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So far I have been somewhat disappointed in the brakes on my S90. By 20,000 miles the rotors had already warped and the braking performance is overall poor (lots of vibration and brake fade during heavy braking) compared to my wifes Audi A6. I just rolled over 35k miles and my brakes on all four corners are completely shot. So as I started searching around for new rotors and pads I noticed the S90 has two different size brakes that could be equipped from the factory both front and rear.

Front - 322mm or 345mm rotors
Rear - 302mm solid rotor or 320mm vented rotors

All the online stores I looked at naturally lined up the smaller front rotors with the smaller rear rotors and the larger front with the larger rears. As I looked at my S90 it is easy to spot the rear rotors are vented, so it has the larger 320mm brakes equipped on the rear, so naturally I assume the front brakes are the larger 345mm brakes and ordered them. Much to my surprise when my rotors arrive, my car is equipped with the 322mm fronts and 320mm rears. This was absolutely astonishing to me and makes zero sense from an engineering standpoint. Considering the front brakes do 80%+ of the braking, I can't imagine how volvo allowed a car to leave the factory with essentially the same size brakes on the front of the car as the rear. After I realized this, it makes sense that braking performance is so poor and the front rotors already warped on my car (not to mention the factory pads only lasted 35k miles on all four corners).

So, rather than taking the easy path and returning the larger brakes, I decided to give myself a "big brake" upgrade. I couldn't find any online store selling new or rebuilt calipers for any of the 2017+ late model volvo's so I took to searching local junk yards. I was able to find a junk yard that had the 345mm calipers with brackets off a totaled XC90 for $60 each with less than 10k miles on them (and the used pads that came in them are nearly new as well:D). None of the parts websites show these calipers are interchangeable between the S90 and XC90, but if you look at the part numbers for the brake pads and rotors, you will notice that they are the same for both cars. So I took the risk and bought the XC90 calipers and it paid off big time. The calipers fit perfectly and greatly improved braking performance. It was no more complex than doing a normal brake job replacing the rotors and pads, the only extra step was swapping the brake line onto the new larger calipers and bleeding the brakes.

For those of you into the mathematical figures behind this change and how significant of a size upgrade it is.
surface area of a 322mm diameter circle is 81433mm/squared or 126.22in/squared
surface area of a 345mm diameter circle is 93482mm/squared or 144.89in/squared
This equates to 12049mm/squared or 18.67in/squared ADDITIONAL braking surface area of the rotor. Which is 15% increase in surface area.

I hope this is helpful for anyone else that is less than impressed with the braking performance of their S90 and notice they are in the same situation as I was with the smaller 322mm front brakes.

BONUS: For those of you that want REALLY big brakes on your S90, I also noticed the XC90 R-Line has an optional 366mm front rotor, now these were never equipped on the S90 from the factory, but my bet is they would be a direct bolt on upgrade as well, No Guarantees on this one though.
 

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So you swapped larger calipers, that presumably have a higher clamping force, but haven't addressed front/rear brake bias?
 

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I vaguely remember reading somewhere that the adaptive cruise, pilot assist and automatic parking brake heavily use the rear pads, and that might be why they are larger than expected in some cars, and why the brakes in general tend to wear out fast in these cars.

Not sure though.
 

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Sorry wandered in here from S60 forum. So feel free to tell me to scram!

"Better brakes" is one of those things, that if you don't define it doesn't mean a thing! There are many aspects you might be looking to improve:

braking "power" - how much stopping force for how much force you push on the pedal
heat capacity - how many times you can stop before the brakes fade
brake feel - this is subjective, but you might see performance drivers desire a firm pedal with a linear feel for good control. Many stock brake systems have soft squishy pedals and are super grabby.

