Enlightening read on wheel offset and effects on suspension and steering

[hammeredsole]

If you've searched for wheels, you might be aware that just about every aftermarket wheel is +38 or +45 offset for the FL5. The OEM wheels are +60. Everyone seems to agree that less offset looks best, but seem to ignore the negatives. Anecdotally, people speak about tramlining, torque steer, loss of precision; and there seems to be a lot of correlation to tire sizing. I feel that a good understanding of suspension geometry is not applied when choosing wheels. The big issue with the FL5 CTR is that it is obviously front wheel drive. The one big thing that makes the CTR such an outstanding FWD car is the clever engineering that Honda has put into the front knuckle design, termed dual axis. This moves the steering pivot point into the wheel, allowing for an ideal scrub radius.

What is scrub radius?

Simply put; it is the difference of the center point of the wheel and the relationship it has with the pivot point of the steering. When we decrease offset (going from OEM +60mm to +45mm) we are increasing the moment (length of the lever) of the wheel center point to the steering axis. This creates a greater effect against the steering with any acceleration or deceleration load placed on the tire. In the case of the FL5, I do not know the OEM specifics yet, but a 15-22mm decrease in offset is a massive change which reduces the beneficial design of negative scrub radius, possibly even pushing it into positive scrub radius. Personally, I will be running OEM wheels until I can find something that looks good, but also has a 55-60mm offset, as I feel the performance factor is far greater than aesthetics. In fact, I'm just going to say it, low offset wheels are performance reducing mods.

Here are some good reads on the subject.

Wheel Offset: Why It Matters (motortrend.com)

Scrub radius - Wikipedia

Scrub radius, how important? - Page 1 - Suspension, Brakes & Tyres - PistonHeads UK

Understanding Steering and Wheel Alignment Angles (superproeurope.com) Look at figure 3 here for a very simple illustration to understand this concept.

From the horse's mouth
Honda Global | Dual Axis Strut Suspension - Picture Book

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[julianobl]

i agree with the concept and theory of not altering scrub radius for the reasons you stated. i'm currently running the Honda OEM+ forged wheels with the same +60 offset. i have not used spacers for the same reason even though i would like a wider stance aesthetically.

on the other hand, i know very experienced and knowledgeable drivers and mechanics/tuners that are using very altered offsets and track the car and do amazing times, so i don't know how much of an impact it really does on the car handling although the theory seems to be there.

 

[TW00Si]

Thanks for sharing. I run my aftermarket wheels with +38 offset but wrapped with all season tires. It would be for street driving. Doubt it will impact much. But when I’m ready for track days, I will be putting on the OEM wheels and tires (till I kill off the tires for something better).

 

[TypeRD]

@hammeredsole Yup! This all makes complete sense to me. The only unknown is exactly as you state ; We don’t know how much reducing the offset changes the steering dynamics. I can see how a +38 or +45 may still work just fine on some tracks (compared to the OEM’s +60). Even if I’m not on a track, I personally still want all of my car’s engineered steering and handling for daily driving. With that said, I tend to agree that it’s probably a safe bet to stick with offsets that are within ~10% of stock, if you want to maintain steering performance. So a +55 offset shouldn’t have a noticeable negative impact…all else being equal (including tires).

I love the OEM wheels. I wish the Honda forged wheels looked as nice. Don’t get me wrong. They’re nice, but I don’t love them. While I await more wheel options in ideal offsets, I’m keeping my fingers crossed that maybe Honda will update the forged wheel option during the mid-model refresh (presumably for 2025)…or maybe Acura will provide a nice forged wheel option for the DE5 that we FL5 owners can adopt.

 

[dandaman15]

If you've searched for wheels, you might be aware that just about every aftermarket wheel is +38 or +45 offset for the FL5. The OEM wheels are +60. Everyone seems to agree that less offset looks best, but seem to ignore the negatives. Anecdotally, people speak about tramlining, torque steer, loss of precision; and there seems to be a lot of correlation to tire sizing. I feel that a good understanding of suspension geometry is not applied when choosing wheels. The big issue with the FL5 CTR is that it is obviously front wheel drive. The one big thing that makes the CTR such an outstanding FWD car is the clever engineering that Honda has put into the front knuckle design, termed dual axis. This moves the steering pivot point into the wheel, allowing for an ideal scrub radius.

