Now that the racing season has started winding down I finally have time to dig into my Prius Prime and start swapping parts. The Prius is quite a bit different than the Lexus RC F GT3 that I work on in IMSA or the Cup car that I’ve worked on in NASCAR, but as my engineer friends say, it’s all about four tires and physics when it comes to cars and how they handle, so all the basic concepts of suspension adjustment transfer over. I’ve learned a bunch about the car, as I’ve successfully installed lowering springs and failed to install a rear anti-roll bar. The most recent set of changes involves wheels and tires. Let’s dig into the details of the latest set of changes and improvements to PROJECT: OPRIUS PRIME.
I spend a lot of time in my car between my various gigs and chose the Prius Prime because I wanted something fuel efficient that was also fun to drive. The Prius Prime handles quite well out of the box, but I decided to take it to the next level with a few key modifications. We left off our last column with a discussion of the TEIN High Tech springs I had obtained from Japan through an auction site. These springs were fairly painless to install on the car, although accessing the top hat bolts required removing the windshield wipers and some of the plastic trim as seen in my video below. The car felt transformed as soon as it was down on the ground because the wheel gaps closed up so nicely and a test drive showed that handling was moving in the direction I was seeking.
The front springs are rated at 145 lbf/in while the rears are rated at 200 lbf/in, so they’re not overly aggressive, but offer a great compromise of improved handling without any noticeable increase in NVH.
Once everything settled out, the car ended up being around an inch and a half lower all around, which was perfect from a clearance standpoint as there was still plenty of gap from the fenders to the tires to prevent rubbing. While it may not seem significant, getting into the car took a few days of adjusting since I had gotten used to the previous height of the aggressive roofline, but it became natural after about a week.
Installing the rear anti-roll bar was not quite as successful as the springs due to the fact that I used old notes and did not actually double check under the car prior to making a purchase. Earlier this year, I borrowed a standard Toyota Prius and examined the suspension, which is where I noticed that the rear anti-roll bar connection matched the Corolla and CH-R. This led me to track down parts made for those cars once I bought my own Prius, which is how I ended up purchasing the 27mm adjustable rear anti-roll bar from Progress Technology.
What I failed to consider at the time was that the Prius Prime had a slightly different anti-roll bar due to some of the battery packaging, which necessities a hump in the middle of the anti-roll bar, which meant that my shiny new bar would not fit. Fortunately I noticed this quickly when I attempted to unbolt the OEM anti-roll bar but now I am on the hunt for one that will properly fit on my Prime.
Another set of components that didn’t end up working out are the GR Corolla performance shocks and struts, which I picked up from a local Toyota dealership. These shocks are intended as an OEM upgrade for the GR Corolla, and since the Prius is based on the same suspension geometry I figured that it would be worth testing out since the set was fairly inexpensive. Once everything was apart I could see that the components would physically all bolt together but actually putting it on the car wouldn’t work out due to the length of the strut shafts on the GR Corolla pieces, resulting in the Prius being slammed on the ground if assembled as intended. The shocks in the rear seemed to be quite a good match, but I did not want to install them without the matching sets in the front. For these reasons, I ended up just installing the TEIN lowering springs on the stock Prius structs and shocks for the time being.
While using OEM components would have worked out great, there just doesn’t seem to be a great solution in this scenario without customizing the GR Corolla components to some extent or moving their internals into a Prius strut housing, which isn’t feasible for the resources that I have in my garage. My next move for this area of the car is to hunt down some coilovers, and the current leading candidate is the Sports-I coilover system from RS-R due the reputation of their builds and the fact that they have an adjustment dial on the bottom of the struts in the front. This is a huge selling point because a traditional top mount adjustment knob requires removing the windshield wipers and trim for access when you wish to make a change.
