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Old 11-21-2022, 11:38 AM   #1
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Front Tire Skids

Been wanting to get a discussion on this topic for awhile now. Can't seem to find any existing threads through various searches so starting this new one....


For anyone wondering what I mean by a "Front Tire Skid", here it is. Imagine taking a curve and suddenly the rig wants to go straight rather than actually turn? Yep...sliding towards the outside of the curve because the steer tires are just sliding rather than gripping. Scary stuff.


I've got 2 years and 20,000 miles of trips under my belt with our 18k, 31' Class A rig. I learned my first lesson about front tire skids very early on and posted under the topic of "safe exit speed". The lesson learned was to pay strict attention to posted speed signs for curves. (as opposed to the 5, 10 or even 15 mph faster in a car) Even then I sometimes find the need to go slower than that to feel safely in control.


The second - and much worse - occurrence was last summer on a 2-lane highway curve. There was no posted curve speed but suddenly I was headed across the oncoming lane and towards the shoulder. I fully believed that we were going to end up in the ditch, rolled over on the side. Luckily by hitting the brake and using as much of the road and shoulder as possible I was JUST able to get it through the curve and back into my lane. We were very close to our destination so the next day I went back to the curve in our jeep to review it. The curve seemed to increase severity part way into it. I later contacted the states road planning authority alert them but there have been no other reported incidences there.



My lesson learned is to stop being so reliant on curve speed postings. I now evaluate every curve visually to make my own assessment of speed. The posted curve speeds are generally very helpful, but on 2 lane roads may not be as comprehensive as needed for our big rigs.


I am posting in the hopes to hear others experiences.
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Old 11-21-2022, 11:57 AM   #2
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What you are describing is severe understeer, or "push".
Something is seriously wrong with the balance/setup of your coach.
Think weight balance, tires, suspension, ride height, alignment....I'd definately get your coach checked out by a reputable frame and alignment shop.
What your describing is definately not normal handling characteristics of a class A following posted or recommended speed limits.
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Old 11-21-2022, 12:42 PM   #3
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Locked steering on toad can cause what your experencing.

To much antisway action ( CHF & Sumo springs or air bags ) can cause unloading on the inner front tire as the RV leans into the turn.

Overinflation on the front tires can cause slipping.

Maybe a combination of all of the above.
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Old 11-21-2022, 01:35 PM   #4
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Definitely not normal. Reads like a hydro plane event. I have the same weight class F53 chassis under my rig and the front end has always very sure footed and responsive to steering inputs in all conditions that I have driven in include some pretty heavy rain.

Last time I had the weight checked I was a bit over 6K lbs. up front and a bit over 10K on the rear or about 90% of max capacity for both axles. Tires set to 80psi which gives the tires a slightly higher capacity then my axle limits which puts me slightly over inflated but not by much. Plus the inflation chart doesn't go under 80 psi and best its not to extrapolate out.

Have you done any mods to the suspension as twinboat posted?.
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Old 11-21-2022, 01:58 PM   #5
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Yep. Front end skid is called Understeer and rear end skid is called Oversteer (In NASCAR - Speak, understeer is Push, and oversteer is Loose). In extreme cases the only difference is which end goes through the fence first. Depending on the handling characteristics of a vehicle, either can be experienced by excessive speed in a corner. Race drivers play on the edge of these conditions, but it's not something you want to experience in a motorhome.

As with Visionquest2's situation, braking during an understeer condition can sometimes regain control while braking during oversteer can accelerate the rear end skid

Quote:
Originally Posted by Alpine36 View Post
What you are describing is severe understeer, or "push".
Something is seriously wrong with the balance/setup of your coach.
Think weight balance, tires, suspension, ride height, alignment....I'd definately get your coach checked out by a reputable frame and alignment shop.
What your describing is definately not normal handling characteristics of a class A following posted or recommended speed limits.
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Old 11-21-2022, 02:33 PM   #6
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Something is way way wrong. What you are describing is the same thing I used to experience in emergency towing with smaller tow trucks.

The first thing I would suggest is get yourself loaded out just like you use the rig, then head down to the scales and get all axles weighed. We are also 31 ft on a workhorse chassis, and it is real easy to get yourself overloaded/ or loaded in such a way as to unload the front axle. When I scaled I discover I had to move some tools to rear compartments to reduce front axle weight, but I have 6ft long aftermarket slide that adds a lot of weight up front. In our coach the water tank is all the way aft under the bunk where it has the most effect on the front axle weight. It's easy to forget that water weighs 8.35lb per gallon so a full 75 gallon water tank is 625 lbs +/-, then the further behind the axle the greater the decrease in front axle weight.

We love our "little" gasser "Big Blue", but all the weight limitations are why we need a DP.
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Old 11-21-2022, 04:05 PM   #7
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I agree with replies #2 and #7; the first step is weigh each corner of your MH. The rearrange your load to put the same percentage of GAWR on both rear and front axle.


