Maximizing BFG Radial T/A Traction

While I'm deciding on whether to switch to a street radial and which one I decided to see how much more traction I can get out of my 275/60R15 BFG Radial T/A's on 8" wide Mopar Rallye wheels. Temp today here in SW Florida is 88 and blue skies. I tested at a giant parking lot that was 90% empty. Thank God most of the "snowbirds" and tourists left for home. I had at least 1/8 mile of clear driving with no cars anywhere near my lane.The parking lot is a sealed blacktop and I'm sure the surface was hot. The car is a 1972 Duster with a mild build 440, 727, 3.23 sure grip.
I started testing with 28 pounds of air in each tire. I had driven 3 miles to the parking lot so the tire temperature was normalized. I used a fat piece of sidewalk chalk and drew a 2" band across the back of each tire while the car was pointed absolutely straight. I jumped in the car and drove at about 25 to 30 miles an hour for the 1/8th mile and brought the car to a stop. I inspected the chalk mark that I had made and at 28 pounds the interior 3 tread bands were completely erased but the outer bands were mostly still covered. So I kept repeating that process while dropping tire pressure a pound each time. I could see the outer band getting less and less coverage each time but the change was slight. When I got down to 22 pounds I stopped testing with the chalk and did a short burnout. The attached pictures show the patch on the blacktop. You can see that all 5 treads of The BFG tire were making contact. I measured the width of the patch on the blacktop and I got 7.5". While the outer two tread bands did make some decent contact with the surface they were narrower than the actual tread on the tire. I'm not sure if that's because those outer treads on the inboard and outboard edges of the tire have a round shoulder probably for when the tire leans in turns.
BFG specs say that tire has a 9" tread width and I measure 9" of "flat" tire surface before the outer band radius kicks in. At 22 pounds I'm measuring 7.5" of tread width from the actual burnout patch.
Has anyone on here done some similar testing? What were your results?
How low of a tire pressure do you think is safe to daily drive this BFG tire? I stopped at 22 pounds because my one test burnout was rather loud and I wasn't looking to attract attention. I'm told that as I continue to drop the pressure I will start to reduce contact with the center of the tire tread. Anyone using a similar size tire to mine... what's the pressure you shoot for when the tire is up to temperature?
I'm planning another session this time starting at 22 pounds. Glad to have reduced it 6 pounds... so far.

Regardless of the tire pressure, those tires are probably the worse tire in existence for traction. They look cool though

I'm interested in your results and hope you have better luck than me. I ran my Dart at the track a few times with a prepped starting line, and I still had no luck. Yeah it was better than the street but I still got gated by drag radial cars. I just couldn't put the power down. I'm only running a 372. I cant imagine with a 440! But in the interest of science, carry on. Myself and I'm sure others are curious if you can get any improvements.

I don't run under 25 on the street. At the strip you could go lower.

Those tires are just not good for traction.

replicaracer43 said:

Regardless of the tire pressure, those tires are probably the worse tire in existence for traction. They look cool though

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Yup. I know this. It's not a track car but it's very fast. Mostly drive it locally for the rush that only an old Mopar big block gives me. Being a plum crazy purple car with hood scoops, fat exhaust note, tape stripes, 440 badges, etc., I get a lot of late model owners that want to test their new performance car they just bought and waxed, against a 47 year old muscle car. I can roast the BFGs but like the post says, I'm just trying to see how much better I can get them. They handle great in normal driving but yes... traction sucks. But then most, if not all, all-weather passenger car tire brands would equally suck. I'm looking at street radials. Want to get some that will not entirely kill handling or wear out in a few thousand miles of hot weather daily driving. Don't want them to be so sticky that they pick up every pebble and seashell on the road. I see some sticky street radials here that get so sticky that a burnout spray-paints black rubber onto rear quarter panel behind the tire. I know it's a compromise but I'm not sold yet.

I've gone down as low as 18 pounds at the strip.

Modern BFG is not as good a tire as Cobras or Avengers.

Freaking beautiful duster!

Question ... Are you running 14 inch on the front of the car ?? I find it is a common thing to do
that with small bolt cars. Is your car small or large bolt pattern ?? Thanks for any info...

PS ....Your car looks great.

