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Do different chassis need different tires?


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#1 JimF

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Posted 05 September 2016 - 01:05 AM

That's a question that I get asked a lot and I have a definitive answer...........sometimes........ :laugh2:

 

OK.......so here's what I mean.

 

  • Some chassis designs such as the "no brainer" that I talk about, work well on most any surface with any tire.
  • Some however, need something a little more specific.
  • The test outlined below illustrates this difference pretty well.

Here are two new chassis that continue to explore my recent theme of brass/wire rail combos.

 

Both chassis are 4" wb X .925 guide lead.

Both use R-Geo .050 angled face brackets.

Both used a std. JK chassis kit as a starter.

Both used the same RH motor for the test geared 9-28

Both used the same Parma Lola T-163 body

Left is 3 rails/side. 2/ .062 brass, 1/.062 wire. Pans are shaker style. All up = 105 gr.

Right is 2 rails/side. 1/.062 brass, 1/.062 wire. This is a torsion car. All up = 100 gr.

 

DSC02552.JPG

 

DSC02553.JPG

 

The cars were tested on this track. (I post the picture b/c this is a a rather unusual track design) My usual tire for this track with most cars is the JK 8713 PP. On a day with good conditions, a good time for a Can Am on this track is ~~ 4.80-4.90. Today, conditions were pretty good.

 

Cars were tested 10-12 laps at 98% of max. I would glance at the timer each lap and note highs and lows. I would disregard any hair laps and the results are the average of the 3 best (non-hair) laps. Because I was not trying to set lap records with each test, I seldom came off and really didn't have many hair laps. 

 

purpleangel.jpg

 

3 rail shaker car (left)

 

JK 8703 PP = 4.82

JK 8713 PP = 4.84

JK 8763 PP = 4.87

JK 8703 PT = 4.86

JK 8713 PT = 4.83

JK 8763 PT = 4.92 a touch loose

Kelly Retro  = 4.94 a touch looser

JK 8713 PT = 4.81 Retested to verify and also to test a different body (O/S 410-L)

 

Conclusion: This is a very good race car for this track and can use just about any tire (approaching no brainer status)

 

Torsion Car (preface....I have built similar torsion cars over the last couple years without much success)

 

JK 8703 PP = 5.09 (Would snap out on exit in fallaway LH 180 in foreground and RH sweeper in background)

JK 8713 PP = 5.06 (Felt similar although clock said it was better)

JK 8763 PP = 5.02 (Starts to feel more predictable)

JK 8703 PT = 4.94 (Beginning to feel racy)

JK 8713 PT = 4.88 (Feeling like I could push the car pretty hard now)

JK 8763 PT = 4.98 (OK but starting to feel loose)

Kelly Retro = 5.12 (Loose and unpredictable)

 

Conclusion: At first, this car felt poor but with some tire tuning it got into the ball park for this track. Some selective narrowing might have been beneficial for this car. This chassis is possibly not ideal for the subtle direction changes on this track. I think it will prove to be better on tracks with more conventional turn configurations. This is consistent with most of the other torsion cars I've built.

 

So.......yes. Sometimes, different chassis designs on the same track will have very different reactions with different tires while other chassis designs may work with almost anything.


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Jim Fowler




#2 Racer36

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Posted 05 September 2016 - 08:18 AM

Great test Jim. Thanks for posting this. I have always found with flexi cars, and now with retro, that tires make all the difference in the world. I fine tune with tire width to find the sweet spot.

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#3 Joexemm

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Posted 06 September 2016 - 11:09 AM

What condition would i be trying to fix through narrowing of a tire? 

 

nosing out halfway through a turn is "too much bite" as long as the guide is right and its flat?

 

Perhaps this has been answered elsewhere but i have never actually narrowed a tire as i always was looking for more bite with the things i have raced


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#4 slotcarone

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Posted 06 September 2016 - 12:31 PM

Great test Jim! You could also try wonder or soft wonder. I have built many JK based torsion cars and they work well on any track we raced on.
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#5 JimF

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Posted 06 September 2016 - 02:58 PM

Great test Jim! You could also try wonder or soft wonder. I have built many JK based torsion cars and they work well on any track we raced on.

 

Thanks Mike:

 

I had Koford SW and SSW available. Tried SSW but wasn't worth a hoot so I didn't report on it. Historically, neither has been worth much on this track. However, my next test will be on a bitey, flattish King and Wonder is often good there so that'll be my next stab at the torsion car.


Jim Fowler

#6 JimF

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Posted 06 September 2016 - 03:10 PM

What condition would i be trying to fix through narrowing of a tire? 

 

nosing out halfway through a turn is "too much bite" as long as the guide is right and its flat?

 

Perhaps this has been answered elsewhere but i have never actually narrowed a tire as i always was looking for more bite with the things i have raced

 

Nosing out on exit might suggest too much bite although usually, tipping is the symptom that I associate with that. Nosing out in the middle of a corner could be too much bite I guess but would prob'ly not be the first thing I'd think of.

 

I'd suggest that you take one pair of your usual tire and narrow it by maybe .050-.075. Then next time you go out to practice or test, run laps until the symptom shows up a few times. Then switch to the narrowed tires and try to run the same pace and see what happens.

 

FWIW....I run narrowed tires maybe 30-40% of the time.


Jim Fowler

#7 Joexemm

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Posted 06 September 2016 - 04:47 PM

Okay so its not super common but i should have a set to try just in case


Joseph Emm

 

"Success is the best Revenge".... - someone smart.

 

C.O.W. retro chassis Everyone that runs one knows Checkers or Wreckers

 

 


#8 Racer36

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Posted 06 September 2016 - 05:49 PM

I first started narrowing tires when we ran 4.5 NASCAR. I found I could shave 3 or4 tents off my lap times be narrowing a set of treated JKs about an eighth of an inch. The car was waaaaay too loose on Wonder and just as tight on full width treated. The narrowed version always worked well.
I do it with flexi cars all the time now, and occasionally with retro.

Dennis Dominey

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#9 Mike Patterson

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Posted 06 September 2016 - 09:20 PM

I have been narrowing tires for years. Rather then carry around every different compound there is, I buy one tire (Alpha 6138), and adjust the width accordingly to track conditions. I have run tires narrowed as much as 5/16" on retro cars. Which, I might add, look much more realistic on an F1 car, compared to the full width tire.


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