Part of the reason for wanting to move to a full coilover set is the option for a variety of adjustments and more spring rate choices. While my current solution of lowering the car has improved the handling to an extent and significantly improved the aesthetics, it has the drawback of impacting the roll center of the car, making the handle worse in certain conditions. You can get a great primer on why that is the case in this column from Huibert Mees, which goes into great detail why lowering a car can often be worse for handling. It’s a great example of why any single change in a suspension system can have a huge impact on handling. I am fortunate that in my situation, the lowering spring improved the handling of the car in most daily driving conditions but I have noticed that there is some unpredictable roll when pushed hard in certain situations.
There are a few ways to correct this, and the first fix that I am examining is to machine a spacer to place between my front suspension upright and the ball joint mounting plate. This can correct some of the issues caused by the lowering springs, but can also introduce some bumpsteer changes (basically, when your steering wheel moves on its own, often after hitting a bump in the road, thus bumpsteer) unless I also build a matching spacer for the suspension tie rod end, so this will still require some research if I decide that I want to follow this path. The most likely scenario is that I will end up with a combination of parts that will result in what I consider the best compromise in handling for my purposes, which will likely mean that I’ll end up with a set of coilovers, stiffer rear anti-roll bar, and some sort of roll center correction spacers eventually.
Wheels and tires were my next item on the list, and my initial plans were to grab some of the 19×8.5 inch wheels from the Camry TRD or Nightshade, but as many of you pointed out, they ended up being a bit heavier than what I was looking for since they are cast and each clock in at 30 pounds a piece, which would be an 8.5-pound increase per corner over the 17×6.5 wheels that came with the Prius.
As a reference point, the optional 19×7.5 inch wheels that are available for the Prius clock in at 28 pounds each. I ended up hunting for forged wheels and found that Lexus offered optional forged 19×7.5 inch wheels for the NX that weight just 24 pounds. I did some math regarding the offsets and the figured out that they would be a perfect match for the Prius and would result in less than a 1% circumference change if paired with a 225/40R19 tire.
The increase in wheel weight wasn’t huge, but we also have to consider tire weight, since adding rubber can tip the scales quickly, and moving from a 195/60R17 low rolling resistance tire to a 225/40R19 all season tire also had an impact as tire weight increased by around 6 pounds per corner. I ended up picking the Michelin Pilot Sport All Season 4 as the tire of choice due to the weather conditions in my area and how I planned to use the car. I considered the Michelin Pilot Sport 4S tire as well but ultimately decided that it wasn’t worth the tradeoff of having to swap back to the 17s once temperatures dropped.
Many may not look at all-season tires for a performance increase, but the car was transformed from a handling perspective once the rubber was installed due to the softer compound and contact patch of the tires compared to the stock low-rolling resistance units.
The car felt like it really woke up and that it could now be pushed with the upgraded tires even with some of the added weight. As expected, the added contact patch and weight in addition to the aero effects of the wider tire meant that fuel efficiency was impacted. I try to plug the car in on a fairly regular basis, and during the first few thousand miles, I was averaging around 44 miles of all-electric range and an overall fuel economy of around 75 miles per gallon. Once I lowered the car that improved to 45 miles of electric range and an overall fuel economy of around 76 MPG. Moving to the big wheels and tires had an immediate impact, and after a few hundred miles, the average all-electric range settled to 38 miles and overall fuel economy dropped to around 70MPG.
Decreasing efficiency obviously defeats the purpose of this type of car to an extent, but as with anything in life there are always compromises, and for my purposes, it is absolutely worth the trade-off for the increase in driving fun and a better appearance. From a big-picture perspective, it’s also still a significant improvement compared to the 25 MPG that I was seeing in my previous car, which means that I am still seeing significant fuel savings even with the compromises that I’ve decided to make.
Outside of the suspension changes, I ended up adding an inexpensive front lip in order to change the appearance of the car and make it look a bit longer and more balanced, but outside of that, I have just been enjoying the ride as it has crossed over the 20,000-mile mark on the odometer.
