tire pressures

[tamanaco]

Dave...some pretty spirited verbage on tire pressure. BTW...hows the BDR running?

[cbreez]

Mr. SkipB,

Sorry this thread was trashed up by Rwilli, Dave, and Jaybird digging up old stuff and the personal attacks on me that are not on subject. Anything I have suggested or advised, please disregard, it's obviously wrong...according to them. I apologize to you.

Dave, I am glad you have some faith in Oltoff and Jaybird, good for you.

Jaybird wants to have the last word on every thread....go for it buddy! You try to dominate every thread on here. Remember, 2 years, you'll be bye-bye, especially with that class-less mouth of yours.

[ROUSHAC]

Car's running real well, Bill. Did OK at Run 'N Gun. See you at Mid Ohio again next June?


Regarding the "pretty spirited verbage", as I get older constant negativity tends to grate more and more on me.

As you can see, cbreez has once again "artfully dodged the bullet" of presenting who he is or what experience he has or even if he has a Cobra by blaming others for his being constantly picked on. I really do think he is nothing more than an internet troll who gets his kicks out of getting others angry (worked with me, that's for sure - maybe I'll get another piece of hate mail from him in a PM).

Look at cbreez's past posts and see how many threads that he has turned into p*ssing matches. Enough already. I will follow the message below from now on with regard to him and hopefully others that think likewise will too.

[Anthony]

Originally Posted by SkipB

I really would like some input from Backdraft owners ONLY on what the optimum tire pressures (F&R) are for the 15" wheel set up with BFG Radial TAs. Because we have a BMW based suspension, input about other car brands is not so useful.

I am looking for the best all around set up for the street. I don't do any competitive events, especially with these tires! I just want great handling, limiited vibration, and the best ride. Not much to ask!

I would think input from other cobra's would be useful, ones with independant suspensions, similar weights and weight distribution, of which all are very similar.

For the best ride, i.e.cruising, you want a lower pressure to absorb the bumps some. If you want best handling, what you are doing is loading the suspension/tire to the extremes on corners, shifting alot more weight on the outside tires than they would nortmally see just with cruising. You will find that the pressure that gives the best ride with cruising will likely be too low to give the best handling, because you will feel the tire kind of roll over on itself as you turn sharpely. You need to increase the pressure for max handling, which may make the ride a little harsher with cruising, but not really that much.

As Oltoff as said, you want above 27 psi for performance with a "street" tire for a cobra. I can tell you that increasing the pressure from 25 to 27 made a noticible difference that I could detect, i.e. wannabe racer, at Mid Ohio.

[Rwillia4]

Independent of the actual tire pressure has anyone had "ride matching" done? I would be interested if this corrects most people’s problem.
I know that the harmonics of the outer diameter of the tires generally come in between 58-68mph (the variation is dependent on the weight of the rim and tire, even if the tire has been balanced in a static condition).
http://www.discounttire.com/dtcs/infoRideMatch.dos

Shaving the tires to make them truly round is also an option, but I don't want anyone else scrubbing rubber off my $$ tires

[Jamo]

Hmmmm....this last weekend, a group of we Cobra owners went on a bit of a drive in the Sierras. A little tussle got started in a local bar. Bartender jumped on the bar...we were told to leave in favor of the locals.

Cbreeze, unless you say you have a Backdraft (ie., the locals)...leave this thread. Now. This is an mfg area, where we don't allow discussions to turn nasty. Come back on it to respond to me, and you'll be gone.

Your posts do have an edge...lose it.

And bythedamnfreekingway...ya damn right I can feel 2lbs. Anybody who actually drives these cars instead of sitting back like they're in a La-Z-Boy would feel it, and most certainly wouldn't be running over 30lbs of air in the tires.

On the BigLetters, I run about 22-23 up front and 20 out back on the track...I like the turn-in with that. Just came back from running 24 all the way around in the Sierras cuz I figured I'd lose a few lbs to the cold up there. When I got back down to the Valley, I was bouncing all over the place. Remember, they are bias ply.

When I ran BFGs and Dunlops (radials) on the KMP (2200 lbs maybe?), I ran 26 all the way around on the road, and it was a nice feel. Not trying to get 50k freeking miles off the set.

[Doug I]

General consensus seems to be that mid to high 20's is a good starting point for road and cruisin' pressures.

For track use use a "higher" pressure

an aside ..... even though they are in their late 70's my folks still take their MG-GTB out for track days. Run 28 all around for the street but up that to ~40 for the track. That takes most of the 'squish' out of the tires .....

I don't think anyone can say 'thou should run X pressure in thee tyres' as there are just too many differences between tyres, roads, cars and even our butts. Everyone can say what works for them and each of us then goes from there to find what works for us.

Something I've been thinking about while reading thru this .... BFG's have a reputation for not being the most round of tyre, nor the most balanced within their construction. Those who used a Hunter load balancer on those BFG's noted an improvement in steering, which no pressure adjustment would fix.

I'm looking forward to running a set of BigLetters - maybe with 4 wooden blocks and low-profile jack I can borrow Jamo's while he's not looking

Doug

[Speedysnake]

Doug I,

I can confirm your thoughts on the BFGs, the front tires were replaced on mine under the tire warranty because the BFG dealer couldn't balance them. As they are now, the tire shop says it's the best they can do without adding weights to the outer rim (might try that soon). They did the Hunter "road force" balance and made me a believer. Since then I've tried various air pressures and found that the lower (22 lbs) air pressure in the front tires "masks" the out of round / balance of the BFGs for highway cruising. Another issue with the BDR is the solid steering column. I'm told that the addition of a flex or "rag" joint in the column would help a lot.

