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Comments
However, the differentials should not care too much. Since that is what they do when cornering, provide one wheel the ability to travel further/faster...so as long as you don't have TOD engaged, slippage shouldn't be detected, and no problems driving down the highway...no limping along. I think if your tire difference is more than a 1/4"-1/2" difference, you may want to think twice before you engage TOD on dry pavement.
Think about it. Distance between the center of the wheel and the ground is all that matters in terms of determining distance travelled per revolution. I may not be explaining this very well, but I'm confident that it is correct.
I don't think so. Imagine a scenario where you could deform the tire in such a way that its shape resembles that of a tank tread - flat on top and bottom with rounded ends and having the exact same circumference as a rigid circular tire. The distance travelled in one revolution will be the same in both instances while the height of the center above the ground for the two cases will be quite different.
tidester, host
Very thought provoking topic.
If you inflate a basketball, or a tire, to a higher pressure, it's actual circumference will increase.
-mike
I was making the case that the height of the center of the tire above the ground is not in itself sufficient to draw the conclusion that the height is the sole determining factor in distance travelled between full revolutions. I.e., you'll need a better argument! :-)
tidester, host
..
I think the best approximation is to use the rim forcing the circumference around once per revolution, and since a few psi of tire pressure is not going to expand two steel belts, the distance per revolution should remain relatively contant with changes in inflation.
IMHO the truth is that a tire is more likely to "stick" to the ground and in the process roll over its total footprint or circumference when it is slightly deflated. On the other hand a more highly inflated tire will "slip" more (look at tires on the snow, ice and rain - if you run a tire specified for 30 PSI at say 36 PSI that tire is more likely to spin when the accelerator is floored). Likewise when you try to push a car with a flat - you get nowhere due to the greatly increased resistance. So, given these fatcs, if you delate the bigger tire to the point that it really grabs or sticks to the ground it will make as many turns as necessary to complete a full rotation (full footprint) since essentially it can't slip. On the otherhand, maybe the tire on the other side an be "induced" to slip by over inflating it, thus eliminating the stress on the LSD. If it is slippery out, this would even more likely to occur.
I know it's a way-out concept, but the idea that only the diameter matters is way out too.
It is the stiff belt under the tread that keeps the rolling footprint constant on modern radials. On many trailer and lawn tractor tire that are not belted, then the delation of the tire would reduce its footprint.
Anyway, discussions are fun!
-mike
There. Seem more like other discussion groups now?
Regards,
Yes, it sure is nice to see differing viewpoints presented without flaming or name-calling. There have been so many different explanations given, I don't even know how many 'sides' there are to this discussion, let alone what each of them is trying to say. But it has been interesting to read!
They have donut spares on subarus, and they have LSDs. On top of it their 4EAT AWD systems is very similar to TOD and the guys over there are quite knowledgeable.
So get off your high horse if some of them happen to give some GOOD input!
-mike
If the casing on the tire could retain a true circle shape (no flat spot,no contact patch) regardless of air pressure, then we could talk about radius and how it affects circumference. But tires on vehicle have that flat spot at the bottom, the contact patch. The contact patch gets longer with lower air pressure. The contact patch is not just a point on the tire like other points. It is long and the leading edge must pass along the ground until it becomes the trailing edge - just like a tank track.
The fact that a tire rotates around a center gives it the illusion of being a circle. The tank track gives no such illusion, but I believe they have a great deal in common, as far as how far the vehicle will travel with each complete revolution.
I believe, the only way to significantly change the distance traveled per revolution would be to have a casing, specifically in the tread area, the could expand and contract easily. As has been noted, modern tires have steel cord construction that I don't think will allow this sort of distortion, even at exceeding low, even no, pressure.
The centrifugal force exerted on the outer area of a tire at highway speeds is huge. Yet, the tire does not change it shape significantly. If it did, you would wear out the center of the tread in a heart beat, as that's what you would riding on at speed.
Go out and measure (circumference or radius) of your spare tire fully inflated. Then, lower the air pressure way down. I doubt that you will see any signifcant change in those measurements. The casing is just to strong.
Very funny tkevinblank.
Gprodick, even at highway speeds, I don't think centrifugal force is sufficient to "expand" a tire to overcome low tire pressure. Why do tires get hot even at highway speeds even when underinflated? Because they are flexing/deforming more around the contact patch. Also, your suggestion about measuring the spare is not relevant since the spare has no load on it and is not rotating.
Despite all the interesting posts, nobody has convinced me that I'm incorrect. However, it also seems that I have also not convinced many of you that I'm correct either.
