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Recreational Cyclocross and Gravelbiking This has to be the most physically intense sport ever invented. It's high speed bicycle racing on a short off road course or riding the off pavement rides on gravel like :The Dirty Kanza". We also have a dedicated Racing forum for the Cyclocross Hard Core Racers.

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Old 05-11-13, 06:38 AM   #1
wheelingmike
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Widest tire question

I'm not sure which forum to ask this question so I will start here.

I have a set of Shimano R500 wheelset that I would like to use on my cross bike. I want to know what is the widest tire that will fit? Is the number in the manual, which is 28 mm, absolute? What happen if I try to squeeze a 30mm (or maybe even a 32mm) tire on it?

Here's a link to the manual. http://www.shimano.com/media/techdoc...9830667569.pdf

Thanks!
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Old 05-11-13, 07:10 AM   #2
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Originally Posted by wheelingmike View Post
I'm not sure which forum to ask this question so I will start here.

I have a set of Shimano R500 wheelset that I would like to use on my cross bike. I want to know what is the widest tire that will fit? Is the number in the manual, which is 28 mm, absolute? What happen if I try to squeeze a 30mm (or maybe even a 32mm) tire on it?

Here's a link to the manual. http://www.shimano.com/media/techdoc...9830667569.pdf

Thanks!
Do I understand that regarding this safety-related question you don't trust the authoritative, highly-reputed manufacturer to provide you the prudent answer, but prefer to ask the 41, a group of cycling folks with as broad a spectrum of ignorance to knowledge as ever existed? And you expect to get a coherent, uniform, and convincing answer to your question that will trump the information provided by the manufacturer. Is that correct?
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Old 05-11-13, 07:22 AM   #3
wheelingmike
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Do I understand that regarding this safety-related question you don't trust the authoritative, highly-reputed manufacturer to provide you the prudent answer, but prefer to ask the 41, a group of cycling folks with as broad a spectrum of ignorance to knowledge as ever existed? And you expect to get a coherent, uniform, and convincing answer to your question that will trump the information provided by the manufacturer. Is that correct?
Well, the wording from Shimano suggests it is just a recommendation - "In order to realize the best performance, we recommend that the following combination be used". If it states "28mm Max" then no question ask. I'm just trying to see if anyone has any experience with putting a wider tire than the manufacturer "recommends". Thanks.
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Old 05-11-13, 07:44 AM   #4
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You'll probably get better answers from the mechanics forum. But, how wide you can go depends on the interior width of the rim, the brake bridge on the bike and the reach of your brakes. I agree that the manual is a guideline, not definitive, since, like tire pressure guidelines on tire walls, such things are dictated by a combination of best performance recs and conservative lawyers that set standards well below tolerances.

As far as rim width, ,you can get pretty much any size tire on just about any width rim of the same circunference, which isn't to say that's a good idea. See chart in attached for some guidelines (toward bottom of article).
http://sheldonbrown.com/tire-sizing.html

The other two issues I assume are not germane since you are using cross frame which should accommodate a wide range of tires.
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Old 05-11-13, 08:13 AM   #5
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Seriously? I think your huge risk is a sloppy ride if the wheel & tire can actually fit on the frame with sufficient clearance ... that's about it. If its a super heavy duty tire like Marathons on a narrow rim I think you may risk a blow off going through a pothole, but I think you'll see the problem in advance because they'll be next to impossible to get on the rim in the first place.
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Old 05-11-13, 08:31 AM   #6
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What is the interior width of the rim? Go to Schwalbe's website for tire width/rim recommendations. Then get your ruler out, and measure the clearance around your current tires.
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Old 05-11-13, 08:37 AM   #7
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Any 700C tire you can fit under your cross bike will work fine with that rim. As others have pointed out, the Shimano recommendation is not hard and fast, and in fact is quite conservative. In the early days of 29ers, the Mavic Open Pro rim was quite popular and worked fine with fat tires. As Sheldon himself wrote, "Many cyclists exceed the recommended widths with no problem."
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Old 05-11-13, 09:31 AM   #8
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Giving a quick look at Sheldon's table and ETRTO standards (via Schwalbe's site), I very much doubt there are any safety concerns at play with using wider tires. 20.8mm rim width translates to around 17mm inner width for most rims (subtract around 4mm). Your rim may be a bit different, so measure first.
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Old 05-11-13, 09:41 AM   #9
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Originally Posted by rpenmanparker View Post
do i understand that regarding this safety-related question you don't trust the authoritative, highly-reputed manufacturer to provide you the prudent answer, but prefer to ask the 41, a group of cycling folks with as broad a spectrum of ignorance to knowledge as ever existed? And you expect to get a coherent, uniform, and convincing answer to your question that will trump the information provided by the manufacturer. Is that correct?
roflmao!
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Old 05-11-13, 09:48 AM   #10
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I measured the interior width of the rim with a caliper and it's 15.29 to 15.40 mm. According to the Shelton's table, I should be able to fit as big as 32mm tire and still be in the green zone. Thanks for the replies.
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Old 05-11-13, 04:22 PM   #11
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Originally Posted by rpenmanparker View Post
Do I understand that regarding this safety-related question you don't trust the authoritative, highly-reputed manufacturer to provide you the prudent answer, but prefer to ask the 41, a group of cycling folks with as broad a spectrum of ignorance to knowledge as ever existed? And you expect to get a coherent, uniform, and convincing answer to your question that will trump the information provided by the manufacturer. Is that correct?
Rolling my eyes so hard at this. It's not rocket science...most cross bikes roll on standard road wheels. Do you really think Shimano did extensive testing and found that a 700x28 is the widest tire that fits safely on these wheels?

It's dumb to blindly believe everything you read on the internet. It's also dumb to discount everything you read on the internet.
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Old 05-17-13, 08:27 AM   #12
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I'll run 32s on mine, no problems, chainstays are wide enough to take it. I dont pump them up as hard as I could do though, maybe about 60psi, so its ok in the mud but runs a risk of snakebite flats if I hit something harder. You pays your money and takes your chances
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