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Old 07-11-11, 05:53 PM   #1
RFC
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Does anyone make a stock replacement rando fork?

I picked up an old Bianchi Randonneur recently, have been riding the hell out of it and really like the trail on the fork.

Now I have the idea of putting a rando style fork on my RB-1.

Is this doable or just plain silly?

Thanks
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Old 07-11-11, 06:19 PM   #2
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What qualifies as a "rando style" fork?

And what do you expect to happen when you change the fork?
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Old 07-11-11, 07:51 PM   #3
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Originally Posted by Bacciagalupe View Post
What qualifies as a "rando style" fork?

And what do you expect to happen when you change the fork?
Well, the obvious, I suppose -- better planing and stability. Do you know of a stock fork or just asking gratuituous questions?
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Old 07-11-11, 08:50 PM   #4
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I'm trying to figure out what you hope to accomplish.

Changing the fork is not like swapping a saddle or tires; you're not going to turn your road bike into a rando bike just by sticking a different fork on it.

You could try to figure out the characteristics of your current fork, then buy one that has more trail. In order to do that, we'd need to know the geometry of the fork you want to replace. But there isn't a "rando fork" which is always going to have more trail or a specific amount of rake.

Also AFAIK "planing" isn't a geometry characteristic, at least not one I've ever heard of.
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Old 07-12-11, 12:19 AM   #5
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Thank you for your somewhat thoughtful, if haughty, response BTW, are you the pcad of this forum?

I would like to respond.

By way of background, I have been riding road bikes since I was 17, which was 39 years ago, sometimes more, sometimes less. It's all part of the daily regime. I don't ride as much as you guys. In the last few years, I've been riding 6,000 to 8,000 miles a year. This one more of a 6,000 pace and AZ summer heat is not helping.

I have a number of road bikes -- both newish and C&V. The collection contributes to my "athletic" pursuits and satisfies my male tendency towards accumulation of gear, etc. The mix of bikes allows me to experiment ("turbo" my gear, as my family says) and adds variety to the workout.

So, recently, I picked up and totally rebuilt the Bianchi Randonneur and 1989 Bridgestone RB-1 in the photos below, and have spent most of my riding time on these two. The two bikes are just about the same size and have the following basic geometry:

Bianchi: ST 72, HT 72

http://bulgier.net/pics/bike/Catalogs/Bianchi-83/11.jpg

RB-1: ST 73.5, HT 72.5

http://www.sheldonbrown.com/bridgest...ne-1989-22.htm

Oh, and as I am sure you are aware, the US Bridgestones were the beginnings and the protypes of bikes now manufactured by Rivendell elves. BTW, the RB-1 has a replacement carbon fork, which is actually very good.

The Bianchi has been a new riding experience. I have rebuilt, ridden and sold two highend mid 1980's touring bikes, including a cherry Miyata 1000. Beautiful to look at, but rode like pigs, IMHO. The Bianchi is much quicker and the long trail provides a very different feel, particularly at speed, and a great deal more stability than the RB-1.

So, it occurs to me that a "traditional" "rando" or long trail fork on the Bridgestone might give me a similar ride.

Now that I have gone through all of this bullsh*t, do you have anything useful to say and/or are you able to answer my friggin' questions, which, again, are:

Will putting a long trail fork on the RB-1 give me a similar ride?

Does anyone make a stock "rando" or long trail fork?

Thank you for your consideration.




Last edited by RFC; 07-12-11 at 01:07 AM.
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Old 07-12-11, 04:51 AM   #6
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You both should be talking about randos with front loads usually having high rake aka offset (wheel sticks out farther forward), not "long trail." There is a formula for trail, in which more fork offset results in less trail. Several on-line tools will allow you to play with some numbers. This, at least, is just math.

RFC, I'm in the middle of having a low-trail fork built for a Trek 610 by a local builder. It's taking quite a while - design coordination, shortage of acetylene, the builder's need to work and manage his LBS setting up for the spring/summer season, and more design coordination. My reason is to get better handling with a front bag load; the change may or may not transform my 1984 Trek 610, a decent bike, into a poor-man's Alex Singer (my guess is, not quite so much). I tried to get my fork re-raked, but that was not possible. The new fork will have a tight low bend like your Bianchi, but 6.5 cm offset, compared to the OEM 5.2 cm on my Trek. I expect trail around 40 mm with the new fork. The target plan is to mimic the geo of the Boxdog Pelican.

