Go Back  R/C Tech Forums > General Forums > Electric On-Road
Touring car battery capacity / c rating for spec motor racing >

Touring car battery capacity / c rating for spec motor racing

Touring car battery capacity / c rating for spec motor racing

Reply

Old 02-13-2019, 11:59 AM
  #1  
Tech Elite
Thread Starter
iTrader: (2)
 
Razathorn's Avatar
 
Join Date: May 2009
Posts: 2,067
Trader Rating: 2 (100%+)
Default Touring car battery capacity / c rating for spec motor racing

So, as I understand it:
  • Capacity: more = more voltage over time due to discharge curve, but more capacity = more wright.
  • C rating: more = Less IR in general, causing more voltage under load. Obviously we don't need 100C batteries from an amp capacity as much as it speaks to IR and voltage under load.
I've got a 7500 orca battery that is basically now a practice pack as it has started to swell and lost a bit of capacity. I'm getting back into TC in 17.5 USGT and 25.5 TC (not VTA.) With my group of folks, I don't think the battery is going to make that big of a difference, but I'd like to get good equipment, and the battery selection is really proving difficult—I'm accustom to mod racing where you've got too much of everything until you turn it down even with a crap pack.

Where do folks generally balance capacity / weight trade off for these classes and what are your experiences with the importance of C rating?

This is a serious question, not a troll. I'm getting back in and despite searching, I can't find any good reference for answers.
Razathorn is offline  
Reply With Quote
Old 02-13-2019, 12:03 PM
  #2  
Tech Champion
iTrader: (6)
 
Billy Kelly's Avatar
 
Join Date: Nov 2014
Location: Far south suburbs of Chicago area
Posts: 9,244
Trader Rating: 6 (100%+)
Default

Problem with C rating is there’s no industry standard for it.

I typically use 2s with 5-7000mah for USGT and 17.5.
Billy Kelly is offline  
Reply With Quote
Old 02-13-2019, 12:29 PM
  #3  
Tech Elite
Thread Starter
iTrader: (2)
 
Razathorn's Avatar
 
Join Date: May 2009
Posts: 2,067
Trader Rating: 2 (100%+)
Default

Originally Posted by Billy Kelly View Post
Problem with C rating is there’s no industry standard for it.

I typically use 2s with 5-7000mah for USGT and 17.5.
Yeah, SMC explained it quite well. I think MOST of the lipos today do pretty well at holding voltage under load, which is why I'm wondering if I can just get away with something like a 50c 5000-5500 pack.
Razathorn is offline  
Reply With Quote
Old 02-13-2019, 12:33 PM
  #4  
Tech Champion
iTrader: (6)
 
Billy Kelly's Avatar
 
Join Date: Nov 2014
Location: Far south suburbs of Chicago area
Posts: 9,244
Trader Rating: 6 (100%+)
Default

Originally Posted by Razathorn View Post
Yeah, SMC explained it quite well. I think MOST of the lipos today do pretty well at holding voltage under load, which is why I'm wondering if I can just get away with something like a 50c 5000-5500 pack.
Should be fine. I usually start with 7000mah for practice and first rounds. Then use a 5000mah for last 2 rounds.
Billy Kelly is offline  
Reply With Quote
Old 02-13-2019, 02:03 PM
  #5  
Tech Master
iTrader: (3)
 
Join Date: May 2010
Location: Chi-Town West Burbs
Posts: 1,649
Trader Rating: 3 (100%+)
Default

Originally Posted by Razathorn View Post
Yeah, SMC explained it quite well. I think MOST of the lipos today do pretty well at holding voltage under load, which is why I'm wondering if I can just get away with something like a 50c 5000-5500 pack.
SMC batteries are you best bang for the buck. The last batch of batteries l purchased were based on weight more than anything. I was looking for ballast to balance my chassis.
mooby64 is offline  
Reply With Quote
Old 02-13-2019, 08:07 PM
  #6  
Tech Elite
Thread Starter
iTrader: (2)
 
Razathorn's Avatar
 
Join Date: May 2009
Posts: 2,067
Trader Rating: 2 (100%+)
Default

Originally Posted by Billy Kelly View Post

Should be fine. I usually start with 7000mah for practice and first rounds. Then use a 5000mah for last 2 rounds.
How are you keeping your car balanced when switching batteries? Do you have weights on the 5000?
Razathorn is offline  
Reply With Quote
Old 02-13-2019, 11:37 PM
  #7  
Tech Regular
 
LzREngineering's Avatar
 
Join Date: Jul 2017
Posts: 277
Default

For spec racing, bigger is better! Since you're planning on racing in classes with relatively high weight limits (correct me if I'm wrong) you might as well go for 8400s
LzREngineering is offline  
Reply With Quote
Old 02-14-2019, 09:05 AM
  #8  
Tech Elite
Thread Starter
iTrader: (2)
 
