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Bike carrier for TT bike with aero wheels
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johnny senna




Joined: 16 Sep 2010
Posts: 453

PostPosted: Sat Apr 30, 2011 12:43 pm    Post subject: Bike carrier for TT bike with aero wheels Reply with quote

Hi Everyone,
I'm currently using a roof mounted Thule carrier system that has been OK for road bikes, but I don't think it is suitable for TT bikes. This is because the aero down tubes don't suit the Thule's clamp system. Also, the aero wheels will obviously catch the wind far too much when the bike is up on the air on the roof.

I am thinking a tow bar mounted carrier would be better. I am looking at this Thule product, the 921 Euroway G2:
http://www.roofracks.co.uk/thule/cycles_towball/921.php

I have 2 questions please:

1) Will the TT bike clamp OK on the Thule 921, perhaps using the seat tube or top tube rather than the down tube?

2) Because the bike will be on the back of the car and quite low down and hopefully out of the wind, will it be OK to carry the TT bike with its aero wheels left on?

Thanks in advance.
John
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JamesBoH




Joined: 02 Jan 2007
Posts: 3474

PostPosted: Sat Apr 30, 2011 3:36 pm    Post subject: Reply with quote

With deep wheels I prefer to have the bike facing forwards - i.e on the roof. Get the fork clamping one.
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GrahamO




Joined: 10 Apr 2005
Posts: 9894
Location: United Arab Emirates or an airport

PostPosted: Sat Apr 30, 2011 3:55 pm    Post subject: Reply with quote

"the aero wheels will obviously catch the wind far too much when the bike is up on the air on the roof"

Not really aero then are they ?

How else except facing forward would the bike go when on the roof ?
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Scoobers




Joined: 04 Aug 2008
Posts: 1625

PostPosted: Sat Apr 30, 2011 4:01 pm    Post subject: Reply with quote

Much rather have my TT bike forward facing than the wind catching the wheels side on.
I've been using the Thule roof mounted system for a couple of years for journeys at motorway speeds.
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GrahamO




Joined: 10 Apr 2005
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Location: United Arab Emirates or an airport

PostPosted: Sat Apr 30, 2011 5:53 pm    Post subject: Reply with quote

For what its worth, there is a Thule Outride 561 bike carrier for the existing Thule roofrack, suitable for TT bikes in the Classifieds section - going cheap

Very Happy Wink
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modoufall




Joined: 31 Mar 2011
Posts: 434
Location: near Stuttgart

PostPosted: Sat Apr 30, 2011 6:17 pm    Post subject: Reply with quote

I wouldn't put my carbon frame in any clamp - my bike rides on the back seat! Failing that, I could imagine using that outrider thingy.
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haych_seedy




Joined: 14 Feb 2010
Posts: 2515
Location: Reading

PostPosted: Sat Apr 30, 2011 6:47 pm    Post subject: Reply with quote

modoufall wrote:
I wouldn't put my carbon frame in any clamp - my bike rides on the back seat!


+1, no way mines going in a clamp.
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johnny senna




Joined: 16 Sep 2010
Posts: 453

PostPosted: Sat Apr 30, 2011 8:09 pm    Post subject: Reply with quote

Thanks guys.
I have 2 further thoughts.

1) I appreciate that having the aero wheels pointing forward makes sense - they are designed to go this way afterall. But what about strong cross winds? Surely that would catch the aero wheels? Do any of you carry a TT bike on the roof with the aero wheels (or even a disc) on?

2) Some of you have said that you wouldn't clamp a carbon bike. But why? I've been clamping our Trek Madones for 2 years now, no bother. The only reason I had reservations about clamping the TT bike was that the aero fram made this less secure than the rounder tubes of the Trek Madone.

Very grateful for your thoughts.

Edited to add a 3rd thought - the fork clamping one looks OK, but the rear aero wheel would still catch the wind wouldn't it?
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GrahamO




Joined: 10 Apr 2005
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Location: United Arab Emirates or an airport

PostPosted: Sat Apr 30, 2011 8:20 pm    Post subject: Reply with quote

People are concerned about clamps going on 'hollow' sections perhaps understandably - crushing is theoretically possible, but unlikely.

A wheel clamp exerts the same pressure as a skewer obviously, so any worries there are unfounded.

No idea about the disc wheel - never tried that.

FWIW I have had bikes on the roof and on the rear Saris bones - if you leave the seatpost belt OFF and put a bike cable through the frame and around the rack, I found the bike lifted up like a wing at high speeds, moving almost horizontal as that was the minimal resistance position. An aero wheel would just lower the speed at which the bike lifted like a wing.

On a rear bike rack, at 70mph, the bike would be near horizontal and offering very little resistance.
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big vern




Joined: 30 Jun 2008
Posts: 342

PostPosted: Sat Apr 30, 2011 9:19 pm    Post subject: Reply with quote

Been clamping my PX carbon and 50mm (semi?) aero carbones on thule roof rack, including a trip through france without issue. I figure if the bikes are designed to safely take me, 90kgs, down a hill at 40mph+ and through bends with all the forces that it entails then as long as you are reasonably careful then roof mounting shouldn't be an issue with a roundish tube, with a TT bike - I guess it depends on the exact shape of the tube and how it would marry up to the clamp
The angle of the wind attack decreases as you drive faster (think of a wind sock on the back of your car and how it would trail directly behind the car as you speed up)
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johnny senna




Joined: 16 Sep 2010
Posts: 453

PostPosted: Mon May 02, 2011 7:27 am    Post subject: Reply with quote

Thanks guys, much appreciated. I keep thinking about this though.
I know bikes are designed for high speed, but not really 90mph. The thing that bothers me is the bike would be held rigid in a clamp and then buffeted by 90 mph winds plus any cross winds. And the force against the bikes is not doubled when wind speed doubles........the cube root relationship between wind speed and wind resistnace (i.e. the force exerted on the bike) means that forces exerted on the bike are much higher than that.
Or am I worrying about nothing?

I chatted to a nice bloke at a TT yesterday who was carrying a TT bike with disc wheel on a toe bar mounted carrier and he wasn't worried by the whole thing.
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GrahamO




Joined: 10 Apr 2005
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Location: United Arab Emirates or an airport

PostPosted: Mon May 02, 2011 8:06 am    Post subject: Reply with quote

johnny senna wrote:
Or am I worrying about nothing


Yes.
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undies




Joined: 14 Aug 2004
Posts: 172
Location: Eastbourne

PostPosted: Tue May 03, 2011 7:52 am    Post subject: 90mph! Reply with quote

Last time I checked 90mph was 20mph above the speed limit! Wink
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gamecat




Joined: 24 Jun 2010
Posts: 86

PostPosted: Tue May 03, 2011 10:17 am    Post subject: Reply with quote

I drove with my bike on the roof this weekend for the first time... has 80mm rims front and back.

Seemed ok despite the high winds but i did keep to the speed limits.

Dont know how i would feel about a long journey with it on the roof though.
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Cowdude02




Joined: 01 Oct 2008
Posts: 477
Location: Rustington, West Sussex

PostPosted: Tue May 03, 2011 12:26 pm    Post subject: Reply with quote

My Cervelo P2C has done many trips on top of the car with a Thule system, 80mm deep wheels front and back with no issues. The furthest trip has been a 700 mile round trip. So long as the straps are done up tightly on the wheels, and the clamp is not over-tightened, it's absolutely fine. Wink
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