Technical FAQ: Frame sizing, wide gearing for road bikes
While watching this year’s Tour de France, there was a segment (because of a crash) on a BMC bike that Richie Porte was riding. Upon close inspection by the camera crew, I noticed that his frame size read 47cm. Now Richie and I are about the same size; I’m 5 ft. 6 in, and I was shocked at how small his frame was. I have had racing buddies of mine tell me that they ride the smallest frame possible. I have been riding 51 or 52 cm frames for as long as I can remember, with a top tube length of anywhere from 53 to 53.7 cm. I have always felt that this was the right size for my body, so why would a pro ride such a small frame? Obviously, he’s running quite a long stem and a setback post, so the question is, can I ride or should I ride a smaller frame and what would be the advantage?
The 47cm size has a 51.7cm top tube, whereas the 51cm size has a 53.5cm top tube. Maybe even more importantly, the head tube on the 51cm is 2cm taller than on the 47cm, and the integrated headset spacer/Di2 wiring cover under the stem on his bike looks to be at most 2cm tall. If you were to remove that spacer to drop the stem the full 2cm on a 51cm to get his handlebar as low as he has it, you wouldn’t have the clean routing of the Di2 wire internally all of the way from the bar into the frame. That would be far too inelegant on a bike with internal routing of everything and this trippy little down-tube-mounted Junction A integrated into it.
His stem looks to be about 130mm, which makes up for the shorter top tube. So he can get the fit he wants on the 47cm, and the advantages of using the smallest frame you can fit properly on are numerous. A smaller frame is stiffer and lighter. It has a shorter wheelbase for tighter minimum turn radius. The longer stem makes for less reactivity to steering inputs (the same length of push of the hand rotates the fork less), so the chances of overreacting to a crash in the peloton are slightly reduced. On the other hand, the low handlebar Porte clearly seeks probably reduced his chances of lifting his front wheel in time and getting back on the road when he went off into the dirt on the inside of the corner on the descent that took him out of the Tour.
You recently wrote about making B-screw adjustments to Shimano rear derailleurs to permit the use of larger rear cogs, up to 36, and maybe even 40, teeth. I’m wondering if there may be some similar adjustments possible to a SRAM Red eTap WiFli rear derailleur. I’m currently running a 32 tooth as the largest cog, the maximum SRAM suggests. Might it be possible to get to a 34 or even a 36?
Good question. I haven’t tried it, but Eric (see letter below) has, and, as you can see, it worked for him.
You tried my suggestion of 11-36 aftermarket cogset on a SRAmano hub using an Ultegra GS rear derailleur, and published it in your column. I asked something similar last year: using eTAP WiFli and a larger cogset to allow LOW gearing at least for some circumstances.
I have been very happy so far with my own experiment.
Bike is a Kent Eriksen 2014 with S&S. It is not drilled out for wiring Di2. I was using the aging triple ten-speed Campagnolo (usually with 53-42-30 and 11-30 (by IRD), sometimes substituting, for exotic travel, a 28 tooth chainwheel from TA Spécialités. Shifting in front was always a bit tedious but having available a 25 gear-inch gear is great for 15+% climbs. For me anyway. I’m 69 now.
I replaced this Campy setup with eTAP and the WiFli rear and put an eleven-speed IRD 11-30 Campy-compatible cogset on my hub and found I loved the electronic shifting. My thumb basal joint arthritis doesn’t bother. But there is no wider Campy cogset around.
So I got a new SRAmano-compatible rear hub in a new wheel and put on a new Shimano 11-32 cogset. Both wheels work great, as you have said in your column, using Campy and IRD and SRAM and Shimano eleven speed parts.
But then I also installed a SRAM 11-36 cogset which, according to the packaging, is not to be used as I am doing it. But my experience so far is that the 50-34 x 11-36 works just fine. Even shifting from the 32T cog to the 36T while standing on a very steep 20-percent-grade street. I did decide to add links to the chain because my chain had the rear derailleur fully stretched forward if I tried the 50×36 combination, full cross chaining, which looked dangerous. I intend, of course, never to do that, but looked down one time to find I had done it by mistake.
The B-screw is not at an extreme position.
Adding three links made the position of the rear derailleur look right but the chain hung pathetically when cross-chained the other extreme, 34×11. Adding two full links (56, including the master link) means both 34×11 and 50×36 don’t look great (see photos) but they work fine to my taste.
I’ll consider whether I will need to use two separate chains. Connex links so far seem to work fine.
I’ll try the Blockhaus climb in Abruzzo on this set up in September.
Thanks for letting us know that this combination can work. I hope it works well for you on Blockhaus.
Feedback on last week’s column:
If bicycle brake pads are similar in construction to motorcycle brake pads (probable) the friction material is porous. Once contaminated with oil or brake fluid, the damage is generally permanent. Sanding may expose a new surface but if the contaminant has penetrated that far, heat will percolate the problem back to the surface.