IMPORTANT FACTORS FOR WHEELS ON RACECARS
With the knowledge that we have learned thus far, why do race cars run lightweight wheels if camber compliance and stiffness is so important?
It was previously mentioned that motorsport-grade wheels are typically heavier and stiffer than what the same company sells to the aftermarket street and club racer, because in the aftermarket, less weight is what sells wheels. Meanwhile professional race teams usually have a slightly better idea of how wheel stiffness affects handling.
In professional racecars, due to the replacement of soft suspension bushings and the addition of stiff roll cages, there is virtually no compliance in the chassis, and very little body roll from the lower ride height and optimized suspension geometry. Because of this, reducing another layer of camber compliance (from the wheels) isn’t as crucial.
Since the tradeoff between stiffness and weight is linear, racecars tend to play on the lower weight side of the spectrum due to the benefits of less unsprung and rotational mass. While there are dynamic losses due to the camber compliance of racing wheels, the benefits of a lighter wheel usually outweigh the losses of braking and accelerating performance from using a heavier aluminum wheel because they can run as much static camber as needed to make the tire work optimally on track.
This is where Carbon Revolution wheels is another game-changer. The technology is new and currently banned in almost all forms of motorsport. If a carbon wheel were to be used on a prototype or GT3 race car, unsprung weight would go down and stiffness would be greatly increased allowing teams to run less static camber. This would result in a significant competitive advantage due to better braking, tire wear, etc…
ON TRACK TESTING
Now that we discussed the technical benefits of lighter and stiffer Carbon Revolution wheels, it was time to put them to the test to see if the theory translates to measurable real-world benefits.
Our test procedure consisted of:
Factory OEM Porsche Aluminum Wheels
-2 slow tire scrub-in laps
-10 timed laps
-Pit Stop/Tire Change
Carbon Revolution CR-9 Wheels
-2 slow tire scrub-in laps
-10 timed laps
-review
Our test was focused on eliminating variables and isolating the difference and benefit of the lighter and stiffer Carbon Revolution wheels over OEM aluminum wheels. In order to minimize temperature differences and its impact on lap times (which can easily account for well over a second), our testing was to be conducted at 8am with 2 slow tire scrub-in laps, a 10-lap run on the OEM aluminum wheels, a quick race car-like pit stop and tire change, then another 2 slow scrub-in laps followed by a 10 timed lap run on the Carbon Revolution’s CR-9 carbon wheels. Thankfully this day there was less than a 5 degree increase from the beginning of the test to the end of the last lap.
There’s no hiding that all car manufacturers benchmark each other’s cars. There are constantly spy shots of camoflaged test mules flanked by competitor cars on the street. As a development driver, I’ve been involved with countless benchmark tests to help ensure Ford cars are better than their competition. Likewise, every manufacturer is doing the same thing. From this experience, I have learned a lot in terms of the effect little variances like time of day, rubber on the track, type of car, weight of car relative to its tire, longevity of a tire, tire pressures for each platform, various tire’s consistency vs 1-lap wonders, etc… Due to the various platforms and types of tires, improper testing can vary lap times by SECONDS. A false sense of security during development can be disasterous for the release of a performance car.
Because of this, proper test procedures are crucial for accurate back-to-back testing for car manufacturers. Unfortunately, (and I’m sorry for bursting your bubble) most car magazines do not have the budget, time, or interest in proving what cars are actually faster, but rather just want “a” time and prioritize photoshoots and the “story” over finding objective performance numbers.
While some magazines use pro drivers (which is better), very rarily will the there be enough time, money, and resources to properly shake down a car, get up to speed and comfortable in it, find the optimal tire pressures, know how fast the tires scrub-in, what lap will yield the best time for that car/tire combo on a new set of tires, have more than one set of wheels and tires mounted, and quickly back-to-back with another car to minimize the change in track conditions. To do this right takes time, people, and money.
