Hi all,
Whats the deal with these then? I could do with some on the front to make fiiting the cycle wings a bit easier. The back seems fine.
So, do they affect handing at all? Cause any more stress on any components? Alter the scrub radius thingy (what is that?)?
Guess who just got new wheels??????
Thanks Guys
Rorty's site will explain this far better than I can - so have a look
If you are using cortina uprights, you need an offset of 19mm. this basically means that the centre line of the wheel is 19mm inside the hub face.
This is because if you draw an imaginary line through the upper and lower balljoints, this line will hit the tarmac at the centre line of the tyre -
but it doesn't. The distance between your imaginary line and the true centre of the tyre is the scrub radius.
Imagine that this distance is 3 feet, your wheels would describe an arc as they move from lock to lock which would be very visible. In reality this
distance is never more than 25mm and gives you the feel in the steering. If it was zero the steering would be totally dead and incommunicative.
If you use a wheel with more offest, this distance reduces and can cock up your handling, so spacers are needed to maintain the correct offset (the
offset is marked on the wheel as ET19 or more usually for a front wheel drive car, ET35)
The downside of having really good feed back in the steering with a decent scrub radius is that if you have a blowout, the offending tyre will try and
drag back against the scub radius and pull badly towards the affected side. Most front wheel drive cars use a negative scrub radius to stop this
problem, making the cars cosy and safe for the average driver.
It does not matter at the rear except that if the offset is excessive , you will put a abnormal load on the wheelbearings.
I am sure that someone else will elaborate on this, so keep checking the thread for more (perhaps better informed) information.
Mark
PS if you are having problems with the cycle wings, perhaps you have wheels with more offset?
Absolutely spot on Mark. The only thing I will add to that is that sticking to the original wheel offset is a good starting point, but not necessarily
set in stone. After all, the Cortina donor probably had 2 to 3 times the weight bearing down on the front axle compared to the average Locost, so less
scrub radius is (theoretically) needed to give the same steering feel than perhaps a locost would. My car now runs with zero offset on the front end,
with fantastic feel through the steering. Wheel bearing wear shouldnt be an issue for the reasons described above.
HTH Stu.
I am sticking to 19mm offset, to be honest, because I don't know any different because my car is not finished. Once it is, and on the road I can experiment, its nice to know that zero scrub is ok on handling because the choice of wheels is far greater in the higher offsets
Let's make this one of those really long treads, can everyone with completed cars give their offsets with uprights used and any comments on
handling.
I have seen images of lots of cars with sierra pepperpots with cortina uprights (this should give a negative scrub radius). can any owners give their
comments?
WE NEED TO KNOW!!
Mark
Cheers guys,
The wheels I've got are from a Fiesta Zetec, and i'm using Cortina front uprights. I'll have a look and see what offset they are, I
just stuck them on to see what they looked like :-)
Didn't the Sierra use 35 or 38 mm offset? I read somewhere it was originally going to be fwd.
Thanks
Standard Sierra was ET38 but the cosworth models may have been different
The sierra uses a relatively high offset because they have a very small king pin inclination (I can see this thread getting very complicated!)
I am just guessing, but the Fiesta Zetec wheels probably have a similar offset to the Sierra.
Cheers, Stu.
This web site: http://www.tyresave.co.uk/fitment.html#FORD says its the same as the Sierra, but my wheels say E 43.5
Does that mean they stick out further in or in further than an ET38 offset?
Cheers
In theory, they stick further in.
HTH Stu.