What causes heavy steering at racing speeds

[Frank Catt]

OR USE A BIGGER KPI, which goes back to my original theory !

[Ross Nicol]

Hi Frank
Is your original theory in a thread somewhere? I would like to read about it. I presume the bigger KPI reduces the scrub radius. I haven't closed my mind to any solution yet so I'm keen to learn about yours. Considering a few weeks ago I didn't know what scrub radius was I've certainly learnt a lot.
Ross

[Jim c]

Front Suspension Geometry

[StuM5]

I've watched this discussion since I viewed Ross N's footage of him racing at PI and thought, I'd like to ask "why he was using two hands through the left corners" but didn't feel qualified to, more importantly, I knew I wouldn't understand the answer. I'm glad someone asked the question but now that they have I must confess, I have, unfortunately, no idea what you guys are talking about - I so wish I did!
I'm just hoping for Ross to say "Well guys this has been an awesome learning experience and as a result I kicked the VW's arse today, and Eric Bana was asking - Who's that driving the GT40?

cheers

[Lynn]

Ross,

I resemble that remark! Having followed this thread, I can now at least understand what Frank is trying to achieve with his increased KPI. What I am having a hard time with is how one can increase the KPI to reduce the scrub radius without getting huge negative camber at the same time. Put another way, I don't recall seeing an upright that allows the spindle to be adjusted to counter act the camber changes that result when changing the KPI. Does someone have a picture that clearly shows this feature in an upright? Or, can anyone show a diagram the illustrates how this is dealt with if I am completely off base?

Thanks,
Lynn

[Russ Noble]

Lynn, usually requires an upright redesign or change. Or offset mount the ball.

Cheers,

[egoman]

Has anyone given a thought to the steering getting heavier at higher speeds being the result of the gyroscopic effect of the wheels .
I raced a outlaw sprint car many years ago without power steering
and the car would become significantly harder to steer at larger high
speed tracks.

[Jac Mac]

Originally Posted by egoman

Has anyone given a thought to the steering getting heavier at higher speeds being the result of the gyroscopic effect of the wheels .
I raced a outlaw sprint car many years ago without power steering
and the car would become significantly harder to steer at larger high
speed tracks.

While watching the video, that factor was on my 'list' of possibilities, but if you have a look, Ross was not having too much trouble applying the lock reqd for any corner, just maintaining that amount of lock once in the corner.

In your case of the sprint car you often see drivers making rapid and quite large steering corrections in the turns at high speed and the gyroscopic effect will be noticeable.

I would suggest that in the GT40 type of vehicle, if it became necessary to use steering corrections of that magnitude that you would be well on the way to the scene of the accident!

One other factor that will make itself felt as a gyro loading is the tendency to fit larger & heavier brake rotors to these cars.
Good point and like all these problems another factor that should be considered when looking for a solution.

Jac Mac

[Trevor Booth]

The gyroscopic action of a wheel only comes into play when you want to change/ move the spinning axis. This force is called precession. precession is the "anti gravitational" or "self righting" force. A car wheel when turned by the steering is rotating about , say, a vertical axis, say, normal to its spinning axis (the stub axle) no gyroscopic force is encountered as the plane (horizontal) of the spinning axis is unchanged, however, in reality, the kpi and castor will promote a slight change in the plane of the spinning axis and some precession will occur. I have really not calculated this but I would suggest that unless speeds are very very high it may not have an effect if at all.
Try the old bicycle wheel held between your hands, it is only when you "lean it over" that any resistance is felt.
BTW when a bicycle rider wants to make a LH turn he actually turns a fraction to the right in order to make the LH turn

The upshot- no i dont believe gyroscopic action contributes to heavy steering at speed

[roaldin]

Gyroscopes - Everything you needed to know

Tim.

[Richard O'Clery]

Originally Posted by Russ Noble

Or offset mount the ball.

What a great project for one of you engineering types with big machines and lots of time on your hands!

You could fab up an upright with a bolt-on top plate that locates the upper ball joint. Make several top plates up with different UBJ distances so you have an instant variety of KPI angles at your disposal.

Then test, test, test to get a feel for how close light-steering theories come to practice. You might have to crank out a range of rim offsets on your metal spinning lathe as well ...

[Russ Noble]

Actually Richard, that is how I have built my upright. I can change my KPI if need be. However I lack the big machines and the time on my hands so won't be experimenting unless I have problems.

I am very confident about my setup and don't expect to have problems BUT as that venerable old dog Jac Mac has pointed out in private emails :- 'Just because I believe something to be true doesn't mean that it necessarily is!!!!'

Thanks for the vote of confidence Jac Mac!