Next is a total wheel alignment, not just a front end job. The alignment tech will/should closely inspect all the steering components to insure worn/defective parts are replaced prior to total alignment. Usual cost is close to $300 at a HDT repair shop, likely much more at an RV repair shop.
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Old 11-21-2022, 05:59 PM   #8
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Agree you have something wrong going on. Not a great comparison but ,you would of felt it rock pretty severely scaring you to slow down before front tires should be sliding out.
Many on off ramps seem to loose bank right at wrong place but highway curves seem pretty consistent and will have reduced speed limit if it's needed.
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Old 11-21-2022, 09:04 PM   #9
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"I learned my first lesson about front tire skids very early on and posted under the topic of "safe exit speed". The lesson learned was to pay strict attention to posted speed signs for curves. (as opposed to the 5, 10 or even 15 mph faster in a car) Even then I sometimes find the need to go slower than that to feel safely in control."


What the OP refers to, by his own admission, is driving too fast for conditions. Many motorhome owners drive their motorhomes as though they were driving a car. Some learn, by accident, that these are two extremely different vehicles, both in weight, tires and driving characteristics.

Depending upon a posted yellow speed limit sign, or absence thereof, is a recipe for disaster as the OP has stated happened in his two "lessons" described. Sometimes, the amount of skid marks just before a turn are leading indicators that others before you have misjudged the appropriate speed for a particular corner.

It took extraordinary luck to have avoided disaster in the second example of going straight through a turn, crossing the oncoming lane and barely escaping going over the edge, before regaining control and returning to correct lane of travel. Be happy that you survived that and forget winning the lottery; that was your lottery win.

Drivers really need to pay attention and drive according to conditions. I would suggest that the OP's motorhome suspension, "not likely suited for competition driving", outperformed the driver performance, to have gotten through a very dangerous situation, and was likely what saved the OP from a very serious accident, thankfully not involving an oncoming driver.

On cornering, a quote from famous race car driver Sterling Moss states, "Go in slow and come out fast; go in fast and come out dead."
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Old 11-22-2022, 12:33 PM   #10
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Agree the OP was sometimes too fast for conditions, but part of the "conditions" is the front end steering/suspension/tires of the coach. He ought to be able to go into curves at the posted speed - they are intentionally conservative to allow for larger vehicles, poor quality front-ends, and inexperienced drivers. Yet he experiences a severe handling problem (understeer).


The advice given is all good. Start the investigation with the simpler things, e.g. weigh-in, tire pressure optimal, verify the tires are in fact steer-axle tire and have a highway use tread pattern, and have the front end checked out and aligned. Once you know everything is up to par, [carefully] see how it handles.
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Old 11-22-2022, 01:55 PM   #11
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This is an informative bit of information about understeer and why it is inherent in all vehicles, quoted from:

CAT DRIVER TRAINING (UK)
An approved/accredited Ford Motor Company driver training & assessment provider


WHY DOES MY CAR INHERENTLY UNDERSTEER THROUGH A CORNER ON CIRCUIT?

It is a safety issue. Manufacturers irrespective of the configuration and drive train layout of the vehicle, tune understeer into a vehicles platform as it is safer. It is less complex to correct than oversteer - itís correction is instinctive: ease out of the gas pedal and the understeer will reduce. For the general public and the untrained driver it reduces the risk of a crash. Oversteer correction is a complex process requiring timely and accurate counter steering input from the driver. It is a skill that needs practice and often tuition to perfect. When faced with a dangerous driving scenario, oversteer correction is not as instinctive as simply reducing your foot pressure on the gas pedal to reduce understeer.
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Old 11-22-2022, 02:07 PM   #12
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You may be a bit light on the front end. Also, those yellow signs are for cars. SLOW DOWN.
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Old 11-22-2022, 02:34 PM   #13
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We find the speed on signs with our motor home to be spot on for the max speed. Anything greater and we start to feel top heavy. We drive more like a Class A truck with our MH. With our autos we push the turn recommended speeds by 5-8 mph anything greater we ware the outside treads on the tires.
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Old 11-22-2022, 04:40 PM   #14
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All - thanks for the responses. I'm not hearing anyone sharing any similar experiences which I guess is a good thing!



Alpine - Its a 2020 rig with a 2019 F53 chassis. First thing I had done when bought in Jan 2021 was a front end alignment and complete tire check. The rig had 6k miles on it when purchased.



Twinboat - I was towing a wrangler though I have no suspicions of non-responsive steering while being towed. I run anywhere from 82 to 90psi in the steer tires though only need 82 so I will adjust those in the future. (I tend to start at 82 in late spring and let the tire pressure go where it will up to 90psi. If it gets so hot in the mornings that its higher than 90 I let air out.) However...the wear pattern on those steer tires is more indicative of under inflation - equally on both tires. I have the CHF front and rear but stock shocks/springs. I suppose unloading of the inner steer tire could be a factor. 2019 F53 chassis.


Sweetbriar - I'll admit to running just a bit over weight specs at 6300# front (7k max rated) and 11800# on rear axle. This rig has tons of storage space but very little CCC so its easy to load up to the max. Its just my wife and I and two medium sized dogs. I'd like to move weight forward but there's no good way to do so with the arrangement of storage spaces both inside and out.



Ray - what is an all-wheel alignment? This rig is only 2+ years old. Each time I take it in for an oil change I ask the service department to give the front end a once-over inspection. No issues to date.


Sherpa Vern - "Go in slow and come out fast; go in fast and come out dead." Words to live by...literally!


As for tires, the rig has Goodyear G670 245/70R19.5 Load range G all around.
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