Wheel sizing and gearing

[Aussie Boy]

1965 C10 fleetside, 230 engine, SM420 Muncie and a 12 bolt rear end. I know with retaining the gearbox I'm battling for top end speeds and low revs but the wife wants the truck left pretty close to standard as it belonged to her father.

With that being said we're lowering the front 2 1/2" with spindles and the rear 3" with springs. Would 17 x 8 wheels covered in 235/75R17 clear the guards and not rub on suspension or steering?

Those wheels will put me around 30" high which will help with engine revs at speed, but what ratio in the rear end would help out? I've used calculators online which gives me an idea (3.73), but I figured asking the guys that have been there and done it would help out also.

Cheers fellas

[SCOTI]

That's closer to a 31" tall tire than a 30". Dropping it down & increasing the tire OD beyond what it was originally (~28") can have some clearance issues especially depending on wheel offset/backspacing. It will be a WAG for someone to provide a definitive Yes or No unless they have a very similar combo.

As far as gearing/drive rpms, the taller combo will make it more highway friendly for sure @ the sacrifice of the low-end gearing grunt.

[Agv63]

When i got my 63 it had a 250 with 3spd saginaw, 3.73 and 31/10.5r15.
Pulling away on was not a problem, can chirp the tyres and cruising was decent at 120kph (75mph) i calculated roughly just under 3000rpm ,no tach to verify just calculated from tyre size and gearing. still had original but sagged springs in it. Some pics included.

Cheers.
Adriaan.

[Aussie Boy]

Originally Posted by SCOTI

That's closer to a 31" tall tire than a 30"

You're right, I must have mis-typed or hit the wrong combo/size. I'll give it a go and see what happens when I put it all together

Originally Posted by Agv63

When i got my 63 it had a 250 with 3spd saginaw, 3.73 and 31/10.5r15.

Sounds like a good deal, I'll be keeping this in mind and start getting some parts sorted ready for the cooler weather to kick in and I can actually do some work in the garage

Cheers fellas

[theastronaut]

My '66 with a 250, 3 speed (same 1:1 top gear ratio as your trans) and 235/75-15 tires will cruise all day at 75 all day no problem, and accelerate up to 85 to pass if needed. I did take the stock fan off and used an HHR electric fan/shroud to free up power, get better mileage, and cut down on engine noise which made quite a noticeable difference, but other than that it's stock. Without overdrive you probably wouldn't want to go much lower than about a 3.42 with a 230 unless your area is flat with no hills.

[61hawk]

Rear end calculator
https://spicerparts.com/calculators/...rpm-calculator