Am thinking of getting a 125cc trails bike gas gas or a beta. The plan is for it to be road legal as I can ride on road to a spots to use it. Questions I have:

A. What speed would a typical 125 be able to reach and sustain?

B. How much damage would be caused to a engine, by using it on road?

C. Would there be any gearing changes I could make, to make the bike a bit more road friendly.

If I got a beta I would be after getting the long range tank and seat setup. Is there anything like that for a gas gas?

I know I have asked a lot of questions, I've been trawling the Internet for the last few days and can't find the information I was looking for. I hope I have posted in the correct forum.

A. Although I haven't done it on a 125, Previous trials bikes geared up will reach around 35-40mph and still be "safe" to rider and machine.

B. So long as you keep the revs to a reasonable level the mechanicals of the engine will be ok. The issue is that trials bikes are jetted very lean because in competition you can get way with it. Riders in long distance road trials often go slightly richer on the main jet to compromise between road and trial setups. The other common mod is to turn the choke on. Choke only works at low throttle openings so its common for riders to regularly "back off" the throttle opening to 1/3. This keeps the combustion chamber temperatures under control.

C. Definitely need to change gearing. Many bikes will allow a gearbox (countershaft) sprocket with an extra tooth which is equivalent to 4 teeth removed from the rear wheel sprocket. You might also go down 2 teeth on the back sprocket as well. It isn't out of the question to change the gearbox sprocket back to the original when you get to the trial. You would need circlip pliers and a rear wheel spindle nut spanner.

All said and done though... its a real pain in the neck and is best avoided if you can. But if you don't have a choice, do what you have to do. You may meet up with someone who will offer you a space on their bike trailer.

Can I suggest that you read the Gasgas, Beta and Sherco SSDT setup advice documents published on this website. Many of the modifications described in that document are relevant with the added benefit of being specific to a certain brand of bike.