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  1. #1
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    Carbon clincher wheel clearance

    Not sure if this is the correct forum. Moderator please move if necessary.

    I'm researching some new wheels and I like the 25mm carbon clinchers. What is the minimum clearance needed at the bottom near the chain stays that's considered safe play? I have plenty clearance at the rear brakes and there's no clearance concerns for the front wheel either. My concern is the chain stay area. I can't get a real accurate measurement of the width down there, but I have approximately 33mm clearance. I will check with Trek to see if they can provide the exact measurements, but thought I'd query you'll until I can contact Trek. I have the Trek Madone 4.6 if anyone out there knows the answer.

    Thanks...

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    correct forum

    Wheels and Tires

    But possibly not. I'll go away now.
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    I was thinking the same, but it seems they only talk about brands and type of wheels and my question is about installation (i.e. the wrenching part), which is why I put it here.

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    Quote Originally Posted by Methodical View Post
    I was thinking the same, but it seems they only talk about brands and type of wheels and my question is about installation (i.e. the wrenching part), which is why I put it here.
    you can get an idea from looking at the clearance on either side of your tire and measuring your tire. Stick something sized to just fit between the tire (Like a feeler gauge if you have one) and the frame in there and measure it then multiply by 2 and add the tire width. The tire is more likely going to be what rubs not the rim, and you will need to know what your tire of choice will measure on the new rims, wider rims make the tires wider.
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  5. #5
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    Quote Originally Posted by Srode View Post
    you can get an idea from looking at the clearance on either side of your tire and measuring your tire. Stick something sized to just fit between the tire (Like a feeler gauge if you have one) and the frame in there and measure it then multiply by 2 and add the tire width. The tire is more likely going to be what rubs, not the rim, and you will need to know what your tire of choice will measure on the new rims, wider rims make the tires wider.
    This.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



  6. #6
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    There's no objective answer. It's true that the tire will be what hits first but it's essentially same question even so.

    The first part of the answer is: Enough so any flex in you bike or wheel doesn't result in rubbing.

    The second part of the answer is: Enough, if you care, to be able to get home with whatever level of un-true wheel you might want to get home with. Obviously you'e not getting home with totally destroyed wheel but un-true wheels happen so the more room you have to still be able to ride the better. Totally subjective what's acceptable here.

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    Thanks everyone for the feedback.

    I purchased a digital caliper meter and measured the distance with and without the wheel on the bike and I have 36mm to work with. With respect to tire size, I plan to run the Continental 4000 700x25 with the new wheels.

    I also measured my current set of tires (Continental 700x23) on the wheels I have now and they are 24.40 mm wide inflated to 120psi, so I figured with 25 mm wheels and tires, it would be around 26.5 mm wide based on the measurement of my current set of tires, therefore leaving me with around 10mm (5 on each side) clearance. Do you think that would be enough clearance? Or should I play it really safe and get the 23 mm wide wheels instead.

    Thanks for any insight...

  8. #8
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    5mm should be ample although I think 120psi is too high unless you weigh upwards of 250lbs. Wonder what the tire width is with 90psi or so.
    In reference to the Assault on Mt Mitchell...
    Quote Originally Posted by merckx56
    The easier solution is to find a biker bar in Spartanburg the night before, go in and pick a fight. The ass-whipping you'll get will be far less painful than the one Mitchell will give you the next day!

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    3mm on each side is sufficient clearance.

    As UpstateSCRider said, 120PSI is too much unless you are a clyde. Just because your tire has that as the max PSI doesn't mean you need to run that high. Use the 2nd box in the link below to enter your total weight (ride, bike and whatever you carry):

    Bicycle tire pressure calculator

    If you ride in an aggressive race position, you will want to change the F/R ratio from 40/60 to 45/55.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



  10. #10
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    Why not just purchase a 25mm tire and install it on your current rear wheel? Even though the rim width is different, it will give you a good idea of how much clearance you'll have i.e., close enough.

