Any downsides to very lightweight wheels?

[250gtswb]

Given that our cars (I'm thinking of the Si, though this would also apply to the Type R) have adaptive dampers, is it possible that fitting wheels much lighter in weight than the stock wheels (say, 19 lb. aftermarket wheels in place of the 28 lb. OEM wheels) might adversely affect the proper functioning of the suspension? I do understand the enormous benefit of reducing unsprung weight, and experienced those benefits firsthand on my 8th Gen Si. On that car I fitted Enkei RPF-1 wheels of the same dimensions as the stock wheels; the RPF-1s weighed much less, and I could actually feel the difference -- in a good way -- while driving. But with the adaptive suspension of the GenX Si, I wonder if a big reduction of wheel-mass might throw the suspension off in some way. The thing is, I love the handling feel and roadholding of my Si's suspension as it is, and would not want to degrade it in any way, but if taking 5 lbs or more off each wheel can make the car hold the road even better and feel even more responsive, well...

Sponsored

 

[bahndrvr]

Given that our cars (I'm thinking of the Si, though this would also apply to the Type R) have adaptive dampers, is it possible that fitting wheels much lighter in weight than the stock wheels (say, 19 lb. aftermarket wheels in place of the 28 lb. OEM wheels) might adversely affect the proper functioning of the suspension? I do understand the enormous benefit of reducing unsprung weight, and experienced those benefits firsthand on my 8th Gen Si. On that car I fitted Enkei RPF-1 wheels of the same dimensions as the stock wheels; the RPF-1s weighed much less, and I could actually feel the difference -- in a good way -- while driving. But with the adaptive suspension of the GenX Si, I wonder if a big reduction of wheel-mass might throw the suspension off in some way. The thing is, I love the handling feel and roadholding of my Si's suspension as it is, and would not want to degrade it in any way, but if taking 5 lbs or more off each wheel can make the car hold the road even better and feel even more responsive, well...

Absolutely none, if you change the overall rolling diameter you may mess with VSA and your TPMS - but simply recalibrating them will resolve that.

 

[250gtswb]

Absolutely none, if you change the overall rolling diameter you may mess with VSA and your TPMS - but simply recalibrating them will resolve that.

My thinking was that the electronically-controlled shocks (and suspension in general) were tuned with 28 lb. wheels in mind, and that sharply reducing the wheel weights might throw the damping rates off.

 

[CanadiaegeanBlue]

Went down to 245/40R17 on my 17x8 ET45 RPf1's for the track. 15.6lbs per corner, car handles like a go kart and I love it. Here's what the changes are:

 

[dmitri]

I asked the same question a while back, the answers there might also be helpful: https://www.civicx.com/threads/wheels.12187/#post-220252

 

[Micah]

Went down to 245/40R17 on my 17x8 ET45 RPf1's for the track. 15.6lbs per corner, car handles like a go kart and I love it. Here's what the changes are:

Glad to hear these clear the brakes of the SI.

 

[CanadiaegeanBlue]

Glad to hear these clear the brakes of the SI.

Was just as glad

A friend who got 17x9 ET45 RPF1's mentioned we need at least 3mm spacers to clear the brakes

 

[Design]

There are indirect side effects to going to a lighter wheel. The first is that springs/dampers are designed to control a wheel with very specific velocity characteristics. Since velocity is influenced by mass/weight, a lighter wheel can alter the damping parameters for which the ADS is engineered. Lighter wheels are easier to control, particularly on the compression stroke. That also means you will feel each and every bump, transition, or click from the road; to the point it may become uncomfortable (unlikely, but possible for ultra-light wheels). Second, lighter wheels transmit more NVH into the cabin. Even if you don't change the tire size/aspect ratio, you will likely experience more road noise throughout. Finally, a different offset/diameter can lead to tramlining at higher speeds. You may notice slight tension on the wheel (even on our cars with EPS) or a tendency to "pull" across the lane.

For performance enthusiasts, these are accepted side effects. But it's worth mentioning for those who do a lot of driving.

