Adjusting Rear Wheel Toe-in

[Guest boggie]

Hi all,

 

I had a rolling road tune last week at Track N Road. they did a great job but pointed out I am losing 30BHP in transmission. A glance at the angle of the rear wheels on the roller illuminated the problem, my rears were not alligned square to it or parallel with each other. So this weekend I built myself a tracking gauge and checked them. Measuring on the rim centre line, the front of the (15") wheels are 10mm closer than the rear. This would explain why my first set of tyres lasted less than 8K!

 

Now the guys at Track N Road suggested that I undo the hub mountings and shim out the front until the wheels are parrallel. By my reconing I need to move the N/S out by 7mm and the O/S by 3mm as this will both get them parrallel and equally spaced either side of the body tub. Is this easy to do? Can I simply use washers between the hubs and subframe? Any help greatfully received.

 

Many thanks, Boggie

[Guest Jabberwocky]

yes mate, the shims can be done. I have just fitted some to mine (it was a camber problem I had but it is the same principle.

[Longboarder]

5mm (3.5deg) toe in each side is excessive and the tyre scrub will eat tyres and sap some power. However for good handling, particularly stability at speed and to reduce oversteer in corners there should never be toe out on the rear. Setting parallel is not the way to go. That advice is bad. The total toe, L+R should be around 2 - 4mm and equally set each side. In practical terms the way to do this is by shimming between the hub and hub carrier as you have suggested. There is no way you can get this accurate enough without specialist equipment and a skilled operator. You could also look at rear camber setting at the same time. You may have seen posts about camber wedges on the board. The ideal would be to get a combined camber and toe wedge machined up after a setup session to measure the correction angles needed. You could do it with washer type shims but it would turn into a trial and error marathon, I think.

 

Nigel

 

p.s. the toyos on the back of mine didn't manage 4000.

[Guest timswait]

Yes, some toe in is desirable for a RWD (although not as much as you have). There's a good description here.

Using washers to pack under the corners of the hub carrier should work, but structurally it's not ideal, you are putting extra stress on the mounting bolts. If you can get tapered shims instead then these will be better.

[Guest boggie]

Hmmm, interesting. Thanks chaps.

 

If I understand it correctly I need to achieve at least 2mm toe-in on the rears (I want to keep it to a minimum as long as stability is not affected) but how much on the front? I am going to try and get the rear end set up using washers for now, at least then I will know what size tapered shims to get. Can anyone suggest somewhere in the south east to get either the shims OR a complete service of supplying the car and them setting it all up for me?

 

Cheers!

[Longboarder]

Out of interest David Baker at Puma Racing has some very good articles on the misinformation many rolling roads give to justify their mods etc. He also explains why coast down losses do not give an accurate flywheel BHP figure. A major part of the drive train friction losses will be tyres/suspension angles/tyre pressures. You should correct camber and toe. Then set standard tyre pressures before the test? Unless this is done you are not going to have repeatable results to check if your mods are working. I have used four different rolling roads in the last five years and never had the tyre pressures checked or asked about. I do however always set them to 20 psi before I go.

In the end I believe the only meaningful figure is BHP at the wheels.

Sorry I don't know any suspension experts in your area or mine for that matter. I would like to check the same things and corner weight the car accurately.

 

Nigel

[Guest SEgan]

I had the same problems with the rear suspension,

 

LINK

 

One of the best modifications I have made. Well worth sorting out.

[Guest boggie]

I had the same problems with the rear suspension,

 

LINK

 

One of the best modifications I have made. Well worth sorting out.

 

Thanks SEgan,

 

An interesting read! In your experience and taking into consideration that I want to move the NS out by 6mm and OS by 2mm, what size wedges / washer thickness should I try first?

 

Cheers, Boggie

[Guest SEgan]

Thanks SEgan,

 

An interesting read! In your experience and taking into consideration that I want to move the NS out by 6mm and OS by 2mm, what size wedges / washer thickness should I try first?

 

Cheers, Boggie

 

It depends where you are measuring from, are you measurments from the rim edge or from the outer edge of the tyre? Before doing anything re-check everything, why is the back not square to the front? I would be tempted to correct each side with equal wedges to move them by 4mm each.

 

You need an accurate figure for the diameter of the rim or tyre (depending on what you are measuring from) in order to work out the angle of correction required using the SINE rule. Using this angle substitute back in using the distances between the centres of the hub mounting bolts to give you the difference in thickness the plate should be from front to back to give you the angle. Or if you are just using washers the thickness of the washers needed under the front bolt.

