- Bike geometry advice needed
If two frames have the same horizontal top tube length, but the following other things have changed, what would the effects be on climbing/descending/handling? If it makes any difference, moving from alu to 853 steel too.
HA from 69.5 to 68.5
SA from 74 to 73
(based on 100mm fork)
Chainstays from 16.75″ to 16.25″
Also, the seat tube has gone from 15″ to 12.7″, but because the top tube is still the same length, will it just provide more standover?
thebunkPosted 6 years agorootes1Member
i have theory that what angle do really is alter the weight distribution…
slacker bikes, more rearward weight, better for downhill , steeper angles weight spread between the wheels better for climbing / general etc etc
would be nice in mags to do an experiment with some scales under each wheel with a rider onboard and see how weight distro affects bikesPosted 6 years agothisisnotaspoonMember
Slacker angles and shorter chainstay will (without doing any manths) give you aproximately the same wheelbase and therefore stability, but with your weight slightly further back when stood up, so more stable when going downhill.
Conversely the shorter chainstay and slacker seat angle* will make the bike wheelie slightly sooner when climbing.
The slacker head angle will slow the steering down slightly, so you might want a slightly shorter stem to speed things up again.
Running a shorter stem seems to favour wider bars for 2 reasons; 1 it keeps the grips the same distance from you so you can keep the same top tube length. 2 they give more leverage which helps with wrestling with slack angled bikes.
Basicly the new bike will be slightly better going downhill than the old one. But TBH the difference wont be night and day.
* seat angle is irelavent, you could run a layback or straight post or the saddle all the way forewards or back and change the angle by 7deg or so.Posted 6 years ago
One hour?! 28 minutes is all you get on the first page at the moment!
What the blazes are you doing if you’re not checking STW every 4-6 minutes anyway?
edit – Lionheart – new seatpost (surely this doesn’t matter?) stem and bars. Stem and bars will depend on the outcome of this thread! (Am thinking 20mm wider bars, 10-20mm shorter stem so far).
Everything else stays the same.Posted 6 years agoreggiegasketMember
all things being equal, the second frame will feel slighly shorter, as the SA is less, so even though they have the same measured ETT length the second bike is being measured from slightly further back.
To sort this out you can either just move your saddle around, or just adapt your riding to it. However, if you fit a shorter stem as well then you’ll make the cockpit shorter still, so just be aware of this.
The new frame is slightly slacker which (equals more stability) but the chainstays are shorter (which does the opposite) so they kinda cancel each other out. I’d suspect you’ll just have to think about how you want the bike to handle and adjust accordingly… the new setup may well descend a bit better (more stable AND yet more responsive) but won’t quite climb as well, or at least one where you end up on the nose of your saddle a bit more.
All these things are a compromise – you just need to decide what you want it to do well and gear the setup around that.
Do you have travel adjustable forks? That’ll help.Posted 6 years ago
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