MTFCA Forum

So, thread on trailering and enclosed trailer doors and garage doors got me pondering about vehicle height. My WWI ambulance project calls for an overall height of 81". But, that is based on a 1917 chassis with 30x3 wheels and tires, but I am using a later chassis with 21" demountables. Is there a height difference,and, if so, does anyone have some measurements as to the overall height difference between an inflated 30" tire and wheel and a 21" inflated fire and wheel. Surely it is not 9".
Thanks in advance.

30 x 3 clincher
30 - (2x3) = 24 inch wheel

30 x 3.5 clincher
30 - (2x3.5) = 23 inch wheel

450-21 balloon
30 - (2x4.5) = 21 inch wheel

Today's 30 x 3 and 30 x 3 clincher tires are actually oversize and can be anywhere from 31 to 31.5 inches in diameter depending on the brand. For actual diameter, refer to the specs by brand on the tire retailers' websites.

450-21 balloon tires are approximately 30 inches in diameter. For example, the Goodyear All Weather balloon 450-21 tire is 30.42 inches in diameter.

signsup wrote: ↑

Wed Feb 07, 2024 10:40 am

So, thread on trailering and enclosed trailer doors and garage doors got me pondering about vehicle height. My WWI ambulance project calls for an overall height of 81". But, that is based on a 1917 chassis with 30x3 wheels and tires, but I am using a later chassis with 21" demountables. Is there a height difference,and, if so, does anyone have some measurements as to the overall height difference between an inflated 30" tire and wheel and a 21" inflated fire and wheel. Surely it is not 9".
Thanks in advance.

I believe the outside diameter is essentially the same, regardless of tire size. The 21" dimension is the inside diameter of the tire. The size is normally stated as "4.50 - 21", meaning a 4-1/2" sidewall height and a 21" inside diameter. So, a sidewall on each side of the tire is 4.5" X 2, or 9". So, 9" + 21" is a 30" outside diameter, just like a 30 x 3 or 30 x 3.5.

4.50 x 21" = 4.5 + 4.5 + 21 = 30"
30 X 3.5 WAS 30" Today's tires are pretty much all "oversize" & so labeled & will be slightly larger.

Faster typists.

Great info. I learned two things today. One, a 30" tire and a 21" tire have the same basic height, when mounted. And, the 4.5 dimension on the 21" tires is not the tread width as I always thought it was, but is actually the sidewall height.
But, bottom line is my package height should be the same regardless of the tire combo. Or, as they say, close enough for government work.

To put it briefly, in two words, Bugger All! But the other posts are far more educational.

Allan from down under.

Well said, mate.
Although I am waiting for the moderators to edit my post mentioning my package height...could be taken out of context.

signsup wrote: ↑

Wed Feb 07, 2024 10:40 am

So, thread on trailering and enclosed trailer doors and garage doors got me pondering about vehicle height. My WWI ambulance project calls for an overall height of 81". But, that is based on a 1917 chassis with 30x3 wheels and tires, but I am using a later chassis with 21" demountables. Is there a height difference,and, if so, does anyone have some measurements as to the overall height difference between an inflated 30" tire and wheel and a 21" inflated fire and wheel. Surely it is not 9".
Thanks in advance.

You defined your chassis etc: I am starting with a 27 Depot Hack chassis and that is what I am converting to a 1917 T ambulance. But, it will always be a T salad. Just trying to represent the species with this project. So, yes, 27 fenders and running boards, radiator and hood and yes, 21" wheels to go over the 11" rear brakes. And, yes, it wil have a starter.
There is always a question if your starting with an unmodified 27 Depot Hack chassis
-Spring height will affect height as well (do they each have 9 leaves)
I don't have an 9 leaves for comparison but old vs new makes a difference. Picture is to give you an idea of differences. Also you overall body weight will affect height.
--
Unofficial Measurements
FRONT Springs --
REAR Springs --
-
1926-27 Front spindles - lower height about 1/2 inch

I have the chassis on jack stands now, but will mount tires and wheels and drop to floor and then measure up to the 81" body top height to coompute body dimensions. I just did not want the rear body to appear out of proportion if there was a significant difference between the original tire/wheel combo on the 1917 chassis and my current 19286 chassis. Spring tension, tire sidewall height, axle drop, etc. will all go into computations. Although, once the body is built and installed, the weight alone will drop the overall height a little, I would imagine. But, close enough for government work.
Thanks for all the tire and wheel info. I learned a lot.