Porsches tend to be light cars with relatively large tires, and do not put heat into a tire (especially the front) as quick as a heavy Mustang or Camaro, which can nail its fastest lap on a new set of tires on lap 1. Because of this, and to reduce a lap 1 inconsistency from not scrubbing off the tire release agent from the tire, we did 2 slow scrub-in laps to ensure lap 1 would be consistent and fast without risking the entire run from a snap oversteer or excessive understeer that would kill the lap average.
Table of Contents:
Page 1 – Intro
Page 2 – Carbon Fiber Wheels used by OEMs
Page 3 – Benefits of Carbon: Lightweight – Rotational Inertia
Page 4 – Benefits of Carbon: Lightweight – Gyroscopic Effect
Page 5 – Benefits of Carbon: Strength
Page 6 – Benefits of Carbon: Stiffness
Page 7 – Benefits of Carbon: Stiffness Continued – Camber Compliance* (Must-Read)
Page 8 – Benefits of Carbon: Durability, NVH & Cost.
Page 9– Important Factors for wheels on Racecars & Track Test Procedure
Page 10 – Wheel Weights, On-Track Testing, Data/Laptime/Tire Analysis, and Conclusion
42 comments
Good article covering lots of different areas. It would be interesting if in the 911 test, the camber was optimized in each case and THEN compare lap times, tire wear, and what the static camber numbers ended up being. Perhaps your lap time differences could be equalized with more static camber for the aluminum wheels. But yes, the tire wear was a good demonstration of the difference in wheel stiffness and camber change.
In your opinion, is there any downside to carbon fiber wheels on a race car aside from cost? They would be fine with the heat for a couple hours stint? No concerns about impact loading or how they would fare in a smaller crash (e.g. an aluminum wheel would bend and get you back to the pit, carbon fiber would shatter)?
More static camber might equalize things in steady state cornering but being able to get away with less camber means a flatter contact patch for better braking and acceleration in addition to not having to deal with camber issues like tramlining and surface mu sensitivity under hard braking.
Someone give me 12k
This is one of the most interesting articles I’ve read on this site in a while! I’m still amazed by how much the aluminum wheels can deflect.
regarding camber compliance; How much influence does wheel size itself have on camber compliance? the article states that wider tires require less static camber, but what about different diameters of wheels? for example would 17’s require less static camber than 19’s?
Diameter does not have as big of an influence on camber as width does. But as the diameter of a wheel increases, it becomes difficult to maintain stiffness without proportionally more weight. An ultra-lightweight large diameter wheel (say 19″) will be far more flexible than an 17″ wheel of similar weight and will require more static camber due to the increased camber compliance.
Interesting, but more an ad than an actual review. Carbon fiber is nice, but still years away from being actually affordable, if it ever is. No mention of the cons anywhere. Like what happens if you hit a big pothole? You can always have an alloy wheel fixed. Try that with CF.
A carbon wheel like this one is more likely to survive an impact that would destroy an aluminum wheel.
There are cons, and your questions and concerns are answered and addressed in the article (yes they can be fixed).
Carbon fiber wheels have been available for motorcycles for years. And bicycles for even longer, I think.
In conclusion, make sports cars a proper weight, like 2300-2800lbs and equip with 16in wheels and well-boosted hydraulic steering and a set of $875.00 aluminum flow formed wheels will work as well, and don’t put the engine in the rear like that dopey beetle you drove….and voila, problem solved, and have more fun driving.
One of the better automotive engineering/technical articles published online ever.
FYI, the spindle/bearing/hub compliance on a typical passenger car during cornering is also around 1 deg per G. Most door-slammer race cars with sticky tires are way overloading the OE wheel bearings and flexing them too much. So lots of potential gains to be had in terms of camber/toe compliance with stiffer wheel bearings or stiffer structures on both sides of the wheel bearings.
Thank you Billy/Mike/MotoIQ for doing these fantastic articles!
Hi Bill, do you have data for the hub deflection? I was wondering because I often fight this when working on production-based racing cars due to its effect on piston knockback on the brakes.
