What causes heavy steering at racing speeds

[Russ Noble]

After reading through my one bourbon and Coke too many comments last night I was feeling I should apologise to Russ but reading further I think I fit in ok.

Russ, If you can't do the Alt number thing you can always cut (ctrl ins) and paste (shift ins) from someone else's message.
Here they are to choose from º ° .



Tim.

Tim you fit in great!

Dunno why the ALT248 won't work for me, (I think my computers slowly crapping out) but the cut and paste does ° Bingo. epper:

Someone told me on another thread I need to improve my internet skills, you guys are all helping.

Thanks

 

[roaldin]

Thank's Iain,

Wow! Nice looking setup!

Russ, I was a geek once, long before the days of Windows. I swear I'm getting better now...
If you think you'll need it occasionally you could put a ° in your signature or somewhere similar so it's always close at hand for cut and paste duty.

Tim.

 

[Russ Noble]

Iain, Very nice, there's a lot of tricky engineering there and great fabrication. How much RF is there? Not a lot I would say.

How about doing a build thread with a few more photos?

Tim, Thanks. Look below!

Cheers

 

[Iain]

I do plan a thread, but I also plan to finish the car, both are proving elusive at the moment !
There is enough RF left to comply with the Confederation Of Australian Motorsport rule book !

Iain

 

[Frank Catt]

Straight Eight, Sorry to digress a little, but I am intrigued by the rocker assembly at the bottom of the shock, looks a superb idea, like to have more details and pics if possible, Frank

 

[Trevor Booth]

Frank,
Go to a motorbike shop, that has been around for some time in various forms, I think but dont quote me that Tony Foales came up with it or a variation in one form or another

Jac Mac,

You would not want to have positive camber created in a corner such that the outside of the wheel/Tyre was loaded up. If a car rolls two degrees that does not necessarily decrease the camber on the outside wheel by the same amount. KPI and Castor + suspension geometry dictate

Ross N
is the hub face 1" towards the 5" piece (inboard) or the 4" piece (outboard)

 

[Frank Catt]

Thanks Trevor, but I am intrigued as to how it works on a GT40 front, surely the ratios etc are critical ? Frank

 

[Russ Noble]

So what are the benefits of the extra complication?

There is obviously longer shock travel, does this give more controlled damping? But would the main feature be that you can design in a rising rate, depending on the angles and leverages? This is not an accidental setup, a hell of a lot of thought has gone into the whole suspension. I wonder what the rear is like?

Talking about complication, why the need for the power steer?

Now that Iain has titilated our taste buds, it's only right that he should start that elusive build thread!

Cheers

 

[Jim Cowden]

I have seen Ians car up close and it is superb.

Know guys are we finished with this deg circly thingy ???????

Jim

 

[Ross Nicol]

Trevor - the hub face is in the 5" inner rim section.It may be less than an inch.I have a rim that I will measure exactly tonight. I'm going to the factory to check the scrub radius tonight.
Ross

 

[Jac Mac]

Trevor,
Yes I realise that, was trying to put in more simple terms (for those who may be getting lost in the tech talk) what was essentially causing the heavy steering on Ross's RF in the fast corners; ie that the tyre contact point on the road was moving from the inner half of the tread width on the straights to the outer half of the tread width during the corner.

Looks like I failed miserably-ha ha.
I see I have a PM from my previous employer- perhaps he has reconsidered his hasty dismissal action earlier today!

Jac Mac

 

[Pete McCluskey.]

Iain, that looks like a very nice piece of engineering. But what I am looking is a pure electronic power assist with no hydraulics involved. You should start a build thread.


Jim, no I haven't, I still cant do the alt 248 thingy it won't work for me and I never give up... maybe it does not work on windows xp?

 

[Ross Nicol]

3 piece front wheel rim detail 4" outer rim, 5" inner rim

Hub surface on rear of centre 5/8" in toward 5" inner rim from rim join. I guess that means my front wheels have a 3/8" positive offset.

Ross

 

[Richard]

.
Has anyone played around with rack position? Apart from changes to bump steer I am led to believe that some improvement in effort and feel may be gained by moving the rack backwards or forwards. Before I try it it'd be great to hear from someone who's done it or has modelled it.
Tim.

It's been more than 10 years since I researched all this front suspension guff for designing my car (that long??), but as I recall moving the rack forwards and back will only change the ackermann (as long as you dial out the toe in / out caused by change in arm length) - I tried to find a keyboard short cut for 'delta'. Can anyone help with that one? Anyway, this change alone won't affect bump steer except wrt the toe change.

 

[Ross Nicol]

Hi Richard
Don't feel bad I'm an electronics guy getting a crash course in front end Guff. I'd have an ASCII keyboard extended character table somewhere but alas the grey matter won't allow me to determine it's location.

Ok I've been under the RH front guard (should've taken the front off).
Looks like I've got 112mm or 4 3/8" for A and 3/8" of wheel offset.

So the total scrub radius is 4 3/8" plus 3/8" = 4 3/4" (121mm). Do I hear a Bloody Hell! from the panel? I await further discussion.
Ross

 

[Ross Nicol]

Actually I believe I have 1/8" of negative wheel offset which is quite close to '0' isn't it.So recalc of scrub radius 4 3/8" -1/8" = 4 1/4"
Ross

 

[Richard]

Hi Ross
Yeah, I'm sure I could find it on the internet if I could be bothered!

That scrub radius does seem a tad excessive!

Good on you for effectively turning your car into the project for this thread. Just be sure your across the Tasman counterparts don't slip a spanner into the equations (to mix my metaphors) so they can beat you at SFOS!

 

[Richard]

Better, Ross, better!

 

[Russ Noble]

So the total scrub radius is 4 3/8" plus 3/8" = 4 3/4" (121mm). Do I hear a Bloody Hell! from the panel? I await further discussion.
Ross

Ross,

You don't hear bloody hell from me!

Below is part of an email (one of half a dozen that I exchanged with Jac Mac before I started this thread) It's self explanatory.

Try this anecdote. Sometime early eighties when Jeff Pascoe was FF Champion.

Jeff and Larry were at Levels, so was I, they were trying a few changes to the car. One setup they tried was increasing the track front and rear by 6” using 3” wheel spacers each side. Jeff went out and when he came back in said the car was handling nicely and he felt he was going faster. The stopwatches however showed he was slightly slower. However no complaints about the handling perspective from the driver’s seat. Those spacers would have added 3” to the scrub radius!!!. They would have also softened the suspension a lot and increased the frontal area, both those could have caused his times to be slightly off. That is why I have always felt scrub radius has no practical effect. In a rear engined single seater/sports racer anyway.


Whilst it is desirable to keep scrub radius as small as possible, I don't think it is a major factor to base suspensiion design on for the track.

FWIW, IMHO I don't think it's the zero scrub on Franks suspension that gives him the benefits, I think it's the high KPI and caster that ensued as a result of the way he went about it. Be interesting to see what effect putting spacers on Franks wheels would have............... Admittedly minimal scrub is desirable for road use as it lessens any kickback due to uneven surfaces etc.

Cheers,

 

[roaldin]

Hi Richard, I was thinking in terms of overall movement inc' up and down when I mentioned bump steer, I refined it to backwards and forward re effort as that's what was presented to me to try.
Looking at it I was a bit ambiguous...

Here's one you can cut and paste - Δ.

Ross - Bloody hell!

Tim.