Frank
The Wheel Guy

I run 28-30 psi in the rears and about 35 in the front, have t/a radials all around. Idk why they get such a bad rap, sure if you try to launch at any rpm higher than 4k you will have a hard time getting them to bite, but they grab decent for street tires. That being said you deff can roast em if you try to but they arent to the point where it makes the car unpredictable. Now start throwing drag radials on there and you may possibly start breaking stuff, i had to put a torque strap in mine shortly after it was built even on the radial t/a’s. Seems like the magical rpm for me is about 4k rpm. She does spin for about 20-30 feet but seems to bite pretty decent. The t/a’s are very predictable though. If nitto made some decent size 15” tires id probably put drag radials on the back and a all season up front. But the bfg look the best

replicaracer43 said:

Regardless of the tire pressure, those tires are probably the worse tire in existence for traction. They look cool though

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You beat me to it. The rubber compound is HARD. Still though, this is a good test and a great way to zero in on the best pressure for traction on any tire. Big thanks to the OP.

Had a set of BFG Radial T/A's on a car once. Pinto station wagon, so needless to say, not enough power to break them loose. Dry pavement they were ok, but rain or snow, they were downright dangerous.

Excellent write up on how to find the optimal tire pressures. I've been doing that for years with great success.

I had Radial TA's on both my hotrods after I got them running, and they were down right dangerous on the street on high powered cars. It was like I was driving on snow covered roads with them on. I could smoke them and the cars would drift sideways even at the upper end freeway speeds.

I ended up putting Nitto 555 Drag Radials and a set of properly adjusted slapper bars on both cars, and now both cars hook up harder than ever, are safe to drive on the street, even when it rains.

The Nitto's don't like freezing weather, in fact they say don't let them freeze; and they start to feel greasy if they get too hot. They are rated to around 186mph and they last a long time (two+ years) if you don't smoke them off all the time.

Great tires for moderate climates. I used the chalk method and run them at 18 psi around town and 22-25 psi on road trips depending how much I load the car. Optimal tire pressure is all about adjusting the shape of the bottom of the tire where it bulges from the weight of the car.

The air pressure required to get the correct shape is different depending on how much a percentage of actual weight on the tire compared to the same tire with the maximum load.

jbc426 said:

Excellent write up on how to find the optimal tire pressures. I've been doing that for years with great success.

I had Radial TA's on both my hotrods after I got them running, and they were down right dangerous on the street on high powered cars. It was like I was driving on snow covered roads with them on. I could smoke them and the cars would drift sideways even at the upper end freeway speeds.

I ended up putting Nitto 555 Drag Radials and a set of properly adjusted slapper bars on both cars, and now both cars hook up harder than ever, are safe to drive on the street, even when it rains.

The Nitto's don't like freezing weather, in fact they say don't let them freeze; and they start to feel greasy if they get too hot. They are rated to around 186mph and they last a long time (two+ years) if you don't smoke them off all the time.

Great tires for moderate climates. I used the chalk method and run them at 18 psi around town and 22-25 psi on road trips depending how much I load the car. Optimal tire pressure is all about adjusting the shape of the bottom of the tire where it bulges from the weight of the car.

The air pressure required to get the correct shape is different depending on how much a percentage of actual weight on the tire compared to the same tire with the maximum load.

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I'm liking the Nitto's. What size Nitto's are you running? What tires do you have up front (brand and size)? Thanks

I would bet the 205/70-14 Michelins that were on my Barracuda hook better than
T/A’ s... I ran them for a while. They look good but are too damn expensive for old tire tech. I think I paid less for the M/T SS Drag Radials I have now. And these 255/60-15s hook 1000x better ! I cant even spin them !
Well... I do have some 2.76s installed for a road trip I did 3 weeks ago...

1BAD72 said:

I'm liking the Nitto's. What size Nitto's are you running? What tires do you have up front (brand and size)? Thanks

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I run the 275/60-15's on my '68 Barracuda convertible with V-rated(149mph) General's 215/60-15's on the front. These are still available. This car currently has a bit of predictable over-steer that I'm comfortable with.

The '70 'Cuda has the 325/50-15's out back with V-rated225/60-15's that are no longer sold by BF Goodrich. There are several other V-rated tires in that size range available including the very expensive Pirelli tires that are direct replacements for some of the older Porsches.

