A discussion on Offsets
08-12-04, 11:43 AM
#1
A discussion on Offsets
Mods, Since this isn't really suspension, and not quite wheels, I decided to post this here.
I have been researching big brakes, wheel sizes and offsets, etc. I have 18" wheels that I actually love quite a bit. When I first purchased them, I did not consider big brakes at the time, as I was not planning to mod my SC400 to such a higher amount of power. Now, I am in the middle of my project, and I want to have better stopping power, but I do not want to sell my wheels.
I bought and tried the Supra TT brakes, and the sides of the calipers would not clear the wheel spokes. So, I sold the brakes. Now that I am definitely implementing FI, Big Brakes are a necessity. So, I am looking at hub-centric wheel spacers. H&R supossedly makes excellent ones, and they are balanced so they are not supposed to cause vibration issues.
Now, my real discussion here is Offset. I understand the Stock SC400 rides on 16x7 wheels with a +50 mm offset. Now, I understand offset to be a measurement based upon the dimensions of the wheel, and that it really determines the hub face mounting of the wheel from the center point of the wheel.
Many seem to state that offset should still be +50mm when one resizes to different wheel widths. I have a problem with this as I understand this subject. Because when going to wider wheels, maintaining a +50 mm offset would cause the inner edge of the wider wheel to move closer to the car, and could cause clearance issues. Plus, it would not widen the trak of the wheelbase as much, and would not offer as much increased handling capability.
Another thought is the more the offset, the further the outer edge of the wheel is pushed towards the outer fenderwell of the car.
So, if I add a +5 mm wheel spacer to the hub, and I have an18" x 8.5" wheel with a +38 mm offset, even though this would actually reduce the offset of the wheel, the net effect is an increase of +5 mm, totalling +43 offfset as far as I can see it. This does get me closer to +50 mm offset, and does not push the wheel further in, but 5mm further out.
My goal is to maintain my current wheel setup, add the big brakes, and still get overall good handling.
What do you experts think?
Ryan
I have been researching big brakes, wheel sizes and offsets, etc. I have 18" wheels that I actually love quite a bit. When I first purchased them, I did not consider big brakes at the time, as I was not planning to mod my SC400 to such a higher amount of power. Now, I am in the middle of my project, and I want to have better stopping power, but I do not want to sell my wheels.
I bought and tried the Supra TT brakes, and the sides of the calipers would not clear the wheel spokes. So, I sold the brakes. Now that I am definitely implementing FI, Big Brakes are a necessity. So, I am looking at hub-centric wheel spacers. H&R supossedly makes excellent ones, and they are balanced so they are not supposed to cause vibration issues.
Now, my real discussion here is Offset. I understand the Stock SC400 rides on 16x7 wheels with a +50 mm offset. Now, I understand offset to be a measurement based upon the dimensions of the wheel, and that it really determines the hub face mounting of the wheel from the center point of the wheel.
Many seem to state that offset should still be +50mm when one resizes to different wheel widths. I have a problem with this as I understand this subject. Because when going to wider wheels, maintaining a +50 mm offset would cause the inner edge of the wider wheel to move closer to the car, and could cause clearance issues. Plus, it would not widen the trak of the wheelbase as much, and would not offer as much increased handling capability.
Another thought is the more the offset, the further the outer edge of the wheel is pushed towards the outer fenderwell of the car.
So, if I add a +5 mm wheel spacer to the hub, and I have an18" x 8.5" wheel with a +38 mm offset, even though this would actually reduce the offset of the wheel, the net effect is an increase of +5 mm, totalling +43 offfset as far as I can see it. This does get me closer to +50 mm offset, and does not push the wheel further in, but 5mm further out.
My goal is to maintain my current wheel setup, add the big brakes, and still get overall good handling.
What do you experts think?
Ryan
08-12-04, 12:02 PM
#3
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I'm not a expert but I wouldn't say its a +43 but rather a +38 with a 5mm spacer. The reason being that a +43 wheel is going to leave the spokes in the same location while changing the location of the outter rim, as you said you understand.
However, there will be different forces, regardless of how small they are, still different as well as a change in the moment arm force applied to the hub and studs. I do realize the changes are almost zero with a 5mm spacer but they will be different so I would classify them differently.
Just my $0.02
However, there will be different forces, regardless of how small they are, still different as well as a change in the moment arm force applied to the hub and studs. I do realize the changes are almost zero with a 5mm spacer but they will be different so I would classify them differently.
Just my $0.02
Last edited by qtb33; 08-12-04 at 12:03 PM.
08-12-04, 12:47 PM
#4
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Re: A discussion on Offsets
Originally posted by SC400T
Mods, Since this isn't really suspension, and not quite wheels, I decided to post this here.
