Wheel Fitment - Scrub Radius

Sketchling

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Hello,

I've been doing research on what wheel and tire fitment to go with for my FK7 and I am a bit confused with scrub radius. I am using www.wheel-size.com for checking custom offsets and have narrowed down to two different fitments that works for me (as little modifications as possible, with stock suspension and no spacers...).

235/40R18 18x8.5 45mm
First one is the "safe" route (I think?) But there's barely anyone running this offset based on Fitment Industries' Gallery.

235/40R18 18x8.5 35mm
Second one is what I see a lot of people running on Fitment Industries' Gallery.
The scrub radius from the 35mm offset is Positive 10mm, which through some reading around and research, could cause the tires to scrub the ground as it turns and cause more wear and reduce tire life.

My question is: How come so many people are running the 35mm offset when the positive scrub radius will cause more wear? Why not stick with the 45mm offset so the scrub radius is zero?

Would be great if someone can clarify or give suggestions on the fitment!

Thanks
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ikbenben

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Simple, looks!!

I did consider sticking as close as possible to stock scrub radius because I didn't want to change the stock geometry too much. I went with 235/35R 19 19x8.5 45mm.
 

Driver56

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I went with 235/40r18 on 18x8.5 with a 35mm offset. Besides scrub radius, you are also widening the wheel base with the lower offset, so it does change the handling a bit. It is very much about looks and personal taste, so do whatever you'll be happy with.
 

gtman

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The guys above are right, it's mostly about looks. I mean it does look awesome. Me, I'm conservative when it come to modding my cars. It's all about your goals. My mod goal is a better than stock sleeper, so I went with 18x8 +48 which is literally only 2mm wider than stock. The setup I bought only weighs 42.8 lbs. though which is a nice unsprung weight savings.

If you go too wide and too low an offset, like you mentioned, you change the scrub radius. You increase torque steer and you potentially put extra stress on suspension components with the new geometry. Also wider wheels and tires tend to be heavier, cost more.

Having said all that though, unless you go drastically wider and drastically lower offset, you'll probably be fine on the street. I definitely considered a lower offset because it does look cool but I kept to my plan. I also remembered the wheel bearing issue I had on a car with low offset wheels. Uncommon but it can happen (wasn't a Honda).
 
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Sketchling

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Thanks for all your responses!

Since as you all say it's mostly about looks, then I would rather keep with the measurements as close to stock as possible :). I'm less about looks, but I'd rather keep all the engineering that Honda's done as close to stock as possible. I really just want better tires and some rims with good strength and looks is a bonus!

I think I'm going with a 235/40R18 18x8 45 offset. Here's hoping I can find the right set of wheels with these measurements ?
 


JT Si

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You're making a huge and likely incorrect assumption the scrub radius with OEM wheels is 0. On FWD cars it's almost always negative.

The Type R has a scrub radius of 0, but it also has an entirely different suspension with a unique knuckle design not shared by any other civics.

No one publishes the scrub radius as a specification for FWD compact cars. (Except in the case of the Type R) The best you can do is measure it yourself to see how changing wheel offsets will affect it.

Negative scrub radius and negative rear camber are common because they improve stability in the event of emergency maneuvering.

That being said, you can't go wrong by maintaining the OEM offset with aftermarket wheels. It greatly reduces the chance that you will affect the steering feel in a way that you don't like.

Unless you know exactly how changing the offset will affect handling and desire the change, I think the only performance oriented reason is to fit bigger brakes. Even then, I'm heavily considering a combination of a minor offset change (5mm) along with a slightly wider wheel to achieve clearance with as little upset to the OEM design as possible.
 
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Sketchling

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You're making a huge and likely incorrect assumption the scrub radius with OEM wheels is 0. On FWD cars it's almost always negative.

The Type R has a scrub radius of 0, but it also has an entirely different suspension with a unique knuckle design not shared by any other civics.

No one publishes the scrub radius as a specification for FWD compact cars. (Except in the case of the Type R) The best you can do is measure it yourself to see how changing wheel offsets will affect it.

Negative scrub radius and negative rear camber are common because they improve stability in the event of emergency maneuvering.

That being said, you can't go wrong by maintaining the OEM offset with aftermarket wheels. It greatly reduces the chance that you will affect the steering feel in a way that you don't like.
Fair enough! That's a good point you make. I was just assuming that the measurements in the calculator database is correct, but I knew it was going to be some discrepancies. I guess what I was assuming is that "0 scrub" = OEM offset :)

Though yes, as you say maintaining OEM offset will reduce any effect on steering...even though it could improve it but I wouldn't want it to go the other way :p. Since clearly I don't know enough about this to be sure. Maybe in a few years I can start playing around with the numbers.
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