Razathorn's Avatar
 
Join Date: May 2009
Posts: 2,067
Trader Rating: 2 (100%+)
Default

Originally Posted by LzREngineering View Post
For spec racing, bigger is better! Since you're planning on racing in classes with relatively high weight limits (correct me if I'm wrong) you might as well go for 8400s
Yes, but no. 25.5 touring car and 17.5 USGT PERHAPS. The electronics are going to be ~300 grams, my old 7500 pack was 315, I've been looking at an 8600 that is 325g. The cars are pretty light now days.
Razathorn is offline  
Reply With Quote
Old 02-14-2019, 09:12 AM
  #9  
Tech Master
iTrader: (21)
 
Join Date: Sep 2014
Posts: 1,293
Trader Rating: 21 (100%+)
Default

I personally run my psycho cells battery pack. of all the batteries i've run, for some reason this feels like the best pack i've ever run. When i upgraded charger setup, it got even better
phatboislim is offline  
Reply With Quote
Old 02-14-2019, 09:56 AM
  #10  
Tech Regular
 
LzREngineering's Avatar
 
Join Date: Jul 2017
Posts: 277
Default

Originally Posted by Razathorn View Post
Yes, but no. 25.5 touring car and 17.5 USGT PERHAPS. The electronics are going to be ~300 grams, my old 7500 pack was 315, I've been looking at an 8600 that is 325g. The cars are pretty light now days.
With a centred-spur car (eg T4) it's possible to achieve perfect balance with approx. 275g of battery and no ballast. The car will come out about 1300-1330g total. Perfect for TC racing. If you go up to an 8400, that's approx 50g more plus 50g balance weight bringing you to about 1440g which is ideal vta territory
LzREngineering is offline  
Reply With Quote
Old 02-14-2019, 10:15 AM
  #11  
Tech Champion
iTrader: (6)
 
Billy Kelly's Avatar
 
Join Date: Nov 2014
Location: Far south suburbs of Chicago area
Posts: 9,244
Trader Rating: 6 (100%+)
Default

Originally Posted by Razathorn View Post
How are you keeping your car balanced when switching batteries? Do you have weights on the 5000?
Never really looked into balance on it. My car was overweight compared to others. I’ve seen no effect in lap times. There was only a minor difference in weight between the two batteries
Billy Kelly is offline  
Reply With Quote
Old 02-14-2019, 10:36 AM
  #12  
Tech Elite
Thread Starter
iTrader: (2)
 
Razathorn's Avatar
 
Join Date: May 2009
Posts: 2,067
Trader Rating: 2 (100%+)
Default

Originally Posted by Billy Kelly View Post

Never really looked into balance on it. My car was overweight compared to others. I’ve seen no effect in lap times. There was only a minor difference in weight between the two batteries
It's funny you say that. We have a traxxas 4-tec 2.0 spec class at my track where a lot of us experienced guys run this plastic traxxas car and have VERY competitive close spec racing, but we also use it as an entry point for new blood. It's quite amazing actually—I got my 9 y/o one of these and we're prepping it for this weekend. Setup is extremely limited on these cars, but I did my very best to test/tune it and got it quite good. That thing is 1320g WITHOUT battery or body. My shorty I was using with it (because it is balanced left to right far better) went bad, so I switched to a 7500 full size pack I had. The ride height was literally 1mm lower on one side in the front. made NO DIFFERENCE. Still qualified and finished 2nd against a tough field. The top 4-5 drivers tend to always be on the same lap and only be separated by less than 10 seconds by the time qualifying is done, and that is with some obvious grenade newbie drivers in qualifying that the only parallel would be basically multiple blue turtle shells from mario cart being fired randomly. Fun stuff.
Razathorn is offline  
Reply With Quote
Old 02-14-2019, 11:33 AM
  #13  
Tech Champion
iTrader: (6)
 
Billy Kelly's Avatar
 
Join Date: Nov 2014
Location: Far south suburbs of Chicago area
Posts: 9,244
Trader Rating: 6 (100%+)
Default

Originally Posted by Razathorn View Post
It's funny you say that. We have a traxxas 4-tec 2.0 spec class at my track where a lot of us experienced guys run this plastic traxxas car and have VERY competitive close spec racing, but we also use it as an entry point for new blood. It's quite amazing actually—I got my 9 y/o one of these and we're prepping it for this weekend. Setup is extremely limited on these cars, but I did my very best to test/tune it and got it quite good. That thing is 1320g WITHOUT battery or body. My shorty I was using with it (because it is balanced left to right far better) went bad, so I switched to a 7500 full size pack I had. The ride height was literally 1mm lower on one side in the front. made NO DIFFERENCE. Still qualified and finished 2nd against a tough field. The top 4-5 drivers tend to always be on the same lap and only be separated by less than 10 seconds by the time qualifying is done, and that is with some obvious grenade newbie drivers in qualifying that the only parallel would be basically multiple blue turtle shells from mario cart being fired randomly. Fun stuff.
I’m still technically a rookie racer. I race my previous times. The others are 2 laps plus ahead.

