Top tube length shrinking on 27.5 have we been coned?

A quick look at 27.5 bikes shows shorter toptubes than 29er bikes suggesting to me the overly long toptube fashion was for the designers benefit at the cost of proper fit for the rider I have found nearly all 29ers to be to long or i end up with a mile of seat tube forced on to a smaller size.

Thoughts?

are you assuming all bikes with a certain wheel size are the same?
Remember how many variations there were on 26″ bikes
Also since when did one measurement make a bike right?

Are we talking about ice cream cones or traffic cones here?

I see most 29ers of medium size running ETT length in excess of 600mm top tubes on smaller wheel sizes seam to be under 600 ❗

I don’t care, but have you got an example of a company whose 29ers have longer ETTs than their comparable 650b bike?

That example would at least be the bare minimum starting point for a boring discussion with appalling collateral damage amongst the kittens within range of God’s smiting apparatus.

🙂

How is it for the designers benefit?
What about reach rather than ETT?

Top tube in isolation doesn’t tell you much – Look at the Transition Scout and Smuggler.

597 ETT on Scout, 610 on the 29″ Smuggler – but they end up with the exact same reach because of the different angles and stack heights.

brant – Member
How is it for the designers benefit?

They nick 10mm of aluminium off each 27.5 top tube. Soon they have a massive pile of aluminium, enough t take over the world

Just forget effective top tube length – it’s a useless measurement for modern mountain bikes.

Two bikes can feel the same length when you’re sitting on them but have an ETT 50mm+ different – the greater the stack height the longer the quoted ETT will be. Furthermore the slacker the seat angle the longer the ETT will be relative to the reach and the greater the forward seat tube offset at the BB the longer the seated reach will get at true saddle height.

If any 29er does not have longer ETT than any comparable 27.5 bike it will actually feel shorter both seated and standing. It’s a shame ETT doesn’t work off a standardised distance from BB rather than horizontal to centre top of head tube.

chiefgrooveguru – Member

standardised

Bike industry types see that word and all run in different directions

It’s pretty remarkable that reach and stack measurements have become a common addition to geometry charts and that someone more random hasn’t already superseded them!

OK I’ll throw some uninformed opinion in as I think I see what the OP means

I think that its to do with trying to cope with the axle crown length of 120mm 29er forks. You end up with high bars so they are put further away so that the “reach feels OK”. Which I’m sure feels great on the steep downs but I wonder how effective it is when trying to weight the front wheel on a corner on the level

I think that its to do with trying to cope with the axle crown length of 120mm 29er forks.

So why do 29rs have 120mm forks? Honestly if you want to generalise think about how 26 bikes are all the same

longer TT for shorter stems me thought, 😀

Shorter stems for T-rex’s

I see most 29ers of medium size running ETT length in excess of 600mm top tubes on smaller wheel sizes seam to be under 600

Makes perfect sense to me. If I bought a 29ers I’d be riding more XC so would prefer a longer reach.

Just forget effective top tube length – it’s a useless measurement for modern mountain bikes.

its not, it is applicable to when you ride the bike sitting down. If you only ever ride a bike downhill out of the saddle then the ETT is not going to be of any use.

See my previous post. ETT works off the variable reference of head tube height so is very inconsistent depending on stack height and is further skewed by seat tube offset and difference between actual and effective seat tube angle at riding height vs head tube height.

I know how ETT works but its still a relavent measure for a bike when taken into account the rest of the geometry.

You’d be better off using reach plus a corrector based on effective seat tube angle at saddle height…

collateral damage amongst the kittens

I suspect this is the OP’s true intention all along

<please imagine pic of kitten with paws on head>

How many 29ers “upgrade” to 650b anyway?

Market is quite different. 29ers more aimed at the XC market, and 650b generally aimed at the trail and AM upgraders from 26″.

Compared to 26″ I’m seeing top tubes being generally longer on 650b. Longer and slacker is the trend.

I know how ETT works but its still a relavent measure for a bike when taken into account the rest of the geometry.

But this thread shows that many don’t know how it works and that they fail to consider the rest of the geometry…

29ers more aimed at the XC market

2012 called and they want their facts back

Reach is relevant when standing but ETT is relative when seated i spend a lot of time seated as it flat terrain I am concerned with so for me ETT is more important than reach and i suspect it is for many how ride 100mm bikes.

Yes but you can’t compare ETT unless the stack heights of the bikes are the same. And unless the 27.5 has 40mm more fork travel than the 29er then the stack height will be less.

Differences in ett are noticeable. Especially if you are sat in fact it’s the only time you can notice. Stack is a pointless measurement as it’s variable based on build. Reach seems more relevant but the ett measurement is more relatable. Having just swapped a bike I know I like a 23.5 top tube when sat. How that relates to the rest of the geometry I have no funking idea as no 2 geometry charts appear the same, some miss off certain info, and published claimed values and actual measured values seem to vary massively. Id quite like to buy a new bike shortly but picking one I think I might like is proving complicated

You also need to consider the length of the stem. Simplified massively If nothing else changes, a bike with an ETT of 600mm and a 70mm stem will have the same distance between seat and bars as one with an ETT of 625mm and a 45mm stem for example, as mentioned above there are a LOT of other factors than just ETT. If you put a layback post it’ll also make the bike feel longer when seated

Yes but you can’t compare ETT unless the stack heights of the bikes are the same. And unless the 27.5 has 40mm more fork travel than the 29er then the stack height will be less.

That’s not really true. Stack height has very little effect on ett. For example, adding 50mm on the stack of a bike with a 76 degree seat angle and 66 degree ha will only effect the ett by something like 8mm, which is pretty negligible given the size of the stack change, for more xc orientated bikes where the ha and sa tend to be closer, the effect is even less, as is the case for bikes that run a kinked seat tube so their actual sa is slacker than the effective sa.

In my opinion ett is a very useful judge of a bikes size, and given its one side of a triangle, it’s as valid as any other… But you have to look at all three factors, ett, sa and reach. However, if you’re looking for a quick and easy guide to whether a bike will fit you, ett is often the best option, seat angle and reach will tell you how a bike will ride better than it will fit you, likewise ett will tell you how a bike will fit you much better than it will tell you how it rides.

You also need to consider the length of the stem. getting on the bike and giving it a ride

Seriously leave the numbers alone and hop on one, give it a ride, feel what works what doesn’t, the obsession over a number etc. gets dull really quick and if you are picking the fashionable numbers then out of date (and therefore crap) really quick too.

650b generally aimed at the trail and AM upgraders from 26″.

It’s not an upgrade