Toe-in or toe-out?

It would be entirely dependent on the geometry of a particular vehicle.

Chris

Slight toe in is right for most vehicles. String and steel ruler can get very acceptable results. (always check again after a short drive.)

I thought it might :-) It sound sounds like an interesting subject that I've neglected for too long, but how do you find out about the geometry of one's vehicle? For the near future, I'll be mostly interested in my old Fiesta, and missus' V40.

I used a piece of rope pulled from around the back wheels last time I changed the track rod ends, but it seems a bit hit-and-miss, hence the question. I decided years ago to decline the offer of having them checked whenever I have a tyre changed, because I've never seen any evidence that they actually do anything other than charge you a few extra quid.

The trend I have seem is for toe in for rear wheel drive and toe out for front.

Yeah, they charge you a couple of quid for checking the tyres for uneven wear patterns which might indicate the tracking needs adjusting; I'll bet they never check it if they can see for themselves what your old tyres are like.

Fiesta is toe in for certain.

and toe in is safer than toe out for stability at speed, a bit like thirty psi is a safe pressure for 99 percent of cars

But isn't the idea of having the right amount of toe in (assuming that is the best result all round) a function of if the vehicle is front or RWD (as mentioned elsewhere)?

So, if it's a RWD then the toe in will reduce as the vehicle goes faster and the frictions (tyre drag / bearings / air resistance etc) will cause the toe in to minimise, ending up with parallel at the optimum?

Whereas a FWD car will cause the wheels to toe in more as the speeds increase (ignoring acceleration loads etc) and hence why you might start with them toe'd out at rest?

I'm guessing if you replace all the suspension bushes with harder ones you wouldn't have to compensate to the tracking changing so much?

So, even if 'some' toe-in is is considered 'good' for most vehicles, too much could knock your tyres out in short order. ;-( [1]

Cheers, T i m

[1] The Mrs managed to reverse slice the Kitcar into a parked (on the other side of the road, facing the 'wrong' way) Daimler Sovereign and the kitcar came to an abrupt halt as our OSR wheel rim caught the NSR wheel hub of the Daimler. The inertia of the car, engine, gearbox and prop shaft going backwards was countered by the back axle going forwards (on the OS) and unbeknown to me at the time, wrapping the rear axle around the prop shaft etc, bending the rear axle tube slightly.

I replaced all the obviously damaged bits (OSR shackles, damper, anti-roll bar) and straightened the dent in the rim and we continued driving it. About 1500 miles later the (M&S) rear tyres were nearly bald and the wear pattern was that of toe in? I took it to QF who said they couldn't measure the tracking on what was the rear of a MkII Escort so I asked them if I could use their gear myself, they let me (and I did). ;-)

It showed there was just under 1.5 deg toe in (as I suspected) and a replacement axle tube was found and fitted, along with a new pair of tyres, which perished long before they wore out (again). ;-)

So, 'even' 1.5 degree of toe in on something that should be nearer parallel (?) had a major impact on the tyre wear.

1.5 degrees is 10 times the amount a fiesta would have on the front. Too much of anything is bad. On the average car I just use a slip gauge and set it to parallel or very slight toe in, never gives any trouble. Big stuff with expensive tyres I get the tracking set with a local place I trust with a laser 4 wheel tracking set up.

The spec should have a tolerance. eg 0-2mm toe in. Aim for middle of the tolerance ie 1mm.

Better for tyre wear to be nearer to 0 unless it wanders at M-way speeds then a bit more toe in is needed. So if your spec is 2-3mm toe in. It would be better to be at 2mm than 3mm.

It seems Ford spec toe in degrees. So you will have to do some trig based on the distance from the axle that you measure the toe in at.

There is a very big difference between degrees and mm toe-in.

Many Fiestas have 0 - 0.2 degrees toe-in.

On a 195/65R15 tyre 2mm toe-in is 0.18 degrees.

1.5 degrees is 8.7mm. That would easily destroy a tyre.

Yeah, maybe I shouldn't have used 'even' here but I was thinking 'most people' would consider 1.5 deg on something as big / dynamic as a car wheel to still be a 'small number'? ;-)

Often (depending on who is determining the baseline). ;-)

And that was sort of my thought. eg. If you set some toe in on something that might traditionally be set toe out, could you end up with an error that might not be 'good'?

So, OOI, if you replaced *any* of the suspension / steering components, do you routinely check the tracking? I ask because we recently replaced the NSF lower arm on our daughters Corsa C (the big / rear bush had rusted out) and didn't check the tracking? ;-(

Cheers, T i m

This is the track width difference between the front and the back of the tyre (in mm)?

Quite! ;-(

That's why I am generally very fussy even when building a trailer (with independent suspension) to ensure the wheels are at least parallel. ;-)

Cheers, T i m

Yes, any steering suspension part changed needs at least a quick tracking check after (hence the side slip gauge I use) In the absence of a check : if the steering wheel is still centred when driving in a straight line. it is a pretty good guide.

the mm difference is taken at hub height, from the wheel rim. If you have made yourself a measuring bar, it is good practice to measure to the same point on the wheel rim: ie: move the car forward half a wheel turn before taking the second measurement (this eliminates any anomaly caused by a damaged wheel rim. Never measure to the tyre, they vary too much.

So you have to do this from the inside I'm guessing (with the tyre fitted in any case)?

Understood.

No, quite, I'd put a straight edge across the outside of the wheel with spacers between the edge and the rim if the tyre was wider than the rim.

As long as you measured both front and back track at the outside diameter of the tyre you could at least measure for parallel (I'm thinking trailers here really) but I'm guessing you couldn't use mm difference unless you did so at some set radius (or did the calcs etc)? eg, 2mm at a 400 mm radius would be the same as 1mm at an 200 mm radius (that you may not be able to measure directly)?

Cheers, T i m

Measuring to the outside is easiest.

Long straight edges on the wheel rim is fine, then measure two points on the straight edges that are equal distances apart to the points on the wheel rims (so about 14 inches apart and starting a set distance from the wheels)

Just to be sure ... I get the straight edges against the two rims and measuring between them front and back but are you just measuring for the difference between the two, no matter what arbitrary radius you chose to take the measurements at? Wouldn't that number be bigger the greater the measurement radius so what number would you use ... or would you just convert that into an angle in any case?

Cheers, T i m