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  1. #1
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    I just got a roadbike. How do I know how large of tires I can put on it?

    Just picked up a neglected Peugeot at a local flea market for $60. She's a beauty, but she's also replacing my ->STOLEN<- mountain bike/DIYbrid that I've been using to commute on for years.
    It came with a 700x23c tire on the front, and a 700x28c tire on the rear. The rear tire is decent/good. The front tire is a decaying gumwall.
    I was thinking I might want to replace my rear tire with a 700x32 and move the 700x28 to the front. I've read that clearance is the concern, is there a formula or a way to check, or should I just measure out another 4mm from the current tire and see if the frame has the space? That simple, no? No other concerns?
    Thankksssss
    Val

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    No formula that I know of. You just have to check what sort of clearance you have with the tires you have now, and then make your best estimated guess at what else might fit. Keep in mind that there is a bit of spread even within the same size depending on make&model. Don't cut it too close unless you're able to return or repurpose the tire.

  3. #3
    Senior Member Bill Kapaun's Avatar
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    It sounds simple for the rear, but......
    IF you have to slide the rear wheel forward to remove it, you have to allow for that, else deflate the tire every time you want to remove the wheel.

  4. #4
    Senior Member GravelMN's Avatar
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    To make things even more complicated, tire sizes aren't consistent among brands or even from one model to another in the same brand. A tire marked 700 x 28 might actually measure 26 or 30 mm. You have to watch clearances at the stays, bridge, fork and brakes. I'm not a fan of running extremely tight clearances.

  5. #5
    Senior Curmudgeon FarHorizon's Avatar
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    Furthermore... If you're a Clyde (like me), and you're putting a wide tire on a narrow rim, be VERY wary of inflating the tire to its full sidewall pressure limit. I did so one day and went out to ride in the heat. The tire blew the Mavic rim apart (split it down the center). I survived without being skewered by the seat post (the seat broke off) or the wheel. I did not, however, escape lower back neurological damage from being dumped on the pavement at 20 mph.

    So yes, the cyclocross folks use wide tires on narrow rims, BUT - the riders weigh little, and they leave the tires at low inflation for better traction.

    So you're welcome to learn from my experience if you wish. Big tires on narrow rims will work, but be aware that you're outside the "normal" stresses that the rims were designed for.

    FarHorizon

  6. #6
    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by Bill Kapaun View Post
    It sounds simple for the rear, but.......
    I was thinking it sounds simple for the front - install your 28mm rear tire on the front rim and give it a trial fit. If you can find a 700X32 tire to borrow, you can trial fit it on the rear aand see if you have clearance issues. Personally, I've found 28mm tires are generally the biggest that will clear road caliper brakes.
    My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.

  7. #7
    rigamortis tortoise LesterOfPuppets's Avatar
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    Quote Originally Posted by Retro Grouch View Post
    I was thinking it sounds simple for the front - install your 28mm rear tire on the front rim and give it a trial fit. If you can find a 700X32 tire to borrow, you can trial fit it on the rear aand see if you have clearance issues. Personally, I've found 28mm tires are generally the biggest that will clear road caliper brakes.
    Depends on the calipers. The 105 calipers on my LeMond can clear pretty fat tires.

    When I get a bike I just go by trial and error. The Lemond came with 23s and I had a pretty big collection to choose from - 25, 26, 28, 30, 32 and 38 mm.

    32 front and 30 rear is as big as it could take. Contact point for fatter tires was fork blade in front and bottom of brake bridge in the rear. the rear might be able to handle 30mm if a wider rim was used.
    1980ish Free Spirit Sunbird fixed * 1996 Mongoose IBOC Zero-G * 1997 KHS Comp * 1990-ish Scapin * Lemond Buenos Aires Triple

  8. #8
    Senior Member RunForTheHills's Avatar
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    Are you going to put fenders on it for commuting in bad weather? That could reduce the clearance.

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    Senior Member GravelMN's Avatar
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    With some bikes from the era where <23mm tires were in fashion, the rims are very narrow compared to the average today. Measure the inside and outside width of your rims, then go to Sheldon Brown's site and look at the recommended widths.

