toe setting

[david stratton]

Gentlemen, I have noticed that in my kart, as you load the front end it tends to toe in.........should i have the toe set loaded(as i do now, exactly o) or set it unloaded on the stand which would result in toe in once i get in the kart..........?????

[Randy Mckee]

You're correct -- Go for zero loaded. Many manufacturers may suggest a slight toe out (1/16").

[John Learmonth]

David,
Nearly all karts will gain toe-in when driver weight flexes the chassis. Typically (ie most karts) the change will be around 2mm of toe gain. With some brands of kart the change will be negligible, but with other karts as much as 3mm (1/8” = 3.2mm) is quite common and up to around 4mm is possible (or at least as much as I’ve seen). Apart from the effect on toe settings, this must also cause some degree of bump steer, which isn’t good.

Its not only toe, camber also changes with driver weight, and much more so than the toe setting. If you were measuring camber from tread to tread with a tape measure, then commonly it can change from zero (without driver weight) to around 10-12mm of camber with driver weight flexing the chassis. These changes represent a very significant level of unpredictability in the alignment that will have real affects on handling and tyre wear.

The amount of any toe / camber change will be dependant on a number of factors, including driver weight, individual chassis, and chassis settings (including scrub radius and even the caster angle). Any factory recommended toe-out or camber settings can only be approximations of any actual toe / camber changes that will occur. The only way to know for sure how much the toe / camber changes on any specific kart with any particular weight and front-end settings is to actually measure / set alignment with the driver in position.

Alignment can be measured / set with the driver in position, but it can be a pain without the right equipment. It just so happens (!) that I manufacture an alignment tool (the ZTB Chassis Alignment System) that will (among other things) measure both toe and camber with the driver in position. The ZTB System will soon be distributed in the US by a company that many of you will probably be familiar with (just in time for Xmas!).

[Bill D Talley]

Don't forget that on a kart with front brakes, most of the toe-in caused by weight transfer will be negated by spindle deflection under braking. This is one of the primary reasons that toe-in increases stability when entering a corner.

Just a little more insight.

Bill Talley
SpeedLab Inc.
Shifterkart Illustrated Tech Talk

[Gary Kozuma2]

Bill,

Your making me think too hard! So what are we shooting for? 0 toe in with kart on ground or should we somehow compensate for the deflection you mention? My limited experience tells me that any amount of toe in with the kart on a stand creates push.

On a completely separate note, in the latest SKI, you stated that a kart needs to be balanced; a stiff front usually needs a stiff rear, etc. My question is why/when do you need a stiff setup vereses a soft setup?

??? Gary K.

[Patrick Hubbell]

quote:

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Originally posted by Gary Kozuma, 41c:
Bill,

Your making me think too hard! So what are we shooting for? 0 toe in with kart on ground or should we somehow compensate for the deflection you mention? My limited experience tells me that any amount of toe in with the kart on a stand creates push.

On a completely separate note, in the latest SKI, you stated that a kart needs to be balanced; a stiff front usually needs a stiff rear, etc. My question is why/when do you need a stiff setup vereses a soft setup?

??? Gary K.

---

The Tool that John Learmoth speaks of is very usefull. I have used one and it is the best tool for setting up the front end of a chassis. Using the ZTB allows you to put the chassis in an active state rather than a static state on the stand. I have used many methods over the years but none make more sense than the ZTB.

I'll see one in the mail soon, right John!

[Bill D Talley]

Gary,

I would start with Zero toe. If the front of the kart "hunts" for a solid line on turn-in then add toe out. If the rear is unstable on turn-in, the front is narrow, front geometry has been removed and the rear has been stiffened. (So you've done everything to tighten the rear on entrance.) Toe the front in and this will settle the rear of the car and reduce turn-in speed.

Normally, you want to use as soft a setup as possible. The easier the kart can transition, the less drag it will create in the corner. Usually as the rear of the kart is softened, less castor and camber can be used to "flatten" the kart. Remeber that a chassis is just a big spring. You want to go into the corner, feel the kart bind just at the apex as you transition from entrance/braking to exit/acceleration.

Use stiffer setups on faster tracks where lateral G-Forces are more prevalent. Softer setups work well on banked tracks and bumpy tracks.
To tighten the rear of the kart for example, I would much rather use a wider stance, stiffer axle and shorter hubs than a narrow rear, softer axle and longer hubs. The reason: The Chassis needs to be in balance. Remember that it isn't just the axle from the bearings out that flexes, it's the whole axle. The center section of the axle is more like a frame member.

