I must stop measuring things!

[greyV8pete]

Having noticed uneven wear on the outer edge of my N/S front tyre I suspected too much toe-in so I started measuring things!

To check the actual track difference between front and rear (for my parallel string toe-in setting method) I made up a tripod gadget that locates in the wheel hub trim.

Using a plumb line to mark the floor and then subtracting front from rear I get 20.0mm difference. So my string check needs a 10mm spacer against each front wheel to get the parallel strings for measuring.

However the Haynes manual says the front / rear track are 1453mm / 1468mm giving a difference of 8mm, which is the thickness of spacer I have used before.

The 10mm spacers show that there is actually too much toe in Q.E.D!

A further quick check shows the wheelbase to be approx 2680mm whereas Haynes shows the Sierra as being 2608mm. Theoretically this will produce an error for the Ackermann angle, although how much this amount will actually affect steering when on full lock is a matter for conjecture.

Has anyone else measured these dimensions on their Cabrio? Peter.

[Sportster-Green]

Re: I must stop measuring things!

may i ask why you started measuring? are there any issues in terms of handling or steering with your car?

was the car recently (or ever) correctly setup from awheel alignment centre?

[Robert in Cumbria]

Re: I must stop measuring things!

Hi Peter,

For years I have used a really simple, basic but infallible tracking gauge, I have owned two but both have been stolen/not returned by borrowers. Unfortunately I can't remember the make, I think it was either Bradbury or perhaps Laycock.

Anyway Gunson make a modern version, not as strong but no doubt will do the job just as well. Here is a link to their site showing the device.

http://www.gunson.co.uk/item.aspx?cat=676&item=1812

The beauty is that you don't need to know the settings, it works for independent rear suspension, if you are running with non spec camber it takes that into account. It only takes a few seconds to test the track if it is in, out or correct. Check out their video.

I remember Charlie Oats, the local Lotus dealer assembled Elans and Sevens at his garage, he used one of these type of tracking gauges to set up the tracking and rear suspension, I remember discussing this with him back then and it was considered the best way to get things right given so many adjustments were needed. Even the ride height alters the tracking on some suspension. This type of tracking gauge 'just works'.

As for the Ackerman angle, 72mm difference in wheelbase isn't enough to cause any adverse effects. Many cars which have 'long' and 'short' wheelbase options have the same steering arms for both, for example the (original) Mini van and estate models were about 4 inches longer than the car but they shared the same steering components and settings.

I have done the Ackerman angle calks but believe me, the spreadsheet gets very complex when you take all the variables into account. I once built a tiny car for a disabled boy using mini hubs and steering, it was about 1000mm wheelbase, with about 900mm track, it wore tyres out in quick time, from memory we ended up heating and bending the steering arms as far into the rims of the wheels as we could and called it quits! That did reduce the scrub on lock but didn't eliminate it, it was good enough for three mph!

[greyV8pete]

Re: I must stop measuring things!

may i ask why you started measuring? are there any issues in terms of handling or steering with your car?

was the car recently (or ever) correctly setup from awheel alignment centre?

The uneven N/S tyre wear was the trigger for investigation.

I have always used my elastic string on all my previous cars and had no problem. Only went to "specialists" twice and they only succeded in making things much worse as they relied on the gadgets, not fundamental knowledge, skill and experience! Peter.

[greyV8pete]

Re: I must stop measuring things!

Aha! Robert, I have just realised from your comments that my Cabrio is the long wheelbase version, hence the equivalent longer dimension than the Sierra! Many thanks.

I remember the Trackrite gauges from years ago. I may invest one of these days. Meantime I will adjust my toe in with the 10mm packing under my string method and re-evaluate. I am also making up a T-frame to check the front camber angles as they have never seemed to me to look quite the same both sides. Maybe an optical illusion but nice to check anyway. Peter.

[greyV8pete]

Re: I must stop measuring things!

