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Old 09-13-2005, 08:57 PM   #1
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Default Using shorter drag radials cause any problems??

I have a set of 225/50/16 drag radials coming for my car. They are a good bit shorter than the stock 225/60/16'* and I'm just wondering if anyone has done this, and if so, did you get any anti-lock brakes trouble codes or any other problems caused by the different height tires?

BTW, I do NOT intend on using these all the time, just for one or two trips to the dragstrip to see how my low mileage stocker does against everyone else'*...
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Old 09-13-2005, 09:17 PM   #2
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Your WOT shift points are based on MPH so you will be shifting at a lower rpm. But you'll have a higher effective FDR too. Other than that as long as the off-set on the rim is ok you'll be fine.
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Old 09-13-2005, 10:51 PM   #3
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Quote:
Originally Posted by 95naSTA
Your WOT shift points are based on MPH so you will be shifting at a lower rpm..
Thanks for the reply. If that is correct, I guess I could always shift the car manually at 5800 or so...but, every car/truck I've ever owned shifted at WOT by rpm, not mph...If @ WOT it shifted by MPH, then in theory, it would have to shift at a higher rpm to be at the same mph (as stock height tires), due to the artificially lower gear ratio caused by the shorter tires....

The shorter tires were specifically chosen to lower the final drive ratio and hopefully get the car up into it'* power range a bit quicker, and keep it there, also hopefully...
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Old 09-13-2005, 11:59 PM   #4
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Quote:
Originally Posted by 95naSTA
Your WOT shift points are based on MPH so you will be shifting at a lower rpm. But you'll have a higher effective FDR too. Other than that as long as the off-set on the rim is ok you'll be fine.
You got it backwards. And the tranny should still shift at the same rpm, it will think you are going the same speed as before, unless you have it reclibrated.
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Old 09-14-2005, 12:15 AM   #5
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Quote:
Originally Posted by jwikoff99
Quote:
Originally Posted by 95naSTA
Your WOT shift points are based on MPH so you will be shifting at a lower rpm. But you'll have a higher effective FDR too. Other than that as long as the off-set on the rim is ok you'll be fine.
You got it backwards. And the tranny should still shift at the same rpm, it will think you are going the same speed as before, unless you have it reclibrated.
I dunno I'm still sticking by what I said with the WOT MPH shift thing.
And the vehicle speed sensor (in the trans) is calibrated for a specific wheel height. If you make the height smaller, it will make the computer think it'* going faster than it really is.
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Old 09-14-2005, 12:18 AM   #6
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Shifts are strictly by RPM'*.
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Old 09-14-2005, 12:30 AM   #7
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The PCM would have no idea anything is different than before, and shift at the RPM it always would.
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Old 09-14-2005, 12:56 AM   #8
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the ABS question still stands though. i think it will cause a problem with the abs, because the back wheels are going "slower", and i believe the abs will engage as soon as he hits it. am i correct.
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Old 09-14-2005, 12:59 AM   #9
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Hmm, yeah, pull the ABS fuse or unhook a wheel speed sensor.
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Old 09-14-2005, 01:29 AM   #10
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You actually gain a little in your final drive ratio with shorter tires.
The shift points are still based on rpm but there are some parameters that are based on mph.
This summer I ran 26" slicks and had no shift issues. A custom tune just for racing would be the better choice but for just getting out the odd street night, your street pcm will fine.
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