Brakes like anything are governed by good old physics, so it's pretty easy to play with the math to see what kind of improvements you can make. You may have done a worthwhile upgrade here, but your math is lacking. I'm assuming by calculating the surface area of the rotor circle you are inferring that there is an improvement in stopping power and/or heat capacity? You're flawed on both counts. I'll make a couple assumptions here: 1.) the piston size of the calipers are the same (it might only be the bracket that is different), 2.) the brake pads are the same. Given those assumptions the actual area of braking is dictated by the pad size not the rotor size. Heat capacity of the brakes is dictated almost entirely by the weight of the rotor. More metal is a bigger heat sink, the more you can stop before you go above what the pads can handle. That's all extreme simplification but good enough for our purposes here.

So most of the time, for most drivers none of these brake upgrades passes any common sense test. Do you need more clamping force? Well if you can engage ABS then you are already able to exceed the limits of the tires, so no. Do you need more heat capacity? Well are you smoking your pads and boiling your fluid on the way to the office, stopping from 90mph multiple times in a row? Probably not. Brake feel, well that's just subjective. Nothing feels like a fixed caliper but getting those Polestar Brembos is probably a pretty penny just for better feels. When you get into track days road courses etc. then upgrades are necessary. Sometimes just racing pads and fluid will do it. On my WRX the 294mm (14lb) rotors weren't enough and an upgrade to 316mm (19lb) Legacy GT brakes were needed to survive track days.

What you have done is increased the size of the rotor, adding heat capacity, as well as moved the brake pad further from the axle which will increase braking power slightly due to leverage. Front brake bias is increased as the engineers had tuned the system with a certain size rotor which you have changed. In my experience the braking system will likely deal fine with a small change like this, I've done a bunch of these swaps to larger factory "options" with no ill effect on ABS, stability and traction systems.

I think you were looking to solve a specific "warpage" problem, and I think you may have solved it, or maybe not, you'll just have to see if you have over time. It's possible that the brakes on some S90 models are undersized. Sometimes undersized brakes can cause "warped rotors" if you drive harder than the average Joe. Now I am using quotes on warped rotors because rotors don't actually warp that way. It's a misnomer, warped rotors have more to do with pad deposits, but don't take it from me, let Carroll Smith and StopTech explain it!

I have the 2019 S60 R-D and that has the 245MM front brakes. In a presumably lighter car. I can feel a little warped disc feeling already at 6k miles. These are good size brakes even for a two ton car. It seems the issue might have more to do with the OEM brake pad choice that Volvo has made. I'll probably ask the dealer to address it for now. Once the wear parts warranty runs out I would probably be looking to make pad change to something that isn't prone to putting uneven deposits on the rotors.

P.S. don't assume rotor "size" is the only indication of braking capability: Using Centric parts catalog, you can see the 322mm front rotors are 28mm thick and over 22lbs. The rear 320mm are 20mm thick and ~15lbs. Similar diameter but not even close as far as heat capacity. The 345mm rotors are 30mm thick ~26lb BTW.
 

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Would a V60 Polestar big brake kit work on a V90?
I am considering test fitting the larger Polestar calipers and some slotted rotors. I am chatting with ViVA Performance also about Polestar Öhlins shocks as an upgrade. Coilovers are also an option.
 

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Discussion Starter · #7 ·
So you swapped larger calipers, that presumably have a higher clamping force, but haven't addressed front/rear brake bias?
Correct, in my opinion, there is likely no difference in front/rear brake bias between cars optioned with the different size brakes. Just like buying an aftermarket big brake kit, the brake bias is not changed there either.
 

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Discussion Starter · #8 ·
Sorry wandered in here from S60 forum. So feel free to tell me to scram!

"Better brakes" is one of those things, that if you don't define it doesn't mean a thing! There are many aspects you might be looking to improve:

braking "power" - how much stopping force for how much force you push on the pedal
heat capacity - how many times you can stop before the brakes fade
brake feel - this is subjective, but you might see performance drivers desire a firm pedal with a linear feel for good control. Many stock brake systems have soft squishy pedals and are super grabby.

