Smaller tires to change diff ratio?
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Junior User
Joined: May 2008
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From: Pitt Meadows, BC
Smaller tires to change diff ratio?
Hey there,
I have an '01 F350 RWD 6.8L 3.73 diff crewcab.
It's getting time to get new shoes for her, and am wondering if I should consider dropping down from the 265's to 245's.....this would give an effective differential ratio of 4.0:1.
Reason I ask is that we tow a 7200lb travel trailer and am hoping the change will get the engine into it's sweet spot without dropping out of OD at the slightest incline. I have a Scanguage and religiously watch my tranny temps while towing, so driving in OD while towing has been fine.
I've considered going to a 4.30 diff, but seeing how I need new tires anyway it might be worth a shot?
I'll lose about 400lbs each in weight capacity even with the E rated 245's, but I've never come close to my rear axle rating when loaded and towing anyway.
Also, if I did do the swap would I have to monkey around to get the speedo reading correctly?
Any advice is appreciated....even "Are you nuts fella??"
Cheers,
Mike
I have an '01 F350 RWD 6.8L 3.73 diff crewcab.
It's getting time to get new shoes for her, and am wondering if I should consider dropping down from the 265's to 245's.....this would give an effective differential ratio of 4.0:1.
Reason I ask is that we tow a 7200lb travel trailer and am hoping the change will get the engine into it's sweet spot without dropping out of OD at the slightest incline. I have a Scanguage and religiously watch my tranny temps while towing, so driving in OD while towing has been fine.
I've considered going to a 4.30 diff, but seeing how I need new tires anyway it might be worth a shot?
I'll lose about 400lbs each in weight capacity even with the E rated 245's, but I've never come close to my rear axle rating when loaded and towing anyway.
Also, if I did do the swap would I have to monkey around to get the speedo reading correctly?
Any advice is appreciated....even "Are you nuts fella??"
Cheers,
Mike
Senior User
Joined: Jun 2002
Posts: 177
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From: Boston
Looking at the same thing Mike, started a thread here a week back!
https://www.ford-trucks.com/forums/1...-downsize.html
See my calculation in there, you'll only be getting a 3.85 ratio by going to the 245's.
I found a good set of slightly used 225/75/16E commercial truck tires, Goodyear G949, I think the class C RVs run this size. Going to give it a shot after last snow later this month, will report back in!
Neil
https://www.ford-trucks.com/forums/1...-downsize.html
See my calculation in there, you'll only be getting a 3.85 ratio by going to the 245's.
I found a good set of slightly used 225/75/16E commercial truck tires, Goodyear G949, I think the class C RVs run this size. Going to give it a shot after last snow later this month, will report back in!
Neil
Bleed Ford Blue
Joined: Apr 2009
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From: Anchorage Alaska
LOL so if thats the case with the C rated tires on my Excursion i could be locked up!
Super Moderator
Joined: Aug 2003
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From: Isanti, MN
I just did some searching around, and you can buy a P-metric tire that's rated to support the weight of these trucks. A Bridgestone P265/75R16 is rated for 2,801 pounds at 44PSI, which would mean that you would be safe with over 5,000 lbs on each axle without even an LT-rated tire. The tire wouldn't blow, but that's about as far as it would go, because the reduced sidewall strength would provide less stability under load.
Going to a smaller size with the same load range should be just fine as long as he keeps in mind the maximum capacity for the tire and how it is effected. Proper inflation pressure will be higher with a smaller size to properly support more weight!
Thread Starter
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Junior User
Joined: May 2008
Posts: 76
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From: Pitt Meadows, BC
Guess I didn't use the diff calculator properly....hardly worth the effort if it only gets me to a 3.85:1.
Totally understand about the lower weight ratings and inflations.....ever trip out gets a psi check.
Cheers.
Totally understand about the lower weight ratings and inflations.....ever trip out gets a psi check.
Cheers.
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Cargo Master
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doesn't really sound like you'll gain enough to make it worth while. I'd just lock OD out and go that way. You probably won't loose that much MPG's either if that worries you because everytime your tranny shifts back and forth you loose some performance. I had a friend who put too large of tires on his truck for the gear ratio and the thing would downshift at every small hill without a load. One time on a long trip he drove part of the trip with OD on and let the truck downshift all the time, the rest of the trip he locked OD out and even though the RPM's were higher the entire time he got better mileage.
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From: Isanti, MN
Also your IP address places you in another country, perhaps things are different in Australia?
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