Drag Radial Tire Pressure

[msb64]

Just wondering what tire pressure works the best in bigger wheel drag radials at the strip, like the 285/40R18s?

I have tried 325/50R15s in the past with pressures anywhere from 14 lbs up to 20 lbs at the strip.

It was hard to determine what actually worked the best, as the front end being so tight created launch/traction issues.

With the larger volume 325 tires, even the sun would create havoc maintaining a desired tire pressure on each side.

This time around I am going to try the Nitto 555R 285/40R18s, with a few changes up front.

I have already dropped 15 lbs off the front end, plus will remove the front sway bar (and its weight) for runs at the strip.

[Wharf Rat]

I've ran many different brands and set ups of DRs and they've all seemed to end up cutting the best 60's at around 15 PSI +\- a pound.

[msb64]

Thanks for the reply.

I wasn't sure if there was any benefit to dropping that low or not with an oem sized drag radial.

I will give it a try then, with the 18" size and shorter sidewall it shouldn't be as bouncy as the 15" ones were at the top end shut down.

[Wharf Rat]

Yup, even on 20 inch DRs I've gone down to 15 and they've been happy. And right, less sidewall=less butt pucker on the big end.

[msb64]

I started out with 20 lbs for a few test runs, but it was way too easy to break them loose.

Right after a pass I dropped them down to 16 lbs and that made a big difference, once I figured out how to launch for the best result.

I kept the burnouts in the 4 second range, and the tires didn't seem to ball-up too much.

At 16 lbs I still had to drive it off the line, slow release on the clutch while slowly stepping on the gas until it got moving enough and then squeeze the pedal right to the floor.

The 60 foot times where not great with the soft launches, best of the day was only a 1.77, but did manage to get an 11.33 and 11.34 though.

The mph also picked up to 125.35, probably because the Nittos where shorter than my old 325s, and I was able to get into 4th gear sooner.

The thing I was most happy with was running with the Raptor shift light for the first time.

They are awesome, no more looking down at the tach, lets you focus on the tree and track and you can't miss that bright flash (red on mine).

I set mine to 5800 rpm to start with, and it seems to work well without pushing the motor unnecessarily.

You were right on about the reduced bouncing at the top end with the 18s shorter sidewall, it was way less than I had with the 15s.

All things considered, for me the 285 drag radial is not a bad street/strip tire once you get it sorted out.

Still running 3.31s in the rear and full stock exhaust system.

[NMAv]

I'm looking at putting a set of either of these Nitto 555R tires on 18 x 10.5/11.0 Bogart drag racing wheels. I'm thinking the 45R vs the 40 as it gives me a tiny bit more sidewall. Thoughts? Not sure about what to put up front yet.

 

 

P305/40R18 106V 180-720 5.0 27.72 12.13 10.0-(11.0)-12.0

2094

@

44

305/45R18 110V 180-690 6.3 28.78 12.05 9.5-(10.0)-11.5

2337

@

44

[msb64]

The 305/40R18s are already 1" taller than the stock goodyears, the 45R18s would be 2" taller.

Both will knock a bit off of your gear ratio, it may not be a big deal if you have 3.73s out back.

Go with the widest wheel that you can safely fit out back, to maximize tire contact to the pavement.

The 305s are just over 12" wide, probably best to run at least an 11" wide wheel.

I went with the 285s because I wanted matching wheels for the street, and didn't have enough set aside to either pick up 4 new wheels, or get another set of oem wheels and have them widened.

As it was, the 2 - 285s plus mounting and balancing was $960 Cdn.

[NMAv]

Never noticed the size was only 27.9. Thought it was slightly bigger. I'll go with the P305/40R18. Running 3.08 gears ~ 1100 rwhp and the car was built primarily for the Texas Mile and mile type events. Something in the 3.3/3.4 gear range would be more suitable for 1/4 miles. It is on my bucket list to have a couple rear ends to roll in and out but I've got to divest myself of a few assets and do things right.