Steel fork query

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bigjim
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Steel fork query

Postby bigjim » 20 Apr 2015, 5:00pm

I've been lucky enough to pick up a 531 unused, never built up 25"steel frame. It's original and made for 27" wheels. It does not come with a fork so I am on the lookout for a suitable fork. I doubt I'll find a good 531 27" fork but there are a few new 700c steel forks available. The thing is will it make a difference as the rear end will have a lot of clearance with 700c wheels but the front, not so much. Will the bike therefore be lower at the front with a non compatable [lengthwise] fork?

LollyKat
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Re: Steel fork query

Postby LollyKat » 20 Apr 2015, 5:42pm

The difference in radius between 27" and 700c rims is only 4mm, so I doubt if you will notice any difference in practice.

Brucey
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Re: Steel fork query

Postby Brucey » 20 Apr 2015, 6:11pm

it is more to do with the clearances than the difference between 27" and 700C; like LollyKat say it is only 4mm difference in brake drop...?

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recordacefromnew
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Re: Steel fork query

Postby recordacefromnew » 20 Apr 2015, 6:15pm

I think the answer depends significantly on the frame, i.e. whether it has a "racing" geometry with close tyre clearance or a tourer with room for guards and bigger tyres. I suspect that would dwarf the design difference of wheel radius of 700c front and 27" back, which is only 4mm. Additionally apart from the potential difference in A2C, different offset/rake of the new forks vs original will also impact handling. Reynold blades came in different lengths and rakes.

For what it is worth the A2C of my originally 27" wheel 531 73 degree parallel 25" "sports tourer" is c382mm while the rear axle to brake pivot is c376mm. A number of 700c fork lengths are given at http://sheldonbrown.com/rinard/forklengths.htm (as indicated measured parallel to the steerer, meaning a2c should be an additional c2.5mm).

The safe way to proceed without trial and error is to ensure trail is reasonable. If you can identify the original headtube angle, you should be able to work out what A2C and rake combination will give you a reasonable/desired trail, see http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry.

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531colin
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Re: Steel fork query

Postby 531colin » 20 Apr 2015, 6:34pm

Is it a fair assumption that it was designed with the top tube accurately horizontal?
If it is, then a bit of playing should get you to both the head angle and fork length, then all you have to worry about is offset to give an acceptable trail.

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bigjim
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Re: Steel fork query

Postby bigjim » 20 Apr 2015, 7:02pm

It's one of these but a bigger 25" frame. It came without the forks. Would a different raked fork be a big deal?
Image
Last edited by bigjim on 20 Apr 2015, 10:08pm, edited 1 time in total.

RogerThat
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Re: Steel fork query

Postby RogerThat » 20 Apr 2015, 10:01pm

I doubt it. Older frames like this usually have quite a laid back geometry so the fork is not going to alter the handling to any great degree.

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531colin
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Re: Steel fork query

Postby 531colin » 20 Apr 2015, 10:20pm

Modern forks are likely to be less offset than the originals, which will slow the handling (even more).

You must be able to find the year and the geo. table?

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bigjim
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Re: Steel fork query

Postby bigjim » 20 Apr 2015, 10:30pm

Well probably. It's the same model as the 1985 one in the picture. However finding a 1985 fork to the exact geo would be a bit of an uphill task I presume. I've put a wanted ad out for an older 27" fork but doubt, if one turned up, whether it would be the exact geo.

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531colin
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Re: Steel fork query

Postby 531colin » 20 Apr 2015, 10:47pm

It doesn't need to be exactly exactly the same.....for example....
10mm shorter will give roughly 1/2 deg steeper head angle......which will be (roughly) cancelled by 5mm less offset
....however 10mm shorter and 5mm more offset would be a real difference.

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recordacefromnew
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Re: Steel fork query

Postby recordacefromnew » 20 Apr 2015, 11:00pm

bigjim wrote:It's one of these but a bigger 25" frame.


A Royal? Below from 84 brochure, 10 speed so 120mm OLN and 73 degree parallel. By 1987 Royals were 700c, 18 speed, with variable geometry dependent on size.

Image

Image

Brucey
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Re: Steel fork query

Postby Brucey » 20 Apr 2015, 11:04pm

I wonder which year was the last year they specced 27" wheels? IIRC Dawes went to 700C earlier than that perhaps?

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RogerThat
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Re: Steel fork query

Postby RogerThat » 21 Apr 2015, 7:57am

There are some ex stock NOS Dawes galaxy touring geometry forks available on eBay at the moment for £39.99 I believe they're uncut steerer so should fit anything. They're ahead fitting but you can buy an aheadset for as little as £8. You didn't state in the OP whether the frame was inch or inch eighth. If it's inch, I would consider buying them and have a frame builder replace the steerer with an inch one, I had this done for a Mercian, cost about £40 again. Still way cheaper than a custom built 631 fork which was going to cost me £145 + paint. These look a very high end fork, they also have a disk mount which is very useful for upgrading the braking power on an older frame (you can also buy a rear drop out mounted adaptor (£20) which would allow you to run disks front and rear on a 531 frame):


http://m.ebay.co.uk/itm/131415287439
Last edited by RogerThat on 21 Apr 2015, 8:07am, edited 1 time in total.

RogerThat
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Re: Steel fork query

Postby RogerThat » 21 Apr 2015, 8:25am

BTW I bought a pair of these forks and upgraded a 1995 mercian 653 to full disc braking, all in, including having the steerer replaced it cost me about £160, cheaper than the cost of a pair of Mercian forks!! I should say I didn't have the work done by them, as it was too expensive. My local frame builder is about 40% cheaper.

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breakwellmz
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Re: Steel fork query

Postby breakwellmz » 21 Apr 2015, 8:57am

bigjim wrote:I've been lucky enough to pick up a 531 unused, never built up 25"steel frame. It's original and made for 27" wheels. It does not come with a fork so I am on the lookout for a suitable fork. I doubt I'll find a good 531 27" fork but there are a few new 700c steel forks available. The thing is will it make a difference as the rear end will have a lot of clearance with 700c wheels but the front, not so much. Will the bike therefore be lower at the front with a non compatable [lengthwise] fork?


Seen this one, it`s got a long steerer?-

http://www.ebay.co.uk/itm/REYNOLDS-531- ... 1c5196e2ee