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mchill  
#1 Posted : Tuesday, January 12, 2021 7:50:29 PM(UTC)
mchill

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Hi Mike,

Firstly thank you for your articles and forum responses, they are really great. I have a few wingless questions (from a midget racer perspective):

1. I understand it is logical to pull the RR wheel spacing in as the track slicks off to compensate for the reduction of lateral weight transfer (due to less g-force pulled), to maintain even loading on each the rear tyres to maximise lateral traction. Do wingless cars ‘bicycle’ when racers substantially overload the RR, or is it when the rear tyres are evenly loaded creating high lateral traction causing a rapid increase in weight transfer to the right causing it to tip over the RR? I’m assuming the former, but just wondering why bicycling tends to occur when people are “trying to get the most out the car” (which suggests they believe they will be quicker with ever more RR weight).

2. What is the fundamental reason a car becomes loose in slick conditions? Slick conditions result in less weight transfer to the right side, so the LR is loaded relatively higher than the RR higher in slicker conditions, yet the car always oversteers more in slick conditions (assuming no setup changes). You would think relative higher LR weight would result in a tight condition. Why does this phenomenon occur?

Thanks,
Mitch
Mike Dicely  
#2 Posted : Wednesday, January 13, 2021 9:30:47 AM(UTC)
Mike Dicely

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Thanks for the compliment Mitch.

A car will bicycle when the lateral g-force on the moment arm between the CG and the tire contact patch of the car is greater than the force of gravity acting on the CG. You can do a free body diagram to calculate this force very easily. The length and angle of this moment arm (as well as the weight of the car) is what determines how much force is needed to make the car bicycle. Things that will make the car bicycle easier are, moving the right side tires in, raising the CG, increasing the lateral force (hooking the car up more or increasing the grip from the track {hitting a cushion}) or decreasing the weight of the car. That's it! So yea, anything you do to increase the traction will make it more susceptible to bicycling.

"so the LR is loaded relatively higher than the RR higher in slicker conditions" You are making a lot of assumptions by saying that. If the car is setup to have a bunch of static LR weight and you've run the numbers to determine that there is not enough lateral force to transfer enough weight to equal things out, then this statement is true.

You have to counter steer simply because there is no friction in the track, you applying a lot of torque to the rear tires trying to accelerate and they spin causing the rear to come around. If it was a 4 wheel drive car car and you were applying this torque to both the front and the rear and things were balanced correctly, the car would just 4 wheel slide.
mchill  
#3 Posted : Wednesday, January 13, 2021 5:20:16 PM(UTC)
mchill

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Thanks Mike, appreciate the quick response.

A few more questions:

3. What should I take away from comparing LR and RR tyres temperatures? Heat is produced by friction, but given we run fixed rear axles and more loading would increase the heat produced, I assume the hotter tyre is typically the heavier loaded tyre?

4. Furthermore, do you believe comparing tyre temperatures is a reliable feedback tool? I question this as sometimes on a slick track running the bottom line the LR runs in brown clay and the RR runs in the black slick, so wouldn’t this heat the RR more and give misleading feedback? Or would the difference in track surface be negligible?

5. Would it be fair logic to always be aiming to have even loading on the LR and RR for the given track conditions, and adjust tight/loose balance with stagger (of course keeping in mind stagger will change corner weights)? Whilst obviously extremely complicated to get this right, is this your interpretation of the ultimate goal for maximum performance?

Thanks,
Mitch

Edited by user Wednesday, January 13, 2021 10:53:09 PM(UTC)  | Reason: Not specified

Mike Dicely  
#4 Posted : Monday, January 18, 2021 7:15:02 PM(UTC)
Mike Dicely

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3. Tire temps are a lot different for winged vs wingless and big vs small tracks. I could never really draw too much of a conclusion from anything there.

4. No

5.Yes, except that you actually want about 30% more weight on the RR due to the larger contact patch, so really its equal weight per square inch of contact surface area.
mchill  
#5 Posted : Tuesday, January 19, 2021 5:32:01 AM(UTC)
mchill

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Thanks again. The most difficult setup change for me to currently get my head around is moving the RR wheel width. As a track slicks off the car typically gets looser in all parts of the turn and changes are often made to add left rear weight in all parts of the corner which typically makes the car drive tighter and often faster (e.g. lower LR rebound for entry, stiffen LR bar for exit as a couple of examples).

I’ve read about your theory of moving the RR in creating a jacking effect which raises the left side of the car, raising the COG and subsequently increasing longitudinal traction. This makes sense, on the basis the longitudinal traction gain outweighs the increase of weight transfer to the RR and the subsequent reduction of lateral traction.

However what are your thoughts on the significance of the rotational moment (in plan view) of the car based on the distances of the left and right wheels from the COG? Moving the RR in will decrease the RR thrust moment arm (in plan view) which would decrease the amount of anti-clockwise rotation of the car which would make the car tighter. How significant do you think this effect would be in relation to the decrease in lateral traction?
Mike Dicely  
#6 Posted : Tuesday, January 19, 2021 9:57:53 AM(UTC)
Mike Dicely

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The only reason the RR thrust moment arm would generate a torque to turn the car left is if it is generating more torque than the LR. This affect is almost null in my opinion.

What racers forget is when they go to a stiffer LR bar or add turns to the LR to tighten the car when it gets slick, is that they are also greatly raising up the CGH. This is why the car gets tighter. If you put a stiffer RR bar in and added turns to the RR, the car would aslo get tighter.

CGH has a much greater affect on chassis handling than corner weight.
mchill  
#7 Posted : Monday, February 1, 2021 4:12:07 AM(UTC)
mchill

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I had assumed there could be a thrust moment as the RR is typically further out from the COG than the LR, so assuming equal thrust from each tyre the car would rotate the car anti-clockwise.

What is your theory for the common tightening effect of moving the LR tire out? I wouldn’t expect this to affect the COG height or the jacking effect of the RR at all?
Mike Dicely  
#8 Posted : Monday, February 1, 2021 2:58:04 PM(UTC)
Mike Dicely

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Wingless it would not make much difference, winged though it can make big changes on entry as the car rolls left. Generally it will make the car tighter on entry only. Agina, there are a million variables to consider. You cant make generalized statements other than equal weights make more traction.
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