Descending on deep rimmed wheels

Adie1971

Just got myself a pair of Planet X 50mm wheels, and I love them to bits, def make me go faster on the flats. However at the weekend I did my first serious descent freewheeling at over 60kph and I was terrified. Had no problem doing this on my Mavic Ksyriums, but with the deeper rimms the front wheel wobbled like mad from side to side, just couldn't hold the bars steady. I feathered the back break a little but if anything that made it worse, so just gripped the drops and hoped. Is this normal?! Also when I was pedalling at near to this speed on lesser descents it felt fine. Any tips on how to handle it would be much appreciated, even if it's just to say I just need to HTFU!

dnwhite88

No wobble at speed is not normal, were you gripping the bars too tight? Try and keep your upper body really loose and keep your elbows bent so they will absorb any vibrations from the road (a lot easier said than done when you get a speed wobble!)

Grill

I've descended at 80kph on 80mm deep sections in the rain with crosswinds on the aero bars of my TT bike. Wouldn't recommend it. I rarely have any issue on my 46mm set although the occasional gust will catch. I keep my weight pretty far over the front when I descend and that seems to help.

Finlaz22

However, be careful not to follow Grill's advice whilst cornering and braking! Not that you should be doing that anyway...

mallorcajeff

Shouldnt make ay difference? Unless its windy? Here in mallorca i go down all the mountains on elites, dura ace c50 and 82mm tubs. Only when its windy funny enough the 50s get a bit grabby but nothing scary.

Alexvs

I've had a couple of wobble events while descending on standard wheels on my old bike and both the guys riding with me on both occasions thought I'd had it and was going down but somehow managed to hold it together and stayed upright. The weird thing is I have no idea what caused it as wasn't all out speed as was just sub 30mph whereas I've been going at 40mph with no wobble. I thought it may be due to a dodgy rear wheel at the time as that started the wobble off first each time. Touch wood I've not had it happen since those 2 and now got a new bike so will be hoping it also doesn't happen on this.

sungod

on descending in general this is good http://www.flammerouge.je/content/3_fac ... escend.htm there's a lot of info in there, not something to absorb all at once, it takes practice

on wobble, the system (you+bike) has a natural frequency, if energy is pumped in at/near that frequency the system will oscillate, that energy comes from you, the wind and the road surface

assuming there's no fault/deficiency with the bike...

stay relaxed, with a light grip on the bars, if you tense up then you can get a situation where the lag between feeling the bars deviate (due to road surface or wind) and your muscles responding to correct it will be out of phase enough to reinforce the deviation, this builds rapidly to full blown wobble as you try harder and harder to correct it

on long gradual fast turns the changing wind angle can cause surprises, the effect seems bigger with deep rims

other ways to help avoid/control wobble...
press one/both knees firmly against the top tube
unload weight from saddle
pedal hard, i.e. power out of it top gear style
if all else fails gently apply rear brake, not the front!

nferrar

Does sound odd if you didn't get it at similar speed on the flat. Were you in an extreme tuck on the descent? When I tuck there's a lot more weight than normal over the front wheel so possibly that might show up something that doesn't happen normally (I've not had it cause a speed wobble though although I don't use aero wheels).

Adie1971

OK guys, thank you for the wealth of replies, especially sungod, lots of reading and learning for me there! Anyone else want to add please do, but genuinely appreciate all the quick responses and advice, I will be out again next Sunday on the same hill, fingers crossed!

Burnsey#23

I have had the same thing happen to me on a decent in north Wales and share your pain. Frightening!! I race a 1000cc superbike most weekends and have had many a tank slapper and some big crashes but have to say that was the most scared I have ever been on two wheels!!
I had a set of 50mm superleggarra wheels on at the time and on reaching approx 50 mph got a horrendous speed wobble, bike was shaking its head off and I was eying up the grass verge on the right hand side at it worst point rather than going down on the Tarmac. I was convinced I had a puncture but on stepping off the bike after pulling in on the side of the road and checking the bike over everything seemed ok with it!!
After researching it online I found few people have had this 'speed wobble'.
General rule of thumb seems to be -
Loosen your grip on the bars (not the natural thing to do)
Raise your bum off the seat
Grip the top tube with your knees

Having said all that I now only ever use my Giant pls1 wheels for any serious climbing/descending and keep the Aero wheels for the rolling roads of the Wirral/TT's and Triathlons.

oldwelshman

Grill wrote:

I've descended at 80kph on 80mm deep sections in the rain with crosswinds on the aero bars of my TT bike. Wouldn't recommend it. I rarely have any issue on my 46mm set although the occasional gust will catch. I keep my weight pretty far over the front when I descend and that seems to help.

Really? lol where was this?
Over the front on a TT bike? You must be an Ajax rider lol

oldwelshman

Adie1971 wrote:

Just got myself a pair of Planet X 50mm wheels, and I love them to bits, def make me go faster on the flats. However at the weekend I did my first serious descent freewheeling at over 60kph and I was terrified. Had no problem doing this on my Mavic Ksyriums, but with the deeper rimms the front wheel wobbled like mad from side to side, just couldn't hold the bars steady. I feathered the back break a little but if anything that made it worse, so just gripped the drops and hoped. Is this normal?! Also when I was pedalling at near to this speed on lesser descents it felt fine. Any tips on how to handle it would be much appreciated, even if it's just to say I just need to HTFU!

I sometimes get a wobble on mine but generally caused by a cross wind or headwind.
I did double check my head set which if loose can cause this.
You can help it by not gripping too hard on bars as others said but also grip top tubes with knees/thighs will also help a lot.

oldwelshman

Burnsey#23 wrote:

I have had the same thing happen to me on a decent in north Wales and share your pain. Frightening!! I race a 1000cc superbike most weekends and have had many a tank slapper and some big crashes but have to say that was the most scared I have ever been on two wheels!!
I had a set of 50mm superleggarra wheels on at the time and on reaching approx 50 mph got a horrendous speed wobble, bike was shaking its head off and I was eying up the grass verge on the right hand side at it worst point rather than going down on the Tarmac. I was convinced I had a puncture but on stepping off the bike after pulling in on the side of the road and checking the bike over everything seemed ok with it!!
After researching it online I found few people have had this 'speed wobble'.
General rule of thumb seems to be -
Loosen your grip on the bars (not the natural thing to do)
Raise your bum off the seat
Grip the top tube with your knees

Having said all that I now only ever use my Giant pls1 wheels for any serious climbing/descending and keep the Aero wheels for the rolling roads of the Wirral/TT's and Triathlons.

Ha I replied before I read this lol

Grill

oldwelshman wrote:

Grill wrote:

I've descended at 80kph on 80mm deep sections in the rain with crosswinds on the aero bars of my TT bike. Wouldn't recommend it. I rarely have any issue on my 46mm set although the occasional gust will catch. I keep my weight pretty far over the front when I descend and that seems to help.

Really? lol where was this?
Over the front on a TT bike? You must be an Ajax rider lol

Well of course I ride for the Ajax

It was down the A4042 towards Pontypool. If course this was after I'd climbed to Brecon and done the Pen y Fan descent.

sloppyschleckonds

Watch out for gaps in hedgerows and field entrances