JimAttrill Posted October 15, 2005 Share Posted October 15, 2005 From the Owner's Manual, page 3: "Anything that improperly causes a difference in individual wheel speeds, such as mismatched tire diameters due to differences in tire wear or tire pressure ... can cause the NoSpin differential to deliver power to only one side of the vehicle ... " This comes with a picture to show how you should measure the diameter of each wheel and adjust tyre pressures to get these equal. However, I think that this reasoning is suspect. What is important regarding wheel speed is not the diameter of the wheel/tyre but the circumference. Tyres of different sizes or wear will alter the circumference whereas unequal loading or pressures will not. If one thinks of a tracked vehicle as an extreme example, the distance from the ground to the centre of the driving wheel will vary, but the length of the track cannot, just as the 'length' of a tyre cannot, especially with the modern steel-belted radials. So a wheel with a deflated tyre will go round at the same speed as a wheel with a tyre at the correct pressure. I am not saying that driving with under-inflated tyres or unequal loading will not affect the steering, but that the effect will not be caused by differential wheel rpm as the wheels will go round at the same speed. I e-mailed Tractech pointing out this error in their manual but never received a reply Quote Link to comment Share on other sites More sharing options...
LR90 Posted October 15, 2005 Share Posted October 15, 2005 From the Owner's Manual, page 3:"Anything that improperly causes a difference in individual wheel speeds, such as mismatched tire diameters due to differences in tire wear or tire pressure ... can cause the NoSpin differential to deliver power to only one side of the vehicle ... " This comes with a picture to show how you should measure the diameter of each wheel and adjust tyre pressures to get these equal. However, I think that this reasoning is suspect. What is important regarding wheel speed is not the diameter of the wheel/tyre but the circumference. Tyres of different sizes or wear will alter the circumference whereas unequal loading or pressures will not. If one thinks of a tracked vehicle as an extreme example, the distance from the ground to the centre of the driving wheel will vary, but the length of the track cannot, just as the 'length' of a tyre cannot, especially with the modern steel-belted radials. So a wheel with a deflated tyre will go round at the same speed as a wheel with a tyre at the correct pressure. I am not saying that driving with under-inflated tyres or unequal loading will not affect the steering, but that the effect will not be caused by differential wheel rpm as the wheels will go round at the same speed. I e-mailed Tractech pointing out this error in their manual but never received a reply Totally agree with you Jim. Take a good radial sand tyre for example, air it well down and it just acts like a tank track. Once revolution equals one circumference of travel (just causes a lot of side wall flex and if it was on the road lost energy from the flexing). Quote Link to comment Share on other sites More sharing options...
john cranfield Posted October 15, 2005 Share Posted October 15, 2005 From the Owner's Manual, page 3:"Anything that improperly causes a difference in individual wheel speeds, such as mismatched tire diameters due to differences in tire wear or tire pressure ... can cause the NoSpin differential to deliver power to only one side of the vehicle ... " This comes with a picture to show how you should measure the diameter of each wheel and adjust tyre pressures to get these equal. However, I think that this reasoning is suspect. What is important regarding wheel speed is not the diameter of the wheel/tyre but the circumference. Tyres of different sizes or wear will alter the circumference whereas unequal loading or pressures will not. If one thinks of a tracked vehicle as an extreme example, the distance from the ground to the centre of the driving wheel will vary, but the length of the track cannot, just as the 'length' of a tyre cannot, especially with the modern steel-belted radials. So a wheel with a deflated tyre will go round at the same speed as a wheel with a tyre at the correct pressure. I am not saying that driving with under-inflated tyres or unequal loading will not affect the steering, but that the effect will not be caused by differential wheel rpm as the wheels will go round at the same speed. I e-mailed Tractech pointing out this error in their manual but never received a reply I'm not sure I agree Jim, Surely the deflated tire has a smaller effective radius and thus a smaller effective circumference. The extra rubber mostly goes sideways causing the extra damaging flex and heat at speed. Now I am no mathmetician and havn't worked it all out on paper but it seems logical. Quote Link to comment Share on other sites More sharing options...
