A question of gearing ( No Triple v Compact debate !)

[jimboalee]

I cross referenced power demand, speed and gradient years ago using a Test Automation motorcycle chassis dynamometer.

It was £120,000 worth of VCA ( Vehicle Certification Agency ) approved 'rolling road' to measure emissions on motorbikes.

I praise PowerCalc to be quite accurate.

Those who don't have the luxury of such a piece of equipment are fortunate today to have PowerCalc on the CTC website. PowerCalc was not available in 1998 and MachineHead was developing his programms. He too, is commendably accurate.

When you have a spreadsheet of your gears, speed and the cadence required to achieve those speeds in each gear, you can use it as a look-up table while playing with PowerCalc.

If there is a gradient on your route which is 'tough', you can change the gears numbers on your look-up spreadsheet to find a more suitable ratio for the climb.

 

[I am Spartacus]

I think you may be a bit of a lone voice in your praise of a 'table' or web calculator being accurate when you read training threads on other forums, but you probably know best.
I'll stick to gut feeling up to the point I can treat myself to a SRAM powercrank - like never...

 

[MacB]

I think you may be a bit of a lone voice in your praise of a 'table' or web calculator being accurate when you read training threads on other forums, but you probably know best.
I'll stick to gut feeling up to the point I can treat myself to a SRAM powercrank - like never...

I find the tables, purely for GI comparison, useful, but only after I'd been riding for a while. I find it pretty easy to remember what gears I've used, when and where, I don't change gears more than absolutely necessary. It sounds really stupid to me now but I still remember my disappointment when I realised that I didn't really have 27 seperate and sequential gears

For the novice this stuff can be pointless, fitness was my big issue. I couldn't get up a hill, I can now do comfortably in a 66 inch gear, with the bottom end of a MTB triple when I started.

 

[jimboalee]

I think you may be a bit of a lone voice in your praise of a 'table' or web calculator being accurate when you read training threads on other forums, but you probably know best.
I'll stick to gut feeling up to the point I can treat myself to a SRAM powercrank - like never...

Question...

How accurate is a SRAM Powercrank?

Within the realms of 'mass produced consumer electronics'?

The machine I was using was calibrated to NAMAS. VCA, ECE and the Environmental Protection Agency in Detroit are very fussy about the equipment vehicle tuners use to issue emissions results.

A lot of tests were done (which incidentally was at the same time the Motor Industry Research Association were investigating electric bikes and recumbents) to correlate road coastdowns to the chassis dyno'.

When I found PowerCalc, it closely agreed with the work at MIRA.

If on other chatboard forums there is a wild variation in results from 'mass produced consumer electronics' PowerCranks and PowerHubs, it does not surprise me in the least.

I doubt very much whether any 'mass produced consumer electronics' could be trusted.

 

[MacB]

Ah, but Jimbo, you must remember that, much as we love what you post, we don't understand a f*cking word of it

 

[MrRidley]

Butting in on the OP'S thread, i have a similiar query, my current road bike has 30,42,52 on the front and 12-25 on the back, would i be able to change this to a 12-28t without any problems ? and would it help me get up the hills that i'm struggling on, any better ? bit of a repeat question i know, but being new to the road bike, i'm after all the help i can get.

 

[MacB]

Butting in on the OP'S thread, i have a similiar query, my current road bike has 30,42,52 on the front and 12-25 on the back, would i be able to change this to a 12-28t without any problems ? and would it help me get up the hills that i'm struggling on, any better ? bit of a repeat question i know, but being new to the road bike, i'm after all the help i can get.

your current lowest gear would be about 32 inches, with an overall range of 32-114, specifics do change based on tyre size and crank length, but the ratios remain the same. A 28t at the bottom would give you a low gear of 28 inches, a noticeable jump. Standard Shimano road deraillers are meant to work up to 27t but most comments I read indicate they will go at least 2t bigger than that. Whether this gets you up hills better is a trade off, it's easier to pedal especially on a long hill. On the short sharp ones I find I prefer getting out of the saddle in a bigger gear.

I run the same rings as you with a 12-26 cassette, the only time I've ever lacked gears is at the bottom end.

 

[lazyfatgit]

Depends on the capacity of your rear mech Jim. theres only so many links it can take up between being fully streched forward and the spring being all the way back.

 

[jimboalee]

For those who have ventured onto PowerCalc.xls, you'll notice the first column is kg. This make a big difference.

In the old days when cyclists were not afraid of a bit of hard work, it was the bike's weight that was used to determine the gearing.

PowerCalc uses the whole vehicle weight. It calcs the power requirement for any set of circumstances.

I have explained this before but here goes again.

A 75 kg bloke putting ALL his weight on a pedal 0.17m away from the B/B will generate 650 Watts peak at 50 rpm.
He won't put ALL his weight on it, neither will it be 0.17m radius all the time, so 3/4 of this is probably MAX, or 490 Watts.

I went to the gym earlier and attempted to simulate this. The gym bike's control loop got 'bouncy' at 450 Watts and was struggling to achieve consistancy at anything over 450 Watts. I was up to it though, standing up and singing a merry song at 50 rpm.

Now let me transpose 450 Watts to a bike on the flat and up a hill.
My Dawes Giro 500 will be at 42 kmh when I'm giving 490 Watts.
It should climb a 10% at 10 mph with that power.
It should climb a 20% at 5 mph.
It should climb a 25% at 4 mph.

4 mph is 43 cadence in 30 x 25.

I hired a bike in San Francisco and climbed their 25% hills in 30 x 25
I was on the limit of my capability,, and it felt like it...

My choice to hire a triple WASN'T 'gut feeling'. It was masochism aforethought.