Rorty
|
| posted on 21/1/05 at 12:20 AM | |
|
Some steering and suspension terms and theories explained
As the title says. Click here.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
|
|
WIMMERA
|
| posted on 22/1/05 at 02:32 AM | |
|
Scrub radius and it's effects seems to be an area that the experts can't agree on
|
|
|
Rorty
|
| posted on 22/1/05 at 02:39 AM | |
|
quote:
Originally posted by WIMMERA
Scrub radius and it's effects seems to be an area that the experts can't agree on
Would you care to expand on that statement?
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
WIMMERA
|
| posted on 22/1/05 at 05:53 AM | |
|
Ingalls Engineering state that the greater the scrub radius(positive or negative) the greater the steering effort required.
Jeffrey Daniels in Car Suspension at Work states, Where the steering axis is in line with the centre of the contact patch (zero scrub) the front wheel
can only be turned by scrubbing the whole patch around it's centre, this makes the steering very heavy at low speeds, he goes on to say, one
answer is to introduce some offset so that at least part of the contact patch will roll around the steering axis instead of scrubbing, and just to add
a bit more flavour, Staniforth in Competition Car Suspension states "centre point steering" provides both lightness and lack of kick back
through the steering wheel that is still a laudable aim but hard to achieve
|
|
|
Rorty
|
| posted on 22/1/05 at 06:14 AM | |
|
OK, I now see what you were talking about.
I disagree with Jeffrey Daniels; zero scrub offers the least resistance. Staniforth seems to agree with this too.
I've never read or heard of Jeffrey Daniels take on the matter. I've never heard a similar argument from anyone else for that matter.
Even if the tyres were rock hard and there was a lot of negative camber involved, any scrub radius would require more effort to turn the wheels as
they'd be taking the long way around. So to speak.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
gazza285
|
| posted on 22/1/05 at 10:37 AM | |
|
I understand what Jeffrey Daniels is getting at, it will be heavier "at low speeds". By low speeds I think he means stopped and the
difference will be minimal anyway. As soon as you reach the dizzying heights of, say, two miles an hour zero scrub is the way to go. I only have one
vehicle with zero scrub and when it is stood still the wheel is very hard to move, but it is a 3&1/2 tonne van.
|
|
|
WIMMERA
|
| posted on 22/1/05 at 10:51 AM | |
|
Daniels is an engineer he's written a couple of books on suspension and handling. I've seen the Daniels argument before on a few
occasions.
|
|
|
Rorty
|
| posted on 22/1/05 at 11:50 AM | |
|
quote:
Originally posted by WIMMERA
Daniels is an engineer he's written a couple of books on suspension and handling. I've seen the Daniels argument before on a few
occasions.
I know who he is. I said I'd never read or heard his take on scrub radius. I didn't say I hadn't heard of jim.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
Rorty
|
| posted on 22/1/05 at 11:59 AM | |
|
quote:
Originally posted by Syd Bridge
Very odd!! I seem to recall that you argued vehemently to the contrary, when I suggested that centrepoint steering, or as close as you can get, is to
be aimed for. This was more than a year ago.
Argued to the contrary of what Syd?
I still stand by what I said with regard to scrub radius whenever that was. I maintain a certain degree of scrub radius is desirable. I don't
know how you translated what I said above to be anything contrary to what I said before.
quote:
What else are you going to come to my way of thinking and experience on?
Who knows Syd? Maybe someday you'll come up with something sensible or intelligent and I may well agree with you.
quote:
Most (if not all) topline racecars have centrepoint(or as near as can be achieved), to make the drivers life easier, avoid
'kickback', and changing steering loads with lateral weight transfer.
You always seem to grasp the wrong end of the stick Syd which may account for your confusion over why a little scrub radius is de rigueur.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
NS Dev
|
| posted on 22/1/05 at 12:32 PM | |
|
oooooh meow!!!
less scrub = less kickback (less moment between contre of contact patch and centreline of steering axis)........simple fact!
A seven won't have heavy steering whatever the scrub radius at low speed, because it weighs f*** all...........simple fact!
Too much scrub radius will reduce the feel through the steering of the grip at the contact patch because the feel will be masked by the moments
imparted on the wheel by uneven road surfaces........simple fact!
All thanks to simple physics!
Beyond these I don't know, and to be honest, a) more people set up suspension and wheels because " that was what they could get that was
nearest to ideal" rather that what was ideal and b) those that worry unduly about these things are usually those that don't get cars
built!
|
|
|
Rorty
|
| posted on 22/1/05 at 01:39 PM | |
|
quote:
Originally posted by NS Dev
oooooh meow!!!
Yes, well.
quote:
less scrub = less kickback (less moment between contre of contact patch and centreline of steering axis)........simple fact!
True. That's what I've been saying, but "kickback" intimates too much, whereas just enough = feedback.
quote:
A seven won't have heavy steering whatever the scrub radius at low speed, because it weighs f*** all...........simple fact!
