Top tube length compared to MTB

Slow Downcp

Also posted in MTB beginners, but there may be others who do both but don;t go in there, so:

Having ridden road bikes for 20 years, I'm fairly happy that the set up is okay. Now looking for a hardtail and, knowing that top tube length is more important than seat tube, wondered if anyone else on here MTB's also and if so how does the top tube length on your road bike compare to that of your MTB?

I'd rather go to try out armed with this advice, than a shop assistant judge the size I need by my height/inside leg.

redddraggon

Slow Downcp wrote:

Also posted in MTB beginners, but there may be others who do both but don;t go in there, so:

Having ridden road bikes for 20 years, I'm fairly happy that the set up is okay. Now looking for a hardtail and, knowing that top tube length is more important than seat tube, wondered if anyone else on here MTB's also and if so how does the top tube length on your road bike compare to that of your MTB?

I'd rather go to try out armed with this advice, than a shop assistant judge the size I need by my height/inside leg.

Top Tube length means very little when you think about road bikes. A bike with a 75deg seattube and 55cm toptube has roughly a different 2cm longer reach than a bike with a 73deg seattube and 55 toptube.

John.T

Top Tube length means very little when you think about road bikes. A bike with a 75deg seattube and 55cm toptube has roughly a different 2cm longer reach than a bike with a 73deg seattube and 55 toptube.

Top tube length is important on a road bike. The seat tube angle is also. Both of the above will have the same reach if you fit the saddle in the same place in the seat post. You will however be further over the BB which may not be what you wanted unless it is a TT bike.
Regarding the OP most MTBs have longer top tubes than road bikes but have straight bars and shorter stems so the position is usualy shorter and more upright. My Santa Cruz has a 59cm TT while my road bikes are between 55.5cm and 56cm.
You need to try some. Aim for a good balanced feel between the bars and saddle to aid body movement on technical stuff.

redddraggon

John.T wrote:

Top tube length is important on a road bike.

In isolation it's pretty much useless though...

John.T

I consider it more important than seat tube length but you do have to consider the seat angle as well. Most of my bikes have 73.5 angles but the Ribble is 74. The seat is further back on the rails on that but the stem is shorter.
The length of an MTB is more relevent as they tend to have very small frames anyway.

Slow Downcp

Okay - back to the drawing board on the quick solution

I'll go any try some out for size - I did (and yes, I realise I was asking too much) go to halfrauds at the weekend to try out the Boardman's and the closest I got to advice was "Yeah, the large looks about right".

John.T

I don't know how tall you are but as a rough guide I am 5'10"+ and all my road bikes are 56cm seat tube, centre to top with around 55.5 top tubes. My MTB is a large with a 59cm top tube. I use a 12cm stem and bar ends as I ride Trailquests which include quite a lot of fast fire roads and some tarmac so favour a slightly longer position. When on the flat bars I am in much the same position as when on the tops (not hoods) on the road bikes. If I was not racing I would probably go for a 10cm stem to improve manoeuvrability. You can not go by seat tube length on an MTB as they vary so much..

Slow Downcp

Cheers John T - I'm a little taller, and road bikes have similar top tubes so I'll start off looking at 59cm top tubes, which would be a medium in the Boardman's. Must admit the large that the salesguy said was "about right" did feel a bit big. Just have to try to make time for test rides I guess.

stevebendall

All my road bikes are betwenn 54 and 54.5cm top tube length, with 11cm stems, but my MTB has an effective top tube length of (from memory) of approx 60cm,

I can let you know the exact measurements tomorrow if it helps

I am very finicky on set up, and even rejected buying some newer MTB's because of the way MTB geometry has evolved with even shorter top tubes these days, and love the fit and handling of my Gary Fisher Genesis gemoetry compared to my road position

That said, horses for courses and any one persons opinion is only exactly that, hence why whether a bike, shoes, saddle or helmet, everything should be taken with a pinch of salt until you've tried it for how it fits you personally

John.T

G F Genisis were all longer than normal. Not sure how much difference it made. My Santa Cruz handles like a dream. I would not call 59cm short though. Pity the rider can not take it nearer to its limits. Something to do with bottle (lack of).

gkerr4

redddraggon wrote:

John.T wrote:

Top tube length is important on a road bike.

In isolation it's pretty much useless though...

I agree that "actual" top tube length means very little - but the "effective" (or horizontal) top tube length is surely very important.

redddraggon

gkerr4 wrote:

redddraggon wrote:

John.T wrote:

Top tube length is important on a road bike.

In isolation it's pretty much useless though...

I agree that "actual" top tube length means very little - but the "effective" (or horizontal) top tube length is surely very important.

Effective and actual top length are both not great indicators of size...

