Rear wheel alignment

[AussieJohn]

Can anyone give definitive answers to my questions? When setting the toe-in is it 3/16" each to the centreline of chassis or 3/16 total? Is the measurement from centre of the tyre front to rear or the measurement on the rim front to rear? Is 3/16 the optimum or max; the car is just used for roadwork with a "slow" old driver.

[rgh0]

I had an email discussion with the Lotus technical manual writer about this a couple of years ago.

While the guy at Lotus could not be certain what the practice was 40 years ago his belief was they would have been quoted as follows

1. Front toe in is total for both wheels (not just one side referenced the car centre line) - rear toe in is for each individual side. referenced the car centreline. This is quoted that way because the front is not independently adjustable side for side while the rear is.

2. Toe in is the total difference between the front edge and rear edge at the wheel rim

Lotus quote a range in the manual - dont have it here - but I recall for example the rear specification is 0 to 3/16th inch. If trying to adjust it I would set for middle of range i.e 3/32 inch each side. But since rear not easily adjustable without modifications I would not try to change unless outside the tolerance band.

regards
Rohan

[AussieJohn]

Thanks Rohan, I have found my car to be very "nervous" when cornering one direction but ok the other. I faffed around with a laser level and found one rear wheel toeing in but the other toeing out slightly. The chassis is a replacement with no apparent damage and the wishbones and bushes look ok. A friend has kindly made a set of adjustable wishbones so this should correct the alignment problem; I am hoping this is what is causing the handling problem, cheers, John.

[john.p.clegg]

Rohan

"This is quoted that way because the front is not independently adjustable side for side while the rear is"

Do you have this the right way round?...surely the front is easily adjustable,the rear less so..

John

[bcmc33]

Toe in is the total difference between the front edge and rear edge at the wheel rim

Rohan,

My teaching and practice has always been that front toe-in/out is half the difference between the front edge and rear edge at the wheel rim. i.e. toe-in/out should be measured from the wheel pivot axis which is normally the centre of the wheel.
I'm currently running what I believe is 5mm toe-in on 14" wheels ? is this 10mm, perhaps?

It's only recently after reading different threads on the subject of rear toe-in that I've given it any thought. The rears would have to be individual settings, but is it full wheel or half wheel measurement? Any adjustment made by the adjustable wishbones shown would, I guess, not result in a pivot point approximately on the wheel centre ? but does it matter that much?

I shall take some time out this weekend to measure the rear toe-in just for the sake of interest.

[AussieJohn]

Hi Brian, I am now a little confused as many of the methods showing how to adjust the front toein measure from centre of the tyre, do they allow for thisin their measurement? cheers, John.

[rgh0]

Rohan

"This is quoted that way because the front is not independently adjustable side for side while the rear is"

Do you have this the right way round?...surely the front is easily adjustable,the rear less so..

John

Hi John
yes I think I git it the right way around -let me expand a mittle more on what I was trying to say - the front is easily adjustable by the tie rods but as the two front wheels are linked by the steering rack you cannot set the toe in of each wheel independently they must be set together. The rears are not esily adjustable but you can set the toe in of each wheel independently so they can be a different amount on each side.

cheers
Rohan

[rgh0]

A couple of more comments having dug out the information I got from Lotus from a guy called Dave Massey who was the Senior Technical Author in 2006

quote from Dave
"As far as connventions are concerned I beleive you may be attributing Lotus with more methodology than it actually enjoys - Even today suspension geometry is quoted differently for new models and variants. As for what happened 30 years ago i can only guess at, but remember that this was a transition period when rear toe in was first becoming adjustable"

So while I believe nothing can be definitely said about how to interpret the data in the Elan manual his and my best guess are the summary I gave in my post above. This is also consistent with the detail given in the 26R manual for wheel alignment which is reproduced on the Golden Gate Lotus Club web site which shows a string line alingment technique and explicitely quotes toe in individually for each wheel both front and rear.

i.e
26R front toe in for each wheel 1/16th inch - total toe in would be 1/8th of inch - the Elan manual quotes front toe in as 1/16th to 3 /16 inch that I and Dave Massey interpret as total, mid specification total toe in is 1/8th of an inch - consistent with the 26R manual number