    Tire Sizing Systems

    The vast majority of road rims will be fine with 23-28mm tire width, but wider can be an issue with very narrow rims. I had a Trek 1500 that came with very narrow rims (don't remember the actual measurement) and 28mm tires looked big on them.

  10. #10
    Senior Member Homebrew01's Avatar
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    Since you already have a 28 tire, you could just try it rather than rely on our guesses.

    Take your rear wheel off, and put it on the front. You can't actually install the rear wheel due to the axle length, but you can put the tire & rim in the brake area to see if it looks like it will work. If it's obviously "no way" because the tire hits the fork, then you saved time removing the tire & remounting. If it's questionable, swap tires & try it to be sure.
    Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike

  11. #11
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    not sure why you need to go 32s in the rear, 28s are already pretty meaty on a road bike

    Do what others have suggested, if the 28 fits the front, then get a match for the rear

  12. #12
    Senior Member SquidPuppet's Avatar
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    Quote Originally Posted by FarHorizon View Post
    Furthermore... If you're a Clyde (like me), and you're putting a wide tire on a narrow rim, be VERY wary of inflating the tire to its full sidewall pressure limit. I did so one day and went out to ride in the heat. The tire blew the Mavic rim apart (split it down the center). I survived without being skewered by the seat post (the seat broke off) or the wheel. I did not, however, escape lower back neurological damage from being dumped on the pavement at 20 mph.

    So yes, the cyclocross folks use wide tires on narrow rims, BUT - the riders weigh little, and they leave the tires at low inflation for better traction.

    So you're welcome to learn from my experience if you wish. Big tires on narrow rims will work, but be aware that you're outside the "normal" stresses that the rims were designed for.

    FarHorizon
    Curious sir. Exactly what size tire on what size rim?

  13. #13
    It's MY mountain DiabloScott's Avatar
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    Quote Originally Posted by GravelMN View Post
    Measure the inside and outside width of your rims, then go to Sheldon Brown's site and look at the recommended widths.



    Sheldon's page is spot on, noting itself that it's a little conservative.
    Still, you have to use real measurements and not trust the rim or tire labels.

    The rims on my commuter are labeled 14mm, I measured 13.5mm on the inside. My tires are labeled 37mm but they measure 32mm when installed on these rims. That puts me a little outside the box and I wouldn't push it any farther than this, but I haven't had any problems.






    http://diabloscott.blogspot.com/

  14. #14
    Senior Curmudgeon FarHorizon's Avatar
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    Quote Originally Posted by SquidPuppet View Post
    Curious sir. Exactly what size tire on what size rim?
    Thread here: catastrophic wheel failure - why?

    And to recap - the brand-new Mavic rims failed catastrophically causing permanent neurological damage - Mavic never responded to the case (to me or the wheel builder) - Mavic never replaced the rims - Mavic pretended that the failure never happened.

    I ride other rims now...

    And I wish I'd consulted an attorney when it happened.
    Last edited by FarHorizon; 12-30-14 at 12:08 PM.

  15. #15
    Senior Member SquidPuppet's Avatar
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    Quote Originally Posted by FarHorizon View Post
    No mention of rim width there.....that's what I am curious about.

  16. #16
    It's MY mountain DiabloScott's Avatar
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    Quote Originally Posted by FarHorizon View Post
    Photos all stripped from the old thread???
    http://diabloscott.blogspot.com/

  17. #17
    Senior Curmudgeon FarHorizon's Avatar
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    It's an OLD thread - Photos probably deleted over time. I don't recall the model # or width of the rim. It was intended as a touring rim, so I'm pretty sure that it was supposed to be for larger tires.

  18. #18
    rigamortis tortoise LesterOfPuppets's Avatar
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    Thread mentions long split in intertube. This is often an indication of tube being trapped under tire bead upon installation. More the fault of tire installer than Mavic.

