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Not sure how close to scale accuracy it is but I use .100 rod for most of my cage work and chassis work.  Of course I have never built a complete pro-mod chassis so I may be off base with this suggestion.

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Check the real rules for the car class and year you're wanting to model.

It will specify the roll-cage tubing diameter (somebody here will know, and will probably chime in).

Divide that by 24 for 1/24 scale.

Here's more related info:


Edited by Ace-Garageguy
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  • 2 weeks later...

A  0.100” rod/tube would be a 1/10” fractional size.  Remember back to like 5th or 6th grade to obtain a decimal equivalent from a fraction divide the top number by the bottom.  i.e. 1/10” = 1 divided by 10 = 0.100”.  

Now  to go the other way and get a full scale measurement multiply the decimal number by the scale.   0.100 X 24 = 2.400 inches the actual mathematic expression looks like 0.100/1 X 1/24 = 2.400” the numerator’s and denominator’s (1’s) cancel out each another and you are left with the first equation or 0.100 X 24 = 2.400”.

Try it with a few other common fractional tube sizes

Fraction   =   Decimal   X   1/24 Scale        or         1/25 Scale                         Tube Sizes Fractional

1/32”        =   0.031”          =  0.750”             = 0.780” say 0.750”     3/4” 1/25 scale  0.020” round up/down tube size 1/2” (?)

1/16 “        = 0.062”           = 0.1.488” say 1.500”    = 1.550” say 1.500”      1-1/2”   Round 0.002 up  0.050 down to size

1/8”            = 0.125”           = 3.00”                              = 3.125”                          3-1/4”  Round up or down 3” or 3-1/2” tube

From here you can probably figure it out; just remember that the prototype’s tubing size and the tubing sizes manufactured are what the deciding factor in rounding up or down to the “correct” tubing sizes.  In whatever scale you are rounding to and using you will likely not be able to tell the difference of the rounding any way, unless you also count rivets I guess.  

For me even from an Engineer’s  standpoint, in building scale models.   There must come a point where what decides what dimensional tube used is what is manufactured in fractional (plastic) versus what is manufactured in full size (metal) tubing that you are replicating.  If there isn’t an exact scale match then round up or down to what is pleasing to the viewer’s eye.  Short of sanding plastic tube down or turning your own on a lathe, when an exact match isn’t there is about all you can do. It is a compromise called “best fit”.

Hope this helps…
Caveats - Assumption that beyond 1-1/2” tube sizes then 0-1/2” increments to the next larger size (or I didn’t look up common mil sizes for tubing). 

Edited by Skip
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I'd just add that fabricated chassis would have several different sizes of tubing plus you'll want extras to start over with or keep going so I suggest getting several sizes and get both tube and rod as sometimes one is better than the other . Watch out for warpage if using plastic it doesn't always happen but it can . 

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Just an opinion, but if the exact size can't be had, go undersize as opposed to oversize.  Paint, especially if primer is part of the deal, will be thicker than correct for 1/25 scale, and will make up the difference (if not exceed it...)

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