Northern California - Fastest speed on Palomares Descent?

I rode northbound on Palomares today. I just got a new garmin edge 305 GPS a few weeks ago and this was my first time using my GPS on the descent on Palomares.

I only hit 43.8mph. My cateye strada said 46mph but I'm pretty sure my GPS is more accurate. Anyone else have a faster time on that descent??

I think I need to pedal harder in the beginning of the downhill. I'm trying to see if it's possible to hit 50mph on that road.

Any tips on reaching a higher top speed on a straight descent?

I hit 46.0mph on it todays ride, and I think we hit over 50 mph on the tandem.

Just get really aero, and don't touch the brakes, pedal in the biggest gear when needed. ;)

I wasn't pedaling too much, so a couple more mph could have pulled out I think.

whoa, is it more or less scarier descending on the tandem???

whoa, is it more or less scarier descending on the tandem???

Depends.. Usually it's a little crazier on the tandem.

-Con: On the tandem you have to take nicer lines (less room for adjusting your line, since it's longer), but that's OK since your line is very important anyway.

-Pro: The tandem is more stable due to the longer wheelbase, and higher weight. Bumps and high winds do not phase it, like they can on your solo.

-Con: You have to get on the brakes harder and sooner, due to the weight you have to slow down. Because of this, you have to manage how you use them to avoid over heating the rims.

-Pro: The rear brake is MUCH harder to lock up than it is on a single. So the rear brake is much more useful on a tandem.


All and all I would say that for a high-speed not to technical descent (like W84 or HWY9 EB) I actually prefer the tandem. It is super stable, it goes really fast if you keep off the brakes and two people can hammer the 53x11.

However for a tricky technical descent. I prefer my solo bike. It's lighter, easier to slow down for turns (I can brake way harder), can take tighter lines.

I rode northbound on Palomares today. I just got a new garmin edge 305 GPS a few weeks ago and this was my first time using my GPS on the descent on Palomares.

I only hit 43.8mph. My cateye strada said 46mph but I'm pretty sure my GPS is more accurate. Anyone else have a faster time on that descent??

I think I need to pedal harder in the beginning of the downhill. I'm trying to see if it's possible to hit 50mph on that road.

Any tips on reaching a higher top speed on a straight descent?

I'd actually rate your cateye over your Edge for speed.

hmm, Now that I check the history on my 305 itself, it shows that my max was 45.5mph, but my data on my computer only shows a 43.8mph max.... weird. I'm getting kinda tired of all these little glitches on my 305..

GPS isn't perfect. Not only is there the possibility of briefly losing signal, but you're being measured as moving over flat ground.

http://www.analyzemath.com/Geometry/formulas/right_triangle.gif

While you're moving along c, your speed is being measured along b. I'm not sure how big of a deal that comes out to in real life, but it's a consideration.

If you have an accurately set up wired computer, that's going to give you the most real numbers.

I've been using my Edge 305 for a month now. I've had a few back and forths in the electronics forum about the speed readout. At first, I couldn't understand why my speed was all over the place heading through Pinehurst, then it was also a joke up Tunitas - just jumping all over the place. I'm at peace with it now, but I don't understand why Garmin wouldn't use the wheel sensor as the primary data source - it's THE most accurate, so why bother with GPS speed?

I noticed on todays ride that Joel was using wireless Cateye for speed/cadence with a 305. I'm quite intrigued by that. Still, the ability to analyse heart rate, cadence and (iffy) speed along side routes is still a winner for me.

I've hit over 50 (barely) on that descent. The trick is that first right hand corner - if you nail the line through there, you shouldn't need to use your brakes, and you'll carry a lot of speed onto the steepest part of the hill.

As for accuracy, I think Beaker and X are right - it's hard to believe that a GPS would give a more accurate speed than something counting wheel revolutions - there's just far less to go wrong, and the accuracy of the two measurements (circumference and # of revolutions over time) should be very good compared to the accuracy of most GPS systems. My 2 cents.

JB

While you're moving along c, your speed is being measured along b. I'm not sure how big of a deal that comes out to in real life, but it's a consideration.

If you have an accurately set up wired computer, that's going to give you the most real numbers.
On a hill like Palomares the effect of measuring horizontal speed vs. slope speed is well under 1% and therefore negligible.

