beicster 

My daughter and I went for a nice long ride including through a few nasty patches with loose gravel and suspect shiny bits that could have been glass. No sign of a leak yet. So far so good.

chrughes

Here's my '91 Fuji Saratoga with a hodgepodge of parts. I had the canti bosses lowered a bit to play nice with the 650b wheels. Sorry for the bad lighting/photos. I'm still waiting on fenders and front rack.

beicster 

No pics.

cheg

FWIW: I was able to run 650b wheels on an early '80s Shogun using Weinmann 1020 sidepulls from a Raleigh Twenty folder with the pads as high as they will go.

mountaindave 

That is one sweet looking Fuji. I had no idea they were making lugged frames into the 90’s. It looks awesome with the 650b wheels. What are those tires? It doesn’t look like the paint job has been touched, or is it a complete repaint? 1x10 drivetrain? So many questions...

ThermionicScott 

I could have sworn that I had already posted my bike to this thread. No better time than the present:



1987 Bianchi Sport SX.
I first built it up as a 650A bike, rode PBP 2015 with it, but wasn't entirely happy with the Col de la Vie tires.
Rebuilt it with 650B wheels (SP dynamo in front) and Pari-Moto tires in fall 2015, and am much happier. I've had two flats in almost 1500 miles.
New low-trail fork earlier this year courtesy of @gugie.

Speaking of presents, this thread turned 10 years old a few months ago, and we forgot to wish it a

gugie 

noobinsf 

Are those the 1.5 or 1.75 Pari-Motos? It looks great!

ThermionicScott 

1.5", and I needed to dimple the chainstays a little for clearance. Thanks!

SquidPuppet

I dig the forward placement of the headlight. What is the trail number with that fork?

ThermionicScott 

Thanks, it's so small and light (B&M Eyc) that I didn't have any qualms about mounting it directly on the end of the fender, and I really like having the light come from that spot. I don't have the spreadsheet in front of me, but the head tube angle is 73° and we were shooting for trail somewhere in the mid-30s, so the fork must have 65mm offset or so.

SquidPuppet

Does it feel twitchy if you ride it with no bag up front?

ThermionicScott 

The steering feels extra-light without the bag but not in a bad way. As long as I'm paying at least a little attention (and as a longtime ADD sufferer, I'm experienced in finding the bare minimum of attention needed to get something done), the bike never feels like I'm going to mysteriously go where I don't expect.

With the bag and up to a couple pounds of stuff, things are great, normal. With the stock fork, I was really fighting the bike when the handlebar bag was loaded, and that got really old toward the end of long brevets.

In full disclosure, the bike has always been a little wiggly no-hands. The frame is straight as far as I can tell, and it may well be that I lean a little to one side when riding, causing the bike to oscillate when it tries to steady itself without steering input. Doesn't seem better or worse with the new fork, so I just always keep a hand somewhere on the bar. At least with the new fork, it only takes a light touch with one hand to keep things under control, so I'm happy. This probably won't be the last bike to get a custom low-trail fork.

gugie 

Rake was right at 60, trail calculates to 38
Pix
Story
My favorite rake calculator - Yo Jim G.!

ThermionicScott 

There we go, thanks!

The Golden Boy 

The Suntour VX "triple" sealed BB unit is great. I've got 2, one on the Trek 720 and one on the Trek TX700. These were the sealed units that came with the Voyageur SP in 1984 and 1985.

noglider 

What happens if you don't modify or replace your fork on a 650b conversion?

beicster 

I did not modify or replace the fork on my 84 Trek 500 when I switched and all seems fine to me. I rode that bike all over the place in various configurations with 700c wheels and other than a cushier and more comfortable ride, I can't tell much difference with the 650b wheels.

For context I will add that I am not a demanding rider and I put comfort above any specific handling trait.

nlerner

The modification being described is to increase fork rake and decrease trail, resulting in better handling with a front load. If you don't do that modification, you might not want to front load. Otherwise, I've never seen the front fork as a hindrance for a 650B conversion. It's clearance at the back end that's usually limiting.

SquidPuppet

Thanks guys. I'm in the pondering stage about having a custom frame and fork made, so this info is appreciated.

ThermionicScott 

Yep! I built up this bike with handlebar bag use in mind. The low-trail fork brings everything into a nice balance with that load.

If that weren't a priority, the stock fork would have been just fine. The vast majority of 650B gravel and mountain bikes have normal to high trail.

Dfrost 

The 650B conversion on my Marinoni, with no change to the fork nor intention of front load, has very little effect on the steering and handling. I was expecting more change, and asked in this thread about that. Now I understand why it never gets mentioned. I’ve also been surprised how little effect is apparent from the resulting lower center of gravity. BTW, I switch back and forth between wheel sizes on that bike, and love it in both configurations.

OTOH, the recent front end mods by @gugie to my 1979 Miyata 912 with specific intent to carry a front load, much like @ThermionicScott’s, have been equally successful, but that bike is not a 650B conversion candidate.

gugie 

Tom, the only consistent reason to do a 650b conversion is to allow for fatter tires. The somewhat recent surge in both quality and selection in this tire size makes it desirable. In most cases, fork clearance isn't an issue.

Many people who do this want to also have fenders with decent clearance. That will disqualify some forks. For vintage bikes, more recent vintages tend to have less clearance than older ones. Scott's fork was the former, so we wanted more clearance.

Finally, many who want a fatter tire and also use fenders with proper clearance also want to put a load on the front end, typically a handlebar bag. High trail forks don't play well with handlebar loads. Low trail bikes don't seem to handle much differently with a front load.

If a bike were purpose built for fatter 700c tires + fenders + loaded front end, the best fork solution would be the same - long enough for the tire + fenders, low enough trail for balanced steering. My early 70's Raleigh Grand Sports happens to fit that description, long legs, lots of rake.

ThermionicScott 

Yeah, some of the BQ folks seem to be really sensitive to the difference in pneumatic trail between skinny 700C and fat 650B tires of the same diameter. I think one theorized [citation needed, I could be thinking of another party entirely] that as racing bike tires got skinnier, bikes were built with more (mechanical) trail to preserve stability. I don't think I'd be able to notice it. I don't push the handling of my bike nearly as much as those guys.

mountaindave 

I did this to my '91 RB-1 and it only dropped the trail a couple of mm, so no noticeable change. The handling is the same. It was high trail to start with, and remains that way.