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Old 03-20-2014, 09:08 AM   #166
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Originally Posted by Brian McGreevy View Post
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
Hey Brian,

I do follow the logic you present, and it is certainly and interesting idea. Although you might be correct, I struggle with agreeing to it for the following reason. You are saying that a more narrow contact patch will generate more grip than a larger contact patch. If that were the case then race cars will all have very narrow tires would they not?

Also I would add that although an interesting concept to debate, I am asking myself, even if you are correct, I don't see how I could use that information to change anything in the way we setup our cars?

I have to say it is an interesting concept however.

I think to fully buy into the idea I would need to see some tire performance curves comparing narrow tires and wider tires. If those graphs showed that a narrow tire would generate more grip than a wider tire given the same vertical force then I could accept what you are presenting here. If such graphs do exists and confirm that, then someone would need to explain to me why race cars don't use narrow tires.

A good discussion for sure.

By the way, like Paul, Brian sent me a very respectful note asking if it was ok to debate this in a public forum with me. For sure it is as long as we are both respectful, nothing but good learning for everyone including me can happen. I don't know everything about setup (far far from it) and love to learn what I don't know. I am a huge fan of learning more about setup, otherwise I would never have spent so much time writing books and apps about it . Setup It is a complex not so black and white game of compromise and has the ability to give you an edge over your competition, which is why I focus so much time on it, for both RC and my full size car racing.

Cheers.
Martin.

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Originally Posted by Atechbh View Post
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.
Hi,

The good news is that the things you are trying are the right things to be experimenting with

You should be able to balance your car with just about any tire as long as the tires are properly glued onto the rim and are of relatively consistent grip across all four tires. (ie. one tire is not 2 years old and the other 3 are brand new )

You did not elaborate on what droop changes you made, so it is hard to comment on that. Having said that, reducing the droop in the rear to about 1.5 to 2mm above ride height should be as small as you go. Also reducing the front droop to not more than 1.5mm above ride height. if you take out all the droop then the car will be very edgy and do unpredictable things.

Since you have already played with rear toe and camber, the next high impact thing to change is the roll center. To get more rear grip you need to raise the rear roll center and to take away front grip you need to lower the front roll center.

To raise the roll center in the rear either add spacers to the outboard point of the upper link and/or take spacers away from the inboard point of the upper link.

To lower the roll center in the front either remove spacers from the outboard point of the upper link and/or add spacers to the inboard point of the upper link.

Now lets talk about the springs. If you put really stiff springs in the front and really soft springs in the rear, this can actually make the car more loose in the middle and exit of the corner. This is because the rear ends up rolling way more than the front in the middle and exit of the corner. As a rule of thumb I rarely run a different spring on the front and rear of the car. If I do it is only typically one step up on the spring rate in the front of the car.

I hope this helps.

Cheers,
Martin.
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Old 03-20-2014, 10:50 AM   #167
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How are you doing that measurement. I slide a ride height gauge under the chassis and lift until I can just see light between the rubber and the setup board. I then compare the difference between the ride height and the number on the gauge. Unfortunately different tires seem to have a big difference in how loose the rubber is so the time between when the tire stops taking weight and when the tire lifts off the board. Is there a better way to determine the "lift-off" point?
hope martin doesnt mind but this guy shows you how its done pretty well
https://www.youtube.com/watch?v=OQt6iv175mw
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Old 03-20-2014, 12:05 PM   #168
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Originally Posted by Martin Crisp View Post
Hey Brian,

I do follow the logic you present, and it is certainly and interesting idea. Although you might be correct, I struggle with agreeing to it for the following reason. You are saying that a more narrow contact patch will generate more grip than a larger contact patch. If that were the case then race cars will all have very narrow tires would they not?

Also I would add that although an interesting concept to debate, I am asking myself, even if you are correct, I don't see how I could use that information to change anything in the way we setup our cars?

I have to say it is an interesting concept however.

I think to fully buy into the idea I would need to see some tire performance curves comparing narrow tires and wider tires. If those graphs showed that a narrow tire would generate more grip than a wider tire given the same vertical force then I could accept what you are presenting here. If such graphs do exists and confirm that, then someone would need to explain to me why race cars don't use narrow tires.

A good discussion for sure.

