If my road bike s/r is 600/400, what can I expect (ballpark) my tri bike geometry to be? The same, more or less.
It’s going to vary, potentially wildly. Also, are you asking about pad stack/reach or frame? For frame, it doesn’t really matter that much because the pad position can be very different from the frame’s numbers on a tri bike. You’re not going to be able to get a good answer without getting a fit first. For the tri bike, you’ll have to account for differences that don’t matter on the road bike, such as upper arm/forearm length, flexibility, saddle fore/aft, and more. Your tri bike fit will also be accounting for general rotation for your body geometry to fit comfortably and aerodynamically on a tri bike, so it could be vastly different measurements compared with your road bike even for a close recreation of the road pedal-stroke (hopefully that makes sense). For any helpful info, you’ll have to get a bike fit from a good bike fitter, even for “ballpark” numbers. I would say, though, that 600/400 is probably large. You’ll be looking, most likely, but by no means definitively, at M(unlikely), ML, L, or XL in tri bike sizing. That’s about as close as you’re going to get if you want a really good fit.
Road bike fit has very little to do with tri bike fit.
Thank you for your response. Let me ask it a different way. How can I use my road bike 600/400 geometry as a guide to purchase a used tri bike online and select a bike that might fit the best? I understand I’ll have to make some adjustments afterwards.
Thank you for your response. Let me ask it a different way. How can I use my road bike 600/400 geometry as a guide to purchase a used tri bike online and select a bike that might fit the best? I understand I’ll have to make some adjustments afterwards.
I wouldn’t.
It may take longer and be more expensive but the best outcome will be to get a preliminary fit with a reputable guy and use those measurements to choose which bike fits you best. That’s the way it’s supposed to be done - it worked very well for me. Lots of resources here at Slowtwitch.
Thank you for your response. Let me ask it a different way. How can I use my road bike 600/400 geometry as a guide to purchase a used tri bike online and select a bike that might fit the best? I understand I’ll have to make some adjustments afterwards.
You can’t use your road bike fit as a guide to purchase a tri bike.
Thank you for your response. Let me ask it a different way. How can I use my road bike 600/400 geometry as a guide to purchase a used tri bike online and select a bike that might fit the best? I understand I’ll have to make some adjustments afterwards.
There is only one realistic way to use your road bike to figure out your tri bike fit - convert your road bike into a tri bike and use that to evaluate your fit. But that’s not exactly cost effective or practical if you don’t actually plan to use it that way.
The best option by far is to get a fit by someone who can put you on a TT/Tri bike rig.