But I agree that GPS is not the best technology for measuring speed compared to the relatively simple task of determining the time per wheel revolution with a regular cyclometer. The GPS measurement can be affected by reflected signals, changes in which satellites are being used in the computation, momentary loss of reception, etc. My all-time maximum speed given by my GPS was 4032 mph - pretty impressive for an uphill ride. But it was created by getting some spurious signals reflected from a hillside that caused my apparent position to take a sudden jump - GPS depends on knowing the transit time from each satellite and assumes a direct line-of-sight path. When that assumption isn't true the calculated position and speed can be affected.

My all-time maximum speed given by my GPS was 4032 mph

:lol:

Cased closed, I think.

I've been using my Edge 305 for a month now. I've had a few back and forths in the electronics forum about the speed readout. At first, I couldn't understand why my speed was all over the place heading through Pinehurst, then it was also a joke up Tunitas - just jumping all over the place. I'm at peace with it now, but I don't understand why Garmin wouldn't use the wheel sensor as the primary data source - it's THE most accurate, so why bother with GPS speed?Tunitas and OLH are particularly bad, and I think the lower section of Alpine is pretty impervious to GPS reception as well.

The reason it's so jerky is that when it regains a signal, it's interpreted as if you just moved over that parcel of land in an instant, giving you things like 90% grades.

As for the wheel sensor, you can supposedly force the Garmin to use it, but the method for doing so is to shut off the GPS receiver part of the computer entirely. Helpful. :rolleyes:

Really, the only thing keeping me using it is that I kind of like having a map of where I've gone, especially when riding places I'm not too familiar with. Other than that and the ability to easily move it to any vehicle (bicycle or otherwise), I could easily get everything I need out of one of the nicer conventional computers. http://www.bikeforums.net/mysmiliesvb/mysmilie_15.gif Kind of a drag.

GPS isn't perfect. Not only is there the possibility of briefly losing signal, but you're being measured as moving over flat ground.

http://www.analyzemath.com/Geometry/formulas/right_triangle.gif

While you're moving along c, your speed is being measured along b. I'm not sure how big of a deal that comes out to in real life, but it's a consideration.

If you have an accurately set up wired computer, that's going to give you the most real numbers.

And being as we are all descending hills much much steeper than the graph it comes into even greater play!

I love that descent, it's one of my faves. I've gotten up to about 42 on it. I know, amateur. :rolleyes: :D

And being as we are all descending hills much much steeper than the graph it comes into even greater play!If it ain't a 45% grade, what's the point?

The GPS can measure large distances more precisely. Your Cateye can measure, with 100% precision, how many times your wheel has gone around.

Hence, the Cateye only gets more INaccurate over distance, for any given margin of wheel diameter calculation error. The significance of the GPS's margin of error decreases as the distances involved increase.

GPS measures your position in 3 dimensions so why would it not account for going up or down hills?

And +1 what reid said ... the error in a traditional bike computer isn't counting wheel revolutions, it's measuring wheel circumference. I've always been curious how much that actually changes with tire wear, tire temperature, and tire pressure.

A man with a bike computer always knows his top speed. A man with a bike computer and a GPS is never sure.

GPS measures your position in 3 dimensions so why would it not account for going up or down hills?

And +1 what reid said ... the error in a traditional bike computer isn't counting wheel revolutions, it's measuring wheel circumference. I've always been curious how much that actually changes with tire wear, tire temperature, and tire pressure.

My GPS gave me a high-speed rating of 41.9mph on Palomares descent. That sounds more than reasonable to me, given my descent trepidation.

My view on the GPS is that I'm taking the measurements as being "pretty good" and am comparing them with older GPS measurements. So, assuming the error is you know, in a consistent range, I'm happy with what I'm getting. I figure every time it puts me 10meters off OLH to the downhill side will eventually be balanced by being 10m off on the uphill side somewhere else.

For what it's worth, my elevation readings on Diablo at the signs were 10ft lower at all 3 signs, e.g. 1990 at the 2000ft sign.

GPS is not that accurate for measuring altitude. Well, portable GPS receivers aren't. Unless they reference it against topo maps. The triangulation the GPS system uses works very well for determining lateral position, but not so well for elevation.

I also imagine lower-power receivers probably latch onto the satellites with the strongest signals, which means the ones further out on the horizon, with weaker signals (but better ability to resolve your altitude) are ignored by the receiver entirely.

A man with a bike computer always knows his top speed. A man with a bike computer and a GPS is never sure.

I remember Alan setting his PR on Tunitas. :roflmao2:

No one should ever be really sure, unless they're riding the same line on a track or something.

