Calga, The Wind and Wheel Depth

[march83]

Interested to hear perspectives from other forum TTers regarding forecast weather conditions up at Calga and wheel selection, primarily the wind.

I can choose between shallow alloy, 50mm carbon and 90mm carbon, I'm sure others find themselves in a similar position (possibly with the addition of a rear disc). At what point do you consider going down in wheel depth based on the forecast wind? Which weather station do you base your selection on? does the wind direction matter a great deal in the calculation.

FWIW, The gosford forecast says northwesterly 15 to 20 km/h winds for this sunday morning. I'm 82kg and i'll probably ride my 90s.

[Derny Driver]

It would need to be quite strong winds to not use a 90. I was just in the USA and at the TTs there the Pro teams were all using a rear disc and something between 75 and 90 on the front in quite blustery cross winds. At 82kg you should have no problem with the deep front.
Myself personally in strong winds I would recommend an 808 or 1080 rear and a 60mm front but as I said the big boys just go the full setup in any conditions and they were setting some unbelievable times. With the weather at the moment you'll be good on the disc and the 90.

[Alex Simmons/RST]

Always use a rear disc if available. Unless you are light and slow or can't handle the bike properly (and that happens with some people's TT set ups as so often they are riding bikes of the wrong size or poorly set up). Front wheel is the one you most need to think about adjusting for conditions.

The faster you are the lower the average yaw angle, that's mostly why the more powerful faster riders can use deeper wheels on windier days.

In the end the only way to know is to experiment in a safe environment. I used Calga as a testing ground for set ups to be considered for more important races. We had filthy wind conditions one day, worst I've ridden in and it was definitely a challenge but I held position and the rear disc was still the right choice. The challenge was more from the larger branches being blown onto the road. Most people were sitting up using bull horns, and quite a lot were walking that day unable to stay on their bike. Never passed so many riders in a TT before!

[DaveQB]

Further to what Alex is saying and what the Flo guys explained in a podcast interview on Trainer Road's podcast, a deeper rear wheel actually helps handling in that it helps move the pivot point of the bike, in a cross wind, further to the back of the back, away from the steering. So with that, a rear disc and a 30mm front wheel should handle the best, although this is only steering and having a disc/30 setup would see you more likely blown off course than a 30/30 but just not getting that scary, sudden handlebar twist you are more likely to get with a same size front and back setup (or bigger front than back, who does that!)

I hope that makes sense.