Brakes like anything are governed by good old physics, so it's pretty easy to play with the math to see what kind of improvements you can make. You may have done a worthwhile upgrade here, but your math is lacking. I'm assuming by calculating the surface area of the rotor circle you are inferring that there is an improvement in stopping power and/or heat capacity? You're flawed on both counts. I'll make a couple assumptions here: 1.) the piston size of the calipers are the same (it might only be the bracket that is different), 2.) the brake pads are the same. Given those assumptions the actual area of braking is dictated by the pad size not the rotor size. Heat capacity of the brakes is dictated almost entirely by the weight of the rotor. More metal is a bigger heat sink, the more you can stop before you go above what the pads can handle. That's all extreme simplification but good enough for our purposes here.

So most of the time, for most drivers none of these brake upgrades passes any common sense test. Do you need more clamping force? Well if you can engage ABS then you are already able to exceed the limits of the tires, so no. Do you need more heat capacity? Well are you smoking your pads and boiling your fluid on the way to the office, stopping from 90mph multiple times in a row? Probably not. Brake feel, well that's just subjective. Nothing feels like a fixed caliper but getting those Polestar Brembos is probably a pretty penny just for better feels. When you get into track days road courses etc. then upgrades are necessary. Sometimes just racing pads and fluid will do it. On my WRX the 294mm (14lb) rotors weren't enough and an upgrade to 316mm (19lb) Legacy GT brakes were needed to survive track days.

What you have done is increased the size of the rotor, adding heat capacity, as well as moved the brake pad further from the axle which will increase braking power slightly due to leverage. Front brake bias is increased as the engineers had tuned the system with a certain size rotor which you have changed. In my experience the braking system will likely deal fine with a small change like this, I've done a bunch of these swaps to larger factory "options" with no ill effect on ABS, stability and traction systems.

I think you were looking to solve a specific "warpage" problem, and I think you may have solved it, or maybe not, you'll just have to see if you have over time. It's possible that the brakes on some S90 models are undersized. Sometimes undersized brakes can cause "warped rotors" if you drive harder than the average Joe. Now I am using quotes on warped rotors because rotors don't actually warp that way. It's a misnomer, warped rotors have more to do with pad deposits, but don't take it from me, let Carroll Smith and StopTech explain it!

I have the 2019 S60 R-D and that has the 245MM front brakes. In a presumably lighter car. I can feel a little warped disc feeling already at 6k miles. These are good size brakes even for a two ton car. It seems the issue might have more to do with the OEM brake pad choice that Volvo has made. I'll probably ask the dealer to address it for now. Once the wear parts warranty runs out I would probably be looking to make pad change to something that isn't prone to putting uneven deposits on the rotors.

P.S. don't assume rotor "size" is the only indication of braking capability: Using Centric parts catalog, you can see the 322mm front rotors are 28mm thick and over 22lbs. The rear 320mm are 20mm thick and ~15lbs. Similar diameter but not even close as far as heat capacity. The 345mm rotors are 30mm thick ~26lb BTW.
The calipers (including pistons) and pads are significantly larger on the 345mm brake setup. I was trying to include some photos to show for comparison but can't seem to figure out how to add photos on this forum. Since the center hub is the same diameter on both size of brakes, all of the additional 23mm of diameter is added at the outside edge of the rotor and is added to the braking surface area of the pad. I don't drive my car hard at all, and that is why i was absolutely astonished by the pathetic inability of the 322mm brakes to take the heat of my normal daily commute (I drive a very easy 100 miles a day commute on the highway). Lets face it, the S90 is no track day car and handles like a pig in mud so I hope nobody is buying it for that purpose but the brakes should have no problem handling normal every day driving, or one would think.... guess i'm just spoiled from my past german car experience.
 

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So far I have been somewhat disappointed in the brakes on my S90. By 20,000 miles the rotors had already warped and the braking performance is overall poor (lots of vibration and brake fade during heavy braking) compared to my wifes Audi A6. I just rolled over 35k miles and my brakes on all four corners are completely shot. So as I started searching around for new rotors and pads I noticed the S90 has two different size brakes that could be equipped from the factory both front and rear.

