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Old 03-05-2014, 03:20 PM   #29
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As a fire department volunteer I had the opportunity to take one of our large Spartan fire trucks onto a skid pad. We would drive 35 miles an hour at an instructor. As his eyes were getting bigger and bigger he would give a signal as to which way we were supposed to go !
You could not hit your brakes! Some dramatic wet turns and a couple of skids but never turned one over. Learned the limits of the equipment. Never lost an instructor either.
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Old 03-05-2014, 05:55 PM   #30
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I agree with the drive assertively. As any vehicle is approaching there are three types of drivers.

1- cognizant - those that are aware and know the drill

2- distracted - texters, those with tunnel view or think they are the only people on the planet

3 confused - those who approach the situation as though it the first time this has ever happened.

A good signal- eye contact - and assertive action wins the day for all.
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Old 03-05-2014, 06:00 PM   #31
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Sorry, NO. If you have a newer version, good for you. However, there are lots of older motorhomes on the road without ABS. My '99 TREK doesn't.

Quote:
Originally Posted by H. Miller View Post
...And of course most any MH still on the road has ABS........
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Old 03-05-2014, 06:54 PM   #32
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Originally Posted by PushedAround View Post
Thanks for the info so far, and for the cautionary advice, but as we all know you can only do so much if a squirrel cuts into your braking area when you are already stopping with some vigor. Being prepared gives you that much more of a safety margin, and my goal is to know just how much margin I have. In the car, I know if I can stop or if I have to swerve. I want to know the same thing in my MH.
Lots of interesting comments to your question. I come from professional motor sports and I am on my 9th hauler. Every day on the road I watch people drive or worse see the accidents they get into and wonder why it is so easy to get a license. When some one says they want to know the limits of a vehicle, I have to say that is a smart driver. Obviously taking it easy is the best bet, but what happens as you get used to the rig, you get more confident, until you have a close call. That teaches you more about your limits, that is, if you survive the close call. As I think most that replied were trying to say, is it is a hard limit to learn. You just have to try testing some of those limits. I drive in the dry, wet and snow (so hard on the coach) and found the two coaches I have now really behave very different on each condition. Mainly in braking. For sure you do not have more traction that braking power. You can lock it up any anything if you brake hard enough. I do suggest you practice braking to learn more of the limit. Now hitting the limit, that can be hard on the coach. I don't know about swerving, that is for sure hard on the coach.

The comments about not swerving for an animal, yeah I think I would not swerve much either as that top heaving sway can get you into trouble. Braking is a better bet to buy time for the animal. To not swerve for a vehicle is a different story to me. I have seen crashed RVs, that is something these just don't do well. Not like the big rigs, these things just fall apart in a crash. One tip, most of the time if people ahead of you (on coming and driving with), start to mess up, often heading to the start of the accident will be the best choice. In a straight line this may not be the case for rear-enders.

I do know that in a slide with one of these class A coaches, if slipper it can still take a lot to get into one, but once it does, it is hard to bring it back unlike a car. You don't want to practice this, unless you do that bus racing in the UK.

In short, I would practice your braking, you can learn a lot about 4 wheel traction from braking. You just need a safe place and different conditions. And you coach setup so it don't break your stuff. No one can answer exactly how much grip, except the one post with the formulas. Interesting to know.

Another thing you can do, is go to some race car driving schools to. I still do this for fun and aways learn more.

Be safe
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Old 03-05-2014, 07:01 PM   #33
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Originally Posted by jmckinley View Post
Truck tires have about 0.7 coefficient of friction on dry pavement and 0.3 on wet asphalt.

Don't worry about brake adjusters, automatic adjustment has been required by law on air brake vehicles since back in the 90's.
True, however they do require greasing the pushrod in the adjuster.

My gut reaction to your post was that a big motor home would fall over before it would slide sideways. Quick calculations based on crude estimate of CG height revealed otherwise.

At 0.7 G cornering (maximum possible with 0.7 tire coefficient):

Overturning moment = G force x CG height x Vehicle weight
0.7 x 4 x 30000 = 84,000 lb ft

Moment resisting overturning = Vehicle weight x Track/2
30,000 x 4 = 120,000 lb ft

Looks like it wouldn't tip until you cornered at 1 G, which the tires won't let you do so you will slide first.

