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One car for all conditions? Tuning with weight - testing updates


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#1 JimF

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Posted 03 June 2015 - 04:56 PM

Primary focus here is the Can-Am shown below but there is also a brand new 4.5" Stock Car that shares the premise.

 

So... why do it???

  • I love to build stuff and can usually build something for about any conditions (within reason).
  • But... I always want to do something new (to me anyway) so this is different for me.
  • I have recently built a couple of good lightweight Can-Ams but they have not been great on flat tracks.
  • Partially because they have been built with too much flex (hence too bitey).
  • Also, I made no provision for adding a lot of weight, so I couldn't get enough weight in the right places.

So... what is it???

  • This is a six-rail/side using a combination of .047" and .039" wire.
  • This is stiffer in twist flex than my recent lightweights.
  • This is made in a very general 4" x 15/16" configuration.
  • I've made pre-planned weight additions that will go quick and easy.
  • These additions will allow me to easily tune where the weight goes as well as how much of it.
  • Here is is in starting form with no added weights. This will go about 86.5 grams without body (92-93-ish all up).

0df17459-91db-40d0-af3f-98c89f16eaf1_zps

 

Here are all the pre-made add ons.

  • The small rear weight tabs add 4.4 grams and are shown shown in place (sooo... 97-ish all up).
  • The two large weight tabs add 8.6 grams (sooo... mebbe 101 all up)
  • The center tray adds 5.0 grams, can be added without soldering, and is mixed and matched with the rear tabs.

ff07fee3-060f-4e82-9dac-7220370a8548_zps

 

Maxed out...

  • Center tray and large weights in place gets this to about 106 grams all up.
  • There is plenty of room for lead on top of the rear tabs or on top of the tray.
  • This could easily get to say 116 grams or so for a good flat track weight.

5430441c-2054-4f89-9288-3ae0f551c8c2_zps

 

Here is the Stock Car... already tested once.

  • This was tested without the center tray and came in at 117 grams all up
  • This is waaay too light for one of these bricks, I knew that, but wanted to test it anyway.
  • Sure enough... fast like crazy but tippy as hell.
  • The center tray adds 5 grams and gives an easy location for 5-8 more.
  • I can add about 4 grams/side on top of the rear tabs.
  • I could add weight to the nose. I usually don't use nose weight but these things sometimes need it.

b5c3a322-98e8-490b-b77d-9266d9cb5aff_zps

 

So the idea with these was to build light but plan ahead for addition of weight in various locations. My current trend is not much weight on the pans and more toward the center-rear. As mentioned, I seldom use much nose weight but once in a while, it works nicely.


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Jim Fowler




#2 Pappy

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Posted 03 June 2015 - 08:24 PM

Cheater's theory is, build it as light as possible and add weight where needed.


Jim "Butch" Dunaway
 
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#3 JimF

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Posted 04 June 2015 - 11:00 AM

Cheater said dat? Hmm... smart guy... :)


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Jim Fowler

#4 TG Racing

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Posted 04 June 2015 - 02:00 PM

I like your idea of "Build light and add weight later". 

 

On a multi-purpose car, what are your thoughts small wire multi-rails vs single larger wire?


Thom Greene

#5 Pappy

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Posted 04 June 2015 - 04:15 PM

Well, you know how Cheater is, Jim, he's one of those deep thinkers. Or beer drinking stinkers. Or something like that.  Sometimes I get confused.  :wacko2:
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Jim "Butch" Dunaway
 
Anything is possible IF you don't know what you are talking about.
 
When you are dead, you don't know you are dead. It is difficult only for the others.
It's the same when you are stupid.

NF-UE

#6 Cheater

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Posted 04 June 2015 - 08:44 PM

Butch is confused most of the time...

Gregory Wells

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#7 JimF

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Posted 05 June 2015 - 10:20 AM

I like your idea of "Build light and add weight later". 

 

On a multi-purpose car, what are your thoughts small wire multi-rails vs single larger wire?

 

Good question and not as easy to answer as one might think. Here are some general thoughts.......

 

  • Cornering speed is generally about power to the track (bite) and managing that bite for driveability.
  • Putting variables (tires, body, preferences...etc) aside, bite is mostly about flex and twist flex in particular.
  • Higher bite cars (smaller rails, rails with forks....etc.) generally have higher cornering speed potential but are often sensitive to conditions.
  • However, they may also have a smaller sweet spot ,be harder tune just right to be in that sweet spot, and a little more critical to drive.
  • Lower bite cars (like a single rail .078" for ex) generally have the opposite characteristics and be easier to drive.
  • The single .078 may have slightly less ultimate speed potential but be easier to find the top potential that it does have.

 

So......for this car, I used more rails for a stiffer flex than I have used in other cars recently. So, this car is probably closer to the flex of a single .078 than many of the others that I've built lately. I think that a single .078" is an excellent choice for a general purpose car and I have used that rail layout extensively for Can Ams, Stock Cars, and anglewinder coupes. It is a good bet that a single .078" will be easy to tune for very good performance on any track type and condition and be easy to drive when done. But.....smaller rail cars may have the potential to be a bit faster if you hit the tune right.

 

Hope that wasn't confusing....................... :crazy:


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Jim Fowler

#8 TG Racing

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Posted 05 June 2015 - 10:31 AM

Absolutely spot on Jim!  Thanks and keep all your great articles coming!!


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Thom Greene

#9 JimF

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Posted 28 June 2015 - 11:54 AM

This car has now been extensively tested and raced once and I'm very pleased with the results. Here's a synopsis......

