1938 knucklehead handling with 16in wheels?

[edgemont]

I've got a 38 frame with 37 forks and 16in wheels on a project bike. I don't want to ditch the 16in wheels right now but I'm wondering if anyone has experience with this set up. Does it get speed wobbles or is it fine? Thanks

[RichO]

The experts might say something different but this is just what I know. in 1940 which was the first that 16" wheels were available, 18" were optional, they had to bump the top bar on the frames to get more rake as with the original rake they did get high speed wobble. I believe your rake is the same or maybe a degree or so less than a 1940 frame before the bump. I like 18" and have them on my 1940. They flex more in the spokes, absorb more shock and the outside diameter is the same as 16's. 18"s are more nimble in handling and the tires are lighter and have a narrower footprint. That's my two cents.

[edgemont]

Thanks Rich. Do you also have a 1940 "swept forward" fork? Or a straight leg 41+?

[RichO]

Mine is an NOS factory replacement fork made in 1941. When I got it it still had the Dudley Perkins dealer tag on it. My frame had been "bumped". It was a California CHP machine and still had the extra left hand toolbox mount on it, police coil, and carb. My original swept fork had been plated and the acid rotted it out from the inside so when I had it blasted to powder coat it was rotted through and held together by the chrome plating. Yikes! Hence the replacement. I dug the fact that it was a Cal replacement fork on a Cal motorcycle. Plus it's a period "bob job" so who cares.

[bobphd]

My 40 is in a 38 frame and the front end is whatever came with a no.4 spring fork. I finished the bike in its present form in 89 and had 16 in wheels/ tires on it until 3 years ago. I never had any handling or wobble problems as some describe in the over 100,000 miles I put on it like this. When I put the 18s on I did notice better handling in the corners but the ride sucked compared to the 16s. I only put about 7000 miles on the 18s and went back to the 16s this year. The ride to me is much better especially on the rough Wisconsin backroads that I ride.
Bob PatzaCBC97EA4-C1A6-414C-BE48-B542041B88DF.jpg

[edgemont]

My 40 is in a 38 frame and the front end is whatever came with a no.4 spring fork. I finished the bike in its present form in 89 and had 16 in wheels/ tires on it until 3 years ago. I never had any handling or wobble problems as some describe in the over 100,000 miles I put on it like this. When I put the 18s on I did notice better handling in the corners but the ride sucked compared to the 16s. I only put about 7000 miles on the 18s and went back to the 16s this year. The ride to me is much better especially on the rough Wisconsin backroads that I ride.
Bob Patza[ATTACH=CONFIG]30324[/ATTACH]

100k miles running 16s in a 38 frame. That's what I needed to hear. Thanks!

[droptopford]

I've got a 38 frame with 37 forks and 16in wheels on a project bike. I don't want to ditch the 16in wheels right now but I'm wondering if anyone has experience with this set up. Does it get speed wobbles or is it fine? Thanks

I'm no expert either but I agree with RichO.
I think a high-speed wobble is possible on just about any bike, although the better designed and maintained, the less likely for it to occur. The geometry of those pre-'41 frames and forks works best and handles best with 18" wheels.

I don't doubt that 16s work best for BobP in his application or that he's had all those trouble free miles. You can probably get away with running '16s too. I'd probably do the same thing to get back on the road, but I'd be keeping my eye open for a set of 18s.

Just my 2c.

[edgemont]

I'm no expert either but I agree with RichO.
I think a high-speed wobble is possible on just about any bike, although the better designed and maintained, the less likely for it to occur. The geometry of those pre-'41 frames and forks works best and handles best with 18" wheels.

I don't doubt that 16s work best for BobP in his application or that he's had all those trouble free miles. You can probably get away with running '16s too. I'd probably do the same thing to get back on the road, but I'd be keeping my eye open for a set of 18s.

Just my 2c.

Thanks. I have a set of crusty 18s that can be rebuilt eventually but wanted to see how people have done with 16s in the real world since they're already on there. I'll give them a whirl for now.

[bobphd]

Another advantage to the 16 in wheels tires is the fact that I have never had the tire bead come off during a flat. Last summer on a county road south of Marquette Mi. I picked up a long deck type screw in the rear 18 in tire while going 50-60 mph. The tire immediately went flat and the tire bead separated from the rim. I was able to get stopped ok but the bike was very squirrelly and it wasn’t much fun pushing it like that a 1/4 mile to the closest house to fix. This fall I picked up a similar type screw near Tomahawk Wi. also in the rear but this time with the 16 in tires on. The tire slowly lost pressure and the bead stayed put. I was able to make it 3 miles back to a gas station with a tavern across the street to repair. I have had many flat tires over the years with 16s and never had the bead separate and cause problems like the 18s last summer. That was the only flat I ever had with 18s and the screw was about 3 in long. There must be something to the wobble problem or the factory old not have done what they did but I have never experienced it on this bike.
Bob Patza

[Rollo]

I have bikes with both 16 and 18 inch wheels and must say I prefer 18 myself. My 18 wheel bikes are all VL's but I am doing and 41 knuckle that will have 18's as it is very low number bike. My 36 Chief also has 18's I find them more responsive and nimble and don't feel as though I'm pushing the front end as much as guiding it but that's just me. The 16.s are cushier but I run 4.50x18 so get some relief there. Just my opinion so do what you wan.t as it's your bike and you riding it!

Tom (Rollo) Hardy
AMCA #12766

[55tmm]

I have a similar question where this discussion left off, I recently picked up an older non correct restoration, it was done to suit the owner but still nice looking, here goes, it's a 1940 ULH,
late 1947 frame, 1940 inline springer fork, 16'' wheels, it sits pretty low. I haven't ridden it yet, does this sound like too much rake?

[T. Cotten]

Nobody seems to want to answer, 55..

But if if it was a serious machine, I would find an off-set top tree (or bars), and tweak the bottom fork to match.

....Cotten
PS: Its easier than you think, if you have the resources.

[55tmm]

IMG_3329.jpeg
Cotton, Thanks for responding, I expected an answer like- change it to offset, new bars and tweaking it seems a lot better than finding a good offset front fork.
Any resources or information as to how they can be tweaked? I did some measuring, and it has 6-3/4 trail.

[T. Cotten]

An off-set was brought to me once, 55tmm,..

That had a factory tag saying it had been tweaked from in-line, and the owner wanted it back in-line.

So I made it fit his in-line bars.

I'm guessing it might have taken a ton and a half in my screw press because it was springy.

....Cotten

[Carl Olsen]

I have an original paint 46 knuckle that came from the factory with a bullneck frame and an inline fork, you are right in the statement that it sits lower, but it handles nicer than my other bikes, other than scraping the running boards on tight turns. I do not have to worry much about that though, as I live in the plains of South Dakota where it is so flat that you can see the curvature of the earth.
Try riding it before you change anything, you might enjoy it more than you think.
Carl