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#1
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Tire Stiffness & trailer swaying
Several people have had good luck towing a glider with a Subaru
Forester. I do not know why mine is different. I just bought a 2004 Forester tried to tow with it. Mine is a nightmare. It is unstable above 50mph. It has a lot of side to side sway above 50mph if there is any steering input. It is almost harmonic in nature – it does not dampen out quickly. If feels like you are driving on Jello. It feels like the problem is much more the tires than the suspension. Though that is hard to prove. Even when parked if you push on the hitch with your foot the Forester will sway side to side [right and left] a lot. You can watch the rim move right and left in and out of the tire. I think the sidewalls are just really weak. The tread is probably relatively soft also. The Forester's tires are Yokohama Geolander G900 P215/60 R16 94H. Even in normal driving the steering response and cornering are poor. [Other Foresters may be equipped with 15" tires, and other models of Geolander tires – rather than the G900]. My Mazda MX-6 [much lower car] has Pirelli P4000 P205/55 R15 87H – it is stable, and if you push sideways it does not sway side to side anywhere near the degree that the Forester does. Steering response and cornering are good. The Geolander G900 has a tall soft sidewall, it is 4.500" above the rim rather than 3.625" for the P4000 [24%higher]. My best idea right now is to change to a shorter and stiffer sidewall tire. I am considering changing from P215/60 R16 94H - an "H" rate tire with 60% width/height ratio, to Bridgestone Turanza LS-V 225/50R16 92V - this is a V rate tire so the sidewall is stiffer and at a 50 or 55 ratio it is shorter. This is the V rated version of the tire that some other Forester owners have [LS-H]. The tread should also be a harder sports car like compound. Some of these tires are rated and discussed on www.tirerack.com. It seems that Steering response and cornering stability are good expressions of my issue. On tirerack there are a mass of good comments on the Turanza tire – though I doubt anyone is towing. As far as I can tell everyone on "tirerack" hates the geolander 900 like on mine. Does anyone else have any Experience changing to a shorter V rated tire for better stability? My trailer does great and stable to 85+mph behind my Mazda MX-6, so I do not think it is the trailer. The trailer is a 1979 Komet with a Mosquito. It weighs ~1800lbs [816kg]. The tongue weight is 153lbs [69kg]. The Forester's manual says to keep the tongue weight between 8-11% of the trailer. 8%=144lbs [65kg] 11%=198lbs [90kg]. [the max allowed is 200lbs on the tongue] The manual transmission version of the Forester is rated for 2400lbs [1088kg] towing capacity. I have already tried raising the tire pressure on the rear tires to 41psi [2.8bar] as recommended by the manual. The trailer tires are about 40psi. Chris Ruf |
#2
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"chris" wrote in message om... Several people have had good luck towing a glider with a Subaru Forester. I do not know why mine is different. I just bought a 2004 Forester tried to tow with it. Mine is a nightmare. It is unstable above 50mph. It has a lot of side to side sway above 50mph if there is any steering input. It is almost harmonic in nature - it does not dampen out quickly. If feels like you are driving on Jello. It feels like the problem is much more the tires than the suspension. Though that is hard to prove. Even when parked if you push on the hitch with your foot the Forester will sway side to side [right and left] a lot. You can watch the rim move right and left in and out of the tire. I think the sidewalls are just really weak. The tread is probably relatively soft also. The Forester's tires are Yokohama Geolander G900 P215/60 R16 94H. Even in normal driving the steering response and cornering are poor. [Other Foresters may be equipped with 15" tires, and other models of Geolander tires - rather than the G900]. My Mazda MX-6 [much lower car] has Pirelli P4000 P205/55 R15 87H - it is stable, and if you push sideways it does not sway side to side anywhere near the degree that the Forester does. Steering response and cornering are good. The Geolander G900 has a tall soft sidewall, it is 4.500" above the rim rather than 3.625" for the P4000 [24%higher]. My best idea right now is to change to a shorter and stiffer sidewall tire. I am considering changing from P215/60 R16 94H - an "H" rate tire with 60% width/height ratio, to Bridgestone Turanza LS-V 225/50R16 92V - this is a V rate tire so the sidewall is stiffer and at