Leg length and Lowracers

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Leg length and Lowracers

Postby John Lewis » Tue May 05, 2009 1:11 pm

I was told that you need at least a 32 inch inside seam measurement for a 406 front wheel lowracer.

Otherwise you have to go to smaller wheels. Not real keen on 16" wheels or a moving BB.

So anybody out there with lowracer experience like to comment. I have only a 30 inch (762mm) inside seam. I think the main concern is to avod pedal overlap.

At the moment I'm building a LWB lowracer. It's long 1829mm and heavy. Should be interesting even if impractical so I'm thinking of SWB and twisted chain FWD.

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by BNA » Tue May 05, 2009 1:23 pm

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Re: Leg length and Lowracers

Postby Kalgrm » Tue May 05, 2009 1:23 pm

Hi John,

I can't offer specific experience, but you can significantly reduce the severity of pedal overlap by fitting 145mm cranks. I've got them on my 'bent and love them - more power, higher cadence and less knee strain. It will also shorten the effective boom length by ~30mm.

Cheers,
Graeme
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Re: Leg length and Lowracers

Postby Freddyflatfoot » Tue May 05, 2009 2:49 pm

Wont be an issue on your bike John! Your wheel is out front of the cranks.
On the SWB style, it can be a problem. Shorter cranks can help, as can raisng the boom higher above the wheel.
I'm not sure about inseam, but my xseam is 40" (5'6' tall), and my SWB has a 451 front wheel. Not that low though, mid racer format, seat height about 500mm.
As far as i know, heel interfernce is only an issue on tight turns, and that can be reduced by using varying techniques.
Cheers!
Rob
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Re: Leg length and Lowracers

Postby John Lewis » Tue May 05, 2009 2:50 pm

Kalgrm wrote:Hi John,

I can't offer specific experience, but you can significantly reduce the severity of pedal overlap by fitting 145mm cranks. I've got them on my 'bent and love them - more power, higher cadence and less knee strain. It will also shorten the effective boom length by ~30mm.

Cheers,
Graeme


Thanks Graeme. I had thought of that as a possibillity. Where did you get them? I know Greenspeed will alter cranks at a price and you can do it yourself if you can find the taps. A commercial ready made source would be nice though. I need to do some scale drawings or some sort of mockup to see what's possible in a bike.

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Re: Leg length and Lowracers

Postby John Lewis » Tue May 05, 2009 2:58 pm

Freddyflatfoot wrote:Wont be an issue on your bike John! Your wheel is out front of the cranks.
On the SWB style, it can be a problem. Shorter cranks can help, as can raisng the boom higher above the wheel.
I'm not sure about inseam, but my xseam is 40" (5'6' tall), and my SWB has a 451 front wheel. Not that low though, mid racer format, seat height about 500mm.
As far as i know, heel interfernce is only an issue on tight turns, and that can be reduced by using varying techniques.


Hi Rob,

Hope the foot is coming good. Yes, no trouble on LWB but I'm looking at a short. I don't have a problem on my SWB Bentech so I can't see the problem on a low racer. Heel interference is no trouble. I live with that on the 'tech. Only took a ride or two to get used to. Just that I've been told that on a lowracer with a short inseam/ Xseam you get hard pedal interference and that's a no no.

Seems to me that putting the BB higher would help but there might be a comfort issue. Some people don't like the BB higher than the seat.

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Re: Leg length and Lowracers

Postby Kalgrm » Tue May 05, 2009 3:38 pm

G"day John,

I got a set of Forza cranks from Power on Cycling in the US, for US$35. The quote on postage to Australia was US$27 for one set.

I ended up buying a set of 145mm and a set of 155mm, just in case the 145mm were too short (they aren't) and the postage came to US$35 for the package.

They are standard square taper road triple cranks - I simply swapped my chainrings across from the old crank set.

Cheers,
Graeme
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Re: Leg length and Lowracers

Postby John Lewis » Tue May 05, 2009 4:07 pm

Thanks Graeme.

Might look at gettin some soon.

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Re: Leg length and Lowracers

Postby Freddyflatfoot » Tue May 05, 2009 4:29 pm

Tri Sled also have short cranks, but I notice only in the 110/74 BCD format.
http://www.trisled.com.au/shop/shopdisp ... cat=Cranks .
As for bb height above seat level, I have about 6" which seems ok.
There are other bikes that have even more, maybe 10" or so?
Cheers!
Rob
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Re: Leg length and Lowracers

Postby raptordesigns » Tue May 05, 2009 4:35 pm

John Lewis wrote:I was told that you need at least a 32 inch inside seam measurement for a 406 front wheel lowracer.

Otherwise you have to go to smaller wheels. Not real keen on 16" wheels or a moving BB.

