rbrides

All my bikes are 52cm, recommended by pro bike fitter and Trek’s in-store bike fitting camera/device.

I am looking for a bike to permanently mount to my indoor smart trainer and have found a 54cm that otherwise meets all my criteria.

I if lower the seat to a proper height and install a shorter stem, would the larger frame be an ergonomic fit? Peddle crank length may be “off” but I don’t know what else would compromise a proper fit.

Thoughts?

Kontact 

That's pretty much it. Fit is saddle height, saddle set back, saddle to bar distance, saddle to bar drop. Generally the only important things different between two sizes is the length of the top tube (about 1cm between a 52 and 54) and 2cm of head tube height. So the 54 will get a shorter stem mounted lower on the steerer tube than your 52.

Iride01 

Check the geometries between the two bikes. Seat tube angle changes between some sizes depending on brand and model. So your butt might be in a different position over the BB when your reach from saddle to bars/hoods and everything else is the same.

Though it might not be significant enough to even be an issue for you depending on how fussy you are about your fit.

blacknbluebikes 

For a dedicated trainer bike? Don't sweat it.

Kontact 

If you measure and set the setback, your butt will be over the BB in the same spot, regardless of frame angles.

Iride01 

Well of course one can get it in the proper position. However the typical way that many measure their contact points on the bike won't give the correct saddle position in relation to the BB. Many tend to only think of the distances between the saddle and the bars or hoods.

The caution I made was just to start them thinking about it. With my leg length the difference between 1 degree of seat tube angle is only about a half inch. But that might make a difference for some that are already have their saddles far back in the clamp or far forward. But then again 1 degree of seat tube angle will be unusual for just a change in size of the same model.

Kontact 

I don't know of any other method to locate the saddle properly except to copy an existing set back or go through whatever fit procedure you prefer to establish a new one. There is no "contact point" method that you can do without using the same methods as copying a setback. There isn't anything about a bike frame that suggests where to put the seat.

And many frames go right from 74 to 73 degrees around size 52.

Iride01 

Kontact I still feel safer saying that because the seat tube angle changes that the saddle might not be at the same distance from the vertical axis off of the BB. I'm not going to assume that because the head tube angle and other things change too that simply measuring from the bars to the saddle will give the same setback.

But I can only assume from you wishing to say I'm wrong that you must think it will always be at the proper setback no matter what bike or model or size. Or do you actually measure to put the saddle the same distance back from the vertical axis of the BB?

Kontact 

I don't know if I'm following you. Why would you try to get setback from the stem?

I use the vertical axis off the BB to set setback every time. With a ruler and a plumb line it is quick and easy to do.
After saddle height and setback are done it is much easier to get the bars in place.

The reason I don't follow the stuff you mention about the frame angles is that there aren't any real reference points on the frame that are useful. Even seatpost clamps vary too much in design to use as good references.

This isn't personal and I don't need to prove you wrong.

Iride01 

Then I think where we differ is that I don't assume that people transferring their position from one bike to the other do anything more than measure saddle position from some point on their bars. And most that measure saddle setback will just measure that from the seat tube and not the vertical off the BB. But that's just an assumption I've come to based loosely on things I've read here and seen done in real life.

Maybe I'm wrong to think that way. I just don't assume from the get-go that everyone always does something correctly. But I also don't assume they are doing it wrong if they don't add something that indicates they are doing it wrong. So sometimes like in my first reply to the OP in this thread post was just a bit of info to get the OP thinking about that. They didn't ask any questions about it so I assume they either understood the implications or it wasn't of consequence to them at the moment.

Kontact 

I am certain that you are right: People do all sorts of dumb things. I just don't get discussing those things as if they are a valid alternative.

Especially when people seem aware of changing stem length and the fact that bikes have different TT lengths. But if you are measuring from the stem, the stem stops being a variable and becomes the reference. Which is not a terrible thing with a tri bike, but crazytown when it comes to a bike that you don't want to lean on your arms.

Anyway, even if you decide to measure from the stem, that still isn't going to reference the seattube angle.

79pmooney

Yes. But I wouldn't settle for a class B fit. I'd go out and buy the seatpost with offset that allows the proper seat location. That and the stem to get the proper BB to bars reach and height and this bike will serve you very well. (Until your wife scares you with "Dinner's ready", you slip off the pedals and seat, nail that high top tube (higher now that you've got a block under the front wheel), you receive irreversible damage and your marriage is never the same. Might be wise to orient the trainer so you can see her walk in. )

dithifer

Are there any videos or article resources that might help with fitting a bike that's too large?

Iride01 

Same basic rules apply. So just watch any of the videos and read articles about fitting yourself to the bike. With bikes that are too big for you, you might have to just learn to live with not being able to get to your ideal position. Some people don't tolerate but a narrow range of fit. Others can tolerate a wide range of fit. If you are the latter, you'll have less issue with the wrong size bike.

Welcome to BF. If you have an actual fit problem, then start a new thread and tell us about it and your bike. Maybe someone can suggest something.

Carbonfiberboy 

You could follow my bike fit primer here: https://www.bikeforums.net/21296948-post3.html

tallbikeman

You should be able to try different variations on your 54cm bike of hand and butt positions. You might find that you like the taller frame, or that it isn't quite right and smaller is better. I have found that playing around with frame sizes is a positive experience. I found my favorite bicycle by getting it used for nothing and rebuilding it to suit me. After several changes over the years I've gotten as close to perfect in my fit on this bicycle and have been able to replicate that position on my other bikes. Good luck with this effort.

zandoval 

Brings back fond memories of my old FUJI. Bike was so tall I had to jump on and off of it... Called it my Horse.

Once on it the ride was all mine!