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Correct Pressures for 17" Tires by Dennis LaGrua
Started on: 04-09-2013 09:52 PM
Replies: 28 (598 views)
Last post by: ILVMYGT on 04-02-2014 11:13 PM
Dennis LaGrua
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Report this Post04-09-2013 09:52 PM Click Here to See the Profile for Dennis LaGruaClick Here to Email Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Like many Fiero owners looking for a more modern look; I just converted over to 17" x 7.5" W wheels with Goodyear Eagle 1 225 x 45 x17 Rear and 205x 45x 17 Front. Using 17" tires gives a much shorter sidewall, flex is probably more of a problem, so it would seem logical that the tire pressures most likely have to be higher. I have heard that some owners run as much as 44 psi tire pressure in these but I have started around 40 psi. I'd like to ask the owners that run 17" wheel/tires what tire pressures have given the best results for....handling, ride, mileage, wear, road noise, traction, (wet and dry) etc.?

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[This message has been edited by Dennis LaGrua (edited 04-10-2013).]

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Report this Post04-09-2013 10:02 PM Click Here to See the Profile for RaydarClick Here to Email RaydarSend a Private Message to RaydarEdit/Delete MessageReply w/QuoteDirect Link to This Post
Wait... 225s in the front and 205s in the rear? Was that a typo?

I usually start out at 35 in the rear (235/45s) and ~30 in the front (215/45s)
I have found that more air seems to wear the centers out more quickly.
I have also found that I wear out at least two pairs of rear tires for every pair of fronts. For every Fiero I've ever owned.
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Report this Post04-09-2013 10:05 PM Click Here to See the Profile for CC RiderClick Here to Email CC RiderSend a Private Message to CC RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
Gosh those pressures seem high.
I would not even run that high at the track.
Street use I run 32 front and 34 back.
This seems to give the best wear.
Hope this helps.

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Report this Post04-09-2013 10:09 PM Click Here to See the Profile for BlackEmraldClick Here to Email BlackEmraldSend a Private Message to BlackEmraldEdit/Delete MessageReply w/QuoteDirect Link to This Post
Anywhere between 33 and 35 psi. That is going to give the best ride, handling, and wear regardless of sidewall height.
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skuzzbomer
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Report this Post04-09-2013 10:34 PM Click Here to See the Profile for skuzzbomerSend a Private Message to skuzzbomerEdit/Delete MessageReply w/QuoteDirect Link to This Post
I ran just above 40 all around on my Fiero. Anything less than that felt... Weird. I'm sure that was the result of the tires I was running, though. Cheapish rubber and the fronts were worn down in an odd way - I couldn't tell that until I swapped wheel sets.

Dropped to 35 when I swapped to 15" wheels before I stopped driving it altogether. Was really comfortable compared to the 215-225/45/ZR17s Front-Rear.

-------------------------------------
My current daily runs 225/45/ZR18s on all corners with a manufacturer recommended inflation pressure of 220kpa - or 32psi.
I bring it up to 250kpa on my compressor, though (metric gauge). The TPMS idiot light comes on when they drop down to 195kpa or so.

................ TL;DR,

Mid 30s will work for whatever you run on the street.

[This message has been edited by skuzzbomer (edited 04-09-2013).]

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Report this Post04-09-2013 10:38 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
I try to keep 40-42 PSI on everything. Sidewall height doesn't really matter for pressure.
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Report this Post04-09-2013 10:44 PM Click Here to See the Profile for BlacktreeClick Here to visit Blacktree's HomePageClick Here to Email BlacktreeSend a Private Message to BlacktreeEdit/Delete MessageReply w/QuoteDirect Link to This Post
Correct air pressure will depend on vehicle weight and tire size. Wider tires will generally have to have lower pressure than skinny tires. And a heavy car will need more pressure than a light car (for the same tire size).

I would suggest drawing chalk lines across the tire tread, to see what the wear pattern is like. If the chalk wears off more in the middle, pressure is too high. If the chalk wears more on the outside, pressure is too low.
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Report this Post04-09-2013 10:45 PM Click Here to See the Profile for jake88gtClick Here to Email jake88gtSend a Private Message to jake88gtEdit/Delete MessageReply w/QuoteDirect Link to This Post
I ran 36 front 34 rear on 215's all round
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Report this Post04-10-2013 02:36 AM Click Here to See the Profile for BlackEmraldClick Here to Email BlackEmraldSend a Private Message to BlackEmraldEdit/Delete MessageReply w/QuoteDirect Link to This Post
I can not tell you how many tires I have put on customer cars because of premature wear from under and over inflation. 35 is the highest I recommend going without sacrificing tread wear. Even 40-45 psi overinflation can drastically reduce tire life.