We we are going to try again this summer to get a 4Tec or other starter class going. We know the cars are selling at the store, just don’t seem interested in giving racing a try. I never planned to race, figure if I can try maybe can convince other like me to try.
Billy Kelly is offline  
Reply With Quote
Old 02-14-2019, 12:01 PM
  #14  
Tech Elite
Thread Starter
iTrader: (2)
 
Razathorn's Avatar
 
Join Date: May 2009
Posts: 2,067
Trader Rating: 2 (100%+)
Default

Originally Posted by Billy Kelly View Post

I’m still technically a rookie racer. I race my previous times. The others are 2 laps plus ahead.

We we are going to try again this summer to get a 4Tec or other starter class going. We know the cars are selling at the store, just don’t seem interested in giving racing a try. I never planned to race, figure if I can try maybe can convince other like me to try.
You should do it. We've got the formula for newbs down to an exact science.

To run on black carpet with a 4-tec 2.0:
Get m4 droop screws to take up the excess travel (make it so the spring is not loose on the shock.)
Drop the rear ride height as low as it goes and put the ride height clip you took out of the rear and put it in the front (rear traction in sweepers)
Optionally get the stiffest traxxas sprint for the front (black stripe) and then I'm at like 3mm ride height clips (adjusting droop screws to take up slack).
Then all we do is sxt the entire rear tire, and 2/3 of the front toward the inside.
(make sure the rear link is in the top option mounting positions, the bottom one is gross on carpet older kits had them installed in the lower optional position.)

The platform wants for rear traction out of the box, and we tend to run shorty packs in the middle or LIGHT full packs all the way forward. The changes I outlined above locks it in. Without the droop screws you traction roll pretty easy on black carpet. With the droop screws, you don't, and it's far easier for newbies if they don't have to CA their fronts sidewalls.

I just bought one for my son and all I did was go buy the $189 ready to run chassis kit plus $5 springs. I already have the droop screws and I'll paint him up a body tonight maybe.

A radio with steering expo is also ideal, which the RTR doesn't have.

I intend to keep racing 4-tec because that class needs to stay strong to attract new blood, but now that I'm back into on-road, I'm setting up 1-2 touring cars in addition. Wish me luck!
Razathorn is offline  
Reply With Quote
Old 02-14-2019, 12:24 PM
  #15  
Tech Champion
iTrader: (6)
 
Billy Kelly's Avatar
 
Join Date: Nov 2014
Location: Far south suburbs of Chicago area
Posts: 9,244
Trader Rating: 6 (100%+)
Default

Originally Posted by Razathorn View Post
You should do it. We've got the formula for newbs down to an exact science.

To run on black carpet with a 4-tec 2.0:
Get m4 droop screws to take up the excess travel (make it so the spring is not loose on the shock.)
Drop the rear ride height as low as it goes and put the ride height clip you took out of the rear and put it in the front (rear traction in sweepers)
Optionally get the stiffest traxxas sprint for the front (black stripe) and then I'm at like 3mm ride height clips (adjusting droop screws to take up slack).
Then all we do is sxt the entire rear tire, and 2/3 of the front toward the inside.
(make sure the rear link is in the top option mounting positions, the bottom one is gross on carpet older kits had them installed in the lower optional position.)

The platform wants for rear traction out of the box, and we tend to run shorty packs in the middle or LIGHT full packs all the way forward. The changes I outlined above locks it in. Without the droop screws you traction roll pretty easy on black carpet. With the droop screws, you don't, and it's far easier for newbies if they don't have to CA their fronts sidewalls.

I just bought one for my son and all I did was go buy the $189 ready to run chassis kit plus $5 springs. I already have the droop screws and I'll paint him up a body tonight maybe.

A radio with steering expo is also ideal, which the RTR doesn't have.

I intend to keep racing 4-tec because that class needs to stay strong to attract new blood, but now that I'm back into on-road, I'm setting up 1-2 touring cars in addition. Wish me luck!
We run outdoor. We’ve got a few in the group with different setups. Mine is still box stock other then tires. Been trying Gravity foams on it. Though this winter haven’t been able to run it much.

We have had pretty much an open invitation for people to come out. I was given a suggestion to try, see if store would send out an email to those that have bought 4Tecs. Will see still months away.

I’ve yet to really run carpet. Only once so that’s still a foreign surface to me.
Billy Kelly is offline  
Reply With Quote

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service