I guess it matters more to me being relatively short. Small bike have short TTs, but they've only got short TTs because the seat tube angle is increased and the head tube angle decreased. By the time I factor in the seatback the reach is exactly the same as larger sizes.

Cervelo is one of the only brands that keeps a constant 73deg seattube throughout all the sizes in the road range (excluding two position posts etc) - but then you get slight problems because of the very short front centre and sometimes massive toe overlap.

Front centre and reach are the important values when looking at frame geometry, TT length alone is too misleading to generate any definitive conclusions.

John.T

Top tube length is important because it is the least adjustable dimension when setting a riding position. The saddle setback is governed by the BB position and you only really have about 5cm to play with on stem length. This limits reach making TT length important. You do need to look at other things such as frame angles. I also look at trail as this affects how stable the bike should be. Front centre you don't have much choice in without compromising fit. I think that seat tube length is about the least important measurement as long as you can get the saddle where you want it. I agree that small bikes are a problem. They have always had to be more of a compromise.
I think we have rather hijacked the thread but hope the OP has found some of this helpful.

redddraggon

Hmm....

55cm TT on a 73deg STA frame is no where near a 55cm on a 75deg STA

but

53cm TT on 75deg STA frame is roughly equal to a 55cm frame with a 73deg frame.

Going blindly off TT would mean I could go to a 2cm shorter TT and use a 2cm longer stem.....but it doesn't work like that.....I'd probably need the same stem length to keep the same reach.

I guess as you are a lot taller than me John, and you take frame sizes that have relatively consistent STAs between different manufacturers, so you (and the OP) could probably look simply at TT length, but for us short arses to get a proper fit between different brands it doesn't work like that.

The massive "knowledgeable" majority do believe that the TT length is the most important measurement, and that's why manufacturers screw up small frame geometry just so they can state a short TT length, when in actual fact the reach hasn't decreased much at all from the frame size above.

Apologies to the OP about going off on a tangent, but a frame geometry isn't all that simple, and when you are a short arse like me, it gets uber complicated, when you have to factor in things like toe overlap as well as fit

John.T

I have never sugested going blindly on TT length only.

55cm TT on a 73deg STA frame is no where near a 55cm on a 75deg STA
but
53cm TT on 75deg STA frame is roughly equal to a 55cm frame with a 73deg frame.

To get the same saddle set back on the 75deg you would need to have the saddle about 2cm further back than on the 73deg one so the effective TT is really the same. You still need to know and take account of the TT length. As I said earlier small frames have always been a problem but I don't think manufacturers deliberatly screw things up. It is very difficult to fit a small person between 2 700mm wheels and get everything in the optimum place. If you are much shorter than about 5' 6" or so 650mm wheels are a better bet but nobody makes them.
I am taller at 5' 10" but when I got my Madone I could have fitted on the 56 Performance fit or either a 58 or 60 Pro fit. I went with the 56 because the TT meant I could use my prefered 12cm stem as on the other bikes and the it had the most trail which made it better for using with tri bars as it is very stable. It is still very sharp in a bunch.

redddraggon

Ok I get you now, I never read your 10.15 post properly. A lot of people do use TT length in isolation though, :?

Slow Downcp

Didn't mean to open a can of worms :oops:

I wouldn;t use the effective TT length in isolation - was just looking to get a starting point. The large Boardman I tried out felt too short a reach, despite looking too big and having a 61.5cm effective TT - guess that's just down to the different riding position. I'll try a few bikes out, starting with around 59cm and take it form there.

Cheers both for your input.

John.T

Red. No problem, we all do it sometime.
Slow Downcp. Don't worry about it. We get like this at times.
When you are trying bikes make sure the saddle is about the same distance behind the BB as on your road bike. This is one point that is important to get right. You can then look at reach. This can be achieved by a longer frame with a short stem or a shorted frame with a long stem. The former is generally better for riding technical stuff while the latter is more for fast blasts. The shorter stem gives faster steering input. For general use I would go for a 10cm stem and a frame that gives a comfortable reach.

keef66

Reddragon, I sympathise. I'm 5'6" but with longer legs / shorter torso than your average shortarse. On a typical 54cm frame the reach is too long, even with a short stem. If I drop into the 50-52cm sizes I have more seatpost out, shorter headtube, and consequently too big a drop from saddle to bars. (I'm the wrong side of 50 now and not as bendy as I was, nor do I appreciate having to ride on my testicles)

I've compromised on a 51cm Racelight Tk with the shortest stem Epic would fit and flipped it to bring the bars up quite a bit. Still I find my arms are straight a lot of the time when on the hoods, butI think that's as comfy as I'm going to get without a custom built frame or a recumbent, and I can't afford either.