Doing a a bit a Googling I came across some interesting tyre test data put on the web by RWTH Aachen university.
Of particular interest is a graph shown the effect of vertical load on self-aligning torque on a 195/50x15 tyre, this is a tyre sized
used by many locaost builders.
Self-aligning torque is created by distortion of the tyre sidewalls important for steering self-centering.
The area of interest is the results from at and below 3000 Newtons vertical force as this represent a typical corner weight for our sort of
car.
The rest of the page contains some other data of interest.
Link to Full Web page at RWTF Aachen
[Edited on 16/8/12 by britishtrident]
+1 I fear that a large % of the LCB community will not have a clue what your on about, for us dullards care to expand on it a bit?
Basically I think the graph shows that lighter vehicles like ours have significantly less self aligning torque reaction than heavier vehicles.
They don't self centre as well as heavier vehicles.
It probably not what the OP was looking at, but anthor interesting view on self aligning torque is.
In order to build lateral force on tyre you need a vertical load and a slip angle. Tyre tests are done with a fixed vertical load and they then sweep
through the slip angle.
As the slip angle increase so does the lateral force until it reaches a maximum. depending on the tyre you may get a small drop off of lateral force
or it holds steady, ie it can't generate any more force so you've reached the limits of the tyre.
Why self aligning torque is relevant is it contributes to what your feel at the steering wheel (its one of the forces trying to put the tyre back in a
straight line, dont confuse this with the effect of castor angle as thats a different force/torque)
The interesting bit is the self aligning torque drops off before the lateral force peaks. This means on a car with good steering feel you can feel the
steering wheel go light just before your reach the limits of lateral force. So you get a warning you've reached the limits before dropping over
the edge!
The effects of suspension geometry (caster and wheel offset) and power steering can mask this feedback, drive a vauxhall and you'll know what I
mean :0
[Edited on 16/8/12 by mikeb]
quote:
Originally posted by liam.mccaffrey
Basically I think the graph shows that lighter vehicles like ours have significantly less self aligning torque reaction than heavier vehicles.
They don't self centre as well as heavier vehicles.
Agreed Bob, just noticed you are based in Swansea. Up until recently I commuted to Swansea from Milford Haven every day. Now self employed but doing
a lot of work with a Swansea base customer. Was there yesterday actually. Small world
quote:
Originally posted by BobM
But the shape of the curve also says that the self-aligning torque increases with slip angle until you get to a peak at about 5 degrees at which point it decreases again dropping to zero at around 12 degrees.
quote:
Originally posted by mikebThe effects of suspension geometry (caster and wheel offset) and power steering can mask this feedback, drive a vauxhall and you'll know what I mean :0
Focus is a lot lot better.
Last time I was involved in steering systems, vauxhall were set up for motorway driving and safety (good straight line tracking and good at staying
straight ahead under adverse conditions). Unfortunately this set up compromises steering feel compounded by the early electric assist systems. They
might be better now but I haven't driven one to find out!
quote:
Originally posted by mikeb
Focus is a lot lot better.
Last time I was involved in steering systems, vauxhall were set up for motorway driving and safety (good straight line tracking and good at staying straight ahead under adverse conditions). Unfortunately this set up compromises steering feel compounded by the early electric assist systems. They might be better now but I haven't driven one to find out!
http://www.pistonheads.com/news/default.asp?storyId=26182
I'm assuming shorter spindle length means less offset (scrub radius) in that article.
You can tell I'm bored
http://www.caranddriver.com/features/ford-revoknuckle-and-gm-hiper-strut-explained-tech-dept
When I said safety I meant things like blow out, split mu braking.
From recollection early vectras had negative offsets (scrub radius) to counter act blow out etc.
The problem with car handling is its very subjective, my friend has always had Vauxhalls and thinks they handle well, When I first drove a focus I
thought the steering was to twitchy but I just wasn't use to the response compared to my ageing motor!
Note: Scrub Radius isn't quite the same thing as the ET offset on wheels btw
[Edited on 16/8/12 by mikeb]
quote:
Originally posted by loggyboy
Interestingly ford has since followed suit on the high offsets, the wifes Fez STs had 55mm!