bark_eater 

Spidey sense tingled and most of another lugged 91 Trek 750 magically appeared in the garage.

The next morning I noted that a new semi-local frame builder just put out a shingle, and posted some pretty reasonable rates.

Squinting, it looks like I could get some pretty fat 26" tires on this frame by moving the cantilever posts, and not run out of bottom bracket height.

The internet sez its been done before.

Any thoughts from the hive mind?

Thanks

ThermionicScott 

Wheel diameter shouldn't be a problem, I'd be most interested in the clearance between the chainstays and the fork blades where those tires will be.

A conversion to use ~47mm tires on 650B wheels might be a good way to split the difference.

bark_eater 

I mocked it up with 26" wheels and 50mm actual tires. Bottom bracket height is 10.5 inches and the tightest spot is 60mm at the the chain stays. The fork clearance is 65mm. I'm pretty sure I could dimple the chain stays and get another 5 mm. The fork rake is 40mm so in theory I'll still have similar high trail numbers going from 700cx38 to 26x50+.

ThermionicScott 

5mm of clearance per side would be plenty for me. My 650B conversion has about 2mm per side.

Clang

Not to be a party pooper, but for the cost of frame mods, new wheelset, paint, etc, for the 700C Trek 750 Multi Track you could just buy a complete lugged Trek 950 Single Track that already runs 26" wheels...

My lugged 750 has its stock 38mm wide tires with room to spare.

I agree that if you really have the itch to mod, 650B is the way to go, since that wasn't an option for any Treks back then.

nomadmax 

What's a "26" RTP" ?

ThermionicScott 

https://www.renehersecycles.com/shop...rat-trap-pass/

fishboat

I'd have to go a big +1 on that suggestion.

A 950 or 970 had a lugged frame up to 1993. I have a drop bar converted 970 with Big Ben (26x2.1) tires on it(currently in touring mode). Fun bike. Rides like a road bike..cushy ride, fast..fun bike. Nice paint too..looks like new.

nomadmax 

Thank you Scott. It's getting be like working for a federal/alphabet agency around here In five years time I'm gonna have to quit using the internet

ThermionicScott 

I randomly stumbled onto an old thread a few weeks ago where people were discussing their "UJB"s so casually that there were no obvious clues what it meant. "Something-something-bike", probably. "Something-Japanese-Bike", perhaps, given that the one or two brands mentioned were of Japanese make. "Ugly Japanese Bike"? Eek, I hope not! After a lot more Googling, it turned out to be "Universal Japanese Bike" (a play on "Universal Japanese Motorcycle", I'm pretty sure) meant to refer to those good-quality but largely interchangeable models from the 70s/80s.

bark_eater 

I looked at the geometry numbers and the 750 and 950 are very close, but.. I will looks like I would drop my bottom bracket close to an inch converting the 750. I ride a Koga Miyata with maxed out tires and the high bottom bracket is not my favorite thing. ...

Lbxpdx

My 1991 990 is relatively light, lugged and ready for 26”. The only things that I would consider if you do go this route is the stock fork is fat, actually called the Super Big Fork and it has a 1 1/8” threaded steerer tube. .

I was looking for a 750 myself and found the 990.

due ruote 

If you are riding places where 38mm won’t cut it, what about the pedal strike risk when you lower the BB?
I am in the mtb camp, but then again I really like the way my rigid Stumpjumper rides.
Maybe if you convert, it will be your favorite bike, but if not it’s a lot to unwind. Just my $.02.

bark_eater 

Not the best picture, but this is my Bridgestone CB-1 with 2.10 tires and fenders.
This is the the benchmark that the Trek 750 would need to improve on, or at least be a lighter drop bar version.

theblackbullet

With a 26" wheel in a 700c frame could roller cams or u-brakes work without modification?

or, I know people use these mounts to go from 26" to 700c conversion:
https://www.ebay.com/itm/17444690414...AaArM4EALw_wcB

I assume they'd work going the other direction.

bark_eater 

Those could certainly work for proof of concept.