jules Posted October 15, 2005 Share Posted October 15, 2005 John is right If you have 35psi in one back tyre and 20psi in the other the the rim will be sitting a few mil closer to the ground which means the cercunfrance of the wheel has reduced. hens the heat build up and dodgy wear meaning the tyre and rim are fighting against each other and the speed from the other wheel will drag it along. so a auto locker will engadge most of the time which you don't want. I am an eng but can't be bothered to work it out. This is why you should run the same tyres front to back and realy allround although due to axle weight the pressure are often diffrant front to back. Quote Link to comment Share on other sites More sharing options...
LR90 Posted October 15, 2005 Share Posted October 15, 2005 If you have 35psi in one back tyre and 20psi in the other the the rim will be sitting a few mil closer to the ground which means the cercunfrance of the wheel has reduced. hens the heat build up and dodgy wear meaning the tyre and rim are fighting against each other and the speed from the other wheel will drag it along. Sorry Jules but circumference, or at least the length of tread, can not change. You do end up with at a lot of side wall flex (and heat build up) though as it goes from small radius at the bottom to large at the top. Quote Link to comment Share on other sites More sharing options...
wailofthesnail Posted October 15, 2005 Share Posted October 15, 2005 I agree the length of tread cannot vary, but as far as I figure it the effective circumference would be reduced due to the increased footprint of the tyre, Quote Link to comment Share on other sites More sharing options...
Petergg Posted October 15, 2005 Share Posted October 15, 2005 My thoughts are. The radius is what counts the length from ground to center of axle, so if you have one tyre low the radius would be smaller and that wheel would have to turn faster to keep up with the other on same axle or in the case of a diff in the middle the diff would be working all the time, I think it would only lock after the speed difference reaches a pre set amount. If it was a lot and if fitted Traction control would kick in thinking that it had a wheel spinning. Peter Quote Link to comment Share on other sites More sharing options...
Neil Marshall Posted October 15, 2005 Share Posted October 15, 2005 Jim, I'm with the circumference argument - deflating the tyre doesn't change the circumference, it just becomes less of a pure circle [ie it elongates/spreads at the bottom, not the top]. Neil Quote Link to comment Share on other sites More sharing options...
Lara Posted October 15, 2005 Share Posted October 15, 2005 Well if you really want a definitive answer go and try it, I just read these comments and have heard it before. So went to prove the theory. In my workshop a tyre with OD of 30" at 10psi traveled +- 4"less than the same tyre at 30 psi. (with a car weighing about 1.5 tones) I have experienced the same thing on my rolling road, tyre pressure does change the speed / RPM measurement. Remember that tyres are rubber and that they also "grow" at high wheel RPM. Lara. Quote Link to comment Share on other sites More sharing options...
Neil Marshall Posted October 15, 2005 Share Posted October 15, 2005 Well if you really want a definitive answer go and try it,I just read these comments and have heard it before. So went to prove the theory. In my workshop a tyre with OD of 30" at 10psi traveled +- 4"less than the same tyre at 30 psi. (with a car weighing about 1.5 tones) I have experienced the same thing on my rolling road, tyre pressure does change the speed / RPM measurement. Remember that tyres are rubber and that they also "grow" at high wheel RPM. Lara. Oh sh*t, I hate a man who measures things! Neil Quote Link to comment Share on other sites More sharing options...
LR90 Posted October 15, 2005 Share Posted October 15, 2005 Oh sh*t, I hate a man who measures things!Neil Yeh, I'm still in flat earth tyre mode. Still won't believe it till I've gone measured it myself. Lara, I'm not sure how you tested this? A chalk ine across the tread, rotate one turn until the line is in the same place and measure distance travelled? I still can't see how the carcass(sp?) of the tyre can shrink (yes its rubber but well reinforced) at lower pressures. Quote Link to comment Share on other sites More sharing options...
