Hi, I am new to this forum, so let me introduce myself. My name is Goran Malmberg from Sweden.
You might have a look at my home site which tells a lot about me. http://hem.passagen.se/hemipanter/ Not really an F1 car, but still something to focus my interest on.
Now, i wonder about what you guys think about the A-arm system (geometry). First, what is the main function of concern? From the drivers point of view, could we say, keeping the car neutral and predictible, which may take the use of low forclines.
Also, what do we say about the Sai angle and scrub radious, is it only to be minimized? Do we have any connections with the same parametersat the rear of the car, or is scrub or Sai (to use the same word as up front) of any influece at the rear?
Goran Malmberg
Long A-arms.
Started by
Goran Malmberg
, Oct 15 2005 08:36
5 replies to this topic
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#2
TestaRoasta
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Posted 15 October 2005 - 15:46
I can tell you that in F1 they have the arms line up in the wheel to keep the scrub radius small and neutral
http://campus.umr.ed...aper/paper.html
http://campus.umr.ed...aper/paper.html
#3
Greg Locock
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Posted 15 October 2005 - 22:53
15500 ft lb/degree is very good.
I like your arm castings, that is a good technique.
Scrub radius
Scrub radius is of no great significance at the rear. At the front old cars used as much as 100 mm quite happily. Modern cars tend to fall into the range +20 mm to -20mm, in order to improve perceived stability under braking (ie reduce steering wheel torque). However, the actual mechanical effect of scrub radius is quite small - if you hold the wheel straight it doesn't cause any significant toe as such, at 20mm, on a typical production car (I measured it on Thursday!)
However, from your diagram I don't think you are talking about scrub radius at all. I think you are referring to the swing arm radius, which in your case will cause a lot of track change in roll, which will cause lateral scrubbing forces, so I see why you called it that! It won't be a huge issue on smooth circuits but on real roads it will make the car darty on uneven surfaces.
I like your arm castings, that is a good technique.
Scrub radius
Scrub radius is of no great significance at the rear. At the front old cars used as much as 100 mm quite happily. Modern cars tend to fall into the range +20 mm to -20mm, in order to improve perceived stability under braking (ie reduce steering wheel torque). However, the actual mechanical effect of scrub radius is quite small - if you hold the wheel straight it doesn't cause any significant toe as such, at 20mm, on a typical production car (I measured it on Thursday!)
However, from your diagram I don't think you are talking about scrub radius at all. I think you are referring to the swing arm radius, which in your case will cause a lot of track change in roll, which will cause lateral scrubbing forces, so I see why you called it that! It won't be a huge issue on smooth circuits but on real roads it will make the car darty on uneven surfaces.
#4
Goran Malmberg
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Posted 16 October 2005 - 08:28
I am really talking scrub radious, or should we say scrub distance, which is a more suitable word for the rear since the wheel doesnt turne. Like you say, scrub for the rear is commonley not discussed. But in a short cambercompensative A-arm system the scrub has a great influence on wheelrate, and we are talking up to 50% reduction and a non linear curve that is also different in roll and heave. Therfore an identical geometry front to rear would be to prefere.
With long A-arms, small scrub and zero SAI, these illness is greatley reduced. But what says the driver that got less signals?
Goran Malmberg
With long A-arms, small scrub and zero SAI, these illness is greatley reduced. But what says the driver that got less signals?
Goran Malmberg
#5
Fat Boy
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Posted 17 October 2005 - 15:39
Originally posted by TestaRoasta
I can tell you that in F1 they have the arms line up in the wheel to keep the scrub radius small and neutral
http://campus.umr.ed...aper/paper.html
Just to clear up something about that paper. The gentlemen that wrote it were not, nor have they ever been F1 engineers. They ran 0 SAI and 0 scrub radius for reasons that nothing to do with a racecar. These reasons were not really addressed in the paper.
Somewhere along the line, people decided 'Zero Scrub' sounded good, and so it became a design goal. It is not necessarily a good thing.
The tire's contact patch delivers a torque through the steering mechanism. The lever arm for that torque is the scrub radius. If you choose to make the scrub radius smaller than the tire lateral deflection, then the steering can get vague to the driver because the sign of the torque changes as the tire flops from one side to the other.
I don't know what F1 designers do with scrub radius, but on other racecars, I haven't seen any big push to minimize it. It is reduced if someone wants to reduce steering effort (along with the caster / caster trail).
#6
Goran Malmberg
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Posted 17 October 2005 - 17:13
"Just to clear up something about that paper. The gentlemen that wrote it were not, nor have they ever been F1 engineers. They ran 0 SAI and 0 scrub radius for reasons that nothing to do with a racecar. These reasons were not really addressed in the paper."
I was really confused about those cars running extreeme "zero angles". Even if I teoretically could think so, I am am sort of question it.
"Somewhere along the line, people decided 'Zero Scrub' sounded good, and so it became a design goal. It is not necessarily a good thing."
"people decided 'Zero Scrub", sounds like it has become the trick of the day! In what racing circles is this going?
"then the steering can get vague to the driver because the sign of the torque changes as the tire flops from one side to the other."
You got a point here.
"I don't know what F1 designers do with scrub radius, but on other racecars, I haven't seen any big push to minimize it. It is reduced if someone wants to reduce steering effort (along with the caster / caster trail)."
Agree! I havent seen zero scrub i F1 either. My point here is to get the same scrub front to rear if the A-arm geometry is short non parallell. As zoon as the A-arms is longer and very much in parallell, scrub dosent make any big difference. I am talkin wheelrate here, not steering to driver relation.
Goran Malmberg
I was really confused about those cars running extreeme "zero angles". Even if I teoretically could think so, I am am sort of question it.
"Somewhere along the line, people decided 'Zero Scrub' sounded good, and so it became a design goal. It is not necessarily a good thing."
"people decided 'Zero Scrub", sounds like it has become the trick of the day! In what racing circles is this going?
"then the steering can get vague to the driver because the sign of the torque changes as the tire flops from one side to the other."
You got a point here.
"I don't know what F1 designers do with scrub radius, but on other racecars, I haven't seen any big push to minimize it. It is reduced if someone wants to reduce steering effort (along with the caster / caster trail)."
Agree! I havent seen zero scrub i F1 either. My point here is to get the same scrub front to rear if the A-arm geometry is short non parallell. As zoon as the A-arms is longer and very much in parallell, scrub dosent make any big difference. I am talkin wheelrate here, not steering to driver relation.
Goran Malmberg
