Tyres

[scramblebike]

Hi Folks.

Anybody recomend what tyres work best on a 250 Bulto model 198 ?

[woody]

Tyres are a personal choice so different riders will recommend different tyres.

However, as regards what you can fit:

If your bike still has the original Bultaco rear wheel (ie: with the Akront rim) you have a decent choice. That rim will accept a tubeless tyre with a tube in it as well as the standard tube type.

I'll assume we are only dealing with the top grade tyres, not budget brands like Mitas, V Rubber etc. They are fine for trail riding or playing in fields but for proper trials use, stick to the established brands.

For tube type rear tyres there are two choices, IRC and Michelin Radial. You can no longer get Michelin X11 tube type rears. If you ride in a lot of muddy sections avoid the Michelin Radial as it is about as effective as a car tyre in the mud. On rocks it is fine. The IRC will grip superbly in mud and as well as the Michelin on rocks but they can have a soft sidewall which can flex and may need a pound or so more pressure than normal to help overcome that, especially in warmer weather, or you are over average weight. If you're around 11 stones, not a problem. Some are better/worse than others.

Tubeless - you have IRC, Michelin X11 or X-lite and Dunlop. The Dunlop doesn't work well with a tube in so avoid that one which leaves IRC and Michelin again. The tubeless IRC has stiffer sidewalls than the tubed version so you won't get the flex. They are excellent in mud and (unless you're very good and can tell the difference - I can't) as good as a Michelin X11 on rocks. I've never tried an X-lite but assume they are better than an X11. In my experience the IRC has a much better wear rate than Michelin and will continue to grip with the edge well scrubbed off meaning you go longer between tyres - I once did the SSDT on my TYZ with a tubelss IRC that had already done a few trials. It lasted the week, just, without being turned.

If you use a tubeless type on the rear you will still need to use the security bolts as they will slip on a tube type rim without them.

For the front, Michelin X11 tube type is probably the best option and works well in mud or rocks. I've never tried an IRC or Michelin X-lite front so can't comment

[ormplus]

mich tube front and mich tube rear , will last for ages and grip well for the wobblers.

[scramblebike]

mich tube front and mich tube rear , will last for ages and grip well for the wobblers.

Thanks. Anybody local sell them ?

[scramblebike]

Tyres are a personal choice so different riders will recommend different tyres.

However, as regards what you can fit:

If your bike still has the original Bultaco rear wheel (ie: with the Akront rim) you have a decent choice. That rim will accept a tubeless tyre with a tube in it as well as the standard tube type.

I'll assume we are only dealing with the top grade tyres, not budget brands like Mitas, V Rubber etc. They are fine for trail riding or playing in fields but for proper trials use, stick to the established brands.

For tube type rear tyres there are two choices, IRC and Michelin Radial. You can no longer get Michelin X11 tube type rears. If you ride in a lot of muddy sections avoid the Michelin Radial as it is about as effective as a car tyre in the mud. On rocks it is fine. The IRC will grip superbly in mud and as well as the Michelin on rocks but they can have a soft sidewall which can flex and may need a pound or so more pressure than normal to help overcome that, especially in warmer weather, or you are over average weight. If you're around 11 stones, not a problem. Some are better/worse than others.

Tubeless - you have IRC, Michelin X11 or X-lite and Dunlop. The Dunlop doesn't work well with a tube in so avoid that one which leaves IRC and Michelin again. The tubeless IRC has stiffer sidewalls than the tubed version so you won't get the flex. They are excellent in mud and (unless you're very good and can tell the difference - I can't) as good as a Michelin X11 on rocks. I've never tried an X-lite but assume they are better than an X11. In my experience the IRC has a much better wear rate than Michelin and will continue to grip with the edge well scrubbed off meaning you go longer between tyres - I once did the SSDT on my TYZ with a tubelss IRC that had already done a few trials. It lasted the week, just, without being turned.

If you use a tubeless type on the rear you will still need to use the security bolts as they will slip on a tube type rim without them.

For the front, Michelin X11 tube type is probably the best option and works well in mud or rocks. I've never tried an IRC or Michelin X-lite front so can't comment

Thanks for information, much appreciated

[ormplus]

iam on wobblers web site scramblebike.

[woody]

mich tube front and mich tube rear , will last for ages and grip well for the wobblers.

Grip from the Michelin Radial tubed rear is non-existant in mud. From experience - unless they have changed the construction/composition over the last couple of years.

I fitted one not knowing their tubed tyre was no longer an X11 and using full hole in 3rd or 4th couldn't even get into the start gate of sections that were cleanable in bottom.

A local rider was winning the local clubman series and for the last round fitted a Michelin Radial to his TLR. He finished almost last in the class after winning it for most of the year. No grip and spinning backwards down muddy banks.

I rode the SWM owned by Dave Dawson a few months back fitted with a Michelin Radial and had to scream it in 4th and paddle it up a bank I'd just been cleaning in bottom on my own bike. He took it back to the dealer he was so p****d off with it and changed it for an IRC.

