Shimano XTR M9100 bleed guide using SRAM method for beginners. Don't gravity bleed. + piston removal

[@GokkunGuru]

This is seriously the best A to Z brake bleed video ever published on YT. I followed this method and my Deore XT’s are like new!

[@zoubtube]

Thank you so much for such a gracious comment. It makes me so glad that people find them useful. More videos to come

[@nosidramuzthetitan9006]

this is the best step by step and scientific Shimano brake bleed I have ever seen! Wow man tnx for this tutorial...

[@zoubtube]

Very glad to hear you found it informative. and thank you very much for the kind comment 👍

[@Vilendank]

I've got a box of various shimano brakes sitting in my garage in kelowna, and after taking them apart -calipers and levers- i was dismayed to see how little tolerance there was (especially the ceramic pistons) and how difficult it was to find spare parts. like you I got spares from aliexpress and the like, to no success, but there are so many different areas where one could be getting the "wandering bite" or endless air bubbles from: caliper piston bore hole, compromised bladder, lever piston seal, bad hose cut, compromised olive/barb, or even just parts slightly out of spec. You've given me a few ideas to test whether any remain salvageable, but I think if one does anything to their brakes at all it's to keep those ceramic pistons (and the area around) as clean as you can and as often as you can.

[@zoubtube]

"but I think if one does anything to their brakes at all it's to keep those ceramic pistons (and the area around) as clean as you can and as often as you can" I couldn't agree more with this. Where I live, we have hard water. It will literally turn a stainless steal sink grey/white in week if not kept clean. They also spray calcium chloride on dirt roads around here to control dust. That S$%T wreaks havoc on bike parts. Both will leave buildup on the edges of caliper pistons, and I'm beyond convinced that whenever people around here complain to me about their brakes not working right, it's because of the buildup. I tell them to clean the piston edges with CLR and a cotton swab, then clean them with alcohol, then use mineral oil or DOT fluid (depending on the brake) to push the piston back in and then the caliper again with alcohol. I'd say 85% of the time, this ends up solving their issues.

[@Dr_Pappa]

Thank you for sharing this, it is such a well made video. Just finished doing my first ever bleed and had zero issues as I followed you step by step.

[@zoubtube]

AWESOME JOb 👏👏🦾 and thank you so much for leaving the comment. It always makes my day when I read that people successfully completed some of these jobs 😊 Now go out there and reap your rewards! 👍

[@jurgenrossaert8437]

Best video in its kind! 👏👍

[@zoubtube]

Thank you very much for the kind comment. glad to hear you found it informative. let me know if there are any questions

[@darojos]

I came the same conclusion as you and have been doing a flush down first bleed for a while. I also discovered that some of the cheap amazon bleed kits have the correct threaded adapter to put a syringe on the top reservoir. This allows me to push and pull from both the top and the bottom. Works pretty well.

[@zoubtube]

"I also discovered that some of the cheap amazon bleed kits have the correct threaded adapter to put a syringe on the top reservoir" For real, can you send me a link? I've never looked into this option. Thanks

[@jakoblester7816]

can damage the bladder by pushing down through the lever wouldn't recommend

[@zoubtube]

@@jakoblester7816 So are you saying that pushing down using an aftermarket syringe attached to a XTR lever body can damage the bladder? It would be great to know what would cause this.

[@zoubtube]

@@jakoblester7816 Are you saying that using an aftermarket syringe on the lever body can damage the bladder when applying pressure?

[@leonardocasadei]

Amazing video!! And super useful! . I have both same problems! #1 small oil linkage under lever. #2 Lever went far forward trough standard stop position. I hope find some similar piston to replace it. Infinite thanks for this instructions!

[@zoubtube]

Thank you for taking the time to watch it. super frustrating that shimano doesn't sell simple replacement parts like this. seems to me they can make very fat margins on small cheap parts like these

[@aramm7052]

I´ve just recently punctured the diaphragm using a syringe to bleed an xt 8100 brake (same cilinder as the 9100), the problem is that the pressure from the syringe falls precisely on the small ramp where the diaphragm is very weak, I have a couple of photos that I can show to you so that you have evidence of this, the syringe is not the best method to bleed the brake from the lever, maybe from the caliper.