Petergg Posted October 15, 2005 Share Posted October 15, 2005 Yeh, I'm still in flat earth tyre mode. Still won't believe it till I've gone measured it myself.Lara, I'm not sure how you tested this? A chalk ine across the tread, rotate one turn until the line is in the same place and measure distance travelled? I still can't see how the carcass(sp?) of the tyre can shrink (yes its rubber but well reinforced) at lower pressures. Centrifugal force, some cars on drag strips only have 1 gear as the wheel spins faster the tyre grows taller the gear gets taller, the speed increase on strip. Mmmmm Must be a better way to explain!! Peter Quote Link to comment Share on other sites More sharing options...
jules Posted October 16, 2005 Share Posted October 16, 2005 Centrifugal force, some cars on drag strips only have 1 gear as the wheel spins faster the tyre grows taller the gear gets taller, the speed increase on strip. Mmmmm Must be a better way to explain!! Peter That could mean taking Centrifugal force into account at speed there is no such thing as a flat tyre Sorry my bad wording the Diamiter/radius changes not the cercunfrance but in the world of maths if the diamiter chanches so must the cercunfrance but it cant there for heat and dodgy wear and a rotation issue leading to the diff issue IE a blow out at speed on a early 2000 (I think it was) Jeep grand cherokee could produce enough drive train wind up to blow the transmition. fact! so much that it was a racall. Also I will work on my experiance the 90 on the road runs at 30 psi all round just under 2 bar in a comp I will run at 12 psi if you deflat you mormal tyre to 12psi it will bearly lift the rimm off the floor then try to drive down the road with it see were im going with this the side wall and tread are leaving there marks all over the place but also it will quickly try to fold and crumple to release the drag. afect it is having between the rimm and tyre. the wheel is moving faster that the other three or trying to anyway Quote Link to comment Share on other sites More sharing options...
JimAttrill Posted October 16, 2005 Author Share Posted October 16, 2005 I guess I'll have to measure it myself ... I'll let you know whether my results agree with Lara's. I don't think centrifugal force will make much difference to the circumference of Landy tyres. Those drag tyres are designed to 'grow' when immense power is applied through them. I don't think my tdi has that sort of grunt I've lost my little windows converter: what are 10psi and 30psi in bar? Quote Link to comment Share on other sites More sharing options...
jwriyadh Posted October 16, 2005 Share Posted October 16, 2005 10*0.06893 and 30*0.06893 jw Quote Link to comment Share on other sites More sharing options...
jules Posted October 16, 2005 Share Posted October 16, 2005 I think 32 ish psi is about 2 bar Quote Link to comment Share on other sites More sharing options...
JimAttrill Posted October 16, 2005 Author Share Posted October 16, 2005 10*0.06893 and 30*0.06893jw Sorry lost my calculator Quote Link to comment Share on other sites More sharing options...
Daan Posted October 16, 2005 Share Posted October 16, 2005 Jim, With a detroit locker, 1 psi difference in tyre pressure left to right does indeed send you off to one side of the road and gives nasty twangy noises from the diff. This is practical experience from my car. The radius does get smaller with a lower tyrepressure, and although the circumference is the same, there is more slip when the tyre thread arives and leaves the road while the wheels turn. Hope my wording makes any sense to you? Quote Link to comment Share on other sites More sharing options...
