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Old 03-04-2013, 01:27 PM   #1
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Default Suspension/chassis tuning question

I'm very familiar w/ chassis tuning and the theoretical reasoning behing changes but a certain recent instance has me stumped. I have a TC5 that we are currently running on a rubberized type gym flooring. It is very dusty until the line is cleaned out by running the cars some. What I experienced was a very severe oversteer on power. Generally I would soften up the rear a tad and i'd be ok. However at this location the only thing that improved the situation, and it improved it signifigantly, was to not only stiffen the rear quite a bit but also stiffen the front as well. When I tried to soften the rear without touching the front it made little to no difference yet stiffening the rear helped. I also lowered the rear inner camber link (raised rear RC) which should hurt on power rear traction I'd think. This all has me baffled. Maybe you guys can shed some light on why stiffening the rear would help an on power oversteer issus. I run a front spool but tried a front diff and it made no difference. I have the rear diff about medium tightness.

35wt losi F/R and 1.5/1.25 sway, Camber was -1/-2.5

Excessive oversteer: Blue (17.0)/Silver (14.5)
No oversteer: Gold (19.5)/Red (22.0)

Last edited by TT_Vert; 03-04-2013 at 01:55 PM.
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Old 03-04-2013, 01:50 PM   #2
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Sometimes you over-roll and it affects the contact patch of the tyres. You'll also find that a car that is rolling will become more inconsistent at the limit because it is changing it's position quite a lot as it loses and regains grip. On high-grip surfaces you don't notice this phenomenon so much which is why cars can get away with softer settings.

I used to run a lot on slippy gym floors here in the UK with spiked tyres and very soft setups wouldn't work, the cars slide was more progressive and controllable with a harder setup. I've also seen it very clearly with the modern 4wd buggies which often handle better with a rear anti-roll bar on the very low grip tracks.

Basically there is a window of roll stiffness and geometry where the tyres are going to work, if you are either too soft or too stiff you are going to have problems.
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Old 03-04-2013, 04:23 PM   #3
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It's very odd as I don't appear to have any slide now. it isn't that it is a controllable slide, I don't seem to have slipping which is good IMO.

Dave

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Sometimes you over-roll and it affects the contact patch of the tyres. You'll also find that a car that is rolling will become more inconsistent at the limit because it is changing it's position quite a lot as it loses and regains grip. On high-grip surfaces you don't notice this phenomenon so much which is why cars can get away with softer settings.

I used to run a lot on slippy gym floors here in the UK with spiked tyres and very soft setups wouldn't work, the cars slide was more progressive and controllable with a harder setup. I've also seen it very clearly with the modern 4wd buggies which often handle better with a rear anti-roll bar on the very low grip tracks.

Basically there is a window of roll stiffness and geometry where the tyres are going to work, if you are either too soft or too stiff you are going to have problems.
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Old 03-04-2013, 04:31 PM   #4
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Here is a video I shot last season - these are the quickest cars at the meeting, 13.5 boosted. They feel and look "planted" - but there is a lot of slide going on as you can see from the slow motion.

+ YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.
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Old 03-05-2013, 02:03 AM   #5
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Is it possible that you were actually understeering a lot, cranking the wheel more, applying power, getting the back end really loaded up, and then it was just snapping away from you?

-Mike
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Old 03-05-2013, 10:41 AM   #6
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Thought RC Crew Chief should have a crack at this one.

http://www.youtube.com/watch?v=0g3nkD3WdBw
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Old 03-05-2013, 01:10 PM   #7
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Quote:
Originally Posted by grippgoat View Post
Is it possible that you were actually understeering a lot, cranking the wheel more, applying power, getting the back end really loaded up, and then it was just snapping away from you?

-Mike
That is possible however I was also having very bad rear traction problems while just going straight. The rear felt like it was nearly on ice at times. I'm running 3deg of rear toe before you ask

Dave
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Old 03-05-2013, 01:11 PM   #8
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Thanks bob I'll look at this in a bit.

Dave
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Old 03-05-2013, 02:00 PM   #9
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Bob, I haven't finished watching your video but I will be purchasing your software as it looks very nice and informative. Can you tell me if there is some forum or documentation provided on how to understand the extrapolated data?
Dave
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Old 03-05-2013, 02:19 PM   #10
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Quote:
Originally Posted by TT_Vert View Post
Bob, I haven't finished watching your video but I will be purchasing your software as it looks very nice and informative. Can you tell me if there is some forum or documentation provided on how to understand the extrapolated data?
Dave
There are help files built into the program and lots more screencast videos on the website to get you started
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Old 03-05-2013, 03:53 PM   #11
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I had been having issues lately after going to a new track with excessive loose neutral power, after fiddling with every setting (diffs, RC etc) it came down to just the wrong tyre compound for the surface.

Went from a Rubber 32deg to a 36deg tyre and its handling well as ever. It was odd as the softer tyre was a lot more slippery, maybe it was just over heating.

I too am going to buy the RC CrewChief, awesome bit of gear there!
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Old 03-07-2013, 07:32 AM   #12
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Received a pm from one of the other guys that race at the track with some more info.

What caught my eye was the huge difference in spring rate ranges between different driver's setups as much as 3 times different (front springs 12# to 35#). That's crazy. Add to that the grip goes away after 2 minutes tells me the main problem as Monsta mentioned above is tires. Maybe you already have the best tire for your surface but I would suggest:

1. Check tire temps after a run to see if they are over/under heated. The Sweep OG tire is for asphalt so you may not be getting enough temp into the tire as the racing surface temp is low (65F).

2. Contact Sweep to see what they would recommend for your conditions. Give them as much info as possible.

Once you are convinced you have the best tire then you can try to optimize the setup.
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Old 03-07-2013, 07:56 AM   #13
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Thanks for all the effort Bob. I think that more of the problem is debris on the tire when you get out of the tiny groove that does eventually develop. There will be dust/glitter, etc. on the tire when you get anywhere out of the groove. It seems impossible to clean the tire during the run after that. When I get out of the groove I have massive pushing not the other way around. The track surface was about 62 degrees, i'll check tire temp but if anything my tractions starts off well until I get some dust on the tires.

Dave
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Old 03-07-2013, 09:02 AM   #14
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Do you or have you guys tried removing the dust/debris with a with a leaf blower or sweeping it with a dust compound. We used to blow the asphalt when parking lot racing. If we didn't it was nearly impossible to drive on even with sugar water.
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Old 03-07-2013, 03:14 PM   #15
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Bob, enjoyed the video and still trying to understand using RC crew chief for setup ideas. Can you elaborate a little more about reading your tires for buildup and relating it to your camber settings. You can use private messaging (or even better your crew chief thread) if you would rather not muck up this thread.

Greg
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