chris_harris_
|
| posted on 3/4/12 at 09:44 PM |
|
|
Wheel Offset Question
Evening all.
Could someone help me out with a wheel offset question please?
I am currEntly running wheels which are 4x108pcd with 38 ET. However I have my eyes on spme with 4x108pcd 15mm offset. Which way is this going to push
the face of the wheel. Inboard or outboard? If inboard presumably spacers wil help me here. If its outboard then I walk away. The wheels are TD Pzro
Race 1.2s at a very good price.
Thanks in advance
Chris
Regards Chris
|
|
|
|
|
Daddylonglegs
|
| posted on 3/4/12 at 09:48 PM |
|
|
IIRC it will psuh the wheels out. If I'm wrong then someone will be along to correct me 
It looks like the Midget is winning at the moment......
|
|
|
coozer
|
| posted on 3/4/12 at 09:50 PM |
|
|
Aye pushes them out.
1972 V8 Jago
1980 Z750
|
|
|
edsco
|
| posted on 3/4/12 at 10:00 PM |
|
|
Are you sure.......?
If you go from a 38ET to a 15ET, what it will be effectively doing is drawing the wheel in closer to the hub. Therefore to maintain the the offset
you currently have, you will need to put in spacers to push the wheel out again.
I say this all coz i had exactly the same issue but in reverse. Needed a 25ET wheel but was sold a 38ET which pushed the wheel out and thus i had an
issue with body work clearance.
I'm sure i am right on this.....or i may end up being corrected someone i am sure.... ;-)
edsco
|
|
|
Dopdog
|
| posted on 3/4/12 at 10:06 PM |
|
|
no its the first way. measure half the wheel then if negative take off the et so 15 is less than 35. this means the 15 will stick out more.
|
|
|
Dopdog
|
| posted on 3/4/12 at 10:07 PM |
|
|
are these the black ones on pistonheads?
|
|
|
coozer
|
| posted on 3/4/12 at 10:11 PM |
|
|
Sierra 38 is getting on for front wheel drive area with no dish, deep dish jobbies on old skool Escorts and so on have a negative offset so the centre
is past the middle of the wheel creating that fantastic deep dish..
So 38 down to 15 moves the inner contact face towards the middle of the wheel (23mm) shifting the wheel, and tyre contact patch (important for
steering geometry) out.
1972 V8 Jago
1980 Z750
|
|
|
chris_harris_
|
| posted on 3/4/12 at 10:14 PM |
|
|
Thanks for the replies. I thought that it would bring them in at first. Then thought out. Then asked here for help.
I think I get it now.
Not seen the ones on piston heads these were elsewhere.
Regards Chris
|
|
|
hootsno1
|
| posted on 3/4/12 at 10:45 PM |
|
|
I need et 15 for my zero if I you could let onto where they are 
If a little hammer won't fix it get a bigger hammer
|
|
|
Dusty
|
| posted on 3/4/12 at 11:36 PM |
|
|
quote:
Which way is this going to push the face of the wheel.
Imprecise question. Not sure what the face of the wheel is. If you mean the
mounting face of the wheel centre then barring adding in spacers the face of the wheel centre is fixed lateraly. After all it's bolted to the
hub which is fixed laterally.
Think instead of the movement of the rim on this fixed wheel centre. The rim can be inset (positive offset) or outset (negative offset). They are all
poor and confusing terms.
Increasing inset or positive offset, positive ET number change, the rim moves toward the car, the bigger the ET number, the more it is moved toward
the car. Going from ET10 to ET30 moves the rim 20mm toward the car as does going from ET-10 to ET10.
Reducing the offset, negative change in the ET number, is moving the rim away from it's centre, away from the car. Changing from ET 25 to ET-25
is a whole 50mm of negative travel of the rim away from the rim centre and car.
So change from ET38 to ET15 is a negative change in offset so the rim must move away from the car and the maths says by 23mm.
You can't correct this with spacers.
[Edited on 3/4/12 by Dusty]
|
|
|
dlatch
|
| posted on 3/4/12 at 11:48 PM |
|
|
you have to take into account of the center line of a wheel where the ET is calculated
so a normal offset is quoted as ET38 ect this is the normal for most cars these days including all hatchbacks ect
so the mounting face of the wheel is 38mm outwards from the center line of the wheel the effect of this is to move the wheel inwards.
a negative ET such as rwd ford use commonly ET -7 means the mounting face on the wheel is 7mm past the center line of the wheel the opposite way to
normal hence the minus figure this as you know pushes the wheel outwards towards the arch lip.
what you also need to take into account when buying a wheel is the total width because replacing a 6" wheel with a 7" wheel even if they
are the same offset with move both the inner and outer of the wheel 1/2" the extra inch has to go somewhere 
easiest was to work out what you need is to measure from your hub face on the car then to whatever will foul the wheel on the inner arch first this is
called the back space.
now for example you have a 6 inch wheel
6"=152mm
half of that = 76mm
now for example lets say you have a allowable back space of 100mm you would need a fwd (postitive offset) type wheel with a ET of 24
if you want to fit a 7" wheel this is where you really need to know the distance from the hub face to your arch lip easy to measure using a
plumb line from the arch.
with both dimensions you can correctly work out exactly what wheel you can fit so get measuring and we need to know width of both sets of wheels
[Edited on 3/4/12 by dlatch]
|
|
|
chris_harris_
|
| posted on 4/4/12 at 05:50 AM |
|
|
Many thanks for the replies. And although my original question may have not been engineeringly accurate (mainly due to the fact that i am a paramedic
and not an engineer) I did get the answers I needed.
In simple terms these wheels won't help me. I would be happy however to share the sourceof these if they would benefit someone else. Thanks
again everyone.
Chris
Regards Chris
|
|
|
