Anyone running 35" or 37" tires with 4.10 or 4.30 gears? - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 13 (permalink) Old 01-24-2008, 04:23 PM Thread Starter
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Anyone running 35" or 37" tires with 4.10 or 4.30 gears?

I'm running 35" tires with a Donahoe Racing 4.5" lift. My truck is a F250 Lariat, 6.4, CC, SB, SRW with 3.73's. My truck feels down on power and my city and towing mileage have suffered significantly (~8 in the city and ~7 towing 8k#). I've done all my research on re-gearing to either 4.10s or 4.30's, but before pulling the trigger wanted to hear from anyone that is running a larger tire and has re-geared.

Any input on how performance and gas mileage is post re-gear?
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post #2 of 13 (permalink) Old 01-24-2008, 04:27 PM
 
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you should not have to regear with 35's. I spoke to a friend of mine who was having the same problem and he had to take it to the dealer and get his computer reflashed.........its a computer issue
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post #3 of 13 (permalink) Old 01-24-2008, 04:30 PM
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I just did all this research for my 06 f-250 6.0L I got 35 toyo mt's with a donahoe 4.5" 4link setup and I decide to go with the 4.10's which is an awesome choice I think the 4.30's will be to much gear. I originally had 31" tires on 17's and the truck rpms are about the same as before and the power and mpg have not changed I think you will be happy with the 4.10's !
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post #4 of 13 (permalink) Old 01-24-2008, 05:32 PM Thread Starter
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Originally Posted by onebadf150
I just did all this research for my 06 f-250 6.0L I got 35 toyo mt's with a donahoe 4.5" 4link setup and I decide to go with the 4.10's which is an awesome choice I think the 4.30's will be to much gear. I originally had 31" tires on 17's and the truck rpms are about the same as before and the power and mpg have not changed I think you will be happy with the 4.10's !
Thanks! I've been reading through all the 6.0 threads and it seems like 4.10's for 35's and 4.30's for 37's. There are a few guys that have 4.30's and 35's and seem to be happy. I'm leaning towards the 4.30's as my next set of tires will be probably be 37's.

What kind of mileage are you getting?
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post #5 of 13 (permalink) Old 01-24-2008, 05:39 PM Thread Starter
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Originally Posted by ralphbaja1
you should not have to regear with 35's. I spoke to a friend of mine who was having the same problem and he had to take it to the dealer and get his computer reflashed.........its a computer issue
I don't believe that I'm having an issue with the computer. I have the most recent flash. On average I get 12mpg per tank and that is with a 70 hwy/30 city mix of driving. My highway mileage is OK at 16mpg running at 70-75mph. When I drive exclusively in the city or I tow the mileage sucks as it take a lot of throttle to get the load moving. My effective gear ratio is 3.41:1 with the 35's. I'm also concerned about the excessive wear on the torque converter with the larger tires and under gearing.
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post #6 of 13 (permalink) Old 01-24-2008, 06:19 PM
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Not to be a leech but since we're on the subject... what about for 38x15.50s? 4.30 or 4.56? I'm with 'sbechtold' about protecting the tranny and getting the rpms back in the right range. I have to go almost 80mph to get to 2k-rpm. Tow/haul is also not as effective since it's way lower in rpm.
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post #7 of 13 (permalink) Old 01-24-2008, 07:53 PM Thread Starter
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Quote:
Originally Posted by ZeroOne
Not to be a leech but since we're on the subject... what about for 38x15.50s? 4.30 or 4.56? I'm with 'sbechtold' about protecting the tranny and getting the rpms back in the right range. I have to go almost 80mph to get to 2k-rpm. Tow/haul is also not as effective since it's way lower in rpm.
I can only imagine how much skinny pedal it takes to get those 38's rolling.

With a 4.30 gear set and 38's you will have an effective gear ratio of 3.58:1
With a 4.56 gear set and 38's you will have an effective gear ratio of 3.79:1

IMO the 4.56 would probably be a bit better as it will help compensate for the additional rolling weight of each wheel and your RPM's will be more in line with the stock tire size RPM's.
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post #8 of 13 (permalink) Old 01-24-2008, 08:23 PM
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Quote:
Originally Posted by ZeroOne
Not to be a leech but since we're on the subject... what about for 38x15.50s? 4.30 or 4.56? I'm with 'sbechtold' about protecting the tranny and getting the rpms back in the right range. I have to go almost 80mph to get to 2k-rpm. Tow/haul is also not as effective since it's way lower in rpm.
I have 38x15.50 and run 4.88 gears and love it. I run 2500RPM @ 70mph according to the speedo but its actually 78mph I have no problem getting the truck rolling I regurally tow my 16,000lb fifth wheel and have towed up 27,000lbs a couple times. I have had the tires and gears since 35,000 miles and now have 124,000 and not a single tranny problem.

sbechtold I would suggest the 4.30 gears if your running 35" tires and towing 8,000lbs. it might hurt your mpg a little running high rpm but the power is worth it in my opinion.
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post #9 of 13 (permalink) Old 01-24-2008, 09:26 PM
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Quote:
Originally Posted by sbechtold
I can only imagine how much skinny pedal it takes to get those 38's rolling.

With a 4.30 gear set and 38's you will have an effective gear ratio of 3.58:1
With a 4.56 gear set and 38's you will have an effective gear ratio of 3.79:1

IMO the 4.56 would probably be a bit better as it will help compensate for the additional rolling weight of each wheel and your RPM's will be more in line with the stock tire size RPM's.
I totally agree its the additional weight of the tire wheel combo is what my concern is.

37x13.5 - 4.30's narrow tire less footprint less drag
38x15.50 - 4.56's if its a driver and doesn't see heavy loads often but if you're using the truck to tow 4.88's would be a good option it will deffintely slow the wear on the tranny and mpg's might not be much different than the 4.56's
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post #10 of 13 (permalink) Old 01-25-2008, 02:21 AM
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Very helpful guys, thanks! :Thumbup:

Now... which brand / where do I get a good set of 4.56's?? I'm unfamiliar with which companies have the good gear sets, and I hear that it makes a difference.

:thanks:



EDIT:
sbechtold, I see on another forum that you mention;
Quote:
You are correct that the rear sterling is a 10.5" ring gear. The install isn't difficult, but does require that the carrier is changed to accommodate 3.91 and up gears. The 3.73 carrier only handles 3.73 and down gears. The carriers are only about $80. The install front and rear parts and labor is $1300.
If one were to have the limited slip (and wanted to keep it), wouldn't the carrier that handles greater than 3.73 cost way more than $80?

Also, is the front carrier all set for up to, say, 4.56?

I can hear my bank account draining again... lol.
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