Rear toe GTD setup

[thierrygt]

Hello, everybody,
i am french and recently purchase a Gtd Mk1.
All settings are to do on my car.
The rear wishbones have not adjustement on ball.
For setting the rear toe, i have add shim, between the front and up bracket arm and the chassis (6 mm).
The rear toe value is +1 mm (toe-out overall).
The build manual advising rear toe-in (0 to 1.6 mm overall).
If i add another shim, the total thickness is 9mm and moving the rear wheels to outside.
How to get the right setting ?
Thanks you for your advice.
Thierry

 

[Malcolm]

Hi Thierry

You need to play with the shims to acheive either straight ahead wheels or toeing in up to 1.6mm overall. If you don't have this the car will have a tendancy to be loose at the rear. Reduce the shims to get the right reading.

 

[Simon]

Which shims are you talking about gents? I'm a bit confused the only place I know of to shim is the inside of the lower arm. Surely that adjusts the camber by moving the whole bottom of the upright?

 

[Mike Pass]

The rear toe in is adjusted at the inner end of the lower reversed wishbone. Move washers/shims from the front to the rear of the inner pivot or vice versa. There are two thicknesses of washer/shim or you can make up your own. It takes a bit of time as you have to move the washers/shims - tighten up and then remeasure the toe in. However if you keep a note of what you did and the effect it had you can easily work out the toe in change for each washer/shim change. Finally tighten up and do a final check. I did a four wheel laser alignment and it was well worth the trouble.
Cheers
Mike

 

[Simon]

mike, surely you don't mean the single bracket attached to the chassis by two bolts?

simon

 

[Howard Jones]

Shim = washer, as on each side of the bushing. The bolt goes thru them. Moving the center of the chassis side of the reverse wishbone forward of rearward (by moving the washers location) changes the effective angle of the wishbone in relation to the centerline of the chassis thus changing toe.

If I remember correctly they all end up on the front of the bushing (max toe in). Set it up this way to start and if you have to much toe in then move them all to the rear. Now if you have any toe out (you don't want any), divide the difference by the number of total washers and make the neccessary adjustment to washer location.

This is a crude system and you will have to live with what you get. Just try to achieve the same sitting on both sides and as near to total 1/8" toe in (1/16" on each side) as you can. You do not want any toe out no matter what you do.

 

[Simon]

Howard,
Of course, what was I thinking!
Thanks

Simon

 

[thierrygt]

Hello,
thanks you for yours answers.
I did not proceed correctly adjustment.
I do it again.
About the front toe, what advise you ?

Thanks
Thierry

 

[Mike Pass]

The GTD build manual states
1.6 - 3.2 mm overall toe in at the front.
0 - 1.6mm overall rear

Cheers
Mike

 

[Howard Jones]

Put about 1/8" total on the front, no more. The front is adjustable just like a standard road car. Anyone with a alinement shop can set it for you. Have them give you a printout of caster, and camber also when they set toe at the front. When you have the measurements let us know what you have.

 

[Frank Catt]

OK Mike, where are these measurements actually to/from ? 0-1.6mm ? We all have out own way of calibrating the set up, but I wonder how many of us actually know what 1/8 th toe in is ? Frank

 

[Randy V]

OK Mike, where are these measurements actually to/from ? 0-1.6mm ? We all have out own way of calibrating the set up, but I wonder how many of us actually know what 1/8 th toe in is ? Frank

This is going to be an interesting read...

Having learned alignment from Master Mechanics many eons ago - I know where I take my toe readings from and will share with you in PM to keep myself honest.

 

[Mike Pass]

The measurements are a direct quote from the GTD build manual. Where the measurements are from or to I know not! I would guess that the measurement would be at the wheel rim as that is where most equipment attaches.
I set my car up with half a degree toe in at the front and a quarter of a degree toe in at the back. Seems OK to me but then I'm not the best person to judge these things. It's a lot better than the previous owner set it once with 8mm toe in on one side and 20mm toe in on the other. The saw tooth wear pattern on the tyre was interesting to say the least.
Cheers
Mike

 

[Ron Earp]

Well dang ol dang ol, - fellows that claim to know what is up but are afraid to draw in public! Well, I'm often wrong in public so not afraid, here goes...