So anybody out there with lowracer experience like to comment. I have only a 30 inch (762mm) inside seam. I think the main concern is to avod pedal overlap.


I'm about a 750 inside seam. I have a SWB lowracer (homebuilt) with the following specs
Wheelbase 1240 mm
Front wheel 20 inch (406)
Rear wheel 26 inch (559)
Cranks Bontrager (Truvativ) 165mm
Seat height 32cm
BB height 56cm (BB height above seat base 24cm)
Seat angle 25 deg approx
Chainline - beside front fork.
see: http://www.aerialpursuits.com/misc/talon.htm

Heel strike is generally only a problem when turning sharp and forgetting NOT to pedal.
Because of the chain line, the radious of turns under power are severely limited and so heel strike does not occur.

I would very much like to be a few inches taller or not have such stubby legs. :-(

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Re: Leg length and Lowracers

Postby John Lewis » Tue May 05, 2009 8:38 pm

Thanks John. That is encouraging news. We'll see how I go. I'll build it in steel though.

I'd like to give the carbon a shot but would need to study a bit first. I think for a first attempt steel will be the go. be interesting to compare the lwb and swb versions whenI'm done.

The short legs is a pain. I sat on Kalgrm's highracer on its 700 wheels the other week to see how I'd fare. It was doable but would not be too satisfactory for commuting start stop as I really had to stretch to reach the ground. I think I'd be right with 559 wheels though.

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Re: Leg length and Lowracers

Postby Poiter » Tue May 05, 2009 9:41 pm

It's not the soft interface of a heel strike you have to worry about.
It's hard interface of a crank arm that will bring you undone.
The NoCom BatMoBent has crank overlap and it works OK so long as you're not trying to do slaloms and as John says forget about pedalling in tight corners.
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Re: Leg length and Lowracers

Postby william » Tue May 05, 2009 10:00 pm

Hi John,
Another place for shorter cranks is Greenspeed. They don't advertise it on their web but if you call Mick he will give you further details.
He devoutly swears by shorter cranks for recumbents. He re-machined mine for about $30 and are 150mm. He likes 135mm on his trikes.
I think they have some Carmina square taper short cranks in stock all the time.

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Re: Leg length and Lowracers

Postby bradwoodbr » Tue May 05, 2009 10:51 pm

I used 150mm cranks on my M5 Shockproof (medium lowracer) and with size 10 feet there was a little bit of heel interference when a heel would scrape the mudguar. But that was my warning sign and never got into any trouble.

I know have 170mm cranks on my Optimat Baron Raptor. I have also kept my size 10 feet :) and find only a little bit more heel strike and only when turning very tight turns that require me to pedal (an uphill zigzag cyclepath). I release my clipless pedals and ride with my heels on the pedals to eliminate heel strike in this situation.

Both bikes have 406 rims on the front.

I think heel strike is only a minor issue and would recommend designing the bike for its major purpose. eg fast, relaxed, comfortable cycling and not put any importance on heel strike.

Many Optima Baron riders actually drop the chain, which causes greater steering compromises in slow corners than heel strike. These guys also state that steering with a dropped chain is only a minor problem when doing slow tight turns. I guess a bike with a bit of challenge for the riders built into it is a better bike than one that is just too easy to ride????

I hope these observations help.
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Re: Leg length and Lowracers

Postby Kalgrm » Tue May 05, 2009 11:17 pm

Good points Brad - under normal usage, heel strike is a rare thing and should not unduly influence the design of the bike.

Cheers,
Graeme
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Re: Leg length and Lowracers

Postby John Lewis » Tue May 05, 2009 11:27 pm

Thanks for all the information guys.

I am not cocerned with heel strike. I have that on my current SWB and can live with it. I simply don't notice it anymore but it tipped me off a couple of times at first. What I am concerned with is the hard interference from pedals and cranks. Probably ok most of the time or in a race situation but it doesn't make for relaxed riding. Peters Nocom is a great racing machine and a thing of beauty but I don't think I'd want to ride it on the cycle path or street.
Thanks for the heads up on Greenspeed william
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Re: Leg length and Lowracers

Postby Poiter » Wed May 06, 2009 6:02 pm

Tri-sled have short cranks for $50 in their on-line store.
http://www.trisled.com.au/shop/shopdisp ... cat=Cranks
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Re: Leg length and Lowracers

Postby John Lewis » Wed May 06, 2009 9:58 pm

Poiter wrote:Tri-sled have short cranks for $50 in their on-line store.
http://www.trisled.com.au/shop/shopdisp ... cat=Cranks


Thanks Peter. I check them out. I need some for a mate wth knee troubles to try too.

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