Allowed: 220mm rotors on the rear of Reign E+ ‘22 onwards?

[big_scot_nanny]

Hi, have googled this, even asked giant a question directly but got a weird incomplete response (you can see it on the website of the Reign).

Can I use, without invalidating my warranty, 220mm rotors on the rear of my 22 Reign E+?

I know many of you have, i am a big fella on big mountains (esp for summer in the alps) and I’d like the extra oomph and cooling at the rear.

Already run 220 on the front, but do not want to screw my warranty, or indeed snap a chainstay or somesuch

Many thanks!

 

[irie]

This prompted me to have a look at what 2022 Trek Rail 5 warranty is for largest rotors. Looks like the warranty is rear max 200mm. The bike's had 220mm rotors front and rear since March 2023 but will be out of 2 yr warranty in a week so who cares.

Edit: but has a lifetime frame warranty I think so will be careful.

 

[Mikerb]

It may make little difference to your braking a bility given it is how much weight you apply to the rear of the bike that provides traction since virtually any brake set up will lock the wheel otherwise, especially downhill. The front brake is far more powerful.

 

[irie]

It may make little difference to your braking a bility given it is how much weight you apply to the rear of the bike that provides traction since virtually any brake set up will lock the wheel otherwise, especially downhill. The front brake is far more powerful.

Braking is about far more than the ability to lock the wheel.

 

[big_scot_nanny]

All good points, but can anyone acutally answer the question: does a rotor bigger than 203 invalidate warranty / is beyond frame specification?

 

[big_scot_nanny]

Argh - so here is an official response from Giant that is not exactly on point. I asked specifically about invalidating the warranty, but I guess I take this as a 'yes, this will invalidate the warranty'.

TBF, I don't want to do anything that would, local dealer has been really good at replacing stuff under warranty so far on my 22 E+1 (Wheels, shock and motor).

Oh well, hot rotors it is

Edit: and I should add, sorry if this is pissing on anyones chips!

 

[irie]

Argh - so here is an official response from Giant that is not exactly on point. I asked specifically about invalidating the warranty, but I guess I take this as a 'yes, this will invalidate the warranty'.

TBF, I don't want to do anything that would, local dealer has been really good at replacing stuff under warranty so far on my 22 E+1 (Wheels, shock and motor).

Oh well, hot rotors it is

View attachment 132487

Edit: and I should add, sorry if this is pissing on anyones chips!

That's neither a "Yes" nor a "No".

 

[big_scot_nanny]

Not particularly helpful, I agree

 

[irie]

Not particularly helpful, I agree

Sounds like the response of someone who doesn't know the answer and can't be arsed to find out.

 

[Shjay]

I think that’s fairly obvious that 203mm is largest size to run. I have seen 1st hand chain stays snap on ally frames in past due to running too large a rear rotor, so would be crash replacement rather than warranty, I did U.K. warranty for a brand 10+ yrs ago,

 

[RoJo]

If clearance isn't an issue, just fit 220s and swap them back if warranty claim is required.
If you look at the mechanics involved, maximum force is determined by tyre grip, which determines maximum torque at the brake. If the rotor is larger then actually the shear force on the caliper mounts will be less to give the same braking torque... There are a few underlying assumptions here, but on face value it shouldn't be much worse for your bike (you would actually be squeezing the brake lever less hard in order to lock the wheels).
Things that will increase stress on the bike are more powerful brakes combined with grippier tyres and a heavier rider, but they are not restricting these things, so bumping up rotor size is probably fine.

 

[irie]

If clearance isn't an issue, just fit 220s and swap them back if warranty claim is required.
If you look at the mechanics involved, maximum force is determined by tyre grip, which determines maximum torque at the brake. If the rotor is larger then actually the shear force on the caliper mounts will be less to give the same braking torque... There are a few underlying assumptions here, but on face value it shouldn't be much worse for your bike (you would actually be squeezing the brake lever less hard in order to lock the wheels).
Things that will increase stress on the bike are more powerful brakes combined with grippier tyres and a heavier rider, but they are not restricting these things, so bumping up rotor size is probably fine.

Agree with you. Was going to do a bit of physics which surprisingly would be as valid today as it was 10+ years ago. But you saved me the trouble, thanks.