What is scrub radius?

Simply put; it is the difference of the center point of the wheel and the relationship it has with the pivot point of the steering. When we decrease offset (going from OEM +60mm to +45mm) we are increasing the moment (length of the lever) of the wheel center point to the steering axis. This creates a greater effect against the steering with any acceleration or deceleration load placed on the tire. In the case of the FL5, I do not know the OEM specifics yet, but a 15-22mm decrease in offset is a massive change which reduces the beneficial design of negative scrub radius, possibly even pushing it into positive scrub radius. Personally, I will be running OEM wheels until I can find something that looks good, but also has a 55-60mm offset, as I feel the performance factor is far greater than aesthetics. In fact, I'm just going to say it, low offset wheels are performance reducing mods.

Here are some good reads on the subject.

Wheel Offset: Why It Matters (motortrend.com)

Scrub radius - Wikipedia

Scrub radius, how important? - Page 1 - Suspension, Brakes & Tyres - PistonHeads UK

Understanding Steering and Wheel Alignment Angles (superproeurope.com) Look at figure 3 here for a very simple illustration to understand this concept.

From the horse's mouth
Honda Global | Dual Axis Strut Suspension - Picture Book

Coming from someone who did suspension design and vehicle dynamics in school for a formula team, I can say that you are seriously exaggerating the effect scrub radius has on performance, especially within a track width change of ~30mm. Its almost hilarious to declare "Low offset wheels being performance reducing modifications" In the realm of going from +60 to +38, when we have all the data from FK8 racecars proving otherwise.

The third link from piston heads does have a very well thought out response and Sam-68 essentially nails it.

A couple points that need to be considered.

• What is the factory scrub radius? Is it negative, zero, or positive? And if so, how much?
• The design on the factory suspension is to reduce negative scrub and push it to zero/positive. This has beneficial track performance with the inducing of negative toe under lift off or braking to sharpen turn in. Reducing offset can increase this behavior further.
• Scrub radius (within the differences we are speaking to on a wheel change) will only result in steering FEEL changes. Increasing the moment adds some weight to the steering. (Adjust the steering to comfort instead of +R if needed to offset this weight).
• Torque steer is mitigated by many other properties of the dual axis design (Kingpin angle, caster, Tie Rod Lengths, etc) that although you may suddenly FEEL the torque loading up the tires differently, the overall design is not sensitive enough to suddenly pull you all over the road by 15mm change in offest.
• If this was such a drastic issue, why are all the FWD TCR cars even wider with extreme lower offset 18x10 or 18x11 wheels? The mechanical advantages gained by running a lighter 18" wheel and tire setup with available popular offsets is greater than utilizing the factory sizing. Please reach out to these guys that they messed up their car by modifying the scrub radius.
  • 
• Tramlining is also mostly induced by added camber. Many times people running these setups will do multiple things at once. I drove my car on stock setup for 1000 miles and swapped to a +38 setup and tramlining had no change. What was better was the softer ride from a larger sidewall when using even more aggressive 200tw tires than factory. Without knowing what the values are its hard to say how much positive scrub radius is even added and at what limit you do see negative effects.
• If performance was actually reduced these setups would not be as popular as they are. This is a car where people are expecting a level of improved performance with mods. If people noticed significant issues, there would be demand for those better performing parts.

There is no issue in liking and preferring the feel of the stock setup. However there is a lot more that goes into it than just scrub radius. Its one of many factors that add up to the exceptional factory handling and dynamics. What is funny is that if the car came with +50 or +45 from the factory people would still think it has some of the best steering ever and they wouldn't know or care what they are missing.

 

[hammeredsole]

Coming from someone who did suspension design and vehicle dynamics in school for a formula team, I can say that you are seriously exaggerating the effect scrub radius has on performance, especially within a track width change of ~30mm. Its almost hilarious to declare "Low offset wheels being performance reducing modifications" In the realm of going from +60 to +38, when we have all the data from FK8 racecars proving otherwise.