It is definately a complex issue. I always like to remove front grip rather than tighten the rear of the kart.

Let me know if this helps.

Bill Talley
SpeedLab Inc.

[ November 18, 2001: Message edited by: BTalley ]

[John Learmonth]

quote:

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Originally posted by BTalley:
Don't forget that on a kart with front brakes, most of the toe-in caused by weight transfer will be negated by spindle deflection under braking. This is one of the primary reasons that toe-in increases stability when entering a corner.

Just a little more insight.

:

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Bill,
That makes sense for a front-braked kart. I haven’t thought all that much about the effect of front braking on toe changes (haven’t had to, front brakes are rare as hen’s teeth here), but this has me thinking about it now (FWIW!).

There are at least two factors (possibly three) at work causing toe change when braking with front brakes,
1) forward weight transfer (causing toe-in)
2) a moment caused by braking force attempting to ‘push’ the front wheels / spindle shafts backward around the king pin axes (causing toe-out).

No 1 will place the steering linkage in tension, and 2 will place it in compression. To some extent 2 must cancel 1 out, but whether it does so completely would be difficult to measure! Both effects will be increased with greater scrub radius, but hypothetically if there were zero scrub radius then 1 would still occur (to a lessened degree) but 2 would cease to occur at all.

A % of the toe-in gain caused by 1 will come from the chassis rails flexing (allowing the king pins to move closer together), and to a lesser degree the spindles flexing (a little bit). At least some of the toe-in gain (1) will be coming from the steering arms twisting under load, but I’d be willing to bet that MOST of the toe-out gain (3) is also coming from steering arm twist (not shaft deflection so much because the shafts themselves are very rigid compared to the steering arms).

Steering arms ought to be very rigid, but with karts (because the tie-rod ends are typically attached in single shear to the steering arms, and the fact that the arms are made from flat plate) they’re the least rigid components in the steering linkage. When the linkage (from spindle shaft to inner rod end) is placed in tension by driver weight or weight transfer, or in compression by braking force, the arms will tend to twist (which will have an affect on toe). It doesn’t take much arm twist to affect the toe setting.

This happens because the outer rod end is attached to the arm above (or occasionally below) the shear plane of the steering arm. Because of the nature of the rod end, and also because many kart manufacturers place a spacer washer (up to about ¼” thick) between the rod end ball and the steering arm, the centre of the rod end ball is usually about ½” (more or less) above the actual arm. This distance from the centre of the ball to the arm creates a ‘twisting moment’, and most kart steering arms don’t resist this very well, especially when the arm has various lightening (weakening!) holes in it (which most do).

The rod end bolt is in single shear, but to avoid the arm twisting it should ideally be in double shear. This would require each steering arm to be twinned, one arm above the other so the rod end can be mounted in double shear between the twinned arms. This is a common design for fabricated steering arms on many racing cars (for good reason), and should be with karts as well. A practical but less elegant solution to arm twist would be to weld a plate over the existing steering arm to beef it up.

With my CRG, driver weight induced toe-in gain / change can be reduced from 2mm to 1mm simply by removing the spacer washers between the rod ends and the steering arms! I can only assume that any bump steer or toe change caused by arm twist caused by weight transfer or braking forces would also be reduced by 50%.

I still think that alignment with the driver in position gives you a more accurate idea of the ‘true’ on track toe setting, even if the effect of braking muddies the picture a bit. The kart spends a lot more of the time with the brakes not applied!

It is notable many kart manufacturers do recommend some degree of static toe-out, and that these recommended settings correlate strongly with (but can only be approximations of) the sort toe changes that driver weight causes.

[John Learmonth]

quote:

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Originally posted by Patrick Hubbell:


The Tool that John Learmoth speaks of is very usefull. I have used one and it is the best tool for setting up the front end of a chassis. Using the ZTB allows you to put the chassis in an active state rather than a static state on the stand. I have used many methods over the years but none make more sense than the ZTB.

I'll see one in the mail soon, right John!

---

Patrick,
There are several ZTB Systems in the mail at present, but unfortunately none are going to your address! I’m sure you know how this situation might be changed!!

PS thanks for backing up my blatant plug!

