8.5" wide wheel, +35 vs +45 Offset?????

[si_well]

Thanks for this. It matches up with a lot of research I did before buying my wheels and it was clear there was going to be some trade for wider wheels and offset due to the scrub radius.

Yeah no problem. I dove into this topic HEAVY researching which wheels to go with myself. Choosing wheels specs is so tricky because you have to make a trade off somewhere. Scrub radius is rarely talked about despite it having a dramatic impact on handling. How the car handles is a higher priority than my wheels looking flush. I think the sweet spot for our cars to achieve a flush look without compromising handling or rubbing is 18x9.5 +45. The only compromise you'd be making is a small, almost negligible, drop in mpg only if you paired them with wider tires. The lowest offset offered from the factory (to my knowledge) for 10th gens is +45, and since the struts can be adjusted to account for that 5mm difference from the +50 wheels my Si comes with, the ideal offset range would be between +45 and +50. Once you go lower than that you begin to sacrifice handling more and more the lower you go. So I guess it's really all about how much handling are you willing to accept being compromised. I personally wouldn't get an offset change of more than 10mm though.

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[Feddy_Ace]

Yeah no problem. I dove into this topic HEAVY researching which wheels to go with myself. Choosing wheels specs is so tricky because you have to make a trade off somewhere. Scrub radius is rarely talked about despite it having a dramatic impact on handling. How the car handles is a higher priority than my wheels looking flush. I think the sweet spot for our cars to achieve a flush look without compromising handling or rubbing is 18x9.5 +45. The only compromise you'd be making is a small, almost negligible, drop in mpg only if you paired them with wider tires. The lowest offset offered from the factory (to my knowledge) for 10th gens is +45, and since the struts can be adjusted to account for that 5mm difference from the +50 wheels my Si comes with, the ideal offset range would be between +45 and +50. Once you go lower than that you begin to sacrifice handling more and more the lower you go. So I guess it's really all about how much handling are you willing to accept being compromised. I personally wouldn't get an offset change of more than 10mm though.

True. I cringe at people running extreme offsets because I can’t imagine the car feels good to drive. Personally my car doesn’t feel bad, but it feels more like a 5 series BMW than a sporty hatch like it did before. This can also have some adverse affects on how you’re used to driving the car. Just the other day I scrapped my bumper cover on my garage while backing out. Now I’m out of $600 to get a new front cover painted, all because I’m not used to how my car responds to steering input anymore. I think the car pivots wider that it used to. I’ve backed out the same spot everyday and never had an issue until I changed my wheels.

I see a lot of people with increased offsets having wheels that are curb-rashed to shit, now I understand 100% why this happens. ?

 

[Derek.]

If people curb their wheels, that's all driver error, not the offset of their wheels.

 

[NonyaBisness]

they're here, more pics will follow this weekend when I get a chance to get them on the car and wash the car.

 

[jscm]

they're here, more pics will follow this weekend when I get a chance to get them on the car and wash the car.

what offset did you get?

 

[SonicBreezerST160]

Yeah no problem. I dove into this topic HEAVY researching which wheels to go with myself. Choosing wheels specs is so tricky because you have to make a trade off somewhere. Scrub radius is rarely talked about despite it having a dramatic impact on handling. How the car handles is a higher priority than my wheels looking flush. I think the sweet spot for our cars to achieve a flush look without compromising handling or rubbing is 18x9.5 +45. The only compromise you'd be making is a small, almost negligible, drop in mpg only if you paired them with wider tires. The lowest offset offered from the factory (to my knowledge) for 10th gens is +45, and since the struts can be adjusted to account for that 5mm difference from the +50 wheels my Si comes with, the ideal offset range would be between +45 and +50. Once you go lower than that you begin to sacrifice handling more and more the lower you go. So I guess it's really all about how much handling are you willing to accept being compromised. I personally wouldn't get an offset change of more than 10mm though.

Agreed!!! 18x9.5", 45mm 245/40's I have taken a lot of the negative camber out of the rear with adjustable camber arms, and the rear fender lips are rolled up flat. The car has great steering response, and tracks down the road as straight as an arrow. If anyone wants to run 9.5" wheels, 45mm, is indeed, the perfect offset.

 

[NonyaBisness]

what offset did you get?

45 offset, hoping to get them on he car in the afternoon Sunday, spent all day Saturday cutting down like 50-100 small trees in the backyard and cutting the pieces out of the damn Kudzu vines that have infested my backyard (and to the environmentalists, probably 60-70% of the trees where already dead due to the Kudzu strangling them).

 

[NonyaBisness]

they are on the car, but it's in the 50's so too cold to wash the car and my impact adapter for half inch drive broke on me so I had to do the last wheel completely by hand.

wheels are Konig Ampliform 19x8.5" with 45 offset

 

[jscm]

what size are your tires? 235?

 

[Jes_si562]

The loss of responsiveness after changing your offset it due to scrub radius. Scrub radius is the distance between the center line of your tires contact patch and where your steering axis inclination (SAI) meets the ground. The SAI is essentially where a theoretical line would touch the ground if it extended from your strut at the angle it's positioned. The best way to think about it is the SAI acts as the pivot point for which the tire pivots around, so the scrub radius is the measurement of how far the center of the contact patch is away from the point which it pivots.

A scrub radius could be either positive, negative or zero based on where the SAI meets the ground in relation to the centerline of the contact patch. All three affect steering differently. Front wheel drive cars are designed to have a slightly negative scrub radius because it's geometry naturally reduces torque steer and adds stability in braking. However, the greater the scrub radius in either direction (positive or negative), the more steering feedback you feel through the steering wheel. It gives the wheels a natural tendency to want to pull straight, giving it a natural tendency to self correct the wheels but it also applies constant slight force on the steering linkage which takes up any looseness or compliance, reducing the tendency of the vehicle to wander when driven in a straight line. Increasing scrub radius (in either direction) overall makes the steering more responsive to initial steering input because when a correction is made, the linkage is already pre-stressed.

Changing your offset changes the center point of your tires contact patch, thus changing your scrub radius. Going from +50 mm to +35mm offset changes your scrub radius to change 15mm in the positive direction, which for fwd cars is a considerable change. Your suspension is a delicate balance of multiple components working together in harmony, and changing one thing can upset that balance. The only way to mitigate a change in offset on your scrub radius is to compensate by adjusting the camber accordingly. Fortunately for us our cars are equipped with some degree of camber adjustability from the factory to account for the variance in offset that one chassis can have for different trim levels. Any substantial change in offset would require an aftermarket camber kit to mitigate it's affect on steering.

I don't know what the exact scrub radius is for our cars, but lets say for example it's -10mm. Changing the offset 15mm would move the center of the contact patch 15mm in the opposite direction making the scrub radius +5mm (a smaller positive scrub radius) resulting in poorer steering response and instability under acceleration/deceleration.

will wheel spacers compaste lost scrub radius?

 

[si_well]

will wheel spacers compaste lost scrub radius?

Wheel spacers will create a greater change in scrub radius.

 

[DougNuts]

Edit: Nevermind, made a mistake on offset calculation.

 

[si_well]

It's important to note that, in order to keep scrub radius the same with wider wheels, you must reduce offset by half of the width increase. Therefore, if you increase wheel width by 1", you would want to reduce offset by approximately 12.5mm.

In other words, if you increase wheel width by 1", you would want to run a +38 offset wheel if the stock wheels are +50 offset.

Not true. If the offset remains the same the centerline of a wheel never changes regardless of width.

 

[DougNuts]

Not true. If the offset remains the same the centerline of a wheel never changes regardless of width.

Yes, you are 100% correct, not sure what I was thinking.

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