The third link from piston heads does have a very well thought out response and Sam-68 essentially nails it.

A couple points that need to be considered.

• What is the factory scrub radius? Is it negative, zero, or positive? And if so, how much?
• The design on the factory suspension is to reduce negative scrub and push it to zero/positive. This has beneficial track performance with the inducing of negative toe under lift off or braking to sharpen turn in. Reducing offset can increase this behavior further.
• Scrub radius (within the differences we are speaking to on a wheel change) will only result in steering FEEL changes. Increasing the moment adds some weight to the steering. (Adjust the steering to comfort instead of +R if needed to offset this weight).
• Torque steer is mitigated by many other properties of the dual axis design (Kingpin angle, caster, Tie Rod Lengths, etc) that although you may suddenly FEEL the torque loading up the tires differently, the overall design is not sensitive enough to suddenly pull you all over the road by 15mm change in offest.
• If this was such a drastic issue, why are all the FWD TCR cars even wider with extreme lower offset 18x10 or 18x11 wheels? The mechanical advantages gained by running a lighter 18" wheel and tire setup with available popular offsets is greater than utilizing the factory sizing. Please reach out to these guys that they messed up their car by modifying the scrub radius.
  • 
• Tramlining is also mostly induced by added camber. Many times people running these setups will do multiple things at once. I drove my car on stock setup for 1000 miles and swapped to a +38 setup and tramlining had no change. What was better was the softer ride from a larger sidewall when using even more aggressive 200tw tires than factory. Without knowing what the values are its hard to say how much positive scrub radius is even added and at what limit you do see negative effects.
• If performance was actually reduced these setups would not be as popular as they are. This is a car where people are expecting a level of improved performance with mods. If people noticed significant issues, there would be demand for those better performing parts.

There is no issue in liking and preferring the feel of the stock setup. However there is a lot more that goes into it than just scrub radius. Its one of many factors that add up to the exceptional factory handling and dynamics. What is funny is that if the car came with +50 or +45 from the factory people would still think it has some of the best steering ever and they wouldn't know or care what they are missing.

Well thanks for the further clarification. To your point of doing multiple changes at once; that's likely the biggest cause of difficulty tracking down unfavorable changes. I suppose my take on it is in the face of the assumption that less offset always = better.

Reducing offset should be calculated with other changes to toe, camber, spring rate, ride height etc., for a properly planned out build. There are thousands of shops that will throw on a downpipe, tune, and lowering springs, and drastically fewer that can properly set up suspension. I'm speaking from my limited experience of suspension tuning, but I can say with experience and certainty that hasty changes made to suspension geometry can and usually will induce unfavorable attributes.

 

[Icehawk]

I have used radically different offset/sized wheels before on the same car:
OEM 14x6 +45 with 185s
15x7 +35 with 195s
16x7 +45 with 205s
13x8 +4 with 235s

Steering effort was noticeably increased on the +4 wheelset, the car also would exhibit some tramlining. Not an issue for me as they were a dedicated autocross setup. It also felt like it would self-center more, a lot like an increase in caster feels. Oddly enough, the CTR's steering feel reminds me a LOT of this setup.

RWD cares a lot less about this than FWD though. For racing, generically speaking, wider tires, wider rims, and wider track are good. There are limits and exceptions of course


I don't like spacers because I've seen what can happen when you aren't careful mounting wheels. Also hilarious when your friend only brought half the needed ones to an event.

 

[CTR]

While I agree that 18” aggressive offset wheels can be better on a race car it requires other suspension modifications to make it handle better than stock.

When I installed 18x9.5 +45 TE37 on my car I immediately noticed that the car handled worse. It also threw up sand and rocks at the bumper/side skirts. I’ve since went back to stock and prefer how it drives. I also don’t feel like I’m destroying the car driving it.

I’m not a professional by any means but I do have some experience driving aggressively. Honda really dialed in the best performance possible and until other modifications are available I believe that others will be disappointed as well.