 

First test (and probably most revealing): Tested at Fast Track Hobbies, Rocklin Ca. Tested on two very different tracks each with very different conditions on that day. Gearing on both tracks was 9-29 on a Retro Hawk.

 

First test on the Purple Angel 'speedway' track. This is about 165' with high speed connected turns that are mostly flat.

  • Bite was up on this test day. Car was tested with JK 8713 PPT and a Parma Lola T-163 with a pretty good motor.
  • Tested with no weight add ons (95 gr.) the car was running competitive speeds from the get go but was a little critical.
  • Added the two rear weight tabs (shown below) bringing it to (99.5 gr) Calmed the car down notably, no loss of speed , easier to drive.
  • Added the center weight pan (105 gr) even easier, again no loss of speed. Starts to get into "no-brainer" category in driving it. For this track, this is probably how I'd race it.

 

Second test was on the 130' Kingleman with mostly flat or mildly banked turns. Bite was off. All weights taken off. (95 gr.)

  • Car was very loose. After a few laps, I switched to JK 8703 PP and improved the situation.
  • With no weights, the car was pretty good but not easy to drive. The "release point" came with little warning.
  • Added the two rear weight tabs. This was one one of the few situations where rear biased weight was not a positive addition. The car got a little too loose.
  • Added the center weight pan......immediately better.
  • Took off the rear weight tabs. Didn't get better but no worse either. Probably not enough of a change.
  • Added 4.0 gr. to the center pan getting back to the 105 gr mark. This was the best of all.

Third test and first race on the ~~ 155' Hillclimb at Motown Raceway in Modesto. Two big straightaways with a mix of flat and mildly banked turns. Bite was up and then some.

  • Tested first with no weights (95 gr) Car was very quick but a little critical.....still.....very good.
  • Added rear weight tabs......in this case, no difference.
  • Added center weight pan.....more forgiving, not quite as fast as with no weights.
  • Decided to race this car even though it was probably not the best car in the box on this day.
  • Raced it with all the weights off (95 g) and JK 8713 PPT narrowed.
  • Finished second to track owner Gene B. who is one of the very best drivers at this track.
  • No complaints, the car was very good, the driver.........uhhh.......notsomuch.
  • In retrospect, probably should have run with add on weights and maybe stayed on a little better.

Conclusions: This is exceptionally versatile.

 

  • Run with no weights when the conditions feel really good.
  • Run with rear weights when you want to loosen the car up.
  • Run with center weights when the track is loose and you want to calm the car down.
  • Run with center and rear tabs when everything else feels too "twitchy".

 

The car shown below is a customer car ready for final assembly and is built longer than the original test car. Original was 4.9" overall, this one is 5.1" overall. This is the layout I'll use moving forward.

 

44313863-43e8-453f-b860-507802914873_zps

 

 

 

 

 

 


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Jim Fowler

#10 Samiam

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Posted 28 June 2015 - 12:53 PM

Jim,

 

How much if any is the movement in the center pan? I have seen cars with the pan soldered solid by .032" wire and floating. Have you noticed a difference in the two methods? 

 

Great thread by the way. Very informative and full of real results that can be directly transferred to our programs. Thanks for posting it. 


Sam Levitch
 
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#11 JimF

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Posted 28 June 2015 - 01:48 PM

Sam:

 

There is very little movement in the center pan. The rear of the pan is suspended by the bite bar which is .055 in a 3/32 (.062 ID) tube. The front is an .025 wire in an (.032 ID) tube. I am not a believer in a lot of "sloppy" movement in the weight plates. That is the main reason that I prefer adding rear weight tabs fixed to the main rails over weight added to the pans.

 

I think the idea of suspending the center weight  via some wire "hangers" as you describe, is a very good way to go. Cap Henry posted a pic of a "War Beaver" that he built that uses this concept, and I like that application a lot. The reason for this one being the way it is, has to do with a quick and easy way to test the car with the weight pans in or out. I suspect that most would test this car in several different configurations and then just leave it one way or the other. Still, the ability to tune more specifically for daily track conditions is not a bad thing at all.


Jim Fowler

#12 Tim Neja

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Posted 28 June 2015 - 10:43 PM

Hi Jim,

Great build!! You say it's a Combination of .39 and .047?  What combination?? :)


She's real fine, my 409!!!

#13 JimF

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Posted 29 June 2015 - 12:03 AM

Hi Jim,

Great build!! You say it's a Combination of .39 and .047?  What combination?? :)

 

Five of .047 and one of .039. The reason for that one is that the R-Geo bracket is a .040 instead of the .050 that I normally use. That rail lines up with the bracket and keeps the spacing right on all the others. You can just see it in this last picture......two rails 047 inside the bracket, one of .039 even with the bracket, three of .047 outside the bracket.


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Jim Fowler

#14 Matt Sheldon

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Posted 01 July 2015 - 09:08 PM

Great as always Jim. On thing you never really discuss is soldering of the main rails. I notice most your builds the mail rails are soldered full length. Obviously this is just another tuning option with the car, but I was curious as to if you prefer it one way opposed to another and if there are different build tips that you may do partial solder lengths?


Matt Sheldon

#15 JimF

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Posted 02 July 2015 - 01:23 AM

Matt:

 

Really good question and not one that I have a pat answer to. Naturally, full length soldering on the main rails and especially on multi rail frames gives a stiffer torsional and longitudinal flex. I do not have a real preference to this other than full length soldering is just what I have habitually done.


Jim Fowler





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