A mate has just invested in a new Trek road bike and it has the standard carbon front forks but isn't sure if his old turbo trainer will snap them.

Basically you have to take the front wheel off, mount them on a axel and then you have a standard trainer on the back.

Obviously it was designed for older racers, but will prolonged use cause the forks to crack/snap?

I rode my old carbon trek up and more importantly down some of the biggest hills around the UK and europe, and when it comes to descending folk seem to feel I have a screw loose. Given the 5 year beating they took, I can't say I would be to worried.

Mmmm I guess if the bike is secure it should move that much.

Must be siliar to planting the front wheel on one of those supports you can buy.

No problem.

Definately fine, provided you load carbon in the direction that its intended to, its as strong as hell. The downward force on the carbon fork when its in the trainer would be the same as when a wheel is attached, and the lateral forces would be no greater than when sprinting on the road I would guess. I use a cannondale road bike with full carbon fork on my trainer, where the front wheel is removed and the fork dropouts mount onto the trainer, and i'd be more worried about breaking the trainer than the forks. The biggest risk to carbon structures is surface impacts that go beyond the lacquer and also beyond the top comsetic layer of carbon weave, and unnatural loads in weird directions, I think too many people are concerned about the fragility of carbon fibre. The stuff is unfeasibly strong, thats the whole point, if it wasnt then every single Formula 1 designers got it wrong 😀 Search the web for information on how Carbon Fibre composites are tested for strength, provided its manufactured well and without faults and that its fitted well then it truly is the most astonishing material

but the loads on the drop-outs are not the same with a wheel mounted.
that is why certain certain forks were not warrantied to be carried on roof mounted bike carriers, they were just not designed to take the load of a 30lb bike swinging from side to side at 60mph.
i'm not saying your forks are going to break just that the forces being put through the dropouts with a wheel attached being ridden hard by a pie-eater are not the same as when mounted in a ridged frame.

ridged frame

is that for extra pleasure gary?

Sod F1 cars, the pansy little runabouts, 😉 what about the new bunch of airliners that have a massive "carbon fibre" content? If it's strong enough to make wings that hold up the body of the plane, 300 fat Yanks and all their tatty souvenirs then these forks'll be fine.

But seriously, it's the rear end that does most of the 'being held' so there's not a huge amount of lateral force going through the forks, certainly no more than, as hugh said, when sprinting.

is that for extra pleasure gary?

it's for those 29'er freaks with their bottle top stem caps and witty singlespeed stickers

If the rear axel is held, why not cut of the front wheel suppourt and just use it like a normal turbo?

There's no way I'd use it like that. The Dropouts just arent designed to take those forces and normal front wheel loads are minimal to say the least because the wheel can move to mitigate problems (which is why on average most people trash morerear wheels than front)

There is plenty of information (including pictures of him training, and him describing his workout sessions on the trainer) out there that Sir Chris Hoy either currently or has used in the past the CATEYE CS-1000 trainer, with a full carbon track frame attached. The cateye trainer is the fixed front dropout type, and apparently he uses it for flat out sprint intervals. I would only be concerned about a catastrophic carbon failure if I was confident that I could apply more frame stress and torque in a sprint than a Chris Hoy at 2000 Watts until then I will sleep easy 😉