CG height of 4 feet is just a wild guess, but probably in the ballpark. Working backwards, it says that it would take a cg height of 5.71 feet to start to tip at 0.7 G cornering.
Just what my owners manual states.
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Old 03-05-2014, 07:03 PM   #34
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ah Ok, still good information. Perhaps I should look at those manuals more. Thanks.
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Old 03-05-2014, 07:21 PM   #35
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In driver's ed they taught me that an average car with average tires on an average clear dry paved road would skid 22 feet at 20 mph (And the speed to skid ratio is Skid - (Speed/10)*(Speed/10)*5.5 feet buy the way.

Of course, few roads are average so that distance is approximate.

Now, what happens when instead of a 2600 pound car you have a 26000 pound motor home?

Same figures exactly.. You see the stopping force is porportional to the weight of the vehicle,, So you up the mass of the vehicle by 10, you increase the stopping power by 10 (This is in an ALL WHEEL Skid)

Thus it boils down to just two variables

One is the coefficient of friction for that stretch of road.
And of course that old Speed--Squared.

NOTE that tire condition is NOT a factor.. Nor is number of tires, or size (This is on clear dry pavement) in "Bad conditions" tire condition may count.

NOW: the big problem is folks tow a car without a braking system

Now we have added to the "Mass" and thus to the kenetic enegery of the consist.. BUt we have NOT added to the stopping power of the motor home's brakes and tires. 22 feet can quickly become closer to 30 (recall this is at 20 MPH and if we triple that, 30 times 9 is 270

(22 times nine is 202) that, is over a consist length more skid.
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Old 03-05-2014, 07:29 PM   #36
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In driver's ed they taught me that an average car with average tires on an average clear dry paved road would skid 22 feet at 20 mph (And the speed to skid ratio is Skid - (Speed/10)*(Speed/10)*5.5 feet buy the way.

Of course, few roads are average so that distance is approximate.

Now, what happens when instead of a 2600 pound car you have a 26000 pound motor home?

Same figures exactly.. You see the stopping force is porportional to the weight of the vehicle,, So you up the mass of the vehicle by 10, you increase the stopping power by 10 (This is in an ALL WHEEL Skid)

Thus it boils down to just two variables

One is the coefficient of friction for that stretch of road.
And of course that old Speed--Squared.

NOTE that tire condition is NOT a factor.. Nor is number of tires, or size (This is on clear dry pavement) in "Bad conditions" tire condition may count.

NOW: the big problem is folks tow a car without a braking system

Now we have added to the "Mass" and thus to the kenetic enegery of the consist.. BUt we have NOT added to the stopping power of the motor home's brakes and tires. 22 feet can quickly become closer to 30 (recall this is at 20 MPH and if we triple that, 30 times 9 is 270

(22 times nine is 202) that, is over a consist length more skid.
Don't skid and you can cut that down by almost half.

wa8yxm, wow, 13,487 posts. That has to be the at least one of the highest numbers I have seen on here. Too bad it wasn't like Youtube, you would be making some good money. Obvious thanks for all the contributions you have put into this forum!!. Thanks
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Old 03-05-2014, 09:09 PM   #37
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"Lock the wheels with ease"? Isn't that what ABS (anti-skid) prevents? And of course most any MH still on the road has ABS........
Quote:
Originally Posted by George Schweikle View Post
Sorry, NO. If you have a newer version, good for you. However, there are lots of older motorhomes on the road without ABS. My '99 TREK doesn't.
correct. My 94 ford doesn't have ABS.
On commercial Trucks and trailer I think all made after 97 have ABS. The 99 School bus I drive has ABS.
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Old 03-06-2014, 07:21 AM   #38
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don't forget every vehicle has a combination gvwr, go over that and you definitely asking for trouble in more ways than one
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Old 03-06-2014, 07:37 AM   #39
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How much grip does it Have????? I Don't think I would want to push that envelope.
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Old 03-06-2014, 07:44 AM   #40
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Old 03-06-2014, 08:01 AM   #41
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Ask this guy

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lol
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Old 03-06-2014, 09:16 AM   #42
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The problem with the question is the original poster used a scenario that the driver of the RV does not have an option. It does not matter how fast you can stop if a vehicle pulls in front of you and slams on the brakes you slam on yours and you either stop in time or you hit them. Does not really matter how much traction your tires have, how good your brakes work, whether or not you have abs, etc. Those are questions you might need answers to when you are making the conscientious decision on how fast to drive, how close to follow etc. Someone pulling in front of you and cutting you off is not something you can plan for and need the characteristics of your vehicle.
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