So, if I add a +5 mm wheel spacer to the hub, and I have an18" x 8.5" wheel with a +38 mm offset, even though this would actually reduce the offset of the wheel, the net effect is an increase of +5 mm, totalling +43 offfset as far as I can see it. This does get me closer to +50 mm offset, and does not push the wheel further in, but 5mm further out.
Mods, Since this isn't really suspension, and not quite wheels, I decided to post this here.
So, if I add a +5 mm wheel spacer to the hub, and I have an18" x 8.5" wheel with a +38 mm offset, even though this would actually reduce the offset of the wheel, the net effect is an increase of +5 mm, totalling +43 offfset as far as I can see it. This does get me closer to +50 mm offset, and does not push the wheel further in, but 5mm further out.
18x8.5" wheel, 38offset
+
5mm spacer
___________________
18x8.5 "wheel, 33 offset
(which is quite aggresive for the SC btw, I dont know if anyone running offsets this low up front without the JDM tire stretch)
The only way to INCREASE your offset would be to shave metal of the backpad (not recommended due to potential damage to the structural integrity of the wheel)
Last edited by D2-AUTOSPORT; 08-12-04 at 12:49 PM.
08-12-04, 02:02 PM
#5
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Maybe I'm wrong, which is possible, but when you move the center of the wheel out then your increasing the positive offset. I may have just confused myself
But isn't the offset all relative to the outter rim itself, not where it sits as a whole? So adding a spacer isn't really changing the offset at all?
But isn't the offset all relative to the outter rim itself, not where it sits as a whole? So adding a spacer isn't really changing the offset at all?
Last edited by qtb33; 08-12-04 at 02:04 PM.
08-12-04, 03:46 PM
#6
There seems to be some confusion in the divagation. There are two important ways to describe the location of the wheel mounting surface: offset and backspacing .
I think to clear the air I have to bring definitions of both terms:
Offset: describes the location of the wheel mounting surface in relation to the wheel centerline
Backspace :describes the location of the wheel mounting surface in relation to wheel`s inboard bead flange
As you can see offsed do not deal with inner tire edge at all. You should maintain factory offset with wider wheels, so the force plane generated by the wheel is in the same place as with factory wheel.
You are correct that maintaining this reqirement with wider wheels will bring inner wheel edge more inboard, possibly causing interference problems.
This is where backspace is usefull, as you can compare particular wheel backspace with maximum backspace for particular suspension setup.
08-12-04, 04:07 PM
#7
Forgot to say why offset matters.
Wheel offset together with another critical component included angle defines so call scrub radius
Scrub radius is dirrectly responsible for turning effort and steering feedback.
Significant changes to in scrub radius may affect handling enough to cause safety problems. Static toe specs may no longer be accurate which could resoult in premature tire wear, wander or shimmy conditions.
Moving the wheel centerline outward (spacers...) multiplies lever effect, increasing road shock, reduces dirrectional stability and increases the load on the wheel bearing
Interesting question from my point of wiev is how much change in factory offset in your collective expirience is tolerated by the SCs suspension w/o obvious handling problems.
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08-12-04, 04:09 PM
#8
Re: A discussion on Offsets
Originally posted by SC400T
[BSo, if I add a +5 mm wheel spacer to the hub, and I have an18" x 8.5" wheel with a +38 mm offset, even though this would actually reduce the offset of the wheel, the net effect is an increase of +5 mm, totalling +43 offfset as far as I can see it. This does get me closer to +50 mm offset, and does not push the wheel further in, but 5mm further out.
My goal is to maintain my current wheel setup, add the big brakes, and still get overall good handling.
What do you experts think?
Ryan [/B]
[BSo, if I add a +5 mm wheel spacer to the hub, and I have an18" x 8.5" wheel with a +38 mm offset, even though this would actually reduce the offset of the wheel, the net effect is an increase of +5 mm, totalling +43 offfset as far as I can see it. This does get me closer to +50 mm offset, and does not push the wheel further in, but 5mm further out.
My goal is to maintain my current wheel setup, add the big brakes, and still get overall good handling.
What do you experts think?
Ryan
[/B]
08-12-04, 04:18 PM
#9
Re: Re: A discussion on Offsets
Originally posted by D2-AUTOSPORT
...
18x8.5" wheel, 38offset
+
5mm spacer
___________________
18x8.5 "wheel, 33 offset
...
...
18x8.5" wheel, 38offset
+
5mm spacer
___________________
18x8.5 "wheel, 33 offset
...
08-12-04, 04:40 PM
#10
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Just a thought, if you would like to keep those 18's why not go with the ls 400 calipers? I'm not sure but aren't they a bit thinner than the supra tt calipers? From what everyone has been saying, the ls400 brakes stop very well too.