No data, only memory. I had a friend 15 years ago who did a year-long benchmark project to measure competitor suspension compliance for a Detroit OE, he probably did 20 cars total. I saw him measure the data on a big flat-plate rig embedded in the floor. He removed the wheel/tire and replaced it on the hub with a stiff alignment-type stand, this allowed visual access to most of the suspension components behind. He put little dimensional measurement balls at all the connection points between parts. Then used optical 3D measurement to measure the position of everything before and after various load cases (simulated 1G cornering, simulated 1G braking, etc.). This allowed measurement of total deflection at the hub and how much individual components were contributing to it. Sort of a poor-man’s K&C machine, but it also gave all the intermediate contributions rather than just the end result.
He said there was pretty consistently ~ 1 deg/G camber flex in the upright/bearing/hub. I don’t remember if he had a measurement point at the caliper mounting ears, this would be relevant to your brake question.
Also, he didn’t know if camber/toe stiffness was consistent among competitors because it was a targeted parameter for suspension design, or if the stiffness just consistently worked out that way after all the other needs (cost/reliability/weight, etc.) had been addressed. Yes, he was relatively isolated from the suspension groups he was feeding the data to.
Interesting, but just curious – was this a sponsored post?
No, and they do not sponsor the site either. This was an independent test that I only agreed to do once they met all of my criteria for a proper (and expensive) back to back test. Expensive because I didn’t want to conduct the test with wheels with differing widths (even 0.5″), differing offsets, 100* weather, different times of the day, etc…
Moto IQ has become more and more paid spots basically masquerading as reviews. You all have to make a living, I know, but there is a lower percentage of real content vs. paid content these days. I read the site less and less…
The concept of stiffness and its effect on camber compliance applies to all wheels. There are a lot of concepts and take-aways from the article that can be used to make better, more educated purchases of ANY wheel.
What do you oppose about this article? I felt Billy did a great job:
– of explaining the science/physics behind the benefits of low mass wheels
– some cool real world example demo videos,
– showing the material property differences
– how stiffness affects camber performance (which I never thought of nor seen anyone else talk about)
– executed a well thought-out test plan
– even if you didn’t believe the lap times, the last picture doesn’t lie.
As far as I know, they didn’t pay Billy anything. I don’t even think he got wheels out of this or anything at all other than he did it for his curiosity. I know they didn’t pay us anything to do it.
I am curious about what you consider “real” content, I mean there are only so many times that you can kick a dead horse. on the subject of suspension setup, I would consider that subject covered by moto IQ already. Yes, i would love to see more garage tips articles, as well as maybe an engine building series of articles. The question then remains what else can they write about? Product reviews, event reviews and project cars? If there are more then please chime in to add more but from the sounds of it people are considering product reviews to be “paid” articles. Then there are project cars which often have sponsored parts in them, so people will also consider those to be “paid” even though on top of all the other costs of running this site there are costs to the parts. Finally there are event reviews, personally this is something i would love to see more on from the motoIQ staff. since these events are usually heavily sponsored by companies, would the general consensus be that they are paid articles? I dont know but i would like to see MotoIQ do a break down of shows such as Import Alliance and Gridlife. Another article series i would like to see is a MotoIQ write up on all of the different tracks around North America like Frank has been doing for the west coast.
So what else would you consider “real” content?
this comment was meant to be in reply to Sport Compact Car Fan
I had a column called “Fast Lap with Billy Johnson” and I put a lot of time into those track notes; something I get paid to do when I coach but am giving the information out for free. Those are some of the least popular and lowest viewed articles that i’ve written, despite having more time invested in writing them.
I guess some people just want negativity and criticisms of products rather than focusing on the positives. I agree that there is some loss of a review being ‘genuine’ when there are no negatives to a given review or car, so it’s a tight rope to walk.
