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27" to 700C Conversion Woes

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27" to 700C Conversion Woes

Old 02-27-13, 09:39 PM
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27" to 700C Conversion Woes

I posted this in the 'show me your conversion' thread, but thought that it might get more views/help in its own thread.

My '73 World Voyageur previously had 27 inch wheels with 27x1-1/4 tires on it.

I got some CR18 wheels and put the only available tires I had on them - Bontrager 32 mm 'race' all weather hard case. The rear wheel went in fine, but for some reason, the front wheel is rubbing on the fender where the fork crown is. These '32mm' tires seems a little bit wider than my 27x1-1/4 tires for some reason. What am I doing wrong? When I yanked out the 700c wheel and tire and threw the 27" back in - no rub at all.

Is it possible that this 700c and tire combo is taller, thus causing rubbing?
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Old 02-27-13, 09:41 PM
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Sounds like the tire's profile is taller than your 27's were... get a different tire?
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Old 02-27-13, 09:42 PM
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Is that even possible? Is there a profile difference between similar width tires?
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Old 02-27-13, 09:46 PM
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I would check the fender fit. Also, actual tire sizes are not a perfect match to the labeled size.
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Old 02-27-13, 09:51 PM
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Originally Posted by Barrettscv
I would check the fender fit. Also, actual tire sizes are not a perfect match to the labeled size.
What do you mean check the fender fit? Everything is aligned correctly, as far as I can tell. Though, I do find it strange that there is clearance everywhere but the area in the fork crown. Why would this be?
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Old 02-27-13, 10:14 PM
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That's the one area where you have little adjustment compared to the rest of the circumference of the fender.

Your 700c tire probably has a taller profile than the 27" tire, even though they're nominally the same width and the 700c tire has its bead 4mm closer to the axle of the hub. It happens.
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Old 02-27-13, 10:17 PM
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We do not know how your fender is attached. Is it rubbing on a a fender bolt that hangs down from the fork crown, or is it rubbing on a fender carrier? I do not know the measurements for 27x1.25 tires off hand, but my guess is that they would be closer to 28mm than 32. That should roughly even everything out though, right? I assume the clearance must have been pretty close before the conversion.
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Old 02-27-13, 10:17 PM
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Originally Posted by DiegoFrogs
That's the one area where you have little adjustment compared to the rest of the circumference of the fender.

Your 700c tire probably has a taller profile than the 27" tire, even though they're nominally the same width and the 700c tire has its bead 4mm closer to the axle of the hub. It happens.
If I buy new tires, how can I be sure they'll not have as tall a profile? Should I just go for 28mm width?
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Old 02-27-13, 10:20 PM
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Originally Posted by acoffin
We do not know how your fender is attached. Is it rubbing on a a fender bolt that hangs down from the fork crown, or is it rubbing on a fender carrier? I do not know the measurements for 27x1.25 tires off hand, but my guess is that they would be closer to 28mm than 32. That should roughly even everything out though, right? I assume the clearance must have been pretty close before the conversion.
Good call. The only thing it could rub on from the inside is the nut from the daruma.

1.25 inches is 31.75mm, so I guess that extra .25mm (or more) was too much?
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Old 02-27-13, 10:31 PM
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Originally Posted by EdgewaterDude
Good call. The only thing it could rub on from the inside is the nut from the daruma.

1.25 inches is 31.75mm, so I guess that extra .25mm (or more) was too much?
^ And I bet there is .25mm of bolt that could be ground off or cut below the nut. I have been there before.
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Old 02-27-13, 10:36 PM
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Originally Posted by EdgewaterDude
Is that even possible? Is there a profile difference between similar width tires?
It can very between different models in brands even... so yes. So got a plan yet?
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Old 02-27-13, 10:45 PM
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I went down and checked a few things. I thought that maybe I could grind off a little bit of the daruma bolt. There isn't much sticking out, or not enough that I feel comfortable filing away.

Second, I did my best to measure the height difference between the two tires. I don't have a digital caliper, but it seems the Bontagers mounted these wheels are wider than 32mm and really bulky for some reason. They're definitely taller than the tire that was on the 27". I think it's crazy that even though I decreased wheel circumference by 4mm, I must've gained it back and then some with a bulky tire.

