Skyhawk frame build / thoughts

Hmmmm.......well, I read this thread last night. And I didn't answer it because I simply didn't have any answers. But the answer you've now received is kinda hard to understand.

So the rest of us had better try to come up with something.

Those rims measure .975, eh? I'll guess that a 1 1/2 or 1 3/4 tire is recommended. I think I'd still try, though, to squeeze in a 2.125. Simply because you want just as much tire as you can possibly get.

Keep us posted, will you? That Skyhawk frame is interesting.

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.

Couple of shots with the Fat Franks mounted on the Grubee Skyhawk frame...rear fender mounted (not recommended). RC

Agreen said:

After some very VERY meticulous measuring and tack welding (repeat) i got the forks extended. It took more time verifying the tube was straight than the actual welding. It's straight though!

Gotta get to a computer to resize the picture...

A new question popped up though. Why us the seat post so big? It measures about 1.075". All my seat posts flop around in there. Think "hotdog in a hallway".

One seat post measures 0.955", and the other is 1.000". Still 0.075" of free play with the biggest one, and that's still a lot. We're not talking horseshoes or hand grenades here!

Click to expand...

If you want to use a smaller post you can buy a seat post shim, ebay etc. measure your seat post diameter in mm & the frames seat tube (inside dimension) in mm. Many different sizes of tubes used in bikes over the years, you could also just buy the correct post, 6 of one...half a dozen the other.

You said you've got your fork figured out, but i'll just post this for info. You can absolutely use a 1" steerer on a 1 1/8" tube, you just need a reducer like this:
http://www.niagaracycle.com/categor...tube-reducer?gclid=COSvn6Cwg8UCFUMV7AodRF4AFg
I'm surprised a shop wouldn't have recommended that. You would just need to bring over the 1" headset from the other bike as well. They may have said you have to use a 1 1/8" threadless because that's what headset that comes with the GT2a.

As for tires, on my GT2a-s I've got 2.3" Duro cruiser tires mounted on DH39 rims which are 1.5" wide. Chain clearance is an issue, don't think I could get away with any wider without moving the engine outboard. I have a couple telltale grease marks on my sidewalls. I am running a 4 stroke though so sprocket placement might be different than yours.

The seatpost is 27.2mm, that's a pretty common modern standard for aluminum frames.

You can convert the mtn bike hub to single speed, there are 2 different kinds, freewheel and cassette. Which have you got? The process is different depending what you've got, and it does require a special tool to remove the clusters usually, unless you want to get creative.

I'm running a coaster on mine, you can space the axle out to 135mm if you have enough axle. There are 2 methods for this as well, you either add spacers inside or outside the locknuts. You just need 12.5 mm of spacers on each side.

Inside locknuts (preferred):


Outside locknuts:

Yowza, that's pretty crusty. You need a splined frewheel removal tool to thread that off of the hub, it loosens counterclockwise. IF you get that off of there, you can thread on a BMX freewheel. Some freewheels can be disassembled and reassembled, looks like this one isn't serviceable if those are two rivets I see in the smallest ring. Also, if it's that rusty, what do the bearings and races look like in that hub?

If you'd rather use the coaster, as long as your axle is long enough to have 135mm of axle between the locknuts and still get threads on the outer locknuts, you're good to add spacers which can be anything from a stack of washers to custom billet 12.5mm purpose made spacers. Might also be easier and cheaper than messing with that freewheel. That part ain't rocket science, you just thread off the locknuts, add spacers to each side and then tighten them back down carefully so as not to bind the bearings.