Not true. I've driven light weight cars with less than 25mm of scrub and the "weight" is not insignificant at low speed, yet the
feedback at higher speeds was spot on.
quote:
Too much scrub radius will reduce the feel through the steering of the grip at the contact patch because the feel will be masked by the moments
imparted on the wheel by uneven road surfaces........simple fact!
True, but who is advocating a lot of, or "too much" scrub radius? You obviously only want sufficient to provide some feel.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
britishtrident
|
| posted on 22/1/05 at 04:55 PM | |
|
quote:
Originally posted by NS Dev
oooooh meow!!!
less scrub = less kickback (less moment between contre of contact patch and centreline of steering axis)........simple fact!
A seven won't have heavy steering whatever the scrub radius at low speed, because it weighs f*** all...........simple fact!
Too much scrub radius will reduce the feel through the steering of the grip at the contact patch because the feel will be masked by the moments
imparted on the wheel by uneven road surfaces........simple fact!
All thanks to simple physics!
Beyond these I don't know, and to be honest, a) more people set up suspension and wheels because " that was what they could get that was
nearest to ideal" rather that what was ideal and b) those that worry unduly about these things are usually those that don't get cars
built!
Yes I agree almost 100% On my my Imp and Davrian racers I was forced to use a lot of scrub radius because the front disc conversion used Viva hubs
which gave a big increase in track outboard of the king pin it didn't make the steering any heavier. It did however make the steering feed
back amplify the effects of poor lateral brake balance, mismatched corner weights and bump/roll steer.
As for kickback from scrub radius to feel it just drive a rwd Escort on a rutted road all i can say is the Escort rally boys must have kept thier
thumbs well clear of the steering wheel spokes.:-)
[Edited on 22/1/05 by britishtrident]
|
|
|
WIMMERA
|
| posted on 23/1/05 at 05:38 AM | |
|
Yes, all the Locosts I've seen with Cortina hubs and uprights(including my own) have a mile of scrub radius, but not many consider it a fault
or they keep quiet about it
|
|
|
britishtrident
|
| posted on 23/1/05 at 09:51 AM | |
|
quote:
Originally posted by WIMMERA
Yes, all the Locosts I've seen with Cortina hubs and uprights(including my own) have a mile of scrub radius, but not many consider it a fault
or they keep quiet about it
Not everybody appreaciates that as they came from the factory the Cortina Mk3+ 5.5x13 rostyle wheel had a different offset from the equivalent
Escort/Capri type. On the escort/Capri the wheel offset was bigger to clear the strut spring pan.
[Edited on 23/1/05 by britishtrident]
|
|
|
NS Dev
|
| posted on 23/1/05 at 10:30 AM | |
|
You are quite right about the escorts britishtrident, you do want to keep your thumbs out of the way, yes, with decent width rubber on the front
(7.5" , and the inability to house any more inset on the escort strut, gives loads of lovely thumb ripping kicks on rough, tarmac rally type
roads!!! That's at a fairly low speed too, (well, below 90mph ish)
|
|
|
Rorty
|
| posted on 23/1/05 at 12:11 PM | |
|
quote:
Originally posted by Syd Bridge
Give an open wheeler or sports proto any scrub at all, and the driver will rip your head off. That's if he has any ability to use his arms after
a lap or two.
On the other hand, not enough castor, and they complain of 'dead' feel. With castor, the more you turn the wheel, the more straightening
load is generated at the tyre, thus more 'feel'. The added benefit is straight line stability and steady 'feel' when
cornering, without the juddering and banging that scrub imparts into the steering and suspension. Castor is also the geometry that allows the car to
self steer on a banked corner. No castor, no self steering. Lots of castor, heavier in flat turns, too light on the banks.
My experience here seems to contradict some of what is being mooted.
Someone's got it back-to-front. If I'm wrong, then an awful lot of highly experienced race drivers don't know what they are talking
about.
The only proviso to this is that these effects are magnified as speed increases. Below 100mph or so, the frequencies are such that kickback(except for
big hits) is manageable, though still not desirable. The buggies which Rorty has his major experience with probably fall into the lower speed
category. Compared to other effects from the solid back ends coupled with bike engines and light weight, and moreso the surfaces (??) they run on,
kickback from scrub is the least of their worries.
[Edited on 22/1/05 by Syd Bridge]
You still don't get it Syd. This is the Locost car forum and we (the rest of us anyway) are talking about (predominently) road going cars.
And since when have you been an authority on off-road racing and my motoring background? I have spent more time in other cars than off-road buggies
FYI.
Don't always make it personal Syd, it shows up your insecurities and ill-breeding.
I'll state it again for the record; I believe a certain amount (varies from one car to another) of +ve scrub radius in a road going car is
desirable. Not so much that it does nothing but kick back at every pothole, and not so insufficient as to leave the steering vague.
Castor as you say, has the effect of centering the steering, but it's different to the feel from scrub.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
NS Dev
|
| posted on 23/1/05 at 11:21 PM | |
|
hmm, interesing, talking of offroad buggies, have a look in my photo gallery, you may see an interesting likeness to some of the things on
Rorty's web pages!
I see some power to weight ratios mentioned too, well be way of comparison, mine is around 400hp per tonne (195 hp in 485kg), and that's
certainly not enough! National champ has nearly 600hp per tonne in my class, and in the top class they have approaching 900 hp per tonne.