    Then return the tire and get a refund. I don't see a reason why this would be taking advantage of a bike shop.

    I did this when I was merely curious as to how wide of a tire could fit on my custom frame. In fact, I did it twice, returning a 28mm tire and trying a 32. I told the bike shop up front I'd be returning the tire unridden and they had no problem with that.

  11. #11
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    Quote Originally Posted by upstateSC-rider View Post
    5mm should be ample although I think 120psi is too high unless you weigh upwards of 250lbs. Wonder what the tire width is with 90psi or so.

    I used 120 psi so that I could see what the tire width is at max pressure. Also, I am still old school when it comes to wheel size and tire pressure, but I've come around as I've research getting a new wheel set. I will adjust tire pressure accordingly.


    Quote Originally Posted by Lombard View Post
    3mm on each side is sufficient clearance.

    As UpstateSCRider said, 120PSI is too much unless you are a clyde. Just because your tire has that as the max PSI doesn't mean you need to run that high. Use the 2nd box in the link below to enter your total weight (ride, bike and whatever you carry):

    Bicycle tire pressure calculator

    If you ride in an aggressive race position, you will want to change the F/R ratio from 40/60 to 45/55.

    Haha! No, I am not quite a clyde, just around 195 pounds. I have come around and will adjust tire pressure accordingly. Thanks for the tire pressure link. I will use it for sure.

    Update: I input my numbers and the 40/60 calculator says to inflate to 87/134 and the 45/55 says to inflate 99/123. I guess 120 is about right then. I guess I am sort of a Clyde - haha!

    What is the purpose of a lower pressure in the front tire?




    Quote Originally Posted by Peter P. View Post
    Why not just purchase a 25mm tire and install it on your current rear wheel? Even though the rim width is different, it will give you a good idea of how much clearance you'll have i.e., close enough.

    Then return the tire and get a refund. I don't see a reason why this would be taking
    advantage of a bike shop.

    I did this when I was merely curious as to how wide of a tire could fit on my custom frame. In fact, I did it twice, returning a 28mm tire and trying a 32. I told the bike shop up front I'd be returning the tire unridden and they had no problem with that.

    Funny you say this. I did just that. I received my 25s yesterday and fitted them on my current wheel and there's plenty clearance. I plan to keep the tires though.


    I use all my measurements, your comments and tips and confirmed clearance with Trek and I have decided go with the 25mm carbon fiber wheels.

    Thanks again for your help and input.
    Last edited by Methodical; 02-12-2018 at 10:22 AM. Reason: make some corrections

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    Quote Originally Posted by Methodical View Post

    I used 120 psi so that I could see what the tire width is at max pressure. Also, I am still old school when it comes to wheel size and tire pressure, but I've come around as I've research getting a new wheel set. I will adjust tire pressure accordingly.

    You might have too. Carbon clincher makers generally don't make 'em to be able to handle high pressures like that. Look into what the rating is for the one's you got.

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    Quote Originally Posted by Jay Strongbow View Post
    You might have too. Carbon clincher makers generally don't make 'em to be able to handle high pressures like that. Look into what the rating is for the one's you got.
    The wheels max is 125 psi. I will have to do some trial and error and see what I like. I've always like my tires hard on my bike, even in my muscle car. The harsh ride never bothered me, but I will try less pressure to see if I like it or not.

    I've placed the order and will just sit back and wait for their arrival.

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    I weigh about 5 pounds more than you and run Conti 25's 90 in the front and 95 in the rear. The will run about 26.5 on a 15 mm rim, 27.5 on a 19 mm rim and 28.2 or so on a 19mm rim(all internal widths)

  15. #15
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    Quote Originally Posted by Methodical View Post

    Update: I input my numbers and the 40/60 calculator says to inflate to 87/134 and the 45/55 says to inflate 99/123. I guess 120 is about right then. I guess I am sort of a Clyde - haha!

