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MazdaSpeed 3/6 - Wheels & Tires HaveMazdaSpeed 3 - Wheels & Tires - Have a question about wheels or tires? Need a calculator to figure out offsets? We have them in here


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 Old 02-18-2015, 08:26 AM   #1
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Default Offset Effects

Apparently wheel size and offset is not just a matter of fitting the fenders and inner suspension components. I've been looking at wheel and tire combos along with possible spring changes and have come across some good info in this article(it's about Hondas, but still gives a great overview of issues not often discussed):

Wheel Offset: Why it Matters - Guide To Proper Honda Wheel Offset - Honda Tuning Magazine

A couple things that seem noteworthy are about offset is how it relates to scrub radius and steering angle, which relates to torque steer and also to braking stability, and stability when traction at each corner varies.

The other big tidbit I noted is the mention of how a lower offset can make a difference in spring rates due to the distance of the wheel which creates additional leverage on the strut. They quote a 10mm decrease in offset created a 5% reduction in spring rate in the example application of an Integra.

It can also affect wheel bearing loads, and only a +35mm on a raced CRX broke the steering knuckles multiple times.

I just ordered 7.5" wheels with +45mm offset. I hope the benefits outweigh any negative effects of what amounts to a 13mm reduction, but it also looks like my planned purchase of stiffer springs could be a better idea than originally thought too.
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 Old 02-18-2015, 08:32 AM   #2
 
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IMHO anything under a 5-10 mm delta won't significantly alter the driving behavior of our cars. Not unless running 235 series tires or greater.
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 Old 02-18-2015, 08:47 AM   #3
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Originally Posted by license2ill View Post
The other big tidbit I noted is the mention of how a lower offset can make a difference in spring rates due to the distance of the wheel which creates additional leverage on the strut. They quote a 10mm decrease in offset created a 5% reduction in spring rate in the example application of an Integra.
I REALLY doubt it's actually a 5% decrease in wheel rate for that tiny increase in offset. Do the math for it.

Originally Posted by license2ill View Post
It can also affect wheel bearing loads, and only a +35mm on a raced CRX broke the steering knuckles multiple times.
There are guys running SLICKS with this car on WAY wider wheels.


You're making mountains out of mole hills, AGAIN. Apply some sense to these questions and you'll probably be ok.
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 Old 02-18-2015, 08:48 AM   #4
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Originally Posted by Design View Post
IMHO anything under a 5-10 mm delta won't significantly alter the driving behavior of our cars. Not unless running 235 series tires or greater.
Yeah, and tire sizes vs actual measured section widths and tread widths can vary a lot too. In my quest for a slightly wider footprint, I found very little to no actual tread width gains to be found between 225 to 245 sizes, and it would be even less without using 8-9" wide wheels.

I suppose I could have found a 50mm offset in a wider rim, but that would only bring it back less than half the distance it will get pushed out with another 1/2-inch more width.

I'm guessing Mazda went through all this between gen changes too, and that's why a 225 on a 7.5" wheel was as far as they would go for the 2010 makeover.
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 Old 02-20-2015, 05:42 AM   #5
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Originally Posted by phate View Post
I REALLY doubt it's actually a 5% decrease in wheel rate for that tiny increase in offset. Do the math for it.
Yeah, I was surprised by this as well. I don't know what the specific math is, but would guess that specific wheel and tire weight also makes a difference. At what point do they intersect and cancel-out? I don't know.

It makes me wonder if this could possibly explain the differences in reported spring rates between generations though, since no one seems to know for sure about those numbers...wheel weights are the same, offsets same, but 7.5" wheel pushes it out 6-7mm, I think.
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 Old 02-20-2015, 06:02 AM   #6
 
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Originally Posted by license2ill View Post
offsets same, but 7.5" wheel pushes it out 6-7mm, I think.
If the offsets are the same it doesn't push it out at all - unless your wheel is wider than your tire. Plug your numbers into any wheel size calculator and you'll see.
Custom rims, wheel tire packages for your ride - RIMSnTIRES.com
Online Wheel and Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit
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 Old 02-20-2015, 06:47 AM   #7
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Originally Posted by shamie View Post
If the offsets are the same it doesn't push it out at all - unless your wheel is wider than your tire. Plug your numbers into any wheel size calculator and you'll see.
Custom rims, wheel tire packages for your ride - RIMSnTIRES.com
Online Wheel and Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit
It doesn't change the track, or the centerline of the tire, but the wheel is mounted further 1/4" out with a 1/2" width gain because the mounting face is moved 1/4" out to maintain the same offset length. It still pokes 6.4mm further away from the hub.
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 Old 02-20-2015, 10:13 AM   #8
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Originally Posted by license2ill View Post
Yeah, I was surprised by this as well. I don't know what the specific math is, but would guess that specific wheel and tire weight also makes a difference. At what point do they intersect and cancel-out? I don't know.

It makes me wonder if this could possibly explain the differences in reported spring rates between generations though, since no one seems to know for sure about those numbers...wheel weights are the same, offsets same, but 7.5" wheel pushes it out 6-7mm, I think.
Wheel and tire weights aren't considered in your wheel rates, only the geometry. I don't know the MS3 arm dimensions, so here's an example:

12" LCA pivot to wheel centerline compared to a 12.25" LCA pivot to wheel centerline, same bump force. The ratio of forces is just 12.25/12 = 1.021. It takes 1.021 times as much force to react the bump force.

BUT, in terms of roll resistance, a wider track increases roll resistance. Using the MS6 track width of 60.2" compared to a 60.7" track width (increase of ~6mm both sides), the roll resistance increases 1.63%. Should be similar for an MS3.



See why I say you should just measure everything and build a calculator?
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 Old 02-20-2015, 10:40 AM   #9
 
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Originally Posted by phate View Post
Wheel and tire weights aren't considered in your wheel rates, only the geometry. I don't know the MS3 arm dimensions, so here's an example:

12" LCA pivot to wheel centerline compared to a 12.25" LCA pivot to wheel centerline, same bump force. The ratio of forces is just 12.25/12 = 1.021. It takes 1.021 times as much force to react the bump force.

BUT, in terms of roll resistance, a wider track increases roll resistance. Using the MS6 track width of 60.2" compared to a 60.7" track width (increase of ~6mm both sides), the roll resistance increases 1.63%. Should be similar for an MS3.



See why I say you should just measure everything and build a calculator?
^This.

Stop making things more complicated than they are.
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 Old 02-20-2015, 12:28 PM   #10
 
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Originally Posted by license2ill View Post
It doesn't change the track, or the centerline of the tire, but the wheel is mounted further 1/4" out with a 1/2" width gain because the mounting face is moved 1/4" out to maintain the same offset length. It still pokes 6.4mm further away from the hub.
The wheel pokes further but since the centerline doesn't change the tire remains in the same spot and does not poke at all.
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 Old 02-20-2015, 01:55 PM   #11
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Originally Posted by shamie View Post
The wheel pokes further but since the centerline doesn't change the tire remains in the same spot and does not poke at all.
On a wider wheel, the same offset measurement is closer to the center of the wheel, so it pokes. If you ran an offset 6mm greater than the original offset on a wheel 0.5" wider, it would remain the same.
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 Old 02-20-2015, 03:17 PM   #12
 
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The offset is measured from the center line of the wheel not the edge.
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