26R rear toe in for each wheel 3/16th inch - total toe in would be 3/8th of inch - the Elan manual quotes rear toe in as 0 to 3 /16 inch that I and Dave Massey interpret as an individual wheel specification, top of the spec range spec is 3/16th of an inch consistent with the 26R manual number. In setting up the Elan for racing going to the top of the spec range to help tame the Elan tail happy nature would be the way I would have expected Lotus to go

It also appears consistent that the toe in numbers quoted are the difference between the front and rear of the wheel at the rim either for each side or for total of 2 sides - the 26R manual quotes the numbers as "measured on the rim"

clear as mud I know but I think its all the data in existence - unless someone has asked Ron Hickman if he can remember anything around such an obscure detail

cheers
Rohan

[AussieJohn]

Hi Rohan, thanks again for all the info. do you think that slight toeout on one side at rear would make the handling touchy? cheers, John.

[bcmc33]

John,

The whole subject is confusing. I know the American method is to measure from the centre of the tyre. (Or center of the tire, if you wish).

Another confusing issue for which, I guess, I need educating is why toe-in at the rear driving wheels?

My teaching was that driving wheels are toe-out and driven wheels are toe-in. The following is from one of the ?bibles? of motoring:
As a front-wheel-drive car pulls itself forwards, the wheels will tend to pivot around the king-pins, and thus towards the centre of the car. To ensure they end up straight ahead, they should sit with a slight toe-out when at rest.
A rear-wheel-drive car pushes itself forward, and the front wheels are rotated by friction... thus they will tend to want to trail the king-pins, and therefore will want to splay apart. To ensure that they run parallel when rolling, they should be given some toe-in when at rest.
The perfect 4WD car will have neutral pressure on the front wheels, so have neither toe-in nor toe-out... however very few companies make the perfect 4WD, so some will have a small amount to toe-in/out, depending on the dominant axle.

I have to say that my AWD Jaguar specifies toe-out on all four wheels.

This subject for the Elan has been discussed many times at club meetings and the best advice that I accept is to judge the toe-in by the wear across the tyre tread surface. I?ve done a few hundred miles on new tyres for normal road travel and flat-out sprint trials and the front tyres seem to be wearing evenly if the spew tags are to be believed.

[john.p.clegg]

Brian

I tend to agree,but from where can we get the definative answer?

John

[AussieJohn]

Hi Brian, this subject is a bit of a minefield but I guess if I can set it up so it drives ok and doesn't scrub the tyres then I think at this point I will call it "quits". Thanks to all for advice, what a great site! cheers, John.

[Craig Elliott]

John, the advice I got from Spyder Engineering when fitting the adjustable rear wishbones they make to my +2 was to set them at 3/16 toe-in (or 4.76mm). I'm not sure if this should be between both wheels or for each wheel (I got someone to set it for me and didn't ask).

I found it made a big improvement to the handling - I guess the change will depend on how far out the settings currently are.

Craig

[AussieJohn]

Thanks Craig, I am hoping for a car that is easier to drive, sounds like this may be the solution.

[rgh0]

Hi John
yes toe out on one wheel at the rear will make the car unstable especially when cornering with that wheel on the outside. So it is definitely worth fixing and seeing if your problem goes away.

A Plus 2 is the sweetest handling car I have ever driven - totally neutral, stable and predictable with no vices and when it lets go it does so evenly and controllably. If you dont have that then keep looking for the problem. The only inherent issue I have ever personally experienced with the Plus 2 handling is that the rear toe in in varies a little between power on and power off due to the longer suspension arms compared to the Elan moving as the inner bushes flex under the load changes. This can cause the car to wander a little at cruise as power is applied especially on a road with some camber. One day I will try stiffer Poly bushes in the rear to replace the orginal rubber ones I have and see if it cures the problem. It also only presents itself when running stiff sidewall 60 profile and sticky compound modern trackday style tyres, presume this is due to their greater grip at lower slip angles than the original tyres.

regards
Rohan