As title really, have a surplus Pike which has just had new debonair spring shaft put in it, but is it too big for my Tarn frame??
I don't really know, but looking at the Genesis website I think it's designed around a 120mm fork. Going to 160 seems as though it might screw up the geometry a bit. The bb will be higher, and the seat tube angle slacker...
It could be worth a try just for a giggle -- you're probably unlikely to immediately die, and at least you'll know whether it feels good or awful.
Alternatively can you dial the Pike down a bit?
120mm to 160mm sounds like too much. The stress on the headtube should be a concern as well as messing up the angles and thus handling.
The Tarn is as slack as a slack thing with 120mm fork.
Give it a go and report back!
Will ride a bit weird, reduce the travel a bit 😉
You will die and the world will end.
I run mine with a 140mm fork and the bb is a bit high with 29" wheels but OK with 27.5 x 2.8.
Try a 27.5 in the front and a 26 in the back.
I wouldn't say its slack, not compared to my Codeine. Would dialling back down to 140 be better but I would lose the debonair upgrade!
I'am a friend of overforking...
My 29er hardtail frame was designed for 100 mm fork - and use it with 130mm fork. Fantastic!
Recent project: my Bossnut V2 had a 130 mm Sektor fork. Put a 150 mm Fox fork in. Felt very strange and out of balance. All the weight was on the rear and rear shock was bottoming out.
But simple fix: the original Bossnut has a 45 mm stem and 2 spacers under the stem. Changed it to 60 mm stem and no spacers and moved the saddle 15 mm to the front as well. All is perfect!
But the weight balance of full suspension bikes is very sensitive.
In your case, hardtail: not as critical, but 40 mm "more travel" means you will have to modify the geo to get the balance right again.
Bit longer stem?
Overloading the frame: love overforking but I try not to overload the frame. No crazy jumps with such an bike! I check for cracks quite often as well...
A 120mm to 160mm jump is quite big. Would think 140mm is more likely to result in a bike that rides acceptably but you never know.
I did until fairly recently have a Kona Caldera from 2004 which came with a 100mm fork and I was running a 130mm Revlatikn u-turn fork in it. I thought it rode better dialled to 130mm than back down at 100mm for most of my trail centre / steeper off piste riding. It did mean the front of the bike was harder to keep on the floor on steep uphills though.
At 160mm you’d be at the very extreme end of travel for a hardtail though - 130mm is around average I’d guess.