Another problem I'm having with the BFGs - I can't wear the %$#&^*@ things out

[Bx1]

I do appreciate the info re: tire pressures. I am looking forward to reducing my pressures and hope that resolves some of the steering wheel 'nervousness' I experience.

[rdorman]

I feel your pain Speedy. Never liked the BFG's. I run the yoko's currently, just for crusing around, at 22 and 24 (rear, 45-55% split a$$ heavy with me and normal load). Up to about 26 all around for autox and such. That road force balancing on the latest hunter machines, so long as the tire jocky knows what they are doing, it great, absolutely great. Once they got done, one tire required no wieght, the others only a tiny bit and none needed on the outside.

[MaSnaka]

Just to throw one more non BackDraft opinion out there... my driving started with the BFG's 15" at 15 lbs, too low, tried 20 lbs, hmmm better, if 20 is better then 25 would be too and so I ended up at 32 psi. Wow, the car was full of pep, rear end spinning and sliding in turns almost effortlessly, too much effortlessly. I found the sweet spot to be 28f 25r, much better traction and stability. I am looking to replace the BFG's with something better in the near future. My car has only been on the street.

John

[Speedysnake]

John,

That brings up another point; The car might "feel" better, but is it faster? I'm putzing around this afternoon, went for a quick ride with all four tires at 22 lbs. The car felt smooth and very forgiving in the corners, lots of warning before it broke loose. Then I ran the pressures up to 28 lbs., same road, felt completely different. Almost like a go kart, tight, more responsive to the wheel, and would jump out from under me. I really don't know which is faster.

[MaSnaka]

Speedy-
I don't know...with all the bad raps I have heard about the BFG tires, I am just going to play it safe until I can upgrade. But the tires were well worn when I got the car and now have an additional 6500 miles and they don't seem any more worn now.

John

[Doug I]

As a general purpose tire the BFG is ok I guess. I mean it works for what's intended end use is. V8's lay far more power into those tyres than they were designed for, so hence the slippin' and a slidin' that people experience. But for day to day driving they are ok - and they don't wear out. Unless you're really really trying.

For track use they are too hard and just don't get the bite that other tyres do. The flip side is that they'll slide with predictability and will let go gradually, whereas other tyres will hold on right to the raged edge THEN land you in a whole world of trouble unless you're really on your game.

Now another question - Which smokes the best ?

[Naumoff]

Originally Posted by MaSnaka

Speedy-
I don't know...with all the bad raps I have heard about the BFG tires, I am just going to play it safe until I can upgrade. But the tires were well worn when I got the car and now have an additional 6500 miles and they don't seem any more worn now.
John

That is the problem. They are made of the same rubber compound as the tires on a forklift.

..........and have the same speed rating.

[rschoeni]

Admit it, drivers buy the 15" BFG m&s 's for the "look" and they also serve to keep the wheels off the ground . Definitely not performance tires.

Your cold tire pressures depend upon the tire manufacturer's recommended hot pressures, your car's setup and the driver's preference. I'd suggest you take the car to an auto-x or 3, and experiment with different pressures.
Regards,
Bob S

[SkipB]

Wow!

I leave the country for a couple of weeks and come back to fire and brimstone about tire pressures! I love this forum!

It is obvious that I need to experiment. It also has become obvious that I should probably ditch the BFGs and get better tires. It sounds like the Yokos are the way to go? I would love billboards, and maybe should go that way.

Christmas is coming and maybe I should ask my wife for a set of large lettered Goodyears to be under the tree. Yeah, right, like that would happen!

Thanks for all the input. I didn't mean to offend any non-Backdraft car owners. I just thought since each brand of car is set up a little bit differently, that perhaps the BMW IRS and front end set up on Backdrafts might have an optimal setting that doesn't apply to others.

In any case, I think this subject and thread are about worn out. Let's move on to more interesting topics.

SkipB

[need4speed]

See if you can get access to a tire pyrometer (probe type) and measure the inside, outside, and center tread of the tires. Hotter in the center means too much pressure, hotter on the inside/outside edges means too little pressure both of which mean loss of contact patch and traction. Temps should be fairly close across the entire tire when pressure is correct. This assumes that you are not running any aggressive camber settings and that your alignment is correct. Once you get the temps close to the same you can fine tune from there depending on conditions and car oversteer/understeer. You can find instructions on using a pyrometer on a number of web sites with more comprehensive explanations than I have provided. Hope this is helpful.

[rdorman]

The Yoko's in our sizes have been discontinued. The Billboards some folks love, other, umm, don't. But they do look terrific! Do some thread reading on them first. Numerious other options as well, all with some compromise. Avon's, firestones, GY's, Hoosiers, S/R's.......

[BFBurk]

Another great thread! I have BFB's and have tried everything to reduce the vibration at road speed, 50-70 MPH. Lowering tire pressure seems to work. If I go down to 15-18 PSI The vibration thru the steering wheel is much reduced. ERA says 25 PSI for front and rear is a good place to start.

I know there are Cobra drivers that think this is a boring thread but threads like this is all that keeps me coming back. We all know there are quirks that have to be addressed when you have a Cobra.

Learning what problems others have had and how they resolved them is very helpful.