I know, I know.....tons of threads about the subject and even more than one or two on the front page, of which, I've read them all :D

I understand what the numbers in the "245/45-17" means :cheers:

My question(s) revolve around the Section Width, Tread Width and Overall Diameter and the Footprint I guess.

What I wanna know is how all of this affects tire performance, more specifically, how do the #s compare and how do they affect preformance?

The #s below are referenced in order of Section Width, Tread Width and Overall Diameter in inches.

I'm looking at the Bridgestone Protenza S03s ($840) in 245/45/17 and 275/40/18:
9.8", 9.1" and 25.7" then for the rears 11.2", 10.2" and 26.7"

Compared to the BFG KDs ($1250) in 255/40/17 and 295/35/18:
10.2", 8.2" and 25" then for the rears 11.9", 9.8" and 26.1"

Compared to tge Protenza S02s ($900) in 255/40/17 and 295/35/18:
10.2", 7.9" and 24.8 then for the rears 11.9", 11.5" and 26.3"

So what the hell do these #s mean? To me....the S03s have the better looking #s altough I haven't a clue as to what they mean :D......someone help me out here :D :cheers:


[Modified by Mean Green 2000, 4:31 PM 8/9/2002]

 

I'd like to know also. Was also curious if you get better traction with rears being 295 than say 285. Extra tire width = more traction?

 

Tire pressure being equal, the area of rubber in contact with the pavement will be the same. Traction will be dependent on the coefficient of friction, which will be a function of the softness of the rubber and, to some extent, the tread design. Softer rubber compounds also dissipate heat better, hence VR labeled tires are rated for higher speeds, but will wear faster.

 

Tire tread width is amount of tire on the pavement, more is better, and tire diameter well affect acceleration to a certain degree. Taller tires will slow down your ablility to accelerate, although your differences are small. :yesnod:

 

OK - I've researched Section and Tread Width a little bit so I'll try to best pass along what I've learned.

The first thing that tipped me off to learning more about section and tread width was that I noticed widths of a given size are not created equally; i.e. 275/40/18 is SUPPOSED to be 275mm across.

While that may be true - I can guarantee you that footprint (or the contact patch - the amount of tread that touches the ground) varies greatly between manufacturers given the same size (275).

Here's what I've read: Section width is measured between the farthest points between the inner and outer sidewalls. This is pretty straightforward and accurate in measurement and consistency...period.

The kicker is tread width. The rule is to measure this from the inner tread shoulder to the outer tread shoulder. As I've read, many manufacturers take a certain degree of liberty in what they consider the "shoulder" of the tread. Some tire's shoulders are squared and others are rounded. On the rounded ones do they extrapolate out 90 degrees to where the shoulder would be if the shoulder wasn't rounded or do they measure from where the tread actually begins?

There is no set criteria or rule for this, so measurements of tread width are not consistent between manufacturers. Therefore, many manufacturers do not post this number at all.

A good example is the difference in the Goodyear Eagle F1 EMT vs. the Firestone runflat. They're both 275's but if you compare the two tires, the Firestone doesn't look "as wide". They both carry close to the same section widths but their tread widths are certainly different.

The Tire Rack (www.tirerack.com) has an excellent explanation of both these terms.

Remember, tire specs are great on paper but before you buy, look at the tires your comparing in person (if the footprint/contact patch is important to you).

Good Luck,
Eric

 

>>>Tire pressure being equal, the area of rubber in contact with the pavement will be the same. <<
This is only true with ungrooved tires. The body of a tire is stiff enought that the tire will bridge over the grooving. The area will be the same minus the difference in groove area.
>>Traction will be dependent on the coefficient of friction, which will be a function of the softness of the rubber and, to some extent, the tread design. <<
Softer rubber doesn't necessarily have a higher coef. of friction. Softer rubber allows the tire surface to catch the rough stone edges of asphalt and make a temporary mechanical bond with the rubber. If the tire slips or spins, the rubber will be placed in shear and will either restrain the tire from moving or will tear off. Softer rubber may be weaker rubber which will lessen traction.

>>Softer rubber compounds also dissipate heat better, hence VR labeled tires are rated for higher speeds, but will wear faster.<<<
Softer rubber may dissipate heat faster, but the heat is generated mostly by tire casing flexure. VR tires may have stiffer casings to limit flexure, lowering heat and providing longer tread life.

Dennis

 

Mark,

Why wouldn't you get S03s in 295/35/18s for the rear? They are wider and a little shorter than the 275/40/18s. Don't they make that size? I have S02s in that size, I'm curious for when I go to purchase new tires...

Herb

 

from what I could find, doesn't mean they don't exist, but I did not find the S03s in the 295/38/18 size :(

 

One thing most people forget is that when you go to a "shorter" tire (smaller OD), you loose contact patch in the front to rear direction. I don't now how much, but remember that amount is multiplied against the entire width of the tread.

Also, when going from a 275 even to a 295, I'll bet lot's of money that the tread design and compound make more of a difference than the width. Also, putting too wide of a tire for the wheel causes more flex. Ever notice that German and Italian sports cars seem to have much narrower tires on wider wheels? This keeps the tread from squirming as much.


[Modified by jschindler, 9:15 PM 8/10/2002]

 

thanks :D....this was exactly what I was looking for :D :cheers:

well, I broke down and ordered the Nittos, I figure at least I'll be able to compare 'em to another one of my options when these go down, which may be at next year's burnout contest :D

 

Geez it's about time!!!!! :lol:

Bob

 

Did you get them in the stock sizes? What is the tread wear on Nittos? I am about a month away from CCWs with the 335's out back. :yesnod: Need those to hold those mountain roads on the way to CI IV. :p:

 

Mark, I think you made a good choice. I know your car is not a daily driver, so rain is not an issue. All the guys I know that have run Nittos say they are great in anything except rain, and a great bang for the buck. Be sure to let us know how you like them.

 

John, I did go with stock sizes but I don't think they make a 335 for out back :(.....I hear a lot of people like the Pilot Sports in that size and it's an agressive tread pattern :)....I think choices are fairly limited in that size too.

I'd love to get a 2nd drag CCW setup :D

I sure will keep the updates coming :D.....for $642 it has hard to beat and even if they wear really quickly I can try out one of my other choices :D