Triathlon - TRI Bike Fit question 54 or 56?

I have a question about getting fitted for TT bikes. There is a possibility that a ride's dimensions are such that they could fit on two different frame sizes (such as, 54cm or 56cm). In this case are there any advantages in choosing one size over the other? Here is my situation, I am 5' 10", and have been fitted for a 54cm frame, with about an 100mm stem length. But, I should be able to ride a 56cm with an 80mm stem. Are there any advantages either way?

The certified bicycle dealer wants to place me on a 54cm, however, I think they want to place me on a 54cm, because I will have more flexibility to tweak my setup. I am fine with that, unless, setting me up on a 56cm would be more efficient.

The reason I initially thought I need to be on a 56cm is because on my 54cm I feel too hunched over the handle bars when I am standing (climbing) and a 56cm would give me an extra 1.5cm of height to help keep me standing up right. I could setup my 54cm with a raiser stem but, then I am really taking away from the areoness of the frame, right? Another concern that I do not have a feel for is; would riding with a shorter stem give me a rougher ride? What about responsivness, should be more sensitive right? When I think about it, a shorter stem should put less weight over my front wheel, that could be an advantage while climbing!

Any thoughts on this issue would be greatly appreciated,
Thanks in advance,

Michael Stenson

Really, I've heard it as a general rule of thumb that a correctly sized bike will use a stem between 90 and 120mm. Your first concern should be the fit in the aerobars, because this is where you should be %90 of the time, at the very least. As far as out of the saddle efforts go, you shouldn't be doing it anyways, it will drain you and time trials and triathlons for efficiency should be conisitent amounts of effort. WHat bike and what basbar is on these setups? Some basebars have dropped hand areas and some are flat. Your predicament maybe easily solved by switching basebars out.

I say go 54, depending on the brand(a 54 to one brand fits like a 52 to others, and a 56 to another) and the type of riding you're looking to do.

I tend to agree with TriGuy. I read your post about 30 min ago and was going to respond but decided to think it over.

The setup on my tri-bike is similar to what you describe with the 54 cm and climbing out of the saddle does not feel great. On the other hand, I was surprised at how well I could climb in the aero position or if need be, on the bullhorns...seated. If I had gone one size larger, I'm sure my aero position would have suffered and that's where I spend all my time.

You really shouldn't be spending a lot of time out of the saddle on a tri/tt bike.

By the way...I ride a 51 cm Cervelo P2 SL and I'm 5'8" with short legs. My road bike is 54. Perhaps that will help...

I agree that I should spend most of my time in the aero position, but why should I suffer if I am not in the aero position? When I am on a road bike I feel great climbing. Why can't I have the best of both worlds?

Current bike: 2001 Cervelo p2K
New bike: 2005 Cervelo P3C

Comparing to what I've seen online, most others your size are going with the 54cm. I have a bike in very similar geometry to the 54(10cm integrated headset with a -17 degree stem) and I don't feel that uncomfortable out of the saddle... Everyone is differnt though

I am 5'9" and ride a 56cm road bike and 54cm tri bike.

Same situation for me...5'10" - 56cm road bike and a 54cm tri-bike. I say 54, but if you feel more comfortable on the 56, it's your ride and go with your gut...

the 54 will allow a more aerodynamic position since you will be able to lower the handlebars more with respect to the saddle. The 54 may also be a little lighter. Just make sure the cranks are long enough. Some manufacturers ship 172.5's with the 56, and 170's with the 54.

Some manufacturers ship 172.5's with the 56, and 170's with the 54.

That's true. I made sure that the 54cm I just purchased came with 172.5's on it before I took it out the door!

Mike,

Excellent question. I have the same dilemma, although I am a step ahead in that I've purchased a 54cm Specialized Transition. I am leaving purchasing the stem to the last based on how my body lays on the frame. So your experience helps.

Like you I believe I could ride a 56 but I have a short torso, 24.5 inches from the inseam to the indentation at the top of the sternum. My inseam is 35 inches. So looks like I'm screwed either way!!!

Would you mind telling me your inseam measurement in inches? I mean w/o shoes, standing on a firm surface, not wearing shoes or your pants inseam, which introduces too many variables.

Thanks in advance.

I noticed on one of your posts that the "New" bike is a P3C. Sweeeeet.........

I think the Cervelo's run longer than most on the top tube, which is probably the more important dimension. The 54 is probably the right choice. Hard to get over the sizing number though, sorta like buying pants, but different...

I have a long torso, so my 56 Cervelo fits quite nicely with a 110mm stem.

Where the wheel is tucked under the seat so much on a P3, you want to get your body even further forward to get your weight more centered over the wheels, right ? A 100mm stem should be fine for control, a little more responsive than shorter, but noticable ?? I dunno.

My Bike measurements are:
Overall:
178.5cm (5'10 1/4")
Torso:
67cm (26.3")
Arm Length:
62cm (24.4")
Inseam:
85cm (33.46")
Hip to knee:
50cm (19.68")
Knee to heel:
49cm (19.29")

I am 5'10" and ride a 54cm Cervelo Dual 10 with 90mm stem. My inseam is about 2" shorter than yours and I thus, have a longer torso. My lbs fitted me for the 54cm but now, I feel that I probably should have went with a 56cm or I guess, I can get a longer stem which is a cheaper trial and error. The reason being, after all my adjustments with the seat and spacers, when I ride on the nose of the saddle with my hips rotated, the top tube is too short. My shoulder to elbow angle is less than 90 degrees.

I also agree with you more than some of the other posters, that there's nothing wrong with trying to feel comfortable out of aero also. Though it is ideal to stay in aero more than less, I think comfort in all positions is important. In more technical tris with a lot of curves and turns or multiple climbs, you may be in and out of aero very often.

With all this said, based on your measurements compared with mine and based on my Cervelo Dual 10, my best guestimate would be a size 54cm for an equivalent dimensioned bike. When you are between bike sizes, most triathletes will err on the smaller size.

I am also 5'10 3/4" and have a 31 3/4" inseam. I have been told by many experts I should be purchasing a 56 over a 54. However these experts are usaully road bike experts and do not participate in tri's. I currently use my road bike for sprints and olympics, but I am looking to do a 1/2 this summer and want to make sure I am purchasing the proper size tri bike. If anyone can provide an additional info it would be greatly appreciated. Thanks

I agree. An 80 mm sten is likely to give an overly quick, twictchy steering response.

Athletes tend to get frames that are too large when they are planning to ride on aerobars. It sounds like the 5 would be a better fit.

Ken

It's nearly impossible for anyone to really say which size bike is right for you. There's so many brands out there with very different geometries and top tube lengths, so a 54 on one bike may be equivalent to a 56 of another brand.

That said, what I have seen and heard with my tri friends, most people go with a smaller sized tri bike than their road bike and will err on the smaller size when stuck with a choice of two sizes.

Just guestimating, I would chose the 54. But you really need to go to a lbs to find out.


I am also 5'10 3/4" and have a 31 3/4" inseam. I have been told by many experts I should be purchasing a 56 over a 54. However these experts are usaully road bike experts and do not participate in tri's. I currently use my road bike for sprints and olympics, but I am looking to do a 1/2 this summer and want to make sure I am purchasing the proper size tri bike. If anyone can provide an additional info it would be greatly appreciated. Thanks