Rear wheel geometry.

[aggie]

I bought a TR4A last November and must confess that,  at the time, I didn't notice this but, now, when viewed from the rear the driver's side wheel looks to be almost vertical against the bodywork which, I guess is normal.  However the passenger side wheel leans in at the top and also seems to toe in.  The car has been converted to use telescopic shocks but I'm not sure which method was used.  Any ideas ?

[Rob Salisbury]

Hi, assuming it's an IRS rear end (if it's a solid axle something very strange is going on!!), then from the workshop manual the rear wheel camber should be 1 degree neg. plus or minus 1/2 a degree and the toe in should be 0" to 1/16" (front and rear), this is with the car loaded with 150lbs on each front seat.

The rear wheel camber will change both with ride height and by altering the brackets (1 notch,2 notch and 3 notch) that hold the alloy suspension arms to the chassis, you can even buy fully adjustable brackets but they need quite detailed setting up.

Cheers Roib  

[Bfg]

Hi Aggie

how much are we talking about ?   When viewed against the bodywork can be very misleading because ;  a) the rear wings may have been fitted at different heights,  b) may not be true (symmetrical) if one is an after market panel, has been dented (even if repaired), and c) because the body tub may not be sitting square on the chassis.  My own car had each of these and quite a few things more wrong.

Also can you tell us if the ride height is the same on either side of the rear of the car (..measured chassis to a level floor, because measuring to the body is subject to a, b & c above)

It's easy to check the camber with a spirit-level placed vertically and longitudinally in line with the axle / wheel centres (I rest mine on the floor and rest it against the wheel arch, and hold it there with a block of wood leaning against it).  Then simply measure the distance from the wheel rim to the spirit-level both top and bottom (of the wheel). The dimension should be just about the same up to 1/16" more at the top.  Note ; The measurement is very likely slightly differently from one side of the car to the other for reason b) & c) noted above, but the difference 0 to 1/16" should be much the same.

A cord pulled tight around the front (aligned straight) to rear tyres, with a 6mm spacer under the cord on the rear tyre (as the track is narrower than the front) will give you a very good indication of whether there is toe-in. Again measure to the rear wheel's rim, but of course this time at the 9 o'clock and 3 o'clock positions. For practical purposes that dimension should be the same. If not then it can easily be corrected with the shims on the trailing arm to chassis brackets. 

If I might refer you to my learning curve through this < here >

Hopefully your car's discrepancies are simply an optical illusion when viewed against the body and wings, or else a matter of how the suspension was (or wasn't !) set up during some previous restoration.

Pete

[aggie]

Thank you both very much for the technical info.  I don't understand all of what you write Pete but it's very interesting.  I have a far better understanding of the various factors contributing to the geometry now.  Actually I did get underneath and check and the set was the same as yours Pete 2u outer and 1u inner.  Each of the brackets has 4 shims.  Everthing looks to be okay with the chassis so I guess a bit of fine adjustment will do the trick.

[Bfg]

18 hours ago, aggie said:

Everything looks to be okay with the chassis so I guess a bit of fine adjustment will do the trick.

good stuff, I'm very glad to hear that..

Should it help, just ask if there's anything I've written that could do with clarification.

Pete

[dpb]

Hi

I have just reassembled the back end of my 4a,   and now working on the camber and toe-in of the rear wheels.    Following Pete's method above the toe in on the RHS needs adjusting, its actually a bit toe-out if anything at the moment.  The LHS is fine.   So this brings me to shims,  and when I took it apart the shims - 2 or 3 on each bracket, were mounted at the front-facing edge of the chassis leg, i.e where the nuts are,   whereas I imagine they should be behind the trailing arm bracket on the rear-facing edge of the chassis leg.  So if I am right they weren't actually doing anything?  Is that right?

And secondly, if i want to make it more toe-in,   the shims need to go behind the inner arm bracket?

Dave

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[stuart]

They definitely werent doing anything there! They go between the bracket and the rear face of the chassis. Toe in would need to be adjusted from a base number of shims so fit two or three to start and then work in or out from there.

Stuart.

[Bfg]

I concur with Stuart, those shims are to adjust for toe-in (not for camber) and as a starting datum ; two were used on the rear face of the chassis leg, under each bracket.  If your car presently has toe out on the RHS then an extra shim under the inboard bracket would start to correct that, ie., three shims under the inboard bracket and two under the bracket by the sill.  If that is insufficient to correct the toe-in then also take one out from under the outboard (next to the sill) bracket.  My rear axles are set up with neutral tracking (ie., neither toe-in nor toe-out)

Just as a reminder, if using the string method of checking the tracking (toe-in), don't forget to add a 1/4" (6mm) packer between the tyre and the string on the rear wheels ..to allow for its 1/2" narrower track.  Of course the front wheels need to be straight ahead and their tracking correct too ..otherwise the measurements you take at the rear axle will be erroneous.

Also the car (or chassis) should be sitting with the car normally loaded. This is very much more critical when checking the camber, but because of the 58 degree angle of the chassis leg and its brackets - the swung-angle of the semi-trailing arms will also effect the toe-in of the wheels.  For checking the tracking then just an approximate ride height (and the same on both sides of the car) is Ok for all practical purposes.

Pete 

 

 

Edited April 24, 2022 by Bfg

[dpb]

Thank you both.  I've started on the correction this afternoon. I did use the string and 6mm packing method,  with wheels as straight as i could get 'em. 

Slow progress but getting there.

[Bfg]

excellent