    What is the purpose of a lower pressure in the front tire?
    You don't need as much pressure in the front for a few reasons:

    1) There isn't as much weight on the front tire.
    2) There are no drive forces in the front.
    3) You have better steering control with a little lower pressure in the front. Hit a road hazard and a rock hard tire is more likely to bring you down.

    It sounds like 100F/120R would be a good place for you to start. Experiment from there. I'm pretty sure 90F/110R would work for you if 100F/120R feels too harsh. IMO, if you need to go higher than 120 PSI on any tire, you need to go to a wider tire.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



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    Thanks for the help. I will try experiment with those tire pressures and see how it feels.

  17. #17
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    Like Steelbikerider, I weigh more than you, in fact probably 200 lbs, but I also run 90/95psi with tubes, and in my tubeless wheels I run 5 or 6psi less in each, both with 25mm tires.
    I remember being old-school and running high pressures and 22 or 23mm tires, even 21's, and I think it 'feels' faster only because every little bump is amplified giving the impression of speed, but like most racing, smooth is faster.
    Good luck with experimenting.
    In reference to the Assault on Mt Mitchell...
    Quote Originally Posted by merckx56
    The easier solution is to find a biker bar in Spartanburg the night before, go in and pick a fight. The ass-whipping you'll get will be far less painful than the one Mitchell will give you the next day!

  18. #18
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    Quote Originally Posted by upstateSC-rider View Post
    Like Steelbikerider, I weigh more than you, in fact probably 200 lbs, but I also run 90/95psi with tubes, and in my tubeless wheels I run 5 or 6psi less in each, both with 25mm tires.
    I remember being old-school and running high pressures and 22 or 23mm tires, even 21's, and I think it 'feels' faster only because every little bump is amplified giving the impression of speed, but like most racing, smooth is faster.
    Good luck with experimenting.
    This.

    The main risk of running lower pressures is pinch flats.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



  19. #19
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    Quote Originally Posted by Lombard View Post
    You don't need as much pressure in the front for a few reasons:

    1) There isn't as much weight on the front tire.
    2) There are no drive forces in the front.
    3) You have better steering control with a little lower pressure in the front. Hit a road hazard and a rock hard tire is more likely to bring you down.

    It sounds like 100F/120R would be a good place for you to start. Experiment from there. I'm pretty sure 90F/110R would work for you if 100F/120R feels too harsh. IMO, if you need to go higher than 120 PSI on any tire, you need to go to a wider tire.
    Update:

    I installed the Continental 4000s 25s tires on my current set of wheels (will have to get another pair for the new wheels when they arrive) and the calculator suggests the following psi for a 40/60 split. I put 80 psi in the front though. So, this is what I will go with - 80/115.

    Front = 74
    Rear = 115

    Question. Are there any pumps out there that allows you to screw onto the presta/shrader valve instead of the flip lever types?
    Last edited by Methodical; 02-18-2018 at 09:39 AM.

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    Quote Originally Posted by steelbikerider View Post
    I weigh about 5 pounds more than you and run Conti 25's 90 in the front and 95 in the rear. The will run about 26.5 on a 15 mm rim, 27.5 on a 19 mm rim and 28.2 or so on a 19mm rim(all internal widths)
    Great. This gives me some idea of tire diameters. I measured the 25s on my Profile Design wheels with a 14mm internal width and they are 25.75" wide. The wheels I purchased are 17mm internal diameter, so it should be somewhere between the 15 and 19mm widths you listed.

    Does Continental have a chart with these figures? I will search, but asked just in case you have a link.

    Thanks

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    Quote Originally Posted by Methodical View Post
    Question. Are there any pumps out there that allows you to screw onto the presta/shrader valve instead of the flip lever types?
    Most, if not all, Lenzyne pumps do.

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    Quote Originally Posted by Methodical View Post
    Update:

    I installed the Continental 4000s 25s tires and the calculator suggests the following psi for a 40/60 split. I put 80 psi in the front though. So, this is what I will go with - 80/115.

