from what i know DOT 5.1 is perfectly compatible with DOT4. I think you're talking about DOT 5...
I have to hold tight cause we're racing on old airports with bad quality pavement and if you're not holding it you can really bounce off the bike... but that's it... every body is having the same conditions so that's not an excuse.
as for height/weight i'm 1.82 m and 75 kg so i think i'm ok for the moment
you;re right about the gym part... i'll go starting this week at least 3 times a week.
I'll DO MYSELF as you suggested every day... no... twice a day to get fit

