Suggestions for tire size for 17" rim in new 2010 EB 4WD - Page 2

Roonie · 06-04-2010, 07:57 PM

Quote:

Originally Posted by NRL

I just wanted to add that another factor to consider to picking tire sizes is the diff gear ratio related to the tire size you want to have.
What's the diff gear ratio running the 315/70/17?
You just don't want to be geared to tall.

For example, running 285/75/16 with 3.73 Diff gear ratio is at the limit of being to tall, climbing hills might be a prob versus using a diff gear ration of 4.10. 305 or maybe 35in max with a 3.73 would be asking for it on the tranny for climbing extreme hills. I'm still debating if 4.10 is the ideal gear ratio. What's everone diff gear ratio running em huge tires?

Is 315/70/17 the same size as 315/70/16?

Thats a good point. What gear ratio does SMB put in their Dynatrac axles with the 4x4 build? I know my van came from the dealer with a 4.10 gear ratio and limited slip axle but obviously that was swapped with the dynatrac during the 4x4 build I am assuming? Does someone know the answer to this question? gear ration of the SMB 4x4 build?

**BroncoHauler** · 06-04-2010, 09:27 PM

Quote:

Originally Posted by NRL

Is 315/70/17 the same size as 315/70/16?

Just a difference in rim size, isn't it?

Checked TireRack.com, and they don't have any tires in 315/70/16.

Herb

charlie56 · 06-04-2010, 11:44 PM

FWIW
I have BFG 315-70-R17 D rated
27,000 miles on the rear 55% tread used
20,000 miles on the front 45% tread used
I have been extremely happy with the tires until our last trip. During the trip I had a very slow leak on one of the rears that I kept adding air to along the way. Lost about a pound a day. Figured I would just repair it if it got too bad, or wait till we got home. Made it home without any problem where I found the leak was in the sidewall where the sidewall meets the tread. (Boy did I dodge a big one there.) I am replacing the rears with Nitto Terra Grapplers 305-70-R17 E rated and keeping the fronts for another year. The overall diameter is almost exactly what the Front BFG's are at their current state. As stated elsewhere, finding 17's isn't as easy as 16's. I'm expecting a little stiffer ride with the E rating and 65psi vs the 50psi BFG's, but a bit more peace of mind. The Nitto tread is a little less aggressive however I found the more aggressive BFG's didn't do all that well in the mud anyway. The Nitto's are in transit now, I will have them installed next week.

scatter · 06-05-2010, 08:03 AM

[quote="Roonie"]What gear ratio does SMB put in their Dynatrac axles with the 4x4 build? I know my van came from the dealer with a 4.10 gear ratio and limited slip axle but obviously that was swapped with the dynatrac during the 4x4 build I am assuming? Does someone know the answer to this question? gear ration of the SMB 4x4 build?
[quote="NRL"]

As far as I know, if your rig came from Ford with 4:10 it still has it. When DynaTrac makes their rear ends, they use the Ford center section.

Also, in my not so humble opinion, 315 tires and 4:10 gears are a perfect match.

Skywagon · 06-05-2010, 09:08 AM

Scatter's tires are 315 X 75 X 16, I believe, and they are almost identical to mine in height.
(315 X 70 X 17). I also run 4.10 gears, Dynatrac both ends.
Bill

**daveb** · 06-05-2010, 12:29 PM

Quote:

Originally Posted by Roonie

What gear ratio does SMB put in their Dynatrac axles with the 4x4 build? I know my van came from the dealer with a 4.10 gear ratio and limited slip axle but obviously that was swapped with the dynatrac during the 4x4 build I am assuming? Does someone know the answer to this question? gear ration of the SMB 4x4 build?

I think the standard on a SMB build is 4.10 but with the new spring packs on the 08 and newer, it allows taller tires to have a bit more clearance. They might have made a change in gearing but I doubt it. SMB suggested 285 75 16 on my 06 but I'm seeing many of the 4x4 rigs coming off the line with 315's. My van is heavy and I pull a SMB trailer so if I were to go with taller tires I would look into lower gears.

SheepShagger · 06-07-2010, 01:40 PM

Quote:

Originally Posted by BroncoHauler

Quote:

Originally Posted by NRL

Is 315/70/17 the same size as 315/70/16?

Just a difference in rim size, isn't it?

Checked TireRack.com, and they don't have any tires in 315/70/16.

Herb

No.

The 70 size is the sidewall height, and 70 measurement is the % of the width. So the two examples used above, 315/70/16 & 315/70/17. The calculation would be (aprox in my head).
315mm - 30% = 290mm
290mm = 8.5"
17" rim + 2x8.5" tire width = 34"
Do the same for the 16" rim, and it'll be 33"

These are close-ish numbers, I can;t be bothered to pull out a calculator.

A 315/75/16 would be close in total height to a 315/70/17 though, as would a 325/70/16