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Old 04-05-2014, 08:56 AM   #1
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Default Touring car tire size, is it time for a change?

The current tire issues at the Worlds warm-up got me thinking about current TC tire sizes, their history and whether or not it makes sense to think about change to at least the width, and perhaps the aspect ratio as well. Current tires are on 24 mm rims, which equate to a 1:1 car equivalent of ~245 mm section tires. I would consider that far from economy car tires, but nowhere near what many GT race cars/DTM cars use. For reference, DTM uses 300/320 section front and rear, respectively. Current WTCC Super 2000 regs dictate a max of 250 mm, but I would argue the car performance of that series is more equivalent to a 21.5/17.5-powered TC (yes I know scale speeds are way different). Given the level of performance of today's electric touring cars, particularly modified outdoors, is it not worth looking at adopting wider tires to increase load capability (and likely, tire life) and realism too? The only widely available slicks I know of that fit this range are the HPI Vintage Slicks.

I would even pose the argument of having different tire regulations for modified vs. spec classes. The full-scale racing world scales tire size with increasing power and performance, so why shouldn't we?

Discuss away.
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Old 04-05-2014, 09:04 AM   #2
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Brian I don't know much but I think Touring cars need a change in tires width's. I would like to see a wider rear tire at the minimum. Even if it is cosmetic move to make the cars have a more scale look!
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Old 04-05-2014, 09:04 AM   #3
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No.
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Old 04-05-2014, 09:05 AM   #4
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RC conventional wisdom says, that "scale speeds are different"

But how is that so ?

Do RC cars not share the same Air density & Gravity as 1:1 cars
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Old 04-05-2014, 09:10 AM   #5
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No
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Old 04-05-2014, 09:13 AM   #6
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Originally Posted by RedBullFiXX View Post
RC conventional wisdom says, that "scale speeds are different"

But how is that so ?

Do RC cars not share the same Air density & Gravity as 1:1 cars
Sure, but if you multiplied everything by 10 you would be getting pretty extreme numbers, i.e. 600+ mph. As it is, our R/C touring cars generate far higher lateral and longitudinal accelerations than their full-size counterparts, mostly due to the scale mass being much less and the CG much lower.

The air density relative to downforce is always an interesting topic. Yes, the amount of downforce, in absolute terms is quite small, but relative to the mass of the car is quite significant.
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Old 04-05-2014, 09:24 AM   #7
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Sure, but if you multiplied everything by 10 you would be getting pretty extreme numbers, i.e. 600+ mph. As it is, our R/C touring cars generate far higher lateral and longitudinal accelerations than their full-size counterparts, mostly due to the scale mass being much less and the CG much lower.

The air density relative to downforce is always an interesting topic. Yes, the amount of downforce, in absolute terms is quite small, but relative to the mass of the car is quite significant.
RC downforce IS insignificant if we can't run upside down as they say an F1 can
What is the scale speed of a 1:1 F1 car ?
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Old 04-05-2014, 09:26 AM   #8
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Originally Posted by RedBullFiXX View Post
Do RC cars not share the same Air density & Gravity as 1:1 cars
One would need to also scale down the air. The general thought is that the Reynolds number should be the same to get reasonable results.

Full-scale designers are constantly begging for larger and larger wind tunnels, simply because the larger scale models they can use give more accurate results.
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Old 04-05-2014, 09:36 AM   #9
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RC downforce IS insignificant if we can't run upside down as they say an F1 can
What is the scale speed of a 1:1 F1 car ?
Real F1 cars generate thousands of pounds of downforce through carefully designed/sculpted wings, diffuser and airflow altering parts. R/C F1 cars have not been developed in this way, and while obviously the wings generate downforce, they are not nearly there. The mere fact that the body is not sealed to the chassis creates lots of turbulent airflow that drops downforce levels.

