Mavic tyres/wheels on descents.

wavefront

Wanted to grab people's thoughts. Alot has been said on these forums about tyres making a big difference, in terms of rolling resistance, climbing, on cornering, in different weather conditions etc. But couldnt find much about descending at speed?

I was in a fortunate position to upgrade my Cannondale Synapse's wheels from the stock maddux rims to a set of new Mavic Krysium Elites. I'm now using the standard mavic tyres that they came with over my usual gp4000s' and whilst everything seems good, I'm noticing the bike doesn't feel as 'planted' on fast descents (45kmh +) and I'm lacking the confidence to now hit my ususl speeds on familiar descents. The front just seems a little twitchy?

What do people think of the mavic tyres on Krysiums at speed? Is it a characteristic of the tyre or the wheels do you think?

Ta.

Grill

I ride Elites with GP4000S tyres and have no issue at speed. I was doing 44mph down the Rhigos in the rain yesterday with no issue. If you don't keep your weight over the bars whilst descending pretty much everything will feel twitchy.

danlikesbikes

Grill wrote:

I ride Elites with GP4000S tyres and have no issue at speed. I was doing 44mph down the Rhigos in the rain yesterday with no issue. If you don't keep your weight over the bars whilst descending pretty much everything will feel twitchy.

^-^ Same set up for me & find they feel pretty well planted though not quite going as fast as Grill or on the same roads

Anonymous

Is it the yksion pro griplink that you have?

I have the newer version (with tread/grooves) and used the older slick ones before that (on R-SYS wheels). They are the only tyres I have had on road bike so nothing to compare with but not had any problems.
I am slightly less brave going downhill these days but have been over 40 mph.

Have just ordered some latex tubes to try in them.

smidsy

I would say it is a tyre pressure issue.

IanREmery

Grill wrote:

I ride Elites with GP4000S tyres and have no issue at speed. I was doing 44mph down the Rhigos in the rain yesterday with no issue. If you don't keep your weight over the bars whilst descending pretty much everything will feel twitchy.

Slight thread hijack, but I get the speed shimmy/wobble usually above 35mph on my Cube Agree GTC. Someone said recently it's because I've got the weight over the front wheel and need to be further back in the saddle.

Is there any concensus over the causes of speed wobbles? (Incidentally, I was very perturbed to find it's also referred to as "Death wobbles"....!)

bjl

What is the best qay to keep your weight over the bars?

sungod

IanREmery wrote:

Slight thread hijack, but I get the speed shimmy/wobble usually above 35mph on my Cube Agree GTC. Someone said recently it's because I've got the weight over the front wheel and need to be further back in the saddle.

Is there any concensus over the causes of speed wobbles? (Incidentally, I was very perturbed to find it's also referred to as "Death wobbles"....!)

certainly move back on the saddle when descending, if you need to brake hard you'll be able to stop sooner and with more control

holding the bars too tight can be a problem, speed wobble, aka shimmy, can be scary, which can tense you up, which can make it worse - your reflexes aren't fast enough, you try and correct it via the handlebars but the lag means you actually amplify it

the system of you+bike has a resonant frequency, if energy is pumped in at/near that frequency then oscillation can start and build up fast

damping the system (knee on top tube), changing the resonant frequency (take weight off saddle), reducing input energy (relax grip), and changing the input frequency (pedal hard to speed up, or gently apply rear* brake) are all options

concentrate on keeping a relaxed grip on descents, keep one or both knees firmly against the top tube, once you've done a few descents without problems you'll get confidence and be less likely to have problems in future

the wind can trigger wobble, or shivering if you get chilled, but you can control it the same way

certainly check the bike, things like a loose headset or wheel bearing might contribute as well, but from what people post it seems riding style is the most common factor

*avoid front braking once a wobble starts

IanREmery

sungod wrote:

IanREmery wrote:

Slight thread hijack, but I get the speed shimmy/wobble usually above 35mph on my Cube Agree GTC. Someone said recently it's because I've got the weight over the front wheel and need to be further back in the saddle.

Is there any concensus over the causes of speed wobbles? (Incidentally, I was very perturbed to find it's also referred to as "Death wobbles"....!)

certainly move back on the saddle when descending, if you need to brake hard you'll be able to stop sooner and with more control

holding the bars too tight can be a problem, speed wobble, aka shimmy, can be scary, which can tense you up, which can make it worse - your reflexes aren't fast enough, you try and correct it via the handlebars but the lag means you actually amplify it

the system of you+bike has a resonant frequency, if energy is pumped in at/near that frequency then oscillation can start and build up fast

damping the system (knee on top tube), changing the resonant frequency (take weight off saddle), reducing input energy (relax grip), and changing the input frequency (pedal hard to speed up, or gently apply rear* brake) are all options

concentrate on keeping a relaxed grip on descents, keep one or both knees firmly against the top tube, once you've done a few descents without problems you'll get confidence and be less likely to have problems in future

the wind can trigger wobble, or shivering if you get chilled, but you can control it the same way

certainly check the bike, things like a loose headset or wheel bearing might contribute as well, but from what people post it seems riding style is the most common factor

*avoid front braking once a wobble starts

Awesome, cheers mate! I remembered reading someone about avoiding the front brake during a wobble. I've only been on the roadbike a couple of weeks so it's all part of the learning process. Bloody scary experience though!

wavefront

Thanks Grill and Dan - good to hear and I'll bear this in mind on my next run. Carbonator, thanks, and yes, the mavic tyres have grooves cut along the sides so aren't slicks.

Will have to try my gp4000's back on the Elites when I get back to the uk as they're what I'm used to!

Smidsy, tyre pressure ? To high, or low? Definitely running 95-100psi on the last run (both the same) but saw the other thread talking about different pressures front and back - I'm 69kg so thought it should be fine?

Again, thanks all for the comments. Luckily it's not speed wobbles, just this felt a little more nervy. Almost as I'd expect in heavy crosswinds!

smidsy

As you never experienced the issue on your previous tyres/wheels it is unlikely to be your riding, hence I took a punt on tyre pressure.

Different tyres often respond better at different pressures, and at your weight you can experiment quite a lot.

There are tyre pressure guides which you can use as a starting point but again you used to descend fine on whatever you ran before, so only a minor adjustment should be necessary.

What width tyres? e.g. 23mm require a higher pressure than 25mm.