[@zoubtube]

And that could very well be the reason why shimano never provided a solution of this type. I've never bled a shimano brake with a lever syringe. I didn't even know it was an option until someone had mentioned it. For those of you who have bought a lever syringe for your shimano brakes levers. be careful using it. Don't apply to much pressure or you risk potentially damaging the bladder Thanks for the heads up aramm. Greatly appreciated

[@madmat1652]

i did a gravity bleed and watched with disgust all the black grime appear from my lever port when using a syringe, 100% gonna use this method next time. One question, you push in the pistons before procedure, that means after bleeding and aligning pads with rotors i will have to add oil, yes?

[@zoubtube]

I fundamentally believe that gravity-bleeding is a bad idea for the vast majority of people. A person needs to have LOTS of experience and be very in tune with their brakes in order to know whether the bleed was successful. Considering this is done on average once a year, an extra five minutes of time will go a long way. " you push in the pistons before procedure, that means after bleeding and aligning pads with rotors i will have to add oil, " To prep for the bleed, I clean the pistons well and make sure they come out fairly evenly, then push them back to insert the bleed block, then press them firm against the bleed block, and then I do the bleed. The bleed block is the baseline. As long as the pistons are moving at a relatively similar rate, there shouldn't be any issue with alignment, as long as the pistons move at a similar rate. IF you still have alingement issues, then I would double check to see if the pistons move at a similar rate. If you find they still don't after cleaning them, push the pistons out using the brake lever to about 3-4 mm. then aggressively clean the walls, you might have to use some CLR with a Qtip's to remove mineral buildup. If you do clean them with CLR, use Alcohol when you're done to remove the CLR. Then add mineral oil to the piston walls, then push them back into the caliper and clean any exposed mineral oil. Then check to see if the pistons are moving equally.

[@madmat1652]

@@zoubtube Thank you for a very detailed response but i dont think i made myself clear enough: what i mean is when I do prebleed piston push in to caliper I kind of "limit" the available space for oil ( and air) , yes? So after bleeding and closing the system i will do the alignment- the pistons will push out a bit and creating more space for oil to fill in, so my question stands Will i have to add oil after alignment to account for moving piston?

[@zoubtube]

@@madmat1652 As long as your using the bleed block for the bleed, then no. you don't add in extra oil. you'll take the chance of over pressurizing the system, which will most likely show itself at the weep hole

[@madmat1652]

@@zoubtube All right, thank you very much

[@chrislai6817]

多謝！

[@zoubtube]

Thank you VERY much for your generosity. It makes me happy to hear that the video was helpful for you. 🤗Let me know if you have any questions 👍

[@filacaamspeter8810]

Thanks for the how-to video. It was a great presentation.

[@zoubtube]

Thank you for taking the time to watch it. If you have any questions let me know

[@nici936]

Great video! I had never done it before but it turned out great. Thank you very much

[@zoubtube]

Excellent Job! Super glad to hear everything went well for you. Now go enjoy the season! 👍

[@kalousr96]

Very nice - clear and right instructions. Love this one ✌️

[@zoubtube]

Super happy to hear that you found this video informative and thank you very much for the kind sentiments. let me know if there are any questions and more videos to come

[@jonibz1456]

Great video! Do you clean the syringe with alcohol between dirty and clean oil or just rinse with a little fresh oil?

[@zoubtube]

I typically use paper towel and a finger to clean the inside of the tube. As for the hose, I'll only use alcohol if there are partials inside it. If you do this, make sure to let the syringe sit until all the alcohol evaporates before using it again. After I'm done with a bleed, clean it all with alcohol.

[@kostak2171]

That makes a hell of a lot of sense! Looking forward to getting my bike back so I can try this out!

[@zoubtube]

Then I'll make sure to work on only one of your brakes and leave the other one for you to try 😁

[@markreyes022]

hi did you find the replacement piston ??

[@zoubtube]

Nope! haven't really look lately. The handle is in the spare parts bin for now. I'll let people know if I solve this. Really sucks that shimano doesn't sell them

[@markreyes022]

@@zoubtube hi one more thing are the piston seals are identical on xt?

[@zoubtube]

@@markreyes022 I can't be 100% sure. I think they are but there might be some differences that are hard to make out. ex: thickness, stiffness, etc they look REAL similar though. wish I could have more definitive info

[@jonjonjonnyjon]

That Park Tool BKM kit comes with a hose specifically for clicking into the caliper's bleed screw, its the one with the little metal insert in the end. You don't need to use the generic hose end.

