Zwift Chat

[theboxers]

I did a little experiment tonight with the Bkool and reduced the tyre pressure to see if it would reduce the watts - not sure why I didn't think of this before! I've been running my rear tyre at 120psi so reduced it to 90psi and joined tonight's race in CAT B as I'm ususally only just over 4 w/kg in Cat A anyway. And the result....4.1 w/kg average - exactly the same as usual! I'll have to try again with at 80psi!

Snip

The reported power for any given speed, weight and slope combination, from a trainer, should remain the same no matter what tyre pressure you have.

The difference will be the power needed to put out those numbers because you are trying to overcome a higher drag on the roller/tyre contact. If you have a power meter, on the bike not trainer, you should be able to measure the difference. Did it feel like you were working harder during the race?

Also you may be of a weight that the lower pressure you were running did not alter the contact patch that much.

The big question here though is how much more power is needed to overcome that increase in drag. From the site below not too much
https://www.bicyclerollingresistanc...ein&b=zipp&maxweight=401&max=23&min=7&minpr=7

 

[bridgy]

The reported power for any given speed, weight and slope combination, from a trainer, should remain the same no matter what tyre pressure you have.

The difference will be the power needed to put out those numbers because you are trying to overcome a higher drag on the roller/tyre contact. If you have a power meter, on the bike not trainer, you should be able to measure the difference. Did it feel like you were working harder during the race?

Also you may be of a weight that the lower pressure you were running did not alter the contact patch that much.

The big question here though is how much more power is needed to overcome that increase in drag. From the site below not too much
https://www.bicyclerollingresistanc...ein&b=zipp&maxweight=401&max=23&min=7&minpr=7

Yeah I get that - what you describe in your first couple of sentences is exactly why reducing the tyre pressure in theory should reduce reported watts from the Bkool. Thanks for the link - interesting! Not sure how much that rolling resistance figure applies to the trainer as opposed the road as slightly different dynamics going on? I obviously don't know the exact pressure I need to get things vaguely accurate - as you say it will depend on my weight and obviously the particular tyre I'm using. I might try reducing it to 80psi next time.

Unfortunately I don't have a PM to compare against - only one ride on a Neo a couple of months ago so it's a bit of a rough guess really! Impossible to say if it felt "harder" - I put in just as much effort as always and hard to compare one ride with the next when it's a different route, and things like group drafting are thrown into the mix

 

[theboxers]

Yes it is very confusing with all the variables. Are you still on bkool? If you are do a series of solo velodrome tests at the various pressures to see if you can notice a difference in effort required. Or setup a climb of 2 or 3% and try that at various pressures.

 

[CXRAndy]

Aside note Lee yesterday did the reverse mountain loop. His previous Bkool time for the climb was 22.00 minutes, his Neo climb yesterday 26.28(261w@166hr).

Actually disregard his bkool time because he was sprinkled with bkool fairy dust 332W @129HR

 

[bobinski]

Thanks Bob. Re: Cats - you might be misunderstanding me. I do agree that if you do the watts for a higher cat that's where you should race. When I said I don't care, I mean I don't care about my ego if I ride in cat B instead of A - I will race in whatever cat my watts suggests though!

I was Paul-apologies.

 

[berty bassett]

Aside note Lee yesterday did the reverse mountain loop. His previous Bkool time for the climb was 22.00 minutes, his Neo climb yesterday 26.28(261w@166hr).

Actually disregard his bkool time because he was sprinkled with bkool fairy dust 332W @129HR

i admit it was one of the first times i had been on Zwift i would guess that i hadn,t turned it off and on again after warming up on bkool (didn't know any better)
i can remember in some of the early rides there was hardly any resistance and you could just fly !
i promise as soon as i found out to turn off and on i did
on a side note on the timer counting up the mountain last night i was on for a pb until i turned off to go up to the tower and that is including the bkool time

soon as i hit the tower steep bit it all went pear shape and just wanted it to end

and yes Bob i was on the neo last night - you had a go yet ?

