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| [GMCnet] Math Question [message #196444] |
Fri, 25 January 2013 11:56  |
Marsh Wilkes
Messages: 155
Registered: January 2004
Karma: -3
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I looked at Jim's reaction arm video again.
I had remembered the figures wrong I was using 75
feet stopping distance without the reaction arms and 42
feet with, that's where I got 1 1/4 coach lengths in the TCFW post.
What Jim posted on the video is 75 foot stopping distance without
and 32 feet stopping distance with the reaction arms, citing a 43%
improvement. That is actually a 67% improvement, 32 feet being 43% of 75 feet.
Question Is the coach stopping from 45 MPH in 32 feet! that almost
sounds too good to be true. I am going to do some research, just like I have time.
Jim please give us some clarification, like stopping distances averaged over
several stops with and without the reaction arms.
Don't get me wrong I am a huge fan of the reaction arm system,
just looking for some clarification.
Thanks
Marsh Wilkes
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| Re: [GMCnet] Math Question [message #196453 is a reply to message #196444] |
Fri, 25 January 2013 13:44  |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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I'm glad you posted this, because the numbers didn't make sense to me, either. Stopping ANY motor vehicle from 45mph in 32 feet would generally require hitting something heavy.  At the very least, stopping in that distance would almost invariably result into the cars behind you piling into your rear bumper.
It's hard to tell from the video, but the "after" video (the one with the reaction arm installed) seems to indicate a stopping distance of about 85 feet, unless I'm missing something. And I could BE missing something, and my last intent is to rain on a great vendor's parade...
Here is how I came to my conclusion... it's hard to tell exactly when the braking starts, but it's obviously happening when the rear of the air bag can be seen expanding toward the rear wheel well. I counted the wheel revolutions after this happened, and got 11 revolutions before a dead stop. Based on a nominal 29.5" tire diameter (which translates into a 92.7" tire circumference), that works out to 1019" of travel, or about 85 feet.
Now the thing is, 85 feet is OUTSTANDING, and about as good as you're likely to get from ANY "normal" passenger vehicle, assuming it has a coefficient of friction to the road of an optimal 0.8. And it's a heck of a lot better than the braking of my GMC, to be sure.
I hope the video can be reworked to include real numbers, so it would be easier to make a judgment as to the performance of the system...
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] Math Question [message #196460 is a reply to message #196453] |
Fri, 25 January 2013 14:59 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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| habbyguy wrote on Fri, 25 January 2013 12:44 |
I'm glad you posted this, because the numbers didn't make sense to me, either. Stopping ANY motor vehicle from 45mph in 32 feet would generally require hitting something heavy. At the very least, stopping in that distance would almost invariably result into the cars behind you piling into your rear bumper.
It's hard to tell from the video, but the "after" video (the one with the reaction arm installed) seems to indicate a stopping distance of about 85 feet, unless I'm missing something. And I could BE missing something, and my last intent is to rain on a great vendor's parade...
Here is how I came to my conclusion... it's hard to tell exactly when the braking starts, but it's obviously happening when the rear of the air bag can be seen expanding toward the rear wheel well. I counted the wheel revolutions after this happened, and got 11 revolutions before a dead stop. Based on a nominal 29.5" tire diameter (which translates into a 92.7" tire circumference), that works out to 1019" of travel, or about 85 feet.
Now the thing is, 85 feet is OUTSTANDING, and about as good as you're likely to get from ANY "normal" passenger vehicle, assuming it has a coefficient of friction to the road of an optimal 0.8. And it's a heck of a lot better than the braking of my GMC, to be sure.
I hope the video can be reworked to include real numbers, so it would be easier to make a judgment as to the performance of the system...
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I agree, those numbers don't make sense.
Here is a link to one of Rick Flanagan's cad drawings of the Chuck Aulgur system:
http://www.gmcmhphotos.com/photos/cad-photos/p34215-swaybar-reaction-arm-combo-10.html
Read the caption. These numbers are what convinced me to go this route on my coach. The braking is outstanding and so is the quality of the kit. I truly have 'car like braking' on my coach along with the others who have done this conversion.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] Math Question [message #196465 is a reply to message #196463] |
Fri, 25 January 2013 16:11 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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| WD0AFQ wrote on Fri, 25 January 2013 14:54 |
As I have mentioned many times, our coach stops like a car now.
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I'm sure that's the case. It's just that 85 feet stopping distance from 45mph IS "stopping like a car", and one that has great brakes, great tires, and well-tuned brakes.
32 feet isn't even close to reality. I suspect someone just slipped a digit when doing the calculations somehow (forgot to multiply the diameter of the tire by pi?).
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] MATH QUESTION [message #196707 is a reply to message #196444] |
Mon, 28 January 2013 20:15 |
KB
Messages: 1262
Registered: September 2009
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wow, I'd dearly love to see that presentation. Do you know if it's available anywhere
for those of us who weren't lucky enough to be at Amana??
thanks
Karen
1973 23'
1975 26'
> As for me, I don't care much about the posted video.
> The presentation that they put up at Amana made it for me.
>
> That one was not just video, he had graphs that were the output for the accelerometers he had attached to the coach with brake event and ground speed traces. That data clearly indicated an improvement of 0.1G......
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] Math Question [message #196722 is a reply to message #196463] |
Mon, 28 January 2013 22:05 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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| WD0AFQ wrote on Fri, 25 January 2013 15:54 |
snip---
Now, I am using the disc version and don't need the arm that much. But, when I hit that brake it will stop on a dime and give me back a nickle. The drum version can not stop as fast as mine, I am sure,
snip---
Dan
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My understanding is drum brakes are better for ONE stop. then they are done. Drums have a self energizing effect, the act of stopping makes them dig in and stop harder. Disk brakes cool better so can stop a second time...
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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