Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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#449147 10/20/20 07:30 PM
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Hi there
Could someone here verify that I have my thinking straight here?

If the wheels I have are a positive 1/2 inch offset... and I presently have about a quarter inch clearance between the front tie rod end and the tire...
then a wheel and tire of the same size but 1/8 inch positive offset should give me 3/8" MORE clearance at the tie rod... correct?

Thanks


Ole S Olson
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Hi Ole,

I agree with your thinking. Less positive offset for the same width wheel means that the inner flange of the wheel is further away from the centerline of the vehicle.


Rusty

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Thanks very much Rusty.
Always like to hear someone else's thoughts.


Ole S Olson
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When adjusting wheel offsets and diameter keep the king pin inclination. If the axis point and tire centre line are separated it will effect the steering. I found out the hard way.
Tony


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Good point Tony.

I describe that as steering offset. It is the distance between where the steering axis centerline intersects the ground and the center of the tire.

You are correct that changing that distance can produce some interesting steering results. There has been a lot of research and numerous articles written about that.

In this case I doubt if a 3/8” change would be very noticeable. I have never tried to determine if these old cars have negative or positive steering offset. Might be an interesting winter (for us) activity. .


Rusty

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Hi guys
I was aware of that exact steering issue and worried about it too.
The vehicle I'm working with is actually a truck. A 1946 3/4 ton to be exact. With 2 piece 15" rims.
My problem is I need at least 1 "new" rim to replace one that was cracked and welded at some point (and now has a distinct wobble)... but the rims for the truck are peculiar to that year and tonnage, and it doesn't look like I'm likely to find one. All 3/4 tons from 1947 to at least 1954 used alike rims but with less offset.

So...
I suppose I can stick with the originals on the front, and switch out the rears. That will widen my rear tread width a bit and change the way the rears track the fronts. Not much though.
That's assuming the 1947-54 rims are visually the same from the outside as the original 1946 rims.
I know... that's a little ocd or "anal" as they say now... but I guess I'm like that. :-)


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Here is food for thought. Your truck was available with difference wheel sizes but the axle setup was the same. That means the near intersection of the two lines would be different.


My 1951 1 Ton is now on the road! My 38 Master 4 Door is also now on the road .
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Excellent point old216.

So I looked up the offsets for the 2 sizes of rims in my 1929-54 master parts book.
The numbers given there don't agree with those at chevy.oldcarmanualproject.com but here is the interesting part...

In both cases the positive offset of the 17" rim is MORE than the 15" rim.
That moves the rim center line IN towards the middle of the truck on the 17" rims (17" was only available with 7.00 tires whereas 15" could be used with 7.00 or 7.50 tires)... even though the point where the center line of the king pin intersects with the road will be further OUT from the middle of the truck by about 3/16 of an inch.

What's up with that?


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Any suspension / rating differences between the trucks with one rim size vs the other rim size?

You likely have tolerance either way as long as you have clearance. Even one brand of tire vs another brand of tire will physically measure differently. Load the bed and cab and the numbers change vs an unloaded vehicle so some range would be anticipated and designed for. The engineers thought/designs may have changed over a few years or have been simply overridden by bean counters or esthetic opinions lol. Road quality was probably a more significant factor at the time than offset as it wasn't exactly a precision surface back then and more than likely a potholed hardpacked surface.

I would expect that the higher the load rating of the truck or the rims from a higher load truck, the further the engineers would try to move the wheel offset to keep it centred over the bearings. Once the load moves further out past the bearing, the cantilever effect puts a huge strain on bearings and this is obviously more significant on a truck that would be loaded more heavily. Probably insignificant for an occasional use vehicle but a head scratcher for those of us who want to know "why?".


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Hi canadiantim

According to chevy.oldcarmanualproject.com the camber and king pin inclination are the same for 1946 and 1947-54.
The caster is slightly different but it looks like one is measured loaded and the other not and are probably the same with that taken into account.
Toe in is nearly the same as well.
And it doesn't show a spec difference for different rim sizes. Just one spec.

I didn't actually measure the clearance, but a quick eyeball would say I don't have any more than 1/4 to 3/8 inch between my tie rod ends and the new Yokohama 7.00R-15 tires I put on this year. They were the only tires that size I could find in stock anywhere near here.

One more interesting thing:
My uncle (who is gone now) told me that when he traded a 1946 1-1/2 ton on a new 1950 2 ton Advance Design, the 1950 steered MUCH heavier than the older truck.
My brother has that truck and it really is MUCH heavier steering than his 1946 2 ton or my 1946 3/4 ton. The wheels on the older trucks can be turned fairly easily with the truck standing still. Even loaded if not in ground that is too soft. Not so with the 1950.
Maybe this had something to do with the rim offset?


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I would not make any assumptions regarding the steering offset and steering effort difference between those 2 trucks. There could be differences in overall steering ratio (not just the steering gear ratio) as well as steering wheel size.

One easy change you could try is to install some 1/4” or maybe 3/8” thick wheel spacers with your current wheels and tires. That is essentially decreasing the positive offset (or adding negative offset).

My guess is that you will not notice much if any steering effort difference.

The quick and cheap way to try that is stacks of washers on the wheel studs. Maybe not at 60 mph!



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The problem I had was by putting 13" wheels where 12" should be. With both rims on the floor the hub face was at the same height. By increasing the diameter of the wheel meant the steering axis moved outside the tire centreline this resulted in the steering being harder to return the straight ahead from a hard (full lock) turn.
Tony


1938 1/2 ton Hope to drive it before I retire

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