I propose a simple experiment for somebody with a few spare minutes. Take a bicycle with fat tires. Inflate them hard. Mark a point on one wheel and a starting point on the ground. Roll forward a few wheel revolutions. Mark the end point on the ground. Measure the distance travelled. Then lower the tire pressure so that you can see visible deformation at the contact patch. Repeat the test with the same number of wheel revolutions. You should see that the distance travelled is less when the tire is underinflated.
sbcooke, since you seem to be thinking that Trooper tires are different than Subaru tires or bicycle tires, you can perform this test using a Trooper.
I think that doing it on the vehicle will be much more accurate than using a bicycle tire. If somebody has a piece of chalk and access to a compressor, it would be easy to check. Make the exact bottom of the tire and the point that it contacts the pavement. Roll forward exactly one revolution and mark the pavement again. Lower the air pressure down to a 10 or 15 pounds, or whatever, and roll forward another revolution and mark the pavement. Measure the two distances. End of discussion!
Maybe we don't want to do that,however, as it's more fun talking about it.
If the diameter was always the same wouldn't it feel like riding on wagon wheels?
-mike
Otherwise, you won't hear from me;)
Here's one for you. The derivation of the word "tire". It was the band at the outside of the wheel that tied all its parts together... hence, tyer, tyre, tire.
There's so much of this crap in my head that I can't get the circumference/diameter argument in there...
I understand what you're saying. My point is that it isn't necessarily true! Gprodick explained it nicely (#7013).
Gprodick: Maybe we don't want to do that,however, as it's more fun talking about it.
Now why do you want to go and put DATA into the mix?? ;-)
tidester, host
If you air up beyond the standard pressure, doesn't the center of the tire swell and bulge out a little? That would increase the diameter ever so slightly.
So running one tire at 26psi and the other at, say, 40psi, you should probably notice a small difference. Probably not enough to make a 245/60 tire equal a 265/70 tire, though.
But if I got a flat on an axle with an LSD, I'd consider putting the donut or smaller spare on the other axle, with an open differential and more tolerance for differences in diameter.
Just my 2 cents'.
-juice
Does the point that contraction ends fall below the normal psi mark?
If a tire contracts and falls alone in the woods, does anyone hear it?
...which begs the question, how do you know the tire fell? :-)
tidester, host
Took me a few years to realize that my canoe moves towards my paddle while the paddle is mostly stationary in relation to the river bottom.
Lot of zen in here :-)
Steve, Host
And a little Newton too! ;-)
tidester, host
How about this argument? Have you ever checked your tires only to find that one was really low?
On radial tires it's really hard to tell when one is low by looking at it. If it looks low, it's probably really, really low (like 15 pounds or less). I've seen people driving on radials with less than 10 pounds of air pressure and having no awareness of it. Now, you may have driven a lot of miles on that low tire before you realized it was low, unless you are very good about vehicle maintainance. I know this has happened to everybody on this forum. In fact, this happens to millions of people everyday. Most of those will drive a looong ways before they figure it out. Heck, most people rarely check their tires. If this difference in air pressure really made a big difference in effective tire size, everybody and their mother would be at the shop with LSD problems.
The people who don't check their TP on a regular basis are the same people who wouldn't know if their LSD was working or not! If it doesn't work, then you only know when you test it out by spinning the rears in snow or what not.
-mike
I found out that the production of Isuzu Trooper will be extended through 2003. They will be coming out of Isuzu's Laguna plant in the Phillipines and will be supplied to Australia and New Zealand as the Holden Jackaroo, and in South East Asia and Africa as the Isuzu Trooper.
A friend of mine who works in Thailand for Tri-Petch Isuzu confirmed this and so does this industry newsletter in Australia,on page 2 -
http://www.mellor.net/mellor/enews.nsf/edition/B2A31786F0293225CA- - 256C8C0021B019/$file/2002.12.11_enews167.pdf
I'm a bit concerned about the replacement being Daewoo based!
Maybe most LSD's are burned up. Would you normally have a burned up LSD without some sort of obvious symptoms? I mean something that would be so obvious that it would get you to take your vehicle to the shop. Or, does it just, sort of, not work
I know that some on this board have questioned if their LSD was working properly, but is there not something that would be obvious when you have an LSD problems.
My guess is that most LSD units are working pretty well. I've not heard that they are that fragile, but maybe they are.
Nevertheless, I gotta believe that if differences in tire pressure threatened their reliability, there would be all sorts of warnings and disclaimers in your owner's manual. I'm sure that someone is running to find their owner's manual right now. Jeez, I sure hope that such a warning doesn't exist.
