Crown race extender spacer to increase AC length??

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tenbikes
Posts: 462
Joined: 11 Jan 2009, 6:41pm

Re: Crown race extender spacer to increase AC length??

Post by tenbikes »

Wilhelmus wrote: 26 Oct 2021, 9:13am Maybe worth bearing :!: in mind that, to produce the item being contemplated, it's not just a case of turning down a piece of mild steel. We are talking about a bearing surface, which needs to be specially hardened. I believe case hardening is the name of the process, and the product name Casenite is lurking in the back of my mind. Also, in my day, admittedly neither yesterday nor the day before, the crown race was such a tight fit on the bottom of the steerer tube that, in order to fit one, it was necessary to freeze the forks and heat the new race, causing them to contract and expand respectively. Maybe, in this brave new world, things are simpler.
A lot of high quality modern headsets eg Hope etc have a split in the bottom race so it can be fitted my hand / fingers. I kid you not. Gone are the days of using a Park seating tool and a big hammer.

I see no reason for the steel to be hardened. In fact I see no reason why alloy should not be used. As long as it is a tight fit on the steerer and the bearing race is a snug it ( finger push fit as above) then I would be happy to ride.
tenbikes
Posts: 462
Joined: 11 Jan 2009, 6:41pm

Re: Crown race extender spacer to increase AC length??

Post by tenbikes »

Ok, this is what I have done as a stop-gap:

I have fitted a spare stem on the bottom of the steerer, and then fitted the crown race, shimmed, above this.

I have assembled and it passes the rocking test, and is smooth.

It looks odd of course , but I'll test ride it later. If it works ok I might mount a QR bar bag mount on the stem using a short section of bar. I have done this before top side. It keeps the bar bag low, and off the bars. Mounting it below the head tube is a logical extension of this idea!.

I'll report back after a few test rides.........
yostumpy
Posts: 994
Joined: 29 Oct 2010, 6:56pm

Re: Crown race extender spacer to increase AC length??

Post by yostumpy »

I have a pair of Kona P2 forks, (non disc) with a strange crown race that is welded about 1" or more up the steerer, to give exactly the thing the OP is talking about. proper factory jobbie , very long steerer tube, 1'1/8, fitted and ridden once. If interested in acquiring these, send me a pm for pics, measurements, etc. Cheers.
tenbikes
Posts: 462
Joined: 11 Jan 2009, 6:41pm

Re: Crown race extender spacer to increase AC length??

Post by tenbikes »

The Kona forks are handy for folk who switch between suspension and rigid: they will be corrected for suspension geometry.

In my case I'm switching from a very long AC Surly 29er plus fork to a 700c Salsa with a much shorter AC and I want to retain the handling characteristics as far as possible.

I'm fairly hopeful that I have a workable solution but obviously a proper test ride is needed to confirm........
PhilD28
Posts: 352
Joined: 26 Sep 2016, 8:31am

Re: Crown race extender spacer to increase AC length??

Post by PhilD28 »

tenbikes wrote: 26 Oct 2021, 5:41pm Ok, this is what I have done as a stop-gap:

I have fitted a spare stem on the bottom of the steerer, and then fitted the crown race, shimmed, above this.

I have assembled and it passes the rocking test, and is smooth.

It looks odd of course , but I'll test ride it later. If it works ok I might mount a QR bar bag mount on the stem using a short section of bar. I have done this before top side. It keeps the bar bag low, and off the bars. Mounting it below the head tube is a logical extension of this idea!.

I'll report back after a few test rides.........
You need to be mindful that you have now increased the moment between the wheel contact with the ground and the bottom headset bearing, this increases the reactive force, while simultaneously making a poorer bearing fit solution (resisting the increased moment via a shimmed bottom bearing) with the steerer tube.
This isn’t a well engineered solution. You may get away with it, or not.
hercule
Posts: 1156
Joined: 5 Feb 2011, 5:18pm

Re: Crown race extender spacer to increase AC length??

Post by hercule »

If it’s of any interest, Kickbikes (a Finnish company that makes adult kick scooters) can supply just what you’re looking for… they use it on their Race Max 28 model to raise the front of the footboard for a bit of extra ground clearance.

https://kickbike.com/showroom_en/kickbi ... ax-28.html

Fun on 2 Wheels who are a Kickbike supplier might be able to get one for you.

https://www.funon2wheels.co.uk/
tenbikes
Posts: 462
Joined: 11 Jan 2009, 6:41pm

Re: Crown race extender spacer to increase AC length??

