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Fork rake angle on 2005-ish Burley Rumba?

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Fork rake angle on 2005-ish Burley Rumba?

Old 12-17-15, 04:14 PM
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Paluc52
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Fork rake angle on 2005-ish Burley Rumba?

I'm hoping to replace a Burley custom True Temper Verus chromoly fork on the Rumba, and don't want to change the handling. I know the head tube angle is 73 degrees. Anyone know the rake angle on that fork? Or how to find out?
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Old 12-19-15, 05:50 AM
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Pretty sure they used forks that we395mm in length with ~55mm of rake for their steel forks, same as a Santana fork.

FWIW, the "Race" models used a True Temper carbon CX fork that was 395mm in length with 47mm of rake for a more 'sporty' feel.
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Old 12-19-15, 12:43 PM
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Originally Posted by TandemGeek View Post
Pretty sure they used forks that we395mm in length with ~55mm of rake for their steel forks, same as a Santana fork.

FWIW, the "Race" models used a True Temper carbon CX fork that was 395mm in length with 47mm of rake for a more 'sporty' feel.
Is this not the rule of thumb? ...

Less rake = more trail = more "stable" (less turny).
More rake = less trail = quicker turning (more "sporty").
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Old 12-20-15, 08:56 AM
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On single bikes, yes... on tandems it gets into semantics and subjectivity.

Shorter rake = more trail / Yes.

Example here would be a tandem with 73 head tube and ~375mm long, ~44mm rake fork (e.g., Co-Motion) with trail in the 2.2 - 2.3" range. Most people who like these "performance" tandems describe them as handling very much like their single bikes. The geometry yields a very stable ride IF the captain and stoker ride cleanly. They are very responsive to subtle steering inputs vis-a-via counter steering inputs and shifting body weight left or right... very much like a single racing bike. The down side is for teams that don't ride clean, especially at slow speeds and when climbing. You can see teams who would probably be better off with longer rake / less trail climbing steeper grades where the captain is countering every low-cadence pedal stroke with a steering input to keep the tandem traveling in a straight line. Clean riding teams who can spin a higher cadence while climbing don't typically have this issue.

Longer rake = Less trail: Yes

Example here is a tandem with 73 head tube and 395mm long, 55mm rake fork (e.g., Santana, Burley) with trail in the 1.8 - 1.9" range. They are less responsive to unintended steering inputs from body weight shifts and require deliberate steering inputs to initiate and curtain cornering, which at very high cornering speeds can feel like understeer until you get used to it coming from a single bike or from a tandem that has longer steering trail. However, there is less task load on the captain when climbing at slower speeds / low cadence even with a lot of body english coming from the stoker.

In the middle ground is a standard Co-Motion road tandem with a 73 head tube and 395mm, 50mm rake fork as well as the Cannondale road tandems in the 2.0" range which at one time used a little less head tube angle with a 53mm rake fork. I have no idea what they use today, but suspect it's similar.

At the far end of the spectrum is Bilenky who use very short steering trail in the 1.65" range, shorter than anyone else but that yield very nice handling tandems. Go figure.
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Old 12-21-15, 06:50 AM
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Originally Posted by TandemGeek View Post
On single bikes, yes... on tandems it gets into semantics and subjectivity.

Shorter rake = more trail / Yes.

Example here would be a tandem with 73 head tube and ~375mm long, ~44mm rake fork (e.g., Co-Motion) with trail in the 2.2 - 2.3" range. Most people who like these "performance" tandems describe them as handling very much like their single bikes. The geometry yields a very stable ride IF the captain and stoker ride cleanly. They are very responsive to subtle steering inputs vis-a-via counter steering inputs and shifting body weight left or right... very much like a single racing bike. The down side is for teams that don't ride clean, especially at slow speeds and when climbing. You can see teams who would probably be better off with longer rake / less trail climbing steeper grades where the captain is countering every low-cadence pedal stroke with a steering input to keep the tandem traveling in a straight line. Clean riding teams who can spin a higher cadence while climbing don't typically have this issue.

Longer rake = Less trail: Yes

Example here is a tandem with 73 head tube and 395mm long, 55mm rake fork (e.g., Santana, Burley) with trail in the 1.8 - 1.9" range. They are less responsive to unintended steering inputs from body weight shifts and require deliberate steering inputs to initiate and curtain cornering, which at very high cornering speeds can feel like understeer until you get used to it coming from a single bike or from a tandem that has longer steering trail. However, there is less task load on the captain when climbing at slower speeds / low cadence even with a lot of body english coming from the stoker.

In the middle ground is a standard Co-Motion road tandem with a 73 head tube and 395mm, 50mm rake fork as well as the Cannondale road tandems in the 2.0" range which at one time used a little less head tube angle with a 53mm rake fork. I have no idea what they use today, but suspect it's similar.