At any rate, Paisan, you had better get to bed. It's late back east and tomorrows a work day:) Sweet dreams.
Some sports cars
Subarus
Some SUVs, most it's an option on
There has been a big move to "traction control" devices that use your brakes controlled by a computer to emulate an LSD rather than a true mechanical LSD. Most offroad/performance experts will agree that LSD units need to have their clutches re-built ever 70-100K of normal use.
To most americans they'd never know that the LSD was working or not, these are the soccer moms of the world. Their LSD rarely ever comes into play because they don't use their SUVs for offroading, something like 1-2% at most ever see offroad, and of those i bet 10-20% of that 1-2% see offroad situations where you use the LSD.
As for warnings... It's all up to the lawyers and stats folks to determine how likely it is that someone will break the LSD, and if so how likely they are to complain about it or even notice it's broken, and then actually do something about it.
Just like the Trooper/Jackaroo gets a higher towing capacity outside the US with the same exact product.
I know that having a 1/4 or more difference in circumference will effect the TOD unit and the LSD is similar (except acts left<->right) that same rule would apply to it.
-mike
A few days ago, we were discussing how the TOD functions and how to check its operation. I stated that one could check the SOTF operation by jacking up the front end and rotating the wheels to observe front driveshaft rotation. I should have tested this theory myself before speaking, but I didn't. Therefore, I went out to my Trooper and tested my own theories. To my chagrin, and with a nod to Mike (Paisan) who was correct, it appears that the front driveshaft continues to turn whether TOD is engaged or not.
This is somewhat of a puzzle to me because I now do not understand what SOTF is doing for this vehicle if the front axle shafts are always connected to the front differential, thus turning the front driveshaft. I had presumed that the SOTF was there to disconnect the half-shafts from the front diff, thereby preventing the front DS from rotating when TOD is disengaged to save fuel. Apparently, this is not the case. It is clear that something is engaging and disengaging (besides the TOD clutch) because I can feel the clunk and clearly hear the whine from the chain in the TOD case when TOD is engaged. Conversely, I feel the disengagement in the steering wheel torque and loss of noise. I'm just not sure what SOTF is doing at this point.
Because I am very mechanically inclined, I intend to get to the bottom of this mystery. I encourage those of you who have disassembled the system to describe its function. Eventually, I will take it apart and report my findings back to the group.
I regret the previous false statements and promise to back them up with tests before I speak up.
Tom
-mike
Thanks.
I'm new to the discussion list and will be purchasing a 1998 Trooper S tomorrow. I believe I'm getting a pretty good deal and from what research I've done, these seem to be really good vehicles. Any 1998 owners out there wish to give me heads up on any thing to look for, quirks, etc?
Thanks,
Jeff
When you actuate 4WD, the SOTF engages the left hand wheel and the transfer case engages the output to the front diff.
Serrano...If you lift the front of the car and spin the tyres with TOD/4WD disengaged, the left hand wheel should spin freely while the right hand tyre will have some load on it because it has to turn the rest of the front axle and the driveshaft back to the transfer case. In either case if you spin one tyre, the other shouldn't turn at all.
If you are getting anything else, like spinning one wheel causing the other wheel to spin at an equal speed in the opposite direction, or the left hand wheel causing the driveshaft to the transfer case to turn then the SOTF hasn't disengaged correctly.
That doesn't mean the SOTF is faulty, yet. Make sure you first disengage TOD/4WD when your engine is running as it needs a vacuum source to operate. If you have TOD/4WD engaged before cutting the engine and then disengage it afterwards, there will be no vacuum to operate the SOTF until you start the engine again.
If you have disengaged with the engine running and it still doesn't appear to be disengaged, then I'd check the vacuum hoses first and work back from there.
I hope that made things a little clearer.
Welcome to the fraternity. You will find everyone here very helpful.
Congratulations on the Trooper! You should get may happy miles ouyt of it.
Regards,
savvas
The truck has 42,000 and showed no signs of tranny trouble now or before.
What could be wrong? and is it safe to drive it with flashing lights to the the shop?
Thank
Sam
Just got the service done, Timing Belt, Water Pump, drain all fluids, etc, etc. Bill approached 4 digits!
However nothing other than routine maintenance for 7 years and 121k miles.
I bemoan the death of Isuzu in the US. I for one would have bought Isuzu again if they came up with a stylish SUV no larger than a Trooper with 3 rows, 18+ MPG (Diesel?), and DVD in the rear.
I wish all the same excellent experience I have had with this truck.
Troop' on!
-mike
-mike
Our 1998 S with Performance Package has been pretty much trouble-free through 77k miles.
If you have more questions, feel free to ask.