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Rear Toe In - again.

PostPosted: Mon Oct 24, 2016 11:22 am
by vincereynard
With all the different tyres and wheels I cannot see how having a toe in measurement in inches or mm can be particularly accurate.

Using a specific angle would remove this problem??

My car has 175X70 / 13, which according to a comparison site, has an OD of 22.6 inches. Assume that is the hypotenuse. Small side opposite the toe angle to be 1/8 inch (0.125) for this exercise.

0.125/22.6 = .00553 inverse sine = 0.316 degrees. Call it 0.32.

Therefore the recommended toe in by Spyder being 3/32 per side would give an angle of 0.24 degrees per side.

Is this nonsense?

Vince

Re: Rear Toe In - again.

PostPosted: Mon Oct 24, 2016 11:52 am
by rgh0
Toe in amount is normally quoted at the wheel rim at axle height so tyre size makes no difference.

Front toe in was typical quoted by Lotus a the total difference between the front of the rim and rear of the rims at axle height of both wheels. This was the normal way front toe in was quoted by manufacturers in the 60's

Rear toe in is less certain as there was no standard practice in the 60's as independent rear suspension was much less common. Rear toe was probably quote by Lotus as the difference between the front and rear of the rim at axle height of the individual wheel versus the car centre line. I say probably because as far as I can find out, know one at Lotus currently knows for certain what the numbers quoted in the workshop manual apply to exactly for the rear wheels on the Elan. For the Europa and Early Esprit it was the individual rear wheel versus the car centreline so Lotus probably used the same convention for the Elan.

cheers
Rohan

Re: Rear Toe In - again.

PostPosted: Mon Oct 24, 2016 4:19 pm
by vincereynard
If it was from the rim, and for individual wheels, wouldn't the published max of 3/16 given in the manual give a large amount of toe in? 3/8" between rims- 1/2 inch(ish) between tyre surfaces!

Re: Rear Toe In - again.

PostPosted: Mon Oct 24, 2016 10:41 pm
by toomspj
Vince

You're spot on. Toe in when measured in MM or inches is from the rim. And yes it's a good amount on the front and generally most people prefer around twice as much on the rear for top track performance.

Re: Rear Toe In - again.

PostPosted: Mon Oct 24, 2016 11:53 pm
by vincereynard
toomspj wrote:Vince

You're spot on. Toe in when measured in MM or inches is from the rim. And yes it's a good amount on the front and generally most people prefer around twice as much on the rear for top track performance.


Remarkable that bears out my trig calculations that suggest 0.24 degrees total front toe in and 0.24 individual rear toe in. That must make a first!

Re: Rear Toe In - again.

PostPosted: Tue Oct 25, 2016 5:46 am
by john.p.clegg

Re: Rear Toe In - again.

PostPosted: Tue Oct 25, 2016 12:01 pm
by KevJ+2
john.p.clegg wrote:Vince

<a class="vglnk" href="http://www.lotuselan.net/forums/lotus-suspension-f42/tracking-t19506.html" rel="nofollow"><span>http</span><span>://</span><span>www</span><span>.</span><span>lotuselan</span><span>.</span><span>net</span><span>/</span><span>forums</span><span>/</span><span>lotus</span><span>-</span><span>suspension</span><span>-</span><span>f42</span><span>/</span><span>tracking</span><span>-</span><span>t19506</span><span>.</span><span>html</span></a>

John :wink:


I'm really thick with things like this, but can you tell me how you set the string lines up? If the front and rear wheels are supposed to toe in, and the result should be a trapezoid, how do you set up reference lines from the rims to begin with?
Sorry if this has an obvious answer :oops:
Kev.

Re: Rear Toe In - again.

PostPosted: Tue Oct 25, 2016 2:50 pm
by vincereynard
I have tried string theory in the past but without success. Hence going to the laser man!

I believe that you have to establish a true centre line first? Or how are you going to measure individual toe in?

Re: Rear Toe In - again.

PostPosted: Tue Oct 25, 2016 2:58 pm
by john.p.clegg
I have now made up a set of four magnetic sight tubes which attach to the rims and give a V good line of sight

1) place the tubes on the front vertical,tubes on the rear horizontal , this tells if the rear wheels are correctly aligned with the front , only available adjustment is by adjustable A frames

2016_1025wheelaligmnent0001.jpg and


2016_1025wheelaligmnent0002.jpg and




2) place the tubes on the rears vertical,tubes on the front horizontal , adjust the toe in...

2016_1025wheelaligmnent0003.jpg and


2016_1025wheelaligmnent0004.jpg and


I did re-orientate the photos but it just didn't want to play...

5 minute job

Simples

John :wink:

Re: Rear Toe In - again.

PostPosted: Tue Oct 25, 2016 3:27 pm
by vincereynard
That's rather neat John.

A quick calc. using the rear having a 1/2" offset would give an angle of 0.2985. Which is close enough to 0.3 as not to matter! Add a horizontal bar, (coming out sideways), to your front vertical tube and you could pop a laser in the rear tube and read it off as a scale.

Vince

Re: Rear Toe In - again.

PostPosted: Tue Oct 25, 2016 3:48 pm
by john.p.clegg
Vince
I did try with a laser but with battery leads etc it was too much palaver and sighting through the tubes is so easy.

John :wink:

Re: Rear Toe In - again.

PostPosted: Tue Oct 25, 2016 4:25 pm
by UAB807F
KevJ+2 wrote:I'm really thick with things like this, but can you tell me how you set the string lines up? If the front and rear wheels are supposed to toe in, and the result should be a trapezoid, how do you set up reference lines from the rims to begin with?
Sorry if this has an obvious answer :oops:
Kev.

Hi Kev,

If you want to try the string method, here's a link to how I do it.

Basically I start off with rigid bars at either end of the car with holes exactly the same distance apart. All you need to do then is centre it up and I do that by using measurements from the hub centres front & rear, allowing for the differences in track. It's fiddly and of course there's the added enjoyment when you trip over an axle stand and move everything.... :)

http://www.martley.plus.com/lotusland2016/europa/16europa17.html

Brian (It's on the Europa, but the principle is the same for both cars)

Re: Rear Toe In - again.

PostPosted: Tue Oct 25, 2016 7:07 pm
by KevJ+2
Thanks Brian...Great stuff.