figuring % grades in TDF

jandbzpapa said:

A question for you informed math/cycle junkies. On the charts they show percent gain in the mountains at about 6-9%. I KNOW it has to be steeper than that. Is there a diff when using metric. I tried to figure out one of the climbs today and think (if I did it correctly) that it came out to about 12 % but the chart said it was 8%. Can some knowledgeable person help me out....please

You'll notice that percent doesn't have units. That means 8% grade is 1 up for every 12 1/2 across whether you are measuring in metres, feet or cubits.

They also say the average grade is 8% (or whatever) meaning they take the length of the road and the height increase to work it out. That doesn't mean there are not steeper sections and flatter sections - it just tells you the average.

Hi,

I was at a function last Saturday where Stephen Hodge was the guest speaker.

As I understand it from his explanation:

The gradient is reflected in the amount of elevation over a 1000metres. eg If an 8% climb would be an 80metre increase in elevation over 1000 metres distance. Hope this helps.

mitosis said:

You'll notice that percent doesn't have units. That means 8% grade is 1 up for every 12 1/2 across whether you are measuring in metres, feet or cubits.

They also say the average grade is 8% (or whatever) meaning they take the length of the road and the height increase to work it out. That doesn't mean there are not steeper sections and flatter sections - it just tells you the average.

thank you for your replies. I guess the question I was asking is is 8% in metric the same as 8% in our system?

jandbzpapa said:

thank you for your replies. I guess the question I was asking is is 8% in metric the same as 8% in our system?

Exactly the same.

jandbzpapa said:

thank you for your replies. I guess the question I was asking is is 8% in metric the same as 8% in our system?

As mitosis said, it's the same in all units. (rise/run)x100 = % As long as rise and run are in the same units, they don't matter. As for the Tour, the stated grades are average, but the roads have switchbacks. For the average to be 6%, the corners of the switchbacks (which are pointed straight up the mountain) are probably at least 15%. That's going to hurt no matter what units you're using. 🙂

jandbzpapa said:

thank you for your replies. I guess the question I was asking is is 8% in metric the same as 8% in our system?

Like I said, there are no units in percent so whether you are in imperial or metric it doesn't matter.

coastal said:

Hi,

I was at a function last Saturday where Stephen Hodge was the guest speaker.

As I understand it from his explanation:

The gradient is reflected in the amount of elevation over a 1000metres. eg If an 8% climb would be an 80metre increase in elevation over 1000 metres distance. Hope this helps.

Which is what I said 1 in 12 1/2 is 8%.