Is acceleration perceived being quicker using smaller overall diameter wheels/tires?
viejoronnie
Effect of diameter driven wheels/tires on acceleration
You have asked a question that will open up a hornets' nest.
The short answer is yes if all other things are equal - unless you get excessive wheelspin. Your increased acceleration will also last for a shorter time because you will have a lower maximum speed which will be reached quicker, so whether you cover the distance in less time will depend on the length of straight.
As with all thing slot car, it's a compromise and you need to hit the right one for optimum performance.
The short answer is yes if all other things are equal - unless you get excessive wheelspin. Your increased acceleration will also last for a shorter time because you will have a lower maximum speed which will be reached quicker, so whether you cover the distance in less time will depend on the length of straight.
As with all thing slot car, it's a compromise and you need to hit the right one for optimum performance.
There will also be a marginal effect from the lower moment of inertia of the smaller wheels requiring less torque to spin them up, releasing more to accelerate the car. I did see the maths on this once, and even understood it, but it was a long time ago now, so it's been pushed to an inaccessible corner of my memory. The context I saw it in was 1:1 vehicles chasing hundredths on the drag strip. Whether the effect would be even measurable at our scales, I've no idea.
The effect is exactly the same as having a lower final drive ratio on an i.c. vehicle, or selecting a lower gear. You accelerate quicker but run out of revs at a lower speed.
A change in your tire diameter is equivalent to a small change in the car's gear ratio. Using a crown gear with more teeth or a pinion gear with fewer teeth will have much the same effect as using a smaller rear tire -- your car won't travel as far for each revolution of the motor. The amount of adjustment you'll get by changing tire diameter will be small compared to what you can achieve by changing the gears.
The best reason for changing your tire diameter is to reduce your car's ground clearance. You want the minimum ground clearance to make your car's center of gravity as low as possible -- reducing its tendency to roll over in a corner.
That said, everything that Gripping Pneus and PatB said is perfectly true.
One thing I will add. For best acceleration you want to gear your car such that you 'chirp' the tires from a standing start. This is because your car produces its maximum torque at startup. Once your car starts to roll that torque goes down, linearly, as the car's speed increases. So a little bit of wheelspin off the line is okay. You should have solid traction and good acceleration out of the corners because the torque will be a bit lower than it would be at startup.
Is that the best possible setup? Ah, maybe not. It all depends on the track. A car geared for maximum acceleration will not have the highest top speed. It will be at a disadvantage on a track with long straights and fast corners. The difference between a winning car and an also-ran could easily be the choice of gearing.
I have recently built a set of three cars for a particular class, identical except for their gear ratios. Which one gets raced depends on the track.
The best reason for changing your tire diameter is to reduce your car's ground clearance. You want the minimum ground clearance to make your car's center of gravity as low as possible -- reducing its tendency to roll over in a corner.
That said, everything that Gripping Pneus and PatB said is perfectly true.
One thing I will add. For best acceleration you want to gear your car such that you 'chirp' the tires from a standing start. This is because your car produces its maximum torque at startup. Once your car starts to roll that torque goes down, linearly, as the car's speed increases. So a little bit of wheelspin off the line is okay. You should have solid traction and good acceleration out of the corners because the torque will be a bit lower than it would be at startup.
Is that the best possible setup? Ah, maybe not. It all depends on the track. A car geared for maximum acceleration will not have the highest top speed. It will be at a disadvantage on a track with long straights and fast corners. The difference between a winning car and an also-ran could easily be the choice of gearing.
I have recently built a set of three cars for a particular class, identical except for their gear ratios. Which one gets raced depends on the track.
I test drove an relatively inexpensive 1:1 EV years ago. With the OEM tires/wheels, I could “chirp” the tires at 45 mpg when “punching” it.
A shoter ratio will provide faster acceleration until you run out of:
AlanW
- traction (if the torque overpowers the tyres)
- torque (as the motor runs up to top rpm)
AlanW
Tire size effects final drive gear ratio the opposite of the way axle gear size does. Quicker acceleration with a big axle gear compared to a small axle gear, but lower top end. Quicker acceleration with smaller tires , but lower top end. .
The physics of inertia are the same as a real car, just scaled down. Always a combination of tire size and gear size make the final drive ratio. Guessing that optimum is to have the axle gear and the tires as close to the same size as possible.
The physics of inertia are the same as a real car, just scaled down. Always a combination of tire size and gear size make the final drive ratio. Guessing that optimum is to have the axle gear and the tires as close to the same size as possible.
Optimal would be the smallest you can get of everything as this would give you the lightest weight, lowest c.g. and the lowest inertia
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