Front - 322mm or 345mm rotors
Rear - 302mm solid rotor or 320mm vented rotors

All the online stores I looked at naturally lined up the smaller front rotors with the smaller rear rotors and the larger front with the larger rears. As I looked at my S90 it is easy to spot the rear rotors are vented, so it has the larger 320mm brakes equipped on the rear, so naturally I assume the front brakes are the larger 345mm brakes and ordered them. Much to my surprise when my rotors arrive, my car is equipped with the 322mm fronts and 320mm rears. This was absolutely astonishing to me and makes zero sense from an engineering standpoint. Considering the front brakes do 80%+ of the braking, I can't imagine how volvo allowed a car to leave the factory with essentially the same size brakes on the front of the car as the rear. After I realized this, it makes sense that braking performance is so poor and the front rotors already warped on my car (not to mention the factory pads only lasted 35k miles on all four corners).

So, rather than taking the easy path and returning the larger brakes, I decided to give myself a "big brake" upgrade. I couldn't find any online store selling new or rebuilt calipers for any of the 2017+ late model volvo's so I took to searching local junk yards. I was able to find a junk yard that had the 345mm calipers with brackets off a totaled XC90 for $60 each with less than 10k miles on them (and the used pads that came in them are nearly new as well:D). None of the parts websites show these calipers are interchangeable between the S90 and XC90, but if you look at the part numbers for the brake pads and rotors, you will notice that they are the same for both cars. So I took the risk and bought the XC90 calipers and it paid off big time. The calipers fit perfectly and greatly improved braking performance. It was no more complex than doing a normal brake job replacing the rotors and pads, the only extra step was swapping the brake line onto the new larger calipers and bleeding the brakes.

For those of you into the mathematical figures behind this change and how significant of a size upgrade it is.
surface area of a 322mm diameter circle is 81433mm/squared or 126.22in/squared
surface area of a 345mm diameter circle is 93482mm/squared or 144.89in/squared
This equates to 12049mm/squared or 18.67in/squared ADDITIONAL braking surface area of the rotor. Which is 15% increase in surface area.

I hope this is helpful for anyone else that is less than impressed with the braking performance of their S90 and notice they are in the same situation as I was with the smaller 322mm front brakes.

BONUS: For those of you that want REALLY big brakes on your S90, I also noticed the XC90 R-Line has an optional 366mm front rotor, now these were never equipped on the S90 from the factory, but my bet is they would be a direct bolt on upgrade as well, No Guarantees on this one though.
I can confirm that the xc90 r-line rotors and calipers fit, 366mm (front) and 340mm (rear)
Need brackets and caliper in the front and just the brackets to the rear

Sent fra min SM-N975F via Tapatalk
 

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So far I have been somewhat disappointed in the brakes on my S90. By 20,000 miles the rotors had already warped and the braking performance is overall poor (lots of vibration and brake fade during heavy braking) compared to my wifes Audi A6. I just rolled over 35k miles and my brakes on all four corners are completely shot. So as I started searching around for new rotors and pads I noticed the S90 has two different size brakes that could be equipped from the factory both front and rear.

Front - 322mm or 345mm rotors
Rear - 302mm solid rotor or 320mm vented rotors

All the online stores I looked at naturally lined up the smaller front rotors with the smaller rear rotors and the larger front with the larger rears. As I looked at my S90 it is easy to spot the rear rotors are vented, so it has the larger 320mm brakes equipped on the rear, so naturally I assume the front brakes are the larger 345mm brakes and ordered them. Much to my surprise when my rotors arrive, my car is equipped with the 322mm fronts and 320mm rears. This was absolutely astonishing to me and makes zero sense from an engineering standpoint. Considering the front brakes do 80%+ of the braking, I can't imagine how volvo allowed a car to leave the factory with essentially the same size brakes on the front of the car as the rear. After I realized this, it makes sense that braking performance is so poor and the front rotors already warped on my car (not to mention the factory pads only lasted 35k miles on all four corners).