At the far end of the spectrum is Bilenky who use very short steering trail in the 1.65" range, shorter than anyone else but that yield very nice handling tandems. Go figure.
This has been my experience, mostly. The situation regarding stability and handling at high vs low speeds is reversed for high vs low trail, though this is an oversimplification. High trail at very low speeds with low cadence requires perhaps a little more concentration to keep the bike straight; true whether tandem or single bike. I have single bikes with both high and low trail, and our Cannondale tandem has 2.6in/66mm trail-very high. At high speeds that bike is very stable and tends to maintain its line, and require active countersteer to initiate a turn or adjust line in the middle of a turn. This is the "cornering on rails" handling that many people like. Low trail bikes are more responsive to subtle inputs at high speeds and may require active steering input to hold the line on a turn. But then is easier to adjust mid-turn. Some describe as twitchy, but is not a problem for a confident descender and easy to get used to. All bikes turn by countersteer but our comotion feels more like turning the bars, where the cannondale feels more like leaning. Our Comotion is probably in the middle range regarding trail.
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Old 12-21-15, 10:39 AM
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Many thanks for the education, folks!
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Old 12-21-15, 01:18 PM
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Interesting topic, maybe beyond the scope of the OP.

I like this quote from the Wikipedia page on bicycle geometry, especially the first phrase:

"Although the scientific understanding of bicycle steering remains incomplete,[SUP][14][/SUP] mechanical trail is certainly one of the most important variables in determining the handling characteristics of a bicycle. A higher mechanical trail is known to make a bicycle easier to ride "no hands" and thus more subjectively stable, but skilled and alert riders may have more path control if the mechanical trail is lower"

Tandems have a longer wheelbase than single bikes and carry a heavier payload, distributed differently. The longer wheelbase increases high speed stability even if the bike has less trail. Our T2000 has just 47 mm trail but certainly feels rock solid at high speed. I'm sure there are other reasons that make some feel that more trail on a tandem results in "sportier" handling when the opposite may be true on a single bike. My guess is that a captain can adjust and even become fond of the handling on any well made tandem. I personally like the combination of high speed stability and low speed forgiveness that less trail seems to give our bike.
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Old 12-21-15, 03:47 PM
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Originally Posted by marciero View Post
This has been my experience, mostly. The situation regarding stability and handling at high vs low speeds is reversed for high vs low trail, though this is an oversimplification. High trail at very low speeds with low cadence requires perhaps a little more concentration to keep the bike straight; true whether tandem or single bike. I have single bikes with both high and low trail, and our Cannondale tandem has 2.6in/66mm trail-very high. At high speeds that bike is very stable and tends to maintain its line, and require active countersteer to initiate a turn or adjust line in the middle of a turn. This is the "cornering on rails" handling that many people like. Low trail bikes are more responsive to subtle inputs at high speeds and may require active steering input to hold the line on a turn. But then is easier to adjust mid-turn. Some describe as twitchy, but is not a problem for a confident descender and easy to get used to. All bikes turn by countersteer but our comotion feels more like turning the bars, where the cannondale feels more like leaning. Our Comotion is probably in the middle range regarding trail.
This was my experience too.

When we got our 1st tapered fork in 2013, that ENVE had only 43mm rake which resulted in too much trail. Heading into tight turns at high speed the tandem wanted to go straight and was always a fight maintaining what I call a "snap carve" (similar feel to carving downhill shaped skis where you can develop some G-force that feels like it is pushing you down into the turn and more grip). You wouldn't notice it as much at speeds in the 20mph range, but above 30mph it became tricky. My wife doesn't understand the technique much, but we do work on it specifically. Her feedback is just that it feels really "swoopy" and she loves doing it. Note, stoker drop bars are a big help. We tested with bullhorns and that was not so stable in these type of turns.

I switched out that fork for a 3T Rigida with 46mm rake and the turning was then perfect for us. Testing different forks on otherwise an identical tandem setup is not something a lot of people do, but if you can, it does provide feedback to assist in dialing in your preference.

Our latest build includes a 49mm fork which I am looking forward to testing out once we get healthy and have rideable roads and weather again.

Last edited by twocicle; 12-21-15 at 03:52 PM.
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Old 12-22-15, 12:05 PM
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Do you know of any carbon forks for tandems that has that much rake?
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Old 12-23-15, 12:05 AM
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The only "tandem" carbon forks I know of are from Co-Motion and Santana. However, since there is no industry standard for tandem rate forks, that designation is somewhat arguable. I'm not sure the Reynolds Ouzo Pro fork was ever truly designated as such by that mfr, but Santana did spec that fork while it was available.

