Showing my age here (tire question)...

[excelguru]

Hate to sound like such a young'n here, but... I keep hearing people talk about wanting radial tires instead of bias-ply tires even though they may both be rated for the same speed. I don't understand what the drawbacks are with the bias-ply tires.

Is it longevity? Noise? Hunting? Something else?

Please bear in mind that I turned 16 in 1987, so radial is all I've ever known.

Keith :)
Unique Motorcars (http://www.uniquecobrareplicas.com)
Southern Automotive (http://www.southernautomotiveengines.com)
Bruce Bunn (the painter) (http://www.jodecoautobody.com)

My Photo Album (http://members5.clubphoto.com/keith355593/1141434/owner-429c.phtml)

[Brent]

Keith I have recieved an enormous ammount of tire information in the last few weeks.


When NASCAR switched to a radial tire they had HUGE problems. The tire they now run is a Bias Ply/Radial hybrid tire.

The tricky part about tires for Cobras is the fact that we have race cars we drive to work.Thats what these cars are. We need the tread caracteristics of a radial tire but we need the weight and feel of a Bias Ply tire.

A Nylon Bias Ply tire will develop a flat spot if it sits in one spot for a while. If it is frequently driven or if the weight is taken off of the tire this will not occur. When it does occur, I have been told, it should only take 1-2 miles for the nylon to reach operating tempurature. When it hits this temp is becomes softer and trues itself.


1. Change in market:

1972 radials held only 8% of tire market

1977 radials grew to 50%

1992 radials had 89% of market

1. Bias Ply Tire info

2. Carcass contains "plies" of rubberized fabric.

3. In cross-ply, cords cross tire at an angle.

4. In belted, bias-ply cords cross tire at an angle and additional belt of fabric placed between plies and tread.

5. In radial-ply, cords run straight across tire and additional belt of fabric included.

6. Radials have better wear and road-holding ability, however, Radials are more easily damaged on the side and less comfortable ride.

Bias ply tires differ from radials on the following items.

Static negative camber requirements are less, usually about 1 to 1 1/2 degree negative is sufficient.
Rim width selection is more critical, because the tread face is flexible, the rim helps support the tire. The rim width should be as large or larger than the section width of the tire.
Air pressure can not be used to reduce sidewall flex (rollover). Excessive air pressure will cause the tread face to bulge, reducing the contact patch.
Bias ply tires give more warning (than radials) about traction limits and have excellent feedback of what the contact patch is doing.
Bias ply tires operate at larger slip angles than radials. The large belt in a Radial tire makes the surface more square and maintains its surface contact under hard cornering.
Because of how bias tires react to cornering loads, the tread can be thicker than radial tires.

Radials generally need more static negative camber than bias tires.
Radials generally provide more breakaway grip than a bias tire, however , they give less warning. This causes radials to be harder to drive at the limit.
Air pressure can be used to reduce sidewall rollover, without having the tread bulge like a bias tire.(That we all like) The may allow you to use a larger sized tire.
Radials are usually heavier than bias tires due to the over wrap plys.
Radials operate at lower slip angles than bias ply tires. The is the main reason Radials have better transient response than bias tires.


Most racing radial tires are alot closer to a belted bias ply tire than a passenger car radial tire. This gives the racing radial tire traits from both bias & radial tires (good feedback & higher breakaway traction).

This is what I am trying to get made for us. The best of both tires in a size we can use.









Brent
4279401
Candy Apple Red/White
402 FE/Toploader/3.54

[Master]

Brent,

Thanks for the information, I too did not know what the difference was between the two. :)

Scott
4279454
SA 428
3:54

[rdorman]

Excellant response Brent. I remember going to Charlotte for the world 600 during the big tire war in the 80's. The tires where litterally exploding entering the corners. By the end, a fraction of the cars where left running and those that where look like they had been in a crash up derby.

I can confirm everything Brent wrote, first hand, on my Cobra. When I went from BFG (round, at least basically round, bricks) to Hoosier TD's (sweet joy), the car litterally came to life. Sure they are a bit rough until they warm up, sure the transient response is not as quick, sure they hunt a bit on uneven pavement, but EVERYTHING else was better. Lap times dropped by 10% (mainly because of compound and lack of tread), the limit was easier to deal with, I lost 16 pounds of unsprung wieght on EACH rear wheel, and that is a large percentage. Something like 13 or 14 for each front. I could feel the difference even before I left the parking lot after having them mounted.

As you can imagine, suspension design is totally different between the various tire constructions. Bias not only require less static camber but also less camber gain, both generally a good thing for a street car since so rarely is there enough. Plus relatively longer tire wear because you don't have to run crazy (3+) camber angles. Many Bias tires do well with as little as .5 degrees. Less sensitive to ackerman, etc.

I didn't blink and eye when I heard these new ones are Bias. Make the compound last longer and ship me a set!

The only thing that keeps me from running TDs until the day I die is no tread. I was driving 140 miles in the rain, on the freeway, last week in the TDs. Scary would be an understatement.

16 in 87???? I didn't realize you where THAT young!

Rick

[excelguru]

Yeah, I was probably one of Unique's younger buyers. One of the many reasons I purchased from them was because they took me seriously when I was looking, but I digress...

Things like transient response, static camber, camber gain, ackerman, fractals, cats, Green Peace... these are things I do not understand. Looks like I need to do some homework on suspension theory.

I have the BFG's and the tread will probably last until my son is old enough to drive. I need something at least a little bit stickier.

Keith :)
Unique Motorcars (http://www.uniquecobrareplicas.com)
Southern Automotive (http://www.southernautomotiveengines.com)
Bruce Bunn (the painter) (http://www.jodecoautobody.com)

My Photo Album (http://members5.clubphoto.com/keith355593/1141434/owner-429c.phtml)

[clayfoushee]

Funny Keith, and I'm not far behind on understanding suspension geometry. But, I wondering whether alignment specs will need to change for these new bias ply tires.

Clay

'98 Unique #9299, 427FE side oiler (452.1-stroker), top-loader (close), 3.31 rear

Annapolis, MD

[nolastyankee]

Wow Keith, I didn't realize that you were such a young whipper-snapper. Perhaps I can impart some of my elderly wisdom upon you...After all, I was 17 in 1987.


Unique 9122 - 289 FIA Cobra - The Legendary "Spence" Car

[rdorman]

LOL. All you young guys. I will admit, I did have to look up fractals again, but Green Peace? LOL

I am really not that much older, 23 in 87. But I did have cars with Bias tires on them!

Alignment specs should not really change much for street use. If at all.

Rick

[patrija]

I think I may have all you guys beat on age ... got the Cobra as a pre-30th birthday present. I'm now about to turn 33. :-)

[rdorman]

Shoot before I turned 30 I had to look for a loan to buy a pack of bubble gum and that was usually turned down! Wiper blades where a common Christmas gift........ that is when the wipers worked!
Rick

[GeorgiaSnake]

I can almost remember 1987 [^] My first driving experience was with retreads and Cobras didn't exist;)

Randy

Unique 289 FIA
Southern Automotive 396
Team III 16's
Brilliant Silver