Rear Wheel Tracking

[djj_engineer]

I have long thought that there was something strange with the rear wheels of FMB.
There is a happy sort of chirrup from the tyres on smooth roads.
A Cabrio owner on Angelsey mentioned that he had 'shimmed' the rear hubs to get a better alignment.
I have just checked mine and the offside seems ok, alomost parrallel, with a small toe-in.
The near side has much greater toe-in. About 5mm.
the check was done with a striaght edge across the tyre and the front of the straight edge was about 40mm inside the outer face of the front tyre.
Has anyone else had their rear alignment checked?
Cheers
Derek

[KitCarGirl]

Re: Rear Wheel Tracking

When I had my old Sierra I remember that the N/S/R wheel also appeared to have about 5mm toe in which seems to be the same as you are seeing. So is it an inherent jig error by Ford that has been faithfully copied by Marlin for their chassis jig or is there a hidden reason why Ford made it like this for the Sierra? Seems a bit odd as you would think that N/S/R outer edge tyre wear would be noticable but I don't remember this as being a problem.

For years I have always checked toe in using 4 pieces of string 2 rubber bands and 4 bent nails, two pieces of wood and a 6" ruler! No this isn't a joke!

Method: Each side of the car, use 2 pieces of string slightly shorter than half the distance from front to back tyre. Tie the centre ends to the rubber band. Tie the outer ends to the heads of the bent nails. Use the bent nails to hook the stretched string around the front and back tyres locating into the tread. Make sure that the string it stretched across the center of the wheel.

Find the track of the front and rear wheels for the vehicle**, subtract one from the other and divide by 2. Cut two 4" lengths of wood of this thickness and place them between the string and the tyre wall nearest the nails, at whichever end of the car has the narrowest track. The string will now create two parallel lines along the car.

Measure from string to wheel rim using ruler. Sapristi! You have the toe in!

** Now for my question. Do you know what the front and rear track widths are for the Cabrio? I need to know this asap as I have just stripped the front suspension on my Hunter to fit new Supaflex bushes to the ARB mounts and TCAs and need to use the above technique to check my toe in! I can also have a look at the rear for you at the same time!

[djj_engineer]

Re: Rear Wheel Tracking

Interesting thought about the Sierra.
Further to my 1st bit I have now taken a reading with a tracking bar on th erear suspension and apart from being unable to reach half way up the wheels I have at least 6mm toein and I estimate it may be as much as 10mm.
Also I now know of three other cars that have toein at the rear.

[greyV8pete]

Re: Rear Wheel Tracking

As per separate email Derek can you please let me have the measurements for your front and rear track. It doesn't matter if your tyres are different to mine as long as you have the same tyres all round. It is just the difference between front and rear that I need the measurements for. I can then set my front toe in and also check what rear situation is with my Hunter.

[greyV8pete]

Re: Rear Wheel Tracking

Just a thought. As the rear wishbone pivot bushes are not parallel to wheel axle centre line the R/W toe will be affected by ride height (wishbone angle from horizontal in static position). Not sure by how much but worth putting in the comparison checks.

[lizbillings]

Re: Rear Wheel Tracking

Doug has checked the Sierra manual which states. The front track is 1453 mm and rear 1468 mm a difference of 15 mm so the Cabrio should have the same difference front to rear. He has had the string out from front to rear wheels and allowing for this difference toe-in seems to be about 2.5mm or less.

[greyV8pete]

Re: Rear Wheel Tracking

As they say if all elese fails read the manual. Have just found my old Sierra manual too and there it is right at the front! This is about 5/16" in real dimensions which is the thickness of the wood strips that I used with my Sierra string checks! QED. Have also checked a Granada manual for interest and front track is 1477, rear is 1492 giving 15mm difference or 7.5mm per side. So the same for that vechicle too.

[greyV8pete]

Re: Rear Wheel Tracking

Have a look at the link http://www.roadsterfactory.nl/02/tech01.htm
Re Some Pilgrim Suomo rear and front tracking issues.

[Dane_Rescueman]

Re: Rear Wheel Tracking

Manufacturers often use(d) the rear toe in as an easy way (bodge)to reduce or control under/oversteer. I would imagine that the Cabrio range would require different settings to the Sierra due to ride height, weight, roll centre and wheelbase. But I may be wrong!