 

[Mikerb]

There are only 2 benefits in using a larger rotor. One is the greater mass of metal overall which would help to dissipate heat...although I think that difference would be minor and probably more effectively achieved using a thicker rather than bigger rotor.
The bigger benefit of a larger rotor is achieved due to moving the braking moment closer to the rim of the wheel. Keep in mind however that it also means the calliper adapter has to enable the calliper to be further from its anchor point on the chainstay...............and that is where any additional torque would have to be absorbed......and it is a point load. I would guess the average chainstay....especially if carbon...would be nowhere near as strong as a 38 fork stancion which is where it is more normal to mount a 220 rotor. Apart from heat build up i would guess the greatest loss of braking efficiency is in the degree of flex between the braking moment on the rotor and wheel rim........mostly in the spoke thickness/pattern/number of/fixing to the rim. In other words a better wheel may deliver more dividends than a bigger rotor!!

 

[irie]

There are only 2 benefits in using a larger rotor. One is the greater mass of metal overall which would help to dissipate heat...although I think that difference would be minor and probably more effectively achieved using a thicker rather than bigger rotor.
The bigger benefit of a larger rotor is achieved due to moving the braking moment closer to the rim of the wheel. Keep in mind however that it also means the calliper adapter has to enable the calliper to be further from its anchor point on the chainstay...............and that is where any additional torque would have to be absorbed......and it is a point load. I would guess the average chainstay....especially if carbon...would be nowhere near as strong as a 38 fork stancion which is where it is more normal to mount a 220 rotor. Apart from heat build up i would guess the greatest loss of braking efficiency is in the degree of flex between the braking moment on the rotor and wheel rim........mostly in the spoke thickness/pattern/number of/fixing to the rim. In other words a better wheel may deliver more dividends than a bigger rotor!!

So what is your recommendation to the OP @big_scot_nanny ?

 

[Mikerb]

So what is your recommendation to the OP @big_scot_nanny ?

learn not to drag the rear brake if that is what he is doing.....if not, and heat build up is the main problem, fit a thicker 2 piece rotor of the same size.

 

[irie]

learn not to drag the rear brake if that is what he is doing.....if not, and heat build up is the main problem, fit a thicker 2 piece rotor of the same size.

This ^^^ neither answers nor provides advice about his question which was ...

Can I use, without invalidating my warranty, 220mm rotors on the rear of my 22 Reign E+?

Assuming that he's neither dragging his brake nor experiencing heat build up, what would be your recommendation?

 

[Mikerb]

This ^^^ neither answers nor provides advice about his question which was ...

Assuming that he's neither dragging his brake nor experiencing heat build up, what would be your recommendation?

the OP stated he was a big fella and wanted "more 00mph and cooling".............and could get no definitive answer whether going 220 would breach his warranty. So I would not risk going 220 but rather fit a thicker 2 piece 203 or even 200 rotor.
There is also a lot to be gained by improving braking technique albeit we have no information about the OPs experience level. Suffice to say the greatest braking power available on a bike, especially downhill, is the front brake...not the rear!

 

[irie]

the OP stated he was a big fella and wanted "more 00mph and cooling".............and could get no definitive answer whether going 220 would breach his warranty. So I would not risk going 220 but rather fit a thicker 2 piece 203 or even 200 rotor.
There is also a lot to be gained by improving braking technique albeit we have no information about the OPs experience level. Suffice to say the greatest braking power available on a bike, especially downhill, is the front brake...not the rear!

Given this ^^^ we are therefore agreed that running a larger rear rotor is unlikely to cause any physical issues.

 

[RoJo]

For the same lever force, the 220mm rotor will give an almost guaranteed 10% more braking force than 200mm. I say almost because the only circumstance it could deliver less is if his brakes run consistently too cool. More likely he'll get more than 10% because of the extra mass and cooling.

However, in reality it is the tyre grip that limits how hard you can pull the lever before the wheel locks, so what will actually happen is he can pull the lever with 10% less force and get the same braking as before, which will be much easier on his hands.

So it's not really rotor size that determines the braking forces, it's the tyres, because even with a 200mm rotor you could pull the lever harder and achieve the same braking torque.

