Re: Skyhawk frame build / thoughts
Hi, 26" x 2.125" rims will clear forks and frame with Fat Fanks "Schawalbe" 2.351" front & rear Fat Franks are a tall tire and clear my Rock Shox mountainbike suspension tire vertically with one half inch to spare. The same tire clears the fork side to side by about 3/8" on each side. Where it gets tricky is at the rear. The fat Franks clear the rear "fender brace support" also by about 1/2" ....many of us don't care for front or rear fenders on most of our builds because of past epic wrecks caused by fender/tire lockup. The Grubee frame design isn't very fender friendly with larger tires, I don't think fenders are a good idea on this frame especially with large tires & wheels. The Skyhawk Grubee frame takes a bit of work to accept a wide tire on the rear, chain contact with the wide tire is to be expected on both the pedal drive side and the motor drive side, with wheel & tire sizes over 1.75" wheel & 1.95" tire. Also remember a wider wheel mounted with a narrow tire makes the tire flare out, looking much larger cause it requires more space.
Photos of my Skyhawk Indian Navaho build can be seen on the Vintage bike/ Board track sub-forum of this site. Titled "Indian sabor/flavor". I used a modified Grubee GT 5 66cc for this build & don't have chain to tire contact problems with the larger wheels and tires mentioned earlier & with about a 100 hrs now total on the frame & 3 motors (I use this bike to break in engines for the other bikes I build) so I'm pretty certain the combo presented here works. I even ran a rear "bobbed rear fender" for awhile till noticing it was rubbing TDC!
To gain pedal side chain to tire clearence I installed a 3 piece 68mm bottom bracket x 105mm cartridge in a Euro style conversion kit that fits into the 2" american style bracket shell that the Skyhawk is designed with . If a bit more room is necessary I use frame spacer washers on the axle to keep the chain from rubbing the frame. Remember that most changes to a bikes drive line will effect other relationships. Tire centered, chain lines not staight, wheel & tire cocked, parts rubbing etc. I use a 2 piece Manic style hub to sprocket adaptor & coaster brake with a 2" center sprocket hole to allow the bent coaster brake lever to clear the sprocket & an axle spacer washer to help clear the frame. It's all pretty tight clearance, but no chain rub. It's not rocket science, but making everything work correctly while fitting more robust parts can be a challenge & you won't often just stumble into satifactory solutions.
I'm certain that I could go with a bit larger tires on my Skyhawk probably 2.5" but any larger would test my day to day patience to the point of not enjoying my build and since I use multiple motors on this frame it wouldn't be worth going any larger. Check the photos on the suggested thread.