What's a good PSI for 225/40r18

[inked_up415]

Can someone recommend the correct PSI range for 225/40r18 tires pls?
Thanks

[james 408]

Can someone recommend the correct PSI range for 225/40r18 tires pls?
Thanks

huge variation here. depends on how long, how fast, which tires, your alignment, your driving style, ambient temps, track temps, and what side of the bed you woke up on.

street pressure: 35lbs (slightly more front pressure than rear - like 1 psi, can help)
track pressure: *edit* 27-33lbs *edit*

bear in mind, the track pressure will not give you more grip for 99.9999% of street applications, cause your tires and drivetime just isn't long enough to get heat in them. furthermore, i wear the outsides of my tires on the street.

Read your tires.

to reduce wear on edges and increase wear on the centers, raise your psi.

[MikeyB3]

I typically run 36 all the way around. But I'm on 235/40/18. The stats probably translate some...

[inked_up415]

Ahh I see thanks for the info. As far as the tires wearing in the center, that's not gonna happen. They always wear the inside cause of the camber.

[MacDaddy]

i usually run a little higher up front since the S4 is pretty heavy up there.

I would do a minimum 35 up front, if you feel like going higher try it out, and yeah, read your tires.

[oppositelock]

I usually run pretty high (like max as indicated on the sidewall) pressures to improve the steering response. I don't find it reduces grip much if at all on the street, but it probably depends on the tire. It does make the tires ride noticeably harsher. If you have a tire with a stiff sidewall like Pilot Super Sports, this might not be worth it. I find it helps Conti DWS mushballs a fair bit though.

[james 408]

I usually run pretty high (like max as indicated on the sidewall) pressures to improve the steering response. I don't find it reduces grip much if at all on the street, but it probably depends on the tire. It does make the tires ride noticeably harsher. If you have a tire with a stiff sidewall like Pilot Super Sports, this might not be worth it. I find it helps Conti DWS mushballs a fair bit though.

don't buy continentals. if you're gonna buy crap buy federal 595 rsr. having to run those types of pressures defeats the purpose of buying the mushy tire in the first place. btw I destroyed the supersports in 1200 miles (outside tread block was peeled off the shoulders). they won't honor their warranty =P the pilot sport cups were the best.

[oppositelock]

I was fooled by all the idiots that gave the DWS 9.0+ reviews on tirerack.com. Turns out 99% of the tire buying public doesn't know shit from shineola. Oh well. They actually have decent grip as long as you load them up smoothly. Pitch the pig into a corner hard and it gets real interesting. First time I hurried to make it through a yellow left-hand arrow the front plowed, then gripped, then the rear started coming around. I was pleasantly surprised to make it out in one piece. Anyway, they do ride real nice on the freeway, if you like that sort of thing.

Federals better than Continentals? C'mon. I did have good luck with Sumitomo HTR Z IIIs on my WRX. Didn't last super long, but a pretty fun tire for thrashing Hwy 9 etc.

[ricekikr]

Federal rsr ftw awesome grip awesomer price

[james 408]

I was fooled by all the idiots that gave the DWS 9.0+ reviews on tirerack.com. Turns out 99% of the tire buying public doesn't know shit from shineola. Oh well. They actually have decent grip as long as you load them up smoothly. Pitch the pig into a corner hard and it gets real interesting. First time I hurried to make it through a yellow left-hand arrow the front plowed, then gripped, then the rear started coming around. I was pleasantly surprised to make it out in one piece. Anyway, they do ride real nice on the freeway, if you like that sort of thing.

Federals better than Continentals? C'mon. I did have good luck with Sumitomo HTR Z IIIs on my WRX. Didn't last super long, but a pretty fun tire for thrashing Hwy 9 etc.

haha, yes continentals are at home in a straight line with your family in the car. they do okay if they're not overheated, your suspension isn't overly stiff, and if you don't make any sudden movements.

federal 595 rsrs are decent, but at $144 per for 265-35-18, it's hard to beat. most tires run north of 200, especially for anything decent. it's just my budget-buy recommendation.

and yes, tire reviews on the internet (I suppose this one included by definition...), especially non-track based reviews, are entirely worthless. tireracks track testing is valuable, however.

[blmlozz]

track pressure: 23-30lbs

What kind of track do you do? Sand dunes?

[james 408]

agreed that pressure is too low for this vehicle for most tires.

[Timtheguru]

Read the tire pressure guide on the fuel door, this should apply to any size wheel/tire as long as it doesn't exceed the tire's recommendation on the sidewall. The tires only tell you what the maximum and minimum to use.

[viceprp]

His original numbers were correct but for a larger sidewall and sticky rubber for dedicated track tires.

[jpurre]

I ran 38-40 psi in my 225/40/18's. I'm currently running 235/40/18's at 36psi. While we are kind of on the subject... The way I go through tires, I don't bother with the expensive ones. I found and tried out some new tires. The Champiro UHP1 GT Radial is a pretty good tire for the money. I've got several thousand miles on them and they are great so far. Tread wear, grip, and tread pattern very close to Michelin PSS. At around $80/tire, I run 'em hard and get new ones in a year.

[james 408]

haven't tried those. cheaper tires are the way to go for most people, top of the line tires will improve grip, but generally will not necessarily last longer. This, however, is not the case if you're overcooking those cheap tires. For instance, I go through tires in less than 2k miles, and the cheaper ones closer to 1k because they don't have the beefed up shoulders or the tread compound to cope with the heat of extended hard drives. pilot sport cups and r888 will last longer in track/extremecanyoning cause they won't blister/melt themselves to death. high-end street tires like star specs or supersports are hybrids, and will still melt themselves after 5-10 minutes. not to mention the tread depth on supersports when new is way too much for hard driving. But the top-end tires (cups/r888) are not the way to go if you'll run into rain and such -- massive hydroplaning issues on the pilot sport cups in the wet.

[Delmed83]

225/40/18: ~ 38 Front, ~ 37 Rear

[Kenrevo]

On my 225/45/17 I ran 42 with slight center wear on the rears after 3 summers. I'll probably do 40 for my new set.

[oppositelock]

federal 595 rsrs are decent, but at $144 per for 265-35-18, it's hard to beat. most tires run north of 200, especially for anything decent. it's just my budget-buy recommendation.

Federal rsr ftw awesome grip awesomer price

Wow, just checked these out. Basically a DOT-legal race tire for ~$140. Where do you buy them around Palo Alto?

[KurtEiger]

I keep mine at 35/35 as stated inside the car door. I'm running OEM 245/40/18 Pirelli Cinturatos. I check cold rubber regularity with a good meter, and they are always +/- 1psi. Took it to dealer for first service, and when I checked the rear were set to 30psi. I'm assuming the tech set them that way for a reason. Any idea why?

[james 408]

reducing rear tire pressure can increase oversteer, however, it does funny things with the contact patch. spreads that large are most commonly used for autocross applications. Most people i've spoken with argue that bars and spring rates are a much better way to balance the car rather than skewing tire pressures to that extent.

why would a service tech do that? lord knows. put it back up to the proper street pressure.

edit: i'm running 35F 33R currently -- canyon carving, it's too high for extended drives but I do a lot of short stints before parking and b/sing. if you're doing track sessions over 10 minutes, i would consider lowering them from the numbers i'm using. but read your tires, get a pyrometer. typically you want to dial in alignment and tire pressure such that the insides are heating up slightly faster than the outside. pyrometer right after you finish your session. if you have too much heat in the center, lower the pressure. too much on the sides of the tire, raise pressure. You get better fuel economy and early session handling from running higher pressures, but late session you will be balooning the tires and wearing hte centers.