We just did a Gridlife Midwest story. I was at Gridlife South but was working on on the Evasive car so could not take pictures!
must have missed that one, my apologies, ill go and check it out! and I look forward to more engine build articles
We have a lot of engine builds coming up, soon!
Too bad there isn’t much options in 17″ or 18″… Never would have guessed good rims/wheels did THAT much of a difference!
Also found the post about tyre size very informative, thank you for sharing 🙂
As far as I know, they didn’t pay Billy anything. I don’t even think he got wheels out of this or anything at all other than he did it for his curiosity. I know they didn’t pay us anything to do it.
They paid for my flight and hotel, but I did not get paid or wheels for conducting this test. I refused to write the article or do this test unless it was going to be a PROPER test. It took 6-8 months to get everything in order to the point I was satisfied that we had everything to do an accurate, scientific back-to-back test to evaluate and quantify the performance of the CF wheels over AL on a car.
Unfortunately every magazine test I’ve seen being conductive is highly flawed and introduce variables far greater than the actual performance difference between whatever they are testing (car A vs car B). It costs money to do proper testing and not many people want to find out the truth, but rather write stories based off the results of poor test procedures.
My concern more than anything, (great article by the way) is kinetic energy.
Let’s take this Porsche GT3 for instance, which hits a pothole at 80mph causing a X kilo-newton of force to bend or deform the rim. (I use kilo-newton for the sake of the explanation).
While the OE alloy wheel would bend or break, (not sure if those GT3 wheels are cast or forged, it doesn’t matter really)…..the OE wheel would be damaged while the Carbon wheels wouldn’t?!?! Or to a lesser degree….
Well, it is impossible to eliminate kinetic energy, therefore that force would have to transfer thru the wheel bearings into the hub carrier, hub, into the shock…..somewhere that shock, SOMETHING would give up. It could be the spindle, a control arm, or even the damper…..causing to crash.
At that point you ask yourself: yes I spent $12K on bling bling wheels that CAN take the force and the abuse, but I crashed because something else gave in.
I have a really hard time believing that the carbon wheels would suck up/ absorbing all the kinetic energy when hitting a pothole, (or something of that nature). They can cope better, yes….but to eliminate kinetic energy, not a chance.
the way I see it, if you can afford to drop 12k on a set of wheels, you can afford to replace wheel bearings or hubs or whatever… also the tire absorbs a lot of kinetic energy, one of the reasons I don’t like running rubber band no sidewall tires…
Great article! I love reading stuff like this. More technical articles like this are needed in our overly “showy” scene. I like to know what actually makes a part better and how it works.
Very interesting post indeed. You are right, this never crossed my mind. But, thinking about it, I wonder how many of us in REALITY actually drives/pushes our car hard enough to cause the wheels to flex to cause camber changes like this given our car is properly equipped for it’s purpose. Also, most of us that goes to the track knows better not to equip ourselves with sub-par quality/cheap wheels to begin with if serious about time. Lastly, there has to be more information regarding the wheel size compared to weight of car and suspension geometry to cause x amount of flex during cornering. Lots of cars out there running larger/wider wheel sizes vs stock. I.e…if i ran stock wheels w/ some track tires and a fully built suspension, the flex would likely to occur or be more than me having an over sized forged wheel.
You’ll notice the difference and improvement in steering feel due to the reduced gyroscopic effect when simply turning the wheel at speeds above 20mph. As mentioned in the article, Forged wheels are not stiffer and will not flex less than a cast wheel, and high quality and expensive light weight aluminum wheels will flex a lot since stiffness is relative to weight. The lighter the (even high quality) wheel, the more it will flex.
3 questions.
I live in Wisconsin and drive an NSX.
1 – How do carbon fiber wheels hold up with salted streets? I’ve owned carbon fiber bicycles, but never rode them outdoors in winter. 30 years ago aluminum rims rusted in winter in the salt, but between anodizing and coatings I don’t see much of that today.
2 – How much weight would these save compared to the standard 2017 NSX aluminum wheels?
