How much clearance is enough?

I'm experimenting with fat tyres, so I switched first from 38mm Challenge Gravel Grinders to 2,0'' Schwalbe Furious Fred. Than I got a great deal on 650b wheelset components, and figured I could try that too. 
I figured that as there was ample clearance  with freds, I could go for 2,1'' Thunder Burts. Well, turns out I have about 3mm clearance on frame with Burts. Is this enough? I ride mostly paved roads (horribly maintained) and some hardpack.

Bike manufacturers would say you need much more clearance than 3mm.  However I have ridden bikes with that much tire clearance before without issues, but its really something you have to decide for yourself.  There are three issues that could cause problems and you have to decide how much of a risk you want to take:

1.  Mud packing up in between the tire and frame.  Obviously this is not an issue if you don't ride in mud.

2.  If you have a flexy frame or wheels you may get some rub when standing and pedaling hard.

3.  If you break a spoke and don't have a replacement or bang the wheel and its gets out of true, the tire may rub the frame making it hard to ride home.

... and if your frame is carbon you want to make absolutely certain that you have good clearance. Mud build up can and will turn into a grinding paste if it doesn't have room to pass through. Few years ago I just about ruined a perfectly good Ibis Hakkalügi running it through some muddy clay. After washing it off that episode left pretty bad gouging in the chainstays and fork, straight through the clear coat and paint on both. Had I not pulled over and used a stick to dislodge most of it I surely would have wreaked it.   

Yes, I thought I was pushing it. The interesting thing is that I have more clearance with 29er tyre (Fred) than with 650b ( Burt). The thing is, I really like running fatter tyres, compared to 38mm I ran originally, it's so much softer on my ass However, when running 29x2'' tyres, I feel that handling is a bit off. I think 48-50mm 650b would be my sweet spot.

I have Furious Freds on my GR250 and I love them.  The GR250 has a low bottom bracket, so the bigger tires work perfect.  But they are only about 48mm, so not a true 2.0 tire.  47mm seems to be the default size for 650b gravel tires now, so there are a lot of options in that size.  My wifes bike is using the Terrene Elwoods in 650b x 47mm.  Clement is eventually going to have 650 x 50 MSO tires.

My bike has les bb drop, so with Freds I feel kind of weird, something I can't really put my finger on and yes, it's a great tyre and super fast on  pavement, it's a crying shame that there isn't a 650b version of it. 

Nbudor wrote:My bike has les bb drop, so with Freds I feel kind of weird, something I can't really put my finger on and yes, it's a great tyre and super fast on  pavement, it's a crying shame that there isn't a 650b version of it. 

The Furious Fred is an old design, they used to have a lot of sizes, but they are phasing them out.  They were actually a horrible mountain tire, they had no traction at all.  The Thunder Burt was designed to replace it.  The real shame is that Schwalbe has not given us larger volume G-One tires.  Those tires are awesome on gravel, but 38mm (in both 650b and 700c) is pretty small by todays standards.

Well, given the increasing market for gravel bikes, naybe 650b version of Fred, or 50mm Burt would have a large audience. I totally agree on g-ones. \nBtw, Clement supposedly has the 50mm version of MSO, but none of the european sellers have it in stock for at least 4 months, have they been discontinued? \n

ridemagnetic wrote:... and if your frame is carbon you want to make absolutely certain that you have good clearance. Mud build up can and will turn into a grinding paste if it doesn't have room to pass through. Few years ago I just about ruined a perfectly good Ibis Hakkalügi running it through some muddy clay. After washing it off that episode left pretty bad gouging in the chainstays and fork, straight through the clear coat and paint on both. Had I not pulled over and used a stick to dislodge most of it I surely would have wreaked it.   

\n \nThat kind of stuff terrifies me. I've made a decision some time ago that only acceptable carbon for me would be road carbon. Gravel, MTB carbon is a no for me.

Nbudor wrote:Btw, Clement supposedly has the 50mm version of MSO, but none of the european sellers have it in stock for at least 4 months, have they been discontinued?