At least on my setup KPI is easy to change. My 50mm scrub is not! (except that I can increase it easily but not reduce it significantly). I've put my money where my mouth is on the scrub issue! When the flag drops...........

Cheers

[Malcolm]

I had a good result yesterday. I put on the shorter steering control arms and instead of the two expected improvements, I got three! 1. The weight of the steering feel increased to how I wanted it. 2. The speed of the steering increased to how I wanted it but the 3rd benefit I overlooked is that my turning circle is now even tighter and on full lock everything under the wheelarch still keeps clear of everything else! The only drawback I can see is that I now have less reason to do spin tunrs when turning round in tigher spaces!

[Jac Mac]

Have a TUX Russ, at 50mm you have less than 50% of the scrub Ross is fighting with + methinks that Lim has already machined in the extra room reqd to reduce it further, your just keeping that little bit info to yourself for now eh? Be an absolute shame if you had to agree with someone-again!°°°

Woof!

Malcolm, It is actually easier on axles etc if you break traction & spin the car round in its own length than being all PC and doing three point turns with the axles etc getting all twisted up--- only problem is that those types that have the heads that swell to fit the regulation one size fits all Motorsport Stewards Cap seem to take a dim view of the practice!

Jac Mac

[Russ Noble]

Jac Mac, I agree with you. There you are I said it!

I still think Ross' steering will improve out of sight when the caster gets evened up. He may find he doesn't need to do anything else, but there again he might. Suck it and see...

Cheers

[Lynn]

I asked the question about adjusting KPI to make sure that I wasn't missing something so that I could make some sort of bottom line statement for the average Joe who has read this thread hoping to improve the handling of his car. It is very unlikely that the average Joe is going to fabricate his own uprights and probably won't make new control arms. But, there is a lot he can do to improve his handling and there are things he can avoid that could worsen it.

Wheel Offset - Take the time to look carefully at the effect of the wheel offset not only on brake caliper and control arm clearances, but also on the contact patch location in relation to the swivel axis of the upright (scrub radius.) The exact style of wheel that blows your skirt up may only be available for a particular make/model of car, but the offset that is required by that car may be all wrong for your car. (Today's front wheel drive cars call for wheels with huge offsets, so that may work to your favor. However, be aware that they may actually have too much positive offset to clear controls arms, etc.) As much as you hate it, you may have to look for a close facsimile that comes in 3-piece wheel that allows for an offset that will minimize the scrub radius on you car. A car that looks good but handles like a pig is no fun at all.

Wheel adapters/Pin Drive adapters: Many have fretted over the unsprung weight that adapters add to their cars, but don't consider the increase in scrub radius that they bring. If you just have to use these for the aesthetics - and I must admit that spinners not only look good, they also just look right - consider where they will put the center of you contact patch and try to use wheels whose offset will compensate or even improve the scrub radius.

Big Brake Kits - Big, multipot calipers look really cool! They can obviously increase your braking effectiveness. But, if their size and placement is going to cause you to use wheels with little, or even negative, offsets, those big brakes may be necessary to slow down enough to get you car to handle through the twisty bits.

Bump Steer - in many cases this is something that can be corrected with modifications to existing parts. Bump steer has received a lot of attention in recent years. As a result, it is far better understood by much broader spectrum of mechanics and shops. The diagram below from an article by Longacre Racing Products on Racer Parts Wholesale’s website shows in the simplest terms where the tie rod ends should fall and the line segment on which the tie rod should lie. Bump Steer kits/modifications will get the tie rod to fit the requirements shown (as much as possible anyway.)


Alignment settings – in most cases, the alignment specs provided by the manufacturer of your car represent a best compromise between good street manners and performance handling. Without the fabricating new suspension parts, it is not likely that you will be able to make huge changes in these settings. That is not to say that there is not room for tweaks and changes for personal preferences or specific uses of the car: a continuum from race track use through highway only cruising. There are a few things to keep in mind though. As much as humanly possible, make changes to one setting at a time. Make changes a little at a time. Be aware that, for all intents and purposes, changes are not made in a vacuum: a change to any one setting will likely change other settings, so always recheck all settings when ever a change is made to any one value. Write down everything you do in great detail. Not only will this help you to understand the cause-effect relationship of the various tweaks that you do, but also it could help you get back to where you started if things really get hosed.

If in the end sorting what you have just isn’t satisfying, reread this thread to consider that kinds of things that will have to be changed and how they will have to be changed to further improve your handling. One must always keep in mind that handling is a highly subjective thing, but, as we said in the US Navy, the guys contributing to this thread “have their shit in one ditty bag.”