 

[bahndrvr]

There are indirect side effects to going to a lighter wheel. The first is that springs/dampers are designed to control a wheel with very specific velocity characteristics. Since velocity is influenced by mass/weight, a lighter wheel can alter the damping parameters for which the ADS is engineered. Lighter wheels are easier to control, particularly on the compression stroke. That also means you will feel each and every bump, transition, or click from the road; to the point it may become uncomfortable (unlikely, but possible for ultra-light wheels). Second, lighter wheels transmit more NVH into the cabin. Even if you don't change the tire size/aspect ratio, you will likely experience more road noise throughout. Finally, a different offset/diameter can lead to tramlining at higher speeds. You may notice slight tension on the wheel (even on our cars with EPS) or a tendency to "pull" across the lane.

For performance enthusiasts, these are accepted side effects. But it's worth mentioning for those who do a lot of driving.

I almost spit water on my computer when I read the added nvh from lighter rims and tires - nothing can be louder than my stock Goodyear All Seasons, the most disappointment aspect of my entire car at this point. Rims stock on Si are 28 and tire is loud, crap and not lightweight either, if he went with say a 17x8 ~15lb rim and then an ultralight tire like a competition 200 or less compound I feel it would be noticeable for all you mentioned. But the truth is more than likely will loose on around 15-20 lbs max on each corner which is what matters, IMO that is not enough to feel the negative effects or even throw off the ADS much at all if any and it certainly would not cause any errors - then throw in the fact that the OP is askign the question and that points to "learning and developing" the skills at this point in time, so the cahgne will be felt positively but without the indepth knowledge to realize the ill effects they would go unnoticed, the largest aspect was it's "plug and play" essentially

 

[Design]

Good points. I think better tires are a given.

My position was more about the molecular compound of a typical lightweight wheel. Strength discussions aside, there is probably less density to absorb road vibrations when compared to OEM cast; all other things held constant.

Shock velocities are incredibly precise on active suspensions. We're probably talking several hundred oscillations or more per minute. And while changing aggregate weight won't throw a code per se, a few lbs are theoretically enough to upset the factory tuning to the point that the platform might feel "overdamped" to some, due to the reduction in aggregate velocity on both compression and rebound.

Again, I think most would agree that these are very small gripes in the performance world. But I still think it's worth mentioning for those wanting to understand the full 360° impact.

 

[bahndrvr]

Good points. I think better tires are a given.

My position was more about the molecular compound of a typical lightweight wheel. Strength discussions aside, there is probably less density to absorb road vibrations when compared to OEM cast; all other things held constant.

Shock velocities are incredibly precise on active suspensions. We're probably talking several hundred oscillations or more per minute. And while changing aggregate weight won't throw a code per se, a few lbs are theoretically enough to upset the factory tuning to the point that the platform might feel "overdamped" to some, due to the reduction in aggregate velocity on both compression and rebound.

Again, I think most would agree that these are very small gripes in the performance world. But I still think it's worth mentioning for those wanting to understand the full 360° impact.

Design I gather from your post you are an engineer as well I helped launch rockets for around 15 years and miss it I took the management of engineers last year for the pay increase but find myself looking st all the recruiters for the senior engineer positions at NASA and SpaceX among many others here just to get back to what I’m really good at!

 

[250gtswb]

I really appreciate all the great replies to my question. Lots of very well-informed people on this forum!

 

[burningoilagain]

18.9 pounds forged wheels. Car feels so much lighter and handles better corning at high speeds.

 

[CanadiaegeanBlue]

Good points. I think better tires are a given.

My position was more about the molecular compound of a typical lightweight wheel. Strength discussions aside, there is probably less density to absorb road vibrations when compared to OEM cast; all other things held constant.

Shock velocities are incredibly precise on active suspensions. We're probably talking several hundred oscillations or more per minute. And while changing aggregate weight won't throw a code per se, a few lbs are theoretically enough to upset the factory tuning to the point that the platform might feel "overdamped" to some, due to the reduction in aggregate velocity on both compression and rebound.

Again, I think most would agree that these are very small gripes in the performance world. But I still think it's worth mentioning for those wanting to understand the full 360° impact.

This is why I love forums! Can't find the quality of responses, and overall willingness of open responses anywhere else

Thank you Design for the insight!

 

[CanadiaegeanBlue]

Update:

Was running Enkei RPF1 17x8 (15.9 lbs) with 245/40R17 Firestone Indy500. Switched back to Konig Ampliform 18x8.5 (19lbs) with factory 235/40R18. Noticeable improvement in ride comfort.

Could be due to the tires, and/or heavier wheels absorb bumps better. I'll reserve the RPF1's for track duty only

Sponsored