fitting a randonneur 650b bike

[erick]

hi, first of all sorry for my inglish, this is not my language so please try to read.

 i need advice to by a soma grand randonneur bike. im not shure in what size (58 or 61).

im 180cm tall, and with a inseame 86cm, prety normal shape. i run a 56 road bike with a 130 steam and a drop of 6-7 cm lower than the saddle and my saddle is 740mm from BB. that bike is enough confortable for a max of 3 hours.

im looking for a rando bike with a shorter reach and a more level handlebar-saddle, becouse in rides longer than 3 hours my neck star to pain.

i draw in bikecad the two sizes (58 and 61), and visually liked more the 61 with less spacers but im a little afraid to go so big in a frame, mybe my draws are all rong, but i find to little seatube show, an im concern tha if i buy a brooks b17 the seat tube will be even shorter

any advice will help

[Alistair Spence]

Erick,

what's your saddle height? Judging on your inseam I'm guessing it's around 75cm, but just wanted to check.

Alistair.

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[erick]

 saddle height is 74

[rcnute]

Sounds to me like the 58 is what you need.

Ryan

On Friday, October 4, 2013 6:37:17 PM UTC-7, erick wrote:

 saddle height is 74

[Alistair Spence]

Ah, yes, I see it on the drawing now that I look. I should have checked that first.

Really, I don't think that the ST tube length comes into it. ST length is mostly a cosmetic, personal preference thing. It affect things like how much seat post is showing, and whether you prefer a horizontal stem extension, or a sloping one.

 

What's more important is which of the other key measurements suit your needs better.

I notice that the front centers on those bikes are pretty long. I wonder about how the 61cm frame with a 641mm front center is going to handle? That's a pretty large number.

Alistair.

Alistair.

On Fri, Oct 4, 2013 at 6:37 PM, erick <erickb...@gmail.com> wrote:

 saddle height is 74

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[Evan Baird]

Depending on how high you run your bars, you may feel that the GR runs a little short in the cockpit. It's intended for long reach bars like the Soma Brevet and the Nitto Grand Randonneur (the bike's namesake). If you run the bars level with a shorter handlebar bag you can more or less size it like a road bike. I like my bars a little higher using a decaleur, so I would go for the largest size I can straddle with the intention of running a shorter stem, and raising the hoods up to level with the saddle. This setup also yields minimal toe overlap issues, although withe the fork rake it's really shouldn't be much of an issue for anybody.

[James McKinley]

Erick,

I am 180 cm tall, with a pubic bone height of 86 cm (the height of the top of a book spine, jammed up between your legs to snub up on your pubic bone. I assume that is what you mean by inseam.)  In shoes with cleats, I am most comfortable using a bottom-bracket to seat-top height of 760 mm, although the 'conventional' height for my pubic bone height would be 740 mm.  Last year I bought a 650B that was specified as a 59 cm frame. The seat tube, measured bottom-bracket to center of horizontal top tube was 58 cm, the horizontal top tube length was 56.5 cm.  (Those are 'theoretical' projections for reference, as the top tube was actually slanted it is on the Soma bike.)  With a 90 mm stem, the saddle top to bars distance was 67 cm.  I ride it with the saddle at the height of the bars.  It's very comfortable for long rides.  I'd also suggest the 58cm frame.

Jim

[satanas]

On Saturday, October 5, 2013 1:26:25 PM UTC+10, Alistair Spence wrote:

What's more important is which of the other key measurements suit your needs better.

I notice that the front centers on those bikes are pretty long.

I'd personally say that they are sensible. I'm about the same size as the the OP and could fit on a 56cm frame - the front centre is actually (just) long enough without needing to go bigger to avoid overlap. Provided the FC is long enough and a reasonable length stem can be used with an "acceptable" amount of spacers and/or slope, then IMHO the frame might just as well be smaller as bigger, unless one os planning on using a large-ish in-frame bag of some sort.

Later,

Stephen

[Alistair Spence]

On Mon, Oct 7, 2013 at 2:53 PM, satanas <nsc.e...@gmail.com> wrote:

I'd personally say that they are sensible. I'm about the same size as the the OP and could fit on a 56cm frame - the front centre is actually (just) long enough without needing to go bigger to avoid overlap. Provided the FC is long enough and a reasonable length stem can be used with an "acceptable" amount of spacers and/or slope, then IMHO the frame might just as well be smaller as bigger, unless one os planning on using a large-ish in-frame bag of some sort.

