Impact of a lower BB on Hill Climbing/Speed

Recumbents and all feet forward machines

Impact of a lower BB on Hill Climbing/Speed

Postby Aushiker » Thu Jun 20, 2013 3:16 pm

I was doing a bit of searching on the Lightening P-38 and came across a posting at MetaBikes from an Australian rider, Paul Worden that describes his decision to go with the Metabike Metaphysic over the Lightening P-38.

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An aspect that caught my attention from Paul's post was this comment …

The bottom bracket was high, so this should be a powerful and aerodynamic bike. The seat was adjustable right down to a neck straining twenty degrees – or you could set it to a more comfortable and hill friendly thirty or forty degrees.


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The bottom bracket is about 83 cm (32.7") with 700c wheels. I notice that Metabikes also sell a MetaThesis which is the same frame but with a 700c rear and a 20" front wheel. They describe the MetaThesis thus

MetaThesis models are based on the efficiency and sporty behaviour of their higher brothers. They are very easy to ride due to the moderate height of seat and pedals. So are ideal for road ride and sporty commuting.

MetaThesis is the perfect fusion of commuting and racing recumbents.


The bottom bracket height on the MetaThesis is 62 cm /24.4". Does the choice of 20" front wheel make that bigger difference to the performance of the bike in terms of speed and hill climbing?

I am curious from the perspective of a the bike as a randonneur and possible tourer. I appreciate that MetaBike do a randonneur model but I am not so keen on the high bottom bracket and hence was curious about the performance of the lower bottom bracket bikes.

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After all the Lightening P-38 bottom bracket height is 24-26".

Thanks
Andrew
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by BNA » Thu Jun 20, 2013 3:25 pm

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Re: Impact of a lower BB on Hill Climbing/Speed

Postby Aushiker » Thu Jun 20, 2013 3:25 pm

One other difference I noted (and I think this is what appeals to me) is the angle of the seat on the Lightening versus the angle of the seat on the Metabikes. The Lightening seat angle is around 50 to 65 degrees versus 20 to 40 degrees on the Metabikes. Does this impact on hill climbing. I guess it impacts on speed but then the P-38 and for example teh Gold Rush Replica are touted as fairly fast bikes.

This riding position appeals to me ...

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Andrew
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Re: Impact of a lower BB on Hill Climbing/Speed

Postby just4tehhalibut » Fri Jun 21, 2013 12:55 am

BB high to seat can mean you need to take more care with bike and shoe set up to avoid numb toe issues, also you might have issues if not experienced at hill starts or traffic stops. BB low to ground can mean issues with heel strike, normally more for SWB but I have on occasion struck a shoe on a kerb or speedhump while hopping my trike. Seat angle can affect your hillclimbing but the tradeoff is that you can sit up and admire the scenery and maybe look over your shoulder for traffic. But then if you have a decent fairing none of this really matters, you can get away with a lot of shenanigans in bike set up behind that shield and still have a chance of speed.

For another opinion here's what Bacchetta says :
"If you’re too upright, you’ll close off your breathing and put your hips in an awkward position. Imagine yourself in your recliner at home. As soon as you recline the chair and put your feet up, your back reclines. This is the same motion on a short wheelbase recumbent. Experiment by reclining your seat a couple of notches before your next ride. If it feels good, recline it another notch. You can do this until you reach the point where it is beginning to get uncomfortable while riding and you’re losing power while climbing.
Too Laid Back. This is actually pretty rare with beginners. But, if you are having problems climbing or just do not feel comfortable at stops and starts (and your leg length is correct), try inclining your seat. Do this the same way as we discussed above, making adjustments 1-2 pin holes in the back at a time."
http://bacchettabikes.com/support/fitting/rider-setup.php.
Bacchetta talks of pin holes or notches as with their standard grenade pin adjustment for the seatstays, the Velogenesis clamps as mentioned in another thread give better, finer adjustment. Some Bacchetta owners have taken the use of the Velogenesis clamps a step further and made seatstays that can be adjusted on the fly to deal with hills then traffic. Some Bacchetta models as well as I think Lightning use pivot stems to allow easy handlebar adjustment. In other words there are many ways to deal with hills and you'll find it somewhere between reclined and upright, speed and comfort.
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Re: Impact of a lower BB on Hill Climbing/Speed

Postby Aushiker » Fri Jun 21, 2013 11:53 am

just4tehhalibut wrote:BB high to seat can mean you need to take more care with bike and shoe set up to avoid numb toe issues, also you might have issues if not experienced at hill starts or traffic stops. BB low to ground can mean issues with heel strike, normally more for SWB but I have on occasion struck a shoe on a kerb or speedhump while hopping my trike. Seat angle can affect your hillclimbing but the tradeoff is that you can sit up and admire the scenery and maybe look over your shoulder for traffic. But then if you have a decent fairing none of this really matters, you can get away with a lot of shenanigans in bike set up behind that shield and still have a chance of speed.


Thanks. I do like the idea of a more upright riding position, aka the Easy Racers Gold Rush or the Lightening P-38.

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Re: Impact of a lower BB on Hill Climbing/Speed

Postby Baalzamon » Fri Jun 21, 2013 12:06 pm

Something local
Just Bents Mind you does say unavailable and a new range is coming soon so might pay to call him.
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Re: Impact of a lower BB on Hill Climbing/Speed

Postby Aushiker » Fri Jun 21, 2013 12:13 pm

Baalzamon wrote:Something local
Just Bents Mind you does say unavailable and a new range is coming soon so might pay to call him.


I thought they went out of business? Spec is not that impressive either.

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Re: Impact of a lower BB on Hill Climbing/Speed

Postby jaffaman » Fri Jun 21, 2013 8:42 pm

Goldrush listed for sale on the OzHPV web site at the moment.
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Re: Impact of a lower BB on Hill Climbing/Speed

Postby Roadie » Fri Jun 21, 2013 9:44 pm

On my Optima lynxx I started with the seat as upright as possible for afew months then tryed as laid down as possible and didn't like it. It was a lot more strain on my neck trying to tilt my head forward enough.I've ended up half way. Also because your balance control comes from your back rather than your arms on a recumbent, I didn't find control as good. The BB on this bike is just above the seat and I find it more effort to have my legs up there than a conventional bike (more tiring).
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Re: Impact of a lower BB on Hill Climbing/Speed

Postby John Lewis » Fri Jun 21, 2013 11:03 pm

I think one of the reasons for the high BB is to get the feet up in the body area that is already creating air resistance and not to have them down lower creating even more frontal area. I suspect those churning feet could have quite an effect.
On my SWB I do have the BB lower and I do have heel strike. I quickly got used to it and it wasn't a problem.

The seat recline is a juggling act for me. I want it up for comfort but at the same time low enough to lessen the frontal area and wind resistance.

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Re: Impact of a lower BB on Hill Climbing/Speed

Postby Aushiker » Sat Jun 22, 2013 12:04 am

jaffaman wrote:Goldrush listed for sale on the OzHPV web site at the moment.


Yes seen it ... older model and I think the pricing is a bit high. If I was to go a Gold Rush it would need to be 2013 model with couplers (if they become available).

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