Help with lense choice please

Very new to photography, travelling to s.america to help with photography for a mountain bike race in the Andes.
I have a Pentax K5ii and would live some advice on a lense to capture the riders both coming at me and whilst they move past at speed.
Any advice would be greatly recieved

Budget?

£600 max.
was going to buy second hand but again, not sure

Well if I were going to shoot a mountain bike race in the Andes with my K-5IIs I would take either the Sigma 70-200mm f2.8 OS or Pentax 60-250mm f4.

More than likely it would be the Sigma though as it has faster AF ... There is also the Tamron 70-200mm f2.8 if you can't find a Sigma.

What weight limit do you have:

I don't have any of the lenses above but 70-200 f2.8 lenses tend to be heavy beasties but by all accounts very good

thats great.
thanks very much

srs are doing the tamron 70/200 f2.8 new for less than 500and it as the macro capabilaty

+1 for the Sigma - fast autofocus and good image quality, and the in lens image stabilisation can be set for panning - but it's a heavy(ish) lens.

The Pentax 60-250 is lighter and has water resistance - autofocus speed is good enough, but it's likely to be the more expensive of the two.

Thanks for the comments.
I will get looking

No contest for me......Sigma all the way,

Pro's
Its f/2.8,
Its all internally Zoomed & focussed (doesn't grow on Zoom or Focus)
Has the fast, accurate HSM, possibly more reliable than the SDM on the 60-250
Is very quiet during focussing...
Switchable Image stabilization
Solid as a rock quality build....

Cons...
It is a bit on the large side
Not as 'WR' as the 60-250 perhaps

Andy

Depends how close you'll be. The 18-135 may be a better option

If you are shooting any kind of action with a Pentax body, be it a K5ll, Kills or a K3, then the Sigma 70-200 f/2.8 is currently your best option.

Fastest and quietest AF speed at this focal range
Very nice rendering and compression

First please consider this one...

For most Pentax camera bodies... While doing certain types of physical activities and carrying a camera (in most any type of rucksack/gadget bag) turn OFF the Pentax in camera SR. I've seen many cameras accidently either left on, or bumped into the on position. In which case, it is eventually possible to have issues with the SR and some Pentax camera bodies.

What are people's thoughts on this?
APO MACRO 150mm F2.8 EX DG OS HSM

Sigma don't make the 150mm macro in Pentax mount and tbh you would be much better off with a zoom lens of some kind for the sort of subjects you are looking to photograph.