On the street;
275/60s want a wider rim, that's why normal pressure is lifting the edges and puckering the first inboard treadband.
I use the 85% rule;
a 275 is 10.8 section (275/25.4=10.8); and wants a .85x10.8=9.2" rim; rounds to 9", if you can find one. I used an 8.5 which then works out to 8.5/10.8=78.8% too narrow but what can you do. A 10" rim would be 10/10.8= 92.6% which is too wide, probably pretty hard to install.
With the proper rim width, you will be able to raise the pressure back into a safe street pressure, altho I have gotten used to 24 in my 295s on 10s...
And if you run a tire on a too-narrow rim, with too low a pressure, I have found that it likes to eat the two treadbands first inboard from the edges; not the outermost. And if you get the tire up to higher MPH,It will try to grow and burn off the center 3
And if you run it at too high a pressure, it will burn off the center three.
When you get down to 24psi, the tire, on a narrow rim, in a corner, will roll over onto the sidewall, which, the first time you feel it, is freaky! I have gotten used to it,lol
But 275 BFGs are too skinny for a 440 anyway. 295s can be fit into a 68 Barracuda tub no problem; and I was thinking the Duster has the same tubs, but I don't know that for sure.
IMO, the widest tire for an 8" rim is 8/85%= 9.4section, which is 9.4x 25.4=239 in metric speak; so a 235. Guys put 245s on those and lower the pressure some to get away with it.
Hope this helps

I did the same a few timeswith my '67 Newport many years ago.
After the tires got some heat into them, the contact patch got better...

AJ/FormS said:

On the street;
275/60s want a wider rim, that's why normal pressure is lifting the edges and puckering the first inboard treadband.
I use the 85% rule;
a 275 is 10.8 section (275/25.4=10.8); and wants a .85x10.8=9.2" rim; rounds to 9", if you can find one. I used an 8.5 which then works out to 8.5/10.8=78.8% too narrow but what can you do. A 10" rim would be 10/10.8= 92.6% which is too wide, probably pretty hard to install.
With the proper rim width, you will be able to raise the pressure back into a safe street pressure, altho I have gotten used to 24 in my 295s on 10s...
And if you run a tire on a too-narrow rim, with too low a pressure, I have found that it likes to eat the two treadbands first inboard from the edges; not the outermost. And if you get the tire up to higher MPH,It will try to grow and burn off the center 3
And if you run it at too high a pressure, it will burn off the center three.
When you get down to 24psi, the tire, on a narrow rim, in a corner, will roll over onto the sidewall, which, the first time you feel it, is freaky! I have gotten used to it,lol
But 275 BFGs are too skinny for a 440 anyway. 295s can be fit into a 68 Barracuda tub no problem; and I was thinking the Duster has the same tubs, but I don't know that for sure.
IMO, the widest tire for an 8" rim is 8/85%= 9.4section, which is 9.4x 25.4=239 in metric speak; so a 235. Guys put 245s on those and lower the pressure some to get away with it.
Hope this helps

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Thank you... I appreciate the info. I have stock tubs and leafs are re-located inboard. A 295/50 BFG is 26.6" diameter. It would fit if I mounted it on an 8"... but will rub the inside tub wall on a 10". Not interested anyway. It Looks like a skateboard wheel in the Duster wheel well. A 295/55 MT ET S/S or a 275/60 Nitto 555R will fit and are around 28" diameter but more importantly both manufacturers say an 8" is acceptable for their tire. Unfortunately I haven't found anyone making 15" Mopar Rallye wheels in a size between 8" and 10" or I would get some. That's why I'm presently looking at ditching the BFGs in the rear. A 275 street legal drag radial like the 555R or ET S/S will support a mild 440 and then some.

Some additional information on the BFGs. What I did was to go to a shopping center near me that had gone out of business. I had a giant empty area to do a few tests. I got some pieces of chalk and chalked the rear tires from inboard edge to outboard edge. Checked my tire pressure and did a burnout. I repeated this until I found that the entire chalk mark had worn away during the burn out indicating full contact patch. I started at 28psi and got full contact at 22psi. Still didn't hook at all in 1st from a dig. Just made a wider tire mark. Going lower than 22psi didn't help either. Went down to 18.

Hyup BFGs are good for breaking loose at 50/55, and spinning to 60,70,80 some say at 93 they were still hazing. I love those tires.

Thanks for the write up. Good info to try out.

I have 2 sets of tires, Cooper Cobra's and Nitto 555R's. The Coopers are awesome for a smoke show but I run them in the colder months. Ran a motorcycle and they were still smoking at 60 mph lol.

Put the Nitto's on and you would swear you lost power because they are hard to break loose. Until a new Mustang 5.0 wants to run and you hook off a roll and leave him looking at your tail lights and wondering wtf happened.

duster2 said:

Question ... Are you running 14 inch on the front of the car ?? I find it is a common thing to do
that with small bolt cars. Is your car small or large bolt pattern ?? Thanks for any info...

PS ....Your car looks great.

Frank
The Wheel Guy

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Large bolt pattern. 215/70R-14 fronts on 6" rims, 275/60R-15 rears on 8" rims. Thank you!