Taking Scrub Radius into Account When Changing Wheel Offset

si_well

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I've been going back and forth like a crazy person over the last two weeks on which direction I should go with purchasing aftermarket wheels and I wanted to hear some feedback from everyone.

I want a wheel set up that does not rub under any circumstances while lowered on Eibach pro springs and have the wheels sit as close to flush as possible (no poke) with minimal upset in suspension geometry. I've learned about suspension components and how their geometry affects how the car drives more in the past two weeks than I thought was even possible. I've since learned how delicate of a balance this is to maintain when making changes to things. My understanding now is that you should deviate from factory scrub radius as little as possible or you risk compromising handling and stability.

If the car is lowered, it changes the angle of the SAI (steering axis inclination) which will help counter the change of offset to some degree, but how much I don't know. Additionally, since the civic comes in varying trims with varying wheel/tire sizes and offsets, so our cars have the ability to change some geometry on the fly by removing the guide pin on the upper strut assembly. From what I've read it only is adjustable to about +/- 0.32 degrees.

Ultimately, my question is how much wiggle room will lowering ~1" and adjusting the camber give me to allow an offset that will be close to flush?

Before doing my homework on all this I originally wanted either 18x8.5 +35-38 or 18x9.5 +38-45 to get a flush look while also adding some width for added handling performance. I now am thinking I should stick to an offset as close to the OEM +50mm in an effort minimize change in scrub radius, so I was thinking about doing 18x8.5 +45. This will only be 11.3mm closer to the fender, which is like ~10mm from flush, but I'm thinking I should prioritize the geometry over fitment: Function > Form.

What is everyone's thoughts about this? Is there a specific threshold of offset change to stay within before causing noticeable adverse effects? Am I over thinking all of this lol?

Any thoughts or advice would be greatly appreciated!!



 

WOPSiWOT

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I feel like I am going to be a lone voice on this, but I think going 18x8.5 +45 makes sense for many of the reasons you state. I have stock wheels, but briefly ran 20mm spacers. Lowered on Swift springs (similar drop) I got rub over bumps (on the fender tabs ... which I could have bent but didn't ... and I gather maybe the 2020s don't have them) and also experienced some increased torque steer. Not crazy, but noticeable. The ride was just worse. Some of that is the nature of spacers, I think, and adding unsprung weight, but I was glad that I hadn't invested a bunch of money in wheels with an aggressive offset. When I've considered wheels more recently, I've been looking at 18x8.5 +45 based on that experience. It won't look as good. I think it will ride better.
 
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I feel like I am going to be a lone voice on this, but I think going 18x8.5 +45 makes sense for many of the reasons you state. I have stock wheels, but briefly ran 20mm spacers. Lowered on Swift springs (similar drop) I got rub over bumps (on the fender tabs ... which I could have bent but didn't ... and I gather maybe the 2020s don't have them) and also experienced some increased torque steer. Not crazy, but noticeable. The ride was just worse. Some of that is the nature of spacers, I think, and adding unsprung weight, but I was glad that I hadn't invested a bunch of money in wheels with an aggressive offset. When I've considered wheels more recently, I've been looking at 18x8.5 +45 based on that experience. It won't look as good. I think it will ride better.
Right, I really don't want to make my ride worse. My goal is to make it perform better, keep the ride quality equal or better, and improve looks; in that order. I think that a nice lightweight wheel at 18x8.5 +45 (Konig has some great options) will do just that, but if I can go +40 or even to +38-35 without making much of a difference, I would rather do that.
 

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I'm in the process of choosing wheels myself, however I'm not planning on lowering mine since I'd have issues using my driveway. Keeping offset close to stock will be optimal for longevity, for sure.
 

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IMHO, I'd recommend keeping offset as close to stock as possible. The biggest difference you'll notice is increased likelhood of tramlining at highway speeds.

Also, it's worth noting that the lighter you go, the more likely you'll notice increased in-cabin NVH (if that matters to you).
 
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IMHO, I'd recommend keeping offset as close to stock as possible. The biggest difference you'll notice is increased likelhood of tramlining at highway speeds.

Also, it's worth noting that the lighter you go, the more likely you'll notice increased in-cabin NVH (if that matters to you).
Oh, I actually thought the lighter wheels would DECREASE noise and vibration in the cabin due to it being less unsprung mass that I assumed would result in less overall force pushing back on the suspension. Plus I figured wider wheels would help as well by distributing the car's weight more evenly on the contact patch of the tire.
 

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Oh, I actually thought the lighter wheels would DECREASE noise and vibration in the cabin due to it being less unsprung mass that I assumed would result in less overall force pushing back on the suspension. Plus I figured wider wheels would help as well by distributing the car's weight more evenly on the contact patch of the tire.
I kinda did too with my 2018. It had traklites on it from 1100 miles on. When I installed the stock wheels and tires to trade it; I couldn't believe how much better it rode and decreased the road noise. So much so I'm not even going to install them on my 2020.
 

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