GT Grade Carbon 105 - Help with Fit

I’m 5’10” and went for the 55cm. I have long body, short leg and after reading they came up big was worried I’d gone for the wrong size. However it’s absolutely spot on, plenty of seat post showing, and a slammed 120mm stem. Perfect. 

6 feet tall, slightly longer leg than body. I ordered the 55 and compared to other bikes, sent it back for the 56. It's a little taller and longer than my 56 Cannondale but I wanted that. I went for the alloy 105, great wet bike!

Im just under 6'1'' and had a go on a 58 and 56cm. The 58 was HUGE and the 56cm spot on. See the GT grade group on facebook -they do run quite big.

I bought a 56..

The stock wheels are tubby. Recommend changing them straight away for some cheapy but goody prime wheels or similar from CRC..

I'm the same height as you but with shorter legs and my 53 ('small' in the UK) 2016 Grade 105 Carbon feels like a perfect fit. These bikes are big, this size is a medium at least by any other manufacturer so don't be put off by 'going small' because really you aren't.

For me, even a small had a bit too much reach and I replaced the stock GT stem (which I think is +-7 100mm, though GT don't specify) with a Zipp Service Course +-6 90mm and it felt bang on. At the same time I replaced the bars with Zipp Service Course 80 in 44cm as I wasn't too keen on the flare of the GT ones and wanted a bit more width on the flat part of the bar.

Also, if you go for the larger size, you won't have very much seatpost exposed. For stock issue it's a very good seatpost and you won't be taking advantage of this if there's not much sticking out above your frame flexing and absorbing buzz as it should.

Generally the level of finishing kit on the Grade is outstanding by comparison to others you might be looking at. This really swayed me especially as, like you, I got a good deal. The Stan's Grail are a perfect mix of toughness and versatility and I would strongly recommend going tubeless as these wheels make it so easy, they were actually designed for the Grade. I'd say I haven't had a puncture since going tubeless but that's not true. It would be more accurate to say I haven't had to fix a puncture since going tubeless. When you find in the morning your tyre is flat, you pump it up and go for a ride and it's fixed! Genius. I used thin rim tape just in the channel, covering the spokes, and fitted Scwalbe S-One (now G-One Speed) with no problems.

Back to the fitting, I'd take the advice of the professionals in your bike shop.  They've seen you on it and they know when a bike is the right size for someone. It sounds like they've got it right to me and as others have said, you can fit a bike out to be bigger but you can't make one smaller.

6ft and I ride a 55. I still feel quite stretched out. I've heard from various sources that the GT Grade runs big so most people tend to go a bit lower than they otherwise would.

Also, the smaller the frame, the less of the triple triangle effect there is on the frame - aesthetically, I think the smaller bikes look prettier around the seat stays and seat post area!!

Good luck, I'm more than happy with my 55 - done 1700 miles on it on tow paths and on road and it's been great. 

Your height is only part of the puzzle, fit depends massively on things like core strength, arm length, flexibility and even as simple as your 'effective torso' length.  Personally I think inseam is almost irrelevant.

A small frame can be fitted bigger but a larger one not fitted smaller (beyond short or a increased angle stem - like a 17 degree).  Limitations in sizing up a smaller frame are obviously bar drop as you experienced, but also toe overlap with front wheel, seat post (can buy a longer one within reason), and handling slows as stem length increases (also note that stem length and fork geometry work together, so some bikes more sensitive than others to length change and some suit a longer or shorter stem by design).

Moving saddle forward will put more weight on hands and neck, it is not a good way to make a bike that's too long fit.

If the 55 is too big and cannot be made entirely comfortable without a stem shorter than 90mm or so then leave it.  If the 53 is too low and can't be made entirely comfortable with spacers and a flipped stem the leave it.

If neither works perhaps a taller more endurance frame would suit, and this is not the bike for you.

I'm 5'9" on a good day and had a 55 carbon grade 105 with a slammed longer stem than the stock one. My inseam is about 32" and seat was set quite high. 53 frame was way too small. Perhaps you're used to a more upright MTB set up,so you could  get the the larger bike and swap the stem for a shorter one with all the spacers fitted . Remove a spacer everyone few months and eventually you'll end up in a new position where you won't need spacers and can go back to the longer stock stem, again adding and removing spacers. A smaller frame at that height may well give you overlap probs if you fit mud guards. 

I think fit is absolutely crucial but it is tied to function. If you want an easier commuter and better off-road bike I'd think about the 55 and maybe shortening the stem. If what you want is mainly a road bike, however, I'd go with the 53 and perhaps a longer stem with a bit of rise.  You might eventually even end up lowering the bike a few spacers as you get used to the position. 

Inseam is the least meaningful measurement. If anything I'd advocate the longer seat post for a little extra flex. Too little tube sticking out makes for a harsher ride, IMHO.

P.S. I'm 6'1". I ride a 56cm road bike and a 19.5" MTB.

I am 6 feet and ride the 56 but could have gone for the 55. The 53 sounds like the best bet for you.

Sorry, probably going to put a spanner in the works but for what it is worth - I am about the same height as you, 20 years older and I have ridden thousands of miles on my 55cm 2015 carbon grade on and off-road with no problems.  

I'm 5'11 and ride a Cannondale 54 everyday. I'm between sizes generally and have always sized down without it ever being an issue.

For the amount of aggro getting the bar height right and you looking like you're riding a childs frame plus even with the stem flipped (or god forbid an ugly 20degree upangled) there might notbe enough steerer length to achieve an ideal/comfy position. Get the bigger size and just buy a stem 20mm shorter.
Some stating this will hqve an adverse affect on handling...okay whatever, I guess when you see 130/140/150/160 stens on bikes for frames that are way too small that doesn't have an effect either and these are often pros.

I'm about an inch taller than you and I'd say that I'm right on the lower limit of being able to fit on the 55cm Grade Ultegra Carbon that I've been riding since November.

For the Dirty Reiver I replaced the setback seatpost with an in-line one which made a big difference in terms of feeling less stretched out but I reckon you'll be better of with the 53cm.

Go for the 53. You say the 55 feels too long, there isn't much you can do to adjust the length without altering the characteristics of the bike for the worse. I always regard the reach as the key measurement on the bike: get it wrong and there isn't much you can do about it. But it quite possible to raise or lower the saddle and bars without any adverse effect.

I'm same height, 55 was way too big, went for 53cm carbon Ultegra. I've got short legs, bike if anything still seems a little large for me, not much seat post showing. Stem is flipped like above suggests too. I ride medium/18" mtbs.

Go the 53 and flip the stem.