[@zoubtube]

The kit has a metal insert that goes into an XTR brake caliper? I thought all the kit had for Shimano brakes was that hard black round knob/cover thing that the hose goes through to helps hold it on the caliper. I must have missed a metal attachment for Shimano. I'll look for it next time. Thanks

[@brendanfisher7903]

Thanks for a great video. I always still seem to struggle once the system is all closed off and fresh then put my pads back in. The pistons then move inwards so the pads find the rotor, then the lever freestroke is just too much and it's no good. What's the trick here you think?

[@zoubtube]

Thanks for the compliment. So I'm not entirely sure what you mean by "then the lever freestroke is just too much". Do you mean there to much throw? To little throw? to tight? To soft? No one brake will meet everyone's needs. it's a very personal thing. some people like instant brake lock, others like modulation. some people like short throw, others like it longer. let me know what you mean with the above and we can go deeper into this

[@brendanfisher7903]

@@zoubtube hey thanks for the reply. Yes I meant there is too much throw. Once the system is bled and the rotor is back in place the first time you engage the lever it almost goes back to the bar, too much throw. My preference is only a short throw. So with my model of shimano lever there is no freestroke adjustment. I overcome this by keeping the funnel attached and open. Remove the wheel and pump the lever so the pistons move inwards, just a couple of small lever pumps then put the wheel back on and check that the lever throw is to my liking. Repeat if less throw still required. This process just seems very manual and not what is typically involved in a bleed. Anyways hope that makes sense. Cheers.

[@joseulloa8769]

Shimanos are so easy to bleed. Have funnel with fluid in it, pump lever up hold lever down, Open bleeder, hold lever all the way down repeat this process till the lever is nice and firm simple as that no syringe need no nonsense method this method works 100 percent of the time

[@zoubtube]

Not going to disagree, but still feel I can't recommend gravity bleeding for people who are just getting started. With a syringe bleed the system can be stressed both down and up in order to agitate any micro bubbles stuck in it. Once some experience and feel for their brakes is gained over time, then I would say give gravity bleeding a shot. but in the end, they are both quick once you get used to them. but syringe is the only method to truly stress the system to be sure.

[@ronmel]

Thanks for this awesome vid. After cleaning and brushing the pistons, what are your thoughts on applying some mineral oil to the pistons before pushing then back in? Of course, also wiping them down as a last step.

[@zoubtube]

Absolutely not an issue as long as you use mineral oil on mineral oil brakes. 👍

[@ronmel]

@@zoubtube Thanks and yes, forgot to mention mineral oil for Shimano brake pistons. Again, awesome video.

[@Justin-ny6un]

What’s your opinion on the freestroke screw (if available) in or out whilst bleeding. I have always left it in (shortest lever throw) All the forums say to unscrew it whilst bleeding, but I’d seen something about ruptured bladder when doing it this way. Unless you screw it back in before closing the lever bleed port. SRAMs bleed manual says to back the dial out in the opposite way of the arrow on the lever. Which puts the contact at the shortest lever throw. So the same as leaving the Shimano screw in.

[@zoubtube]

what a coincidence. I have a bike here with XT brakes and was planning doing a bleed video (right after i'm done rebuilding the shock ,fork and dropper) just for this reason. I've always extended the handle out and unscrewed (counterclockwise) the free stroke screw a couple of turns. Never had an issue with the bladder on an XT, and I've done quite a few over the years. very solid brakes set imo

[@Justin-ny6un]

@@zoubtube The last bleed I done when I swapped my frame I unscrewed by two turns and lever fully out. Does unscrewing allow more fluid in the system? Not sure of the lever/master cylinder mechanics. I’ve never had an issue with wandering bite point, there’s so many reasons why people say it occurs. Air trapped in caliper, in the freestroke screw etc. Does it make sense to follow how SRAM recommends with their brakes, in the position which provides the shortest lever throw, which is fully clockwise. This way doesn’t give you any adjustment though if you want the shortest/closest bite point. If it started all the way out it could be brought in to match front and rear lever travel as pads wear.

