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Recommended tire pressure
I just got my first replica, a used BDR with the standard 15" BFG package and I have a couple of questions.
1) What's the recommended tire pressure. These aren't your normal 3000# + grocery getters? 2) WHY would someone put a "S" rated tire on a car with 300+ HP at the rear wheels, did they really think the car would not be driven over 112 mph???? A temporary problem, being worked on as of this thread. I just want to insure they're properly inflated. PS: Anyone want a complete 15" package, they're for sale, make me an offer. The car has 1300 miles on it. I'm going with 17's and "V, W, Y or Z" rated tires. |
MTPockets,
People that go for originality in their replicas go for 15 inch tires. Unfortunately there isn't enough demand in the market place for any of the major tire manufacturers to make true "high performance" 15 inch tires in the correct size for a Cobra. So folks use what is available which normally boils down to S rated tires. Someday I will get a second set of 17 inch tires in stickier rubber for track use. I also still hope that some day someone does make better performance 15 inch tires. Something that hooks up better and with stiffer sidewalls. But for now, the 15 inch Yokohama Avid S/T are just fine. PS. Don't get caught up in the tire rating too much. The rating you refer to has to do with sustained speeds in excess of 112 MPH for LONG periods of time (in the case of S rated tires). Unless you are going to be on the track, I don't think you will see 112 MPH except MAYBE for a very short burst. Trust me, the S rated tire will not explode under this circumstance. |
Let's call tire rating "Peace of Mind". Let's say the BFG comes apart at 120, the least it will do is rip fiberglass to hell. The worse is my obit listed on CC. I've gone over this car end to end, looking for "short cuts" that may have been taken during it's assembly. So far I've only found a few, nothing major however as I tell people that want to go for a ride>>>No air bags, no crumple zones, no door reinforcement, no door locks and no roll bar on your side. That's the difference between a closed casket for you and an open one for me. I do plan on taking my car to the track, the first thing the safety tech will look at is the tires, so, they're coming off.
PS: Thanks for the intel on the Yoko tire. May stick with the 15" wheels. |
My set up is 275/40/17 on 17/10" in front. 335/35/17 on 17/12" in rear. I have Dunlops on mine.
Tire pressure is 22 front, 24 rear. Sticks like glue. Ride is better than my Mini Cooper S. Jack |
Jack - you guys that run so low air pressure, isn't their a problem of wearing out the outside of the tire soon ? I know it would help in my comfort but, I don't want to wear out the tires fast just for a nice ride.
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I run the old bias Goodyear 'Bill Boards'. Not DOT approved and says right on them for "Racing Only".
Any idea what kind of speed rating these may have? Such a thing was unheard of back in the day. I've been to 130 plus with them. :D BIG tires and light car equals low tire pressure with no problems. I run around 24 psi, no unusual wear. |
Ernie: There is no acknowleged speed rating done on the "For racing purposes only" tires. They are for off hiway usage exclusively hence no liability implied or accepted. To be accepted for "Hiway Usage" they must be DOT approved which they are not. Many people use them for that but they have significant limitations regarding road hazards, sidewall strength and treadwear.
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Play around with tire pressure. On rough roads with a "spirited turn", the car may bounce out. I use only 18 PSI in both front and rear.
Of course, on an excellent road or track, 25 PSI is better. |
I don't put enough miles on the car to worry about 'mileage' from my tires. But I DO worry about 'strength' concerning pot holes, flat potential, etc.
The Goodyears are little more than 'canvas bags', VERY light weight. A good thing for performance, not so good for long life. But boy do they hold the road! Even in wet weather these are great tires! |
Funfer2
Well the car weighs only 2600# with my 240# contribution. Not sure of the load ratings on the tire but its got to be significantly more than what's needed. I am running rather wide wheels to insure proper contact pressure. And these are cold pressures, start putting some force into the driving effort and they heat up quickly. To be properly sure I checked tread contact the modern way, four pieces of white paper followed by white chalk. Oh yea also asked Mr. Hudgins, who told me to run them at 22/24 and "don't worry". Jack |
Armond at CA Cobra recommended the following tire pressures for the BFG Radial T/A 15" tires.
Front BFG P235/60R15 = 28 PSI Rear BFG P295/50R15 = 25 PSI I have used these recommendations and they seem to work very well for me. |
Tire pressures depend on what type and brand tire you are using, as stated above. I have Yokohama Avid's on my SPF. The Cobra shop suggested 20-22 lbs. Not nearly enough for my application. The tires were letting loose without prior notification, twice causing red flags to fly high. I went home, pumped them to 30 lbs. and have been happy ever since. Much more predictable and stiffer sidewalls equalling quicker steering response.
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Get a pyrometer and measure the temps across the tread with them hot - then adjust tire pressures until they are even.
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I do have a digital temp gun for checking cylinder and the tire temps on the sprint car. When I get the cobra out from it's winter nap, I'll give it a try.
Thanks |
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