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2016-08-28 4:18 PM

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Subject: The Right Bike

I have three bikes which each tend to stay at three different locations.  So, riding two of them on the same route for a head to head comparison does not happen that often.   Recently, they have been shuffled around as I was upgrading one of them with lots of new components.  This story is about the other two bikes.  The ride is on very rural roads near Norris Lake in Tennessee.  I had my Trek Madone 6.9 SSL here last week.  It is a lightweight carbon bike with compact crank(50-34) and and the biggest cassette available for its group, 11-28.  Lowest combination of 34/28.  This week I had a Litespeed Tuscany.  It is a titanium bike with triple crank and a low gear of 30/28.  I thought I would be writing about ride and gearing when I conceived the comparison, but the story is really about brakes.  The Madone has 23 mm tires, the Tuscany 25, both sets are Continental GP 4000 IIs.  The weightw loaded with a water bottle and tool kit are probably 18 for the Madone and  21 for the Tuscany.

The ride is very hilly with lots of 16-20% grades.  The road surface is rough in several sections of chipseal pavement rather than asphalt concrete (blacktop) and some is just broken up from winter weather and heavy trucks.  So I figured the difference in absorbing vibration would be important.  I could certainly tell a difference between the two and I sort of like the titanium for this but carbon has a taut, racy feel that is nice but might be fatiguing on a really long ride on chipseal.  The larger tires probably make more difference than the frame material.

The gearing is noticeable.  There are some short really steep sections on the road along the lake.  The GPS watch shows 25-28%.  I think that is high but there are sections that are legitimately 16% average over a couple of hundred yards.  Folks that is steep.   I got around on the lighter bike and higher gearing ok.  The day I rode the Madone was hotter and I came back more tired but probably could survive this ride with the compact.  i have a slight preference for lower gears but it is not as much as I expected.

The real difference is braking.  The Madone has a older version of Bontrager carbon wheels that are super light but have a slick surface.  The Tuscany has Zipp 101 aluminum wheels.  I should point out that there is 1420 feet of climbing on this ride.  There is equally 1420 of descending.  Some of these are 16-20% too.  This Madone wheels with cork brake pads were a lot scarier than the conventional pads not the Tuscany.

It is not even close.  The Tuscany stays at the lake.  The Madone lives in Oak Ridge.  The Siena is in Atlanta. All is right with the world.

TW



Edited by tech_geezer 2016-08-28 4:47 PM


2016-08-28 10:17 PM
in reply to: tech_geezer

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Subject: RE: The Right Bike
Just curious. Do your Carbon fiber wheels heat up much on your descents?
2016-08-28 10:37 PM
in reply to: NeilsWheel

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Subject: RE: The Right Bike

Originally posted by NeilsWheel Just curious. Do your Carbon fiber wheels heat up much on your descents?

These hills are fairly short so I don't think the heat buildup is a problem on this route, but heat is a problem for carbon clinchers on longer descents.  My specific problem is that the braking power is not as good as with aluminum.  I had a harder time controlling the speed on the descent.  The hills tend to end with a sharp turn at the base, sometimes with a puddle of sand.  It takes a lot more grip on the brake levers to keep the speed down with the Bontrager RXL wheels.  The problem is that I felt like it was not as safe to control the speed.  Failure of the rim under heat and tire pressure is also a problem for carbon clincher rims under more severe braking conditions.

 

TW 

2016-08-29 7:38 AM
in reply to: tech_geezer

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Subject: RE: The Right Bike
I was just wondering about that. I had a flat on my carbon front wheel on a descent. When I went to change it, the rim was so hot I could barely touch it.
2016-08-29 8:41 AM
in reply to: NeilsWheel

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Subject: RE: The Right Bike

That is a real problem with carbon wheels.  The resin gets weaker at elevated temperature.  The tire pressure goes up.  Ergo, bad things can happen.  The top carbon wheel manufacturers are coming up with higher temperature resins and more thermally conductive rims to reduce the problem but for heat dissipation aluminum is better.

The other alternative is not to use the brakes.  See my post about Richard Branson from a few days ago.

TW

2016-08-30 7:12 AM
in reply to: tech_geezer

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Subject: RE: The Right Bike
Modern carbon rims and brake pads don't really have much of a problem at all with heat... I'm riding ENVE 6.7's with SwissStop Black Prince pads and never had a problem (and yes, I do have some serious descends around me, SWPA is hilly and so is NH, where we also ride a lot).


2016-08-30 8:44 AM
in reply to: audiojan

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Subject: RE: The Right Bike

Yes.  I mentioned that wheel manufacturers have worked on the problems and newer rims are much better for braking, heat dissipation, and strength at elevated temperature.   But the choice of the right bike was not between a new set of carbon wheels and aluminum.  It was between two bikes that I already own with their current wheels.  By the way, I said the wrong model name for the Madone's wheels.  They are Bontrager Race XXX  Lite.   These wheels went out of production the year I bought them, 2012.  Since then, some carbon wheels are a great deal better, certainly not all. 

I am glad your carbon wheels are good for steep descents.  Mine are not.  As riders, we need to be aware of the potential problems with carbon wheels on long, steep descents.  That was my conclusion.

Originally posted by audiojan Modern carbon rims and brake pads don't really have much of a problem at all with heat... I'm riding ENVE 6.7's with SwissStop Black Prince pads and never had a problem (and yes, I do have some serious descends around me, SWPA is hilly and so is NH, where we also ride a lot).

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