[@Justin-ny6un]

@@zoubtube Thanks it’s mainly the position of the screw for the bleed and Shimano doesn’t state it anywhere so thought I’d ask. Next time I’ll try bleeding with it out, will have to see how many turns it takes for it to stop having an effect. Yeah I have used the freestroke, to adjust and it does work as long as you reset your lever position. I know it works, unlike the majority who say the Philips head screw does nothing :) I think the only useful position is the screw completely in though, too much travel with it out. Think I’m going to try the thicker SRAM HS2 rotors. Also considering the Code RSCs still, I wanted the Stealths but the hose routing is ugly.

[@CyclingWithOliver]

I watched both videos on Shimano bleeding, excellent. However, when I tried to follow it as a manual when bleeding, the extra interventions and explanations made me a bit confused. If you have the energy for it, I suggest you make a script for a step-by-step Shimano bleed, that involves all the steps to be done, number the steps, and add corresponding chapter titles. Make it a short tutorial, that shows the steps to be done, without the explanations, that I can easily follow. Then if people want explanations, they can watch the two long videos at the correct chapter marks. Also, you might clarify if the lever position should be adjusted at the beginning of the bleed or at the end, and whether the lever's bleed port should be open or not when adjusting the lever. In your other video, it seems to be open, but it is not mentioned. Also, whether you recommend the funnel-and-syringe or syringe-and-syringe method.

[@zoubtube]

Thank you for such a great recommendation. I will get it done and it's probably going to be sooner than later as i'm in the middle of a new bike build series 👍

[@no-hope-in-the-pope]

what top cap/spacer shim is that that also has the garmin mount? I need that!

[@zoubtube]

I believe this is the top cap your asking about? www.amazon.com/Best-Tek-Garmin-Computer-Adjustable/dp/B07N1QVGNM?pd_rd_w=MZhow&content-id=amzn1.sym.4311067e-a9df-4e8a-a5ce-d6836ea1723b&pf_rd_p=4311067e-a9df-4e8a-a5ce-d6836ea1723b&pf_rd_r=6RBAS4J92YR0SFASR770&pd_rd_wg=3SWGf&pd_rd_r=58a36f2e-2770-4277-bf55-795d9e9b9b12&pd_rd_i=B07N1QVGNM&psc=1&ref_=pd_bap_d_grid_rp_0_13_cp_i

[@harryparkinson]

maybe k-edge garmin mount

[@smw36164]

Great video, really do appreciate the detail you went into. Would you happen to have a link to the tube brushes you use please?

[@zoubtube]

Glad to hear you found the video informative. I bought the brushes at a local hardware store in a discount bin. The following at amazon should work just as well. amzn.to/4aytddh Hope this helps

[@Motorcykey]

God bless you

[@zoubtube]

Glad to hear the video was helpful for you. let me know if there questions. 👍

[@janeztomazic5546]

hey thanks for this; i wonder why do you have to put in some oil in the syringe in the first part when you take out the old oil ? You just need vacum to take it out.... Thanks

[@zoubtube]

Thanks for the comment and the good question. Admittedly, I put more oil than usual in the syringe in the video when purging the system of old oil. But I always add a bit of oil to the syringe for two reasons. To mitigate any chances of introducing air into the system. To help determine that I removed the air bubble when connecting the tube to the bleed port before starting the bleed. Is it overkill? Yes. Does it help to ensure a better bleed? Yes, especially for people just starting. I believe syringe/s and/or reservoirs for any brake job should always have some fluid in them and never be completely empty through the whole process. But that's just me. Thanks for the question

[@chrislai6817]

Tks a lot for the sharing 😊

[@zoubtube]

Thank you for your time to watch the video, and again, thank you for your generosity. It is much appreciated 🙂If there are any questions feel free to ask anytime

[@gaddobronx6740]

Your videos are great. But why don't you use the handle bar stabilizer that mounts onto the bike stand. Makes doing brake bleeds a lot easier, especially if the handlebars aren't moving around.

[@zoubtube]

Glad to see the video was of use for you. I actually do use a stabilizer but I only use it when bleeding rear brakes. though now that you mentioned it, I need to remind myself to get a new one because the one I have is on it last legs

[@rmerdatuin8378]

what olive needle of XTR m9120 BH59 Or BH90

[@zoubtube]

BH90 is the brake hose. olive needle kit part number is Y8JA98020

[@themechanic8195]

Brilliant!!!