I have picked up more parts for test fitment including a set of GR Corolla brake calipers, which I was able bolt up to the car for mock-up, but found that my current wheels were a bit too close so that has been shelved for the time being while I decide whether I want to consider a different type of wheel in the future. One consideration is moving to something like an 18-inch Enkei RPF01 in the future which would result in a six-pound reduction in wheel weight from the current Lexus wheels that I am using and likely offer multiple benefits. For now I’m happy with the balance and look of the car and plan to enjoy it for a while before I dig into any future options but I am also always open to suggestions for cool components to try out.
the car is brake by wire with a (hydraulic backup) i would not modify the brakes at all bro. it will lead to some really jerky stops and a lot of drivability issues as the car switches from regen braking to mechanical braking. the ABS system is not designed for that and it won’t know what to do with the bigger brakes. Also with the heavy regen braking of the phev inverter motor you don’t need need as big of brakes.
Also, the whole point of brakes is to overcome the inertia of the tires. having big brakes with all season tires is kind of a waste. you would get a lot shorter stopping distance with performance summer tires.
I absolutely support the BBK, but do note that the RPF1 is pretty infamous for not providing a lot of caliper clearance. I love RPF1s to bits and run them on the front of my Lotus (with 8mm of spacer to clear the calipers), but it may be better to look into a more modern wheel design such as a flow formed Konig wheel.
That’s a good note. I have a template for the caliper so will have to check around.
Going from 44 to 38 EV miles is quite the drop with the new wheels/tires. I wonder how much of that is rolling resistance of the new tires versus aero resistance of the new wheels. Any chance you could gin up some smooth wheel covers to try and figure it out?
Armchair theory: I’d think putting some very sticky summer tires on the factory wheels would give you an approximation to what the extra contact patch and not as sticky all season rubber would be. That info would allow one to gauge what the impact of the non-aero wheels mean as well.
The contact path difference is huge. The old tires are listed as a 195/60R17 but only had a 145mm contact patch. The new tires are 225/45R19 and the contact patch is almost right at 225mm.
The width and weight of the tires also definitely has an impact and I agree that the change in wheel shape is likely creating some dirty air off the faces so an aero cover could help to an extent there.
the biggest hit is going to be the tires. going from narrow low rolling resistance tires to wider performance all seasons is what is causing most of the effeciency drop. the weight and increased diameter is secondary and the wheel surface is last.
Think it is more tire width related. IIR my 2014 Camry SE Hybrid is 1-2 mpg worse rated than an LE/XLE solely due to wheel/tire package.
I love reading about these long term upgrades and all the planning that goes into it. Im really jealous of people who can figure out suspension geometries and tire fitment. I really would like to upgrade my wheel/tire package on my Mazda3 but with all the research I have done, it’s all just jargon to me and I never end up pulling the trigger.
Upgrading wheels and tires to a manageable size on a recent-generation Mazda 3 is fairly easy. On my 2018, I went from 18×7 ET50 to 18×8 ET45, and 215/45/-18 to 225/45-18. The Enkei TS-V cuts about 8 pounds per corner. Lowered on Racing Beat springs, with a bit of front toe-in tweak, that combination works wonderfully. Popular web forums will help your mission.
I have checked out Tire Rack just to see what direction I might want to go for a wheel/tire combo and have been perusing Reddit to see what others have done but you’ll get 4 people in a row who all say totally opposite things so hard to sift through all that sometimes haha
I am wanting to go down in size from the stock 18″ set up to a 17″ to be able to get a little more sidewall to cope with crappy roads in the southeast. It sounds like you have the ideal set up that I would eventually like on my car, nothing crazy but lower some unsprung weight and lowered a bit
I live in the dusty energy country of Texas, where the roads vary from glass smooth to rough and ripply. I originally thought of a similar 19″ solution like the the author here, but 40-series isn’t necessary. Instead of going down to 17″, staying at 18″ while going up a tick from 215 to 225 with the same 45 aspect ratio improves ride a bit with negligable speedo/accel difference. Definitely get lighter wheels within your budget. I also installed Koni Special Active FSD struts with the Racing Beat springs. Better damping is essential.