Post by tenbikes »

Ok, so I have been out for a short spin.

The AC length, with the mods is -15 mm and the BB to front axle is +5mm compared with the original fork.

I could feel the difference between the two forks whilst still in the drive way, but it was very subtle.....and whilst maybe not quite as good was certainly good enough, and a clear indication that running it without an extension would not be good!

Yes, it is a poorly engineered solution, bit was only ever intended as a short term test.

The Kickbike spacer is certainly worth a look, thanks for that.

TB
MikeF
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Joined: 11 Nov 2012, 9:24am
Location: On the borders of the four South East Counties

Re: Crown race extender spacer to increase AC length??

Post by MikeF »

I can see that changing the front tyre size whilst keeping the rear the the same will alter the head angle, but you'll have to explain how what you've done has altered the angle.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
tenbikes
Posts: 462
Joined: 11 Jan 2009, 6:41pm

Re: Crown race extender spacer to increase AC length??

Post by tenbikes »

MikeF wrote: 27 Oct 2021, 3:49pm I can see that changing the front tyre size whilst keeping the rear the the same will alter the head angle, but you'll have to explain how what you've done has altered the angle.
Pretty much exactly the same as going Mullet.......ie bigger front wheel. Not tyre size, that is a miniscule change. My gravel bike is 29/27.5. I've run 29/26 before, known as a 69er.

This bike is 26x2" and 26x1.5" : not much difference .

Head angle without the mods would be significantly steeper. With mods only slightly steeper.
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531colin
Posts: 16034
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Crown race extender spacer to increase AC length??

Post by 531colin »

tenbikes wrote: 27 Oct 2021, 1:48pm...........

The AC length, with the mods is -15 mm and the BB to front axle is +5mm compared with the original fork.................
What are you wanting to achieve here?

In round terms, shortening the A/C length 20mm will steepen the head angle about one degree.
10mm fork offset change is "equivalent" to about one degree change in head angle.

So (compared to the original fork) the head angle is about 0.75 degree steeper, and with the increased fork offset you have the equivalent of about a degree and a quarter steeper head angle. There are a lot of bike designs where a change of that magnitude would make the handling more than a bit unusual.
tenbikes
Posts: 462
Joined: 11 Jan 2009, 6:41pm

Re: Crown race extender spacer to increase AC length??

Post by tenbikes »

531colin wrote: 27 Oct 2021, 5:20pm
tenbikes wrote: 27 Oct 2021, 1:48pm...........

The AC length, with the mods is -15 mm and the BB to front axle is +5mm compared with the original fork.................
What are you wanting to achieve here?
What I wanted to achieve was a fork more in keeping with the rest of the bike in terms of visuals, but to retain the handling characteristics of the original fork. To this end I have tried to replicate the AC, but the forks have a slightly different angle, hence the +5 when under by 15.

The bike was a second hand custom build. It handled very well indeed, but a massive 29er+ fork looked out of place, especially with 26" wheels and narrow tyres [2", that is narrow for the forks]. Surly forks are fine especially where they need to be bomb proof. I have a Surly off road bike and love it, but for this bike a Salsa fork was called for. Lighter, slimmer, double drop out eyelets, stainless drop outs.

My mods have just about achieved my aims. The bike is a little more lively front end. I'm a sensitive soul and I can feel it, but only just. It handles just as well at speed / downhill.

I'm happy with the switch, but will try and sort a neater looking solution, unless the lower stem works out well for small 'bar' bag.
tatanab
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Joined: 8 Feb 2007, 12:37pm

Re: Crown race extender spacer to increase AC length??

Post by tatanab »

I think the problem here is misunderstanding what you have achieved.

1. Title says you want to increase AC by raising the fork crown race.
2. Your solution says you have reduced the AC by 15mm.
tenbikes
Posts: 462
Joined: 11 Jan 2009, 6:41pm

Re: Crown race extender spacer to increase AC length??

Post by tenbikes »

tatanab wrote: 27 Oct 2021, 6:43pm I think the problem here is misunderstanding what you have achieved.

1. Title says you want to increase AC by raising the fork crown race.
2. Your solution says you have reduced the AC by 15mm.
No quite! I have increased the AC of the Salsa fork from 410 to 455. This is still 15 short of the Surly's 470, but a massive improvement.

Using the Salsa at 410 would have really changed the handling. I never tried this, but don't have to to know it would be horrible compared to what I had.

But never mind the numbers: it is all about the ride. And the ride is still very good :)
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