[John Learmonth]

quote:

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Originally posted by Gary Kozuma, 41c:
Bill,

Your making me think too hard! So what are we shooting for? 0 toe in with kart on ground or should we somehow compensate for the deflection you mention? My limited experience tells me that any amount of toe in with the kart on a stand creates push.
.

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Gary,
IMO if you set to zero toe with the driver on board then you have a more accurate baseline from which to make any adjustments. Consider that for most corners you will be attempting to do most of your braking in a straight line, and that once turned in any braking you may still need will generally be much less than on the approach to the corner. You always want to minimise rolling resistance, IMO using toe settings to tune handling should be a last resort!

[Dave Embry]

John,

Of course we love our ZTB also!! We had it out using it on the scales with one of our karts at the Supernationals and you should have seen the looks of people walking by and trying to figure out what it was!!

Using the ZTB, we now are able to set our toe "dynamically" (with the drivers weight actually in the kart) so are able to set it accurately. One thing I've wondered about was......what does toe out do to make the kart turn more? As I see it, when you initially turn in, the inside front tire will press down on the track (raise that corner of the chassis) raising the outside front tire to the point that it's either actually off the track or having so little weight on it that it's uneffective. So that tire is essentially the only contact patch on the track until such time that the eccentrical forcers begin to take effect (the kart starts to actually turn and the weight begins to shift as it "tip" over the line from the inside front to outside rear) and the weight "tips" over onto the outside front and rears. This only happens after the kart has begun to turn so since both tires aren't touching the pavement, toe should not effect the very initial phase of turn in. Of course, once the outside front comes down and makes contact and takes the load, then both fronts would be in contact and would then toe could come into play.

Does having say "toe out" then cause a "drag" or scrubbing of the front tires, slowing the front end and causing the rear to come around more (looser compared to the fronts)? I know that's what will happen if you have too much toe when you are going down the straight....the engine has to use power to push the fronts which are basically fighting each other and scrubbing as you go down the straight.

If this were the case, then you may have good initial turn in, then as the outside front comes into play and with too much toe...the rear then gets loose quickly.

So it seems that toe out would cause more front scrub, (front feeling "firmer" with more positive control?) which causes the rear to be looser compared to the front. What other effect does toe have on the handling of the chassis? Seems as though toe would almost always be the slower option to take to cure an ill handling chassis since you could probably find a better way to get more front grip (the same as adding toe in my example) or reducing rear grip?

[John Learmonth]

Dave Embry said:

>> One thing I've wondered about was......what does toe out do to make the kart turn more? As I see it, when you initially turn in, the inside front tire will press down on the track (raise that corner of the chassis) raising the outside front tire to the point that it's either actually off the track or having so little weight on it that it's uneffective. So that tire is essentially the only contact patch on the track until such time that the eccentrical forcers begin to take effect (the kart starts to actually turn and the weight begins to shift as it "tip" over the line from the inside front to outside rear) and the weight "tips" over onto the outside front and rears. This only happens after the kart has begun to turn so since both tires aren't touching the pavement, toe should not effect the very initial phase of turn in. Of course, once the outside front comes down and makes contact and takes the load, then both fronts would be in contact and would then toe could come into play.<<

Dave,
As I see it (and as usual the following is all only IMO), toe (in or out) has handling effects particularly at the very moment of turn-in, and since a good corner entry depends on good turn-in, and good mid corner depends on good entry etc, then toe has effects through the whole corner whether or not it might be having any direct bearing on handling at any moment in time.

Toe out increases the front wheel height change caused by caster / scrub radius / KPI, slightly increasing the unloading of the outside front and the loading of the inside front as the steering is turned. It does this because as the front wheels rise / fall (with steering input) they don’t do so in straight lines, but in curved arcs.

These arcs tend toward the horizontal as the wheel turns and rises, and toward the vertical as the wheel turns and falls. Because of this, when the outside front is turned into the corner it doesn’t rise all that much, but as the inside front is turned-in it falls dramatically. Consequently almost all of the front wheel height change (causing weight jacking) comes from the fall of the inside front. It also means that almost all front grip at turn-in comes from the inside front.

When the wheels are toed out at the straight ahead, they’re further back (behind the king pins) and further into the more vertical sections of their arcs of vertical (steered) travel than they will be at zero toe or with toe-in. This will cause the inside front to fall more and the outside front to initially rise more for a given amount of steering input (than if there is no toe-out). This will have a subtle effect increasing jacking effect, acting in a not dissimilar manner as if you had slightly increased the caster angle.

