Look to the tires for this? That's what I think, but comments welcome
 

Was out on my "road" bike the other day on a group ride with some young brisk riders and ended up with just me and the leader together up front. Kept up OK but had to work a little harder than he was I am sure. But I think I had a specific handicap and it wasn't my platform pedals. I don't think that much of it can be attributed to lack of tight aerodynamic clothing, not bike weight because my bike is CF and in any case the syndrome was this: on a long downhill, my new roadie friend is coasting and pulling away from me whilst I pedal. I have flat bars but was hunkered down. He was in the hoods so our postures were similar. Of course, he is running 23s. I am running 28s which are so much more forgiving of road hazards and chip seal, etc., but it is my thought they hurt me in this particular case.

I do all my own work and can assure you my brakes do not rub. I can't see type of hub bearings making this much difference. The man was bigger and heavier than I am, but, being bigger, should have presented more aerodynamic resistance in proportion to his weight.

Tires are some kind of Bontrager 28s with Spin Skins and were inflated 110 frt, 120 rear.

I guess I will just have to get on EBay or AliBaba and order another CF frame, fork and etc. from China and build my #8 bike to leave permanently set up with 23s. :)

Or maybe shave my legs? :) :)

Don in Austin

My money is on wheel/bearing differences. His weight can't be discounted so easily either.

My money would be on the weight difference. weight definitely translates into faster descents.

Agree on the weight - yes the bigger person will have a little more air resistance, but not nearly by as high a percentage as their weight difference; i.e. someone twice as heavy doesn't have nearly twice the frontal area.

And there can be considerable difference in the rolling resistance of tires even if they have the same width. In general tires with minimal tread pattern and the most flexible sidewalls will have less rolling resistance.

I can't see much point in running 28s and using such high pressures. Lowering them probably won't influence your downhill speed, but it will improve comfort and likely the handling, too. I rarely run above 95psi on my tyres, from 23s to 28s, even on the tandem

Lots of things influence speed- the main one being the engine- but style of bike-quality of wheels- rolling resistance of tyres and on the downhills also the weight of the rider.

When coasting downhill I go faster than almost everyone I ride with, and it is mainly because I am the heavier rider. Obviously I also present a larger front to the wind, but that can be minimised by getting aero.

Other things that make a difference are bearings: really nice hubs do help. Tyres would be well down towards the bottom of my list, especially at the pressures you are running. Wide tyres actually roll better than narrow tyres at the same pressure.

Comfort and handling is good. I had been getting flats on a regular basis so I bought Spin Skins. Happy to say a few weeks have gone by without a flat. The instructions with Spin Skins stress the importance of keeping pressures up. On the ride I was referring to, the road surfaces are quite good, so there is little downside to the high pressures.

My engine is what it is. But on the downhills the other rider's engine was turned off.

Training aid for downhill speed:

http://i1216.photobucket.com/albums/...3/twinkies.jpg

If you want to minimize your rolling resistance, the two things you should do first is remove the spin skinz and get some latex tubes. Going to 23s might actually increase your rr; but either way it'll be a small a difference.

Or, you could pick up some rocks at the top of each hill and carry them to the bottom. That way you'd be flattening the hills slightly, working against the phenomenon whereby the hills get bigger each winter. ;)

Don, you have got to get the proper clothing! Padded shorts and bike jersey and you
Will be faster than the wind!
lol

His Weight.

+1 - that and position... hold the bars at the stem and have your body crunched in on the descents (move the hands out if it is a curvy descent) and keep your feet parallel to each other--at 3 and 9 o'clock, knees together at the bar and elbows tucked inside your chest. Not comfortable for lon g stretches, but it will do wonders for your downhill speed regardless of bike. If he still gets away from you, look into the other things mentioned in this string of comments.

train safe-

I don't think the other rider was any more hunkered down than I was. Tires are worn out anyway so I have decisions to make re' flat resistance vs. tolerance of imperfect road surface vs. speed.

I have been steadily moving the bars down since the ride I wrote about. Over the last 4 years my back is fine with lower and lower bars. 4 years ago I had to use extenders on the steerer to get them high enough to prevent my back from bothering me, but not no more!

Costs nothing and can't hurt with downhill speed.

Same ride tomorrow morning, we shall see.

Don in Austin

I know when I tossed my Bontrager B's 25mm and went to Michelin Krylion 23's the difference was immediately noticeable. Other than body weight, I'd start with tires and move on. Also want to stress the difference getting aero can make when you go above 15mph.

In as much as equipment (on the bike) makes a difference, tires make more of a difference than anything. I would guess that hubs rarely make a difference at all.

Rider position is a big factor in aerodynamics.

Weight is not as important as the surface-area-to-mass ratio. I'm not very heavy, and I always win coasting contests, and I suppose it's because I'm pretty lean.

For me it seems to be tires, hubs and wheels. There was a big difference between my old Open Pros even with my Dura Ace hubs and my new K Swiss with Hope Hubs and high quality cartridge bearings . I know Cone and Cups can be adjusted but when spinning the two sets of wheels side by side the Hope hubs have always spun longer. I have tried putting my two bikes upside down and next to each other and spinning the wheels together. Every time my Hope Hubs are still spinning long after the Dura Ace had stopped. And the Dura Ace were just rebuilt and serviced. I have even switched wheels on the two bikes and still the Hand built Hope wheels spin easier and longer. I tend to use the same tires on both bikes and I haven't discovered a big speed difference between 23s and 25s. I have tried the two bikes on the same hill and the wheels do make a difference in acceleration and distance when coasting. Not as much in top speed maybe but they get up to speed quicker and go farther before I have to pedal. Not a scientific study I agree but that is what it turned out to be for me. As far as your flat bars go how wide are they compared to your friends drop bars? On my old Masi Café Solo the flat bars had my hands wider and so my shoulders even hunched over would he wider creating more resistance than I would be down in the drops in the position described earlier, making myself as small as I can.

We have a 10% downhill for 1/2 mile that is dead straight and is always a spot for coasting. I find I can catch the heavier riders by drafting but as soon as I pull out to overtake them I lose speed rapidly. Admittedly the others are 30 + lbs heavier than me but I can catch them rapidly from 5 yards behind using drafting But that bit more speed gets lost as soon as I am taking full wind resistance.

Then wheels--I have several sets and the wheels and tyres do affect speed. Have a 50 mph coasting hill not far away and I did it with a bunch of other riders. When we got to 40 mph two of us just pulled away from the others. The bikes were good and the riders competent. Got to the bottom and the two of us that had the speed looked at each other with grins as the others arrived. Coincidence?? but we both had Ultegra wheel sets compared to the others OM or cheaper wheels and weight of rider did not come into it as we were the lightest two among the group.

And My C.F. TCR will not take certain wheels at speed. Put a set of stiff wheels on that and I lose handling above 35 mph. Stiff wheels and stiff frame with a lightweight on board and I can't keep it on the road.

+ 1 for wheels - at 220 I know down hills and the new set of wheels I had build are definitely faster then anything I've had b4 -

+1 without doubt it's weight as I know from my 215 lb. Can't go fast uphill, but I catch 'em downhill.

'A group ride with just me and the leader up front . . .'
You call that a 'group ride'?

I'm going with aerodynamics. I know the OP feels he was hunkered down on his flat bar bike, but at downhill coasting speeds all the little things make a progressively greater amount of difference and the faster you go the more difference it makes.