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Old 05-19-2002, 10:09 AM   #91
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The rear of my car starts to swing and oversteers when I steer my car to the left at any speed, while the car handles perfectly fine when I steer it to the right. And on some occasions, the swing is tremendously bad, in the sense that the car spins.. Is there any thing I can do to my setup in order to solve this problem?
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Old 05-19-2002, 11:11 AM   #92
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That sounds like a tweak issue. Have you checked your car on a tweak board?

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Old 05-19-2002, 11:45 AM   #93
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Hmm... no, I haven't. I do not have the tweak bored and I doubt my car can be used with the tweak board as it is just a HPI Micro.
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Old 05-20-2002, 02:19 PM   #94
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Proudwinner: You raise a very good question. Although I have not done a lot of experimenting with softer rims and I prefer a stronger rim to reduce the risk of warping after hitting somthing, different "stiffness" of rims will provide different handling characteristics. My guess is that softer rims might provide you with more grip on surfaces that don't provide a lot of grip to begin with.

Trips: Thanks for you support!
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Old 05-20-2002, 02:28 PM   #95
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sosidge:

Thanks for the feedback on the book. I am constantly looking to improve it, so I really do appreciate the feedback. In the spirit of constant improvement what are you finding when you make caster changes that differs from what my book says. Thanks again for your feedback.
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Old 05-20-2002, 04:31 PM   #96
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Quote:
Originally posted by proudwinner
Here's one for ya, how do softer wheels affect handling vs. stiffer wheels. Team Orion makes some really soft wheels where they almost feel like rubber. I'm thinking wheels should be as stiff as possible so there won't be any runout when power is applied to them, is this correct? Now it's just the inside of the wheel that is super soft not the outside.
proud,

nylon vs. abs, hard plastic. i prefer a wheel w/ a slight flex. i've been using the new yokomo hard discs - they're supposed to be truer and more rigid, but i've already cracked a few. the best luck i've had are w/ the yok. nylon discs or the proline wheels. haven't cracked a proline yet. the gumby pattern works well and looks sharp. since your having to shell out more for the prolines, you might as well get a nice looking pattern.
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Old 05-21-2002, 08:22 AM   #97
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mcrisp

here are the things I chose to differ on in the book

You say more caster (implying a greater angle from the vertical), would give more steering.

However, i find less caster (shallower angle) gives more steering, both at the corner entry and in mid-corner.

This is on a pro3, going from 8 or 10 deg caster down to 5.

I wonder if this is down to going from ideal to less ideal camber angles as lock is applied - i.e. too much camber and the tyre will lose grip.

I also felt some of your descriptions were a bit over-simplified - like with shock angle, where you didn't point out that a more angled shock has a greater change in it's rate of compression as the suspension is compressed - i.e I believe it gets comparitively softer as the suspension is compressed

Also I felt your explanation of toe failed to take into account ackerman angles on the front.

I also felt the description of anti-squat and kick-up was a bit unclear - your diagrams suggested that cars run with negative kick up at the front to act as anti-dive, which they don't.
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Old 05-21-2002, 09:56 AM   #98
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sosidge:

Thanks again for taking the time to help me improve the book.

Caster: If you are getting more steering at corner entry and mid corner, then it sounds like your are simply finding the optimum caster angle to give you the optimum camber angle in the corner, given the static camber you already have. As you clearly understand and as I point out in my book, you can take adjustments too far and actually get the reverse of what you are looking for. This is an important point to remember. For example although in general if you want one end of the car to grip more then you soften the suspension at that end of the car. However if you soften it too much you will actually loose traction. The concept of going too far with an adjustment and getting the opposite results is why I was not surprised that you were getting results that differed from my book.

If it is only the initial turn in that gives you more steering then as I discuss in my book, less caster can give you more initial steering. Less caster will give you a much quicker initial steering response because you keep a larger contact patch of the tire on the ground during this initial turn-in point before the car reaches the extent of it’s “roll”. When the car does reach the extent of it’s “roll” however, you could end up with a smaller contact patch with less caster and this is why you might have less steering during the middle or end of the corner.


