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Old 03-19-2014, 04:20 AM   #151
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Any thread that has Martin and Paul posting in it is awesome. And we benefit by the discussion. The driveshaft angles and diff heights are not always considered by the average rc'er but learning more about what is happening when changes are made in this area will help us all.

Steve
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Old 03-19-2014, 12:21 PM   #152
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Originally Posted by frozenpod View Post
Hi Martin, expanding on the wheel base question, how about track width.

This is my understanding, the wider the track width the more even the load on the inside and outside tyre theoretically resulting in more lateral grip.

But setup books suggest ie to increase front grip reduce the front track width.
yes you understand things correctly. Just to back that up with some math.

Here is the formula to determine lateral weight transfer

LWT = (CarWeight x CGHeight)/ TrackWidth

Algebra tells us that the larger the track width the less lateral weight transfer will happen.

So if your trackwidth is wider, resulting in less lateral weight transfer, then this will keep more vertical load on the inside tire resulting in more lateral grip.

As I explain in the app and mentioned in my previous post, the greater the difference in vertical load between the inside and outside tire, the less lateral grip you will get due to the tire performance curve.

Cheers.
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Old 03-19-2014, 12:22 PM   #153
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Originally Posted by corallyman View Post
Any thread that has Martin and Paul posting in it is awesome. And we benefit by the discussion. The driveshaft angles and diff heights are not always considered by the average rc'er but learning more about what is happening when changes are made in this area will help us all.

Steve

yeah...Pauls point about cvd angles is certainly something to consider when the angles are large.
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Old 03-19-2014, 12:51 PM   #154
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Martin,

What areas of change would you consider with this scenario:
Car has the right amount of steering in all stages of the turn, but it is very hard work to drive, it's not effortless steering. Seems to almost big down a little mid corner.
Other expert drivers have driven my car with same conclusion.
It's fast, I'm getting great times, but would like it to flow through corner better.
Any ideas?
I have your apps, but can't really know what to do for this scenario!
The track is indoor, very smooth ash felt, with great grip (not really high grip, more med-high)
Thanks
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Old 03-19-2014, 12:57 PM   #155
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Martin,

What areas of change would you consider with this scenario:
Car has the right amount of steering in all stages of the turn, but it is very hard work to drive, it's not effortless steering. Seems to almost big down a little mid corner.
Other expert drivers have driven my car with same conclusion.
It's fast, I'm getting great times, but would like it to flow through corner better.
Any ideas?
I have your apps, but can't really know what to do for this scenario!
The track is indoor, very smooth ash felt, with great grip (not really high grip, more med-high)
Thanks
Three things to try come to mind. First I would run a diff up front with about 1m cst oil. Second, I would reduce the rear toe-in from 3 to 2.5 assuming you are running 3 degrees. Third I would lower the rear roll center slightly by about 0.5mm to 1mm.

cheers
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Old 03-19-2014, 01:02 PM   #156
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Originally Posted by Martin Crisp View Post
yeah...Pauls point about cvd angles is certainly something to consider when the angles are large.
Well also consider this:
If a vehicle is setup with low roll centers (I am mainly referring to the lower inside points), the angle of the CVD at ride height will not be parallel to the ground for any modern TC, but will be angled up. This angle is still most likely within the normal operating angle where power transfer is reduced very little. When the vehicle accelerates, however, you are inducing more angle to the rear CVDs and thus potentially creating some bind in the suspension, similar to what Paul discussed. Given how sensitive these cars are to what are really very small adjustments (i.e. a < 0.5 lb/in spring rate change or a 1 mm change to an upper camber link point can be perceived), it is not surprising that diff height in concert with roll center height and also potentially wheelbase can have a big effect on handling.

See the following chart for an example of how universal joints transfer power at different operating angles:
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Old 03-19-2014, 01:20 PM   #157
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That's why some drivers are using esc driveshafts in the rear as well as the front.
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Old 03-19-2014, 03:23 PM   #158
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Originally Posted by Martin Crisp View Post
yes you understand things correctly. Just to back that up with some math.

Here is the formula to determine lateral weight transfer

LWT = (CarWeight x CGHeight)/ TrackWidth

Algebra tells us that the larger the track width the less lateral weight transfer will happen.

So if your trackwidth is wider, resulting in less lateral weight transfer, then this will keep more vertical load on the inside tire resulting in more lateral grip.

As I explain in the app and mentioned in my previous post, the greater the difference in vertical load between the inside and outside tire, the less lateral grip you will get due to the tire performance curve.

Cheers.
Thanks Martin,

How does the contact patch come into play in relation to lateral grip?

IE you have negative camber to maximize the outside tyre contact patch but this results in less than maximized contact patch on the inside tyre.

