245/70/16 Too Big?

[Rusted]

Found some steel wheels and tires for a decent price but will these be too big for my 620? If not how will it affect driving/speed?

[datzenmike]

That's a 29.65" diameter tire, yours are around 23.65", the speedometer will read 25% out!!!!!! Worse this will affect you overall gear ratio. By going to a 29.65" tire the truck will feel like you took the differential out and put a 3.489 ratio in. If you have the standard 4.11 differential in your '79, it will feel like 3.27!!!!!!!!

 

I have no idea on the fitment... the offset may be so wrong that the tire sticks out and the body comes down on it on bumps and turns. You will find that you have to slip the clutch a lot more when starting from a stop, and even worse if carrying any load. Your acceleration will be severely limited making passing dangerous. You will have to down shift on hills out on the highway and on windy days you may not be able to use 5th gear at all. I would not do this.

[Rusted]

30 minutes ago, datzenmike said:

That's a 29.65" diameter tire, yours are around 23.65", the speedometer will read 25% out!!!!!! Worse this will affect you overall gear ratio. By going to a 29.65" tire the truck will feel like you took the differential out and put a 3.489 ratio in. If you have the standard 4.11 differential in your '79, it will feel like 3.27!!!!!!!!

 

I have no idea on the fitment... the offset may be so wrong that the tire sticks out and the body comes down on it on bumps and turns. You will find that you have to slip the clutch a lot more when starting from a stop, and even worse if carrying any load. Your acceleration will be severely limited making passing dangerous. You will have to down shift on hills out on the highway and on windy days you may not be able to use 5th gear at all. I would not do this.

Appreciate the response! I’m convinced I want no part of these now. Found some 15x9ish rims I might pick up and put some fancy tires on.

[datzenmike]

Rim size has little to nothing to do with tire height. You could still run 16" but select a tire that is close to 24" and as wide as will fit. Be sure you check the fit of any rims. Off set is the key. If they stick out too far from the body it will come down on it hitting bumps (more so carrying a load) and scrape the fenders on a turn. Try for rims that keep your tire choice inside the fenders. Rims with negative offset hugely affect the scrub radius making then harder to turn when parking.

[Charlie69]

I will be running 205 55/16 on my 66 520 but I have a 1980 720 chassis and Belltech 2" lowered spindles.  I have also upgraded to the vented rotor disc brakes from a 1985 720.  The wheels will be 2000 Isuzu trooper wheels.  This tire and wheel combination works well for my setup. The 1980 720 chassis is the same as the 78/79 620 chassis in the front.  The Isuzu wheels have a -38 offset.  I might run 1/2" spacers and longer wheel studs in the rear.

 

 

 

 

 

 

 

 

Frank Rizzo's Cactus Green Datsun 620 with Isuzu Trooper wheels.

 

 

Frank Rizzo's Cactus Green 74 Datsun thread

Edited February 25, 2020 by Charlie69

[datzenmike]

On 2/24/2020 at 7:15 AM, datzenmike said:

Rim size has little to nothing to do with tire height. You could still run 16" but select a tire that is close to 24" and as wide as will fit. Be sure you check the fit of any rims. Off set is the key. If they stick out too far from the body it will come down on it hitting bumps (more so carrying a load) and scrape the fenders on a turn. Try for rims that keep your tire choice inside the fenders. Rims with negative offset hugely affect the scrub radius making then harder to turn when parking.

 

To add to this.... running 10" rims and 6" wide tires stretched so they tuck.... well it offends my eyes and sense of what is safe. I thought this fad was over like mad camber.

[Rusted]

10 hours ago, datzenmike said:

 

To add to this.... running 10" rims and 6" wide tires stretched so they tuck.... well it offends my eyes and sense of what is safe. I thought this fad was over like mad camber.

I’m not a fan of stretched tires and much prefer the beefy look. I think I’m set on 15s so I don’t have to go too low profile. Very helpful information didn’t even think about the offset.

[demo243]

Don't know what the wheel specs are other then they are 15's --- these are 215/65r15s on my 620; 3" blocks on the back, and backed off torsion bars up front. The rear passenger side appears to just clear the fender, the rear driver just kisses the fender. Fronts are ok--- but I don't know the wheel offset or width.

 

 

[datzenmike]

That's a 26" diameter tire. Two inches larger than stock so the speedometer is a hair under 5 MPH out at 50 MPH. This taller tire is 'seen' by the engine as changing to a 3.98 differential..... not  problem for a KA.

[Charlie69]

The Isuzu wheels pictured above are 7" wide wheels.