Jeff Neese

I must say that I'm surprised, considering that this is the C&V community, that more people are not trying to discourage the OP from hacking up this frameset. They aren't making any more of these, and this would just take one more out of circulation.

In addition to my '91 750 (with drop bars), I have a 970 and two 930s, in various configurations over the years. Drop/flat/butterfly/alt bars, fat tires and skinny tires, indexed trigger shifters and bar end friction, you name it I've tried it. They're excellent platforms for experimentation. But, those frames are still intact. I might even be able to turn them back to stock if I wanted to. In addition to riding them, I consider myself the custodian of some very excellent vintage bicycle frames. Whether they belong to me or someone else in the future, they will hopefully live on forever. We're supposed to LOVE classic and vintage bikes and promote their preservation, not share ideas on how to hack them up. There are plenty of other bikes that could be used for this project. Don't molest the vintage lugged Trek frames.

But that's just me.

Dylansbob 

Too bad you're not on the west coast or I'd have to try to sell you my 990.

Personally, I'd run DTHs over RTP. Performance is close enough for me, prices are half, and the bonus of not giving JH any money. (I don't like that guy...)

bark_eater 

My Bridgestone CB-1 has 2.10 Tioga Power Blocks, which is the biggest I could get under fenders. I was going to try DTH's on another mountain frame, a raised chain stay Nishiki Ariel, which has a 1 1/8 threaded fork, which would make swapping in a modern fork easier, but will still have a jacked up bottom bracket height. I enjoy the heck out of the CB-1, and would buy another to run as a drop bar bike with out all the racks bags and baskets. The Trek 750 is a bird in hand though. While I truly respect the protests of the preservationists, and those who are still looking for one...............

leftthread

I have a 750 and would agree: just try using the existing Matrix Titan Tour 700c rims and fit the widest tires possible on them first.
On the hybrid forum 45s seem to be workable.
I would try other mods upstairs, like Jones H bars maybe.

ThermionicScott 

I wonder, if you chose the right canti brakes, if you could have another set of posts stuck on for 26" wheels without needing to remove the old ones.

All the "you'll take a rare bike out of circulation!" hysterics don't apply if it works.

Jeff Neese

Sure it does. Even if it "works", that hacked-up frame would be of little interest to anyone but the OP. Someday, someone will say "Who would have done this? They obviously didn't know what they had."

ThermionicScott 

They're brake posts on a steel frame. A competent framebuilder could move the posts, and fairly easily move them back to the original location if desired. Some bike customizers even have their own cachet. To my mind, lowering the bottom bracket height to 10.5" is arguably an improvement that the OP wouldn't get by just buying a 950.

If you care enough, make an offer on the OP's frame.

bark_eater 

Anyone's head going to pop if I throw a Fuji Finest into the "garage war"? I was thinking about the fork and how the bike will still ride like a mountain bike with a high trail. At this point I have a garage full of bike projects and probably not enough spring left in the ol' mortal coil to get to them all...

So I have one of those Soma Champs Elysee Forks that is supposed to go on another 531 frame. When I got it the first thought was "this is a mountain bike fork". Seems like this would be a good match for the 750. I paid a full kidney for that fork and the idea of stripping chrome and adding posts pains me a bit, but again bird in hand.

The Fuji comes in as a fork donor. That frame is a rust bucket that I should not have bought, but with the sunk cost fallacy of time, gas, and tolls, I ate that particular shyste sandwich. I think the Fuji fork would be a better fork for the 531 frame...but... Its going to get powder coated. This is rust, not patina pixy dust beusage. But thats all background noise..

So in my mind at least, I've got the means, motive and opportunity to put together a 26" low trail and lower bottom bracket "allroads" bike based on my "spare" Trek 750.

Another bit of trivia, is that I'm solidly in the Clydesdale camp, so it might even "plane"......

clubman 

We're are all on your side when it comes to well preserved classics but I'd balk at putting a production Trek on the endangered species list. After all, the OP's just trying to make a better ride for himself, not a rat-rod or vanity project.

There's an wise proverb found in the dusty digital corners of ye olde C&V. It's your bike, do what you want.