Spiderbox

i'm running falken ziex ze 512s on 215/45/17 on 17x7 42 offset
rubs on full lock on left turns

the ride is extremely rough. i drive in and around the nyc area, i gotta drive real slow sometimes because i feel like i'm gonna damage something.

anyone know the tire pressure recommendation for these tires?
I emailed falken directly and i havent gotten any response. on their website they list the max cold pressure at 51 psi.

Neothin

as you lower pressure, more rubber will be put onto the road. This increases friction and will decrease your gas mileage.

just a heads up

TerribleTed

I would bet that max pressure is way to high for the weight of an xB. I woudl think maybe in the 30-40 range somewhere might be way way better. Without manufacturer recommendation about all you can do is lower the pressure and drive, see how it handles and once happy that way (assuming the tires aren't flat at that point) watch the tread wear and adjust up or down accordingly. center wear means too high a pressure, edge wear (on both sides) means too,low a pressure.

Your full lock left rub is likely the same thing as my xB. Check the tiedown hook behind the rear inside of the left front wheel ( welded to the subframe just behind the strut kinda). my left one is welded fatter and farther out than my right one, there fore causing rub on left lock only (well actually I can very slightly rub right also). I bent the tow hook in about 1/8" at the lowest point with a hammer just to be sure the tire cant rub the egde of this metal. Now when it hits it only rubs the flat side of it causing no damage. But I don't hold it turned full left lock still. With mine if I simply kinda turn all the way left but don't hold against the stop it doesn't noticibly rub.

Neothin is correct higher pressure will slightly effect MPG. I would sacrifice an MPG or 2 for a more compliant ride.

Are you on factory springs?? I found those to be very stiff and jittery riding. I replaced with Goldline 2" drop springs and the ride improved so much it was amazing. They are progressive rate in the rear I think this is the reason why. ( I am not sure I would want a 2" drop on NYC streets tho, I have been there many times and they are fubar, so perhaps some progressive springs with a bit less drop?) People rave about Monroe shocks making a big difference also in ride quality...I have no need for them at this time, but they might be worth a try for you. A number of articles on here about those ...try search.

hotbox05

about 32 psi should work ok. and the oversized 215/45's should be kinda soft.

Spiderbox

perhaps soft in other parts of the country, not here
i have it on 40 now i guess i'll try 32.

hotbox05

that size tire is pretty plush ride. the 40 psi is insane. when you go down to 32 you will love it. .

Jhhnn

Yeh- you're way overinflated at 40- something in the 30 psi ballpark is more like it.

Get an inexpensive tread depth gizmo at any auto parts store- map your current tread depth, then remeasure after a few 1000 miles... the correct inflation pressure is whatever gives the most even wear...

stew32

Say the total weight of your xB with you in it is 2,700 lbs.
Car is supported by four tires. 2700 lbs/4 tires = 675 lbs/tire.
You put 32 psi (lbs per square inch) of air in your tire. 675 lbs/32 psi = 21 square inches.
So neglecting the stiffness of the tire and assuming each tire supports the same weight, you'd have a 21 square inch contact patch.
You have a wider tire than stock which means more those square inches are from the tread width rather than the deformation of the tire.
Less tire deformation, stiffer ride.

Anyway, you should probably try close to the original spec tire pressure like everyone else said. Even if you could go lower, you don't have as much sidewall for the tire to deform when you hit a pothole or something.

You could also try putting some chalk across the tread and driving a few feet. If the pressure is too high, you'd be able to see the chalk on the tire where the sides don't touch the pavement? Same result without waiting 1000 miles to wear your tires unevenly.

Spiderbox

thanks thats a great idea

hotbox05

close to stock tire pressure is not ok for 215 width.

you will think you are going to flip over as soon as you hit an on/off ramp.

TerribleTed

I would think that 30 might be a low limit as well. Thru experimentation you should find the sweetest setup for those tires your driving style and your vehicle. Wider profile tires generally need a little more pressure than stocky profiles to work best...but the max rating is generally way too high unless you are a truck loaded to the max weight of the tires capability. Even with older more standard tire dimensions the max and manufacturers recommendation are only references. My 1972 Suburban ate rear tire if you set them at the tire placard settings (way overinflated, ate the center off them) of 30 PSI. 25 PSI wore great tho and handled fine ( I didnt carry a load of crap in it on a daily basis, and added air to the tires when I applied a heavy load. My Corvairs are supposed to run less air in the front due to the front of the car being light. Factory recommendation on orig bias plys was 14 PSI front and 28 PSI rear. Thru experimentation with radials I like now 22 front and 32 rear on 45 PSI max rated tires. You would think that 20 PSI might be too little in such a tire but is this application it works great and wears well

hotbox05

14psi ? wow. crazy. no wonder they'd roll. all the tire roll.

