Comparing geometries on two Planet-Xs

StudentC

Hi

I know Planet-X has been done to death on here, but I'm confused. I'm looking at the Pro Carbon and the RT 57, and these are the geometries of the two frames in 'medium':


Pro Carbon
RT-57
Head Angle (°)
72.5
72.5
Head Tube Length (mm)
145
135
Effective Top Tube Horizontal (mm)
547
543
Seat Angle (°)
73.5
74
Seat Tube Length Centre to top(mm)
480
540
Chainstay Length (mm)
408
405
Stack (mm)
544
539
Reach (mm)
385
388

To me, that looks like the RT-57 is a more aggressive / racier geometry (longer seat tube, shorter head tube), and that's what a couple of people on previous threads here and elsehwere have suggested.

However, Planet X's website has this:

"Think of it (RT-57) as being in between the Pro Carbon and the N2a, but off to one side. Those two bikes have our classic, long-top-tube road racing geometry, This makes for a bike that's fast and surprisingly comfortable for long rides, if you're flexible enough that it fits you. (Tour de France bikes have geometries like this, and riders wouldn't put up with over 100 miles a day for three weeks if their bikes weren't comfy).
The RT-57 is a little shorter for any given size. For example, a size L Pro Carbon has a stack (the vertical distance from the bottom bracket to the top of the head tube) of 565mm and a reach (the horizontal distance between those two points) of 397mm. In an RT-57, a 56cm frame has a 557mm stack and 389mm reach.
In real terms, that means the cockpit is about a centimetre shorter, so if you're not long in the arms and body, or as flexible as a top pro, it'll fit better. But it's still fast, light and racy – lighter than the Nanolight, in fact. (But still heavier than the N2a.)"

Which seems to suggest that the RT-57 is more suitable than the Pro-Carbon is you are less flexible (i.e. that the Rt-57 is less aggressive).

Am I being an idiot and misunderstanding what they are saying?

obviously I'll try the two and see which works better, but I'm confused. Thanks.

niceonetom

The frames are very close in terms of size, to the point that I doubt there's anyone who could reasonable claim one fits them and the other doesn't.

The claim that "The RT-57 is a little shorter for any given size" is not borne out by the number you've posted. The RT57 appears to have both more reach and less stack - ie bars further and lower, but only slightly, 3mm out, 5mm down. 3mm in reach is barely detectable for most people and a 5mm spacer cancels out the stack difference.

Confusingly, the RT57 manages to have a longer reach despite having a shorter ETT, this is because it has a steeper angled seat-tube. The 0.5* difference there equates to maybe 0.5mm to 1.0mm of difference in terms of how far the saddle is behind the BB; that's well within the range of what can be accommodated by sliding the saddle fore/aft on the rails so don't worry about that either.

So, if your numbers are correct then the explanation on the PX site seems misleading and unhelpful, but probably isn't going to put anyone on a bike that really doesn't fit. Maybe they're correct for the 56 but didn't notice the difference is seat angle for the 54?

For what it's worth I've owned a Pro and liked it, but I'd take a punt on the RT57 if only because it'd a little less dated looking and might be a little stiffer (not necessarily a good thing if you prefer a cushy ride, but for racing stiff is good).

StudentC

Thanks for that niceonetom, good to see I'm not the only one thinking that the PX spiel doesn't make complete sense!

If you have any further wisdom....

What I'm looking for is something lighter and just generally nicer than what I currently have (5-year old 10.8 kg bog standard entry level aluminium frame). Stiffness isn't a big deal - the only bits of racing I try are the likes of the Orwell women's crit league where the aim is to not be last, so it's the rider not the bike which is the issue there! I've fairly poor flexibility and a bad back, hence trying to get the fit is the main issue really.

The Pro Carbon has ultegra and then everything else is standard non-fancy Planet-X bits. It's £1000 (sterling).

The RT-57 is a friend's (so second hand). Has Dura ace groupset, carbon bars and seatpost (neither of which I really care about) and nicer wheels (I can't remember what right now, but they were definitely a decent enough upgrade from the Planet X standard). I haven't seen it yet, he promises it's in good nick and that the components are still in good nick. He reckons he wants about £700 for it, but I'd say I could get him down from that.

So for me the frames are similar, it's whether (if they both feel nice) second hand dura-ace and nice wheels for ~700 is a better deal than new ultegra for 1000.

Going to try the Pro Carbon today and then hopefully taken the RT-57 for a spin at the weekend. Decisions, decisions....

niceonetom

Certainly the RT57 sounds like bar far the better deal. If you've got poorer flexibility that its current owner then see if there are any spacers above the stem or if it would be possible to flip the stem to give you more rise (that or replace it with a shorter one if necessary). A Pro Carbon bought new should come with an uncut steerer-tube which would give you that adaptability straight off the bat.

Either bike will fell like an absolute weapon if you're coming from 10+kg of alu.

StudentC

Thanks for the thoughts. Certianly either will be nicer than what I have - road someone else's Pro Carbon (different size, slightly too big) last weekend for a couple of hours and it was a lot of fun.

Was thinking that playing around with stems might do it for me allright. We'll see!

Thanks.

Lumen

niceonetom wrote: »

The 0.5* difference there equates to maybe 0.5mm to 1.0mm of difference in terms of how far the saddle is behind the BB; that's well within the range of what can be accommodated by sliding the saddle fore/aft on the rails so don't worry about that either.

cm

niceonetom

Lumen wrote: »

cm

Good catch. I meant cm.

0.5cm to 1.0cm is what would have to be accommodated by the saddle rails to nullify the effect of the 0.5° difference in seat tube angle.