Tire Clearance (In)consistencies
 

I am not a framebuilder, but just had a custom CX frame build by a well-respected shop. I just received the frame and threw on a wheelset to check clearances, only to notice that the clearances at the seatstay, chainstay and fork are consistently inconsistent. Using an accurate caliper, I measured:

seatstay to tire: 21mm
chainstay to tire: 9mm
fork to tire: 16mm
(tire used was 32mm)

The fork clearance looks incredibly awkward to me, and I can barely increase the tire size because of the chainstay clearance. The fork looks like it was built for a 44mm tire, while the rear looks like it was built for a 32mm tire. As builders, how acceptable/unacceptable is this? Thanks for any opinions!

http://www.bikeforums.net/recreation...clearance.html

Did you tell the builder what size tires you planned on using? Lots of clearance on the fork is a Good Thing for an off-road bike, as it lessens the chance of debris causing a face-plant.

Yes, I told him the max tire size I planned on using was 32mm. He nailed it on the chainstay clearance, but the fork looks like it was built for a completely different frame. I don't plan on riding 32mm rear and 42cm front...

??? Why would you have to do that? The additional clearance offers you safety in preventing debris pick-up from jamming your front wheel.

What about the extra front tire clearance won't work for you? I don't think the frame's performance will be changed with less or more clearance. Is the fork a crowned design or carbon or unicrowned? If a crown is used then the choices available that fit the minimum specs might not be many. Andy.

That was sarcasm. Just drawing attention to the fact that max tire size doesn't match front to rear.

Aesthetically it doesn't work for me, and the fact that I requested a frame built to a max tire dimension and that was not delivered. (Side note: he did ask me what the max tire size was to be; I didn't make a special request) Sorry, but I can't answer to your other questions specific to the crown.

If you take a look at any CX bike you will find similar clearances to yours, including the variations. These are because of geometry (not cycling frame geometry, but plain old maths geometry), tube sizes for the respective frame members, and conventional wisdom. Bikes are made up of triangles. Chainstays are shorter than seatstays, so therefore come at the bottom bracket (from the axles) at a steeper angle. The tire is very close to the apex of this triangle, and the chainstays are also larger relative to seatstays, so clearances here would be narrower. On the seatstays, they have a longer distance to travel, so the angle is shallower. The tire is also nowhere near the apex of this triangle, hence the differing clearances. Forks are a good place to have as much clearance as possible as mentioned above.

It sounds like you're nit-picking about things that are normal, if not accepted. It also sounds like the frame builder accommodated your desires, you just didn't know EXACTLY what you wanted going into the build. If this was an issue for you, you should have mentioned it to them before hand.

No reason why you can't run the same size tire front and rear, yes?


Well, just that, I guess. :(

Would you have preferred less clearance above the front tire, which would mean a shorter fork length, and then a taller headtube and/or a bunch of spacers to get your bars at the appropriate stack height for you?

The difference in clearance between chainstays and seatstays is normal. As for the fork, there are really only two widths available for those fork crowns. The narrow width for road tires would not have enough clearance for your 32mm tires, so the builder really had little choice on the side clearance. The top clearance on the fork probably has something to do with the fact that 395mm seems to be the accepted standard axle to crown height for cross forks. The builder probably built the fork with a 395 ATC so that you could switch forks in the future, without affecting the geometry of the frame. This is only a guess at what happened, your builder could provide you with the actual answer.

As a side note, I find it odd that a well respected builder would hand off a bare frame to the customer.

A quick check of aftermarket forks and you will find what dsaul is saying is true.

Yep, this is all absolutely true. Got back in touch with the builder, he explained it to me, and it all makes perfect sense now. I just wish I knew that info beforehand, so that I wasn't so shocked and think something was wrong when it was finished. Either way, I was in the wrong thinking something was amiss.

As for the bare frame, I requested it bare. Just plan to give the steel and brass fillets a fine sanding/shine, apply his decals, and give it a 2k semi-gloss clear-coat.