drag radials...shorter or taller ? - TCCoA Forums
 
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post #1 of 7 (permalink) Old 03-13-2009, 06:48 AM Thread Starter
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drag radials...shorter or taller ?

Hey guys, I've tried searching but can't seem to find an answer. I'm going to be getting a set of 15" Mickey Thompson ET Street radials but need to know if I go with a shorter or taller tire to give me the effect of more gear in the rear end. I have 3.73 gears now but really wish I had gone with the 4.10's. I know it was posted somewhere but can't find the info I'm looking for.

Thanks,
Jon

1996 T-bird, 4.6 with ported PI heads and VT stage 2 cams, JBA shorty headers, 3000 stall converter, 3.73 gears and just about every bolt on available.
Dyno tune results: 275.9rwhp and 301.4 torque.
Best 1/4 mile time: 13.65 at 99.52 mph.
Now I need more gear, more stall and some drag radials !!
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post #2 of 7 (permalink) Old 03-13-2009, 07:43 AM
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From the gear end a shorter tire would sound better BUT in reality a shorter tire with far less contact area per revolution will be horrible with traction if you have some HP.

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Last edited by Mark M. TCCoA VP; 03-13-2009 at 07:56 AM.
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post #3 of 7 (permalink) Old 03-13-2009, 07:47 AM
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I run 4.10's...I also run 26x8.5x15's.
Has great takeoff...I was cutting 1.88 60's with about 170 rwhp(a guess on power, could be more, could be less).


but yeah, a shorter tire will make it act like it has more gear(more take off).

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post #4 of 7 (permalink) Old 03-13-2009, 11:00 AM
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QkTbird,

As you are learning from these posts, tire sizing is a complicated subject. Regarding your original question: a taller tire does reduce your effective overall gear ratio, and a shorter tire increases it. Which direction is appropriate depends on how much power your engine is making and where in the rev range it is making it. Naturally aspirated cars tend to make less power, and to make it at higher rpm. So, a shorter tire and/or numerically higher axle ratio benefits this type setup. Cars with positive displacement superchargers make more power at lower rpm, so a higher axle ratio is not necessary, and can in fact be a disadvantage because the increased torque can overpower the tires.

That is where I find myself now. When my car was NA, I switched from 3.73 to 4.10 gears for improved acceleration. But now that the engine is blown, I'm fighting traction problems big time. The long term solution may be to put the 3.73 gear set back in, but for now I'm going to try taller (and wider) drag radials. The 295/50-16 ET Street Radials are theoretically 27.7" diameter, which will effectively reduce my 4.10 axle ratio to 3.85.

MikeB
1997 Thunderbird Sport
5.0L-2V PI S/C
540 RWHP / 492 RWTQ
11.28 @ 123 MPH
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post #5 of 7 (permalink) Old 03-13-2009, 03:12 PM Thread Starter
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Thanks for all the info guys.....so now I'm still undecided. LOL

I'm going to go with Mickey Thomson ET Street Radials and can't decide between the 235/60/15's or the 255/60/15's. My car is making 276hp and 301tq NA at the wheels and I've ran a best of 13.71 @ 100.54mph in the 1/4 mile and that was running 245/45/18's on all 4 corners. The 245/45/18's are 26.7" tall and the 235/60/15's are 26.1" and the 255/60/15's are 27.1" tall. It's only about a 1/2" either way but I kinda think I should go with the 255/60's since they're .6" wider. I want to stick with the 15" rims I have that are 6.5" wide and I think the 255/60's would be fine on them.

So....what tires do you guys thinkI should get ? Let me know.

Thanks,
Jon

1996 T-bird, 4.6 with ported PI heads and VT stage 2 cams, JBA shorty headers, 3000 stall converter, 3.73 gears and just about every bolt on available.
Dyno tune results: 275.9rwhp and 301.4 torque.
Best 1/4 mile time: 13.65 at 99.52 mph.
Now I need more gear, more stall and some drag radials !!
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post #6 of 7 (permalink) Old 03-13-2009, 04:00 PM
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QkTbird,

You'll make better use of the extra tread width offered by the 255/60-15 if you get wider wheels. MT shows the approved width range as 7.0-9.0". You are probably still safe at 6.5", but I believe your contact patch will be better with a wider wheel.

MikeB
1997 Thunderbird Sport
5.0L-2V PI S/C
540 RWHP / 492 RWTQ
11.28 @ 123 MPH
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post #7 of 7 (permalink) Old 03-13-2009, 08:22 PM
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if i were you, i would not even consider the 235. the 255's will be bulging a little BUT i have 15x7 rims with a 275/60/15 drag tire on it.

97 Tbird 4.6
VT built block, fox lake PI heads
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4.10's, KB boost a spark.
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