We're actually talking about me picking up my fork and bike next week - I'll let cha'all know how it works.

Can you measure the offset of your Bianchi's fork? My uncalibrated eyeball of your photo does not cry out "Low Trail!"

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Old 07-12-11, 05:00 AM   #7
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Quote:
Originally Posted by Bacciagalupe View Post
I'm trying to figure out what you hope to accomplish.

Changing the fork is not like swapping a saddle or tires; you're not going to turn your road bike into a rando bike just by sticking a different fork on it.

You could try to figure out the characteristics of your current fork, then buy one that has more trail. In order to do that, we'd need to know the geometry of the fork you want to replace. But there isn't a "rando fork" which is always going to have more trail or a specific amount of rake.

Also AFAIK "planing" isn't a geometry characteristic, at least not one I've ever heard of.
I agree about planing (whatever it really is), but to facilitate good handling with a front bag, you want more offset or rake, not more trail. At least in bicycle terminology. For some reason, the terms are used differently in motorcycles and automobiles.
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Old 07-12-11, 08:06 AM   #8
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Thank you both for the clarification. I appreciate it.
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Old 07-12-11, 09:46 AM   #9
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Whoops, mixed up "trail" and "offset."

Anyway....


Quote:
Originally Posted by RFC View Post
Thank you for your somewhat thoughtful, if haughty, response BTW, are you the pcad of this forum?
I'd commit seppuku immediately if that was the case.


To answer your questions:

1) No, you can't make the RB-1 ride exactly like the Bianchi just by changing the fork.

The geometry of these two bikes aren't particularly close; it's just that they both use traditional straight top tubes. The RB-1 is a race bike, the Bianchi is a rando bike. Even from the photos (and confirmed from specs) I can see that the Bianchi has a longer chainstay, a slacker HT angle, a fork with a lot of offset. The RB-1 also has more BB drop, and the tubing is probably different as well.

If you use a fork with more offset, in some respects it will be more stable -- the wheelbase will be a little longer and you'll have less trail.

However, numerous other critical aspects won't change: The rear wheel will still be closer to the pedals on the RB-1, the rear triangle on the RB-1 is still smaller and therefore stiffer, the RB-1 has a slightly lower center of gravity. If the tubes are different, this will affect the frame's stiffness and ride quality.

Also, you'll be reducing wheel flop, which can degrade handling at slow or moderate speeds. So it will be more stable in some conditions, but not others.


2) Forks don't independently have "low trail," they have "offset." Trail is calculated with both offset and HT angle.

The stock RB-1 has 45mm of offset, and forks up to 55mm should be available off the shelf. However, it's entirely plausible that the new fork already has 55mm of offset, it's impossible to tell from a photo.

As per Road Fan, if you want more than 55mm of offset you're looking at a custom job. What he doesn't tell you is that given the same HT angle, more offset reduces the wheel flop. (AFAIK most fork designs avoid going over 55mm of offset to keep the wheel flop in check.)

Nor do all rando bikes use forks with high offset. For example, the 58cm Masi Randonneur (http://www.masibikes.com/steel/randonneur/) has a 73 HT angle and 43mm of offset. It uses a longer chainstay to get a longer wheelbase, which increases stability and comfort.

As such, there is no such thing as a "rando fork." You can get forks with varying offset, you can get forks with and without eyelets, you can get forks that are stiff or compliant, but there's too much variety in rando frames for there to be a rando-specific fork.


You could try a different fork; it's a bit of work but it's not going to break the frame, and it's a reversible change.

That said, it just doesn't make sense. It's like putting a hitch on a Camaro. The RB-1 is reputed to be an excellent road bike and will most likely offer an excellent ride for 60-100 miles, while altering the geometry will turn it into a mediocre rando bike. I don't see that it's worth the time, effort and resources.
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Old 07-12-11, 10:25 AM   #10
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Thanks. Now, that wasn't so hard, was it?
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Old 07-12-11, 11:37 AM   #11
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Thanks. Now, that wasn't so hard, was it?
Your initial question was so poorly posed as to have essentially no content. Bacciagalupe reasonably asked you to clarify just exactly what you are asking. You are the one who is out of line, here.