    Even though it says split was on spoke side of tube. Tube may have been twisted a bit, as can happen when it's trapped under the bead.
    1980ish Free Spirit Sunbird fixed * 1996 Mongoose IBOC Zero-G * 1997 KHS Comp * 1990-ish Scapin * Lemond Buenos Aires Triple

  19. #19
    Senior Member GravelMN's Avatar
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    Quote Originally Posted by FarHorizon View Post
    Furthermore... If you're a Clyde (like me), and you're putting a wide tire on a narrow rim, be VERY wary of inflating the tire to its full sidewall pressure limit. I did so one day and went out to ride in the heat. The tire blew the Mavic rim apart (split it down the center). I survived without being skewered by the seat post (the seat broke off) or the wheel. I did not, however, escape lower back neurological damage from being dumped on the pavement at 20 mph.

    So you're welcome to learn from my experience if you wish. Big tires on narrow rims will work, but be aware that you're outside the "normal" stresses that the rims were designed for.

    FarHorizon
    I don't recall the model # or width of the rim. It was intended as a touring rim, so I'm pretty sure that it was supposed to be for larger tires.
    Sorry to hear about your injuries, but I'm a bit confused, was this a narrow rim with a tire larger than it was designed for, or a touring rim made for wide tires?

    _______________


    OK, found more info in your old thread:

    Quote Originally Posted by FarHorizon View Post
    Facts are as follows:

    This wheel was 36-spoke, 3-cross, custom built, tensioned, and true.
    The wheel had about 500 miles on it when it detonated.
    The tire was a WTB Slickisaurus 700x37c inflated to (Mfg. recommended) 85 psig.
    Rev Chuck who states he built the wheels for you adds:

    I built this wheel and three otherss for FH. It was built up to Mavics spec for tension using a Park tensionmeter to measure.
    It is a CXP 33. And it was picked over the Deep V because of the inserts, my reccomendation.
    The Mavic CXP33 is a lightweight road/tri rim with an ETRTO of 622x15. The maximum tire width recommended by Mavic is 28mm. You were running 37mm tires at the maximum pressure on a touring bike. According to Bicycle Quarterly per Sheldon Brown's Website a 37mm tire with a 150 pound load per wheel the recommended pressure is still only around 70 psi. http://www.bikequarterly.com/images/TireDrop.pdf . If my calculations are correct that means for 85 psi to be a correct rear tire pressure, with a 60R/40F weight distribution, you would be looking at about 300 pounds combined weight of bike and rider. Combine a heavy load with an inappropriate tire width for the rim and that's asking a lot.

    It looks like you picked the wrong rim for the job. If you wanted strong touring rims for 37mm tires, Mavic A319 or A719 would have been much better choices. Without pictures or other info it's hard to tell just what happened but it's hard to blame Mavic if you were using tires way outside of the manufacturer's recommendations.
    Last edited by GravelMN; 12-30-14 at 05:30 PM.

  20. #20
    Senior Curmudgeon FarHorizon's Avatar
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    I didn't select the rim. I selected the wheel builder, described my needs, and he built the wheels.

    Nevertheless, it's water under the bridge. The rim was used with wide tires but within the sidewall pressure of the tire. The rim failed catastrophically. I bring it up because the title of this thread seemed to warrant it.

    And, as I recommend to the OP - be wary of exceptionally wide tires on narrow rims.

  21. #21
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    Hey y'all... thanks for the responses. There's a community bike shop in this town that's open Sundays and Wednesdays (but not today) where I've been putting in a dozen hours or so a week. It's pretty disorganized, but there are mountains (literally) of virtually every type of component you can imagine. I guess I'm just going to see what fits this Sunday.. I'll keep in mind that markings are more or less meaningless! There isn't much clearance left (~6mm to frame), I'll probably end up just keeping the 28 on the back and getting a better front tire, probably a 25 or a 28. Depends a lot on what's available in the mountain in good condition.

    Also:
    not sure why you need to go 32s in the rear, 28s are already pretty meaty on a road bike
    because I'm coming off a hybridized mountain bike and have BMXer experience/lifestyle, so it's a little hard for me to resist jumping up curbs/flying off them. Not tryin'a eat pavement though, so I've resisted. I'd just like something a little meatier/lower PSI/that's not gonna pop if I'm bunny hopping. I know the response to this is "that's not the right bike for what you're doing, then."

    Are you going to put fenders on it for commuting in bad weather? That could reduce the clearance.
    Nah, but good thing to consider, thanks for mentioning!

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