I believe the current 3rd party fork vendor list that is being spec'd by other tandem builders is ENVE, Whisky, and TRP.
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Old 12-23-15, 09:15 AM
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Originally Posted by Paluc52 View Post
Do you know of any carbon forks for tandems that has that much rake?
By "that much" I"m assuming you're referring to the Burley OEM spec of 55mm, 395mm length AND with a 1.125" steerer. The closest you'll find would be a new old stock (NOS) Reynolds Ouzo Pro Tandem which were made with 55mm of rake / 395mm length in both the 1.5" Santana steerer spec and the more common 1.125" steerer spec for other tandems. We have one I keep around for our Calfee that I picked up from John Slawta at Landshark a few years back. They pop up now and again on ebay, but I'd hold out for a NOS model vs. one that had been used unless you're confident you're buying from an owner who really knows the fork history / cut steerer length. You don't want to buy a fork that's been cut too short for your handlebar height needs, that was subjected to really heavy loads (we have a 1.5" model on our triplet that's seen 450lb team weights) or was on a roof-topped tandem that was banged into an overhead obstacle.

There was also a composite Bontranger Satellite Tandem fork make for the last few model years of the T2000 that has has 50mm of rake, same as the Co-Motion standard composite forks. They are the correct length vs. the very short length / short rake ENVE or other composite forks that tend to be a little shorter than the 395mm length used on Burley. 50mm is actually a pretty nice middle ground for anyone with a 55mm steel fork who doesn't want to see a huge change in their tandem's handling. Again, same rules of engagement apply: look for a NOS model.

That's about what I'm aware of, but I haven't been keeping up.

All that said, I'd stick with a steel fork for the Rumba; the juice isn't always worth the squeeze when chasing weight savings or reduced road chatter.

Last edited by TandemGeek; 12-23-15 at 09:23 AM.
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Old 12-23-15, 10:24 AM
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Originally Posted by TandemGeek View Post
On single bikes, yes... on tandems it gets into semantics and subjectivity.

Shorter rake = more trail / Yes.

Example here would be a tandem with 73 head tube and ~375mm long, ~44mm rake fork (e.g., Co-Motion) with trail in the 2.2 - 2.3" range. Most people who like these "performance" tandems describe them as handling very much like their single bikes. The geometry yields a very stable ride IF the captain and stoker ride cleanly. They are very responsive to subtle steering inputs vis-a-via counter steering inputs and shifting body weight left or right... very much like a single racing bike. The down side is for teams that don't ride clean, especially at slow speeds and when climbing. You can see teams who would probably be better off with longer rake / less trail climbing steeper grades where the captain is countering every low-cadence pedal stroke with a steering input to keep the tandem traveling in a straight line. Clean riding teams who can spin a higher cadence while climbing don't typically have this issue.

Longer rake = Less trail: Yes

Example here is a tandem with 73 head tube and 395mm long, 55mm rake fork (e.g., Santana, Burley) with trail in the 1.8 - 1.9" range. They are less responsive to unintended steering inputs from body weight shifts and require deliberate steering inputs to initiate and curtain cornering, which at very high cornering speeds can feel like understeer until you get used to it coming from a single bike or from a tandem that has longer steering trail. However, there is less task load on the captain when climbing at slower speeds / low cadence even with a lot of body english coming from the stoker.

In the middle ground is a standard Co-Motion road tandem with a 73 head tube and 395mm, 50mm rake fork as well as the Cannondale road tandems in the 2.0" range which at one time used a little less head tube angle with a 53mm rake fork. I have no idea what they use today, but suspect it's similar.

At the far end of the spectrum is Bilenky who use very short steering trail in the 1.65" range, shorter than anyone else but that yield very nice handling tandems. Go figure.

Very good summary. Tire width does also play a role because the larger contact patch requires more turning input and offsets some of the lower trail. Our tandems are similar to the Bilenky in trail but also use 38-42mm tires at 70 psi +/-. With 25-28mm tires at higher pressures I prefer Santana like trail.

Word choice is an issue in these discussions. I would describe longer trail tandems as having more weight actuated steering while lower trail tandems require more input with the handle bars. This gets away from the idea of quick and slow. I feel low trail tandems actually react faster than a longer trail tandem once the captain has learned to turn the bars and not rely on leaning alone to start the turn. The problem is that this style is different than what the captain has always done when longer trail single bike riding.
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Old 12-23-15, 11:42 AM
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Originally Posted by TandemGeek View Post
All that said, I'd stick with a steel fork for the Rumba; the juice isn't always worth the squeeze when chasing weight savings or reduced road chatter.

Point well taken. Thanks again.
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