I live around Atlanta and travel a lot up into the Carolinas where the roads somehow are even worse. I’ll definitely keep that in mind about staying at the 18″. Im really not super worried about performance as the turbo 3 is plenty quick for what I need on the street and Im not tracking it or anything. Do occasionally take it up into the mountains though so it’s nice to have that in the back pocket.
My worry about lowering it is that I throw a lot of weight in it to travel with for work. I had Tein Street Basis Z on my Miata which lowered it almost 2 inches but really didn’t change anything when it came to getting over speed bumps and drastically improved ride quality and handling. Koni’s were on my short list though right behind the Teins.
nah, come on, suspension/wheel combo is pretty much painless to get right these days. Just have some fun with an online wheel calculator – I can recommend https://www.wheel-size.com/calc/, which is pretty straightforward and shows differenced between setups. All you need is basic wheel specs and then you can test and tweak all day!
I know there are more resources than ever so thanks for the recommendation! I’ll have to check it out and start playing around with it.
Wheel-size.com has awesome data. I also like using willtheyfit.com.
You don’t need brake calipers, this is not a track car. Invest in stainless lines if you want pedal ‘feel’, but spend your coins on high perf brake pads.
Instead of getting a new swaybar, just replace the soft rubber swaybar bushings with polyurthane, this is my favorite ‘low dollar’ upgrade on any car because it makes the car ACT like it has a much stiffer bar, but doesn’t affect ride quality at all. It just keeps the bar straighter/less deflection, and the response of the vehicle improves quite a bit. And it’s cheap!
Those wheels are fancy but boat anchors. You also went to a wider tires which is going to kill your MPG but give you more grip; do you need more grip? I would think a lighter wheel would be a better move; but something with an aero disc would be even better. Rota Circuit 8/Konig Helium are CRAZY light, but not very aero. Brotiform has some aero wheels that would look amazing.
The other thing to look at would be underbody aero; you can do a lot with coroplast (corrugated plastic, like yard signs). Look for someone making greenhouses and you can usually score cutoffs for cheap.
I am planning to track it when the weather gets warmer and Carbotech is already working on some brake pads for me.
Increasing the durometer of the sway bar bushings can have some impact on the handling but they can also often result in increases in NVH so will see if there is a reasonable compromise there.
The impact of the wheels is listed towards the end of my story and was something that I fully expected going into it. I have looked at some stuff from Rotiform and the aerodisc options are a great suggestion that I will dig into in the future.
Fortunately I have access to an excellent carbon fabricator so if I do approach underbody aero I can likely get some stuff made up.
…. bro if you’re installing lowering springs and considering coilovers, you already seem to not care about NVH. And the swaybar bushings are PIVOTS, as in, even if they were made of solid steel, they aren’t an impact/compression NVH adder. You don’t need to do underbody out of carbon, that is a fairly poor use case for it since it can easily get damaged. Coroplast is what you want. Or sheet aluminum, but coroplast is lighter, more damage resistent, easier to cut, etc. Look into it.
I used coroplast for the body shells on my human-powered/electric “bicycle”(3-wheel microcar that did 50 mph at the time without the burden of taxes and insurance costs, going hundreds of miles for pennies of electricity, currently undergoing upgrades because I want AWD and 0-60 mph in 4 seconds).
The material is surprisingly strong, and if oriented correctly with other sheets of the same material, even impact-resistant in a minor wreck. I got rear-ended by a truck while stopped at a red light, without injury. The rear bulkhead I designed saved my ass, and I was able to repair the tail section with stolen election signs. No seatbelt or safety harness, either. Not bad for a total death trap.
the prius is brake by wire there is no pedal feel. also the regen braking does the heavy lifting of the stopping the mechanical friction brakes are barely used. i did not have to change my brake pads on my prius until it hit 100k miles. and although there was basically no pad left it mostly drove fine except for panic stops.
I second the poly bushings. I’ve done them before and they were a cheap, effective upgrade in terms of response and feel (not the NVH kind) with zero downside.
