If you fall between bike sizes, should you choose smaller or larger than perfect

[Andre Jute]

Thorn is a maker with enough sizes to fit everyone, but the trend in bikes generally is for fewer sizes with bigger holes in the range than was classically true.

Generally speaking, LBS/salesman/designer wisdom these days is that when there is no perfect fit in the available sizes between cyclist and bike, to choose the smaller of the bracketing sizes.

Personally, since I pay for a custom bike, I expect it to fit perfectly, or to be easily adjustable to fit perfectly, and certainly to have enough adjustment range to adapt to increased experience and, unfortunately, increasing age too.

That, in my experience, means going against the received wisdom of choosing the smaller available bike and choosing instead the one that is marginally larger than the precise spot size. The larger bike, given only that it is proportionately scaled with longer chainstays,  generally rides smoother, it is more stable at speed on both the level and downhill, and it is less wearing to ride, more comfortable. I don't notice the small cost in hauling more weight uphill; instead I notice that the slightly longer wheelbase makes pedalling uphill easier by tracking truer. Moving through each of the many micromodes of bicycle operation and use, in each instance the bigger bike is more pleasing over the longterm.

That's my opinion anyway. YMMV.

Andre Jute

[Danneaux]

Andre,

There is some real wisdom there in your post, and it squares with my own experience over the years.

I found myself on the horns of this dilemma when moving from my 560S Sherpa to the Nomad. With drop handlebars, I "could" have ridden either a 565M or a 590M. At first blush, the 565M would have been the right choice, but I went with the 590M and have not regretted it, and fitted a 60mm stem to accommodate my (compact) drop handlebars with brake levers far forward in a normal position. I have the same fit as I did on my Sherpa, and am able to sit more easily upright on the larger 590M frame than I would have on the 565M. The 590M is taller, which made it easier to get my handlebar-tops at the same level as my saddle-top, which I prefer.

Thanks to the generously sloping top tube, standover clearance is generous enough to be a non-issue in all conditions including off-road, so no loss there in choosing the larger frame.

One factor making the choice harder was the difference in weight rating (carrying capacity) between the 565M and 590M. The smaller frame was made "stiffer" thanks to the shorter tubes and therefore had a 3kg higher rating. I picked up a bit of that "lost" capacity by going with an M frame (shorter top tube better suited for drops) than if I'd gone with an "L" (long top tube frame really too long for drops in my case, and a 5kg lower cargo rating). I detailed a bit of my reasoning here, under the "Sizing" heading: http://www.thorncycles.co.uk/forums/index.php?topic=4523.msg22073#msg22073 Andy Blance thought the larger 590M frame might be a bit more stable. I'm glad I went with it and am happy for my needs.

A larger frame can also mean more of the carried weight falls within the wheelbase of the bike, which can aid stability as well.

For the few racing bikes I've tried but not owned, a small frame seemed an advantage for out-of-saddle sprints. The shorter seat tube and lower top tube made it easier to rock the bike from side to side without fouling my knees, and the lower top tube made it easy to get a nice, low position -- all of which is unsuitable for my style of touring. For the touring bikes I choose to own instead, I much prefer a larger frame if given a choice, so long as standover is adequate and my positioning is good. Horses for courses, really, and suitable positions for each.

All the best,

Dan.

[revelo]

I would agree with Hobbes that slightly larger is probably better, PROVIDED the standover clearance is adequate.

1) When the frame is too small, you'll get a truly gigantic stack of spacers over the headset if you choose to ride in an upright position, like me.
2) If you use flat bars, a small frame may result in a very long stem, which is weaker than a short stem, all other things being equal. A broken stem when hitting a bump while riding fast downhill will lead to a nasty spill.
3) Because I tour with a load on dirt roads, I'm l less concerned about a smooth ride than heel clearance for the panniers. The larger frame is better here as well.