Kick-up: I went back and checked the diagrams. You are correct, there is a "typo" in the kick-up diagram. The "Positive Kick-up" diagram has some text saying "towards front of chassis", and it should say "towards back of chassis". Time to fire my editor eh! . Sorry about the error and confusion. This will be corrected, thank you. Although I did intend the text to say "towards back of chassis", I have run negative kick-up at the advice of David Spashett at a foam tire race earlier this year.

Toe and Ackerman: Yes it is true I did not include an explanation of Ackerman. I already have plans to include this and other topics such as tires and inserts in the next version.

Over Simplified Explanations (e.g. shock angles): This is a tough one to balance, as different readers like different levels of complexity. You are correct that in general layed down springs do change their compression rate more than stand-up springs. However, for most cars, layed down springs are more progressive in their compression rate and thus get stiffer as they are compressed. This is because as the lower “A” arm starts to lift up, then the force against the spring is getting closer to the plane the spring is on.

In addition to adding something that talks about the above paragraph, what do you think about adding the following concept to this section on shock angles/springs? It provides a more complete explanation of why layed down shocks are softer.

In my "simplified" explanation I suggest that a layed down shock gets compressed less and thus is softer. There is actually more to it than that as this explanation does not always hold true when the springs have truly constant linear spring rates. I have talked with some engineers about this and the way they explained it to me is as follows. When a spring is vertical (lets call this vertical plane the Y-AXIS), then the entire force of the spring pushes against the Y-AXIS force that is compressing the spring. If however the spring is layed down then only a portion of the springs force is applied to the Y-AXIS force that is trying to compress it. This is because the force of the spring is now split between the Y axis and the X Axis. In other words the more the compression force is on the same plane as the resistance force of the shock/spring the harder the suspension will be.

I was also thinking of adding some content around progressive spring rates.

Thanks again for your help in making this a better book.
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Old 05-21-2002, 11:38 AM   #99
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mcrisp Sorry but I disagree with your analysis of caster below.

Caster is one of those adjustments that nobody seems to agree on my associated and schumacher manuals both contradict each other.
In my experience more caster increases turn in in a 2wd off road car but reduces exit steering. In a touring car the affects can be reversed (but not always).

Everybody accepts that if they change the position of a ball stud for a camber link it alters both roll centre and camber change. Caster is another adjustment that affects multiple things.

Firstly there is the obvious effect of the change in effective camber angle during the corner. This affect could do anything to the balance through the corner depending on the camber link settings. This is the dominant effect of caster mid corner. It may be less significant on exit and entry though.
Camber itself can be split into two effects. There is the contact patch of the tyre but there is also camber thrust. A tyre sitting at an angle will twist to try and become flat to the track. This twisting induces a sideways force. If camber angles are equal and opposite on the two sides of the car this force cancels out. If the angles are different or the wheels lean in the same direction as with caster there will be a resultant force though.

Secondly there is the weight jacking effect. This increases steering response on initial turn in. To see why weight jacking occurs take a tyre and measure its height in the upright position. Now lean the wheel so it has lots of camber. If you measure the overall height you will find it has changed. This causes weight transfer between front and rear. According to the amount of ackerman there will also be a small amount of lateral weight transfer. The softer the suspension is the less significant this affect becomes as the force on the spring is proportional to the change in length of the spring. This is why buggies have such extreme caster angles.

Thirdly caster causes a change in track width when the wheels are turned. It is probably not significant with the small caster angles on a touring car but is at 30 degrees on a buggy. The increase in track width will change the roll centre and also soften the suspension on the outside wheel whilst stiffening the inner side suspension.

With a touring car you may also need to be careful of the affects of caster heating the tyres. The same applies to camber. The twisting of the tyres responsible for camber thrust generates heat. This can change the balance of the car through the race.

The significance of each of the above effects is going to vary depending on a variety of factors such as type of car, camber link settings , driving style.
You will never get a definitive answer that works all the time for caster. It is one of those adjustments you have to try for yourself.
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Old 05-21-2002, 12:51 PM   #100
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Hey DW.

