Aprilia, would these modifications improve an 06 Spec B? I believe the suspension on these differs slightly form the standard Legacys but by how much I don't know.
Many thanks in advance.
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Thank you Aprilia.
The comments on suspension alignment chime with my experience very nicely. On my last Legacy the near side front tyre was wearing very badly before I got the dealer to do a complete realignment.
On my present Outback the there appeared to be a fault with the crank position sensor. The problem seemed to re-occur several times, but after a full check it turned out to be a wiring fault, seemingly a loose connection. It hasn't re-occurred since, fingers firmly crossed.
Espada III, I thought that you had a Legacy 3.0l Spec.B
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Aprilia would these modifications improve an 06 Spec B? I believe the suspension on these differs slightly form the standard Legacys but by how much I don't know. Many thanks in advance.
Sorry, I don't know enough about the Spec B model to say.
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Hillman - sorry, no just an Outback 3.0Rn. Spec B would be nice, but I like the higher position of the Legacy on stilts and the auto box. I've given up on stick waggling (as George Bishop once said!).
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Cheers Aprilia - by the way do us all a favour and write a book will you. I'm serious.
I do believe he has written a book, IIRC it used to say so in his 'about me' bit of his profile.
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While we're on this topic, an antiroll bar increases roll stiffness at that end which encourages weight transfer. Wouldn't this make that wheel more likely to slide? What I'm saying is - doesn't a stiffer anti roll bar mean less grip for the tyre?
Or is it worth doing (with the Subaru at least) because you limit the suspension travel and it has less grip in bump or droop anyway?
Gareth
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While we're on this topic an antiroll bar increases roll stiffness at that end which encourages weight transfer. Wouldn't this make that wheel more likely to slide? What I'm saying is - doesn't a stiffer anti roll bar mean less grip for the tyre? Or is it worth doing (with the Subaru at least) because you limit the suspension travel and it has less grip in bump or droop anyway? Gareth
Gareth, the answer is 'both at the same time'...
I don't want to start writing a book on Subaru suspension - but here are the basics.
Tyre "grip" is calculated as traction divided by loading, so as loading goes up so does traction, assuming constant amount of grip. The 'caveat' is that the coefficient of friction for the tyre is not constant with loading, it decreases as loading increases. So, let's say a tyre is taking a load of 600kg (which would be about right for an Impreza, to take an example) then if it could generate 600kg of lateral traction before slipping then Grip = 1.0, which is as good as it gets with a premium tyre!
Say, in a corner, weight transfer might increase the load on the outer tyre to 1000kg then it might generate 800kg of lateral traction - result is Grip = 0.8. The grip has dropped slightly due to the higher load.
Thus increasing weight transfer (fitting a bigger diameter ARB and so increasing roll stiffness) results in a reduction of grip at that end of the car under hard cornering. This is what all the textbooks tell you and is the traditional 'suspension tuner' approach to changing handling.
However, that's not the whole story. On the Subaru front strut-type suspension (and on other cars too) the change in camber under modest roll angles is quite small. But under hard cornering (lots of roll) the camber change becomes rather large. The wheels tend to go to quite large positive camber angles and so you end up 'driving on the sidewalls' and mushy understeer sets in because the tyre contact patch is reduced. Note that the rear suspension is slightly better in this respect - there is less camber change there, so under very hard cornering the rear grips better than the front - which suits most drivers.
The outcome of the situation described above is that by increasing front roll stiffness two things happen - (1) weight transfer increases, reducing grip somewhat; (2) roll angle (and therefore camber change) decreases, which increases front tyre grip. And the overall result is that in most situations (2) outweighs (1), and front grip increases, meaning less understeer. At very high cornering loads (1) prevails and so the car understeers 'in extemis' - which is what you want.
At the rear the situation is a bit different becasue the geometry is different and there is little camber change with roll on an Impreza (even less on a Legacy, which has a better rear suspension geometry than the Impreza). Therefore increasing rear roll stiffness reduces grip at the back due to the straightforward load transfer effect, we don't really have to concern outselves with camber change.
However, both the Legacy and the Impreza have a chassis which is extremely stiff, so to some extent increasing rear stiffness has some impact at the front, and vice versa.
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I do believe he has written a book IIRC it used to say so in his 'about me' bit of his profile.
