Road bike Geo – Compact / Non-compact setup?

Following on from the other road bike fitting thread on here last week…

I’ve been looking to improve the general fit and feel of my geared road bike the lately too.
Having Spent several weeks riding only my cheapo, gas piped, Fixie which is both significantly heavier and obviously lacks a few gears, I’ve gotten back on my Geared Road bike and it just feels Slow, Draggy and Cramped… I’m not really enjoying it and I actually appears to be slower when riding it on the flat…

Having looked into it I believe my Geared Roadie has what’s known as “Compact” Geometry which appears to mean lower BB, a slacker Seat angle and sloping TT, placing the riders weight bias slightly further back supposedly, aiding cornering and probably something else, sprinting? dunno. and gives more stand over, that’s my understanding of it (I’m sure I’ll be appropriately corrected)…

Now can anyone tell me is there any way to make my “Compact” framed bike as comfortable to ride and as fast as my non-compact framed bike?

I’ve only ever heard of Compact meaning the sloping top tube. Never heard about it relating to a lower BB, slack seat angle etc.

So long as you setup the contact points the same, I see no reason why it should be any difference between the two bikes you mention.

yeah, compact usually just means sloping top-tube, but your road bike will most likely have slightly different angles to your fixie, depends if that is designed with proper track geometry or something more suitable for fashionable about-town use, steeper angles will make it feel twitchier and therefore faster even if it isn’t, your road bike might be designed more for all-day comfort than a few laps of the track or just nipping down Costas

as above try to replicate the contact points and go from there

Well that’s the thing I’m still not too sure what “Compact” really means, I read a couple of interesting articles on how Road geometry a while ago describing how shifting a rider’s weight bias back and placing the BB lower helped with cornering for crit’ bikes as well as helping to make a frame fit a slightly wider range of riders and perhaps assumed that this was what “Compact” Geometry was aimed at…

I think I’m going to have to measure them both up properly, having tried to rather simply match the contact point positions in terms of seat nose to bar centre and Crank centre to Seat I’ve got it in my head that I’m still sat slightly too far behind the BB (on the compact one), which will be placing undue stress on my knees too so I’m thinking longer stem, shift seat forwards (maybe even took at an inline post) but I need to measure both bikes up and see where the comfy one differs from the mare first.

I can sort of visualize the possible issue in my head, but I think I need to measure and draw it up to get things straight and work out what to do next…

Just wondered if there were any Guru’s on the topic knocking about on STW today.

cookeaa – Member
Well that’s the thing I’m still not too sure what “Compact” really means

well, ‘compact’ is a catch-all term usually referring to a sloping top-tube and one manufacturer’s ‘compact’ will be different to another manufacturer’s ‘compact’, and your road bike geometry will be different to your fixies geometry, but both of those can vary widely from manufacturer to manufacturer, without knowing the geometries of your different bikes it’s going to be hard to give any advice, which may be as simple as “they’re different, get used to it”

“Compact frame” is just a dropped top tube.

The main reason why your road bike might feel sluggish is geometry. How old is your road bike? How old is the fixie? Modern geometry has now fixed on 72.5-73 degree head tube, which makes for more sprightly handling. Older bikes viewed 72 degrees as racing bike and anything steeper as track. What about seat tube angle. Are you in exactly the same position over the bottome bracket? Don’t go by saddle position on the rails, a one degree change in seat tube angle is a cm difference on the saddle rails. Are you sitting further back on the roadie? How long are the horizontal top tube measurement? A longer bike and shorter stem will feel different to a shorter tt and longer stem.

If the contact points are in exactly the same points on a bike with the same geometry, then the only difference in handling will be frame material (weight) and tube diameter (stiffness).

I suspect the two bikes are set up very differently.

I thought it was more then just a sloping top tube…something about making both the front & rear triangles smaller and therefore the overall frame stiffer. Persuasive, huh?

edit: The concept is simple: A toptube that slopes downward from the headtube to the seattube reduces the size of the front and rear triangles.[/url]

Well it has to make a smaller rear triangle, otherwise it’s a mixte 😉 . I love them by the way. TCR and Defy rider. My Kona is only semi-compact with a slightly sloping TT. The Defy rear is much smaller. But rigidity is really tube diameter realated. You can make a very rigid conventional frame (Pegoretti) and a flexy compact frame (Litespeed Ghisallo)

In terms of geometry, traditional is horizontal top tube, compact is sloping TT but then just to confuse things you can have semi-compact – a slightly sloping TT. In theory at least, you can replicate the exact same positions on each (assuming angles are all the same) but the compact will have much more seatpost showing.

In practice, it’s likely that the geometry of the two bikes varies quite a bit hance why you can’t immediately replicate the position or feel. But bear in mind that ride feel can be changed dramatically just by putting an extra 20psi in the tyres…

I was going to suggest tyre pressure and possibly compound making a difference as much as geometry. Could the fixie be stiffer than the geared bike?

My singlespeed/fixie feels more sluggish than the 5lb weight difference to my geared road bike. Position feels ok and fairly similar on both bikes, so I’m putting it down to a combination of weight, a longer wheelbase on the ss and heavy duty tyres.

I just thought compact geometry meant smaller triangles with more seat post showing for improved standover, but it shouldn’t necessarily feel cramped or short if its the correct size. And will vary from manufacturer to manufacturer.

A poorly set up road bike will feel crap next to a basic but tight singlespeed/ fixie. There’s more to go wrong, more to be a bit loose, more to be a bit worn out.

It needs to all be working optimally, brakes, gears, hubs, bearings, tyres etc then it’ll feel right. That’s why your fixie is so good, pump up the tyres and pedal. Geometry’s neither here nor there.

Well I’ve measured the contact points and a couple of other bits and bugger me if they’re not actually really bloody close to one another…

Fixie’s BB is 9mm higher and 12mm further forwards saddle is about 10mm further forwards too, meaning that relative to their respective BB’s the fixie’s saddle is only about 2mm further forwards…

wheelbase is almost spot bollock on the same.

Fixie’s bars are 17mm lower though, both using a very similar 120mm /440mm compact drop, so changing bar position on the Geared bike is worth looking at (stem flip?) but I’m not sure it would be wise to shift the seat too much, maybe a little further forwards and make sure the bars come a similar amount with that…

I was expecting massive differences but TBH they’re not really all that significant…

But yeah “Compact” and “Standard” achieve pretty much the same position on the bike…

Geared bike is Aluminium with a Carbon fork, Fixie is very cheap PG steel tubes throughout, neither seems particularly flexible…

Fixie is using on 28mm Rear / 23mm F tyres, geared has 23mm bot ends all at 100psi… that bigger rear tyre could be part of the difference I suppose?

Hubs are all rolling nicely, rims are true, chains are lubricated…

Geared bike is noticeably lighter, will have to weight them both some time…

Maybe I just get on with the fixie a wee bit better cause there’s much less to think about…

Next step is some DIY motion capture with the turbo trainer I reckon, I feel the need to measure and test every bastard thing now…

Bed time now though…