Now I'm trying to look around for 28mm tires. I figure those ought to be a safe fit in the fork, or so I hope.
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Old 02-27-13, 10:51 PM
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Never tried the Bontragers, but in Conti, the Gatorskins in 700x28 measure 28mm in width on a 19mm rim. Conti GP4 Seasons in 700x28 measure 26mm in width on the same rim. Height is different as well (the Gators are taller). It happens.
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Old 02-28-13, 01:09 AM
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Originally Posted by EdgewaterDude
I went down and checked a few things. I thought that maybe I could grind off a little bit of the daruma bolt. There isn't much sticking out, or not enough that I feel comfortable filing away.

Second, I did my best to measure the height difference between the two tires. I don't have a digital caliper, but it seems the Bontagers mounted these wheels are wider than 32mm and really bulky for some reason. They're definitely taller than the tire that was on the 27". I think it's crazy that even though I decreased wheel circumference by 4mm, I must've gained it back and then some with a bulky tire.

Now I'm trying to look around for 28mm tires. I figure those ought to be a safe fit in the fork, or so I hope.
My understanding was in a perfect world 32mm 700c is the same as 27x1.25 so if the tire was somehow "beefier" for lack of a better word, it kind of makes sense.
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Old 02-28-13, 07:44 AM
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i dont know specifics, but id say that 700x23 are almost an inch shorter than 700x32's. ive fit 700x23's on a 26 inch mountain bike frame.
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Old 02-28-13, 08:24 AM
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Originally Posted by EdgewaterDude
I went down and checked a few things. I thought that maybe I could grind off a little bit of the daruma bolt. There isn't much sticking out, or not enough that I feel comfortable filing away.

Second, I did my best to measure the height difference between the two tires. I don't have a digital caliper, but it seems the Bontagers mounted these wheels are wider than 32mm and really bulky for some reason. They're definitely taller than the tire that was on the 27". I think it's crazy that even though I decreased wheel circumference by 4mm, I must've gained it back and then some with a bulky tire.

Now I'm trying to look around for 28mm tires. I figure those ought to be a safe fit in the fork, or so I hope.
Rather than use a nut with the daruma bolt, trim the daruma bolt, enlarge the hole in the fender and use the shortened female end of a seatpost binder bolt as the "nut". This will increase the clearance by a few mm.
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Old 02-28-13, 11:47 AM
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Originally Posted by ColonelJLloyd
Rather than use a nut with the daruma bolt, trim the daruma bolt, enlarge the hole in the fender and use the shortened female end of a seatpost binder bolt as the "nut". This will increase the clearance by a few mm.
^This is genius! Thank you, Colonel, for sharing your brilliance.
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Old 02-28-13, 12:25 PM
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I can't take credit for it. It was southpawboston who shared the trick with me.
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Old 02-28-13, 01:11 PM
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I'm late to the thread, but if the 27" tires are older, they might have been made in a time when tires weren't as "honestly" sized as they are now: https://sheldonbrown.com/tire-sizing.html#dishonest
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Old 02-28-13, 02:19 PM
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I go with the profile theory- but it is in fact 700C tires that usually vary widely even while marked the same sizes-

In fact almost any tire you actually take a ruler out aand measure comes in at a narrower width than marked- usually about a full 1/8"

I had a 32 mm on the back of my motorized cruiser, I had to take off- although it went on the 18mm rim, the profile was tall, and I noticed this mushy feeling back there- the profile was too TALL for the rim width and actually bending sideways too much to feel right- the 28mm works fine with no sway

here it is with the 32mm still
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Old 02-28-13, 02:58 PM
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World Voyageur! Pics please!
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Old 02-28-13, 06:29 PM
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Originally Posted by ilikebikes
World Voyageur! Pics please!
Boom!

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Old 02-28-13, 06:39 PM
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I guess I've just been lucky, but every 27 inch to 700c has been no problem for me.Pretty much just slap them in and adjust the brake pads. Just lucky I guess.
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Old 02-28-13, 08:35 PM
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Originally Posted by manicmike
I guess I've just been lucky, but every 27 inch to 700c has been no problem for me.Pretty much just slap them in and adjust the brake pads. Just lucky I guess.
Have you used larger tires with fenders? I know that I wouldn't be having this issue if it weren't for the fender being there.
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Old 02-28-13, 08:50 PM
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I can't even get fenders in my 700c frame up front. But that's a whole other issue..
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