a 50 or 55 ratio it is shorter. This is the V rated version of the tire that some other Forester owners have [LS-H]. The tread should also be a harder sports car like compound. Some of these tires are rated and discussed on www.tirerack.com. It seems that Steering response and cornering stability are good expressions of my issue. On tirerack there are a mass of good comments on the Turanza tire - though I doubt anyone is towing. As far as I can tell everyone on "tirerack" hates the geolander 900 like on mine. Does anyone else have any Experience changing to a shorter V rated tire for better stability? My trailer does great and stable to 85+mph behind my Mazda MX-6, so I do not think it is the trailer. The trailer is a 1979 Komet with a Mosquito. It weighs ~1800lbs [816kg]. The tongue weight is 153lbs [69kg]. The Forester's manual says to keep the tongue weight between 8-11% of the trailer. 8%=144lbs [65kg] 11%=198lbs [90kg]. [the max allowed is 200lbs on the tongue] The manual transmission version of the Forester is rated for 2400lbs [1088kg] towing capacity. I have already tried raising the tire pressure on the rear tires to 41psi [2.8bar] as recommended by the manual. The trailer tires are about 40psi. Chris Ruf You're right that tow vehicles often get overlooked when trailer sway is an issue. You can increase the stiffness of a tire a lot by just increasing the air pressure. Try adding another 10PSI to the normal inflation pressure and see what happens. If that helps, sidewall stiffness is likely to be the problem - if not, the problem may be elsewhere. There is another issue with SUV's suspensions that are intended for real offroad operation. Often roll stiffness is greatly reduced compared to normal passenger vehicles to minimize the neck-snapping side-to-side motion on rough trails. This softer roll compliance combined with a higher CG also means that trailer sway will induce a side-to-side rolling motion in the SUV that, in turn, augments the trailer sway in a nasty feedback loop. The fix is to replace the wimpy rear sway bar with a stiffer aftermarket one from a company like Addco. Depending on the vehicle, you may also want to replace the soft rubber sway bar bushings with a harder material like urethane. The penalty for this modification is that the ride will be less comfortable on rough surfaces. Bill Daniels |
#3
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"chris" wrote in message om... The Forester's tires are Yokohama Geolander G900 P215/60 R16 94H. Even in normal driving the steering response and cornering are poor. [Other Foresters may be equipped with 15" tires, and other models of Geolander tires - rather than the G900]. Chris. My Tahoe on Geolanders (nice tire) handles very poorly at less than 44 psi all 4 corners. This is a truck rated tire and very succeptable to underfilled type of problems. The symptoms sound like low tire pressure. First, have a tire shop check the pressures. THEN use your gauge to make sure it is in the ballpark. I've seen cheapo gauges read way off after being dropped, not to mention not being very close to begin with. Does your hitch have sufficient drop. If you are using the same reciever/ball you probably need to change top a lower dropped unit. If the ball is too high and the trailer is appreciably "nose up" they seem to want to oscillate back and forth without much provocation. Just thiinking out loud................ Scott Correa |
#4
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Since my original write up I have learned the following: The dealer told me that the 2004 model is the first to be equipped with the Geolander G900 tires, previous years had a different model tire. This is the only change to the suspension that he is aware of between the 2003 and 2004 model. The Maximum tire pressure on the tires is 44psi, so I upped the rear pressure to 44psi and the fronts to 41. [for towing the manual says 29psi front, 41psi rear]. I also changed the hitch from a straight one to a "drop hitch" it is now 1.5" lower than the straight one. The drop hitch is about 4.0" shorter than the "lift hitch" [bent receiver hitch] that I originally tried. The hitch ball is on a short receiver. A test drive showed that the lower hitch/ball placement and the higher tire pressures are an improvement. However still not acceptable. I think the higher pressure stiffened the tires but not enough and the tread is still too soft. I have heard another Forester owner has had good luck with 75-100lbs of tongue weight. An additional test drive was done after I moved several items out of the front of the trailer to the back of the Forester. This reduced the tongue weight to 118lbs [down 35lbs from 153]. The swaying seemed worse with the lower tongue weight. [This follows the logic I have heard many times]. Chris Ruf |
