Technical Tire pressure for a light car.

I know this topic has probably been beat to death but I wanted to hear opinions.
My modified is powered by a 2.0 Pinto and the car only weighs 1552 lbs.
Tubeless Coker 5.00-16 ribbed front & Goodyear 6.50-16 diamond tread with tube on rear.
I want the best ride for a car that's awfully light with a fair amount of unsprung weight. Weight distribution is evenly distributed to all 4 corners. I have been running 18lbs./front & 15lbs/rear.

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Start with 30lb then go down a pound or 2.What do they have on the sidewall?Nice ride too.

 

I run 20 in front & 25 rear , myA weight is 2,540 ..
I think about my air pressure , tire's say 32 & 40 ,at that pressure it a very harsh ride!
I do not know if a tire getting ready to let go , if there will be a indication ,

 

I'd be looking at low 20's . Test for tread contact and move up or down.

 

22 lbs all around in my 32 roadster. Comfortable ride for a fly weight car. Does steer with noticeable higher effort.

 

Personally I would not go below low/mid 20s .
Experimenting is key, and comments above.
Neat car !

I think we need lots more photos to give a better answer........

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I run 22# in front, 24# in back. My 32 weighs 2520#. It's un-driveable at 32-35#

 

How does it ride with the 18 front and 15 rear that you are now running?
By the way....super nice T modified you have there!

 

I think it rides pretty good, I guess what worries me about running low pressures is hitting a pot hole and losing the bead! (If that's possible?) If I run more pressure it beats you to death!

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My 26 T coupe weighs 2000 lb. Front tires are 155x15 with 16lbs of air. Rear tires are 275/60x17 with 19 lbs of air. All 4 tires have a slight bulge at the ground. The ride is good and the handeling is also for a 103 in. wheelbase. Hope this helps.......................

 

Did you mention sidewall plies? It is difficult to get these to ride nicely - your unsprung weight to sprung weight ratio is out of kilter! Those axles, brake assemblies and wheel/tire combos are designed to support a car or pickup twice your weight.

 

I think you're right, the rears say 4 ply, the fronts don't say but I'm sure they are 4 ply also.
I just don't know how low I can safely run them.
I have seen Modifieds with no front brakes to keep the unsprung weight down but that's just crazy!!!

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Apart from air pressure in the tires, what about the springs? Looks like an full pack in the rear? (Stiff)

 

The bulk of the leaves in the rear spring are cut short and used as spacers and to add sprung weight. As you move out toward the ends I eliminated leaves to allow movement and to soften the ride.

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call Mr Coker or some one on his staff.

 

I have done that and was told to inflate to 30 to 35 lbs. (Maybe a liability issue if under inflated?) That would be rock hard on my car!

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I run 25 in the front, 15 in the back.


I'd like to run a little less in the front to smooth the ride, but the SBC is a hefty lump. Roads where I live vary from abysmal to merely awful, so sorting the ride is not so clever. Rear springs are 250lbs. They were 200's in the pic, but I changed them out last week. No idea how much the car weighs, not a lot for a guess.

 

Borrow a pyrometer or infrared thermometer to measure tire temps in 3 spots across the tread - outside, center and inside. If the center is hotter, bleed some air out. Add air if the edges are warmer. See how close to even you can get all 3 temps on each tire. You might need a digital tire gauge if you start to get anal... I'd say if you can get within 10-15 degrees, you should be pretty close.

Don't think I'd go lower than your current pressures, without screws to keep the beads on the rims!

From a REFORMED pavement roundy-pounder... Good Luck, post your results too! - Tim

 

Where did you get those slick rear tires?

 

I am leery of going below low 20's myself. My T modified is a bit heavier than yours, and I'm running 18. Anymore and the front tires seem to bounce a lot. Tube shocks might fit that, I'm running level shocks all the way around.

 

My modified weighs 1995# I have 8 ply rear radials with 15# the fronts are 155-15 and I run 30#. After finding a bent front rim, the car is capable of being driven without white knuckles! Haha, but seriously! The car is undrivable if the rears are anything higher than 20#. I'm still working out spring rate issues, I'm down to one leaf (quarter elipticals) on TSC trailer springs. I've got a 40 Ford spring that's gonna get cut up to build a new spring pac on the front. The balance between sprung vs unsprung, light car with too stiff of a sidewall makes for a real challenge to get the car to drive on anything rougher than a pool table. I would love to hear from Elders that drove the cars we all are trying to replicate, and see how they rode and handled for real back when this hot rodding stuff was a new endeavor.

 

shawnsauto1

I agree with you, 18 is as low as I feel comfortable to run in the front. I'm OK running 15 in the rear because I'm running tubes in them. I am also running friction shocks and they work as well as you can expect! The bounce is the problem running higher pressures.

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a boner

Lester Tire Company, they are 6,50-16 Goodyears.

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Thanks!

 

Six banger Tim gave the best reply and his advice is very good. I do the same thing on circle track cars. . Bobby.

 

Maybe try swapping the 8 ply tyres for 4 ply

 

I used to run 28 in the front 560/15 WW and 26 in the rear L78/15 WW on a 32 Roadster 2400lb
I also ran my ride on the softer side of stiff for the suspension, beam up front 4 bar with jag coil overs on the rear.
Got very even tyre wear, excellent ride and good handling.
With your lighter car maybe lower pressures might be OK but the key will be are the tyres the suspension or is your springs soft enough to work.
I have seen many cars with really stiff suspensions and they hop all over the joint when they hit a bump.

 

On my RPU i run 24 in front and 15 in the back, i would like to run less in the back to get a full tire footprint, but i cant spin the wheel in the tire at that pressure but would not go any lower. JW

 

1750 lb T, 2000 with me in it. Radials now 24 front and rear. Tube shocks. Make sure that there is suspension!!!!! Mine was frozen in the shackles for a time and the ride was bad. It's great now after about 5 years of tinkering and the occasional hop off the ground from the high unsprung weight is only in the back and isn't as bad as my Jeep, as a comparison.
I think when our pioneers were young they were tolerating a lot worse conditions and ride quality was not in their vocabulary.

 

All tires have load rating at a given pressure. Its on the sidewall. So, here's a place to start. Lets say the load rating is 1000# at 40 psi. That corner of your car weighs 500 #. Start out at 20 psi, and go up from there. I run big and littles, car is 50/50. 28 in front, 18 in rear. Right on the load ratings, and its perfect.