I went to the ANRA event this weekend and had a blast! Just put new tires on the car: M/T Pro Drag Radial, 9x30-15. These replaced 10.5x30-15 bias ply slicks. For my first run, I used 16 psi. The tires gave me a 1.65 60'. That was terrible compared to my old tires that gave me a 1.58 typically. Everyone told me to go up in pressure to make them work better, but I instead went down to 12 psi, which was the low end of the recommendation from M/T: http://www.mickeythompsontires.com/tech-bulletins/street-air-pressure-guidelines

At 12 psi, the car gave me a 1.52 60', which is the best ever with the car. Multiple people said I should go up on pressure rather than down and that if I put 20 psi in the tire, it would do even better. Since I was going into competition rounds, I didn't want to change anything and ignored them. I continued to get great 60' times.

The next time I can get some T&T runs, I'm going to try higher pressures to see what happens, but I'm very interested in the experience of you guys. Relevant specs on the car:

About 3300 lbs. with me in it
Super Stock leaf springs + Caltracs and drag shocks
727 with 3500 stall, 4:10 gears
500" big-block with a 260 @ 0.050 solid roller

I run the Pro Bracket Radial in a 28x10.50. Mine has had the best 60ft of 1.41 at 19 psi. In reality it was probably higher, I made 3 passes in 40 minutes and that 19PSI was the cold pressure before the first run.

Pretty new to drag radials myself as I haven't made a full pass yet. We started at 16 psi stone cold, the rear shocks are valved for radials. We were wadding up the bias plys real bad with the shocks set up for radials so I'm guessing you can go with a lot more aggressive settings with Radials. Our second "go for it" pass produced a big wheelstand and the landing did some damage after I lifted. There's some more info in the "tips for a drag radial newby" thread.
HTH's

If the track is good, I've run up to 21 psi in my 295-65 M/T ET Street radials. Typically gets quicker as air pressure goes up.

Yep. Dragging less of a flat pair of tires down the track

what width rear rim ? That will affect psi . Do you have radial valved,tight, rear shocks ? Did you alter rear shock settings going to radials ? What sort of power/ ET ?
Whatever works for your car is best .
For what its worth , with Hoosier 275 radials I ran 17 1/2 - 18psi on a 8" rim . Similar with MT ET street radials . With MT Pro bracket radials I went to a 10" rim , with the 28x10.5 I ran 18psi , I now run the 29.5x10.5 version @ 19 psi . Looking at launch pics may even prefer another 1/2psi or so .

Oh yeah I was running 1.42-1.48 with my 505 , with my 440 I am around 1.5-1.52

Tex

They are 10-inch rims. I didn't change the shock settings for the radials. I hadn't thought about that.

ET is 10.60 to 10.70. I probably have about 550 hp at the wheels.

I didn't realize there was a thread about drag radials. I'll have a look.

My M&H Racemasters like 21.5 on my car.

see if you can get startline video or pictures , see what is happening

Tex

Generally speaking most drag radials like more pressure than any bias ply does, that being said I haven't raced a set of radials in a lot of years so keep that in mind. the last set of legal NHRA stocker bias ply tires I raced on where 9x30 on a ten inch wide rim that ET the best with 16.0 to 17.0 Lbs. cold, the 60 ft. and reaction times where great on those tires
Do you know how accurate your tire pressure gauge is?
Are you using a low tire pressure gauge or a regular gauge that goes up to 60 Lbs. or more?
I've seen decent quality low pressure tire gauges vary a hoop, some read low and some read high compared to a very good known calibrated test gauge
I suggest you use your tire gauge only, DO NOT LOAN it out EVER Add air 1/2 lb. at a time until the 60 ft. and reaction times slow down and then go the other way down 1/2 lb/. at a time until it reaches the limits on the low side The number on the gauge doesn't really matter as long it reads the same every time with the same pressure in the tire, what does matter is the time slip

Which tire are you using?

Good point. It wouldn't be the first time I've chased a gremlin that turned out to be bad data! My gauge is a low-pressure type, so I'm measuring at the top of the scale for the radials. Same gauge I've used with my old slicks. I think it was pretty accurate, but I should probably use another gauge to compare with

I am using a 275-60-15 on a 68 Runner just shy of 4000lbs.

Valving a rear shock for radial is looser than the equivalent bias ply shock on extension at least.