Davidc
Guru
- Location
- Somerset UK
Poor frame designs
- Thread starter tradesecrets
- Start date
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snailracer
Über Member
Coke cans are aluminium. Baked bean tins are steel. And steel is real.
henshaw11
Well-Known Member
- Location
- Walton-On-Thames
>Perhaps it is semantic, but Henshaw I would welcome to be enlightened as to what purpose the unnecessarily long and unsupported version of the seat tube above the top tube serves, given by your own estimation the seat post needs to reach a couple of inches below the lower weld of the top tube? From an engineering design standpoint, imho it is an unnecessary weight at best given the leverage, load path and stress concentration caused by the seat post there, and a potentially dangerous trap for the unwary at worst.
As mentioner by myself/others - more standover height, and you need some region of the seat tube to deflect 'cos you've got a clamp over it - if it were too short it might actually stress the region around the welds more (which IIRC tend to be harder too = less flex)
Unless you actually know what the tubing dimensions/characteristics etc, the fact there's a design change doesn't mean a fat lot.
Go have at other mtb frames around - eg Specialized ,Santa Cruz- that configuration's not uncommon at all. And you do realise that many frames come from a relatively small number of manufacturers - so that if a manufacturer's tooled up for a one set of designs it may actually make more sense for someone to adopt that, rather than insist on something different.
For all I know (or equally give a toss), it could as much be a fashion statement !
Take a look at some time trial frames - more upright, but *loads* of seat tube...
As mentioner by myself/others - more standover height, and you need some region of the seat tube to deflect 'cos you've got a clamp over it - if it were too short it might actually stress the region around the welds more (which IIRC tend to be harder too = less flex)
Unless you actually know what the tubing dimensions/characteristics etc, the fact there's a design change doesn't mean a fat lot.
Go have at other mtb frames around - eg Specialized ,Santa Cruz- that configuration's not uncommon at all. And you do realise that many frames come from a relatively small number of manufacturers - so that if a manufacturer's tooled up for a one set of designs it may actually make more sense for someone to adopt that, rather than insist on something different.
For all I know (or equally give a toss), it could as much be a fashion statement !
Take a look at some time trial frames - more upright, but *loads* of seat tube...
MacB
Lover of things that come in 3's
- Location
- Farnborough, Hampshire
Just doing a bit of thread resurrection here as I'm curious on this subject as to what are the pros and cons around seat tube/top tube interface design. Specifically extending the seat tube above the top tube and by how much.
I can see that a forward facing seatpost clamp slot would require a minimum extension to avoid the slot getting too close to the welds.
I can see that a forward facing slot could reduce gunk getting in seat tube
I can also see that it can allow for a steeper TT angle without overly reducing the amount of seat tube available for seatpost insertion.
I can see how this is helpful for frames with shaped seat tubes where a seatpost can only go down so far.
I can see how a longer extension above could require some form of additional support.
What I can't seem to find is anything concrete on the actual strengths, or pros and cons, of the various design options. Looking across manufacturers I can find a variety of clamp slot orientations, seat tube extensions above TT, additional supports and various inserts. I can even find variations across a manufacturers range or from year to year, as indicated by the Carrera changes upthread.
I do understand minimum insertion depths for seatposts and can contrast that with frame insertion requirements. I would also err to the cautious side in this area being of the larger persuasion and running a setback seatpost.
But say you wanted something pretty bombproof, not downhill/all mountain bomproof, but otherwise sound. Assuming you don't care about the slot orientation(or would prefer rear facing, think permanent mudguard/splashguard in place), would you be better to:-
1. sacrifice a bit of standover by shallowing out the TT slope and having less seat tube extension - but still retaining comfortable standover - if so what amount of extension above the TT is about right?
2. keep the TT slope but support the seat tube extension above the TT in some way - if so which way is best?
3. do a mix of both, so shallow the slope but also keep the above TT extension by increasing overall ST length, and add in some additional support for good measure.
Bike useage I'm thinking mild XC, not racing, trail and rough stuff touring, but built for tanklike durability rather than speed.
I can see that a forward facing seatpost clamp slot would require a minimum extension to avoid the slot getting too close to the welds.
I can see that a forward facing slot could reduce gunk getting in seat tube
I can also see that it can allow for a steeper TT angle without overly reducing the amount of seat tube available for seatpost insertion.
I can see how this is helpful for frames with shaped seat tubes where a seatpost can only go down so far.
I can see how a longer extension above could require some form of additional support.
What I can't seem to find is anything concrete on the actual strengths, or pros and cons, of the various design options. Looking across manufacturers I can find a variety of clamp slot orientations, seat tube extensions above TT, additional supports and various inserts. I can even find variations across a manufacturers range or from year to year, as indicated by the Carrera changes upthread.
I do understand minimum insertion depths for seatposts and can contrast that with frame insertion requirements. I would also err to the cautious side in this area being of the larger persuasion and running a setback seatpost.
But say you wanted something pretty bombproof, not downhill/all mountain bomproof, but otherwise sound. Assuming you don't care about the slot orientation(or would prefer rear facing, think permanent mudguard/splashguard in place), would you be better to:-
1. sacrifice a bit of standover by shallowing out the TT slope and having less seat tube extension - but still retaining comfortable standover - if so what amount of extension above the TT is about right?
2. keep the TT slope but support the seat tube extension above the TT in some way - if so which way is best?
3. do a mix of both, so shallow the slope but also keep the above TT extension by increasing overall ST length, and add in some additional support for good measure.
Bike useage I'm thinking mild XC, not racing, trail and rough stuff touring, but built for tanklike durability rather than speed.