I don't know squat about GTDs but if I were you I'd use toe plates, one on the outside of each wheel and two tapes and measure the total toe (you'll find diagrams on the web how to do this as well as toe plates for sale). I'd start out as Howard says, with a total toe in of around a 1/8th of an inch, 1/16th inch on each side, and see how that feels. Drive car, go from there.

Now, I have assumed that both of your front wheels are aligned together. You'll need to string your car up to make sure that is the case so that your total toe measurement isn't just toe all in one wheel. When I re-aligned the Z last week I found I had about 1/8" of total toe in the rear - but it was all in the left rear wheel, not good! We fixed that. My method might be wrong but it must have worked for me, I took home a win last weekend at VIR in the Z with a personal best laptime to boot.

 

[Trevor Booth]

the measurement is at the bead seat of the tyre i.e. the rim diameter.
What you are actually setting is an angle, a linear measurement is just the easy way to measure it for most people.

 

[Frank Catt]

Ron, what Randy and I have tried to draw out is what the majority of members know about setting toe. We all have our own methods, some conventional like toe plates and string computers, others have more radical and unconventional ways of doing it. Without doubt just about every car that comes in my shop is set way out, wheels pointing in every direction, and most of these said to have been proffesionally set up. It seems that few builders want to admit they havent a clue, and most modern alignment shops with their computer equipment cannot cope the complexity of multi link rear suspensions. Your comments may be meant to be fun, ours are aimed at being helpfull by drawing out discussion.

 

[Ian Anderson]

I would like to learn more

Now I can see how the measurements should be taken at the rim diameter But surely is you change from a 15 to 17 inch wheel your 1/8 inch will need to be closer to 9/64ths inch (or whatever the actual Pythagorus comes out at)

Is there a "standard" rim diameter that should be used to get comparisons?

Now from memory from my 100cc international karting days we ran something like 1.5mm toe out measured on the 4 ir 5 inch rims (can't remember) damned twitchy in a straight line but great in corners!

Ian

 

[Howard Jones]

There isn't a magic number that will work perfectly for every car, but if a GTD with standard syspension parts is set up with a total TOE IN of 1/8 inch at the front and 1/16 - 1/8 of an inch total TOE IN at the rear it will be pretty damn close and certainly close enough for a road car.

I expect that when someone asks for a measurement that they are aware of how to use the given setting to adjust the car.

I know that many people who race their car have found a "best" setting based on the individual cars configuration. The information I have provided is a good starting point and will not be so far off that the tires get ruined or the car is dangerious to drive.

The place I use on my car to measure toe is the center of the contact patch on the front tires and likewise on the rear. This will also be the the point on the tire that is 1/2 of the total height off the floor. Same height on both side.

Of course the the measurement must be made from the exact centerline of the chassis. Then you will have each tire pointed inward 1/16 of an inch at the front of the tire in relation to center of the wheel/axle on each side and thus 1/8 total toe in.
It is helpful to draw a line around the tire with a ballpoint pen as it is turned. Be sure to do both tires in the set (F or R) on the same point. (centerline of the tire)

This all takes careful measurement but is nothing that can't be done by a newbe if he is in fact careful. This is the main reason that cars are setup all wrong. People don't care much about someones elses stuff. This is why I mostly do things myself.

 

[Trevor Booth]

Ian,

The toe in or out as the case maybe, is dictated by the car, not the wheel diameter.

1/16 toe in on a 13" wheel car may not suit a 15" wheel car, or it may well be OK on the 15" wheel car, it is merely a "setting" dictated by what you want to achieve in handling and road feel that you are comfortable with. On the same vehicle a road setting may not suit a track setting and Vica Versa

The way Howard does it is what he feels comfortable with on his particular car , he has arrived at a "setting" by the method he uses ( and nothing wrong with that).
If you then put the car on a wheel aligner it would be a different "setting" as the method of measurement is different.

It does not matter how you do it, it is the "setting" that you obtain for your purposes that is important.