By the way, like Paul, Brian sent me a very respectful note asking if it was ok to debate this in a public forum with me. For sure it is as long as we are both respectful, nothing but good learning for everyone including me can happen. I don't know everything about setup (far far from it) and love to learn what I don't know. I am a huge fan of learning more about setup, otherwise I would never have spent so much time writing books and apps about it . Setup It is a complex not so black and white game of compromise and has the ability to give you an edge over your competition, which is why I focus so much time on it, for both RC and my full size car racing.

Cheers.
Martin.
Martin,
We fully agree that wider tires will generally provide more peak grip because of their increased contact patch, all other things equal. To the point I was trying to make though, lateral friction coefficient increases with slip angle on almost all tires, for a given load. See the following chart for reference: https://www.tut.fi/ms/muo/tyreschool...1_14_thumb.gif
Large negative static cambers introduce "squish" into the inner half of the tire and the sidewall, and this non-uniformity introduces a slip angle at that part of the contact patch, albeit small in comparison to normal cornering slip angles. This increase in slip angle increases the cornering friction coefficient, which allows for higher instantaneous lateral grip as you turn-in. As the car rolls, you want to maximize contact patch as the weight transfer occurs. Too small, and you decrease your lateral grip potential. Every R/C tire works a little bit different and different driving styles favor different ways of getting them to work. This is one way to tune a car to turn-in sharply, assuming your camber gain is aligned to provide the optimum contact patch at peak roll angles. I myself do not prefer it, but I've tried it and seen it used before. It was particularly noticeable with foam tires on carpet.

That said, there are caveats to the "wider is always better" saying. In low-mass cars, like Formula SAE or Formula Ford for instance, a wider tire does not always provide the best overall grip because of tire heating. On a Formula SAE car without aerodynamics (wings, diffuser), where total vehicle weight is ~600 lbs with driver, a 10" wide tire will work poorer than a 7" wide tire because there isn't enough loading on each tire to get it to operating temperature. This is much more of an issue for full-size race cars than for R/C cars, but at a certain point it still applies.
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Old 03-20-2014, 12:57 PM   #169
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this is great keep,the discussions going
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Old 03-20-2014, 01:46 PM   #170
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Originally Posted by Brian McGreevy View Post
Martin,
We fully agree that wider tires will generally provide more peak grip because of their increased contact patch, all other things equal. To the point I was trying to make though, lateral friction coefficient increases with slip angle on almost all tires, for a given load. See the following chart for reference: https://www.tut.fi/ms/muo/tyreschool...1_14_thumb.gif
Large negative static cambers introduce "squish" into the inner half of the tire and the sidewall, and this non-uniformity introduces a slip angle at that part of the contact patch, albeit small in comparison to normal cornering slip angles. This increase in slip angle increases the cornering friction coefficient, which allows for higher instantaneous lateral grip as you turn-in. As the car rolls, you want to maximize contact patch as the weight transfer occurs. Too small, and you decrease your lateral grip potential. Every R/C tire works a little bit different and different driving styles favor different ways of getting them to work. This is one way to tune a car to turn-in sharply, assuming your camber gain is aligned to provide the optimum contact patch at peak roll angles. I myself do not prefer it, but I've tried it and seen it used before. It was particularly noticeable with foam tires on carpet.

That said, there are caveats to the "wider is always better" saying. In low-mass cars, like Formula SAE or Formula Ford for instance, a wider tire does not always provide the best overall grip because of tire heating. On a Formula SAE car without aerodynamics (wings, diffuser), where total vehicle weight is ~600 lbs with driver, a 10" wide tire will work poorer than a 7" wide tire because there isn't enough loading on each tire to get it to operating temperature. This is much more of an issue for full-size race cars than for R/C cars, but at a certain point it still applies.

Hey Brian.

Thanks for the info. Can you better explain the diagram you referenced in terms of what each line is representing and what conclusions we can draw from that? I assume the 295/75R22.5, 11R24.5 and 10.00-20 are referring to tires sizes? But I don't know which ones are larger than the others as they seem to be using very different measurements. Is the 11R24.5 a wider tire than 10.00-20? Do they have the same aspect ratio and same construction...otherwise there are too many variables to draw any conclusions from that graph.

