Bias Ply Tire Pressure
 

I am looking for feedback on tire pressure and amount of 'wrap' on our tires at launch. I know people on here have more experience and I was hoping to hear what pressure other people have run bias ply tires at. We are running 14.5psi, 3600rpm launch and 30 x 9 x 15 Hoosier D05's on a 10" rim in this video. 1.55' 60 ft in this video as well while weighing in at 3440 w/ me in the driver's seat. We are only running bracket races currently, but the car is setup as a skinny tire SS car. Thanks for the help.



https://youtu.be/t9U--APlFBQ.

Re: Bias Ply Tire Pressure
 

That looks pretty darn good. The weight of the car, how much hit, and how much hp affect it. I ran a 3055S MT on my 68 Camaro with 12 psi, and the slick always looks good in slomo.

Clark

Re: Bias Ply Tire Pressure
 

Andy., when I run the bias tire, Hoosier 30x9x15 D 05 I run minimum 18 lbs and up to 22 lbs depending on the track. Car weights 3400 plus. Looks like your climbing the tire and should pump it up 2 lbs at at a time to see what your car likes best. Good luck.

Re: Bias Ply Tire Pressure
 

You also need to watch the surface of the tire for full contact "feather".. The tire will tell you if it is making proper full contact.
Bias tires work the sidewall. Most of the time Too little air over works sidewalls.
Somewhere I have a real good picture of a run with my car when it was killing the sidewalls from low air pressure.

Re: Bias Ply Tire Pressure
 

Thanks for the reply's and experience shared. Our buddy Dave has been all over us to add more air. Looks like I will this Sunday at Milan. Nostalgia Drags with Nitro Funny Cars, Gassers and 1990 and older bracket racing. Should be a good time!

Re: Bias Ply Tire Pressure
 

I'm with Joe I normally would run 18 to 22 psi and have ran it at 24 before. My car most races at 3650 and sixties around 1.47 Like Joe said keep adding in 2 pound increments until you find the sweet place.

Re: Bias Ply Tire Pressure
 

Update. I went to Milan on Sunday (9-27-20) and bumped the tire pressure up 2# to 16.5 for the one and only time run I got. Car launched hard and the 1/8th picked up .02 and 1mph from previous runs in similar air for my Dad. I ran my best et and mph ever with the car. 11.20 @ 119.75 mph @ 1950 DA. Video looked good too. Below is a still of the difference from the 14.5 and 16.5psi launches at the same 3600 rpm and all other aspects of the car being the same. Dad is racing Friday night at Milan in Open Comp and we are going to push him to put 18.5 psi in the tires for Q1.


Open Comp is a .500 PRO tree, qualifying on reaction time class w/ no dragsters or delay boxes. Your dial-in all night is .10 faster than your best Qualifying ET. 56 car field and I have seen as many as 89 cars trying to qualify with the bump being as low as .039 RT! Lots of whomping at the stripe and brake lights too. Dad is tied for 10th in points, which is pretty darn cool.


Youtube link of TT1 from Sunday. Full speed and then slo-mo:
https://www.youtube.com/watch?v=67n8ydKrU24

Re: Bias Ply Tire Pressure
 

For reference and because I like seeing numbers and data, here is the corner weights of the car prior to installing the Qa1 Rear Upper control relocation kit at the diff. Other reference items to note. Car as weighed this day and as we race it now has 4 wheel iron drums, Diehard big battery in the stock RF location and the car does not have any ballast bars or boxes in it. 10 gal alum fuel cell in the middle and rear of the trunk. Memory was about 7-8 gals in the cell when we weighed it. Kirkey seats, no rear seat.

DVD players in the headrests, 12" sub box in the trunk and R12 a/c too (all kidding...:D)

Re: Bias Ply Tire Pressure
 

Well... my two centavos...
Air 'em up 1/2 lb. at a time 'till the 60 ft. falls off, then back up 1/4 lb.
I'm a dinosaur... but that's how we did it back in the stone age...
Your mileage may vary.

Re: Bias Ply Tire Pressure
 

Thanks for the insight and that is a solid approach. The car was designed 10 years before I was born and I am 41 now. Dinosaur approaches are valid...:D

Re: Bias Ply Tire Pressure
 

I would go to the extreme and put about 20-22 pounds in maybe even 23-24 --see what happens if it likes it try more---if it doesn't back it down from 20 to 18 see what happens---1/2 or 1/4 pound increments are for fine tuning when you eventually find the sweet spot--you will wear the car and tires out if go the" itty bitty" pound route--are you looking for 60 foot times or are you looking for overall ET & MPH?---you can make a car 60 foot and decrease the overall performance--overall the higher pressure side walls look a bit better but how does the foot print look?? is it wallowing the tires as it moves forward or is the pattern pretty uniform across the tire marks on the track???--FED 387

Re: Bias Ply Tire Pressure
 

The 2 lbs increase and previous reduction in launch rpm are helping the car to plant the width of the contact patch and not pile the tire up on the contact patch. We are going after a solid flat patch, to minimize wallowing and thus decrease launch variances. It is a bracket car that we are looking to refine the combo on for repeatability sake. We are ultimately looking to print timeslips with W's on them

Re: Bias Ply Tire Pressure
 

Andy-- I fully understand the concept of bracket racing --REPEATIBILITY---if the car runs the same number regardless if it has 10 PSI or 20 PSI in the tires who cares what the tires look like at launch--all you are trying to do & accomplish as I understand it is go from point A to point B in XXX seconds correct??? so wallowing, tire pressure , launch RPM, removing a spark plug wire(LOL) etc should not come into play other than to get the same exact number eveytime what ever it takes correct??
I feel the tire needs more air and thats what I would do --plus are the rims drilled for screws? have you tried running with out them?? your sidewall photos would look different as the wrinkles now coincide with the screw location(IF you r running screws) if not then more air will help take away those wrinkles--By the way great looking car !!!!! Also have you looked at the tires in REALLY SLO MO out to about 20-30 feet to see what they are doing and what the footprint looks like as the car is moving forward??--FED 387

Re: Bias Ply Tire Pressure
 

More than anything no matter the pressure you settle according to any given track condition, you want both fires to look identical, it tells you equal force is applied to the tires.

Rearend rotation has it lifting the driver front higher with more force being applied to the left rear. You want the tread and sidewall to wear even..

You can accomplish this with a bigger diameter sway or double adjustable dampers front and rear. BMR used to sell a huge bolt in factory location sway bar and may still..

I see the rear shocks are factory location as well, Viking or vari shock QA! probably sell a factory bolt in D/A for a Chevelle. If you do D/A dampers let us know I'll suggest how to adjust them so the rear bumper is level to the track surface, as it leaves the starting line - wears the tread and sidewall evenly..

https://i.imgur.com/TsHE7P3.jpg

Re: Bias Ply Tire Pressure
 

car looks like its twisting from left to right as it launches---left slick does not look as if it is planted the same as the right also rear bumper looks higher on the left side vs right side---might just be the angle of the pic but the right sure looks like its dipping---Also left front tire appears to be higher on the launch but again it could be the angle of photographer--FED 387

Re: Bias Ply Tire Pressure
 

looking at the slo mo from the left side you can see that the right slick is definitely wadding up --look at it real close the inside front of the tire

Re: Bias Ply Tire Pressure
 

Yep --look at .14 on the video starts to wad the tire up