I have a M bike with front and rear suspen. I would like to get a rear rack that can afford more weight capacity. What kind of rear rack is proper for it. thanks.

A bike with suspension is pretty limited on what kind of rack you can use. In the rear about all you can use is a seatpost rack

https://www.amazon.com/gp/product/B00...W697S0XFMBGAV1

Have a look at the Cold Springs and Sherpa racks on this page, the photo galleries for those two models show them fitted to bikes with rear suspension.

He has suspension and I'm assuming no brazeons. Neither of those racks would work.

Why not?

Did you see any of the photos of those racks attached to mountain bikes with rear suspension and without braze-ons?

Cold Springs photos:https://www.oldmanmountain.com/Pages/RackPages/RackGalleries/Pages/csRear_gallery.htm
Sherpa photos: https://www.oldmanmountain.com/Pages/RackPages/RackGalleries/Pages/sherpaRear_gallery.htm

I suspect that the OP might be talking about a car mounted rack to transport the bike anyhow.

Tail gate mount or hitch mount?

I really love my hitch mount X-Port from Performance Bike (no affiliation).

Good guess but not. I don't even have a car. Anyway. I found some pic. It may be one of cheap solution.

https://www.amazon.com/gp/customer-me...e=UTF8&index=1