Downforce from GT cars is in the hundreds of pounds relative to their 2000+ lb weight. R/C touring cars need to only generate in the range of 0.5 - 1 lb of downforce to generate equivalent levels relative to their weight. The fact that we can 'feel' changes between bodies that are very similar in profile means that there is significant downforce. Those differences between race bodies are often the change in center of pressure, i.e. shifting where the majority of the downforce acts relative to the CG of the car, rather than a large change in total downforce.

Anyway, back on topic. For those who are saying "No", do you have a justification for your reasoning, or are you content to say no because it's simply something different?
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Old 04-05-2014, 09:38 AM   #10
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Interesting topic. Maybe a poll should be created too.
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Old 04-05-2014, 10:00 AM   #11
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There is a couple of ways of thinking about it. I'm not a scientist or an engineer, nor will I pretend to be.

What is the difference in gains between PSI of contact area and friction/psi of the tire contact patch? I'm just going to pull numbers and they are totally unrealistic numbers so don't pick them apart. Lets say you have a 24mm, tire width that we have now and when it's on the car, ready to o on the start line it spreads out and gives 96 square mm of contact patch, but it creates 3 psi of weight on the tires.
Now you have a 28mm width tire, it will create 112 square mm of contact area. Now you've reduced the weight on the tires contact patch to maybe 2psi. Are the friction gains, assuming the same surface on both tires, going to make up for the lack of pressure on the tires? I know the cars will weigh the same and have the same wight pushing down on the tires but it comes down to surface area as well.

I hope this makes sense to people. If not I can try and explain it better.

Again, I am no engineer or scientist or anything. Hopefully someone will have better answers.
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Old 04-05-2014, 10:00 AM   #12
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I'm not into league racing of RC cars, but I think this is something that definitely should be looked at, considered and even experimented with, at least on a trial-run basis.
How long have RC cars been using the 24mm wheel/tire? How many technological advancements have been made to RC car chassis and motor/esc since then?
Are the 24mm tires now being pushed beyond their limits?
If increasing tire size could increases competitiveness and continue progression, why not?
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Old 04-05-2014, 10:11 AM   #13
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Originally Posted by Scottmisfits View Post
There is a couple of ways of thinking about it. I'm not a scientist or an engineer, nor will I pretend to be.

What is the difference in gains between PSI of contact area and friction/psi of the tire contact patch? I'm just going to pull numbers and they are totally unrealistic numbers so don't pick them apart. Lets say you have a 24mm, tire width that we have now and when it's on the car, ready to o on the start line it spreads out and gives 96 square mm of contact patch, but it creates 3 psi of weight on the tires.
Now you have a 28mm width tire, it will create 112 square mm of contact area. Now you've reduced the weight on the tires contact patch to maybe 2psi. Are the friction gains, assuming the same surface on both tires, going to make up for the lack of pressure on the tires? I know the cars will weigh the same and have the same wight pushing down on the tires but it comes down to surface area as well.

I hope this makes sense to people. If not I can try and explain it better.

Again, I am no engineer or scientist or anything. Hopefully someone will have better answers.
Very good questions. The only time where you would want to have smaller contact patch is if you don't have enough mass and/or downforce to properly load the tire and get it to its operating temperature. Otherwise, as long as you can get the tire to operating temp, larger contact patch will always produce more grip. The friction between the surface and the tire increases with increasing contact area, all other variables held constant (tire temp, pressure for a pneumatic tire, tire construction).
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Old 04-05-2014, 10:16 AM   #14
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Nope.
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Old 04-05-2014, 10:25 AM   #15
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It probably is time to change. We use to run 26mm back i the foam days. But with every manufacturer make 24mm plastics and rubber and massive numbers being made for controlled tire racing it isnt going to happen. The only way it really would, is if a major race like the nationals or worlds didnt have a control tire. And 1 or 2 manufacturers made a tire and wheel combo for that race and it won. And not only did it win, but cars of the same chassis, and on 24mm tires did poorly.
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