Hi, I am looking @ a 2018 QR PR6. It is a 52cm. My BMC road bike is a 51. I am 5'7 1/2"; inseam 30.5"; my road bike seat height is 28.5" from BB and 36" from center of pedal. I have never had a tri bike before or been measured for X, Y, and Z. The QR site indicates 50 or 52 for 5'7", and 52 for someone 5'8". I am trying to confirm if the 52 is right for me, and if I get it maybe a good plan would be to take it to a fitter to dial in seat height, bars, pads, and crank. Do you have any thoughts on this? Thanks.
I have very strong thoughts on this....
The absolute best way to buy a tri bike is to GET FIT FIRST. And this is one of those things where you either do it right or not at all: go to a fitter who checks off these three boxes: they are educated in tri fit, experienced in tri fit, and they MUST own a dynamic fit bike*. Then you do fit, pay them whatever they ask, give them all your money because you'll leave with your exact Pad Y and Pad X telling you what will fit and what wont. Have them prescribe this bike you're interested in and 3 others. And you'll have all your fit coordinates (seat height, set back, cockpit detials, etc. etc. etc). The fit is done, you were part of the process, it's perfect - and you don't even own the bike yet!!!
*the dynamic fit bike is a critical piece of tooling. It's expensive and committed fitters purchase them becuase you simply cannot nail, dead-on a prescriptive fit without one. There are only really 5 of 'em: Shimano, Guru DFU, Purely Custom, Exit, and Muve. You need to interview the fitter, quiz them about where they tri fit education came from (they need to say Slowtwitch, Guru, Retul), ask them which dynamic fit bike they use (they need to name of of the previous), and ask 'em how many tri fits they do.
What I'm about to do it good but not as good as the above. Imma take what you've given me (morphology) and what you've left out (you didn't mention some catastrophic accident that left half your vertebrae fused or some such extreme thing) and I'm going to plug that into a formula, season with experience as a long time fitter and bike fit instructor, and over 2 decades of coaching triathlon full time and shazam... I've got some info to share. Again, it's good, it's not as good as the above...
I think your Pad Y is in the neighborhood of 600mm and your Pad X is roughly 460mm. A 2018 Quintana Roo PRsix size 50 will fit you and here are the options (because there's a few ways to arrive at these numbers).
To get our Pad X of 460...
You need either the 90mm stem or the 110mm stem. 2018 was a near year for a proprietary QR stem and they only made three lengths: 75, 90, 110
If it's the 90mm stem the bracket that holds the arm pads needs to be set rearward and then use the rear armrest hole.
If it's the 110mm stem then bracket goes rearward and use the middle armrest hole
To get your Pad Y of 600...
The stem has this clam shell system inside the base bar clamp. You should put one half of the clam shell on top the base bar and the other half below so you're in the "middle" setting. Then you only need you only need 10mm of arm pad pedestal to get to 600. Now this is a Profile-Design aerobar so it's easy to find bits you need to dial to perfection (bits= spacers and screws).
Some other notes to consider for your first tri bike. You must have a saddle that allows you to sit, in comfort on the front half of the saddle (look at any an all profile view pics of anybody at Kona and you'll see a lot of saddle behind their bum). You should ride 160mm cranks at the longest and prolly 155s so find our how long the cranks are on that bike and if they are longer, work the price down as you're gonna want shorter cranks.
Ian Murray http://www.TriathlonTrainingSeries.com
I like the pursuit of mastery
Twitter - @TriCoachIan