled drivers is that a narrower tire will require more slip angle to generate the same grip, and unless you're used to the feeling of travelling up to 10-12 degrees off from where your car is pointed, it's going to make you uncomfortable and ultimately slow because you will shy away from those high slip angles. Keep in mind the grip hasn't necessarily changed, just the slip angle. I think ultimately that's where some of the sense of "speed" comes from when most people change to wider tires. They're now generating more grip closer to their slip angle "comfort zone," thus the idea is born that wider tires generate more grip.

I will qualify that statement with a disclaimer that there is a lot unknown about tires and how they really work(yes, we can do tire tests, but AFAIK tire modeling does not work well without this emperical data), and changing tire width does change contact patch geometry which could potentially produce more grip due to mechanical keying in the right setup. That said, you're still really dealing with the same tread compounds acting on the same asphalt - besides mechanical keying and shearing, the friction generated is tied to normal force which is a constant(i.e. car weighs the same).

As for suspension bushings - I'm not a fan of polyurethane at all. At least rubber does have a spring effect to it, but poly is just nothing but friction once installed. You can minimize this with grease, but much sooner than you think, it's back to tons of friction. I run them on my front LCA and swaybar bushings for lack of anything better being available at a "happy" pricepoint for me.

[McCoy]

There are to many factors to blindly say what tire size or tread compound someone should go with, it should really come from your expereince, overal car setup, as Wisass and Def have stated, the tracks that you frequent, the average temps that you drive in, and so on... What I found worked at my local track (big track, good surface, minimal traffic), didn't do so well at the track in Seattle, to much traffic and and an older track surface with less grip didn't help on getting my hoosiers up to temp. The next time I visit PIR I'll most definetly just use the street tires and enjoy the track.

As for what tire size to run on a given wheel, I've always seemed to run on the larger tire size, not on purpose, just how it worked out (225/45 hoosiers on 15x7's on the sentra) and have always been happy with how the car handled, I went through 3 sets of takeoffs in one year with the sentra. As for a 275/40/17 tire on a 17x9, I'm doing it... do I recommend it, no... go with a wider wheel if possible. I only did it to fit everything under my stock fenders and just to see if this setup will work, the tires were basically free and was a good way to see if a 275 width RA-1 is right for me or not on track.

It's important to note that each company have slightly different sizing for their listed sizes. My recently acquired set of 245/45/17 Hoosiers ($100 for a set of 5) are the same tread width (within 2-3mm) as the 275 RA-1's that I will be using this year and are typically designed to fit on a smaller wheel. So make sure to take that into account when you try to stuff a set of 275 R6's under your stock fenders because you knew that Monty could fit 275 RA-1's under his.

If you have a weight/power ratio in the 10:1 ratio, and can actually drive the car, I'm sorry to say but a 235 width tire probably is not going to cut it on track... well it might, but I'm not sure how long it's going to last verses a larger tire. This is part of the reason I've always gone to a larger tire, not because I'll be that much faster, but more to have the damn tire last longer through the year. The set of 225 hoosiers on the sentra lasted me a good 4 days, same as the set of victoraciers, and the other set of hoosiers.... but damn was the car fast through the turns for those first 5-8 laps :)

[ckcadavona]

The class that I'm thinking of going into(DSP) allows poly and unlimited tire/wheel size with the exception of DOT approval or sphericals and a 15x7 rim with any DOT approved tire you could fit on that little rim.

I'll end up keeping my poly and running a 17x9 and 255's all around to start with if I decide to go up in class next year. That is if I'm happy where my driving is at by the end of this year or if I feel like spending mo money on the 240.

Also, it seems that the DSP mods would be more track day friendly.

[Def]

I'd honestly go with stock bushings or Nismos over poly. So much friction with poly with no "spring." At least with rubber bushings you have them providing some (very inconsistent) springrate and a little damping via internal hysteresis.

I think more friction is the last thing our rear suspensions need.

[Wiisass]

Def, it's autox, the bushings would only have 60 seconds of driving time on them between greasings. I think the grease could last 60 seconds.

[jmauld]

I'd honestly go with stock bushings or Nismos over poly. So much friction with poly with no "spring." At least with rubber bushings you have them providing some (very inconsistent) springrate and a little damping via internal hysteresis.

I think more friction is the last thing our rear suspensions need.

I agree here.

My car is setup for DSP.

I do have poly in the front control arms, but I wanted to make sure they only moved straight up and down. To be honest, those bushings are so thin that having rubber in them really isn't that big of a deal. I have the NISMO bushings in the T/C rods so that they can continue to flex as needed.

I haven't touched the rear arms. That system is way too complicated to blindly throw poly bushings at it. You're almost guaranteed to bind something if you're not careful.

You can have a very capable setup and still keep rubber in the factory arms. Just make sure they aren't worn out, and if so, replace with the NISMO stuff as needed.

[jmauld]

As for DSP and track cars, there are two big areas where a DSP setup hurts you on track. You can't upgrade the cooling or the braking systems.

I fight with this setup all of the time, because I want to get back on track, but I also want to stay in DSP. The stock 240 brakes are GREAT at an autocross because they are so small and light. Not so great during a track session.

I've been thinking about making a bracket that would allow me to switch to a larger diameter rotor and keep the stock calipers. That way, it would be a relatively quick swap between a track setup and autocross setup. Seems like too much trouble for what would amount to a hack job. :)

[BigOdom1]

I have all Nismo bushings (in every arm except front lower, rear upright) in mine except for 1 steering rack bushing from es and the other from nismo. also have SPL solid sub-frame and differential bushings but i didn't feel that there is a binding issue there. i recommend them everywhere, I guarantee if you have the original TC rod bushing that it is done and oozing. The nismo dont need to be greased but are a pain in the butt to press in.

[Def]

Def, it's autox, the bushings would only have 60 seconds of driving time on them between greasings. I think the grease could last 60 seconds.

I installed an Energy Suspension poly bushing in an extra set of Z32 uprights I had. 3 months later, with them just hanging out in my garage, the bushing has essentially fused together. I tried to press out the inner sleeve and it was going no where with me cranking on a vise as hard as I could. They had plenty of supplied grease on them upon install, so I can only guess the grease, as thick as it is, will run and poly does NOT like things rotating against it.

If you're not going sphericals in the rear suspension, I'd just leave the bushings alone or spend $$$ for Nismos.

[a_ahmed]

^Yeah im waiting on ur sphericals :P


I need them, thats the LAST thing i need to purchase before i have the car track ready :P Im not going polyurethane on uprights lol.. hell no..

I have polyurethane on ALL stock arms though :( Can't wait to install all the spherical adjustable arms (as soon as i get ur sphericals that is :P)

By the way one suggestion.. change the steering rack bushings to the aluminum ones I swear to God difference is night and day.. i cant explain it AMAZING results.

On s13 also i got the aluminum steering column bushing... huuge difference all this

The car feels very direct, very responsive and this is with busted moog tie rods lmao.. like i said cant wait to install the spherical stuff... oh man...