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  #1  
Old 08-26-2016, 09:47 AM
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Much slower after 275/55R20

Hi all,

Just wondering if any of you with bigger tires, 275/55R20, experienced a significant difference in acceleration.

My 2013, 3.6 AWD, is now 3.3 seconds slower to 60 than stock. I am running Diablosport/hemifever 87 tune, AEM drop in filter and Gibson axle back (single side). Before this mods it felt slower than now. So they definitely helped.

On a previous post I commented on this and agreed that the bigger tires and higher altitude (4,000 ft.) affects power and speed but I'm not sure it can add 3.3 seconds to a 0 to 60 run.

What is your experience after installing 275/55R20 tires?

Thoughts?

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Old 08-26-2016, 09:51 AM
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Re: Much slower after 275/55R20

Are you accounting for the 5% difference in speedometer/odometer readings? 3.3secs is still a lot, but that's something to consider as well.
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Old 08-26-2016, 09:54 AM
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Re: Much slower after 275/55R20

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Originally Posted by AkXb70 View Post
Are you accounting for the 5% difference in speedometer/odometer readings? 3.3secs is still a lot, but that's something to consider as well.
I should have mentioned that I calibrated my speedometer with the Diablosport. Verified with GPS.
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Old 08-26-2016, 10:30 AM
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Re: Much slower after 275/55R20

Not sure then. Is this 3.3 secs different from your own recorded times in the same weather conditions or from manufacturer times?
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Old 08-26-2016, 10:43 AM
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Re: Much slower after 275/55R20

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Originally Posted by AkXb70 View Post
Not sure then. Is this 3.3 secs different from your own recorded times in the same weather conditions or from manufacturer times?
Own recorded times.

8.5 seconds, @ sea level, calm wind, 65 degrees, 2 years ago.
12.8 seconds, 4019 ft, elevation, 84 degrees, very strong wind, yesterday.
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Old 08-26-2016, 11:29 AM
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Re: Much slower after 275/55R20

I've noticed a difference but not 3 seconds of a difference. I have 275/55/20 BFGs if that helps... They are a LOT heavier than stock tires
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Old 08-26-2016, 12:27 PM
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Re: Much slower after 275/55R20

Quote:
Originally Posted by Mininuke View Post
Own recorded times.

8.5 seconds, @ sea level, calm wind, 65 degrees, 2 years ago.
12.8 seconds, 4019 ft, elevation, 84 degrees, very strong wind, yesterday.
That's probably the biggest factor. On a NA engine, that's a significant hindrance.

If you had 1/4 mile times, you could use a drag times calculator like the one below to get an estimate of what the altitude and weather are doing to your acceleration. It may not account for all of the change, but it has to be a large chunk.

DA Calculator - Density Altitude Calculator - DragTimes.com
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Old 08-26-2016, 01:13 PM
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Re: Much slower after 275/55R20

Quote:
Originally Posted by AkXb70 View Post
That's probably the biggest factor. On a NA engine, that's a significant hindrance.

If you had 1/4 mile times, you could use a drag times calculator like the one below to get an estimate of what the altitude and weather are doing to your acceleration. It may not account for all of the change, but it has to be a large chunk.

DA Calculator - Density Altitude Calculator - DragTimes.com
Cool. I will see if I can get a 1/4 mile run and use the calculator.
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Old 08-26-2016, 01:15 PM
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Re: Much slower after 275/55R20

I know this doesn't really help the OP but before I bought my Hemi, I was wondering if the 3.45:1 gears in the 3.6L would work in the Hemi differential (Hemi 3.09:1)?

and I think the SRT has 3.70:1 gears, if you could get the SRT gears you might be able to recover some of your lost acceleration but at the expense for fuel economy and top speed.
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Old 08-26-2016, 01:25 PM
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Re: Much slower after 275/55R20

Quote:
Originally Posted by five.7 Hemi View Post
I know this doesn't really help the OP but before I bought my Hemi, I was wondering if the 3.45:1 gears in the 3.6L would work in the Hemi differential (Hemi 3.09:1)?

and I think the SRT has 3.70:1 gears, if you could get the SRT gears you might be able to recover some of your lost acceleration but at the expense for fuel economy and top speed.
It would probably be cheaper to sell the 3.6 wk2 and buy a hemi 5.7 than swapping differentials etc.

Shit Auto hellcats have 2.62 rear ends. where manual has 3.70
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Old 08-26-2016, 01:48 PM
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Re: Much slower after 275/55R20

Quote:
Originally Posted by xJoshxx View Post
It would probably be cheaper to sell the 3.6 wk2 and buy a hemi 5.7 than swapping differentials etc.

Shit Auto hellcats have 2.62 rear ends. where manual has 3.70
nah, only cost $1k to swap (parts and labor) the 3.07:1 gears in my 2005 Viper for the 3.55:1 gears in the 2015 Viper.

I will look into a gear swap on my GC down the road.
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Old 08-27-2016, 03:38 AM
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Re: Much slower after 275/55R20

Running the same sized tire/wheel and my 0-60 is 6.2 secs. I have the 3.0 ecodiesel though.
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