Maybe think of it another way, he could instead buy some really powerful hope tech V4 brakes and some super high friction pads which even with 200mm rotors might give more braking force potential than an upgrade to 220mm with his existing brakes, however this is totally allowed by the manufacturer. If they would happily allow a brake caliper upgrade it would make sense that a brake rotor diameter upgrade would also be fine. They amount to the same thing and are both limited by rear locking, pulling harder when the wheel is locked won't increase brake torque.

 

[irie]

... so what will actually happen is he can pull the lever with 10% less force and get the same braking as before, which will be much easier on his hands ...

Which is precisely why I run 220mm rotors, single finger braking

 

[RoJo]

Yep, it's pretty necessary on an aggressive eBike. I run 220mm both ends on all my bikes. Particularly in Morzine this gives way less arm pump as you're not pulling on the brakes dear life.

 

[Mikerb]

For the same lever force, the 220mm rotor will give an almost guaranteed 10% more braking force than 200mm. I say almost because the only circumstance it could deliver less is if his brakes run consistently too cool. More likely he'll get more than 10% because of the extra mass and cooling.

However, in reality it is the tyre grip that limits how hard you can pull the lever before the wheel locks, so what will actually happen is he can pull the lever with 10% less force and get the same braking as before, which will be much easier on his hands.

So it's not really rotor size that determines the braking forces, it's the tyres, because even with a 200mm rotor you could pull the lever harder and achieve the same braking torque.

Maybe think of it another way, he could instead buy some really powerful hope tech V4 brakes and some super high friction pads which even with 200mm rotors might give more braking force potential than an upgrade to 220mm with his existing brakes, however this is totally allowed by the manufacturer. If they would happily allow a brake caliper upgrade it would make sense that a brake rotor diameter upgrade would also be fine. They amount to the same thing and are both limited by rear locking, pulling harder when the wheel is locked won't increase brake torque.

all true....but I would add one other factor and that is rider weight applied to the back wheel.

 

[Mikerb]

 

[big_scot_nanny]

Thanks all, good dialogue. To address some questions: (TL : DR below in bold)

Drag brakes? Yep!
Experience level? Huge fat mincer, but tries to ride hard.

My desires are mostly coming after a truly 'shit your pants' moment last year during our annual alps trip. Now, I used to live in Switzerland, ridden in the alps lots and lots so plenty of experience of big vertical descents and lots of braking! But last year was my first time on really big mountains with an ebike so quite a bit heavier than anything from years previous. FYI I favour Hayes Dominion A4s on all bikes, inc my Reign.

On the descent into Weisen on the Alps Epic Trail in Graubunden, there is a long long section of steep, fast trail and I felt my brakes go a bit funny. Not cooked, not boiled, they were still braking, but felt oddly 'soft' as I was trying like buggery to halt myself to make a sketchy, flat and loose corner. I happened to look down at my front wheel (was not able to see the rear), and the front disc braking surface was visibly warping and wobbling from side to side. I stopped. They did not collapse or fold on itself and kill me, but as it gently rode then next bit I watched as both discs 'righted' themselves.

This, to put it mildly, put the shitters right up me, as the thought of brake discs catastrophically failing on a trail that steep and exposed is horrifying.

These were Galfer Wave 2mm discs - 220 on the front, 203 on the rear. I bought them as they were cheap, and 2mm. Thinking about it now, the same feeling happened a couple of times locally at the heaviest braking moments of local 500m+ descents on the same discs.

I replaced them with Swisstop catalyst discs which have been OK, and worked just fine for the rest of the holiday without warping incidents, and I have never experienced this before.

TL : DR However, it has now driven me to look for the biggest, best heat-dissipating, discs I can fit to try to minimise the risk of this happening again.

It seems this is a known issue with the Galfer wave rotors (well, I read it on t'internet somewhere once I started googling about those discs), and 2mm is the widest disc I can use in A4 calipers.

 

[big_scot_nanny]

I must admit thatI do often think about the physics behind the conversion of all the kinetic/potential energy in a 115kg, 2m tall bloke hurtling downhill at 50kmh into heat, which is really the only place the energy can go. Terrifying!

 

[mtbbiker]

Thanks all, good dialogue. To address some questions: (TL : DR below in bold)

Drag brakes? Yep!
Experience level? Huge fat mincer, but tries to ride hard.