Following further string and ruler checks and adjustments, toe in now mid (Sierra) limit at 1.0mm toe in total. Steering fine and no "squeal" now on shiny car park corners. Result! Peter.

[greyV8pete]

Re: I must stop measuring things!

Having recently fitted some new tyres (same as usual Toyo Proxes T1R) I still get a residual annoying slight pull to the left (worse on more heavily cambered roads). Toe in still at 1.0mm total.

So I finally bit the bullet and bought a Sealey Castor / Camber gauge which I have mounted on the T-frame that I made a while ago. I need to mock up a couple of simple turntables to check castor and KPI but meantime have checked the camber. Results are interesting.

Camber checks:
Front N/S 1.5 deg –ve
Front O/Side 2.0deg –ve
Rear N/S 2.25deg –ve
Rear O/S 2.5deg –ve

N/S/F VIEW
FRONT O_S CAMBER FRONT VIEW.jpg

CHECKING GAUGE
FRONT O_S CAMBER CHECK.jpg

The rear camber correction is no problem as I can use more shims between the hub carrier and the swing arm (later when I have saved some pennies for Supaflex rear bushes first).

The front poses a problem. If my maths is correct, then to get the zero degrees camber recommended in the build manual I need more shim at the top inner wishbone mounting than the lengths of the studs will allow ( and still give the nyloc nuts inserts something to locate on)! The alternative of using adjustable TCAs (like CosworthCabrioLee did some time ago) is an additional cost that I would like to avoid. That said the front wheels fitted to my Hunter have always been a tad outside the front wings so bottom TCA adjustment would be preferable to top shims.

Meantime I have ordered a set of Supaflex bushes for the top inner wishbone bushes, before I start adjusting anything else.

As soon as I have made up the turntables I will be able to frighten myself even more!

I will be interested to know if other Cabrio owners achieve the 0 degrees front camber that the build manual recommends for road use and if not, what camber figures they have?
Peter.

[Mickaleen]

Re: I must stop measuring things!

Hi,

I had this problem with the near side. The camber was well out. I placed shims on the top wish bone to pack out. You will have to keep a check on the off side making sure both sides read the same.

Kind regards
Mike.

[greyV8pete]

Re: I must stop measuring things!

Hi,

I had this problem with the near side. The camber was well out. I placed shims on the top wish bone to pack out. You will have to keep a check on the off side making sure both sides read the same.

Kind regards
Mike.

Hi Mike. That's interesting. Approx what thickness packing did you use and how many degrees of error did it correct? Peter.

[Mickaleen]

Re: I must stop measuring things!

Hi Peter,
I didn't have the equipment you show in the pics above, I used a level and drew out full size and measured the amount of packing I required.
The top wish bone used about 6mm approx.
The negative on the N/S could be plainly seen compared to the O/S. I can't remember the exact degrees.
I made the shims out of galv plate.
The ground clearance must be set as per the Marlin instruction manual. This dimension must be maintained throughout while adjusting the N/S, you will find you will have to pack out the O/S side as well.
This will ensure the camber will be the same on both wheels.
Hope this helps.
Kind regards

Mike.

[greyV8pete]

Re: I must stop measuring things!

Hi Peter,
I didn't have the equipment you show in the pics above, I used a level and drew out full size and measured the amount of packing I required.
The top wish bone used about 6mm approx.
The negative on the N/S could be plainly seen compared to the O/S. I can't remember the exact degrees.
I made the shims out of galv plate.
The ground clearance must be set as per the Marlin instruction manual. This dimension must be maintained throughout while adjusting the N/S, you will find you will have to pack out the O/S side as well.
This will ensure the camber will be the same on both wheels.
Hope this helps.
Kind regards

Mike.

Thanks for the quick reply Mike.

That 6mm packing ties in well with my original quick calcs. However as there is already approx 1.5 and 3.0mm shim in there already if I add another 6mm the studs that hold the top brackets to the chassis will be too short for the nylock nuts. I suppose that I can always grind off the existing bolts and get longer ones tack welded in their place.

