RC Foam Tyre Guide (Shore, Diameter & Setup Help)
Foam tyres do more than just change grip. They also affect how the car rolls, how stable it feels, and even your effective rollout as the diameter changes.
In simple terms: softer foam usually gives more grip but wears faster, while harder foam usually rolls freer and lasts longer.
What Shore Means
- Softer foam = more grip, more drag, more wear
- Harder foam = less grip, freer rolling, less wear
- A softer tyre can help a low-grip track, but too soft can make the car feel stuck or lazy
- A harder tyre can calm the car down, but too hard can make it slide and lose drive
Why Diameter Matters
Tyre diameter changes how the car feels because it changes the distance travelled per rotation. A bigger tyre can make the car feel taller geared, while a smaller tyre can make it feel shorter geared.
- Bigger diameter = slightly taller feel, can smooth the car out
- Smaller diameter = slightly shorter feel, can give more punch
- As foam tyres wear down, the car can feel different even if the gears stay the same
That is why tyre choice and gearing should always be looked at together.
Width and Diameter Rules
- Tyre width must be 25mm to 26mm
- Maximum tyre diameter is 60mm
- There is no minimum tyre diameter, but wear will still affect how the car feels
- The tyre must cover the entire wheel edge to edge
- Tyre additives are not allowed
Even within those limits, tyre size still matters. As foam tyres wear down, the car can feel shorter geared, more reactive, and less stable. A larger diameter tyre can calm the car down slightly, while a smaller diameter tyre can make it feel more lively and punchier.
Because width is tightly controlled, most setup changes come more from shore, diameter, and overall tyre condition rather than from major width changes.
Front vs Rear Changes
Front and rear foam choices do different jobs, so changing only one end can make a big difference.
- Front tyres affect turn-in, steering response and stability on entry
- Rear tyres affect drive, traction and how planted the car feels off the bend
- If the car feels loose on power, look at the rear first
- If the car refuses to turn, look at the front first
Front Grip and Stagger
Tyres do not only affect rear drive. If you need to free the front of the car up, front tyre choice can make a big difference to how the car turns in and rotates mid-corner.
- More front grip can help the car turn in better
- Less front grip can calm the steering down if the car feels too sharp
- Stagger can also affect how the car wants to turn
- On minis especially, stagger can be a very noticeable tuning aid
As always, make one change at a time so you can feel what the car is actually doing.
What To Change
If the car is tight in the corner:
- Try a little more front grip
- Try reducing rear grip slightly if the car is pushing too much
- Check tyre diameter and make sure one end has not worn far more than the other
If the car is loose off the bend:
- Try more rear grip
- Check the rear tyres are not too hard or too worn
- Check the car is not effectively overgeared because of tyre size changes
If the car feels stuck and slow:
- The tyre may be too soft for the grip level
- The car may have too much drag from the rear
- A slightly harder tyre may free it up
If the car is nervous and skittish:
- The tyre may be too hard for the surface
- The rear may need more support or more grip
- Check wear and side-to-side condition
Tyres and Gearing Work Together
Changing tyre diameter changes effective rollout, so if you fit a different size tyre, the gearing can feel different even with the same pinion and spur.
If you want to work that out properly, use the gearing calculator alongside this guide.
Open the RC Gearing Calculator