So, rather than taking the easy path and returning the larger brakes, I decided to give myself a "big brake" upgrade. I couldn't find any online store selling new or rebuilt calipers for any of the 2017+ late model volvo's so I took to searching local junk yards. I was able to find a junk yard that had the 345mm calipers with brackets off a totaled XC90 for $60 each with less than 10k miles on them (and the used pads that came in them are nearly new as well:D). None of the parts websites show these calipers are interchangeable between the S90 and XC90, but if you look at the part numbers for the brake pads and rotors, you will notice that they are the same for both cars. So I took the risk and bought the XC90 calipers and it paid off big time. The calipers fit perfectly and greatly improved braking performance. It was no more complex than doing a normal brake job replacing the rotors and pads, the only extra step was swapping the brake line onto the new larger calipers and bleeding the brakes.

For those of you into the mathematical figures behind this change and how significant of a size upgrade it is.
surface area of a 322mm diameter circle is 81433mm/squared or 126.22in/squared
surface area of a 345mm diameter circle is 93482mm/squared or 144.89in/squared
This equates to 12049mm/squared or 18.67in/squared ADDITIONAL braking surface area of the rotor. Which is 15% increase in surface area.

I hope this is helpful for anyone else that is less than impressed with the braking performance of their S90 and notice they are in the same situation as I was with the smaller 322mm front brakes.

BONUS: For those of you that want REALLY big brakes on your S90, I also noticed the XC90 R-Line has an optional 366mm front rotor, now these were never equipped on the S90 from the factory, but my bet is they would be a direct bolt on upgrade as well, No Guarantees on this one though.
Golly, I'm just about to purchase a new 2019 S90 T8 hybrid and before I read your post I had just returned from talking to a Volvo service tech about brakes on this car. My conversation with him was mainly focussed on regenerative braking from the rear and the potential for a different sensation or feel on the brake pedal. Not a lot of the Z90's have been around so he was not really up on this car. However, since the car I'm interested in is 400 miles from me, I haven't driven it yet. And I am wondering how different Volvo's regenerative brakes will feel? So I guess I'll just have to fly all the way down to L A to press the peddle. Funny, but having just sold my C6 ZO6 from 8 years of high performance driving events on California road courses, brakes and brake feel have been critical to me. After loosing my brakes four times on track, I was not the only driver that has concluded that Corvette's Achille's heal is their calipers and rotors. Finally I changed the car to big brakes and never looked back. So here again I find myself zeroing in on brakes.... The tech did mention that owners of these cars were going through a lot of pads, both front and back. Having owned 5 Volvos, I too have gone through a few pads but having driven 3/4 of a million miles, I bet I've averaged 60K+ miles on these. All of my cars have shown more wear on the front while I hear many Volvo models wear pads quicker on the rear. Lots of various reasons out there for this but I suspect that with the trend of going to all wheel drive, more braking from the rear can help steer a car straight especially in wet or icy conditions. With this in mind, Volvo seems to want the rear to do a lot of the braking for safety reasons. However since I am looking at a hybrid version this time, I was just told that the rear pads will last a lot longer due to the electric regenerative braking in the rear axel. Hmmm, maybe I'll find out if the feel of the braking is not a deal breaker for me. Anyone else out there drive a pre 2020 year S90 T8 and not be able to get use to the regenerative feel?
 

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I cannot speak for Volvo’s regenerative brakes, but can speak to regenerative braking in general having driven several Ford Fusion Hybrids from 2010 to the 2019 model year, while at the same time driving cars and large SUVs with only normal brakes. My conclusion was that the first time driving the hybrid, the brakes were a little grabby. But after driving a few miles, I got used to them and did not notice a difference between the hybrid and non hybrid vehicles.
 
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