 

I estimate about a 1.5 difference if using a plate or 1.5mm washers under the front edge.

 

All the best

 

Sean

[Guest old_timbo]

I've been noticing bump steer from the back over uneven roads. A couple of months ago I measured the toe in and I think it is the cause as it is larger than it should be. I've got the camber wedges fitted already and I used lengths of angle and a steel tape to make the initial measurments. These are the numbers I've come up with:-

 

 

5mm deviation from parallel over 500mm on each side of the car, so what is angle X?

 

 

 

Tan X = 5/500

 

 

 

X = Anti Tan 0.01

 

 

 

X = 0.57 degrees

 

 

 

Tyre diameter for 205/50 15 is 586mm

 

 

 

So 586 Sin 0.57 = 5.83 mm toe-in each side - definately too big.

 

 

 

Really want say 2 mm of toe-in, so how much shimming is required at the hub?

 

 

 

Angle needs to be

 

 

 

586 Sin X = 2, Sin X = 2/586 = 0.0034

 

 

 

Anti Sin 0.0034 = 0.19 degrees

 

 

 

Therefore shimming needs to reduce toe-in by 0.57 - 0.19 = 0.38 degrees

 

 

 

If the distance between centres of the front and rear bolts on the hub is 75mm (need to double check this)

 

 

 

Shim thickness = 75 Sin 0.38 = 0.5 mm

 

Have I done my sums right?

 

I think I will try a couple of suitable thickness washers each side and see what the effect is. If noticable then maybe I will need a more sophisticated solution.

 

Tim

[Guest SEgan]

I've been noticing bump steer from the back over uneven roads. A couple of months ago I measured the toe in and I think it is the cause as it is larger than it should be. I've got the camber wedges fitted already and I used lengths of angle and a steel tape to make the initial measurments. These are the numbers I've come up with:-

 

 

5mm deviation from parallel over 500mm on each side of the car, so what is angle X?

 

 

 

Tan X = 5/500

 

 

 

X = Anti Tan 0.01

 

 

 

X = 0.57 degrees

 

 

 

Tyre diameter for 205/50 15 is 586mm

 

 

 

So 586 Sin 0.57 = 5.83 mm toe-in each side - definately too big.

 

 

 

Really want say 2 mm of toe-in, so how much shimming is required at the hub?

 

 

 

Angle needs to be

 

 

 

586 Sin X = 2, Sin X = 2/586 = 0.0034

 

 

 

Anti Sin 0.0034 = 0.19 degrees

 

 

 

Therefore shimming needs to reduce toe-in by 0.57 - 0.19 = 0.38 degrees

 

 

 

If the distance between centres of the front and rear bolts on the hub is 75mm (need to double check this)

 

 

 

Shim thickness = 75 Sin 0.38 = 0.5 mm

 

Have I done my sums right?

 

I think I will try a couple of suitable thickness washers each side and see what the effect is. If noticable then maybe I will need a more sophisticated solution.

 

Tim

 

Can also be done with ratios!

 

5mm deviation in 500mm is equal to 5.86mm in 586mm

 

5 : 500 5.86 : 586

 

You want to reduce this by 3.86mm over 586mm

 

3.86 : 586

 

If the distance between the bolts is 75mm divide the above ratio by 586 on both sides and multiply by 75.

 

(3.86/586)*75 : 586/586*75

 

0.494 : 75

 

Therefore it looks like we agree on the maths!

 

Sean

[Guest old_timbo]

Great! Just need to find some good quality washers to give it a try. Anyone know what diameter the hub bolts are?

 

Tim

[Bob Tucker]

Am I missing something here?

 

Didnt Ford design the right amount of toe-in when they designed the whole rear Sierra subframe?

 

If so, then any deviations must be the resullt of bent arms or dedion tube........innit?

 

Or does altering the effective ride height burger things up? IE toe-in as well as camber?

 

Bob

[Dave R]

lowering definitly toes the rear in

[Guest timswait]

Or does altering the effective ride height burger things up? IE toe-in as well as camber?

Yes. Look at the position of the mountings for the trailing arms. They're not parallel to the axle line so you get change in toe as the arms move. Quite common, a sort of rear wheel steer improving stabilty as the car body rolls on a corner.