Some people value appearance more and that’s fine.

I do think people should be made aware to avoid the same mistake if they care about handling. I look forward to more lightweight 19” options in +50 and higher offsets.

 

[Icehawk]

While I wouldn't expect 15mm to make a noticeable difference, as you widen the track you increase leverage on the suspension.

 

[CTR]

While I wouldn't expect 15mm to make a noticeable difference, as you widen the track you increase leverage on the suspension.

It might be downsizing to 18” wheels that was more detrimental than the offset.

I’m considering the new 19” Spoon SW388. I think they learned the same thing in testing. Otherwise they would just keep cranking out the 18x9.5 +40.

 

[sugarl4nd]

Based on my own experience, downsizing to 18" is indeed more detrimental than 'stay 19" + changing the offset'. I think staying OEM configuration is the best since the car was engineered that way from Honda.

 

[optronix]

I don't think the whole "but racecars do it" angle is helping anyone. Is the race car otherwise stock? No?

Irrelevant.

Also the assumption that demand would somehow be affected, also highly skeptical. Give me some data that validates the reason people buy wheels, performance vs looks.

My guess is that people buy wheels off what they see on Instagram, probably not through extensive research on how they would negatively impact scrub radius.

 

[dandaman15]

I don't think the whole "but racecars do it" angle is helping anyone. Is the race car otherwise stock? No?

Irrelevant.

Also the assumption that demand would somehow be affected, also highly skeptical. Give me some data that validates the reason people buy wheels, performance vs looks.

My guess is that people buy wheels off what they see on Instagram, probably not through extensive research on how they would negatively impact scrub radius.

In most of those series the factory suspension mounting points are retained and they use helm joints or hard rubber/solid bushings replacing a lot of the OEM ones. Ofcourse aftermarket dampers/springs and other parts are added... They still start with a factory civic body in white and use the dual axis strut setup and all factory mounting points. That also doesn't take away from the fact that people striving to do everything possible to eek the most performance out of the car are doing exactly what laymen are saying is "bad". It's not irrelevant, you can look at stock class Time attack cars as well if you want something to reference thats less modified. People with nearly unlimited budgets running complete custom wheels are choosing to run 18's over any other size should point to something.

Wheels developed for the FK8/FL5 chassis follow the same process all chassis specific wheel fitment applications take. Spoon and Mugen are not going to release wheels that will damage their reputations and offer negative performance over factory. Spoon and Mugen work directly with Honda in getting chassis/suspenion information and they both concluded 18x9.5 +40 or +45 is best. The 19" Spoons coming out will most likely be +45 as well since they use the same factory as the Regas coming out in that same size. All these independent companies making chassis specific wheels all ended up around the same spot?

Why people buy wheels is somewhat irrelevant to the reason why the products are developed in those particular sizes. It wasn't for hard parking instagram flexers when you are talking about Titan 7, Rays, Volks, Mugen, Spoon etc. They aren't going to invest millions of dollars in forging molds to produce wheels in a size that everyone hates and feels makes the car worse. These companies also do a considerable amount of R&D when coming to the sizes they offer.

 

[hammeredsole]

In most of those series the factory suspension mounting points are retained and they use helm joints or hard rubber/solid bushings replacing a lot of the OEM ones. Ofcourse aftermarket dampers/springs and other parts are added... They still start with a factory civic body in white and use the dual axis strut setup and all factory mounting points. That also doesn't take away from the fact that people striving to do everything possible to eek the most performance out of the car are doing exactly what laymen are saying is "bad". It's not irrelevant, you can look at stock class Time attack cars as well if you want something to reference thats less modified. People with nearly unlimited budgets running complete custom wheels are choosing to run 18's over any other size should point to something.

Wheels developed for the FK8/FL5 chassis follow the same process all chassis specific wheel fitment applications take. Spoon and Mugen are not going to release wheels that will damage their reputations and offer negative performance over factory. Spoon and Mugen work directly with Honda in getting chassis/suspenion information and they both concluded 18x9.5 +40 or +45 is best. The 19" Spoons coming out will most likely be +45 as well since they use the same factory as the Regas coming out in that same size. All these independent companies making chassis specific wheels all ended up around the same spot?

