rear toe out

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rear toe out

Postby jerseypug » Mon May 21, 2018 11:04 pm

i have just swapped the wheels over on my compact ready for a rally on saturday and noticed that the inside of both the rear tyres was really worn. i had this problem before and replaced the rear beam thinking that something was bent. now that it is happening again i checked the rear toe and found it to be toeing 2 degrees out. i have had a look on the net and all i can find is 0 toe is ideal.
I spoke to a friend with an e30 rally car and his tyres wear on the inside also.
i am running gaz coilovers about standard ride height with a m42 4pot. the tarmac tyres are hankooks and the dirt tyres are michelins. i am quite a fan of the handbrake and do like a slide so the tyres are going to suffer but I'm surprised how uneven the wear is
Image
does anyone know what the idea rear toe should be?
i jacked the car up about 100 mm from the diff and checked the toe and it was still toeing 2 degrees out.
nothing looks bent and both the rear tyres are wearing the same. i am extremely economical with my tyre buying and these ones were bought second hand about 4 years ago and have had a hard life
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Re: rear toe out

Postby Spac » Tue May 22, 2018 1:23 am

While I cannot speak about specific numbers, changes to toe and camber as the wheel moves through its travel are both inherent to semi-trailing arm rear ends.

You will probably find that the rear toes in and gains significant negative camber under acceleration, and this is probably where the excessive wear comes from.

My suggestion is to remove one rear spring, support the body at ride height, and then jack the hub up and down. Measure the toe and camber at various points. Then look carefully at the geometry changes - you may find that a change in ride height or possibly limiting the travel will have you working in a better range that avoids significant tyre wear.
For example, when I built the struts for my old gravel RX-7, I gave them heaps of travel (about 280mm, IIRC). This seemed like a good idea, except that at full droop the geometry went to pooh - lots of positive camber and lots of toe in. Landing from jumps was simply terrifying until I used travel limiting straps to avoid the last 40-50mm of droop travel, and kept the geometry under control.
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Re: rear toe out

Postby petsracing » Tue May 22, 2018 10:15 am

My guess is your rear arms will be bent we usually need to change ours every 3rd rally as the rear wear gets to excessive
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Re: rear toe out

Postby jerseypug » Wed May 23, 2018 6:33 am

i measured my daily road compact and the rear toe was 0.1 degree toe in. I'm not sure if that is where it should be but seems a lot better than 2 degrees toe out. i have extra arms so will change everything on the rally car but will measure the old arms to try and see what has bent. i will have to keep it as it is for the rally on saturday and change it afterwards as i don't have any time.
Image
i put this together last night, it has z3 arms e30 325i diff and e36 328i shafts (only tried one to see if it fits ok, the lh shaft is the z3 shaft that is putting up a fight to get out of the hub) it works out 65mm wider per side which should work out well with the arches i have and to balance up the extra width of the e46 arms on the front.
Image
This is with standard arms, 25mm spacers and e46 wheels
I will get the z3 armed rear beam cleaned up and fit new bushes and should be able to straight edge the disks before i fit it to check that it is roughly where it should be.
The rally i am doing on saturday has huge pot holes on the corners which the car hits pretty hard and this might be the cause of the bending.
i won't worry about the arms on saturday and will measure them afterwards, with any luck i might bend them straight!
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Re: rear toe out

Postby jerseypug » Sun May 27, 2018 10:38 am

i finished the rally yesterday with the toe out and shredded my rear tyres after 4 short stagesImage
the outsides were ok but they were coming apart on the inside
apparently this could be caused by a bent rear beam so i will swap the arms into another beam and see how they line up.
this is stage 4 and the noise at the end is the tyres coming apart.
https://www.youtube.com/watch?v=sIdfXMrudwY
i don't take it too seriously and the car is pretty low with very stiff springs but i really enjoy the event and would rather compete in the wrong car than not at all. Lots of fun and smiles
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