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Where do people measure toe-in?


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Hello All,

I’m slightly confused about setting front wheel toe-in. This confusion comes about from reading different information on various websites that all talk about toe-in, but all seem to tell you to measure it in different places.

I have always believed that the toe-in should be measured at the outer limits of the outside of the steel rims. (That way it does not matter what tires you have on the car..)

I remember shops that hired out the kit to do it and I'm certain that you pressed two steel bars up to the steel rims. Front and back of the rim on each side and there was a mirror sort of thing that you looked at and twiddled a knob to discover ... urm ... something...


Some websites agree with this.

But…

Some websites say that you measure it from the center of the tread, and some say that you measure it from the bulge caused by the tyre sidewall.

I appreciate that if we are talking about the toe-in in degrees (or parts thereof), you don’t get into such confusion, but as most (all?) people who do their own tracking use distance measurement it’s important to get it right.

An 1/8 inch difference measured at the three places I mentioned will result in different angles of toe in.

So which is right?
Your wisdom is appreciated

Charlie

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I calculated back to “angle”, and then measured on the rim. If you are not sure your wheels are absolutely straight, do the measurement, then to roll the car so the wheels rotate 180 degrees and then take a 2nd measurement and average the outcome of the 2 measurements.

Waldi

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I use a diy trammel bar and measure at the front and rear of the tyre using a horizontal straight edge across the sidewall. I set toe parallel as the suspension bushes are nylatron/ stainless with little give. Book values will be for rubber bushes, with polybushes neeeding rather less I guess.

Peter

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I set mine parallel as taken off the rear wheels on my solid axle car. 
I use the string method to do this. Measuring off the outer rim front and rear of each wheel.
 

very stable driving with a steering box even at speed. 

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You do it the way the pros do.
Measure across the front of the rims and then against the rear of the rims on the same wheel. * The difference between the front dimension being less than the rear is the toe in amount, or if the rear of the wheel is less than the front, it’s toe out.

It can make considerable difference to how the car drives. If all the suspension is correct and with suitable spring rates about 3/16 to 1/8 toe in normally gives good results and a reasonable amount of understeer ( which is safe). As the toe progresses to neutral (dead ahead) the handling will become less defined and then as the toe goes too out it becomes more nervous.

Having a car which understeer is good, it allows you to change the handling as you drive by applying more power which increases the front tyre “slip” angles so reducing front grip and allowing the handling to change to neutral and then oversteer.

Mick Richards

* If you don’t have a toe in gauge you can do this using 2 suitable length thin sticks which overlap by a good amount and tie wrap them together. Then slip them apart onto the inside of the front wheels inside edge ( from the front) and mark one stick against the other with marker pen. Then squeeze the sticks back together to remove, and carry out the same measuring process against the back of the wheel, and compare against the marked dimension of the front of the wheel. Compared to the front smaller is toe out, and larger is toe in. The difference between measuring at centre line of the wheel as against the bottom of the wheel is so small as not to make any difference, it’s comparative, it’s how the car drives that matters.

 

Edited by Motorsport Mickey
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Thanks all for the comments.

Seems like I was doing it right by measuring to the rim.
I note what Peter said about measuring from the tyre sidewall, but if you are going for parallel (Like him) I guess you can measure from anywhere. I’ve just spent a day building a trammel bar, after he mentioned it.

Thanks Waldi for the tip on rolling the wheels 180 degrees.

Hamish said “…very stable driving with a steering box even at speed... “. Good to hear because that is what I have got!.

I’m sure that Mick is right about how important the toe-in is. I think that getting the right set up with toe-in and tyre pressures can make the difference between a car that is impossible to drive and one that is a pleasure.

When I first drove the car a couple of years ago after a 40 year lay up I could not keep it in a straight line without constant correction. I hadn’t checked before I drove it and found loads of toe-out. Made some adjustments and it became drivable.

Thanks,

Charlie.

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after my full body off resto I simply installed the shims where they were before, and also the track rod lenghts were set to the same, assuming it would be about ok. It was not, I had a huge toe-out. Funny, isn’t it?

I aligned all four wheels myself, using a simple laser. It was a day work, and when I had it checked on a professional station, the results were very close to mine. I felt proud:)

Cheers,

Waldi

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Charlie,

The piece of kit with steel bars and mirrors that you refer to is Dunlop tracking gear.

They use 2 steel bars set on the wheel rim. A dial is set to the specific wheel diameter and when the mirror image is lined up the gauge reads an angle which is converted to a measurement - toe in or out - on the dge of the dial.

Dave McD

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9 hours ago, Dave McDonald said:

The piece of kit with steel bars and mirrors that you refer to is Dunlop tracking gear.

Dave,

Thanks for that. I see there are several on eBay, like:

https://www.ebay.co.uk/itm/234562672688

Seeing the pictures took me back to my teenage years!

Charlie

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No secret that I use the string method, and measure to the rim (more accurately with the bottom pin of a vernier gauge).  The string method does however need to take into account (via packers on both front and rear tyres, under the string) the difference in front and rear track, and equally any difference in front and rear wheel and tyre (type/ size / make), and any wheel spacer.  My own car has the same wheels and equally new tyres front and back so it's easy.  Measuring to a tyre bulge is generally inaccurate and even more difficult where tyres are differently worn (or scuffed) &/or the pressures (front and rear) are different too.!

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^ 1/8" packer on the front tyres, under a taught string at the front, means the toe-in doesn't cause the string to bulge around the back of this tyre.  1/4" more,  ie., 3/8" packer on each rear tyre under the string ..accounts for this model of TR having a 1/2" narrower rear track.

 

And as Peter, correctly points out . . . 

On 5/23/2022 at 4:21 PM, Peter Cobbold said:

Book values will be for rubber bushes, with polybushes needing rather less I guess.

^ This is because toe-in was set to also compensate for bump and brake steer, including deflection of (rubber) bushes as they are loaded in a corner &/or when responding to road surface irregularities ..ie., where the wishbone twists slightly back ( = toe out !).   Similarly, this happens in the rubber mounts of rack & pinion steering of later cars, and in the bushes of rear axles ..which explains why my TR4A IRS  also has zero to 1/16" toe-in at the rear.

I understand that more modern tacking, castor and camber equipment uses the brake disc to measure from. I'm not sure if that works with drum brakes (wheels off but wheel nuts back on). 

It should also be emphasised that toe-in (..or toe-out set on some track-racing cars) is measured for the axle, and not of each wheel.  So, for the side screen cars ; 1/8" toe-in is measured, by the string method or side trammel bar as an equal 1/16" difference (to the front and rear of the wheel rim) on both sides  ..not 1/8" difference..

Pete   

 

 

Edited by Bfg
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On 5/24/2022 at 2:05 AM, Motorsport Mickey said:

If you don’t have a toe in gauge you can do this using 2 suitable length thin sticks which overlap by a good amount and tie wrap them together. Then slip them apart onto the inside of the front wheels inside edge ( from the front) and mark one stick against the other with marker pen. Then squeeze the sticks back together to remove, and carry out the same measuring process against the back of the wheel, and compare against the marked dimension of the front of the wheel. Compared to the front smaller is toe out, and larger is toe in. The difference between measuring at centre line of the wheel as against the bottom of the wheel is so small as not to make any difference, it’s comparative, it’s how the car drives that matters.

I would really love to understand this, but I don't. Can you provide a diagram or something that illustrates it please?

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