Is your point that the additional "squishing" increases the slip angle on the tire, and it is this additional slip angle that is giving the tire more grip?

Lets assume the "squishing" does produce a greater slip angle. I assume this might be the case as the tire tries to reform itself to its natural shape it will naturally slip across the surface towards the outside of the tire.

I would need to see some formal test results showing that additional slip angle on a narrower contact patch would produce for initial turn-in grip than that same tire with lets say zero static camber with a full contact patch, before I would believe the theory.

I can total see why a wider tire in SAE cars may not work well, because just like autocross there is not enough time to generate heat into the larger tires. I think however for our RC car racing and for road racing in general that is not so applicable as there is time to generate heat. Having said that I do agree that there is a point where going to larger tire is not going to generate a faster lap time, given the additional weight and drag a larger tire would produce. For example if I put 335 width tires on my underpowered MX5 cup car, I would go slower than running a better tire in the 225 to 245 range. As with most things, when you take them to the extreme the opposite often applies.

But we do agree that within reason/limits that a larger contact patch will give you more grip and faster laptimes.

Cheers.
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Old 03-20-2014, 01:54 PM   #171
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hope martin doesnt mind but this guy shows you how its done pretty well
https://www.youtube.com/watch?v=OQt6iv175mw
I have been thinking for a while to include some videos in my app. Videos on subjects such as...

a) How to un-tweak a chasss
b) Walking through a reasonable order of setup adjustments when setting up your car. i.e. what should you do first, second third...etc.
c) what to check on your car between rounds to ensure consistent handling
d) body mounting approaches that affect the way your car handles - Hey Eric Epp - want to work on that with me?
e) Setting up your steering throw on your radio - do's and dont's (This one is for Mark Frechette )
f) Pre-planning where you will make your passes on the track
g) perhaps a video for each of the different setup adjustments to augment the written text in the app.

Let me know which ideas you like the most and if you have any other ideas.

Cheers.
Martin.
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Old 03-20-2014, 02:11 PM   #172
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Originally Posted by Martin Crisp View Post
Hey Brian.

Thanks for the info. Can you better explain the diagram you referenced in terms of what each line is representing and what conclusions we can draw from that? I assume the 295/75R22.5, 11R24.5 and 10.00-20 are referring to tires sizes? But I don't know which ones are larger than the others as they seem to be using very different measurements. Is the 11R24.5 a wider tire than 10.00-20? Do they have the same aspect ratio and same construction...otherwise there are too many variables to draw any conclusions from that graph.
This chart actually is showing truck tires of different sizes and constructions, but it simply illustrates the point that while the slopes are different, the trend is the same.

Quote:
Originally Posted by Martin Crisp View Post
Is your point that the additional "squishing" increases the slip angle on the tire, and it is this additional slip angle that is giving the tire more grip?

Lets assume the "squishing" does produce a greater slip angle. I assume this might be the case as the tire tries to reform itself to its natural shape it will naturally slip across the surface towards the outside of the tire.

I would need to see some formal test results showing that additional slip angle on a narrower contact patch would produce for initial turn-in grip than that same tire with lets say zero static camber with a full contact patch, before I would believe the theory.
I wish I had some data other than the theory and what I've tried in R/C and on a formula car. It is also probably very dependent on the stiffness of the sidewall. The slip with this part of the tire is likely to react differently because of the construction in that area compared to the main contact surface alone. Just like a lot of these adjustments, they can be influenced/masked by other parts of the setup, so perhaps the way I setup the car makes it more noticeable than for others. Try 2.5-3 deg of front camber and take away some camber gain and let me know

Quote:
Originally Posted by Martin Crisp View Post
I can total see why a wider tire in SAE cars may not work well, because just like autocross there is not enough time to generate heat into the larger tires. I think however for our RC car racing and for road racing in general that is not so applicable as there is time to generate heat. Having said that I do agree that there is a point where going to larger tire is not going to generate a faster lap time, given the additional weight and drag a larger tire would produce. For example if I put 335 width tires on my underpowered MX5 cup car, I would go slower than running a better tire in the 225 to 245 range. As with most things, when you take them to the extreme the opposite often applies.

But we do agree that within reason/limits that a larger contact patch will give you more grip and faster laptimes.