How would you trade off the amount of negative camber for best lateral grip.
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Old 03-19-2014, 04:44 PM   #159
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Originally Posted by frozenpod View Post
Thanks Martin,

How does the contact patch come into play in relation to lateral grip?

IE you have negative camber to maximize the outside tyre contact patch but this results in less than maximized contact patch on the inside tyre.

How would you trade off the amount of negative camber for best lateral grip.
Always focus on maximizing the contact patch of the outer tire
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Old 03-19-2014, 04:49 PM   #160
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Originally Posted by frozenpod View Post
Thanks Martin,

How does the contact patch come into play in relation to lateral grip?

IE you have negative camber to maximize the outside tyre contact patch but this results in less than maximized contact patch on the inside tyre.

How would you trade off the amount of negative camber for best lateral grip.
The non-linearity curve of normal force (weight) vs. lateral grip that Martin talked about earlier usually becomes steeper when you have a smaller contact patch. Changes in load to the tire will have a greater change in lateral grip, but with the caveat that they will reach the 'overload' point at a smaller normal force and then will start to produce less grip as you continue to load the tire. Some tires fall off gradually as load increases, others drop off dramatically.

The biggest thing large amounts (2+ deg) negative camber offers you is it takes advantage of that curve before you've reached the maximum and gives you a smaller initial surface area to put the load on, and therefore more pressure at the contact patch, which will create more grip entering the corner. If your camber gain is not balanced with this, you will limit the overall grip of the car as you'll never let it reach its maximum contact patch mid-corner.
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Old 03-19-2014, 05:02 PM   #161
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Originally Posted by Martin Crisp View Post
Three things to try come to mind. First I would run a diff up front with about 1m cst oil. Second, I would reduce the rear toe-in from 3 to 2.5 assuming you are running 3 degrees. Third I would lower the rear roll center slightly by about 0.5mm to 1mm.

cheers
thanks Martin
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Old 03-19-2014, 05:09 PM   #162
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Originally Posted by Brian McGreevy View Post
The non-linearity curve of normal force (weight) vs. lateral grip that Martin talked about earlier usually becomes steeper when you have a smaller contact patch. Changes in load to the tire will have a greater change in lateral grip, but with the caveat that they will reach the 'overload' point at a smaller normal force and then will start to produce less grip as you continue to load the tire. Some tires fall off gradually as load increases, others drop off dramatically.

The biggest thing large amounts (2+ deg) negative camber offers you is it takes advantage of that curve before you've reached the maximum and gives you a smaller initial surface area to put the load on, and therefore more pressure at the contact patch, which will create more grip entering the corner. If your camber gain is not balanced with this, you will limit the overall grip of the car as you'll never let it reach its maximum contact patch mid-corner.
Hey Brian,

Are you trying to say that with negative camber you will have more grip on initial turn in because there is a smaller contact patch before the car completely leans into the corner?

....I just want to understand your point before I comment on it.

Martin.
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Old 03-19-2014, 05:51 PM   #163
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Originally Posted by Martin Crisp View Post
Hey Brian,

Are you trying to say that with negative camber you will have more grip on initial turn in because there is a smaller contact patch before the car completely leans into the corner?

....I just want to understand your point before I comment on it.

Martin.
Yes, and obviously like with anything, only to a point, and only on turn-in. The turn-in generates the weight transfer, but before it has progressed very far, you're generating more friction on the outside tire precisely because of that smaller contact patch. I understand the physics very well, but I have found in this brief case that the normal load increases quicker than the gain of overall tire friction coefficient as surface area is increased. The car feels a little more edgy right off center. As soon as the rest of the weight transfer happens and the car rolls, however, you want the larger contact patch to increase the normal force-carrying capability of the tire and your overall grip level.

Also, as I'm sure you know Martin, you actually don't want the tire perfectly perpendicular to the track surface at max roll because of tire/sidewall squish. Slight negative camber at peak roll will actually give you a slightly greater contact patch than if the tire were perfectly upright. I spent hours looking at competition slick tire data...this one kinda cements in there
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Old 03-19-2014, 06:42 PM   #164
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Always focus on maximizing the contact patch of the outer tire
Thanks.
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Old 03-19-2014, 07:19 PM   #165
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Hey Martin.
I have a tbo3r racing 21.5 carpet. The rear is very loose on corners , slides around on me on most corners. I have increased from 2 to 3 deg rear toe and have tried putting rear camber more neg from 1.5 to 2 to 2.5. Have also tried stiffer front springs And then softer rear then stiffer all around. Ride height at 5mm but have also tried front at 5.5. Also switched tires. Need more rear grip. Have tried changing droop as well.
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