Question: Express an equation differently

Hello fellow maple struglers!

This is my first question, so hopefully I did it in the correct manner. My problem (I think) is of a simple nature, but I can't seem to get it to work. The equation I have is the following:

All is nice and well and as you all can see it depends on two variables. Now what I want to do is to express the function in a shape where it depends on the ratio t/d only. Simple calculus shows that for this equation it is rather easy, where the result is:

(62,8*t/d+0,0945)/pi

Now I would like to know whether it is possible to automate this in maple, such that I can plot Wr_over_p as a function of t/d. I know I can simply use the form above and make the plot, but further down in my maple file I have an equation which is much more complex, and I want to plot thatone as a function of t/d as well.

I hope I have made my problem clear to some of you guys, but if you require some further explaination than please let me know. Thanks in advance for your help, I hope there is someone who can help me with this!