dunkleosteus

So I just got my hands on what appears to be an '84 Trek 850 frameset in pretty ugly shape. I'm quite excited about it! I'm hoping to turn it into a 650b touring+ ride hard do anything bike. I never did any bike restoration before. Do you have any "I wish I knew this the first time" tips for me?

The Golden Boy 

First thing- there's no such thing as a 5 minute job.

Second- you've got a pretty cool bike- a great all-rounder with some decent 'cred' behind it.

Third- You'll probably have trouble with the 650B thing because of the canti mounts- you're probably going to have to stick to 26" which isn't a bad thing.

Have a good idea of where you want to go with this- what you want to do... This was an upper tier bike for it's day- it came with all top of the line parts on it. I would personally keep that in mind wherever I'm taking this build. You don't want to put less than "really good" stuff on it. IMO.

You said it's in "ugly shape," make sure your fork isn't bent, make sure you don't have any frame damage- ugly is fine, broken is bad.

It's probably spaced at 128, so you should be able to squeeze a 130 in there without cold setting.

Grease the snot out of the seat post, stem and pedal threads.

You've got a great platform- let's hear about what you have for ideas!!!

The Golden Boy 

And get some more posts in and post some pix.

Pix or it didn't happen.

fietsbob

850 is a 26" wheel mountain bike stick to 26" wheels or you need to pay a frame builder to move the brake posts

1st do the math & measurements will a 650B wheel be too tall ..

dunkleosteus

Thanks! I'll add some pictures as soon as I can. Everything looks straight to my eye. It's mostly ugly because the paint is chipped all over and it seems like someone spilled paint on it? There's a tiny ding in the top tube, but I rode a trek 620 with a much larger dent in the same spot for like 8 years and didn't mind it. I read that some people filled their dings, so I could eventually make it look nice. There's rust in spots where the paint's chipped but the inside of the seat tube looks pretty clean. Should I worry about rust in the top and down tubes too?

About the canti posts - I was thinking they'd be less of a problem going up in wheel size (26 to 27.5 in my case) than down, since the fulcrum is still on the right side of the lever arm. Not sure I'm making sense. I guess would need cantis with a longer adjustable range. Does something like that exist?

dunkleosteus

+1 for math

I was thinking 650bx47 or so. Something like WTB byways for an all-road type build. The diameter is comparable to the stock tires, which were 26x2.125s. I'll certainly consider sticking with 26 though.

fietsbob

AKA 27.5 in the now jargon
Sutherlands
"47-584 R =342 ..(D is 2x that).. 559 - 47 R=321 "..

ryansu

If I may suggest, get the bike safe - stops and shifts -and then ride it allot before you tear into it. This forum is littered with tales of lots of work and $$ lavished on bikes only to find out the bike doesn't really fit work etc. I can tell a few tales myself. Also riding the bike will reveal what you may want to keep as well as what you will want to change. And I will echo the fact that 26 tires are good and there are lots of options for road type tires in that size and beefy ones too- your Trek should fit up to 2" tires without a problem. There is a thread on here somewhere for Mountain bike tires. I had a 1992 Trek 850 pass through my hands earlier this year and kinda wish I had held onto it, nice bike. Have fun and post pictures!

dunkleosteus

Hm there is a lot of bogus info out there on 650b methinks. I was looking at a source which claimed that 26x2 was comparable to 650x42 which seems wrong now that I look at some charts. Oof. Is there a way to calculate diameter from tire size? Now I think the equivalent to 26x2.125 would be closer to 650x38. It seems that 650x47 would raise the bike 1cm over 2.125. I'll keep pondering it.

ryansu - sweet whip! I like that purple. Any purple bike of mine invariably gets named The Purpetrator and gets up to no good.

branko_76 

I know nothing about 650B wheels, what is it and why are you drawn to it?

ryansu

dunkleosteus the easiest thing might be to find a 650b wheel and test fit it (local shop or a willing forum member) but I think there is no shortage of 26" tires for all sorts of terrain/size - road, dirt, single track etc. And for a first Resto mod it might be a path of least resistance/tears