Cheers.
Agreed much on the applicability to R/C cars. 1/10th sedan tires tend to both come up to temp quickly and maintain temperature very well if the car is balanced. I suspect that is due largely in part to it not being a pneumatic tire. Definitely agree on road racing, where tire warm up is a factor into preparation for qualifying, racing and the loads are consistent enough and long enough to generate enough heat within a lap or two.

Good discussion!
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Old 03-20-2014, 02:19 PM   #173
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Quote:
Originally Posted by Martin Crisp View Post
I have been thinking for a while to include some videos in my app. Videos on subjects such as...

a) How to un-tweak a chasss
b) Walking through a reasonable order of setup adjustments when setting up your car. i.e. what should you do first, second third...etc.
c) what to check on your car between rounds to ensure consistent handling
d) body mounting approaches that affect the way your car handles - Hey Eric Epp - want to work on that with me?
e) Setting up your steering throw on your radio - do's and dont's (This one is for Mark Frechette )
f) Pre-planning where you will make your passes on the track
g) perhaps a video for each of the different setup adjustments to augment the written text in the app.

Let me know which ideas you like the most and if you have any other ideas.

Cheers.
Martin.
All of those sound great! I would watch em all!
Get crackin! LOL!
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Old 03-20-2014, 02:23 PM   #174
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Good discussion Brian.

For sure something to do some testing on and compare initial turn-in.

Regarding slip angle helping with initial turn-in....as you no doubt know, this is why some toe-out in the front tires helps with a sharper initial turn-in. i.e. the slightly greater slip angle will generate more grip (depending on the tire). It also gives the inside tire especially a greater slip angle just after initial turn in to again give more grip. However as you turn more and more the slip angle on the inside tire gets too great (especially as ackerman kicks in) causing less grip in the middle of the corner.

cheers.
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Old 03-20-2014, 02:31 PM   #175
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Hey Martin,

Good seeing you racing again this past weekend @ The Can Nats!

M.Moore
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Old 03-20-2014, 02:55 PM   #176
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Those r all big truck tires and each of those 3 size tires all have a contact batch of about 9". I can put a tape measure to the ones we have in our repair shop to confirm but we r talking 2" difference at best between them
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Old 03-20-2014, 02:58 PM   #177
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About the only difference I can think of between these tires (from memory) r side wall height. The 295 is the low profile of the 3 then the 11r then the tallest sidewall is the 10.00....
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Old 03-20-2014, 04:11 PM   #178
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Hi Guys,

I can comment with personal experience regarding tyre width.

I found with my real race car that 255's provided more grip than 275's of the same tyre. I had previously run 235 of the same tyre that provided lower grip and struggled with heat compared with the 255's. The 235, 255 and 275 all the same tyre had very square side walls.

With he 275's when you exceeding there capability they would suddenly let go and were hard to control at the edge.

It is also worth mentioning that the narrower tyres were better in damp and wet conditions.

But to add further information I later tried a different tyre with different side wall construction, slightly rounded and slightly softer. This tyre provided more grip than all the tyres I had run previously and they were 285's. I have only used this tyre in a 285's so I can comment how this tyre would perform with alternative widths.

But based on what I have seen, width does have a roll as does side wall construction and potentially the rubber compound.
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Old 03-20-2014, 07:12 PM   #179
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Default Serpent s411 eryx gear ratio

Martin, I have a Serpent s411 ERYX. I am trying to figure out my final drive ratio. Would you know where to start? It has a 38 tooth gear on the diff and a 19, not sure what the diff is. Thanks!
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Old 03-20-2014, 08:01 PM   #180
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Martin, I have a Serpent s411 ERYX. I am trying to figure out my final drive ratio. Would you know where to start? It has a 38 tooth gear on the diff and a 19, not sure what the diff is. Thanks!
I think you meant to say your spur was 38 and the pinion is 19?

On the Serpent S411 I am fairly sure the internal ratio is 2.0

The calculation for Final Drive Ratio (fdr) is as follows

((spur/pinion)*internalRatio) = fdr

(38/19)*2) = 4.0

By the way, there is an gear ratio calculator in my app that allows you to calculate the fdr. The calculator also allows you to figure out the required pinion given a desired fdr and spur. ...or figure out the spur given the desired fdr and pinion.

Cheers.
Martin.
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