Recommended tire pressure

OK, I searched all the forums (thank God for the "Search" function!) and couldn't find what I need, so here goes (Jim W's not here til Tuesday - maybe we can take a Poll!!):

I have 205R16's on the front, and 225R16's on the back.

I've been running 16 pounds in the front and 18 pounds in the rear, and it seems to be OK - handles very well, rides nice and all that. The only reference I found to Speedster tire pressure was an old GB post about lowering down to 18 - 20 pounds when at the drags. If he's normally running higher than that, then how high? That seems a bit high for the weight of the car (and GB had much smaller tires on his first car - this was in 2003).

What are other people running in tires of my size (or close)??

Thanks, gn

I have a spyder, not a speedy, but weight is pretty similiar. The fronts are 205's and the rears are 225s on 16" wheels. Started out with 35 lbs in each one. Way too high. I'm down to 25 cold now. I'm a little concerned about going much lower, I don't want to peel a tire off a rim, but it still "feels" like too much pressure. The guys on the spyder site have suggested as low as 17. I did that one time and the car had a strange almost greasy feeling that was really unnerving. Of course, it was also wickedly out of alignment. I'm going to keep dropping mine a pound or two at a time and will let you know what I wind up with.
angela

Gordon, I seem to remember 23/28.
I went through the same search you did a few months ago.
I'm getting so senile, I ended up making a "cheat sheet" I keep in the car for my 4 vehicles.
I'll double check and let you know.

Thanks, guys......

I've been running under 18 lbs. for three years and never felt as though it was greasy. I still feel pavement divisions, especially at the rear, but I have a 19mm anti-sway bar back there, too.

Did about half a dozen really solid starts when playing around with a G-Tech and never noticed any turning of the tires on the rear rims (I had a reference line drawn next to the valve stem supports, and nothing ever moved).

When I dropped them down at first, I remembered my old Beetle having something like 24 pounds in each, this car is about 2/3's the weight, so I started at 20 and found it pounding a bit so went to 18, then 16 and left it there. I was also looking at the sidewall "pooch" (a technical terms from the old Dune Buggy days) and it never got to as deep as my wife's CRV, so I figured I was OK.

It would be neat to measure tire tread temps across the tread surface and set them up that way, but th technology is way beyond what capabilities I have, so I shot-gunned it instead.

gn

Wow,

I'm running much higher pressures. About 26-27 in front, about 30 in back. 185/15's Kumho's. I was running a little lower but felt the slow speed turning resistance was too high. I am happy with that combo at theis time and also helps gas milage I'd think.

Bruce

I run about 23 / 28 cold and 34 / 38 for an autocross on concrete with the same tires (195 50 15). I actually have a tire pyrometer but never used it on the speedster. On the street it is hard to get good numbers because things don

Gordon

Michelin MXV4 195-65-15 on 5

Wow, you guys are really running a lot higher than I am.

How I arrived at my 16 front/18 rear:

I took the weight of my car (1650 lbs) and compared it to a "real" 356A which supposedly weighed 1808 lbs. "dry" plus the weight of the fuel (according to my 1959 owners manual). That's about 10% less.

My original owners manual tells me to run 20 lbs. front, and 26 rear on the street, if I have the original tire size and application rating, but those were for Bias-ply tires, which have a much stiffer sidewall, along with a number of other variables, like they're much narrower than mine.

I am running much larger, Continental tires, putting more "patch" on the road and, therefore, would seem to need less pressure to do the same job. When Porsche switched over to Continental tires for racing back in the 50's, they were running 30/30 lbs., but I'm not doing any racing with these, so I took a SWAG and just dropped everything 10% from the manual and tried that. It's been pretty good, so far, even though I dropped the rear more because it was too stiff, but if I were to do any serious autocrossing, I would probably run them up to 26F/28R, just to stiffen up the sidewalls a bit.

Don't forget: Porsche racing 356's were running 185X16 Bias Ply tires. I've got 205X16X6" wide front, and 225X16X7" wide rear radials and, even though the radials should be "greasier" in corners and need a bit more air pressure, these are wide enough that the effect is muted, somewhat.

Anyway, it's interesting to see what others are running, and I may play with a little more pressure to see what it handles like (and it should improve mileage somewhat, too!).

Thanks, Gordon

Gordon, I'm running the same size tires as you. I've settled on 23 front and 28 rear (maybe a pound or two higher on both ends for an extended freeway trip). I think the important thing is to maintain at least a 4 or 5 pound difference front to back, depending on vehicle weight. Tire specs can have a big effect also. Especially when it comes to that "greasy" feel. My Dunlop SP-8000 dry weather max performance type tires really like to "hunt around" on some concrete surfaces. Almost feels like low tire pressure. I just try to ignore it. The reward comes when you get back onto some curvey blacktop and that same tire embraces the road like velcro.

My JPS has Kumho Ecsta HP4s (185/65/15) which are considered "sticky but stiff" tires. I'm running 28 front & 32 rear. I've gone up and down the tire pressure range, but 28/32 feels right to me.

Running 16/18 and my car would waddle like a duck, if the tires would even stay on the rims at all during spirited cornering.

The Vintage owners manual I downloaded from this site says 22/22.

Well, I think I'm "getting religion" on this, as I think I spun one or both rear tires slightly when doing some "drag strip runs" while playing with a G-Tech gizmo.

I didn't notice anything after for a while, since I was still in South Carolina and never got to drive much over 50 MPH around town and the shaking sets in around 65. Got on a turnpike here in Rhode Island and it shook a lot. Got the tires re-balanced and should get it back out there tomorrow to see what's what (spent today visiting the grandchild-to-be!!)

My 1959 Porsche owners manual tells me to run 20 front and 24 rear on much skiinnier tires, but I think I'll try Dave's recommendation of 23 front 28 rear for this tire size and work around that. Also just got my air compressor back from Chris, so I can actually change things now!

Thanks, guys.......this has helped a lot!

Gordon
One of the "Pressurized Speedstah Guys" from Rhode Island

24F / 28R - 165R15 - ...

You definitely, definitely want more pressure than 16/18. NOW I know why there was a little waddle in the car in quick turn transitions! On a really hot day, if you were to really dig the car into a corner, the sidewalls are going to be pretty unhappy, and may even cause some damage to the sidewall. Been there, done that, bought the T-shirt.

You probably won't turn the tire on the rim in just straight line acceleration. Your car is just too light - it'll just spin the rears before that happens, I bet. Hell, I've run down to 15psi at the track in my car with more than 3x the HP with traction compound on the asphalt cutting ridiculous 60' times, and I've never spun a tire in a rim.

You want a stiffish tire to provide a pretty neutral feeling, and make your suspension do the work for ride quality and to keep that tire on the ground in spirited cornering. If the sidewall is flexing because the pressures are too low, you get all sorts of funky feedback and risk rolling it up off the rim if you're already cornering hard and have to dig in even harder because you need to make a sudden correction for whatever reason.

I know low-profile tires are the rage in Fall River, but you don't want to join the crowd because you blew the bead off the rim. :)