Yeah, I think that's fair. I didn't mean to imply that the front centers on those Soma's was a deal breaker.

I have size 13 feet, and like them pretty far forward on the pedal, with the ball of my foot ahead of the pedal axle, which has the effect of making my foot size seem larger than it is, from a perspective of TCO. 

To avoid TCO, with Hetre tires and Honjo fenders, I need a front center of 620mm. When I saw a front center of 641mm on that 61cm Soma it just kind of jumped out at me, because it's an area of frame design that I've spent some time looking into. 

The longest FC I currently run on any of my bikes is 630mm. This is on a grocery getter/porteur type bike. I feel that when the FC gets this large it slows the steering down, which is fine by me on a utility style bike, but perhaps not desirable by some on what might be considered more of a "road" frame.

Even though I've designed and built frames that eliminate TCO, I'm not currently convinced that using it as a driving design parameter is a good idea. Not sure about that though, I'm still evaluating it. 

Of course, what others prefer for themselves is up to them. I'm just throwing out my observations on the matter.

Cheers,

Alistair.

[Stephen Poole]

On 8 October 2013 10:23, Alistair Spence <alspe...@gmail.com> wrote:

I have size 13 feet, and like them pretty far forward on the pedal, with the ball of my foot ahead of the pedal axle, which has the effect of making my foot size seem larger than it is, from a perspective of TCO.

I wear size 45 shoes with the cleats a fair way back, and have found I need 625mm to have clearance with 700x25 + fenders - the same diameter as Hetres + fenders. 610mm is acceptable only with smallish size 44 shoes and the foot well back on the pedal, but otherwise there is significant overlap, and I have a couple of bridge approaches where this is very annoying.

I'm not convinced that making the front centre a bit longer than average (which is usually too short IMHO) causes any problems. On MTBs it's a different story, and I tend to have problems getting enough weight onto the front tyre when cornering. It's all very well making the front centre longer to avoid going over the bars on descents, but those descents have corners too!

Later,

Stephen

[erick]

i still can´t decide.....

it´s seem the 58 a safe bet, plus have lighter tubing, but i find to short the 170mm headtube and aesthetically like much more the 200mm headtube in the 61.

i have done my measures again and im 181cm tall, and use a saddle of 750mm. i draw again the bikes and its seem that the 61 with a 100mm stem is still shorter than the 58 with a 110mm stem

but in thing likes tubing and front center geometry i don´t know anything...

[Alistair Spence]

On Mon, Oct 7, 2013 at 7:08 PM, Stephen Poole <nsc.e...@gmail.com> wrote:

I wear size 45 shoes with the cleats a fair way back, and have found I need 625mm to have clearance with 700x25 + fenders - the same diameter as Hetres + fenders. 610mm is acceptable only with smallish size 44 shoes and the foot well back on the pedal, but otherwise there is significant overlap, and I have a couple of bridge approaches where this is very annoying.

Hmmm. Those numbers don't jibe with my experience. I just double checked the front center on the bike I was referencing, using trammel points and a steel rule: 

Size 47 feet for me, 620mm front center, no TCO. Maybe you're running longer cranks though? I'm running 172.5's.

I don't agree that 700x25 tires are the same size as Hetres. 700x25's tires are a touch larger than Hetre's, which have a diameter closer to a 700x19 or 700x20 tire. 

For Hetre's I get 673mm for the diameter. 700x25's are typically 683-685mm, or at least the ones I have measures are.

Anyway, not trying to split hairs here. Just relating my observations.

Cheers,

Alistair.

[Kyle Martin]

It looks like you have a 90mm stem on the 61cm frame.

Can you measure from where the seat post intersects the saddle to the hoods or end of the stem? That measurement compared to your current ride will likely help.

I am your same size and saddle height so I'm interested in your decision on this frame, I'm also considering it.

[Stephen Poole]

On 9 October 2013 07:48, Alistair Spence <alspe...@gmail.com> wrote:

Size 47 feet for me, 620mm front center, no TCO. Maybe you're running longer cranks though? I'm running 172.5's.