[@zoubtube]

glad to hear the video was informative for you. If you have any questions let me know

[@juanlozano6716]

You can actually purchase the syringe part SYRINGE HOLDER ASSEMBLY WITH STRAP Item #: 2578A on park tools

[@zoubtube]

Yup! I bought 4 of them last summer. best part of the park tools set imo. amazing it took so long for someone to make them

[@superdave8137]

What ever came about with the piston?

[@zoubtube]

The brake handle with the new piston is still sitting on my workbench. I haven't installed it to test yet. Will do so next month when I get more time and let you know how it goes.

[@LukasLamla-uv6qo]

​@@zoubtubeso you have found the replacement? Probably not the original one but the aftermarket? Pleaee share the link then. Thanks a lot

[@elyasibest]

Top, Top, Top.

[@zoubtube]

Thank you very much. I'm very glad that you found the video useful

[@ArnaudLi77]

Hi, are all bladers removable? (On Shimano latest levers)

[@zoubtube]

That I know of, yes.

[@crislee4057]

The Syndicate always gravity bleeds in their pits. Ask Marshy. ❤

[@zoubtube]

Understood. But these are people with LOTS of experience and time to bleed a system between runs if needed. My videos are meant for those who are either just getting into performing their own services on their bike/s, or need a boost of confidence in order to perform a service that might look intimidating to them. When it comes to brake bleeding, I honestly can't recommend gravity bleeds to this group of people. The chances of them not properly bleeding a system are high, and they won't have the experience to know if the bleed was successful or not. With traditional syringe bleeding, as shown in this video, if they take their time, they can make sure that the bleed is successful. Chances are they will only bleed once a year, so bleed time is irrelevant imo. Something to do on a rainy day 😉

[@John-mb7yl]

U don't want to reuse the mineral oil as it has been aerated. Use brand new unopened bottle each time

[@zoubtube]

Agreed, but I don't believe I ever mentioned to reuse oil in the video, nor did I use any reused oil

[@silaslai5913]

While bring moto cross to bic Dot break fu.

[@zoubtube]

Not sure what to make of this but if you were trying to ask if you can use dot fluid with these brakes, NO! Mineral oil brakes are not compatible with dot fluid and vise versa

[@mamo4731]

Have you thought of degassing the oil from dissolved air before using it? I was thinking of buying VEVOR vaccum chamber a week ago and put the oil in a jar to degass it. If you use a syringe and pull while having the finger on the tip, you'll see the dissolved air form bubbles, expand and go to the top. The syringes will not allow you to create pressure low enough to remove all dissolved air. Or you can use it like this guy kzbin.info/www/bejne/hYjSnp6NgN6Eh68. Forcing air to the top and pumping the lever. The tiny bubbles on the calliper would expand and move with ease. It would leave brakes sharp! You could also use it to remove dissolved air from fork/shock oil. kzbin.info/www/bejne/sGWomKucappogrc

[@zoubtube]

"Have you thought of degassing the oil from dissolved air before using it" I believe I sort of mentioned this in either the Shimano or SRAM brake service video. Degassings brings gas out of solution, which will only happen in a depressurized (vacuum) state (Henry's law). Brakes will either be equal to surrounding atmosphere or under pressure (compressed) in just about every scenario. The only time this "might" be helpful is if you were to go ride at very high elevation. ex: if brakes were bled at the base of a very tall mountain (like let's say revelstoke) and then you ride at the top. but even then I'm not sure if it would depressurize enough to bring the air out of solution or feel any additional sponginess . This is a major focus in scuba diving as this is what causes the benz, but with nitrogen instead of air As for the vacuum pump, it will absolutely work for the job, but I try and make these service videos for people to service their bikes with the most basic tools possible. They will still need the bleed kit, but not sure if most would purchase the vacuum pump for this service. thank you very much for the info though

[@norcoteamti395]

Revelstoke?!?! Are you from Canuckistan?

[@DaninVA]

Great video/content, but say too long.

[@zoubtube]

Thank you very much for the comment. It's all still a learning curve for me. ironically, I've been trying to train myself to talk a bit slower in order to help people from other countries to better follow/understand or translate the videos, but this makes them even longer . eventually I'm sure I'll find a good balance. 👍

[@a8f235]

Shimano service dept. entered the chat: *_Noooooooooooooooooooooooooooooooo..._* *_...ooooooooooooooooooooooooooooooooo..._*

[@zoubtube]

🤣🤣🤣 I'm sure their response would be "We recommend you buy a new set of brakes instead of bleeding" 😁

[@iamcyberpunk68]

I said this for years

[@zoubtube]

So it was you that channeled through me to get this video done 😁Thank for watching it.