3 – How aero are your carbon fiber wheels? the look more aero than my NSX wheels. As a former Cat 1 cyclist, aero wheels are near and dear to my heart.
I’ve been thinking about putting all weather tires on the aluminum wheels and the high performance summer-only tires on carbon fiber wheels.
1 – Read Page 8: they meet all OEM standards for durability, corrosion, etc..
2 – I do not know how much 2017 NSX wheels weigh.
3 – I am not aware of any work that has been done in terms of designing the wheel for aerodynamic purposes,.
Your NSX will be faster with far better steering feel and communication with the CF wheels.
I enjoyed this article a lot. A lot of food for thought when choosing wheels for the track. Thank you Billy for covering all the basics and thoroughly explaining the details by having pictures and videos.
I myself have used the TE37 for almost 2 decades and I wonder how they would compare.
Thanks! Those are iconic JDM wheels. I still have a set of CE28’s for my NSX.
The strength comparison chart is misleading. Yes, unidirectional carbon fibers can be 3 times stringer than steel. But a commonly used carbon fiber prepreg laminate is equal to the strength of steel at the best. In practice, considering the way CF wheels are designed and mage the strength of the material is equal to aluminum. This is why the weight advantage is only 50% on CF wheels vs Aluminum. But CF has substantially better fatigue resistance so the maximum allowable stress is higher. Also, CF wheel production is difficult to control. Some wheels will come out very strong and some will fail easy.
The material graphs are provided as an example of why carbon fiber composites are becoming the material of choice for applications where weight, stiffness and strength are a priority. The data is from a simple single axis material coupon load test and obviously does not provide the full picture of the multi directional loading that complex structures are subjected to in the field and engineers design them to. The intent of the graphs is to easily show people in very simple terms carbon fiber has some characteristics that are superior to metals and we have data to support that conclusion.
No one has claimed wheels should be 3x lighter if design in carbon composites because of the material graphs.
“In practice, considering the way CF wheels are designed and mage the strength of the material is equal to aluminum. This is why the weight advantage is only 50% on CF wheels vs Aluminum.”
-If your statement was correct the part would be the same weight as aluminum…
Carbon fiber has material properties that are better than metals and when combined with sate of the art manufacturing method has resulted in significant weight savings. 50% is a significant improvement over the status quo and provides a demonstrable performance improvement. Simple material properties aside, we have listed many industry examples where products are benefiting from the superior properties of carbon fiber composites. Many consumer product and aerospace have used carbon fiber composites superior material properties for stiffness, strength and fatigue to reduce weight and improve performance. Road bikes, airplanes, sail boats, F1 chassis, golf clubs, wings, road cars are all made lighter and stiffer from composites. All these applications benefit from the weight saving achieved by using composite materials to increase performance and efficiency. There’s a reason all of these examples have switched to carbon fiber construction.
Carbon Revolution wheels are not pre-preg and modern and state of the art composite manufacturing is very repeatable. Carbon Revolution wheels are made under a state of the art quality system (TS16949) and OEM’s like Ford, Renault and Ferrari are not going to sell consumer products with a high degree of structural variation. But let’s not speculate about the repeatably of composite manufacturing …
There are countless real-world parts made of carbon fiber that are repeatable and have been in market for many years: BMW i3 and i8 chassis, Composite drive shafts, Downhill skies, Mountain bike and road bike fork, frames and wheels, Formula one chassis and suspension links, and many more…
I’m late to this party. I hope I can add something useful. I was invited to the Carbon Revolution facility as I was selling test equipment that may have been suitable for QA. I saw the process of manufacture.
I know something about carbon fibre also. It’s extensively used in aerospace, including military applications. They had a 20″ wheel that they said I could pick up. I braced myself, heaved it up – and it was a featherweight. Not having a tyre fitted helped, but I was blown away by how light they are. They are the real deal. I hope they become mainstream. I would fit them to any vehicle in a heartbeat.
Oh, and I did not get the sale. They ended up using Mercedes test facilities instead.