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P-38 Front wheel clearanceI recently purchased a new P-38 Ultegra with 20" 406 front wheel equipped with a Schwalbe Durano 23 mm tire. The front tire fork clearance is minimal. In fact, if I pump the Durano to full pressure, it rubs the fork crown. The only practical way to ride is to under inflate the Durano to between 85 and 90 pounds. This doesn't seem to adversely effect the bikes performance; but even with this under inflated tire, I regularly pick up road grit and pebbles which cause the tire to rub the fork crown. In one case, I picked up a small pebble while descending at 40+ mph. The pebble caught in the fork crown, and seriously gouged the tire. Very scary! Continental makes a less hefty 23 mm 406; but I've been warned bt Tim B., that this tire is extremely hard to mount, and not recommended. Is there any other 406 tire on the market, that may give me better fork clearance --- or is there any other solution to this problem?
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P-38 Front wheel clearance
Tim B. kindly returned my phone call yesterday; and gave me some more info. about P-38 front wheel clearance. My Ultegra P-38 is a performance oriented machine. It uses a uni-crown fork which is both lighter and stronger than a traditionally dual brazed fork crown. The down side to the uni-crown design is limited wheel clearance of about 1/8" using high performance 23 mm tires like the Shwalbe Durano which came with my bike. Tim offered to switch out my fork with a traditional fork using dual brazed crown. The old style fork will accommodate wider tires and fenders; but at the cost of significant weight gain. I'm a confessed weight weenie and performance nut-- I'll stick with the uni-crown fork and put up with occasional problems with road gunk and such. If however, you are into touring, and want to use fatter tires or a fender, then the old style fork is the way to go.
tight fit between fork & tire plus tight fit between tire & rim
Hi again Bob,
Some ideas off the top of my head:
Sounds like you have two separate fit problems: 1) fitting a Schwalbe Durano-shod wheel into your Lightning fork, and 2) fitting Continental tires - such as the Gran Prix - onto your front rim.
Tim can supply the P38 with a variety of different forks. I am not sure exactly which fork you have on your bike. But it sounds like the bike you have is equipped with the unicrown-style fork that was previously used with the 16" and 17" wheels. Lots of extra room when used with 16" or even 17" wheels. Not so with the ISO 406 20" wheel.
I am assuming that you have a caliper brake mounted on the rear of the fork, and that your fork is rigid, not suspended.
I am using a fork like this on one of my Lightning bikes, and as you say, the fit is EXTREMELY tight, even with skinny ISO 406 tires. Fatter tires are impossible to fit. I am using a Continental Gran Prix 406 tire, and there is just barely enough room to squeeze into the fork. My fork has V-brake studs mounted in front for a 16" ISO 349 front wheel, but I wanted to try the larger 20" ISO 406 wheel instead. So I put a caliper brake on the rear of the fork.
I would write to Tim at Lightning about this problem. He might be willing to do a fork switch with you, so that you could get something roomier. It is nice to have the freedom to mount fatter tires sometimes, such as the Greenspeed Scorcher. This gives a much cushier ride. It is also nice to have room to mount a front fender.
Regarding the rim / tire fit problem: With some rims, the Conti tires are a royal pain in the ass to mount and remove. With other rims, it is no big deal to get it on and off. There is a range of variation in rim size, even when all rims are alleged to be ISO 406. Likewise tires can run a tiny bit large or small. Get the combination of a ever-so-slightly large rim, and an ever-so-slightly small tire, and you have a major mounting/dismounting problem.
With a Velocity Aeroheat rim, the Conti Grand Prix goes on and off without much trouble. With a Velocity Razor rim, I lose skin on my hands trying to get the damn thing on and off. The Razor is a little bit more narrow in width.
Safe riding,
Joel
P-38 front tire clearance.
Hi Joel - thanks for all of that useful info. I think my best step is to contact Tim for a fork replacement. In my neighborhood, it's "chip seal" season. Not that riding on fresh chip seal is fun on any bike; but on my P-38, with it's narrow front wheel clearance, it's impossible.
Cheers - Bob
PS: I'm not a stranger to tight rim/ tire combinations. An engineer from Zip once explained the problem to me. There is some variability allowed in both rim diameter and tire bead diameter for any particular size. Neither wheel nor tire manfacturer's want to be sued in the event of a tire blow off. Therefore many wheel rims are built a bit on the large size, and tire beads a bit tight. Some combinations are just about impossible to mount- eg. Zipp 404 and Conti GP's.
PPS: Not sure why Tim's forks are so tight. My guess is that there are issues with brake caliper reach. If he designed a fork with more clearance, he might be forced to use custom break calipers with longer reach. Custom anything costs big bucks for a small manufacturer.
Front tire clearance
I'm using a Velocity Aerohead (not Aeroheat) rim, with a Schwalbe Durano 28-406 and I seem to have enough clearance not to experience the same road grit problems that you have. On the other hand, it's the dry season here and I haven't run into chip seal.
There used to be little metal and plastic gizmos you could mount on your bike that would lightly brush crud off the tires as they rotated. I haven't seen them on the market for 30 years, though.