#5
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I don't know how long it does take for certain people
to recognise, that SUV's and 4-wheel drive cars - are built for use in the outback and not for driving in towns - have a high CG and are handling worse on windy roads than any normal cars with good suspension (European/Japan cars) - have big tires to suit off road driving, which are worse on normal roads, worse than normal or low profile tires. - often do not have independent side stable suspension on the back which give them bad side stability (push the car sideways on the rear bumper and let it go - if the hole car swings around the vertical yaw axis then it does not suit towing) - have bad aerodynamics and produce more turbulence behind, which has again bad influence on the trailers stability. Conclusions: Quite any car is better for towing, in handling and safety than a SUV. I prefer to rent a 4-wheel drive for holiday in the outback, own a small car with common rail turbo diesel engine (2000 ccm, 110kW, 250Nm at 1750 rpm, and 4.5 to 6 liters per 100km consumption). Like that I can pay many tows with the saved money I do not spend on petrol. I can tow any trailer with brakes up to 1500kg stable with 100km/. And on a windy road the SUV just disappear in the rear mirror. But I cannot compete offroad with these monsters. I don't mind because I only need offroad function perhaps 7 days a year. How often do you need offroad capability? Think of it when you buy the next car. Chris "chris" wrote in message om... Several people have had good luck towing a glider with a Subaru Forester. My Mazda MX-6 [much lower car] has Pirelli P4000 P205/55 R15 87H - it is stable, and if you push sideways it does not sway side to side anywhere near the degree that the Forester does. Steering response and cornering are good. Chris Ruf |
#6
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Heresy! Devil out, be gone.
You are preaching to the 'hit it with a bigger sledgehammer' mob here lad. If it aint got 5 litres of V8 petrol engine and 200kgs of tongue weight it aint right! :-) Ian - 2300cc ( petrol I will admit ) Ford MPV and about 53 kgs tongue weight a proven 100mph combination! "CH" wrote in message ... I don't know how long it does take for certain people to recognise, that SUV's and 4-wheel drive cars - are built for use in the outback and not for driving in towns - have a high CG and are handling worse on windy roads than any normal cars with good suspension (European/Japan cars) - have big tires to suit off road driving, which are worse on normal roads, worse than normal or low profile tires. - often do not have independent side stable suspension on the back which give them bad side stability (push the car sideways on the rear bumper and let it go - if the hole car swings around the vertical yaw axis then it does not suit towing) - have bad aerodynamics and produce more turbulence behind, which has again bad influence on the trailers stability. Conclusions: Quite any car is better for towing, in handling and safety than a SUV. I prefer to rent a 4-wheel drive for holiday in the outback, own a small car with common rail turbo diesel engine (2000 ccm, 110kW, 250Nm at 1750 rpm, and 4.5 to 6 liters per 100km consumption). Like that I can pay many tows with the saved money I do not spend on petrol. I can tow any trailer with brakes up to 1500kg stable with 100km/. And on a windy road the SUV just disappear in the rear mirror. But I cannot compete offroad with these monsters. I don't mind because I only need offroad function perhaps 7 days a year. How often do you need offroad capability? Think of it when you buy the next car. Chris "chris" wrote in message om... Several people have had good luck towing a glider with a Subaru Forester. My Mazda MX-6 [much lower car] has Pirelli P4000 P205/55 R15 87H - it is stable, and if you push sideways it does not sway side to side anywhere near the degree that the Forester does. Steering response and cornering are good. Chris Ruf |
#7
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Not all SUVs are created equal (I won't get into all-wheel-drive cars,
