Question about PZeros for our tire experts

[alfie43]

I recently changed tires sizes wheel I installed new wheels and I an experiencing some performance differences between my old and new Pirellis.

I moved my OEM 275/40s to the front on 9" wheels. I installed new PZeros 305/35 with 10.5" wheels on the rear. Sounds like a plan right?

Yes, it is, but here is the problem; my new 305s have less traction on hard acceleration than the smaller 275s. Same brand, same tread design, and larger width (10.725" to 11.895") but they break loose more readily. I'm not talking about racing, but full throttle 1st and 2nd gear roll outs.

Yes, I am running a Maggie and putting out a lot of power (562RWHP), but a smaller tire getting more hook up than a larger tire....how can that be? I am at 34 psi.

Perhaps one of our expert tire vendors can shed some light on this phenomenon?

Alfie

[SSambumbia]

160 or 220 threadwear?

Are the new wheels lighter or heavier ?

[emsguy]

okay. here is my take on it. I may not be right, but follow my logic and think about it.

for a given vehicle weight and tire inflation pressure, the sizes of the tire patches must be the same. by this I mean that a 3000 lb car with tires inflated to 30 psi must have a tire contact patch of 100 square inches spread over the four tires (3000lbs divided by 20 psi = 100 square inches)

assuming 50/50 front to rear and 50/50 side to side corner weights (not real world, but it works great in this example) each tire contact patch must be 25 square inches (100 divided by 4). a wider tire must still have the same total contact patch area as a narrower one, so the contact patch is wider side to side but shorter front to back. it still must be 25 square inches. that's why a wider tire corners better - every tire lifts the outer edge when cornering, but a wider tire stil lhas more of the tread in contact with the road.

maybe, just maybe. for accelleration, a narrower and longer tire patch is better than a wider and shorter one. I don't know. I was a road racer, not a drag racer. I was more concerned with cornering than accelleration.

but I think the principal is the same.

does that make sense?

[khislop007]

Give um time to break in. I'm sure your 275's were like that when they were new and when they got broke in you just got used to them.

[Mr. Wyndham]

It's interesting you're noticing this...

An old professor of mine once explained to me how wider tires are not always better given everything else stays the same (weight & Coefficient of friction, most importantly).

Think of it like snowshoes versus cleats in an extreme example...

I'll admit I never gave it much thought...

[bandier]

Originally Posted by khislop007

Give um time to break in. I'm sure your 275's were like that when they were new and when they got broke in you just got used to them.

I go with this answer. My new tires always seem slicker at first even when it's the same time.

[alfie43]

The new 305s are rated "220 Treadwear and AA Traction"....same is the oem tires

I have listened to everyone's opinions and ideas, but with all due respect, I'm not sure if we hit the answer yet. Of course, I asked the question, so what do I know?

As for the footprint size analysis, I would think that the bottom line is; larger tire larger footprint should be more traction, but that's not the case.

I've smoked off enough of the new surface of the 305s to conclude, it aint about "breaking them in".

I do wonder if wheel weight difference plays a part here???

...mystery still unsolved.

Alfie

[emsguy]

that's what I am saying. a larger tire does not necessarily have a larger footprint. just a differently-shaped footprint. regardless of the size of the tire. if the inflation pressures are equal, then the area of the footprint should be equal. it's just math.

now, let's look at another way. if you have a 3000 pound car with four tires inflated to 30 psi, you have 100 square inches of footprint spread over four contact patches (one for each tire). now, if you have the same 3000 pound car, but reduce the tire pressure to 15 psi, you now have 200 square inches of contact area (3000 divided by 15). that's why reducing your tire pressure increases the tire contact area.

as you can see by this simplified equation, the tire size is not a relevant variable. I believe that the tire size (tread or section width) affects only the shape of the tire contact patch, not its size.

but I am not a tire engineer. I could be wrong. but the logic seems right to me.

[Snake Slayer]

Originally Posted by alfie43

I recently changed tires sizes wheel I installed new wheels and I an experiencing some performance differences between my old and new Pirellis.

I moved my OEM 275/40s to the front on 9" wheels. I installed new PZeros 305/35 with 10.5" wheels on the rear. Sounds like a plan right?

Yes, it is, but here is the problem; my new 305s have less traction on hard acceleration than the smaller 275s. Same brand, same tread design, and larger width (10.725" to 11.895") but they break loose more readily. I'm not talking about racing, but full throttle 1st and 2nd gear roll outs.

Yes, I am running a Maggie and putting out a lot of power (562RWHP), but a smaller tire getting more hook up than a larger tire....how can that be? I am at 34 psi.

Perhaps one of our expert tire vendors can shed some light on this phenomenon?

Alfie

Have your tried inflating them to the factory pressure of 36? You may need to play with air pressures.

[alfie43]

emsguy,

i really do appreciate your input and your attempt to help, but i disagree with your math and physics, i.e., "3000 pound car with four tires inflated to 30 psi, you have 100 square inches of footprint". you cant say that alone without bringing tire size into the discussion.

There are additional variables that affect the footprint; tire size being the most important. i don't see the math that says there is a proportional relationship between tire inflation pressure and footprint. Proportion is the key word here because you applied it in your example. Certainly more pressure will decrease footprint and less will increase, so there is a relationship, but not in direct proportion.

Changing from radial tires to bias ply tires will change the footprint dramatically with the same psi. for the sake of argument, what if i put 165/70-14" tires on the car with the same psi? Same footprint? i don't think so. Size matters.

Not trying to dismiss your help or wanting to start a debate, just reacting to your post and adding to the discussion.

BTW, My keyboard won't type some uppercase letters.

Alfie

[Shu71]

I wonder if the middle of the treadpattern is not providing as much traction at the same tire pressure as with the stock 275. Back in the day of wide 50's on cars (late 70's early 80's) you could do a burnout and see the middle not as black as the outside edges. Maybe try a few more lbs of air and see if that helps. If the overall width is wider than the rims are supposed to support, then this could very well cause the lower traction in the center of the treadpattern.

[alfie43]

Originally Posted by Shu71

I wonder if the middle of the treadpattern is not providing as much traction at the same tire pressure as with the stock 275. Back in the day of wide 50's on cars (late 70's early 80's) you could do a burnout and see the middle not as black as the outside edges. Maybe try a few more lbs of air and see if that helps. If the overall width is wider than the rims are supposed to support, then this could very well cause the lower traction in the center of the treadpattern.

That's the exact line of thinking that i was going to pursue. Just waiting for the rain to stop so that i can test that theory.

Alfie

[newagemuscle]

Time for a drag radial Mariano.

[Rudy@Tirerack]

How long have you had the tires on the rear? New tires will have a mold release agent when new. This usually takes about 200-300 miles to wear off. This mold release agent is slippery and will cause the tires to have less grip. Also a full tread depth tire will have less grip than a worn down one. This is why drag radials come with less tread depth new. A couple things to consider.