Why people buy wheels is somewhat irrelevant to the reason why the products are developed in those particular sizes. It wasn't for hard parking instagram flexers when you are talking about Titan 7, Rays, Volks, Mugen, Spoon etc. They aren't going to invest millions of dollars in forging molds to produce wheels in a size that everyone hates and feels makes the car worse. These companies also do a considerable amount of R&D when coming to the sizes they offer.

To split the hairs here, I think there's a relatively middle ground to this. I think race wheel manufacturers are trying to sell wheels, and will likely make wheels in the most popular offset in order to sell more wheels. Most of the talk about offset is in relation to how it looks, and zero conversation about geometry. I think if someone is actually setting up a racecar, they are looking at all things considered. As far as Mugen and Spoon go... most of their stuff is tacky garbage to begin with.

I think +45 offset probably lands in a workable zone of geometry, especially with customized suspension. I also agree with the opinion that Honda probably selected +60 for a reason. I'd be very curious to see a geo chart of OEM FL5, at the very least as a starting point for future mods.

 

[optronix]

In most of those series the factory suspension mounting points are retained and they use helm joints or hard rubber/solid bushings replacing a lot of the OEM ones. Ofcourse aftermarket dampers/springs and other parts are added... They still start with a factory civic body in white and use the dual axis strut setup and all factory mounting points. That also doesn't take away from the fact that people striving to do everything possible to eek the most performance out of the car are doing exactly what laymen are saying is "bad". It's not irrelevant, you can look at stock class Time attack cars as well if you want something to reference thats less modified. People with nearly unlimited budgets running complete custom wheels are choosing to run 18's over any other size should point to something.

Wheels developed for the FK8/FL5 chassis follow the same process all chassis specific wheel fitment applications take. Spoon and Mugen are not going to release wheels that will damage their reputations and offer negative performance over factory. Spoon and Mugen work directly with Honda in getting chassis/suspenion information and they both concluded 18x9.5 +40 or +45 is best. The 19" Spoons coming out will most likely be +45 as well since they use the same factory as the Regas coming out in that same size. All these independent companies making chassis specific wheels all ended up around the same spot?

Why people buy wheels is somewhat irrelevant to the reason why the products are developed in those particular sizes. It wasn't for hard parking instagram flexers when you are talking about Titan 7, Rays, Volks, Mugen, Spoon etc. They aren't going to invest millions of dollars in forging molds to produce wheels in a size that everyone hates and feels makes the car worse. These companies also do a considerable amount of R&D when coming to the sizes they offer.

I really want to believe you. Not so much about 18s; I've said many times how much I hate how 18s look on the DE5. But I just don't think speculating on why manufacturers pick given offsets to manufacture is all that compelling- it's already been said, they're in business to sell wheels. If they only catered to race cars there would be a whole lot of margin to miss out on...

And anyway another point that is being missed with all this race car talk is how the car feels. As much as I'd like to think I'm Lewis Hamilton, I'm not, and about 99% of the time I'll be spending in my car will not be on a racetrack. I personally really enjoy the way my car's steering and handling feels for my purposes- pretty much backroads jaunts 3-4 times a month and a "motorsports-type event" 4-7 times a year. I don't want to do anything to jeopardize that. So arguing over what reasons race cars decide to go with 18x9.5+38 is still pretty irrelevant to me, whether they use factory mounting points or not. There are many compromises that are overlooked when chasing lap times; I'm not about that life.

There's a couple different sets of wheels I could buy right now in 19x9.5+45 that I really like. I'm still looking for definitive evidence that if I go that route I won't hate the changes it brings. I really could care less if there's a performance impact or not- I care more about the sensory element anyway, and I'm not convinced it's worth compromising so I can be hella flush yo.

You can get custom offsets for some higher end wheels right? I know you can with HRE but I was hoping some of the Japanese brands offer this too...

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