I would also go brake pads first. Unless you’re repeatedly stopping hard to the point where even better pads can’t work with the heat, there shouldn’t be much need for larger ones. That’s an upgrade I made that I regretted. Performance pads made a huge difference (and that was in the days before lackluster, but long-lived and low dust ceramics were common OEM choices), but I was still eating stock rotors. The fix there was going to cryo-treated rotors (I know it might sound like snake oil BS and I was skeptical, but also willing to try it. They lasted 3 times longer and barely pulsed even when worn almost down to the vents). I eventually went with bigger brakes because I had to change out the pads and rotors anyway and figured I’d throw on some calipers and brackets and “upgrade” and it threw the brake balance off, added weight, and degraded feel a little. That was an ancient non-ABS car that had hydraulic brakes with great feel, though, so it might not be applicable. Anyway, I would always start with pad upgrade before going larger.
Indeed. Kind of felt like my experience was falling on deaf ears that didn’t understand what I was talking about.
Lol, I work just down the road from vasser Sullivan. Small world. What are your plans, if any, to increase hp/torque?
Not planning on making any powertrain changes.
So a lukewarm hatch? 😛
Warm-ish Hatch? I’m happy with the power it produces and don’t see a reasonable way to make big gains without impacting the original use case of the vehicle.
It falls almost exactly halfway between the Civic Si and VW GTI when it comes to horsepower.
Any chance of this thing getting a turbo in the engine and a more power-dense battery pack with a reprogrammed control system in the future? I’d love to see this thing ripping off 11s in the 1/4 mile, while still getting 60+ mpg in normal use as a daily.
No plans to make any engine modifications.
I want supercapacitors!
If I had the time and money, I’d totally try and get your help building a sleeper 10 second prius. Imagine the looks of shock when it smokes everyone and bypasses gas staions.
Pure EV conversion of a Gen II Prius would be the easiest route. Then you could turn it into a series hybrid if you want to go beyond the battery’s range capabilities.
I own a 2022 Camry XSE hybrid (which is a different platform) but I’m doing much of the same things to it that you are doing here with the Prius.
Because the Camry TRD exists, it was easy to slap on a stiffer rear swaybar from the TRD. Really aided cornering balance. The XSE shocks and springs are already a good balance between sporty/comfortable for me, so I’m leaving those stock.
As far as wheels and tires, I downsized from the stock 19×8’s to some Enkei RPF01 17×8’s. Yes, I would definitely recommend them for this build. I weighed the stock wheels/tires vs the new wheels/tires and found that I lost 10.7 lbs per corner. This payed several dividends:
Tying it all together, I have camber bolts on the front shocks to give me an extra degree of negative camber in the front to avoid prematurely wearing out the sidewalls of the front tires. Together, this setup ends up being a lot more competent than most people expect a Camry to be.
Great to hear that you’ve been able to make such huge gains.
Despite running wider, stickier tires than stock (Continental summer-only tires), the unsprung weight loss means that I’ve actually gained 1-2 mpg relative to stock. A pleasant surprise.
That IS interesting! Yet another reason to love sidewall.
Calling the Prius Prime a “Hot Hatch” is really stretching it. You do you…
That is the whole point. In stock form the Prius Prime is NOT a hot hatch (at least by modern standards) and the point is to see if it can be stretched into one.
But OP is admitting he’s not going to add any power at all, and keep the drivetrain stock. So… I mean… that’s not very ‘hot’
Which is why I specified “at least by modern standards”.
The original hot hatch the Mk1 VW GTI had a 0-60 of 9.7s. This Prius has a 0-60 of 6.5s. That ain’t bad and is certainly enough to have fun.
Unless of course you are of the opinion a manual transmission is a requirement for a hot hatch. In which case this Prius will never be one.
I mean I guess if you think of things in 1980s performance, it’s already a hot hatch bone stock.
’80s performance was plenty fine for me as a teen. Why would I need more as a grownup?
