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Minimum Safe Front Tire Clearance

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Minimum Safe Front Tire Clearance

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Old 06-28-18, 12:20 PM
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Minimum Safe Front Tire Clearance

So I see my front tire (32c) clearance is about 8mm (bottom of the fork crown).
I want to increase the cushiness factor.
I want to put a Northstar handlebar, and ride more upright...so I reckon a wide tire is in order.

If I go for a Panaracer Pasela 700x38, then the clearance is 2mm by my calculation 8-(38-32)=2.

Is 2mm enough?
My concern is will it lock up the front wheel, if some debry gets jammed into there while I'm bombing down a hill?

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Old 06-28-18, 12:31 PM
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2mm clearance wouldn't bother me, but don't trust advertised widths as an indicator of actual width or height.
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Old 06-28-18, 01:05 PM
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Originally Posted by tyrion View Post
2mm clearance wouldn't bother me, but don't trust advertised widths as an indicator of actual width or height.
Same.
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Old 06-28-18, 01:33 PM
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The 23's I originally put on the 84 Nishiki road bike I acquired were beating me up. So I put 700 by 32s on a few years ago. The clearance at the fork crown and rear brake Bridge were a millimeter at best. I could only inflate the tires to 85 PSI before they would rub. This worked out okay except when the occasional pothole or bump world cause the tires to rub momentarily. Over the 5 years of these tires I never had a problem with debris causing damage...or the occasional rubbing.

For what it's worth I am now running 28s at 90 to 95 PSI, and I am happier with the clearance both at the tops and in the rear, especially with regard to the chain stay.

Also, on my main commuter I am running 700 x 35, which leave about a millimeter or so with my full fenders, and while debris gets spun around and shot out occasionally, even that hasn't caused damage.

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Old 06-28-18, 02:55 PM
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just the fork crown is the concern? take an angle grinder to it & take off a mm or two
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Old 06-28-18, 02:57 PM
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Originally Posted by rumrunn6 View Post
just the fork crown is the concern? take an angle grinder to it & take off a mm or two
Same issue with the back...the piece of metal going across the seat stays have ~8mm clearnace with tire.
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Old 06-28-18, 06:17 PM
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Originally Posted by mtb_addict View Post
Same issue with the back...the piece of metal going across the seat stays have ~8mm clearance with tire.
don't want to grind that, that's for sure. unless you build something new to bridge that span
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Old 06-28-18, 06:44 PM
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I think there are some websites that measure tire sizes.

But the only way to know for sure is just to get one or two tires, and try them out.

You can check your local bike co-op and see if they have some battered tires that you can play around with.

FAT tires can cause issues with mounting tires and brakes... usually not insurmountable (mount flat?), but it can be a pain.

Also, lateral clearance can be an issue if the wheel goes out of true, broken spoke, or even if the rear wheel shifts slightly in the dropouts.
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Old 06-28-18, 07:59 PM
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Tight clearances are NP except during winter in heavy snow or slush.
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Old 06-29-18, 09:12 AM
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Originally Posted by mtb_addict View Post
Same issue with the back...the piece of metal going across the seat stays have ~8mm clearnace with tire.
That's called the brake bridge whether or not it is where a caliper brake is mounted.

I just put nominally 28mm tires on my road racing bike, and there was a 1mm gap between the rear tire and the seat tube. The tires' width was 29mm by my caliper. It made me nervous, so I swapped tires from another bike of mine. The others were also nominally 28mm, but they measure 27mm, so now I have 3mm which I'm OK with. And tires aren't completely round in profile, so while height is proportional to width, they are not always the same.
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Old 06-29-18, 09:25 AM
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Originally Posted by noglider View Post
1mm gap between the rear tire and the seat tube
I've noticed my contemporary road bile is tight in this area too. OK with the 25s I use but sometimes wonder about 28s.



steel bikes from the '70s always had gobs of room at that spot

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Old 06-29-18, 09:42 AM
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@rumrunn6, wait until you see the next incantation of my 1971 Raleigh Super Course. I'm switching from 27" to 700c, and I have 37mm tires to go on it. Gravel bike!
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Old 06-29-18, 10:00 AM
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Originally Posted by noglider View Post
@rumrunn6, wait until you see the next incantation of my 1971 Raleigh Super Course. I'm switching from 27" to 700c, and I have 37mm tires to go on it. Gravel bike!
Have you measured to see if this will work. I had 700c x 35s on my 72 SC and the clearance was way tight. I'm using 32s right now.

