breanach8

On a pervious aluminium bike I regularly hit 70kph and was comfortable but carful in doing so.
On my last two carbon bikes and more so my my 2013 trek madone any thing over 50 has me felling very nervous indeed. The highest I hit was 62kph and I felt it felt unstable. I would nearly go as far to say it got a speed wobble. I certainly would not have liked to be going any faster. Now any descents I hold back a lot and find myself doing catch up to the others.

Any ideas?

Shimagnolo

Plug in your numbers and see how much trail each bike has.
It sounds like the Al bike has more than the CF bike.

https://yojimg.net/bike/web_tools/trailcalc.php

Burton

Nothing to do with the material. Check the wheelsets for spoke tension and bearing play and the headset for tightness. That Madone should be stable at speeds over 100kmh

breanach8

From what I can make out mech. Trail is 56mm on my new bike. I unfortunately do not have the data on the previous bike.

breanach8

Wheels were just checked over two weeks ago and all ok there. I will check over the HS but I have not noticed any issues there.

fietsbob

I just hold my speed down to be within My comfort range. since I'm Just an Old tourist.. its not that High..


I suspect the gear supplied to the Pro's is perfect or it's discarded.. sent back ..

Phil_gretz

Your issue is not related to carbon, but to harmonic structural behavior within your bike/rider combination at speed. The selling LBS should help you diagnose this - possibly by having a rep go with you to the descents and test ride the bike.

If it's not an adjustment issue, then Trek would be very interested in knowing more, too. Again, I've not come across this with the Madone, but with steel tourers with imbalanced loads that produce speed-related shimmying. Even that can be corrected by re-distributing and re-balancing the load side-to-side and front to back.

Take it to your shop and tell them about it...

furballi

The other carbon bikes may have resonant frequencies that are closer to 50. If possible, swap out the wheels and saddle from the Al bike to the carbon bike and retest. If the carbon bike is still unstable at speed, then you need check for a lose headset.

Mr. Beanz

How long have you been riding the Madone?

I have hit 46 on my Cannondale 98 R-900 (alum) and 45 on my carbon/alum mix Lemond Chambery with no problems.

At 30 mph I could descend comfortably with one hand on either bike.

I then got a 2012 Madone 4.7 and wow what a difference. It felt very unstable at 35 mph. I don't know if it was the lightweight of the bike or the fact that it has a huge diameter headtube and bearing setup that made the difference in steering and handling.

Once I got used to the bike, I can now do 30 mph with one hand and 42 with confidence. Maybe you just need some time on the bike to get used to the handling.

I will say it acts very different from the other two with 1 1/8 heasets with the 1 1/2 set up.

Carving these mtn descents at 25 (max 43 mph) was like nothing on the other two bikes. When I switched to the Madone, WHOAH BABY! Took me about a month to get used to it. A year later, it's like nothing.

rm -rf

It's probably just that you aren't used to the new bike's handling. When I changed to narrower bars, my bike seemed very twitchy. It's great now.

Like Mr Beanz said, ride it for a few weeks and see if you get used to it. Do a lot of easy downhills at a comfortable speed, on familiar roads. Gradually increase the speeds on later rides.

Are you riding in the drops, instead of on the hoods? I'm a lot more stable and confident in the drops on fast downhills.

~~~~~

Speed wobble is a very strong oscillation. Here's an example on youtube. Watch the rider ahead at the 30 second mark. Scary.

Often, speed wobble is made worse by using a death grip on the handlebars. Of course, if you are nervous already, that's a typical thing to do. When I would do downhills with gusty winds, that's how I rode. And it's the only time I got a speed wobble, when a sudden strong gust hit from the side.

To help stop a speed wobble, grip the top tube between your legs, and don't brace your arms. This changes the bike+rider oscillation frequency.

There is some evidence that a front wheel that is off center can contribute to speed wobble, from either a badly built wheel, or a fork that isn't even on both sides. But with a new Madone, that's not very likely. And you had similar symptoms on a previous bike. But you could easily check the front wheel for bad dish, by flipping it in the dropouts and seeing if the brakes are still centered.

fietsbob

I note watching; The pros hang on to the top center of the bars when they get into their..

let's see how much time i can cut off the GC going down this mountain .. mode..

breanach8

Tkanks very much for all the info guys. I am using the loose arms and knees on the bars technique but its going to take time to build up the confidence on the one. I am not heading out to dash down the fastest hill around to see how it is at 72kph! I ride with guys and having discussed this issue some have told me on the same descent they have hit 80kph, 50mph! I also was told that adding small weights to the drop ends could change the frequency helping the issue I bit too. Not to fond of doing that after spending money on a light weight bike! I have only about 500k done on it so far so I guess I need to quadruple that figure to really get a feel for the bike. The road surfaces hear in the West of Ireland don't help either, they're bad really bad. Always pothole watching and they soak up energy. On one stretch of road the surface changes for slightly rough to a newly resurfaced one on a up accent and when you reach that piont its so much easier to climb. But that's a different story

Burton

If the roads at all rough - suggest you skip the speed. With no suspension you'll be only marginally in contact with the ground which will compromise any emergency braking you might have to do. Its a nice bike - just have fun with it - there's a time and place for everything.

rm -rf

(You seem to be doing everything right. My comments above were more for a fairly new rider.)

Wow, those must be steep downhills. My fastest downhill maximum is about 44 mph / 70 kph, but it was a safe, smooth road with broad curves and no side roads, dogs, or deer. I wouldn't try 50 mph on a rough road.

fietsbob

I'd slow down . I'd hate to rear end a Manure Spreader being towed down the road, as they are, often..

shipwreck

I must ride to much. When the bike started to wobble I clenched my hands like they were on brakes, and twisted my foot like I was unclipping for an emergency stop!