    Front = 74
    Rear = 115

    Question. Are there any pumps out there that allows you to screw onto the presta/shrader valve instead of the flip lever types?
    I'm 185lbs and have been running 90 to 100 psi in my rears, 23 and 25mm tires. 115 seems excessive for a rear at your weight. You could probably run a few lbs less pressure with no ill effects.

    One thing to remember is that all our pumps readings are within a window and my 90psi may be 85 or 95psi on your pump. In fact your 115 could be 100 or maybe 122, so any one of us could be running more or less psi than we think.

    Once you find pressures that you like the best bet would be to use the same pump to get those pressures. If you have more than one pumps match them against each other so if you use the other one you know how many lbs to pump to on that one.
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    Quote Originally Posted by Jay Strongbow View Post
    Most, if not all, Lenzyne pumps do.
    Thanks. I will check out those pumps.

    Quote Originally Posted by velodog View Post
    I'm 185lbs and have been running 90 to 100 psi in my rears, 23 and 25mm tires. 115 seems excessive for a rear at your weight. You could probably run a few lbs less pressure with no ill effects.

    One thing to remember is that all our pumps readings are within a window and my 90psi may be 85 or 95psi on your pump. In fact your 115 could be 100 or maybe 122, so any one of us could be running more or less psi than we think.

    Once you find pressures that you like the best bet would be to use the same pump to get those pressures. If you have more than one pumps match them against each other so if you use the other one you know how many lbs to pump to on that one.
    I used the calculator with me and bike weight as specified and that's what I got. However, when I use just my body weight, it recommends 104 psi in the rear. Should I just use my body weight only?

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    A light bulb just went off in my head.

    If the tire measures wider than the stated manufacturer size when installed on a set of wheels, should I use the actual measured width for the tire psi calculator?

    For example: Continental 4000IIs 25s measure at 28mm on a set of wheels. Do I use 25 or 28mm for the psi calculator as this would make a big difference in the suggested psi?

    Thanks...

  25. #25
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    Quote Originally Posted by Methodical View Post
    Thanks. I will check out those pumps.



    I used the calculator with me and bike weight as specified and that's what I got. However, when I use just my body weight, it recommends 104 psi in the rear. Should I just use my body weight only?
    Full weight, as you did. I think of these calculators as a good place to start and then fine tune from there. A lot of things come into play that these calculators don't\can't take into calculation.

    Tire construction for one. How stiff or supple is the tire, some tires work better at lower pressures than others. Do you ride heavy or light. A "light" rider can run less pressure than a "heavy" rider. I'm not talking weight but how you ride over obstructions, some people ride thru them and others kinda gravitate over them. How strong of a rider are you, a hard sprinter will flex a rear tire more, needing more psi than a non sprinter.

    I've read most of Jan Heines take on this and he's of the opinion that there is a rather large window in the tire pressure window that "works". Too low a pressure and the tire squirms and too high a pressure and the tire bounces over obstacles\debris. Within that pressure zone the performance holds pretty much the same, and that seems to hold true in my experience.

    When I look at those calculations, like the one that gave you 104psi, I take them with a grain of salt. My pump is at 5lb increments, and is at floor level at the bottom of the pump and the hash marks are near enough to one another that I'd be lucky to get the needle between two of them.
    I have a mark that I can rotate around the gauge to index on the pressure I want and pump to it, then ride the bike for a week or two before doing any more than a thumb check. I don't notice things going south with the ride characteristics.

    On my 650b\42mm tires I'll pump to about 50rear\45front and I'm good for better than a month. In fact I've ridden those tires for as much as two months before noticing any degradation in ride quality and at that point the pressure is at about 40psi.
    But at these low pressure I wonder about the gauges accuracy. Everything works as I like it but when I read about cyclists riding these same tires at 30-40psi it leads me to believe I need a dedicated low pressure gauge for truer readings.
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