Should my turbo trainer do this (and if not, how to solve?)

barrybridges

I've got a Tacx Sirius set up in the garage. It has adjustable resistance, but I never bother to adjust it as I just use the gears.

Whenever I put in an interval/sprint, I find that the momentum/intertia of the rear wheel travelling fast means that the actual resistance drops massively.

Or - to put it another way - when I really give it some welly, it'll take a few seconds and actually the resistance drops massively because the speed of the wheel on the turbo means I need to put less effort in to keep it spinning.

I'm assuming it shouldn't do this and that the resistance at a high gear should remain hard no matter how much power you're putting down?

The rear wheel is in good contact with the trainer - it's fine when I'm not sprinting - but there seems little point in doing intervals on the trainer if it gets easier the more power I put down...

lucan2

Have you wondered why it has adjustable resistance?

barrybridges

Lucan2 wrote:

Have you wondered why it has adjustable resistance?

Sadly, the adjustable resistance doesn't work anyway - it's been jammed for years and despite attempts to try and fix it, remains stiff.

Even so, I'm not sure this is the issue. It's not the resistance per se, it's the fact that when the rear wheel gets up to a high speed the momentum of it on the roller wheel negates whatever resistance is there. It only takes maybe 1 second for the resistance to totally drop off.

I'm really not convinced that TTs were designed so that anyone doing intervals has to manually increase the trainer resistance for every one. When you're mid-interval, it would be such a faff to do and I'm sure that's not the issue. In any event, what about people with trainers that don't have adjustable resistance?

The problem is best summarised by saying that the effort needing to keep the rear wheel going at a hard speed is much less than the effort needing to keep it going at a low speed.

kettrinboy

Could still be tyre slippage, on my turbo i need the contact patch or indent of the roller into the tyre to be pretty good to avoid slippage when simulating sprints.

danowat

barrybridges wrote:

In any event, what about people with trainers that don't have adjustable resistance?

Change gear.

My fluid turbo has no resistance, you just change gear to adjust it.

cyco2

My turbo has variable resistance and watts output. The bike on it has a fixed gear. At say a resistance of 3 it simulates a slope and pedalling slowly (85rpm) the watts output shows 200. As I increase the cadence it shows an increase in wattage until 120rpm it shows 300 watts. It will seem easier to pedal at that rate pushing out 300 watts but for an interval my HR increases and I sweat which is also an indicator of power output. Oh and heavy breathing. If you were to do this on the road then wind resistance would be a major factor and make it feel even harder.
If you were able to use a power wheel you would see the increased wattage with revs. and together with your senses would know you were training.
The feedback like resistance setting and HR etc. you get on a turbo trainer is very crude compared to watts but it can still be a very valuable training tool at that.
Ignore the feeling of ease and keep at it because it is easier to develop more power at higher cadence.

bobones

I don't think what you're describing is abnormal, and I don't think the resistance is actually changing, just your effort.

I see it like this: you need to put more power down to accelerate the wheel initially. Once the wheel is up to speed, you don't need to apply as much power to keep it at that speed because the inertia of the flywheel will help keep the wheel turning. However you will need to apply a constant amount of power to stay at that same speed, just less than you needed to get there in the first place.

It seems that the resistance is just a bit too low for you in the current stuck position. You could try using a much higher gear and clamping the roller a bit tighter against the tyre to get more resistance. If that doesn't work, try to fix the stuck resistance (might be just a new cable required) or get a new turbo.

barrybridges

Thank you for your advice. Bobones described the problem far better than I did in my original post!

I think you're right. Yesterday I tried doing the sprints in the largest gear and actually found I couldn't get the wheel up to the same speed with the same inertia, so I think the issue is actually not having enough resistance.

Or in other words: I have enough resistance for when I'm not sprinting, but before a sprint I ought to nudge it up a gear to solve the problem.