I think that choosing or rating LiPo packs only based on the C-value isn't the whole truth. When racing limited motor classes I think one of the most important thing is to to get as much power as possible from the battery. This means you have to get highest possible average voltage during your run. C-value usually has nothing to do with it. Like I said in previous post, when you drive 5-minute runs you can only draw average of 12C from the LiPo. Drawing more than average 12C would mean you won't finish because of flat battery
Most of the LiPos are more or even twice as much.
You need highest possible average voltage during your run to get maximum power. Now we should look at the discharge charts to see what really matters. Sadly I don't have any at the moment to show you.
Basically you get higher possible average voltage from the LiPo by:
1) having the biggest capacity LiPo that can fit, is allowed, can be bought, won't make your car too heavy. Having bigger capacity battery means that after your run you have more capacity left in the battery. This means you have higher average voltage. When you run 17.5T stock you probably use only 1500mAh. If you have 5500mAh battery you'll end up with 4000mAh left in it. The average voltage from that battery will be MUCH HIGHER than using 2800mAh battery. Although both will do fine, the big capacity battery gives you huge advantage because of the much higher average voltage.
2) having the LiPo work at its optimum temperature. I think this lowers its internal resistance I do warm the LiPos up to 50 degrees Celsius before racing. This keeps the LiPo voltage higher under load. Without load it seems not to make any difference! Cool your LiPo down to 5 degrees Celsius and yuo won't get almost any power out of it, voltage drops fast with load, its quite drastic!
Like said for 5-minute run you only need to have 12C capable LiPo and most of them are. So having 20C or 25C 5000mAh LiPo really does not make any difference directly. The difference MAY come from the fact that probably the 20C LiPo has bigger IR than the 25C one which means you could get better higher voltage during your run. But I would then take the 5500mAh LiPo instead
Another thing. Higher C-valued LiPos tend to be MUCH heavier, they have worse capacity to weight ratio than lower C-valued LiPos. This probably has to do with the structure of the cell. So you should always look at the weight of the pack also!
It might be better to get lighter lower C-valued LiPo with higher capacity than heavier (which might put you over the weight limit!) higher C-valued LiPo.
I think reading that EFRA will limit the capacity to 5500mAh. I think in a short time we see 2S LiPos with 5500mAh. Today there are 5300mAh and 5400mAh packs out. But then, because we need higher overall voltage during a run we still need the biggest possible capacity and we would like to get the 6000mAh battery that isn't allowed
Do you see problem rising from this fact
I don't know if EFRA will do testing and approval like ROAR is doing. Anyway I see manufacturers soon puting 6000mAh cells into hardcased LiPos and marking them as 5500+mAh
"New" technology, many things to consider, many wrong decisions can be made...
Please disagree with my opinion if you think I'm wrong. This is just the way I'm seeing things at the moment - running LiPo in 1/10 stock and trying to get the maximum out of the power system (motor+esc+LiPo).
Different LiPo 5-15C discharge graphs would be nice to add to this thread. Also the LiPo temperature graph with 10-15C discharge current.