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1/32 Scale Wheels Sizing

Hi people, As I was working out scale wheel sizes to satisfy a recent urge to make some cars look right, I thought it might be helpful to any others that felt the need  Wrench
All sizes are rounded to the nearest 0.1mm.
Measurement is the outside diameter of the visible part of the wheel once a tyre is fitted, not the actual size manufacturers' list, as that is usually the largest diameter.
This does vary depending on the manufacturer, but as a guide a 16.5mm wheel will have a visible diameter of 14.3 making it a 1/32 scale 18" wheel.

17.9mm @ tyre rim = 21"
17.1mm @ tyre rim = 20"
16.3mm @ tyre rim = 19"
15.9mm @ tyre rim = 18.5"
15.5mm @ tyre rim = 18"
14.7mm @ tyre rim = 17"
13.9mm @ tyre rim = 16"
13.1mm @ tyre rim = 15"
12.3mm @ tyre rim = 14"
11.5mm @ tyre rim = 13"
10.7mm @ tyre rim = 12"
9.9mm @ tyre rim = 11"
9.1mm @ tyre rim = 10"

For clarity, the measurement is "D" as shown on Pendle Slot listing for thee new Staffs wheels. Link
[+] 7 members Like Savage GT's post

Sorry Savage but I must disagree with your sizing list.
The diameter of a car wheel is quoted as the diameter of the bead on which the tyre locates not the overall diameter of the wheel.
The depth of the bead which holds the tyre onto the wheel must be added to the wheel diameter to get the overall visible diameter.
The bead on most wheels is about 5/8 to 3/4 inch depending on the material the wheel is made from.

This diagram should make what I am saying clear.

If we assume 3/4 inch bead we must add 1.5 inches to the quoted diameter of any wheel to get the visible outer diameter.
This give a revised list at 1/32 scale as follows;

20 inch = 17.1mm
19 inch = 16.3mm
18 inch = 15.5mm
17 inch = 14.7mm
16 inch = 13.9mm
15 inch = 13.1mm
14 inch = 12.3mm
13 inch = 11.5mm
12 inch = 10.7mm
10 inch = 9.1mm

These have all been rounded to the nearest 0.1mm

So to take an obvious example
A Formula 1 wheel must be 13 inch diameter but it's visible wheel diameter will be approximately 14.5 inches diameter.
At 1/32 scale that is 11.5mm, not 10.3mm.

There seem to be a number of Slot Car manufacturers that don't understand this which is why many cars are fitted with under scale wheels.
I seem to remember having to explain the above to Andi Rowland a few years ago.

[+] 4 members Like Mick Kerr's post

Hi Mick,
I was not aware the measurement of a real wheel was to the bead, and having measured my 19" wheel at 20.5" you are absolutely correct  Beer 
I already realised many slot cars had undersized wheels, but now they are more so than I thought !

Could a mod to edit my post to replace the dimensions with the list below, and thank Mick for the corrections please :)

17.9mm @ tyre rim = 21"
17.1mm @ tyre rim = 20"
16.3mm @ tyre rim = 19"
15.9mm @ tyre rim = 18.5"
15.5mm @ tyre rim = 18"
14.7mm @ tyre rim = 17"
13.9mm @ tyre rim = 16"
13.1mm @ tyre rim = 15"
12.3mm @ tyre rim = 14"
11.5mm @ tyre rim = 13"
10.7mm @ tyre rim = 12"
9.9mm @ tyre rim = 11"
9.1mm @ tyre rim = 10"
[+] 2 members Like Savage GT's post

Thanks JasonB  Thumbup

Wheels for slot-cars are a very frustrating aspect. Scaling to the correct size and then finding the appropriate wheels is a big challenge, more so for enclosed wheel cars rather than for single-seater types. Then finding suitable tyres with an age-related sidewall profile is a real pain.  
The various wheel and tyre manufacturers are tending to get the message though though so hopefully this challenge will reduce. 
It would be ideal if resin/other shell manufacturers would specify what wheels and tyres fit their products but I suspect that the artisans simply produce a shell that looks right without really thinking about the need for wheels.


Forum Precepts:  Don't hijack or divert topics - create a new one.   Don't feed the Troll.
[+] 1 member Likes Scuderia_Turini's post

Yes...if someone could decode tyre sizes and insert sizes, and which part of the wheel their diameters reference, that would assist me greatly!

