broadband speed drops

[mikejf]

I have VM 120meg and if I plug my laptop into my router wirh a 1m ethernet cable I get 120meg. If I then plug in a 30m ethernet cable instead the speed drops to 80meg.
I thought 100m was the max run. Any ideas wht it would drop by 40meg?

Thanks Mike

 

[Caged]

The cable is probably broken.

 

[bremen1874]

Or just cheap junk.

Edit:

And the 100m assumes that 90m of it is solid core with an additional 10m of patch cord at the ends.