It was still enough to get you killed.
Humans are quite fragile. Jason’s Changli has enough performance to get one killed.
I don’t disagree. It just sort of negates doing anything to it, if it already qualifies. You’re not building a hot hatch if you already have one.
It qualifies in acceleration but acceleration isn’t everything.
Hot hatches were also about handling (and maybe braking) which is what I think is being addressed here. Also arguably low cost and practicality too.
Guarantee this has more grip than 1980s hatches, and better slalom times. This thing probably would run circles around most 90s hot hatches too, tbh.
Next time on The Autopian…
Handling notwithstanding (which is what Bozi’s working on) 0-60 in 6.6 seconds for the Prius Prime is definitely in traditional hot hatch territory. It’s on par with a GTI, a Clio, a Civic Si, a Veloster…the list goes on.
I have a 24 Mazda3 turbo hatch which by all accounts is considered a mild hatch. Has a claimed 5.6 0-60 if I remember reading that right somewhere. To me a hot hatch would be something like you said in the 5-7 second range for 0-60 but it’s really the driving dynamics more so than outright speed. And that’s exactly what Bozi is putting his focus on. It sounds like he uses it as a commuter car too so why would you want to mess with that MPG too much?
I’m strongly gravitating towards a new Civic Hybrid Hatchback Sport Touring. I wouldn’t upgrade much but the rich Civic aftermarket should make easy without all this guesswork.
I really like the blue that they have available for the Civic Hybrid hatch.
i like the tan/khaki color. it has a military vibe.
I really like the medium blue (only) available in the hybrid sedan, which is different from the smurf blue in the hatch, which I like also. But my “parking neighbor” has a smurf blue M2. We’re different people, but he’s a nice gent and somehow it would feel weird. The tan is growing on me, but interior only available on all-black and I really want the lighter interior if possible.
Just got myself into a similar situation with my newly-acquired ’17 CX-5 FWD. Some Internet “experts” say that suspension upgrades designed and sold for a Mazda3 are a direct fit, while other “experts” say, “wellllll… maybe, kinda-sorta, but…”
I have heard of the Mazda 3 owners using CX-5 parts to lift their cars so some of it will likely work in the opposite direction as well. It’s just a question of doing some measurements to make sure that everything will be in a range where you want it and actually work as intended.
>GR Corolla brake calipers
Would this really do much? My (admittedly unsophisticated) understanding of hybrid systems is that the regenerative braking does the lion’s share of the work while the caliper brakes are mostly there for panic stops. I remember reading that hypermilers can go the life of the car without brake work for that reason.
Regen does absolutely do a lot but I also drive the car in a lot more of a spirited manner so I get quite a bit of use out of the friction brakes as well.
Unless you’re experiencing fade, which I doubt you will on the street, it’s a downgrade as it adds more sprung weight with no benefit.
They do perform a lot of your braking in day-to-day driving, but I definitely use the friction brakes every time I drive, and not just for panic stops. As a general rule, hybrid regenerative braking is much less aggressive than regenerative braking in full electric cars.
My Prius should show up in a month or so. Your changes are right up my alley so thanks for going first!
What trim and color did you pick?
White Prius Prime XSE with a solar roof. I hadn’t thought of 18 inch aftermarket wheels. Really opens up a lot of options. I just spent a couple of hours looking at them and am impressed with the Enkei’s you mentioned.
That’s an excellent combo.
Good to see your byline here and catch up on your projects! Do you think you will do the coilovers before the rear bar? Thinking you might be able to dial those in to negate the need for a larger rear bar. Though a bigger bar out back might balance things out just right. I’m often entertained by the behavior you get when disconnecting the front bar for a similar reason.
The coilovers are towards the top of the list right now so there is a high likelihood that I will pick them up before any other components. Scaling the car and adjusting the coilovers should get me in a much happier range for where I want the car to be and additional changes will be decided from there.
Great build, very fun to follow, thanks for sharing! I love the idea of handling focused fun hybrids.