I have some off-road experience too, and yes, although the setup is different to go quickly, the same parameters are relevant! (seem to work, even
with a crap driver i.e. me!, got first in club, 2nd in league this year)
[Edited on 23/1/05 by NS Dev]
|
|
|
Rorty
|
| posted on 24/1/05 at 12:34 AM | |
|
quote:
Originally posted by NS Dev
hmm, interesing, talking of offroad buggies, have a look in my photo gallery, you may see an interesting likeness to some of the things on
Rorty's web pages!
I see some power to weight ratios mentioned too, well be way of comparison, mine is around 400hp per tonne (195 hp in 485kg), and that's
certainly not enough! National champ has nearly 600hp per tonne in my class, and in the top class they have approaching 900 hp per tonne.
I have some off-road experience too, and yes, although the setup is different to go quickly, the same parameters are relevant! (seem to work, even
with a crap driver i.e. me!, got first in club, 2nd in league this year)
[Edited on 23/1/05 by NS Dev]
900 hp per tonne is pretty impressive. I presume they're some of the twin engined cars?
How times change. My fond memories of autograss are of a RV8 on a Renault transaxle mid-mounted in a Fiesta.
We race on circuits like motocross tracks, complete with all the jumps and table tops. 400 hp per tonne coupled with 14" of travel is quite a
buzz. It makes a CR500 seem tame!
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
WIMMERA
|
| posted on 24/1/05 at 12:36 AM | |
|
How much offset did the Rostyle wheels have? The Cortina wheels that I've measured have 41.4 mm offset (stamped on them)but that still gives
3+" of scrub. I have a set of Mondeo wheels that have 49.5mm offset. The fact that Cortinas have such a small KPI angle doesn't help the
cause either, but it is a good feature in other respects. I have fabricated a set of uprights with a live stub for the new car, which should address
most of the problems and they have a weight advantage.
|
|
|
Rorty
|
| posted on 24/1/05 at 01:10 AM | |
|
What's the standard tyre size for those wheels?
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
WIMMERA
|
| posted on 24/1/05 at 05:31 AM | |
|
Can't help with standard tyre sizes, they were bare wheels when I got them, the Mondeo wheels are 15x6 the Cortina 13x5.5 also have a set of
aftermarket Peugeot 7x16 with 20mm offset all 108 PCD
|
|
|
NS Dev
|
| posted on 24/1/05 at 08:41 AM | |
|
quote:
Originally posted by Rorty
quote:
Originally posted by NS Dev
hmm, interesing, talking of offroad buggies, have a look in my photo gallery, you may see an interesting likeness to some of the things on
Rorty's web pages!
I see some power to weight ratios mentioned too, well be way of comparison, mine is around 400hp per tonne (195 hp in 485kg), and that's
certainly not enough! National champ has nearly 600hp per tonne in my class, and in the top class they have approaching 900 hp per tonne.
I have some off-road experience too, and yes, although the setup is different to go quickly, the same parameters are relevant! (seem to work, even
with a crap driver i.e. me!, got first in club, 2nd in league this year)
[Edited on 23/1/05 by NS Dev]
900 hp per tonne is pretty impressive. I presume they're some of the twin engined cars?
How times change. My fond memories of autograss are of a RV8 on a Renault transaxle mid-mounted in a Fiesta.
We race on circuits like motocross tracks, complete with all the jumps and table tops. 400 hp per tonne coupled with 14" of travel is quite a
buzz. It makes a CR500 seem tame!
Yes, the really high power to weights are pretty much confined to the twin bike powered cars, where they are using two bored and stroked hyabusas,
around 245hp each, in a spaceframe special!
Still plenty of v8's around though, they tend to compete in their own "v8 race" further back from the pack of twins at the front!
The 2 ltr car engined specials can hack it at the top as well though, but are expensive. Phil Rogers won the champion of champions race at the
autograss nationals 2004 in a 2.0 millington engined car, beating everything else, but blew an £15,000+ engine as he went over the line!
|
|
|
Fred W B
|
| posted on 24/1/05 at 08:47 AM | |
|
So, what do the experts reccomend as a maximum scrub dimension for fast road and track day use, om a midengined car??
Lets learn from all this debate
Regards
Fred WB
|
|
|
WIMMERA
|
| posted on 24/1/05 at 09:09 AM | |
|
No idea Fred, have heard that 25% of tyre width is a good starting point but no doubt others will have a different slant on it, it's not the
easiest thing to change which I suspect is the reason it's generally overlooked
|
|
|
WIMMERA
|
| posted on 24/1/05 at 12:08 PM | |
|
Yes Syd the new uprights are built to achieve zero with the Mondeo wheels I mentioned earlier, but , until I drive it I won't really know. A
Ford suspension designer suggested the 25% of tyre width as the max, (as Fred asked for) to me some time ago, so thats what I've done, two sets
of wheels with different offsets and an assortment of wheel spacers should see me right. Now a question for you Syd, what components do you use to
achieve zero scrub.
|
|
|
