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PostPosted: Fri Feb 16, 2018 3:24 pm 
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Al, I'm switching back to the Goodyear bias and will let you know how it works out. I either lost my ability to drive fast or the radials do not work well on a solid rear car. It should be noted that in GT3 at the runoffs, the first place car on Goodyear bias, was 3 seconds a lap faster than any radial shod car. And its trap speeds were no faster than several others. I think that speaks volumes.


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PostPosted: Fri Feb 16, 2018 4:53 pm 
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Location: The Mountains of Colorado
Jason@SportsCar wrote:
My car turned about as good as my Suburban on bias tires, radials brought it to life.



Yup, never looking back.

Plus the car is now 2" narrower and I have no dropoff in time during the race. Usually the last lap is just as fast, if not faster, than my first couple. Could never do that on bias.

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Mazda Jon
AKA Suzuki Jon
2009 Mazda MX-5 12A GTL #04
SCCA Member #97968


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PostPosted: Fri Feb 16, 2018 4:55 pm 
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Location: The Mountains of Colorado
Mazda Jon wrote:
Jason@SportsCar wrote:
My car turned about as good as my Suburban on bias tires, radials brought it to life.



Yup, never looking back.

Plus the car is now 2" narrower and I have no dropoff in time during the race. Usually the last lap is just as fast, if not faster, than my first couple. Could never do that on bias.



Wait!!! I was wrong. The radials sux on GTL cars and everyone should go back to bias...... 8)

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Mazda Jon
AKA Suzuki Jon
2009 Mazda MX-5 12A GTL #04
SCCA Member #97968


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PostPosted: Fri Feb 16, 2018 5:27 pm 
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Al Seim wrote:
It would be interesting to quantify the rolling resistance issue.
It is difficult to quantify the rolling resistance issue. What usually happens is there is a data point that indicates a higher top speed with the radials, the thought being that all else being equal there must be lower rolling resistance if there is a higher top speed for the same setup. The problem with this thinking is that all else is not equal. In my case the radials had a larger circumference, so the same 4th gear rpm produced a higher top speed. Was it the tires or was it that the motor was right in a sweet spot for power and with a bigger tire we went faster.

Al - as for radials on a FWD car, you need to talk to some of the other FWD drivers, Kevin Ruck comes to mind, and you will quickly realize the advantages for your type of car. My understanding is it is a no-brainer.

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PostPosted: Fri Feb 16, 2018 5:57 pm 
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The radial almost surely works better on a rear semi trailing arm car. The toe and camber change in roll uncouples the bias tire. So you BMW 2002-320-325 and Porsche 924-944 and Nissan 280zx-300zx ect.. should be on radials.


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PostPosted: Fri Feb 16, 2018 6:02 pm 
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Al

The radials are generally the right choice for our cars.
If the car is really light like Chuck’s you may find that bias is a valid choice in cooler conditions.

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Chris Schaafsma


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PostPosted: Fri Feb 16, 2018 7:03 pm 
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Location: Kannapolis N.C.
I hope that all of my competitors and the competitors of my customers choose bias ply tires.

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Sam Moore
SCCA competitor since 1983


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PostPosted: Sat Feb 17, 2018 1:18 pm 
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Sam Moore wrote:
I hope that all of my competitors and the competitors of my customers choose bias ply tires.


:lol: :lol: :lol: concur, but then I'm driving a FWD HP ex ITC Car.


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PostPosted: Sun Feb 18, 2018 7:44 am 
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Location: Oregon City, Or.
I ask these questions to mostly because my new car has been competitive on bias and I am not sure about switching. My old car I did tons of work to get it right on radials which included much higher spring rates and tire pressures. I did run much more camber In the front and I pushed the rear axle as far as I could -1.2. I fell the next step in the rear would be de-cambered tubes and ball end axles.
All of that said I liked the radials better than bias and I really liked the fact that the radial stayed under the car for the length of a race

Thanks for the input on this.

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Joe Harlan Member #175515


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PostPosted: Mon Feb 19, 2018 8:28 pm 
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Joined: Fri Jul 29, 2016 3:51 pm
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When I was driving the Civic it was competitive with the Bias tires. I switched to the radials after the initial testing of the tire, using my car. It was consistently faster on radials. The main thing is when I ran against Bob Weber on Bias I'd be on corded fronts after the race and on radials they would be done, but not corded.

James -r


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