[djj_engineer]

Re: Rear Wheel Tracking

Further to above. I have placed a note in the next pitstop.
FMB may have some wear on the rear swing arm bushes and the swingaxles do change toein with ride height.
Also the track on FMB measured at the wheel centres is the same front and back
Cheers
Derek

[greyV8pete]

Re: Rear Wheel Tracking

Derek, Somewhere in a safe place I still have a set of new rear radius arm bushes that I bought for my Sierra but never fitted also a new centre D-mount for the diff. If you want them let me know. PL.

[greyV8pete]

Re: Rear Wheel Tracking

Finally finished the font suspension job! Supaflex bushes at inner end of TCAs and in compliance bushes have dramatically improved steering response and I thought is was good before! No noticable increase in roughness or noise though. Have checked my rear toe in with the string method and it is 6.5mm toe IN for BOTH rear wheels! I think we need to know more about why Mr Ford designed it like this before changing and finding we have just invented another problem. From what I have found so far I think that rear wheel (bump) steering is worth investigating.

[milliemarlin]

Re: Rear Wheel Tracking

What a good append.

I have measured Millie’s wheels this weekend. This prompted me to adjust the front toe in as it had changed slightly. At the back she has a toe out. I am convinced this is causing excessive wear on her wheels. Her original tyres only lasted about 9k miles. The tyres always wear much more on the inside edge. I know there are a couple of other cabrios that also exhibit rear toe out.

All dimensions in mm. Measurements taken from strings 1680 apart to the front and rear of the rims are as follows. The rims are 420 diameter at the widest point.

OSR NSR
R 14 11.5
F 18 15

OSF NSF
R 14 17
F 15.5 16

This gives the rear about 7.5 mm toe out. Front 1.5 mm toe in.

I would really like to fix the rear toe in this as I think it makes the back end much more likely to skid. When driving down a straight road she will sometimes wiggle her backend if one side or other looses grip, such as driving over a drain cover.

My understanding is that for a road car the wheels should be parallel to minimise wear. The 2 mm toe in recognises the fact that rolling resistance will tend to push the wheels back and out reducing toe in at speed.

Her rear wheels also have a camber. The top of the rims is 8-10 mm more in towards the car than the bottoms.

I wonder if this might be part of the problem. Since the trailing arms are not parallel to the centre of the axle. I guess I could check this by raising the rear of the car on a jack and rechecking. I am reluctant to raise the back end as a permanent solution.

One way to fix it might be to elongate the trailing arm bush holes in the chassis. I guess that a mm or so elongation in the right direction might be enough. Mind you, I am reluctant to introduce a sloppy fit on such important mountings though. I don’t suppose there is just enough play there already.

Her front wheels need to be packed out too but that is largely a matter of laziness.

Logically it is probably most efficient just to change the tyres every three years than fiddle about for hours trying to fix this. But then there isn’t much logic in building a kit car and this represents a challenge.

Paul

[djj_engineer]

Re: Rear Wheel Tracking

Hi Peter
The swinging arm bushes would be really usefull if you could find them.
Paul when my rear suspension is higher there is less -ve camber but the wheels toe out more. I have put a piece in the next Pitstop.
Yours is the only Cabrio to date that has toe-out at the rear
Cheers
Derek

[greyV8pete]

Re: Rear Wheel Tracking

Sorry I Derek can't find bushes so far. Will keep looking.
I spoke to Nick Derrick from Dorchester at the Westpoint K K Show on Sunday. He has just completed a Cabrio and has used washers to shim his rear suspension to eliminate toe in and camber problems (skipping on drain covers etc when cornering). My rear camber as a rough check is about 10mm more "in" at the top than at the bottom. However my Hunter suspension was raised at my request by Marlin at Crediton, after I bought it S/hand, as I was hitting the exhaust silencers on even low speed bumps. Maybe we should all quote our front and rear ride hights as well as the other stuff? Final thought, the weight of our cars and rear overhang (i.e. weight behind the wheels) is much less than a Sierra so the basic Sierra toe & camber settings may be irrelevant? Final final thought, what diameter front anti roll bar is everyone using? Mine is ex Granada 28mm so although roll is effectively zero the car does tend to follow every road variation. Nick said on Saturday that he had change his to a 24mmdia Sierra one to avoid this.