Selecting a proper gear ratio for '08 F250 - Diesel Forum

Connie42 · 05-08-2007, 01:10 AM

I just ordered a new 2008 F250 Lariat with all the options I wanted. But when asked what gear ratio I wanted I responded with 3:73. After thinking about it I began to wonder what happens to performace if I put a little bigger tire on it, say a 34" diameter tire. Do I significantly change the sweet spot in the torque curve and reduce my economy? Should I change my order to a 4:10 to compensate? I do tow a toy hauler that when loaded is about 10K lbs. That is about 24 times per year or about 25% of the time that I'll be driving this truck will be towing something.
Opinions welcome and encouraged.
Thanks
Bud

Diesel_Aggie · 05-08-2007, 02:50 AM

Any time you go with a taller tire acceleration and hill climbing power will decrease. You are planning to tow a 10,000 toy box and being in California I suspect you will encounter some pretty steep hills and hot temperatures. I think most people with toyboxes loaded with toys are also performance enthusiasts who enjoy acceleration. Based on these assumptions I'd say go with the 4.10s if they are available. It sounds like this probably is not your daily driver so the slight fuel mileage penalty is not going to be a big issue. I'd strongly encourage you to look at the pin or hitch weights on your toy box and confrim that you will be in the trucks rated capacity. Better to realize a 350 would be a better truck now than later. I'd also spend some time researching the weight capacities of the wheels/tires you plan to add. Most larger tires in the range you are talking about will have a lower weight rating than stock. You may want to post your same questions over on the towing forum. There are some very smart people there who have lots of towing experience.

SmokeyWren · 05-08-2007, 09:06 AM

[ QUOTE ]
I just ordered a new 2008 F250 Lariat with all the options I wanted. ... Should I change my order to a 4:10 to compensate?

[/ QUOTE ]

The only gear ratio available for an F-250 with a diesel engine is 3.73.

Same story with F-350 SRW.

The only way to order a 4.10 rear axle ratio is to move up to an F-350 DRW - as in dual rear wheels or dually or Dooley.

The 3.73 will be about perfect for towing a 10,000-pound trailer with a stock truck. If you later decide to ruin the truck with huge tires, then just plan on the cost of a gear ratio change to be part of the total cost of that mod.

Need me a 7.3 · 05-08-2007, 01:57 PM

[ QUOTE ]
[ QUOTE ]
I just ordered a new 2008 F250 Lariat with all the options I wanted. ... Should I change my order to a 4:10 to compensate?

[/ QUOTE ]

The only gear ratio available for an F-250 with a diesel engine is 3.73.

Same story with F-350 SRW.

The only way to order a 4.10 rear axle ratio is to move up to an F-350 DRW - as in dual rear wheels or dually or Dooley.

The 3.73 will be about perfect for towing a 10,000-pound trailer with a stock truck. If you later decide to ruin the truck with huge tires, then just plan on the cost of a gear ratio change to be part of the total cost of that mod.

[/ QUOTE ]

Hmm, Smokey...intersting that you think a 34 inch tire would "ruin" a truck. Arent the big stockers at about 32 1/2 to 33?

tzurick · 05-08-2007, 03:07 PM

33.2 to be exact for the stock 18 Conti's and 34.1 for the stocks on 20 inch rims

Connie42 · 07-08-2007, 05:30 PM

Thanks Guys.
I got my truck and stuck with the 3:73's. Added 35" Nitto's on 20" rims and it looks and rides terrific.
Speedo is a little less than 5% slow. Pulls my boat and tow hauler like they're not there.

jgoff78 · 07-09-2007, 03:59 AM

im wearing 325/65/18' (~34.5) tow 10k or more regularly and doesnt seem any different then with the stock tires

borg54 · 07-09-2007, 08:40 PM

i just put on 35" on 20's on my 350 and i have noticed a small change in accel. For me the tradeoff was worth it for the off-raod (yes i do)and looks. Fit fine with no mods. I would have wanted the 4:10's but as everyone knows ford wont give us what we want...

while i think the acceleration can be helped with a few more HP's the big difference i noticed was BRAKING. My truck definitely does not stop as quickly with the new wheels. a couple of times i almost ran into the back of someone on the freeway cause the truck took it's sweet time slowing down.

Gabby · 07-09-2007, 10:06 PM

[ QUOTE ]
Thanks Guys.
I got my truck and stuck with the 3:73's. Added 35" Nitto's on 20" rims and it looks and rides terrific.
Speedo is a little less than 5% slow. Pulls my boat and tow hauler like they're not there.

[/ QUOTE ]

Aw man you "ruined" your truck! [img]/ubbthreads/images/graemlins/shrug.gif[/img] [img]/ubbthreads/images/graemlins/warmsmile.gif[/img] [img]/ubbthreads/images/graemlins/phoney.gif[/img]

Gabby · 07-09-2007, 10:08 PM

[ QUOTE ]
i just put on 35" on 20's on my 350 and i have noticed a small change in accel. For me the tradeoff was worth it for the off-raod (yes i do)and looks. Fit fine with no mods. I would have wanted the 4:10's but as everyone knows ford wont give us what we want...

while i think the acceleration can be helped with a few more HP's the big difference i noticed was BRAKING. My truck definitely does not stop as quickly with the new wheels. a couple of times i almost ran into the back of someone on the freeway cause the truck took it's sweet time slowing down.

[/ QUOTE ]

Oh no not another one that "ruined" their truck too? [img]/ubbthreads/images/graemlins/shrug.gif[/img]

Connie42 · 07-31-2007, 02:43 AM

I know what you mean about breaking. It does take a bit longer to brake but i though it was my imagination since I only had the stock tires on for one day.
All in all very worth the trade.
By the way Gabby those tires on your truck look very close to 35's too!
You're truck doesn't look ruined [img]/ubbthreads/images/graemlins/smile.gif[/img]
http://good-times.webshots.com/album/560091589NMcXfr