To the OP (and also @noglider): Have you considered using 650b wheels? I converted a 90s Bianchi road bike to 650b a year or two ago to use fatter tires and it turned out great.
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Old 06-29-18, 11:04 AM
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Originally Posted by noglider View Post
@rumrunn6Gravel bike!
sounds like a fun project! you got some gravel down in NYC?
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Old 06-29-18, 11:16 AM
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Originally Posted by rumrunn6 View Post
sounds like a fun project! you got some gravel down in NYC?
Probably, but I don’t know. I ride it upstate on the weekends. I’ve been going to Minnewaska State Park Preserve, and now I can take it to the Mohonk Preserve.
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Old 06-29-18, 12:55 PM
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@Hoopdriver, I have considered 650b but I don't think it will be necessary. I will see how those tires fit.
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Old 06-29-18, 02:01 PM
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the current caliper brake wont work with 650b rims. would need longer brakes arms.

maybe get some drum brakes...interesting.

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Old 06-29-18, 02:33 PM
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No, don't get drum brakes. They're crazy heavy.
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Old 06-29-18, 05:55 PM
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Originally Posted by noglider View Post
@Hoopdriver, I have considered 650b but I don't think it will be necessary. I will see how those tires fit.
Yep, if you can fit your desired width that would be great. Even with the smaller diameter wheels, I still had to dimple the chainstays for additional clearance

Originally Posted by mtb_addict View Post
the current caliper brake wont work with 650b rims. would need longer brakes arms.

maybe get some drum brakes...interesting.
Yeah, I had to mount Tektro R559's. I'm pleased with them.

Originally Posted by noglider View Post
No, don't get drum brakes. They're crazy heavy.
I have drum brakes on my commuting bike. I think they are perfect for my use as they work reliably in all weather, provide good modulation of braking, and don't produce that black aluminum muck that rim brakes do in wet weather. That said, they are certainly heavy and thus I would only recommend them for an all weather use.
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Old 06-30-18, 05:27 AM
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Originally Posted by mtb_addict View Post
If I go for a Panaracer Pasela 700x38, then the clearance is 2mm by my calculation 8-(38-32)=2.

Is 2mm enough?
My concern is will it lock up the front wheel, if some debry gets jammed into there while I'm bombing down a hill?
When pushing my luck on clearances, I find it's better to just buy and install the tires and see how they look. There's variation in width and height versus nominal size, and the math can only take you so far.

Originally Posted by noglider View Post
@rumrunn6, wait until you see the next incantation of my 1971 Raleigh Super Course. I'm switching from 27" to 700c, and I have 37mm tires to go on it. Gravel bike!
Post photos! Sounds like a fun bike. What tires did you find that are 37s instead of 38s?
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Old 06-30-18, 08:13 AM
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Originally Posted by Archwhorides View Post
Tight clearances are NP except during winter in heavy snow or slush.
Oh, yeah...that. My snow bike has at least an inch of clearance.
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Old 06-30-18, 09:49 AM
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I put two drum brakes on a Surly Cross Check, already a heavy frameset. It was a waste of mass for my kind of riding.

But they suit some purposes very well. That's what they use on the fleet on Citi Bike. The bike weighs 50 pounds, an absolute tank. But it's the right bike for the job, since all kinds of people ride them and abuse them. Drum brakes have the longest maintenance interval of all bike brakes, and they are very reliable except perhaps on mountains, but we have no mountains here.
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Old 06-30-18, 09:06 PM
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Originally Posted by noglider View Post
@rumrunn6, wait until you see the next incantation of my 1971 Raleigh Super Course. I'm switching from 27" to 700c, and I have 37mm tires to go on it. Gravel bike!
I'm patiently planning the same project for my 1985 Schwinn Traveler, which is already single speed. It's not an urgent need, and my existing tires still have plenty of rubber left, so I'm just waiting for clearance sales. Rims are on hand, and tires are on the way.

Meanwhile, I checked the clearances every way past Sunday.
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Old 07-01-18, 09:59 AM
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My commuter has 1/8" of clearance under the fenders. Studs keep the space clear but it adds a little drag in certain snow conditions. In dry snow conditions the rooster tail is pretty cool.

Originally Posted by BobbyG View Post
Oh, yeah...that. My snow bike has at least an inch of clearance.

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Old 07-01-18, 12:33 PM
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My drum brakes are on my antique stumpjumper,
they're perfect for when the road ices over

and stopping on black ice needs be carefully modulated,
so the studded tires still bite .

I cut the front mudguard so the fork crown itself is the lowest clearance,

the rest of the mudguard was attached to the front of the fork..
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