Apparently Clement's gravel tires were made by a sub and sold under the Clement name. Clement MSOs probably won't be restocked, but you might be able to find some Donnelly (ugh) MSOs - http://www.bicycleretailer.com/international/2017/08/28/donnelly-sports-ends-clement-license-launches-donnelly-cycling

dkoor wrote: \n \nThat kind of stuff terrifies me. I've made a decision some time ago that only acceptable carbon for me would be road carbon. Gravel, MTB carbon is a no for me.

\nWell don't ride in mud so I'm not risking that much, but I agree that I'm pushing it. I think the max my bike can teasonably handle is 50mm in 650b or 45mm 700c.

reubenc wrote:

Apparently Clement's gravel tires were made by a sub and sold under the Clement name. Clement MSOs probably won't be restocked, but you might be able to find some Donnelly (ugh) MSOs - http://www.bicycleretailer.com/international/2017/08/28/donnelly-sports-ends-clement-license-launches-donnelly-cycling

\nRealistically, this means no MSOs this year.

If you can guarantee dry conditions it might be okay. Usually you would need 5mm. It's mud that could be a problem, although in dry conditions you could still suffer frame rub and therefore paint damage.

Nbudor wrote: Well don't ride in mud so I'm not risking that much, but I agree that I'm pushing it. I think the max my bike can teasonably handle is 50mm in 650b or 45mm 700c.

Yeah... if for the most part you ride on good gravel it could be ok.

When I think of how much I tend to crash with MTB on relatively 'good' terrain it would be next to most stupid idea in my life to go MTB carbon.
And I'm talking about flat, a bit demanding off-road, with larger potholes and those irregularities only tractors can "make".

dkoor wrote:Yeah... if for the most part you ride on good gravel it could be ok.

When I think of how much I tend to crash with MTB on relatively 'good' terrain it would be next to most stupid idea in my life to go MTB carbon.
And I'm talking about flat, a bit demanding off-road, with larger potholes and those irregularities only tractors can "make".

\nA (sponsored) rider once told me to avoid carbon. You crash on a steel, titanium or aluminium bike and you can get away with dents and superficial damage, whereas carbon can shatter. The sponsored guy was just given a replacement carbon bike, of course!

chunkyhugo wrote: A (sponsored) rider once told me to avoid carbon. You crash on a steel, titanium or aluminium bike and you can get away with dents and superficial damage, whereas carbon can shatter. The sponsored guy was just given a replacement carbon bike, of course!

Makes sense.

I punched a hole in the left chainstay of my Jamis Renegade running 40mm GK’s during Dirty Kanza this year - the danger is real. I didn’t know I had done it until I got home from Kansas. A local carbon specialist repaired it and I guess it’s ok until it isn’t. I run a 35 mm in back and a 40 mm up front now.

dkoor wrote:Yeah... if for the most part you ride on good gravel it could be ok.

When I think of how much I tend to crash with MTB on relatively 'good' terrain it would be next to most stupid idea in my life to go MTB carbon.
And I'm talking about flat, a bit demanding off-road, with larger potholes and those irregularities only tractors can "make".

Maybe.  I have a 20 year old carbon mountain bike that I ride hard and put away wet.  

7 years ago if flew off the top of a car at 80mph.  Destroyed the fork and wheels, but the frame is still going strong.

Carbon hates point loads.  It doesn't make a good sword, but it is pretty tough in other loading.
Agreed - it really doesn't like abrasion.

ljsmith wrote:

The Furious Fred is an old design, they used to have a lot of sizes, but they are phasing them out.  They were actually a horrible mountain tire, they had no traction at all.  The Thunder Burt was designed to replace it.  The real shame is that Schwalbe has not given us larger volume G-One tires.  Those tires are awesome on gravel, but 38mm (in both 650b and 700c) is pretty small by todays standards.

I recently bought 650bx60mm.  They are amazing.  Agreed - more sizes would be great - not as much choice in the 700c sizes.

Well, I got myself a pair of terrene ellwoods in 47. I tried mounting them and I managed to seat the front tire in about 3 tries with my diy inflator. However, I failed to seat the rear, I have given up because I noticed that sealant is seeping through valve holes on both wheels, meaning I will have to change the tape. Grrrrr.