Standover clearance is really the critical measurment. I'd advise getting the largest frame with adequate standover clearance. And be generous here, because that's a nasty injury waiting to happen if standover clearance is not adequate.

I'd also advise picking the medium top tube for almost everyone, so you can sit upright, as you surely will want to do once you break free of the mentality that the goal of bicycling is speed rather than enjoyment.

Note the stack of spaces on my bike below, which is NOT sized up, but rather exactly what Andy Blance recommends for someone my height (590M frame and I am 180cm tall). With the 565M, that stack of spacers would be still higher:

[Danneaux]

Note the stack of spaces on my bike below...

<nods> Yep, mine has 'em too, and happy to accept them as a way to keep the uncut steerer that does what I need.

Not that it makes a whit of difference structurally, but Thorn now offer "tall" spacers that remove some of the poker-chip effect and considerably improve the appearance of a spaced-out steerer. You and I are nearly the exact-same height and I also ride a 590M Nomad (albeit with my preferred drop handlebars) and was amazed at how much nicer the tall spacers improved the appearance. A small thing to be sure, but more congruent with my aesthetic tastes. Fewer pieces to keep track of when servicing the headset with replacement bearings as well.

SJSC root search results for headset spacers here: http://www.sjscycles.co.uk/page/find/?name=headset%20spacers&page=1
Thorn Alloy 1-1/8 spacer kit showing the new taller examples here: http://www.sjscycles.co.uk/thorn-alloy-headset-spacer-kit-1-1-8-inch-3mm-to-108mm-prod27590/ ; includes 24mm and 48mm spacers as well as the more usual 3, 6, and 12mm.

Best,

Dan. (...who puts mechanics and ergonomics first, but is a fusspot for aesthetics)

[revelo]

I'm not concerned about aesthetics. However, the Park "Big Blue Book of Bicycle Repair" recommends no more than 40mm between stem and headset, whereas I currently have 115mm.  They don't explain the reason for recommending no more than 40mm. Perhaps it makes it difficult to get the headset adjusted properly. I'm not too worried, because I can't see this is as a serious safety issue, but it does give me pause about using say 135mm of spacers, as would be required with the 565M.

My other bike repair books ("Zinn and the Art of Mountain Bike Maintenance" and "Bicycle Maintenance and Repair" by Todd Downs for Bicycling Magazine) are silent regarding huge stacks of spacers, so maybe it is a non-issue.

[Andre Jute]

A short steerer is another roadie shibboleth with unspoken corollaries that deserves to be buried without honours. I just don't see that the height of the spacer stack is an engineering issue. Nor, not being inculcated with the idea that the form of the bicycle is fixed by the UCI (at all) or by whatever that Belgian rode half a century ago, do I see the height of the steerer exposed above the head tube as an aesthetic issue. One of the most beautiful bikes ever made, and by far the longest lasting design, the Pedersen, has a headtube that is either incredibly short or two feet of mostly empty space enclosed in four pyramid tubes.

Andre Jute

[Erudin]

For longer rides I like to ride the largest appropriate frame size, or "French Fit". I use a locking spacer on my bikes that have a big spacer stack.

http://www.competitivecyclist.com/html/fit/traditions_of_road_riding.html

[Pavel]

A short steerer is another roadie shibboleth with unspoken corollaries that deserves to be buried without honours.

Perfectly put!
I rather like the versatility and "gasp" the look ... of the well endowed steerer look.  Far away from "racer boy" is esthetically pleasing to me!

[Matt2matt2002]

Until I bought my Raven a few months ago, I was riding a Dawes Sardar small framed bike.
I was always having problems with knees and back.
Since shifting to a large frame all,those problems have gone!
I was hesitant about riding something bigger than the Thorn sizing recommend but feel bigger is better.

Matt

[JWestland]

Rumour has it tall head stacks on Crabon steerers aren't a good idea, hence short ones on modern bikes I'd say as generally trends for those are taken from road races, not practical use.