Unless we are talking about 3/4 ton+, 32-35psi is the range for almost all vehicles manufacturer recommendations. Companys spent millions to research that, and I'm not one to dispute that.

[This message has been edited by BlackEmrald (edited 04-10-2013).]

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Report this Post04-10-2013 07:59 AM Click Here to See the Profile for BrianbClick Here to Email BrianbSend a Private Message to BrianbEdit/Delete MessageReply w/QuoteDirect Link to This Post
Take a look at the sidewall. That pressure will yield the longest tread life and traction.
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Dennis LaGrua
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Report this Post04-10-2013 09:24 AM Click Here to See the Profile for Dennis LaGruaClick Here to Email Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Raydar:

Wait... 225s in the front and 205s in the rear? Was that a typo?

I usually start out at 35 in the rear (235/45s) and ~30 in the front (215/45s)
I have found that more air seems to wear the centers out more quickly.
I have also found that I wear out at least two pairs of rear tires for every pair of fronts. For every Fiero I've ever owned.


That was a typo. It's 225 x 45/17 rear and 205 x 45 /17 front. If you consider the light weight of a Fiero I would say that your estimates will probably work. I do expect a harder ride from the 17s but hope that its not bone jarring.


------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Powerlog manifold, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
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Report this Post04-10-2013 09:46 AM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Brianb:
Take a look at the sidewall. That pressure will yield the longest tread life and traction.


This is a common misconception. The markings on the sidewall only indicate the pressure that should be used when you are running the maximum permissible load (weight) on the tire. For example, a tire sidewall that reads 44psi at 1500 lbs means that the tire is rated to carry a maximum of 1500 lbs weight safely, and at that weight, the tire pressure should be 44 psi to prevent tire failure due to excessive sidewall flexing and overheating.

If you run 44 psi on the same tire with a corner weight of say, 750 lbs, the overinflation will cause the center of the tread patch to bulge out causing a loss of maximum traction and premature wear along the center of the patch. Conversely, if you don't put enough pressure in your tires, the center of the tire patch will cave upwards and result in a loss of maximum traction and worn outer edges of the tire tread.

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Report this Post04-10-2013 09:52 AM Click Here to See the Profile for JustinbartSend a Private Message to JustinbartEdit/Delete MessageReply w/QuoteDirect Link to This Post
I used to keep 40-44 psi in the front. I noticed that it wore the center out faster. I just put new tires on(RE-11a 225/45R17) and have them at 30 to see how these do. I think the front end of a fiero is too light for the max pressure.

I think a good test would be to have a gopro or similar camera right on the fender watching the tire flex as you take some hard corners. I'm not sure how much flex is desired though. Could ask a tire manufacturer possibly.

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Report this Post04-10-2013 11:06 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
1. Fiero and many cars uses 30PSI Cold.
2. Max Pressure is Max Cold Pressure.
3. Max Weight is per Wheel at Max Pressure. Take Axle Weight on label on door and divide by 2 to get appox tire weight load. Example: Rear axle 1819 / 2 = 909.5 tire load at max car weight (including cargo etc)
4. Change Tire Pressure will change total "Spring Rate" on suspension. NASCAR etc is an example using tire pressure to adjust suspension "on the fly." In Street use, is why you often get problem when tire pressure is unequal on an axle.

Using wide/narrow tire on most car still get same pressure as OE. or maybe +/- 1-2 PSI.
You need Very wide tires mess w/ pressure... Like balloon tires on trucks or big slicks on drag cars.

Sidewall does not matter in calculating tire pressure.

See my Cave, Tires

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Report this Post04-10-2013 11:16 AM Click Here to See the Profile for pcarClick Here to Email pcarSend a Private Message to pcarEdit/Delete MessageReply w/QuoteDirect Link to This Post
Standard way to determine correct tire pressure: Drive the car a few miles to warm up the tires then immediately measure the temp across the surface of the tread; outside, center, inside. If the outside/inside are warmer than the center, add air. If the center is warmer than outside/inside let some out. Ideal pressure is when the temp is even across the tire surface.
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Report this Post04-10-2013 11:18 AM Click Here to See the Profile for Marvin McInnisClick Here to visit Marvin McInnis's HomePageSend a Private Message to Marvin McInnisEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Bloozberry:

The markings on the sidewall only indicate the pressure that should be used when you are running the maximum permissible load (weight) on the tire.


 
quote
Originally posted by theogre:

Using wide/narrow tire on most car still get same pressure as OE. or maybe +/- 1-2 PSI.
...
[within reason] Sidewall does not matter in calculating tire pressure.



