tire size and gear ratio

Duster 318 · 10-21-2013, 09:45 PM

I have 28 inch tall tires and a 4.30 gear and I want to put 29.5 radials on my 318 duster would this affect my e.t. and mph? and what gear should I have in it for the bigger tires?

JimL · 10-21-2013, 11:28 PM

Just looking at tire size/gear ratios, the closest to what you have now would be a 4.56 gear. As far as the et and mph, you have to look at the power curve of your engine and the rpm you want to cross the finish line.

Mike Taylor 3601 · 10-22-2013, 08:45 AM

MPH X Gear ratio X 336 divided by tire height = RPM . you can calculate difference and figure what you need to get rpm you want.

Auto will be slightly higher depending on % of converter slip,can also determine how good converter is working roughly anyway.
Stick will come out just about dead on calculation.
Mike Taylor 3601

mannymen · 10-22-2013, 09:46 AM

Try this formula 26.4/28= ? X your gear = actual ratio.

My wording may not be correct, but whatever.

What is your stroke, vehicle weight and 1st gear ratio?

Jim Kaekel · 10-22-2013, 11:24 AM

Don't forget that radials do not grow.

1320racer · 10-22-2013, 12:01 PM

when comparing like size slicks, radials will increase your trap RPM by 200-300.

Duster 318 · 10-22-2013, 04:38 PM

thanks for the help i want to try the 29.5 radials with a 4.88 gear

10-21-2013, 09:45 PM	#1
Duster 318 Junior Member Join Date: Dec 2012 Posts: 42 Likes: 0 Liked 0 Times in 0 Posts	tire size and gear ratio I have 28 inch tall tires and a 4.30 gear and I want to put 29.5 radials on my 318 duster would this affect my e.t. and mph? and what gear should I have in it for the bigger tires?

10-21-2013, 11:28 PM	#2
JimL Junior Member Join Date: May 2013 Posts: 70 Likes: 0 Liked 0 Times in 0 Posts	Re: tire size and gear ratio Just looking at tire size/gear ratios, the closest to what you have now would be a 4.56 gear. As far as the et and mph, you have to look at the power curve of your engine and the rpm you want to cross the finish line.

10-22-2013, 08:45 AM	#3
Mike Taylor 3601 VIP Member Join Date: Oct 2008 Location: Somerset,Ky Posts: 1,362 Likes: 336 Liked 279 Times in 96 Posts	Re: tire size and gear ratio MPH X Gear ratio X 336 divided by tire height = RPM . you can calculate difference and figure what you need to get rpm you want. Auto will be slightly higher depending on % of converter slip,can also determine how good converter is working roughly anyway. Stick will come out just about dead on calculation. Mike Taylor 3601

10-22-2013, 09:46 AM	#4
mannymen Senior Member Join Date: Apr 2003 Posts: 728 Likes: 5 Liked 13 Times in 7 Posts	Re: tire size and gear ratio Try this formula 26.4/28= ? X your gear = actual ratio. My wording may not be correct, but whatever. What is your stroke, vehicle weight and 1st gear ratio? __________________ N/A

10-22-2013, 11:24 AM	#5
Jim Kaekel VIP Member Join Date: Jul 2002 Location: Michigan Posts: 1,226 Likes: 133 Liked 529 Times in 107 Posts	Re: tire size and gear ratio Don't forget that radials do not grow. __________________ Jim Kaekel 3836 STK

10-22-2013, 12:01 PM	#6
1320racer VIP Member Join Date: Nov 2007 Location: New Jersey Posts: 2,628 Likes: 160 Liked 759 Times in 379 Posts	Re: tire size and gear ratio when comparing like size slicks, radials will increase your trap RPM by 200-300.

10-22-2013, 04:38 PM	#7
Duster 318 Junior Member Join Date: Dec 2012 Posts: 42 Likes: 0 Liked 0 Times in 0 Posts	Re: tire size and gear ratio thanks for the help i want to try the 29.5 radials with a 4.88 gear