TerribleTed

Nah they rolled because of the combo of people putting too much air in the front and the early (pre 1964) ( my car is late, 1965 and later and the rear end is set up alot like a corvette with two 1/2 shafts) swing axle rear suspension design (vws did the same thing on basically the same setup at that time). Gotta remember also Bias plys were much stiffer sidewall so 14 on them was like 20-25ish PSI on todays tires

Jhhnn

I think stew32's suggestion about the chalk will help put you in the ballpark wrt inflation pressure- certainly can't hurt.

OTOH, paying attention and using a tread depth gauge down the road will definitely help get your money's worth out of the tires... you definitely want to try to achieve even wear, which may not be possible if you've put a lot of miles on at 40 psi...

So using the depth gauge now helps you understand what you have to work with... and to achieve even wear from this point forward...

Under-inflation is safety hazard with heavy loads and sustained highway speeds, particularly in hot weather- there's more flex in the sidewalls, which means more heat, which increases chances of a blowout...

In the case of tractor trailer rigs with dual wheels, running a flat can easily cause the flat to catch on fire, usually out in the middle of nowhere... just stand back and watch it burn... some years ago, one of my employer's new vehicles burned to the ground somewhere in western Kansas as it was being delivered... once the rubber starts to burn, just say buh-bye... the usual fire extinguishers don't have a chance in hell of putting out a tire fire...

moonray

Yes be carefull not to run too low an airpressure as the tire will generate more heat and heat is a tires worst enemy. I run 45psi in my nittos which have a 50psi max rating. Yes they ride stiff but there also a 35 series profile with not much sidewall forgiveness. When I ran 17" tires/wheels the ride was the same - very firm. I don't think I would run anything lower than 35psi just for a safety factory.

Jhhnn

I don't mean to misinform or alarm people about underinflation issues- underinflated tires will show too much bulge in the sidewall, and will wear faster on the outside than the tread center. Vice-versa for overinflated tires. Either one is a waste of money because of reduced tire life...

Maybe somebody who has the factory optional 17" wheels and tires can chime in to tell us if Scion recommends some inflation pressure other than the 29 psi of standard 15" tires. It's in the manual, and on the sticker in the driver's door rocker panel... If that were different for 17" wheels, Scion would say so, I'm sure...

As I've said, the correct pressure is whatever gives even wear across the tread, which is the best compromise between all the factors- ride, safety, wear, traction and handling...

Which is why checking the pressure and wear on a regular basis is so important...

TerribleTed

The key indeed is even tire wear. Exactly where this point of tire pressure nirvana is depends on the car, the driver, and how the car is loaded when operated. The only way I know to find this point is close watching of wear ( I really like the chalk idea, but keep in mind turning will wipe the chalk off more of the fronts likely screwing with your data), and adjusting till you get it right. I wore out 2 pairs of rear tires on My old suburban from over inflation(over 5 years) before I figured out that they really needed to be at 26 PSI to wear evenly. The Suburban is big and heavy, the tires were passenger car types, there fore I assumed wrongly that closer to max pressures would work best. OH, and don't forget every tire design is different, just beacuse your Nittos wore evenly at 28 PSI does not mean that your Kuhmos of the same size will wear the same at the same pressure. There may be some magic formulas to tell us how to get it right on , but I am sure some tire manufacturer has burned it long ago (likely right next to the plans for 100 MPG carburators), as having tires wear longer is not in their best interests

Spiderbox

i dropped it down to 32 psi the ride is plush and soft like a man's anus but it doesnt handle quite as good as it did before. btw it was actually on 44psi previously. i'm gonna give 38 a try.

TerribleTed

You got the idea. Apply air drive, apply air drive, remove air drive, remove air drive, find sweet spot and keep it there. Keep in mind also that front and rear pressures will not necessarily be equal for the best effect. LOL just gave you more work to do!!

hotbox05

38 is awfully hight. but hey whatever works. just go up in 2 psi equivelents just make sure you measure the pressure when cold. when a tire heats up the pressure goes up by about 4psi.