If the steering is toed-in then the wheels will be statically in front of the king pins and more in the section of the arc of steered movement that is flatter (more horizontal) and the effect will be less front wheel rise / fall for a given steering input. This will have a subtle effect not dissimilar to slightly decreasing caster.

Probably a more significant affect is toe causing each front tyre to already be operating with some amount of slip angle even before the steering is turned. Looking at the inside front (or rather, the wheel that will become the inside front the moment you turn in), any toe will mean that even before you turn the steering wheel the ‘inside front’ is trying to turn the kart (but can’t because of the equal slip angle of the ‘outside front’ . This means the (potential) inside front effectively has a ‘pre-loaded’ slip angle at turn-in.

If this ‘pre-loaded’ slip angle is caused by toe-out, as you turn-in it will take less time for a meaningful level of slip angle to develop at the inside front. Keeping in mind that nearly all the front grip at turn-in comes from the inside front, the initial steering response will be more immediate with this toe-out induced ‘pre-loaded’ slip angle.

The opposite will also be true, ie if the front end is toed-in the inside front will have a ‘pre-loaded’ slip angle, but in the wrong direction. When the inside front is turned it will take more time for the slip angle to develop in the correct direction. The wrongly directed slip angle will have to lessen to zero slip angle, and then rebuild in the correct direction. This will make steering response slower.

If the steering response is too slow then it will take longer for ‘G’ force to develop, the risk being that the inside rear will not remain unloaded, and the kart will continue to understeer.

>>Does having say "toe out" then cause a "drag" or scrubbing of the front tires, slowing the front end and causing the rear to come around more (looser compared to the fronts)? I know that's what will happen if you have too much toe when you are going down the straight....the engine has to use power to push the fronts which are basically fighting each other and scrubbing as you go down the straight.<<

Scrub caused by toe-out will slow the kart in the corner as well as on the straight. Keeping in mind that Ackerman will always create steered toe out, this is why (IMO) its best to have the kart set up to just 4 wheel ‘drift’ slightly from about mid corner, and especially at corner exit (ie be able to negotiate the mid corner to exit phase with the kart describing an opening arc but with the steering more or less at the straight ahead position).

I’ve found its quickest when the only steering input needed is to actually turn-in, beyond which the kart completes the turn with the steering more or less at the straight ahead. The kart will still require minor steering corrections, but when the chassis is really working well the attitude of the kart can easily be controlled mostly with the right foot (this isn’t possible on all corners of course, not unless you have heaps of grunt). This is what I’m more or less aiming for when setting up my chassis, to be able to steer the front wheels for the minimum time and to keep the steered angle to a minimum to keep the kart ‘free’ through the corners. Any and all of the time the front wheels are turned the front tyres are slowing you down.

>>If this were the case, then you may have good initial turn in, then as the outside front comes into play and with too much toe...the rear then gets loose quickly.<<

Maybe. Whether or not a front ‘braking’ effect in the corner caused by toe will make the rear ‘loose’ I’m not sure, it could be but I think if so then only by a substantial toe as caused by excessive Ackerman effect, not a small toe as caused by toe setting / alignment. The front ‘braking effect’ might conceivably transfer enough weight from the rear to make the kart oversteer. If the transition from travelling straight to turning is too sudden then you can get a bit taily sometimes.

>>So it seems that toe out would cause more front scrub, (front feeling "firmer" with more positive control?) which causes the rear to be looser compared to the front. What other effect does toe have on the handling of the chassis? <<

It will create scrub, but won’t make the chassis feel more stable (at least not in my experience). I’ve only really noted any direct affect at turn in, but this doesn’t mean there won’t be other affects later in the corner.

>>Seems as though toe would almost always be the slower option to take to cure an ill handling chassis since you could probably find a better way to get more front grip (the same as adding toe in my example) or reducing rear grip? <<

I think deliberately using toe (other than zero) to address a handling problem is a case of curing one problem with another problem. Even if it does ‘cure’ a problem (which it may up to a point), it will make the tyres work harder, which means you may not pay the price of the ‘cure’ immediately, but you might pay it later when the front tyres start to die (you know, after you started off pole in the final……!!).