John_T Posted October 17, 2005 Share Posted October 17, 2005 The point Tractech were making is valid. If one tyre is bigger than the other (and we seem to be getting to the point where it is proven that an under-inflated tyre is in effect "smaller") the Detroit NoSpin will momentarily disengage on a regular basis. Its normal mode is fully locked and hence Tractech's comment on only driving one axle. This happens when you corner and the outside wheel "unlocks" to allow a differential function. This is also why you should never use a Detroit Locker on a Series Landy with selectable 4 wheel drive. I have driven with a Detroit Locker in my Landy for years and have never had any problem (they very occasionally get confused and give out a "twang" as they settle themselves down). I find that driving in a circle on full lock with the window open is a good way of checking that you have not broken a halfshaft. The diff gives out a regular clicking as it "indexes" (i.e. the cam clutch is forced out to allow the outside wheel to over-run the inner). The instructions come with typical American dire warnings that handling on the over-run in bends can be affected but I have never noticed a problem.....could be if you have different sized tyres!!! Quote Link to comment Share on other sites More sharing options...
ltwt1981 Posted October 17, 2005 Share Posted October 17, 2005 Can you expand on why not use a locker on a series motor? Quote Link to comment Share on other sites More sharing options...
Ex Member Posted October 17, 2005 Share Posted October 17, 2005 Static load radius is all that matters. Measure from the ground to the axles centerline. Inflated circumference has no impact on the rotation of the tyre. The tyre deforms and has a rolling radius/circumference smaller than the unloaded one. Quote Link to comment Share on other sites More sharing options...
nicksmelly Posted October 17, 2005 Share Posted October 17, 2005 I've got a Detroit locker (no spin) in the back of my 90. The instruction manual that came with the diff definatley says not to be used in vehicles with a wheelbase less than 100". This has nothing to do with tyre sizes But... When I push the throttle hard the front end pulls to the left and when I let off the throttle it pulls to the right. It under steers going in to roundabouts at speed then suddenly over steers when the diff releases. It undertseers if you coast round a corner at speed. It clunks, clonks, releases inappropriatley making the vehicle jerk. It's sometimes difficult to release the centre diff lock now i've fitted it. If I knew all this before I bought it I'd have saved up a few more months for an ARB. Nick... the smelly one Quote Link to comment Share on other sites More sharing options...
john cranfield Posted October 17, 2005 Share Posted October 17, 2005 This is also why you should never use a Detroit Locker on a Series Landy with selectable 4 wheel drive. Who ever gave you that idea! I've been running a Detroit locker in the 109 for years. In fact most applications for the Detroit are part time 4v4 systems or even 2x4 axles. John Quote Link to comment Share on other sites More sharing options...
John_T Posted October 18, 2005 Share Posted October 18, 2005 John, you are quite right saying Detroits can be used in 2 wheel drive vehicles (in fact they quote their use for cars and trucks). However, there is a problem with using them in Series landies which thankfully you have not encountered (maybe because it is a 109). I have come accross several 88 inch Series 3 where the half shafts snap for a pass time. This is because when on full lock on a tarmac gradient with a load up, all the power a Series 3 can muster, plus the weight of the truck is a resting on the shoulders of on poor halfshaft and unfortunately it can become an unequal struggle given the size of a 10 spline Series shaft. A Trutrac is a far better option for a Series. It is not a problem with permanent 4wd due to at least 3 shafts sharing the load when on tarmac. I have a mate who runs a Series 2 hybrid with series transmission and 90 axles. In his case the halfshafts didn't break but he kept tearing wheel studs off. He went back to an open diff and I bought the locker! Quote Link to comment Share on other sites More sharing options...
Troddenmasses Posted October 18, 2005 Share Posted October 18, 2005 I drove with a detroit locker in the rear of my 88" series 3 for about 2 years. After the first few miles, I pretty much forgot that it was there. The only time that it caught me out, was driving like a bit of a tit around roundabouts in the wet, when it would swap between understeer and oversteer at odd moments. My dad got in to drive it once, and absolutely hated it. Every time he went around a corner, he would lift off because he was driving a little too quick, and the detroit would un-lock, giving him a little nudge sideways. I had the strengthened half shafts in the back, and know that the setup is as strong as houses. I drove like a bit of an idiot both on and off road, and never broke anything to do with the detroit. It probably isn't the best thing to put into a daily driver that you use 4 times per year to go off road, but if you accept the slightly lively handling, they completely add another dimention to off road driving. Quote Link to comment Share on other sites More sharing options...
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