 

[<Tommy>]

The difficult thing with judging BKOOL watts is the inconsistent variables. Tyre type, tyre wear, tyre pressure,tyre slip at different moments. If you could get all these things the same, and BKOOL watts were consistent then maybe you could work out the difference to real watts. But I think the BKOOL unit performs differently from one day to the next too so... . Makes my head hurt!!

I think you’ve just got to find a race category that works for you. And maybe when the unit is performing really oddly you will recognise it.

Paul last week I got the sense you were thinking of pulling the trigger on a new trainer, The boss say no?

 

[bobinski]

i admit it was one of the first times i had been on Zwift i would guess that i hadn,t turned it off and on again after warming up on bkool (didn't know any better)
i can remember in some of the early rides there was hardly any resistance and you could just fly !
i promise as soon as i found out to turn off and on i did
on a side note on the timer counting up the mountain last night i was on for a pb until i turned off to go up to the tower and that is including the bkool time

soon as i hit the tower steep bit it all went pear shape and just wanted it to end

and yes Bob i was on the neo last night - you had a go yet ?

 

[bridgy]

I was Paul-apologies.

No worries at all

 

[bridgy]

The difficult thing with judging BKOOL watts is the inconsistent variables. Tyre type, tyre wear, tyre pressure,tyre slip at different moments. If you could get all these things the same, and BKOOL watts were consistent then maybe you could work out the difference to real watts. But I think the BKOOL unit performs differently from one day to the next too so... . Makes my head hurt!!

I think you’ve just got to find a race category that works for you. And maybe when the unit is performing really oddly you will recognise it.

Paul last week I got the sense you were thinking of pulling the trigger on a new trainer, The boss say no?

Well it won't happen this side of Christmas, that's for sure!

And I agree with what you say about trying to get accuracy with the bkool - bit of a wild goose chase, especially with so little to measure against! I still think its worth doing a little bit of tinkering though!

 

[<Tommy>]

Well it won't happen this side of Christmas, that's for sure!

And I agree with what you say about trying to get accuracy with the bkool - bit of a wild goose chase, especially with so little to measure against! I still think its worth doing a little bit of tinkering though!

I think it’s worth it too. I’m suprised lowering the tyre pressure made no tangible difference to the end result to be honest. I think I read somewhere that Chris Froome used to adjust his brake calipers to increase resistance through brake rub. Just saying....

 

[Randyberlin]

I think it’s worth it too. I’m suprised lowering the tyre pressure made no tangible difference to the end result to be honest. I think I read somewhere that Chris Froome used to adjust his brake calipers to increase resistance through brake rub. Just saying....

Whorty used to run low tire pressure and no fan just to lull everyone into complacency

 

[bridgy]

I think it’s worth it too. I’m suprised lowering the tyre pressure made no tangible difference to the end result to be honest. I think I read somewhere that Chris Froome used to adjust his brake calipers to increase resistance through brake rub. Just saying....

Whorty used to run low tire pressure and no fan just to lull everyone into complacency

Forcing my brakes to rub or turning my fan off are both most definitely a step too far

 

[Whorty]

Yeah I agree Andy - I don't care about the Cat I ride in at all, it's all about having an enjoyable race. The only thing I don't like about Cat A is I often spend most of the race in no mans land after getting dropped by the front group - occasionally I do join up with a couple of other stragglers which is good, but not always. Probably the same problem for anyone who's borderline between two categories of course

I'll have this if/when I go up to B from C. Currently I have a good race in C and usually with a group, but if/when I go to B I'll be dropped by everyone early and be on my own the rest of the way round. I think the key is choosing races where there are lots of riders in each cat and hope that I can link up with some top C riders once I lose B. I'll give it a go and see what happens.

 

[Whorty]

Forcing my brakes to rub or turning my fan off are both most definitely a step too far

To be fair, i didn't force the brakes to rub ... I was just too dumb to realise what was happening LOL