many of which are *not* designed for offroad use). My Jeep Liberty is nicely sized for my purposes. I had a landout last year in a freshly plowed field. Nothing but a very off-road-capable 4WD vehicle could have performed the retrieve. I was sure glad I had the Jeep! Then there are the cars I've pulled out of ditches with it during the winter. But you are right about the issues with high CG, off-road tires, etc. Anyone who drives such an SUV like a sports car is a fool. -Doug "CH" wrote in message ... I don't know how long it does take for certain people to recognise, that SUV's and 4-wheel drive cars - are built for use in the outback and not for driving in towns - have a high CG and are handling worse on windy roads than any normal cars with good suspension (European/Japan cars) - have big tires to suit off road driving, which are worse on normal roads, worse than normal or low profile tires. - often do not have independent side stable suspension on the back which give them bad side stability (push the car sideways on the rear bumper and let it go - if the hole car swings around the vertical yaw axis then it does not suit towing) - have bad aerodynamics and produce more turbulence behind, which has again bad influence on the trailers stability. Conclusions: Quite any car is better for towing, in handling and safety than a SUV. I prefer to rent a 4-wheel drive for holiday in the outback, own a small car with common rail turbo diesel engine (2000 ccm, 110kW, 250Nm at 1750 rpm, and 4.5 to 6 liters per 100km consumption). Like that I can pay many tows with the saved money I do not spend on petrol. I can tow any trailer with brakes up to 1500kg stable with 100km/. And on a windy road the SUV just disappear in the rear mirror. But I cannot compete offroad with these monsters. I don't mind because I only need offroad function perhaps 7 days a year. How often do you need offroad capability? Think of it when you buy the next car. Chris |
#8
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"GeorgeB" wrote in message ... On Fri, 26 Sep 2003 03:04:36 GMT, "Chris Ruf" wrote: The Maximum tire pressure on the tires is 44psi, so I upped the rear pressure to 44psi and the fronts to 41. [for towing the manual says 29psi front, 41psi rear]. Generally, you don't want to harden up the fronts ... the sideways force from the hitch doesn't generate much torque to bother them. Hard fronts, even not pulling a trailer, often cause high steering sensitivity. Tongue weight lightens the load on them. That is one of the reasons for a weight-distributing hitch. Be careful here to understand the four wheel drive system in your vehicle. (I think the Subaru uses a central differential and not a viscous coupling for its full-time 4WD.) However, any full-time 4WD vehicle will suffer very expensive damage to the transfer case if the front and rear axles turn at different speeds for an extended time as they would with different tire pressures. My Jeep uses and central viscous coupling instead of a center differential so all four tires must always be the same diameter else very expensive repairs are in the offing. Bill Daniels |
#9
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"tango4" s comments read:
Ian - 2300cc ( petrol I will admit ) Ford MPV and about 53 kgs tongue weight a proven 100mph combination! Ian a proven TINSFOS man Tim - Peugeot 106 1100cc A legal 60mph combination -- Tim - ASW20CL "20" |
#10
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I guess the "Ariana Wussies" have hit this forum - even if they aren't from
the US Give me a break, there are so-called SUVs that can blow the doors off of anything less than a new Ferrari and out corner anything built in Japan. In fact, I'll take my two wheel drive pickup truck and challenge you in whatever 1000 cc turkey you drive and race you an any road, any track, anywhere and drub you soundly - and I'll drub you in a straightaway towing a 2000# load. And, yes folks, I really can do it! If you want to push this BS, go to Green Peace. Drive what you want where and when you want. The other responses to this thread were on point, what will make his vehicle handle better while towing. Please get with it. Let the games begin! ADP "CH" wrote in message ... I don't know how long it does take for certain people to recognise, that SUV's and 4-wheel drive cars - are built for use in the outback and not for driving in towns - have a high CG and are handling worse on windy roads than any normal cars with good suspension (European/Japan cars) - have big tires to suit off road driving, which are worse on normal roads, worse than normal or low profile tires. - often do not have independent side stable suspension on the back which give them bad side stability (push the car sideways on the rear bumper and let it go - if the hole car swings around the vertical yaw axis then it does not suit towing) - have bad aerodynamics and produce more turbulence behind, which has again bad influence on the trailers stability. Conclusions: Quite any car is better for towing, in handling and safety than a SUV. |
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