Tight frame-tire fit

My geared 29er, BlueShift, has a Big Apple tire on it right now. I started with the Nanoraptor which had quite a bit more clearance than the Big Apple. I like the ride of the Big Apple better, especially at high pressure.

Our group went on a ride Saturday and I pumped the tire up to 60psig and brought it along. It made a grinding noise like a garbage disposal. I could still barely see clearance from the top of the tire to the bottom of the crown but the wheel was slightly out of true and it rubbed occassionally. Not enough to make the horrible grinding noise I was hearing. I thought it was one of the bearings going out.

Wobbly-John was in town and he surmised that the tire picked up bits of grit and ground against the crown. I still thought that was not the problem, it was too loud. When I got home I let air out of the tire (down to 35psig) and the problem disappeared. In 5psig increments I found that I could run the tire at 50psig and still have clearance.

The tire must have stretched over time because I remember (as well as I can still remember) that I had run it at 60psig before. I left the tire deflated while stored and put a large label on it reading “50 psig MAX.”

So what made the grinding noise?

Musta been the Starbucks he was passing at the time.

Wobbly-John and U-Turn are correct. Grit from the road and coffee chaf from Satrbucks were grinding on the crown.

pics of the clearance? sounds pretty close.

You should add “also for unicyclists!” as you know unicyclists tend to ignore max pressure labels on tyres.

That’s interesting that the BA seems to have stretched. I have carefully measured my BA size when it was new. Must remember (as well as I can remember) to do it again. Although on average I have only 40 - 50 psi in there. This could be a way to increase your wheel size for free, as much as air is for free.

Clearance at 60 psig is zero. Clearance at 50 psig is 1mm. The increased wheel diameter doesn’t buy you much speed if it’s dragging on the crown.

Here’s a link to the clearance with the Nanoraptor tire.

that looks like plent of clearance.

Harper said the Nano had plenty of clearance, its the BA thats giving him the clearance problems.

Don’t worry Harper, once you’ve got a few hundred miles on the beast you’ll have worn an extra mm from the tyre and will be able to get it to 60psi no problem :D. Just get riding!


I’ve never seen the frame of blueshift up close before. That thing is beautiful. 50psi isn’t bad in the BA though. I’d be pretty happy with that.

Tire-crown clearance of BlueShift frame with Big Apple tire at 60 psig.


Tire-crown clearance of BlueShift frame with Big Apple tire at 50 psig.



The above two photos show the clearance with the Big Apple tire at the two different pressures. Sorry I got so much wash out from the flash in the second one. You can see through the frame in it at least.

I’m running a Big Apple in a Sem XL frame, and it has similar clearance issues. But I don’t think the irregularities are due to wheel imperfections, I think they’re due to tire imperfections; I noticed the problem the first time I rode the tire after building and truing the wheel. With that much air in it, slight differences in the way the tire bead is seated can make enough difference to rub the frame.

Like you, I can reliably run the tire in the narrow frame at 50 psi.

Greg, I have a Dremel with sanding drums, and a nice blue magic marker…

Why would I want to grind a rubber tire and then try to color it blue?

LOL :smiley: :smiley: :stuck_out_tongue: :smiley:

Harper, really, why not just shave a bit off the crown right there? Who needs a dremel, that could be done with a file (actually, a half round file is preferrable, since it won’t clog as readily as a sanding disc). Well, I guess I that won’t happen…

I do like the look of that frame… Is it professionaly anodized, or a homebrew job? Kudos if you did it yourself.

Steve Howard designed and built the frame. He had it professionally anodized. You know I’m not about to touch that frame with a file. How are your projects coming along? Are you buying accessories for your machine tools?