Top speed on Saturday was 44 mph just coasting.

My max on Palomares is 48 mph, this is with a full sprint over the top and down. I've been trying to break 50 but think I either need to gain a little extra weight or draft a bigger rider going for it.

On the descent on Felter/back Sierra Rd, I was also topping out at 46 mph by myself. With a pull and draft off Glen/gw_12, I did break 50mph.

Top speed on Saturday was 44 mph just coasting.

My max on Palomares is 48 mph, this is with a full sprint over the top and down. I've been trying to break 50 but think I either need to gain a little extra weight or draft a bigger rider going for it.

On the descent on Felter/back Sierra Rd, I was also topping out at 46 mph by myself. With a pull and draft off Glen/gw_12, I did break 50mph.

^^
:lol:

GPS is not that accurate for measuring altitude. Well, portable GPS receivers aren't. Unless they reference it against topo maps. The triangulation the GPS system uses works very well for determining lateral position, but not so well for elevation.

I also imagine lower-power receivers probably latch onto the satellites with the strongest signals, which means the ones further out on the horizon, with weaker signals (but better ability to resolve your altitude) are ignored by the receiver entirely.

In this case I think that Chris's readings would be from his barometric altimeter rather than the GPS part of his Edge - of course, that's subject to atmospheric variation.

If I had the "perfect" cyclo computer, I still think it'd be mostly a Garmin EDGE but with speed coming from my wheel. Yes there are miniscule errors that "could" theoretically cause a problem when you add them up over time, but for speed this doesn't matter.

FWIW, when I compared distances measured by my Cateye computer with reported distances for known routes, I found it pretty accurate. Having seen that GPS routes can incorporate mistakes through poor coverage - e.g. this ride up Tunitas, I'm not so sure that a wired computer might not be more accurate for total distance. Either way, both systems are more than adequate for my purposes in that respect

http://i321.photobucket.com/albums/nn384/RDW5980/2009_05_23_PeninsulaRide/Tunitas_GPS.jpg

It would be cool if the computer could autocorrect the wheel diameter factor :)

I've been trying to break 50 but think I either need to gain a little extra weight or draft a bigger rider going for it.


I think you just figured out my secret! Even after dropping close to 20 pounds this year, I'm still over 210.

JB

I've always been curious how much that actually changes with tire wear, tire temperature, and tire pressure.

A 700c wheel should be 622mm diameter - so a bare wheel has a roll out of 1954mm.
A 700x25 tire should be about a 2105 mm rollout (~335mm radius)
A 700x23 tire should be about 2097mm.

Lets say you travel a mile on a perfect 700x25 tire (1,609,344mm = 1 mi), your wheel rotates 764.53 times.
Now if your tire is worn down 3mm (evenly), it's got a new diameter of 332mm and a rollout of 2086mm. Your computer would read 764.53 revolutions, which now would only be 1,594,831mm instead of the 1.6xx mm in a mile. Your computer would read 1 mile when you would have really traveled only 0.9909 miles! Over 100 miles, you'd loose 1 mile. Whether a tire would last 100 miles with 3mm of rubber already gone is a different story...
If your only down 1mm of rubber, you loose 4,905mm per mile, just over 3%

But the results would be the same if your measuring a 700x25 but actually using a 700x23.

A 700c wheel should be 622mm diameter - so a bare wheel has a roll out of 1954mm.
A 700x25 tire should be about a 2105 mm rollout (~335mm radius)
A 700x23 tire should be about 2097mm.

Lets say you travel a mile on a perfect 700x25 tire (1,609,344mm = 1 mi), your wheel rotates 764.53 times.
Now if your tire is worn down 3mm (evenly), it's got a new diameter of 332mm and a rollout of 2086mm. Your computer would read 764.53 revolutions, which now would only be 1,594,831mm instead of the 1.6xx mm in a mile. Your computer would read 1 mile when you would have really traveled only 0.9909 miles! Over 100 miles, you'd loose 1 mile. Whether a tire would last 100 miles with 3mm of rubber already gone is a different story...
If your only down 1mm of rubber, you loose 4,905mm per mile, just over 3%

But the results would be the same if your measuring a 700x25 but actually using a 700x23.


I think you meant 0.3%.

1mm at 50mph, the error would be 0.150 mph
3mm at 50mph, the error would be 0.450 mph

You guys forgot about the effect from being leaned over vs straight up and down (will affect the measured speed slightly). ;)