Thanks for the feedback. Perhaps I did not make myself clear enough in the post you commented on, but I completely agree with you that there are situations where the same adjustment can achieve different results. In fact I state that in my book.

Since I wrote the book for touring cars and not off-road I focused on how the adjustments affect touring cars in general. Although I am sure a lot of the books contents could be applied to off-road, it really is focused on touring cars.

I wrote this book with the idea of condensing 1000 page chassis setup engineering books into simple to understand concepts. In this approach I choose to not to explain every possible situation that can arrise and why, otherwise it would be another 1000 page engineering book. Instead of focusing on all of the exceptions and every possible aspect of chassis setup that can affect handling, I choose to focus on the more common results of adjustments for touring cars.

Thanks again for your feedback.
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Old 05-21-2002, 01:59 PM   #101
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The offroad stuff was just for example.
The point I was trying to make was that you don't need to go to extreme set ups for caster to have an entirely opposite effect even from one touring car to another.

For example my tc3 manual says the opposite from my sst98 manual for the effects of caster. The manufacturers don't even agree on the affects. The associated and schumacher off road manuals also disagree.

Note how the schumacher tourers use a massive 10 degree caster combined with unusual front camber link settings. The sst 98 relied entirely on caster to generate different front and rear roll centre heights and I think the current schumacher are the same. (suspension geometry was exactly the same front and rear.)

I know I go into more depth than most people but your explanation didn't seem to consider anything except for tyre contact patch which often isn't the dominant factor on corner entry and exit. I know you are trying to simplify everything but oversimplifying can be worse than no information at all. Not trying to antagonise you but it's one of those little things that really irritate me.

For years I always ran the cells forward on my car in order to get more steering because all the manuals say it gives less rear end grip.
They neglect to mention that it kills all turn in and gives more lateral grip to the rear tyres as there is reduced side load on them.

Give me a few 1,000 page engineering text books any day.
I think there is potentially a gap in the market there. Nobody has written an engineering text book with relation to model cars. Yes there are plenty of texts relating to full scale racing but try and find one that mentions caster for example. Not a common adjustment on full scale vehicles. Gearing theory is also totally different with an electric motor. Just about everybody at my local club thinks that if you gear down you get more acceleration and less top end. Perfectly true with an internal combustion engine but they forget that an electric motor produces maximum torque at low revs so gearing up loads the motor more reduces revs and can actually increase acceleration in some cases.
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Old 05-21-2002, 03:16 PM   #102
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Hey DW,

I completely understand the desire to cover all aspects, as this is the way I like to think about things. Sorry that my lack of covering all aspects in my post "irritates you".

I know what you mean about the TC3 manual. When I had a TC3 and read the section in the manual that said I should move the battery to the front for more steering, I did not agree with their conclusion for the same reason you point out.

The good news is that I have had a tremendous amount of positive feedback on my book, with the common theme being, "easy to understand" and "the adjustments do what your book says". As demonstrated in the "Customer Feedback" section on my website.

In the end there are different levels of understanding chassis setup and it sounds like you are like me in that you like the 1000 page engineer book. However not everyone will want to read such a book and thus I believe there is a market for my book.

Given that you like the engineering books, I would highly recommend the following book, if you don't already have it. "Race Car Vehicle Dynamics" ISBN : 1-56091-526-9. It's not cheap, but it provides about 1000 pages of engineering formulas to explain just about anything you will want to know. It was referred to me from a chassis engineer who use to work for one of the major car companies.

Anyway, it has been great chatting with you!

cya,
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Old 05-21-2002, 07:31 PM   #103
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BAsed on the last two posts I guess I'll have to try the cells to the rear for the first time this weekend...

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Old 05-21-2002, 10:24 PM   #104
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Trips that sure is a bumpy road your going down in the Porsche....
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Old 05-21-2002, 10:29 PM   #105
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Kool paint schemes on your site BigDogRacing!
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