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I've recently bought a Planet X pro carbon in medium size...... Right from the off the sizing felt a bit strange and it just felt short in length. It's great to ride but high speed feels really unstable downhill, one time even getting a pretty violent speed wobble.
Anyways...... I was looking at the frame measurements and the important one ..... Top tube length ....... Is strangely not what it should be according to the Planet X web site ( although other measurements match ) ..... The top tube measures at 530mm ....... But according to Planet X web site should be 545 on a medium frame ...... This missing 15mm is roughly the amount I'm feeling the bike is too short, and funnily enough is the extra length I had in mind to change the stem by before I measured the frame !
Does anyone have a pro carbon frame in medium that they could measure for me to check? I want to see if this is a general thing or somehow I have a frame that's wrong ! .
It's the top tube measurement I'm after .... Centre of seat post to centre of fork post ?
Did you measure the top tube or the effective top tube? The top tube will be 530mm I'd say; effective top tube will be longer
The best way to get a definite size confirmation is to measure the head tube, if it's 145mm you've got a medium. It's the way the PX builders do it if they are in any doubt.
have you had a bike fit?
Yes head tube is 145 mm .... Yes top tube is 530mm ...... I'm not seeing how effective length could add 15 mm ?
trigonometry innit
It's the top tube measurement I'm after .... Centre of seat post to centre of fork post ?
This is 530 on my medium.
Check the seat post,if its a standard px alu post they only have 12.5mm layback where most layback posts have 25mm, that's 12.5 shorter straight from the off
Ok. Guys ....... Another question then...... What could be causing speed wobble or unsteadiness at 35 mph + ????
Stem is around 105mm ...... Would a 120mm help ? It just seems long ?
105mm is short for a road bike, 120mm may well help. Are you decending on the drops? If not, do so as that may help as well. And are you gripping the bars tightly? Again, if you are, try not to as a more relaxed grip can help. Finally, when I decend I tend to hover just off the saddle and almost grip the saddle with my legs, not sure if this is textbook technique or not but it works for me.
Ok. Guys ....... Another question then...... What could be causing speed wobble or unsteadiness at 35 mph + ????Stem is around 105mm ...... Would a 120mm help ? It just seems long ?
Speed wobble could be anything. something loose? Gripping bars too tight? Wonky wheels?
Hard to know if a longer stem might help; it could do, or you may be fine with a 105mm. Personally, I use 140mm stems as descending is much better with some weight on the front end.
My old road bike was a Felt..... Which has a slightly shorter stem..... And slightly longer top tube ..... Never experienced any issues with that ...... Descending on drops on both bikes .......
For some reason the Planet X just feels too short for some reason and I've convinced myself I think that this is the issue .... Just don't have the confidence on it at speed.
I think I may compare all the measurements on both bikes and see where they differ.
Oh yes .... Forgot to mention.... Changed the wheels over and it made it a tiny bit better but not a little lot !
which model felt did you have?
What colour is it?
Felt f95
What colour is it?
The Planet X ? White
Theres your problem 😉
I guessed that would be your answer ....... Trap sprung ...... It's actually black 🙄 😉
I can measure mine tomorrow its got the same stem length i think too.
Fwiw i don't experience wobble.
Edit- if it really is black we might have matching bikes... awkward
Aren't they known for having a flexy front end, could be the wobble cause? Are you sure you need a medium, they are a very compact design, maybe you need the next size up?
Have you got many spacers under the stem?
High stem can make a bike feel short and handle a bit crap.
Especially a short one like that.
It's probably you.
relax
I really don't think it is as down the same descents on my other bike I have no issues ......
I've just checked everything on forks is all tight and solid and fitted a 120mm stem to see how that feels.
The spacers are unchanged from stock ...
It was raining after I changed stem so little point in heading out but will hopefully give it a try tomorrow!
Thanks everyone for input
I had a Pro x in large. The FSA's went first and that massively improved things (crosswinds etc).
Then the F&F went and I became alot happier.
OP are you on FSA's? I know you think its TT but try others wheels too
I had one of these as my first road bike and experienced a pretty terrifying speed wobble on it whilst descending off exmoor. Had no control over the bike until it slowed due to the levelling of the road. I then analysed what I did and whether I could reproduce it.
Turns out I was descending with my weight back (as you would on a MTB). Adjusting to bring my bodyweight over the bars prevented it from happening again. Something to do with the resonance of the frame at a certain speed I think. Other people suggested holding a leg against the TT when descending.
I guessed that would be your answer ....... Trap sprung ...... It's actually black
Lucky you didn't get the blue one, hora had all sorts of problems with the blue one!
hora ... Already changed the wheels from Vision stock ones to Mavic from my old bike .... Really didn't like them in cross winds ..... Went out tonight on 120mm stem and found it quite a bit better ...... Going to tweak my seat forward a little more too as it does seem better with more weight forward over bars ...... Got some progress though !