There is no such thing as a "rando style" fork, because "rando style" encompasses everything from the latest carbon fiber wonderbike, to a Rene Herse bike from the 50's, to a Surly LHT, to a unicycle, to ...

If what you mean is a steel fork with a given amount of rake/offset, or equivalently, with a specific amount of trail, given tire size and head tube angle, then there are manufacturers that can do that. I had Waterford build me a 64mm rake fork for my Gunnar Sport. They used an A.Homer Hilsen fork as the base design. With a 650Bx38 tire, the bike has 37mm of trail and 10.7mm of wheel flop; it handles perfectly when it has my normal rando front-end load in the largest of the Gilles Berthoud bags. It does have a little shimmy when ridden no-hands and loaded with a 400Km's worth of food at the start of the ride, but this improves through the day as I eat the food.

Another source of forks with generous offset is some of the older Trek models up until 1984. My '84 Trek 614 has 52mm of rake and a head angle of 73, so its front-end geometry is almost identical to the current Velo Orange Randonneur, which has 53mm of rake. With a 650Bx38 tire, trail is 46.5 and flop is 13.
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Old 07-12-11, 12:19 PM   #12
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Your initial question was so poorly posed as to have essentially no content. Bacciagalupe reasonably asked you to clarify just exactly what you are asking. You are the one who is out of line, here.

There is no such thing as a "rando style" fork, because "rando style" encompasses everything from the latest carbon fiber wonderbike, to a Rene Herse bike from the 50's, to a Surly LHT, to a unicycle, to ...

If what you mean is a steel fork with a given amount of rake/offset, or equivalently, with a specific amount of trail, given tire size and head tube angle, then there are manufacturers that can do that. I had Waterford build me a 64mm rake fork for my Gunnar Sport. They used an A.Homer Hilsen fork as the base design. With a 650Bx38 tire, the bike has 37mm of trail and 10.7mm of wheel flop; it handles perfectly when it has my normal rando front-end load in the largest of the Gilles Berthoud bags. It does have a little shimmy when ridden no-hands and loaded with a 400Km's worth of food at the start of the ride, but this improves through the day as I eat the food.

Another source of forks with generous offset is some of the older Trek models up until 1984. My '84 Trek 614 has 52mm of rake and a head angle of 73, so its front-end geometry is almost identical to the current Velo Orange Randonneur, which has 53mm of rake. With a 650Bx38 tire, trail is 46.5 and flop is 13.
Guys, give it a rest or get a sense of humor. I do know what I'm talking about and understand what you're saying. And I view Bacciagalupe's response (1&2)) as being more than a little dense and obstuse.
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Old 07-12-11, 05:29 PM   #13
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So what's the trail on that Bianchi?
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Old 07-12-11, 05:52 PM   #14
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One pretty surprising result when I consulted with my builder on the new high-offset fork, is that a much longer brake would be required if i didn't want to go with cantilevers. The bike is a 1984 Trek 610 with the 52 mm fork, possibly the same as the one thebulls is talking about. A number of years ago I had the original fork de-raked (yes, I added trail) to improve the bike's stability. I wanted it to feel more like a race bike. It ended up with trail around 59 mm with 28 mm 700c, and the original brakes fit just right. When I wanted to try low trail I first added a front rack and bag to that bike and went out for some test rides. It was not to hard to control with one hand at speeds above 16 mph, needed two hands from around 9 to 14, and needed good attention at lower speeds. This was with about 12# in the front bag.

BTW, my Mondonico makes a much better racy bike.

My next trial was on my Woodrup, which had a 5.5 cm offset resulting in about 48 mm trail with 700x32 Paselas. With the same load setup on the front and the Paselas it was much easier to ride at any speed, but difficult one-handed and no-handed. Nonetheless I did four metrics on it last summer. Frame has been sold.

Questing less trail, I found a local builder to build me a 6.5 cm fork for the Trek, maintaining a level frame. The long blades of this fork require either Cantis or Mafacs, and I am going with the Mafac brakes. Needless to say, it will have endless fender clearance. This bike will not be soft and cushy in the front, since the great fork length necessitated use of fairly stout Dediaccai fork blades, not the cute slim New Continental ovals of the 610 Trek. We'll see how it goes. The bike will end up with geometry very similar to a Boxdog Pelican, and with luck it will handle about as well.

RFC, your new fork may end up forcing some unforeseen changes.
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