My desires are mostly coming after a truly 'shit your pants' moment last year during our annual alps trip. Now, I used to live in Switzerland, ridden in the alps lots and lots so plenty of experience of big vertical descents and lots of braking! But last year was my first time on really big mountains with an ebike so quite a bit heavier than anything from years previous. FYI I favour Hayes Dominion A4s on all bikes, inc my Reign.

On the descent into Weisen on the Alps Epic Trail in Graubunden, there is a long long section of steep, fast trail and I felt my brakes go a bit funny. Not cooked, not boiled, they were still braking, but felt oddly 'soft' as I was trying like buggery to halt myself to make a sketchy, flat and loose corner. I happened to look down at my front wheel (was not able to see the rear), and the front disc braking surface was visibly warping and wobbling from side to side. I stopped. They did not collapse or fold on itself and kill me, but as it gently rode then next bit I watched as both discs 'righted' themselves.

This, to put it mildly, put the shitters right up me, as the thought of brake discs catastrophically failing on a trail that steep and exposed is horrifying.

These were Galfer Wave 2mm discs - 220 on the front, 203 on the rear. I bought them as they were cheap, and 2mm. Thinking about it now, the same feeling happened a couple of times locally at the heaviest braking moments of local 500m+ descents on the same discs.

I replaced them with Swisstop catalyst discs which have been OK, and worked just fine for the rest of the holiday without warping incidents, and I have never experienced this before.

TL : DR However, it has now driven me to look for the biggest, best heat-dissipating, discs I can fit to try to minimise the risk of this happening again.

It seems this is a known issue with the Galfer wave rotors (well, I read it on t'internet somewhere once I started googling about those discs), and 2mm is the widest disc I can use in A4 calipers.

I have the Dominion A4 and love them. IMHO rotor brand matters as well. I run 220 f & r. Started with the new SRAM HS2 rotors and thought not bad, but I wanted more power with less hand pressure. Then upgraded to Magura MDR rotors and wow, these made the difference I was looking for. The only issue with these, because of the floating rotor is the front is starting to rattle. The other rotors I wanted to try was the new Galfer Shark rotors. Those have been getting good reviews, but expensive.

 

[Mikerb]

As per the video a couple of posts above, there are different quality rotors and rotors also wear...........maybe you were just unlucky with the rotors you were using. If you are in a situation ( like the one you described!) where the brakes are being really tested, take some advice from the motor racers ( I was one!!) ...................brake hard, then leave it alone.......brake hard a gain if need be a little later i.e short hard stabs. As long as the front wheel is straight there is far less chance the wheel will lock up since just like a car, all the weight is being thrown forward onto that wheel even if on the flat, but even more so if going downhill. The other piece of advice is to brake hard when still going straight. Heat only builds up all the time the rotor is still turning with the brake pads in contact so make that time as short as possible whilst achieving the maximum retardation.

 

[postimtb]

I don´t think that you will have a problem with the frame, I have 223mm rotors from/rear and 0 problems.

 

[Redlemon]

Argh - so here is an official response from Giant that is not exactly on point. I asked specifically about invalidating the warranty, but I guess I take this as a 'yes, this will invalidate the warranty'.

TBF, I don't want to do anything that would, local dealer has been really good at replacing stuff under warranty so far on my 22 E+1 (Wheels, shock and motor).

Oh well, hot rotors it is

View attachment 132487

Edit: and I should add, sorry if this is pissing on anyones chips!

That Giant UK guy above is completely clueless on recommending 203mm max rear rotor size when Giant are speccing 220MM F&R on the 2024 Reign E+1.

There's no way Giant would deny a warranty claim for that reason when they're doing it from the factory.

I'll be on my 3rd season with a 220mm SRAM HS2 rear rotor and not a single issue.

 

[Plummet]

Argh - so here is an official response from Giant that is not exactly on point. I asked specifically about invalidating the warranty, but I guess I take this as a 'yes, this will invalidate the warranty'.

TBF, I don't want to do anything that would, local dealer has been really good at replacing stuff under warranty so far on my 22 E+1 (Wheels, shock and motor).

Oh well, hot rotors it is

View attachment 132487

Edit: and I should add, sorry if this is pissing on anyones chips!

That response does not preclude the use of a 220 rotor.

If you are worried they may not cover warrantee then slap a 220 rotor on there. If the frame snaps. Take the bike to the shop with a 203 rotor bolted back on for warrantee purposes.....