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Good morning! I’m new to this group. Excited to be on board. I’m currently restoring a 1978 F150. Trying to decide on wheels and tires. My original plan was 35x12.5x15’s. I have a 4” lift and put in new 4.56 gears. Im running the original but rebuilt C6 tranny with a slight stall and 203 transfer case. The engine is the original 360 FE block with a 445 stroker kit. Can’t wait to hear her fire up for the first time. Anyway I believe I have the perfect set-up for 35’s but recently decided I’d like to go bigger. I want the more aggressive look of the bigger tire but worry about gear size and lower RPM’s for the big 445 stroker. Cruising around town she‘ll rarely be over 55 mph. Anyone running 37’s on 4.56 gears? I put in aftermarket radius arms that run parallel to the frame and kick out at the end for more room so I don’t believe clearance will be an issue at all. Thanks for your help!
If you like the look of bigger tires with less lift go with the 37s. I liked 35s with no lift on mine, but it rubbed a bit so I went with 33s. 33s with 3.50 gearing isn't too bad. Helps if you do end up on the freeway. From charts I've seen stock tires with 3.50 gearing should be pretty much the same as 35s with 4.10s or 37s with 4.56s. If you think stockish gearing would be ok, again, go with the 37s. If you want more gearing and don't do much highway you should be able to go quite a bit higher numbers than 4.56 with 37s.
That 4.56:1 earing will help turn up from stop those 35s, even 37s, but gearing won't help brakes in a time of sudden / greatest need, and then there's handling that gets a ding. 35s and 37s are gonna be some deal heavier and that has a few implications for suspension wear, ride, bumps, force needed to change tire direction like when steering, etc.
Just to compare to a std gear like 3.50:1 with a near stock size 31" tall tire, a 35" tall tire would need 3.95:1 gear to have same engine rpm at a given speed, but 37" tires would need 4.18:1 gear to do the same, so 4.56:1 is plenty of gear for either.
As far as comparing say RPMs at say 55 mph, using 3.50:1 gears with 31s will have the engine turning >2,300 rpms. My '77 has that gear and I've run 31s for near 40 years and GPS and before I had GPS, radar told / tells me that the speedo is near "***** on accurate", and Sun provided rpms.
At that same 55 mph, 4.56 gears with 37s will spin the engine a hair over 2,500 rpms ... and with slightly shorter 35s, a hair over 2,600 rpms.
If you run those 4.56s with a short 31" tall, you'll see near 3,000 rpm.
The gears would be fine with 37's, but that is pushing it pretty hard for the front and rear axles. Most off-roaders recommend 35's max with the standard Dana 44. The center section of a 9 inch is legendary for it's strength, but wheel bearings don't hold up well under increased loads. That's why the F250 had the D60 rear and heavy duty duty D44 or D60 up front.
Ahh that makes sense. The Dana is a 75’ so it’s the thicker steel casing but the extra wear on the gears makes sense. I didnt think about that. I did upgrade the steering with this power steering conversion kit from benchwork. Super thick steel molly Tie-rod and drag-link with this massive gear system. Awesome stuff.
37's are pushing it on a 4" lift. From what I see, most 4" lift kits/systems say 35" max tire size.
When I bought my truck it had 36's on it. It looked like it had plenty of room around the tire. Friends said I probably had a 6" lift, but I have no idea what I have. So I went up to a 38" tire. Too close for comfort and could possibly hit off roading, so I added a 3" body lift. That was cheaper than new tires. I'm guessing now that I have a 4" lift. This time around I'm going back to a 35 or 36. No body lift and hopefully my springs aren't whooped. All I can say is, don't buy too big a tire and then wind up using a body lift to compensate.
Also, I always liked the larger brakes with the larger tires. So that would be my other reason for picking the 35's on a 150.
I put 33's on my 15x10 Mags with a 4" lift - I think it looks great though did have concerns at first it may look too small... but the polishes lip of the Mags make it standout really nicely.
I run Ironman 285/75R16 tires.
At 40psi they measure 32" tall mounter on the truck. The spare tire measures 32.5" with 40psi.
Factory specs state 32.8" diameter.
They are wearing flat and even.
I like them.
What's funny is they are a few inches taller than the factory size tires but now my speedometer is right on from 30mp all the way up to 80mph.
Interesting.
My first set of tires for my '76 were 7.50 16 Deestone D503 bias ply deep lug traction tires.
Using the calculator at 65mph, 29" diameter, 4.10 gears, 1.1 4th gear it was running at 3100 rpm.
The 32" Ironman tires run 2800rpm.
35" with your 4.56 gears and a 1.1 3rd gear in your C6 at 55 mph, 2400rpm. 37" 2280rpm.
At 65mph 35" 2845rpm and 37" 2700rpm.
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