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Old 02-02-2008, 10:00 AM   #1
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Gear Ratio for 35's

Hello all,

We are getting an EB SMB V-10 with a 4:10 gear ratio from Ford. My question is, do we have to change our gear ratio if we wanted to upgrade to the 35" tires? We would most likely use our rig for traveling cross-country and going on the road most of the time. Any suggestions? Tires and rims combo suggestions? Thanks in advance!
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Old 02-02-2008, 10:18 AM   #2
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We've got 4.10's and 33" tires. I think we are at 62mph@2000 rpm. The 35" tires are only about 6% taller and they should be about 58mph@2000 rpm, or about 2400rpm@70. Should be OK. Probably not worth regearing to save a couple of percent on fuel economy.

Mike
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Old 02-02-2008, 11:50 AM   #3
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Hi Mike,
What type of lift did you get form S&K? Can u PM me or post some pics of your rig? Thanks, Ray
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Old 02-02-2008, 02:20 PM   #4
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I just posted 4 pics of our rig from last year's vacation.

Mike
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Old 02-02-2008, 09:50 PM   #5
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I am running 35" BFG A/Ts with stock 4.10's. I lost a little power when i switched from 33's. If I were ordering a new van I might spec 4.56 gears but only if I was going to use the Dyna_trac rear axle. I do a fair amount of off-roading and do feel the lower gears would be of some help. Also would help performance on the highway but I would not go the cost if I was using the stock Ford rear axle.

Overall evaluation: the 4.10's are OK but 4.56's would be better.
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Old 02-03-2008, 10:14 AM   #6
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Boy, sorry about my math:

Quote:
We've got 4.10's and 33" tires. I think we are at 62mph@2000 rpm. The 35" tires are only about 6% taller and they should be about 58mph@2000 rpm, or about 2400rpm@70.
Your tires are larger and your rpm's should be lower. About 66mph@2000 rpm and about 2100rpm@70mph. And the lower rpm/bigger tires may not do anything to your fuel economy.

Mike
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Old 02-03-2008, 06:14 PM   #7
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I have heard that at some point it will start to mess up the correct shifting of the transmission. I decided to re gear, even though I am only going to 34's. oclv
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Old 02-03-2008, 07:19 PM   #8
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From what I have read, the 4:10 are good with 33" tires. We are thinking of going a little bigger with the 35's. I have heard the same thing about messing up your transmission in the long run if not geared properly. Any one running 4:10 with 35's? Any problems with it?
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Old 02-03-2008, 09:04 PM   #9
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I've got 4:10s with 35" tires and 16,000 miles on our 6.0 SMB. No problems so far and I like the 2,000 RPM at 68 mph. The low end torque with the diesel helps though. I had 3:73 gears in my '96 van with 265x75x16" tires and it was geared a little too high. That had a 5.8L gasser though.
If I was to do it over again, I'd stay with the 4:10s and the 35s. Just got 17 mpg on the run from Reno to Mexicalli. Kind of neat not having to fill up till we got to Mexico where the cost of fuel is MUCH cheaper.
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Old 02-05-2008, 03:47 AM   #10
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4.10 gears and 35" tires will put you on par with a 3.55 axle and stock LT245/75R16 tires.

http://www.grimmjeeper.com/gears.html
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