Thank you both for posting the correct information. The misconception that "higher pressure is better" has shortened the life of many a tire ... at the same time reducing both vehicle performance and comfort.
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Report this Post04-10-2013 03:11 PM Click Here to See the Profile for aaron88Send a Private Message to aaron88Edit/Delete MessageReply w/QuoteDirect Link to This Post
The less tire pressure you can run and still wear evenly the more tire you will have on the ground. The more tire you have on the ground the more traction you will have.

I ran 26psi when I had stock tire size (with even wear). Now that I have wider tires I run less. Just to clarify this is not for a drag car, this is for daily driving and performance for road speeds less than 200kph (120mph).

.
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Report this Post04-10-2013 04:14 PM Click Here to See the Profile for BoostdreamerClick Here to Email BoostdreamerSend a Private Message to BoostdreamerEdit/Delete MessageReply w/QuoteDirect Link to This Post
Tire pressures should be set according to your style of driving and road conditions. The flatter and straighter the roads and the more gentile you are with the gas pedal, the more air you can run in your tires. Less pressure for curves, hills, and performance driving.

Check your tire pressure "cold" (about four hours or so after last being driven). Drive your car as you normally would. Immediately check your pressures again when you arrive at your destination. The pressure should have gone up 10%. If not, adjust your cold pressure accordingly. If the warm pressure was over 10% more than your cold pressure, increase your cold pressure. Decrease cold pressure if your warm pressure is less than 10% higher than cold.

Sounds a little complicated. It's not.

Jonathan
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Report this Post04-10-2013 04:43 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by pcar:
Standard way to determine correct tire pressure: Drive the car a few miles to warm up the tires then immediately measure the temp across the surface of the tread; outside, center, inside. If the outside/inside are warmer than the center, add air. If the center is warmer than outside/inside let some out. Ideal pressure is when the temp is even across the tire surface.

Yes, this is one reason why NASCAR uses tire temperature. In their case, 1 PSI too hi/low can cause a tire wear problem or even a blowout.
Problem is most people don't have an accurate and fast thermocouple/thermistor and the meter to measure tire temperature. Dealing w/ street generated temps on most steel belted radials, 2-5PSI might not change Temperature enough for cheap units to measure result.
Cheap probe units, like units sold as kitchen gadgets, are too slow and you can't get good readings. By the time you can take the third reading the tire has cooled off enough to screw up the results.
Cheap infrared units available to most people, like Harbor freight and others, are fast but may not be very accurate.
HF Cen-Tech - item#69465 is +/-2%... 2-4% can skew the results. 2% low in one reading but 2% high on next read...

 
quote
Originally posted by Marvin McInnis:
Thank you both for posting the correct information. The misconception that "higher pressure is better" has shortened the life of many a tire ... at the same time reducing both vehicle performance and comfort.

Yup
An other example... hyper milers use high pressure to "save money on gas" but eat tires...
Better is using Tire Construction to gas saving like some Michelin models. People have no clue that changing tire brands/models can hurt/help your mpg.

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Report this Post03-30-2014 12:14 PM Click Here to See the Profile for solotwoSend a Private Message to solotwoEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by theogre:

1. Fiero and many cars uses 30PSI Cold.
2. Max Pressure is Max Cold Pressure.
3. Max Weight is per Wheel at Max Pressure. Take Axle Weight on label on door and divide by 2 to get appox tire weight load. Example: Rear axle 1819 / 2 = 909.5 tire load at max car weight (including cargo etc)
4. Change Tire Pressure will change total "Spring Rate" on suspension. NASCAR etc is an example using tire pressure to adjust suspension "on the fly." In Street use, is why you often get problem when tire pressure is unequal on an axle.

Using wide/narrow tire on most car still get same pressure as OE. or maybe +/- 1-2 PSI.
You need Very wide tires mess w/ pressure... Like balloon tires on trucks or big slicks on drag cars.

Sidewall does not matter in calculating tire pressure.