The Cabrio build manual says ground clearance should be 270mm front and 225 rear. It also says that the front lower TC arms should be horizontal.

My ground clearance is 252 Front / 202 Rear but my arms are already level, so if I raise the car it will make the arms droop down, which may cause bump steer?

I have 205/55x16 tyres which according to an on-line calculator have amost identical rolling radius to the 195/65x15 that seems to be in the build manual. Likewise my wheels (Fox 6.5" rims with 35 offset) are also in the range listed in the build manual, albeit at the max offset figure.

I will do a very rough check by jacking the chassis by the 18mm difference and recheck how much the camber has changed.

Although the top shims are the quickest (and cheapest) fix, I am concerned that my already slightly protruding wheels will be even further outside the front wings.

The alternative to minimise this is using adjustable TCAs but that gets rather pricey!

Peter.

[andyf]

Re: I must stop measuring things!

The first thing to say is that it will pull to the left and the amount will depend on the camber of the road. I got really fussy about this with the rally car until I drove it down the right side of the road and found that it pulled to the right. It's worth doing this test because what you are looking for is balance. As for the camber measurements I would recommend turning the car around and repeating the measurements to make sure that they're not being affected by the floor level. I wouldn't be too worried about the absolute camber measurements, the most important thing is to get them the same side to side. Then the final measurement depends on the observed tyre wear, if it wears off the insides too quickly take some camber off. You may not find that this is the case because if you spend more time driving down windy B roads the steering won't be dead ahead that much ;-)

As a reference on the sunbeam I used to run 3.5 degrees of negative camber on the front.

[Mickaleen]

Re: I must stop measuring things!

Hi Peter,

My problem was wear on the inside of the N/S front tyre, too much negative camber. If you have wear on the outside of the N/S front tyre then you have too much positive camber.
Just thought I should point that out.
Jacking up the front of the car will change the camber towards positive camber and negative if lowering.
Kind regards

Mike

[andyf]

Re: I must stop measuring things!

Yes, all measurements must be taken with the suspension fully loaded

[greyV8pete]

Re: I must stop measuring things!

Thanks to all for the above feedback. My original wear on the N/S/F tyre was due to too much toe in which I fixed. Having fitted new front tyres I hoped that all would be nice and even but have still had the niggle of the slight pull to the left. I did try driving on the other side of a cambered road as andyf suggested and it straightened things up rather than pulling to the right, hence my persistence in trying to get it resolved. I did also check the garage floor but that is level ok.

However today I have made some encouraging progress. I have finally found the pair of TV turntables that I bought a few years ago for modifying to do front wheel camber checks. They were of course in a safe place! Taped up the top and bottom plate holes and fitted rubber O-rings around the bearing track to stop grit and dirt from the garage floor getting into the ball bearing and now need to add a protractor of some kind to measure the +/- 20 deg needed for castor and KPI checks. Will sleep on that one. Once complete I will find some wood of the same thickness to put under the rear wheels to keep things level for the checks.

Meantime I had a think about Mike’s reminder about ride height and re-read the build manual. As I realised it is of course the steering rack arms that need to be level and not the lower suspension arms I rechecked mine and they were going uphill slightly from the rack towards the wheel. I jacked the front up under the centre of the chassis cross member by 18mm (the amount that mine was lower than the build manual figure) and the steering arms became level! I rechecked the camber and the readings have improved. They are now N/S 0.75 deg and O/S 1.25 deg. I can’t believe what a difference that small ride height change makes. Levelling the steering arms is bound to make the steering feel different.

Next job is to find the C-spanner for the front coilovers, also in a safe place somewhere, and get the ride height corrected. Supaflex bushes are ordered for the inner front top wishbones so will get all that done plus a bit of extra shimming to try and even the front camber to 0 deg while the brackets are off not forgetting another toe in check at the new ride height. Then I can worry about checking the castor and KPI. Peter.

TURNTABLES.jpg