[@iamcyberpunk68]

should have used a new olive

[@zoubtube]

I agree that this is best practice, but over time I've learned that modern day brakes are WAY more forgiving with olives then they were, say prior 10+ years. I will say that I should have mentioned your point about the olive in the video. so many things to remember when making these videos 😔

[@iamcyberpunk68]

video was ok lol ok lol ok lol dragged it out a bit.

[@zoubtube]

trust me when I tell you "ok" "basically" and "essentially" drive me NUTS when editing in post. I REALLY need to cut that S@$T as its effecting me at work . I've become really sensitive to them, and in my newer videos I've done a bit of a better job, but I really need to get it under control. We'll get there. 🙄 Thanks for watching

[@jotarr982]

Aliexpress

[@zoubtube]

I couldn't find a piston for a M9100 but I did find one for a M8100, which has been delivered, measured (not exactly identical in size but close) and installed in the handle. but I don't feel comfortable having my buddy test it considering this is the front brake. We ended up buying him a new handle. I'm planning to test the handle with the aftermarket piston on my bike. I plan on doing an update video on whether is works or not 👍

[@clauspetersen9353]

I love when someone is more clever than the guys who designed, and manufactores the system. I doesn’t make sense to you, because you don’t know how it is designed. You seem to ignore completely that the brake levers are designed to only be one way oil flow. Doing it your way you risk the lever to lock up with a complete brake failure as a result. Your way may result in death or injuries.

[@zoubtube]

I never claim to be "more clever than the guys who designed, and manufactores the system" in any of my videos. As a fellow architect/engineer I have the great respect for others in the field. But that's not to say there isn't room for improvement in some cases (FOX, I'm aiming that one at you and all your custom service tools). Also, Many final product decisions aren't made by the actual engineers (We'd have longer-lasting products if they were, imo, but the bean counters don't like that idea) "You seem to ignore completely that the brake levers are designed to only be one way oil flow" Did you ever consider how ignorant this statement is? "Doing it your way you risk the lever to lock up with a complete brake failure as a result. Your way may result in death or injuries." So you're saying that using Shimano's syringe method (the folks that "designed and manufactured the brakes, btw") of finishing the bleed from caliper to brake handle is wrong? Bleed your brakes whichever way makes you happy. But for those who decide to bleed using a syringe method, remove all dirty oil downwards first (from lever to caliper), then bleed the brake upwards, from caliper to lever, and lightly agitate the system during the process in order to help with removing air bubbles that might be stuck to walls or in tight spots.

[@iamcyberpunk68]

ok ok ok ok ok ok ok ok ok ok ok ok ok ok ok ok

[@zoubtube]

🤣🤣" OK", "basically" and "essentially" drives me crazy when I edit. It actually affecting me at work. What I need is an AI bot to remove these for me in post . Thank for watching and I promise I'll be cutting but on these 3 words in future videos 😉

[@MrBirdshell666]

one of the worst videos about bleeding i ve ever seen. Applying so much force like you did here - is the best way to damage the rubber membrane in the oil tank. also, the cause of the dirty oil coming from a hose is that shimano brakes have no any protection from debris (on purpose, to reduce a brake's life, so you would go and buy a new one), so dirt and sand gets into the system at the lever side. no need to reinvent anything, just carefully read shimano's serviceguide, its is straightforward

[@zoubtube]

Ironically, I go over the points you mentioned above in detail in the video. The discoloration in the system comes basically entirely from within the system due to heat and wear (particularly the piston seals). If dirt were to come in from outside the system, then you would have a leak that would ABSOLUTELY expose itself under pressure. Gravity drain (not bleed) and heavily used system, and you will see darker-colored fluid at the caliper side and lighter-colored fluid at the end of the drain process. I've bled a ridiculous amount of these brakes since hydraulics were first released and have never run into an issue with bursting a bladder due to a bleed. I'm not saying it can't happen; if you're careful, it shouldn't. Now, 10+ years ago, bladders would disintegrate over time, but that's a whole different situation that was solved a long time ago