See my Cave, Tires




Good info to know. I just had the summer tires unmounted and remounted. I have had the car about a year, so last summer I played with the tire pressure trying to find a happy medium. I noticed when installing my winter tires the car actually rode smoother. So when the tire store removed & remounted my summer tires because of a ware issue on them(inside tire tread was wearing, I had it aligned last year) when I bought the car. The tech asked what pressure I had them at and I told him I think they were at 34 and I thought PO said he had them higher, could be wrong on that. I checked them in the garage this morning and they are at 29. I found driving on them yesterday the ride wasnt bad. Then finding this post with the Ogre's comments, makes a lot of sense to me now. I'll run them for a while at 29/30 area and see how they do. Yokohama S Drive, 225/45 17 front, 255/45 18 rear. By the way to all who are contemplating going to larger tires, dont go bigger that 17. I had the fronts on the rear for a short time last year and it rode better and they didnt rub in the back like 18's have several times. Just my observation on my car.
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Report this Post03-30-2014 03:32 PM Click Here to See the Profile for DooberSend a Private Message to DooberEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'm running 40 all the way around, so far haven't really had any noticeable tread wear on the inside. Lower than that in the rear and it likes to sway more than I prefer... so until I get some solid bushings or an '88 cradle, that's where she stays.
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Report this Post03-30-2014 10:56 PM Click Here to See the Profile for doublec4Click Here to Email doublec4Send a Private Message to doublec4Edit/Delete MessageReply w/QuoteDirect Link to This Post
I've been using 32psi front and back on my 225/45/17 tires. I've had nice even tread wear.
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Report this Post03-31-2014 08:47 AM Click Here to See the Profile for 2.5Send a Private Message to 2.5Edit/Delete MessageReply w/QuoteDirect Link to This Post
The thing that probably can be affected by running 17s is the chance of denting a rim because there is less tire before the edge of a big pothole contacts rim. I'm not sure how real that danger is.

I run usually 35 in back and 30 in front on my 17s.
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Report this Post03-31-2014 05:59 PM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
I run 40-45 pnds on every car for years. If you have the correct size tire for the rims you have, and its got a proper alignment, the tread will wear evenly all the way across. I never have a tire wear off on the edge or center of the tread, except when I used to run 30-32 pnds. Theres way more benefits with higher pressure than low or recommended ones. Ive always thought the factory recommendation was just bs to make the car seem to ride better. I dont have any official stats, but Ill bet theres way more blowouts with low pressures than higher ones. As far as Nascar goes, did you see all the cars that blew out tires at California that were below the recommended pressures ? Just about every car in the race had multiple blowouts. Not any blew out to overpressure.
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Report this Post04-01-2014 04:09 AM Click Here to See the Profile for GodSendClick Here to Email GodSendSend a Private Message to GodSendEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Raydar:

Wait... 225s in the front and 205s in the rear? Was that a typo?

I usually start out at 35 in the rear (235/45s) and ~30 in the front (215/45s)
I have found that more air seems to wear the centers out more quickly.
I have also found that I wear out at least two pairs of rear tires for every pair of fronts. For every Fiero I've ever owned.


Nevermind

[This message has been edited by GodSend (edited 04-01-2014).]

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Report this Post04-01-2014 12:23 PM Click Here to See the Profile for 2.5Send a Private Message to 2.5Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by rogergarrison:

Ive always thought the factory recommendation was just bs to make the car seem to ride better.


Unless you are just on a track where they keep things flat and smooth with no seams or bumps, it does actually make the ride better. Might be easier on the suspension than 45 lbs too. But to each their own, over inflating will get you better mpgs, and easier burnouts.

[This message has been edited by 2.5 (edited 04-01-2014).]

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Report this Post04-02-2014 03:31 AM Click Here to See the Profile for DooberSend a Private Message to DooberEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'm 100% on board with psi=ride quality. I have a copy of the '87 FSM, and it lists 30psi. Mine have deflated to 30 from the typical 40 I run them at, and there is definitely a noticeable difference. If I ever go up to a 17" tire, I'll probably run them closer to 30 for daily driving, just because the sidewall is so much shorter.
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Report this Post04-02-2014 10:06 AM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
Higher air pressure also somewhat protects a rim from damage from potholes too. Low pressure is much more likely to pop the tire at the bead or cut the sidewall. The shorter the sidewall, the more chance.

[This message has been edited by rogergarrison (edited 04-02-2014).]

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Report this Post04-02-2014 11:13 PM Click Here to See the Profile for ILVMYGTClick Here to Email ILVMYGTSend a Private Message to ILVMYGTEdit/Delete MessageReply w/QuoteDirect Link to This Post
How about measuring the weight on each tire at a scale? For each axle take the highest tire weight and use the manufacture recommended pressure for that weight. The manufacture provides load tables for their tires. I use this method on my truck and motorhome. On the truck when I am running empty I use one pressure and a higher pressure when it's loaded with a trailer.
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