If you're going to use a Michelin rear, use a tubeless X11, they'll work fine on the Sherpa with a tube in.

If you're never going in mud the Radial will probably be ok. I'll never use one again.

[smelling123]

Grip from the Michelin Radial tubed rear is non-existant in mud. From experience - unless they have changed the construction/composition over the last couple of years.

I fitted one not knowing their tubed tyre was no longer an X11 and using full hole in 3rd or 4th couldn't even get into the start gate of sections that were cleanable in bottom.

A local rider was winning the local clubman series and for the last round fitted a Michelin Radial to his TLR. He finished almost last in the class after winning it for most of the year. No grip and spinning backwards down muddy banks.

I rode the SWM owned by Dave Dawson a few months back fitted with a Michelin Radial and had to scream it in 4th and paddle it up a bank I'd just been cleaning in bottom on my own bike. He took it back to the dealer he was so p****d off with it and changed it for an IRC.

If you're going to use a Michelin rear, use a tubeless X11, they'll work fine on the Sherpa with a tube in.

If you're never going in mud the Radial will probably be ok. I'll never use one again.

Hi Woody - thanks for the posts, you sound like you know what youre talking about. Can I ask how you 'feel' the difference between the IRCs. Ive just looked and mine is the tubeless type. So stiffer sidewalls and it actualy looks fully inflated with only 4psi in.

What difference would I feel if I got the tubed type next. Its on a Bantam running with a tube.

Im very happy with the IRC tubeless - just wondered what the difference would be?

cheers mate.

[woody]

With the softer sidewalls of a tubed IRC rear, you can feel the sidewalls flexing which translates as similar to having a puncture.

As I mentioned before, the tubed IRC rears can be inconsistent, so some have the flex and some don't. Also it depends on your weight, if a rider isn't too heavy then the sidewalls aren't under as much pressure so they may not flex noticeably.

It's generally noticeable under several conditions:

- Turning uphill, as soon as power is applied the rear of the bike will step out as the tyre rolls on the sidewalls as you start the uphill cambered turn.

- On cambers, the rear will try and roll down the hill.

- Under hard acceleration, even in a straight line (say in the lead up to a climb / step) the rear can step out as the walls flex under the acceleration, putting you offline for the hazard.

- Over rocks - if you try and ride over the points or tops of a series of rocks, like up a stream, the tyre can try and roll off the point down the side of a rock instead of holding firm and staying on top.

What tends to happen is people put more air in to try and stop the flexing, but too much and you'll lose the footprint of the tyre and therefore grip. Generally you'd run a tubed IRC rear at 1psi more than other types, although more can be required. We've had one that rolled still with 7psi in it but that was an absolute one-off.

A good idea if you're buying off the shelf rather than mail order, is to get the tyre and hold with each hand by the bead with the tread into your chest. Then, as hard as you can pull the sidewalls apart. If they open right up like Great White's mouth, the sidewalls are soft. If they only open out a little then the sidewalls are harder and that is the one to go for. Compare it with a tubeless one if there is one on the shelf.

Like I said before, it isn't all tubed rears that are like this, but a percentage are, so it's best to bear this in mind when buying.

[smelling123]

With the softer sidewalls of a tubed IRC rear, you can feel the sidewalls flexing which translates as similar to having a puncture.

As I mentioned before, the tubed IRC rears can be inconsistent, so some have the flex and some don't. Also it depends on your weight, if a rider isn't too heavy then the sidewalls aren't under as much pressure so they may not flex noticeably.

It's generally noticeable under several conditions:

- Turning uphill, as soon as power is applied the rear of the bike will step out as the tyre rolls on the sidewalls as you start the uphill cambered turn.

- On cambers, the rear will try and roll down the hill.

- Under hard acceleration, even in a straight line (say in the lead up to a climb / step) the rear can step out as the walls flex under the acceleration, putting you offline for the hazard.

- Over rocks - if you try and ride over the points or tops of a series of rocks, like up a stream, the tyre can try and roll off the point down the side of a rock instead of holding firm and staying on top.

What tends to happen is people put more air in to try and stop the flexing, but too much and you'll lose the footprint of the tyre and therefore grip. Generally you'd run a tubed IRC rear at 1psi more than other types, although more can be required. We've had one that rolled still with 7psi in it but that was an absolute one-off.

A good idea if you're buying off the shelf rather than mail order, is to get the tyre and hold with each hand by the bead with the tread into your chest. Then, as hard as you can pull the sidewalls apart. If they open right up like Great White's mouth, the sidewalls are soft. If they only open out a little then the sidewalls are harder and that is the one to go for. Compare it with a tubeless one if there is one on the shelf.

Like I said before, it isn't all tubed rears that are like this, but a percentage are, so it's best to bear this in mind when buying.

Thanks very much Woody,

Think I'll stick with the tubeless to be honest.

cheers Stu