PS I had a purple Bianchi MTB briefly that I called Barney

dunkleosteus

I feel like this is a trick question, lol. Who am I to know my own motives?

eeuuugh

You can calculate the height of a wheelset plus tires by adding the ISO dimension of the wheel to the doubled size of the tire. A 26" wheel is ISO 559--that's 559 millimeters. A 2" tire is ISO 50, so it'll keep the rim 50 millimeters off the ground, and run 50 millimeters above the wheel at the top, adding 100 millimeters total to the height, for a final measurement of 659 millimeters. 650b rims are ISO 584, so 38mm tires will make them the same height as a 26" wheelset with 2" tires.

That said, 42mm tires will only raise the height of the *bike* by ~4mm. 42mm from the ground to the rim, and then 294mm (584÷2) from the rim to the center of the axle.

In most cases these measurements will be approximate. Most tires are plus or minus 2 millimeters from their stated dimensions, and they often tend to expand a little over time as the rubber develops more stretch. Then they'll shrink again as material wears off from riding.

To use 650b wheels on a frame with cantilever/v-brake posts meant for 26" wheels, you need an extra 13mm of brake adjustment. The only brake in production I know of that will give you that much is the Paul motolite, which are very spendy. They're an evolution of the Avid tri-align cantilever brake, which might also work. Tektro made a similar cantilever in the early 90s.

Andy_K 

I think you're better off sticking with 26" wheels. People switch from 700c to 650B to get more tire clearance. Going from 26" to 650B will have the opposite effect. That said, if you really want to do it (and I've been known to do things like that even after everyone tells me it's foolish), this is the product you need:


https://www.universalcycles.com/shop...s.php?id=67799

Edit: that will only work if your canti studs are removable. There's a very good chance they aren't.

branko_76 

Not a trick question. I have only used 27" wheels for my 70's era 10-speeds and 700C for 80's era 12 speeds.

What is 650B? Is it a rim size, tire size?


...

T-Mar

Oy vey, another C&V oxymoron - restomod.

ryansu

See St Sheldon the Brown here

branko_76 

Thank you.

So, as I understand it, 650B is a tire size designation that fits 26" rims. Is that correct?

Velo Mule

That is fair. Ride the bike. Then you'll get a better direction for the things that you might keep and what might change.

For instance, if you are on the road and paved paths most of the time, smoother tires may be desirable. If you find yourself going longer distances on it, then handlebars with more positions might be good. Some of our members use these bikes as touring bikes. They work great as touring bike because they are built strong, have strong wheels and have plenty of tire choices. For touring you may want dropped handle bars or even butterfly bars also known as trekking bars.

Do you want bags, fenders, racks, a kickstand, lighting? These will also be things to think about and then what bags, fenders, kickstand and lights?

Since it is an older bike be sure to go through hubs, bottom bracket, headset and derailleur pulley wheels to clean and refresh them.

The Golden Boy 

No- 650B is a wheel size, like 700C.

ryansu

Nope two distinct sizes. One way to cut through the tire sizing confusion is to focus on the ISO, again Sheldon, the ISO for a 26" MTB is 559 for 650b its 584 two different rim sizes and different tire sizes.

The Golden Boy 

The important thing is the distance from the axle to the canti post- the tire size is irrelevant.

branko_76 

Okay, now I get it. Thank you, again

JohnDThompson 

You may need different cantilever calipers. Borrow a 650B wheel and see if the current ones can be adjusted to reach the rim. Some have more range adjustment than others, IIRC, the 850 came with a Shimano caliper that offered a few millimeters of adjustment.

That said, I have to wonder why you want 650B wheels. The bike was designed to use 26" (559mm bead seat diameter) wheels, and there are plenty of decent quality tires and rims in that size.

Out of curiosity, early 850s used Reynolds 531 "All Terrain" tubing; later production used Tange "Prestige." Which do you have?

Rocket-Sauce 

Or brake pad extenders.
https://www.aliexpress.com/item/4000...archweb201603_