can a 194mm steerer tube replace a 170mm one?

General Discussion about electric bicycles.
Post Reply
doubledipsoon   100 W

100 W
Posts: 150
Joined: Feb 22 2013 8:31pm

can a 194mm steerer tube replace a 170mm one?

Post by doubledipsoon » Dec 05 2020 9:30pm

I'm a dinosaur with a 170mm "threaded" suspension front fork. I know these are relics, but I have an opportunity to replace my worn out one with a new 194mm threaded one, NOS off Ebay. Will this 24mm extra length produce any problems as far as securing it, as it has 40mm of top thread. I have a sneaky suspicion that there may not be enough thread left to secure it with the spanner nuts. Are there guidelines on whether you can use a longer steerer tubes? Or any tricks I'm unaware of? I know, I know, I should just convert over to a threadless type, but I'm "resistant to change".......

User avatar
amberwolf   100 GW

100 GW
Posts: 32242
Joined: Aug 17 2009 6:43am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: can a 194mm steerer tube replace a 170mm one?

Post by amberwolf » Dec 05 2020 10:43pm

First, is the longer steerer also the same diameter?

For the other, you can calculate if it has enough thread for your needs.

1. Mark your existing fork, while installed, on the threads with a marker, at the top of the bearing cone nut (without any of hte other washers/nuts that go above it installed).

2. Take the nut off and fork out, then put the bearing cone nut back on, until it's top is at the same point it was at when marked. Now mark the threads on the fork where the bottom of the nut ends. That shows you the point you *must* have threads to.

3. Measure the distance from that point down to the bottom end of the steerer.

4. On the longer steerer, deduct the total thread length from the total steerer length. The remainder must be the same or less than the distance in step 3. If it is greater, then there isnt' enough thread to allow correct installation of the bearings.

docw009   100 kW

100 kW
Posts: 1412
Joined: Aug 02 2015 7:43am
Location: Chicago area suburbs.

Re: can a 194mm steerer tube replace a 170mm one?

Post by docw009 » Dec 05 2020 11:43pm

It's not easy to cut those threads if yiu need more. I had a steerer tube that needed two more inches of thread. I bought a die, but it wasn't sharp enough. It bogged down after two turns. A bike or machine shop might do it for you. Sure looks easy on youtube though.

SInce I had two inches though, it was possible to convert it to threadless, and I did. In your case, with only one inch of excess tube, you probably don't have enough unthreaded metal for a threadless collar. Can't put a collar over threaded metal. Too weak.

doubledipsoon   100 W

100 W
Posts: 150
Joined: Feb 22 2013 8:31pm

Re: can a 194mm steerer tube replace a 170mm one?

Post by doubledipsoon » Dec 06 2020 10:37am

After careful analysis of your diagnostic procedure, and a little more brainstorming, my sneaky suspicion became evident- there is not enough thread to secure the steerer tube to the frame stem with the top securing nut- so it's off to the threadless steerer tube universe, with fangled star nuts, and spacers. My stored initial ebike has a threadless suspension fork which should convert easily to my BBSHD ebike, as all the headset parts, bearings, caps etc. look interchangeable. I'll probably have to drive down the existing star nut, cut the top of the steerer tube (it looks alot longer) and add another fangled star nut to complete the project. OK, thanks for the input- I'm ready to adapt.....Any suggestions for a future pricey and excellent air shock, threadless, 26", V-Brake, 1 1/8" diameter?

docw009   100 kW

100 kW
Posts: 1412
Joined: Aug 02 2015 7:43am
Location: Chicago area suburbs.

Re: can a 194mm steerer tube replace a 170mm one?

Post by docw009 » Dec 06 2020 1:48pm

If you want to eventually return the donor steerer to your original bike, you may not have to cut it. Add spacers under the newfangled star nut when you transfer the fork. You can also cut spacers to the desired length too, if needed,

If the handlebars get too high with the spacers, you can even put the spacers above the stem collar. I did that on a bike when I wasn't sure what I was going to finally do, and it's still that way. There was some concern in the back of my mind about a 1" protrusion being a safety hazard, but heck, there's an LCD over it anyway.

Pentti M Reku   10 mW

10 mW
Posts: 28
Joined: Oct 29 2020 2:51am

Re: can a 194mm steerer tube replace a 170mm one?

Post by Pentti M Reku » Dec 06 2020 4:08pm

You could use a spacer between the top nut and upper bearing race, though you need likely something better than a modern threadless spacer.

This was just about the nicest new rim brake fork I could find:

https://www.ebay.com/itm/RockShox-Recon ... SwS5lfffXO

If used vintage suits you better get a SID model, those are nice and light. Might be hard to get parts for the older ones though.

doubledipsoon   100 W

100 W
Posts: 150
Joined: Feb 22 2013 8:31pm

Re: can a 194mm steerer tube replace a 170mm one?

Post by doubledipsoon » Dec 06 2020 7:50pm

What's up Doc? I thought there were limits on how many spacers you can use- I'll have to do more homework on that one......I have no idea what I'm doing with this conversion, so it's a "monkey-see-monkey-do" off You tube viewing.....I'm still trying to figure out why threaded steerer forks were replaced by the threadless types. Sometimes the evolution of "things" causes more complications, complexities, and hidden costs. But, then again, I've downsized pretty much to the max and am still living in the 60's........Pentti, I laughed when I saw the cost. If this SRI off the Currie eride blows out after a few weeks, it'll be the 4th suspension fork in 3 years, and I'll go for it. I guess those agricultural dirt roads with tractor thread prints were too much for the coil type shocks. I mean, are air shocks better than coils? I hope so.

User avatar
Chalo   100 GW

100 GW
Posts: 8604
Joined: Apr 29 2009 11:29pm
Location: Austin, Texas

Re: can a 194mm steerer tube replace a 170mm one?

Post by Chalo » Dec 06 2020 11:52pm

doubledipsoon wrote:
Dec 06 2020 7:50pm
What's up Doc? I thought there were limits on how many spacers you can use-
Not with a steel steer tube. Pile them sumbitches up as far as you please. The only risk is from ridicule.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

doubledipsoon   100 W

100 W
Posts: 150
Joined: Feb 22 2013 8:31pm

Re: can a 194mm steerer tube replace a 170mm one?

Post by doubledipsoon » Dec 07 2020 12:16am

Right on, Chalo! OK, one more tid bit of info to make my ebike the coolest thing on Planet Earth. Sounds like you're the man, so here's another question from the new kid on the block- My old blown threaded suspension shock steerer tube is 6" long, and I'm converting it to a threadless suspension shock steerer tube, so that's 3 full inches longer. Can I skip cutting the threadless steerer tube and just put in spacers to compensate for the longer tube? Hey, this is too easy.....

User avatar
Chalo   100 GW

100 GW
Posts: 8604
Joined: Apr 29 2009 11:29pm
Location: Austin, Texas

Re: can a 194mm steerer tube replace a 170mm one?

Post by Chalo » Dec 07 2020 12:29am

doubledipsoon wrote:
Dec 07 2020 12:16am
My old blown threaded suspension shock steerer tube is 6" long, and I'm converting it to a threadless suspension shock steerer tube, so that's 3 full inches longer. Can I skip cutting the threadless steerer tube and just put in spacers to compensate for the longer tube? Hey, this is too easy.....
Yes, you can do that. You’ll need a star nut, or an expander plug, or an adjustable spacer to set bearing preload. You can put the spacers below or above the stem as necessary to get your desired bar height. Once you’ve accumulated enough mileage to know for sure how high you want your bars, you can cut off the excess if you want. Or not.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Post Reply