Yes, I've written two books on automotive engineering and contributed to two others. Fortunately one of them was taken up by the SAE and sold very well, especially in the US.
I've also published about 50 papers, but these were mostly associated with work done for either VM's or component suppliers and are not the kind of thing that the man in the street would read, they were published in journals read by professionals in the industy. Mostly to do with sensors, actuators and automotive control systems (e.g designs for accelerometers, yaw sensors, knock sensing, combustion , ABS control systems etc etc).
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Just to add a little to the above (sorry to go on, this has just come to mind)..
In the past I have gone out on both road and track with drivers who complained about their cars handling; but two things to bear in mind..
1. Driving style is very important. One of the posters on this forum maintains that non-turbo Imprezas are no good and 'not a sporty drive'. On a winding road the good driver in a non-turbo will easily beat a poor driver in a turbo any day of the week. Most drivers never receive any tuition in how to handle their car at speed and most have no knowledge of chassis design - its all been learnt by trial and error, and some people are slow learners..LOL!!. A lot of drivers tend to 'hook' their car into the corner and try to play about with the line and and speed half-way around the corner. The tyre can only generate so much traction - if you brake or accelerate then that reduces the amount of lateral tractive effort available at the tyre. Put simply, maximum cornering force is developed when you're neither accelrating or decelerating in the corner. In practice, due to drag forces etc then a little throttle to preserve equilibirum is what you need. So set the car up for the corner on the straight, choose your line and come off the brakes as you enter the corner.
2. Tyres make a big difference if there are largish camber changes. So a soft sidewall is not too good on a Subaru, the tyre tends to heel-over and over a period of time the shoulders will wear out. Something with a stiff sidewall is better (this is one of the theories behind the use of ultra-low-profile tyres). Also a few more PSI in the tyre tends to stiffen it up a bit. Again, its a compromise though, because too stiff of a tyre will result is loss of contact over road imperfections.
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I have often wonderd about sidewall design on tyres - Goodyear NTC-5's, for instance, seem to have sidewall that seems to 'bend' all of a sudden - so in a sharp corner you seem to have lots of grip, and then suddenly it all goes !
If I understand what you are saying, in a car with a stiff suspension setup - like my Focus for instance - you should choose a tyre not just for grip, but one with a stiff sidewall? And in a car with a softer suspension setup, would a tyre with a softer sidewall then actually grip better (unless you started fitting ARB's) ?
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I took my Subaru Outback 2.5S in to Macclesfield Motor bodies today for a geometry check. I was told that it wouldn?t take more than 45 minutes, but was I surprised when they found that the data wasn?t on their machine memory ? No, not really. Hence it lasted at least twice that time, getting the data by phone and doing the job, and then another half-hour while the technician explained the results to me. Cost £80:00 plus VAT. The setup is within limits apart from the camber, which is fractionally out. The technician said that it was so little, and such a job to fix that if it was his car he would leave it. He opined that the allowable tolerances are quite wide. Any comments, anyone ?
One of the reasons that I went for the Outback instead of the Legacy was the bigger tyre profile. Some of the roads in our district have a very bad surface, and I had a bad habit ot touching the kerb to feel where I am while parking. The bigger profile saves the rim. I've almost managed to stop myself doing it !
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I am surprised he didn't have the four wheel alignment data. It's in Autodata and I would have thought a reasonably modern aligner would have it. They usually get software updates every few months, and most now have virtually all cars (including grey imports) on the database.
The tolerances on most cars are quite wide - it allows for wear and for fitting tolerances at the factory. For example, the front wheel toe-on on your car is 0+/- 1.5mm, but you would notice quite a difference between those extremes. Ideally the technician should set the alignment to the centre of the tolerance range and not just leave it - although many will take the lazy way out and not bother so long as it is somewhere within the tolerance band. Camber is 0.5+/-0.5, with a 0.3 degree L/R tolerance. Camber is easy to adjust at the front (an eccentric bolt at the bottom of the strut). It is not easily adjustable at the rear, although you can buy and easily fit camber adjustment bolts.
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I got the impression that they were running over time and didn't want to do any more than I had stictly asked them to do,viz., check it out.
I didn't ask what kind if machine they used, but I think that I once saw the company recommended in the HJ site under recommended places to go for that kind of thing.
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