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I never put much thought into calculating the ideal pressure, honestly I've always adjusted based on how much sag the tire shows under the weight of the vehicle, and tread wear. It's worked out nicely for me so far, with the exception of some cheap cheap tires I put on my Mountaineer one year. They didn't last long enough to fairly gauge, so I won't count that set.

It's not a bad idea, especially if you're running a smaller sidewall... Honestly, I hate having limited options for tires, but I don't want to go to a bigger wheel.

_-Night-Shade-_ wrote:Wow Nd4SpdSe, no wonder you got amazing fuel economy! I'm sure I'd see a significant gain pumping up my tires to 40+ PSI but that's a little hardcore for me, that's some hypermiler tactics. And as much as I like good fuel economy, I like even tire wear more. Especially once you get into expensive grippy tires - you want those to last. I keep mine at around 32psi and I don't usually pump them up again till they get to about 25psi.

One of these days I'll throw on my stock rims with 205s before going on a lengthy trip and let you know what kind of gains I get.

I never had an issue with uneven tire wear, maybe it's how I drove or the regular racing that I did. I didn't do it for the fuel economy, I perfered how they felt, felt responsive and not squishy, stiffer ride, also combined with my suspension didn't really help the kidney killing, lol.

One thing that came to mind, but something we made sure of was that the VAF was level. This was something to make note when putting/making a CAI, otherwise it did affect response and performance at low throttle. Of course when hard on the gas, the amount of air being sucked in would overcome the affect of gravity on the VAF. Maybe this is common knowledge for the VAF but nothing I've really ever read on here in a very long time.

Not a bad idea, the logic behind it is sound. Mine's pretty horizontal, maybe 30 degrees of tilt.

Me and a few local guys did a few custom CAI's for our cars, and even a few revisions of each. I don't remember whose it was, but I think the VAF was pointed at a 45 degree or steeper, and the damn car wouldn't work well unless you were HARD on the throttle, it was pretty funny trying to pull it out of the driveway and boggled us until we figured out how picky the VAF was.

I imagine extreme angles would have a noticeable effect, I'm surprised more people don't mention that in rough idle situations.

How did a fuel mileage thread turn into a racing discussion??? Ryan, I didn't realize the majority of your daily driving and fuel economy calculations are done on the track. It's gonna be completely different tire pressures when you're racing. And also, it's much more complicated than just tire pressures. If you're eating up your sidewall it's also camber settings, body roll, etc. so don't come to conclusions so quickly.

FYI if I drove around on 50PSI all the time my tires wouldn't even last to see track time because they would look like the top illustration in this pic! Seriously did people forget the basics of tire wear???

_-Night-Shade-_ wrote:How did a fuel mileage thread turn into a racing discussion??? Ryan, I didn't realize the majority of your daily driving and fuel economy calculations are done on the track. It's gonna be completely different tire pressures when you're racing. And also, it's much more complicated than just tire pressures. If you're eating up your sidewall it's also camber settings, body roll, etc. so don't come to conclusions so quickly.

A fuel milage thread didn't turn into a racing discussion. A suggested low tire PSI turned into an example of how low PSI will de-bead your tire, if you get into any sort of turning situation above grocery getting.

Your idea of max PSI in the tire is not correct. The construction of the tire will let it hold upwards of 200PSI (ask me how I know). now, THAT is unsafe. You could put 60 PSI in a car tire and notice the wear and never blow it (factor of safety, say thank you to an engineer) that is also a terrible idea, but 40 isn't bad, its decent, depending on what you do with the car.

The one thing I think we do agree on, is that the max press on the sidewall is indeed the max press you should put in it, ever, for any reason.

For grocery getting and DD'in.... the door sil pressure is what you should roll with.


I indeed know a respectable amount of suspension dynamics, It'd be nice if you could realize I don't have rocks rolling around upstairs.

I usually run my cars at 40 to 44psi. You can expect 5-10% better mpg than running at say 35psi. When I ran my Cobalt at 44psi (a little harsh) and drove on a smooth road at 45 mph the gauge in the cobalt would read close to 60mpg.

I get consistent 30-33MPG on 37-40 PSI, which topped my former mileage of 29-32

It's not a lot more, but my tires have all worn evenly, and the mileage is better. I do feel bumps more though.

roads must real good in Oregon, you wouldn't be doing that here.

Eugene is good for the most part, I avoid the poorer roads whenever possible. When not, I drive slowly. It's kind to the suspension, tire pressure aside, so it's a no brainer.

The road I live on was repaved only about a year and a half ago, but they've torn it up for utility work these past few months. It used to be smooth as glass, now it's crap. I have to avoid 1/3 of it entirely, since it's torn up on both sides, literally right where your tires run if you're centered in your lane.

I recently had two MX-3's at once, both GS with the stock K8. They both got a consistent 30 mpg highway, and about 25 mpg around town.

One is gone now, and I just put a KLZE in the other. I haven't gone through a tank yet, but I'm just hoping for 23 mpg around town.

If you're kind on the throttle, you should get 25 city. If you truly baby it, and run higher tire pressure(still within reason obviously), with minimum weight in the car, 30 would be possible. 25 would be very reasonable to expect if you occasionally put your foot down.

I'll post up my K8 mpg as well. 24-25 city 32 Hiway (at 60 mph). I am running stock sized 15" Falken 912 tires at 32 psi. I have a 3" internal diameter CAI that I custom made and I am running RR racing ceramic coated headers into a stock exhaust minus the resonator. I know most will laugh (and have laughed) at the size of my CAI on my stock K8, but I measured the internal diameter of the VAF and matched the piping to that. I wanted there to be the least amount of air flow velocity discrepancy between the stock air box configuration and my CAI. I dont run rich and have no issues passing emissions. I do notice a dramatic difference in my mpg if I average 70 mph rather than 60 on the freeway.. but considering the jump from 3100 to 3600 rpm I dont think the drop in fuel efficiency is abnormal (down to 27-28). Anyway, thats how my GS rolls

Cheers

Tunes67

PS. Btw.. anyone that knows me (or even seen me for that matter) knows that I am most definitely NOT running minimum weight in my car at anytime I am behind the wheel LOL