I love gears 

A good Scale reference for tyre diameter would be this page

For your contemporary 1/32 GT racers a scale front tyre diameter on a 18 inch rim could go as low as 20,6mmø, rears as high as 22,5 mmm
Meaning that the run of the mill 1/32 tyre is about 2mm to low, not to mention racers sticking to "zero grip tires" with a total wheel diameter of barely 17 mmø  Rollingred

So why are most slotrace wheels too small? Well its a bit of a slotrace chicken and egg situation.
Most 1/32 (plastic) regs are based on "box stock" rules,  makes like Scalextric and Carrera do come with pretty close to true scale tyres 
But if a slotracer can't change the position of their axles, running small tyres and wheels is the simplest way to lower your car, improve your CG and magnetic motor downforce, reduce weight.
For most slot racers need for speed overrules True Scale appearance.

with kind regards

(26th-Apr-20, 01:47 PM)BourneAgainRacer Wrote:  Yes...if someone could decode tyre sizes and insert sizes, and which part of the wheel their diameters reference, that would assist me greatly!

Slot-it Part numbers represent a combination of DWG (sizing) and compound. 
Eg PPT1219F22. (Policar mold 1219 compound f22)

Sizing is OuterDiameter x TyreWidth in millimetres.
The DWG in parenthesis below is the the tyre mold used in manufacture and fixes the unfitted tyre size.
NThe DWG does not represent the material used. I'll list that further below.

14.2 X 8 (1096)
14.6X 8.4 (1214)
16.1 X 8 (1088) 
17.2 X 9.5 (1159) 
17.8 X 9.5 (1228)
19.8 X 9.8 (1140) 
16.5 X 10 (1067) 
17 X 10 (1170) 
17.8 X 10.5 (1167)
18 X 10 (1207) 
18.5 X 10 (1045) 
18.8 X 10 (1027)
19.5 X 10 (1171 & 1121) 
20 X 10.5 (1120) 
20.5 x 11.7 (Policar 1219 slick)
19 X 10.5 (1152) 
19.9 X 10.5 (1046) 
20 X 11.3 (1172) 
19.8 X 12.2 (1028) 
20.4 X 12.4 (1068 from the packaging but 1608 on the sidewall.

Sizing inner diameter:
Typically manufacturers list their wheels by the largest diameter (the bead) which is not the same as the rim diameter (visible once the tyre is fitted) do not list inner diameters
The non "F1" tyres seem to fit wheels on 15mm (bead measurement) 13.5 mm (rim) without stretching.
These tyres will easily stretch to fit a "non air hub" rim of 15.5mm but deform badly if fitted to an air hub of similar size, sinking into the air well and ruining the contact patch. The tyres can also be stretched further with gentle warming.

The "F1" tyres have the same inner rim diameter (12mm) but are a lot less stretchable and will only fit hubs listed as "F1" type.
The "F1" tyres will fit "Formula1" hubs from slot-it, policar, NSR and and All-Slot-Car.

Unfitted tyre Diameters taken from actual tyre digital calliper measurements:
1068/1608 has an inner rim diameter of 12mm
1170-E1 has an inner rim diameter of 12mm
1207-f22 has an inner rim diameter of 12mm

Compound type
All slot.IT compounds are "rubber" unless stated, eg "S1" and "sponge". 
Slot-IT does not make Urethane tyres.
The single letter refers to the compound used

Compound hardness
In some cases, The number is the durometer measurement, in others , lower number is harder, bigger numbers are softer.
Slot.IT have moved from the "1 to 4 " numbers to durometer readings, then back again but it's not possible to know why this would be.

Compound, hardness and descriptions taken from various sources
- P1 hard for smooth plastic tracks - Discontinued
- P2 Medium for smooth plastic tracks - Discontinued
- P3 Soft, for use on smooth plastic track
- P4 Anti-wear for use on abrasive plastic track (Ninco)
- P5
- P6
- S1 (Silicone) smooth dust free track
- Z series tyres (Low Grip), for front wheels
- C1 
- F15 
- F22 DiSCA homologated tyre for endurance events.
- F35
- E1 "harder but grip very well on Ninco (track)" (Maurizio Ferrrari 2012)
- N18 DiSCA homologated tyre for endurance events.
- N22 "A racing compound which from our testing works extremely well at least on Ninco, wood, and that can be glued and trued equally as well" MF 2012)

"For the F and N series, the number is the shore hardness" (MF 2012) 
All of the different tyres will fit on any of the hubs which produce, except the "f1" tyres which only fit the f1wheels.

[+] 1 member Likes Nonfractal's post

Thank you. It's was the inner diameter sizing that I was missing, but if most non-F1 tyres fit 12mm/13mm rims then perhaps not so much of an issue.

I love gears 

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