I suspect the variable here is cleat position; my cleats are almost all the way back on the shoes, i.e., centre of cleat to shoe toe is ~110mm.

Nominal tyre sizing IME means little, but I've seen it suggested that Hetres are ~670mm diameter, which is about the same as many nominally 700x23-25mm tyres. I agree that with an *actual* width/height of 25mm then the 700C diameter will be more like 680mm, but listing measured dimensions plus the name and nominal size of every tyre referred to every time might get a bit old.

Also, I really do NOT wish to have any overlap, and would prefer to have a few mm to spare rather than none. YMMV...

To the OP: I'm 180cm tall, have a saddle height of 750mm and would personally get either the 55cm or 58cm Soma frame, probably the former. Note however that I DO NOT agree with the fashion of riding the largest possible frame size, and do not need or want the bars to be as high as the saddle or higher. The frame I'm about to have built is going to have a seat angle of 72 degrees, a 150mm head tube, an effective top tube length of 590mm, and an actual seat tube length of 509mm, with a sloping top tube, and so does not really match up with the prevailing short top tube + tall seat tube rando frame fashion. It will, however, fit me very well.

Later,

Stephen

[erick]

i have two road bikes, my racing bike measure 72.5cm from the intersect post-saddle (without consider seatpost clamp) to the center of the stem clamp, with a saddle to handlebar drop of 7cm.

my other road bike setup for longer distance has a measure of 69.5cm interrsect post-saddle to center of stem, with a drop of 2cm.

the soma 61 with a 90mm stem has a measure of 70,3 cm. the 58 model with a 110 stem has a measure of 71,5 cm

[Alistair Spence]

On Wed, Oct 9, 2013 at 8:07 AM, Stephen Poole <nsc.e...@gmail.com> wrote:

I suspect the variable here is cleat position; my cleats are almost all the way back on the shoes, i.e., centre of cleat to shoe toe is ~110mm.

Maybe, but I jam my cleats all the way back in their slots too. When I'm riding flat pedals the ball of my foot is forward of the axle by a bit. We seem to be getting different measurements here, odd, but oh well.

Nominal tyre sizing IME means little, but I've seen it suggested that Hetres are ~670mm diameter, which is about the same as many nominally 700x23-25mm tyres. I agree that with an *actual* width/height of 25mm then the 700C diameter will be more like 680mm, but listing measured dimensions plus the name and nominal size of every tyre referred to every time might get a bit old.

I made a simple tool that lets me accurately measure tire diameters. The numbers I quoted are actual measurements.

Also, I really do NOT wish to have any overlap, and would prefer to have a few mm to spare rather than none. YMMV...

Got it, and that does make sense, especially on a mass produced bike. Better to err on the side of having more clearance, than less, espeically if TCO is a deal breaker. 

To the OP: I'm 180cm tall, have a saddle height of 750mm and would personally get either the 55cm or 58cm Soma frame, probably the former. Note however that I DO NOT agree with the fashion of riding the largest possible frame size, and do not need or want the bars to be as high as the saddle or higher.

Just to provide a counter point for the OP to consider, my saddle height is 720mm and I ride a frame with a 60cm seat tube. It is the best fitting bike I've ever owned. I find that being able to get the bars level with the saddle is crucial for comfort (for me). 

This has nothing to with fashion, it's just what works. I could achieve the same fit with a smaller frame and more seatpost/stem stickout, but I prefer to less. Again, not fashion, more of an aesthetic preference.

From the drawings provided by the OP I'd go with the 61cm, but obviously I have a preference for larger frames. Others, quite legitimately, will have other preferences and priorities, and will choose differently. 

There can be more than one correct answer here imo, unless we start talking racing, and racing bikes. At that point, comfort is much lower down the priority list and the rider is obliged to fit the bike, which will be designed around a much narrower/less negotiable set of parameters.

Alistair.

 

[erick]

the story ended with a 61 frame, and find the fit pretty perfect.  i painted the bike in a grey-blue color and drilled the frame for intenal cable routing, now is rolling but still need to add fenders and a rear dyno-light.

 

[erick]

[Evan Baird]

That looks awesome. Just awesome.