Hi,

My bike (27.5) came with a set of Schwalbe Rapid Robs fitted, which are 2.25" which I run at 40psi ish. I've noticed lots of people mixing and matching tyres with different tread patterns, widths etc. I was just wondering what's this all about? Is it for really fine tuning how the bike rides? as in, a newb like myself wouldn't really notice? Is it better to have a big grippy tyre up front, narrower faster tyre at the back? Or Vice versa? Is it all terrain dependant?

Thanks

Typically people will run a wider front tyre than rear as they are doing different jobs, here's the reasoning http://blog.artscyclery.com/gear/front- ... binations/

Add in to that things like different compounds (typically harder compound roll better but doesn't grip as well) and tread and sidewall strength and you have lots of options

I run Bontrager XR4 2.35" on the front and Bontrager XR3 2.2" on the rear.

a bit more grip up front to keep the front end secure. Less rolling resistance out back where it counts the most. Thats the general idea. Wider profiles offer more grip and comfort, but not neccesarily more resistance off road

Ahha, thanks for the info. Just out of curiosity, on the site they list a particular discipline as "Cross Country", I'm right in thinking riding fireroads, trails, bridleyways etc fits in to this category?

Related, 40psi is pretty high. Are you fairly weighty? I'd be bouncing all over the trail running those sorts of pressures.

Consider 'cross country' to be just 'riding your bike' ... a little bit of everything.

And yes, Richard's right ... 40psi is pretty hard, especially up front.

ootini wrote:Ahha, thanks for the info. Just out of curiosity, on the site they list a particular discipline as "Cross Country", I'm right in thinking riding fireroads, trails, bridleyways etc fits in to this category?

Cross country seems to mean different things to different people: I'd use it for what you describe but others would use it for slightly more technical stuff.

Pressures: you don't mention if you are running tubed or tubeless. Generally the bigger the tyre volume, the lower the pressure you need. For tubed the starting point is between 30-35psi, increase by 1psi if the tyres squirm too much or you get pinch flats, lower it if you bounce around a lot. For tubeless, the Stans formula is weight in stone multiplied by 2 then subtract 1 for the front and add two for the back. I.e. if you and your kit weigh 13 stone then you get (13 * 2) = 26 => 25psi for the front and 28psi for the back. This sort of ties in the points about larger volume & lower pressure on the front. Again this is a starting point, even when you've got it sorted you might want to vary it according to temperature and altitude (remember Boyle's Law from school?), I'm 13 1/2 stone and run 24/28 on tubeless.

And again ... we're not American

s8tannorm wrote:

And again ... we're not American

Yeah, what's this "dry" thing mentioned?

Thanks for the advice. I'm 13.5 stone and to be honest, any bouncing around I'd just put down to lack of experience / skill.

I might drop the pressures to 28-30, see how I get on. Thanks again.

ootini wrote:Thanks for the advice. I'm 13.5 stone and to be honest, any bouncing around I'd just put down to lack of experience / skill.

I might drop the pressures to 28-30, see how I get on. Thanks again.

Tubeless and 22F/25R here. 12.5 stone. I'd consider 30+ if I was doing a very long stretch of tarmac.

I am using Rapid Robs and 40psi is where I would be for long road sections. They do bounce around a lot if there are sections of off-road - but you sometimes you have to make a compromise based on the route you are riding.

I like the Robs on dry tracks, I find them pretty fast and fairly hard wearing. I do find them lethal in wet conditions, I have lost the front a few times now when I couldn't be bothered to change over to a different tyre

I think I'm using something like 20/24 tubeless at the moment (10st 9lbs). I start out with 22/26 because that seems ridiculously low, but I almost always let a little bit out once I'd been riding for half hour or so.

Richard G wrote:I think I'm using something like 20/24 tubeless at the moment (10st 9lbs). I start out with 22/26 because that seems ridiculously low, but I almost always let a little bit out once I'd been riding for half hour or so.

You're riding so fast they've warmed up and the pressure has increased

Pressure first - then worry about tyres after. Tyres are sorta like sexual partners, everyone has different tastes, and some make no sense to me.

johnnystorm wrote:

Richard G wrote:You're riding so fast they've warmed up and the pressure has increased

Would explain the steam.

There are certain rules though that to get optimum performance you must obey, even if they are just to avoid derision:
Tyre logos and valves or wheel logos must be lined up
Same make of tyre front and rear (but you are free to choose the type and compound of tyre)
Must be talked about as though they make a massive difference to the result of your event, even if the engine was broken.

slarge wrote:There are certain rules though that to get optimum performance you must obey, even if they are just to avoid derision:
Tyre logos and valves or wheel logos must be lined up
Same make of tyre front and rear (but you are free to choose the type and compound of tyre)
Must be talked about as though they make a massive difference to the result of your event, even if the engine was broken.

I have the same make and model of tyre on my bike, with the tyre manufacturer aligned dead centre to the valve.

They are however different colours.

Is this allowed?

Zippy wrote:

slarge wrote:There are certain rules though that to get optimum performance you must obey, even if they are just to avoid derision:
Tyre logos and valves or wheel logos must be lined up
Same make of tyre front and rear (but you are free to choose the type and compound of tyre)
Must be talked about as though they make a massive difference to the result of your event, even if the engine was broken.

I have the same make and model of tyre on my bike, with the tyre manufacturer aligned dead centre to the valve.

They are however different colours.

Is this allowed?

GET OUT!

Rim width can affect the pressure you can run at too. I've an ikon 2.35 up front. It was around 20 on a crest rim for unladen riding. Now it's on a 35mm wider rim its 15psi with my kit on the bike. I'm 65kg and haven't noticed any rolling or unwanted deflection in it.

I like the wide rims. Working well for me.

So what's the consensus, presta or schrader?

ianfitz wrote:Rim width can affect the pressure you can run at too. I've an ikon 2.35 up front. It was around 20 on a crest rim for unladen riding. Now it's on a 35mm wider rim its 15psi with my kit on the bike. I'm 65kg and haven't noticed any rolling or unwanted deflection in it.

I like the wide rims. Working well for me.

Ian, what's the width at the widest point on the 2.35" Ikon, on a 35mm rims?

Ian wrote:

ianfitz wrote:Rim width can affect the pressure you can run at too. I've an ikon 2.35 up front. It was around 20 on a crest rim for unladen riding. Now it's on a 35mm wider rim its 15psi with my kit on the bike. I'm 65kg and haven't noticed any rolling or unwanted deflection in it.

I like the wide rims. Working well for me.

Ian, what's the width at the widest point on the 2.35" Ikon, on a 35mm rims?

Don't have any calipers, or anything similar so measurement is eyeballed off a tape measure - 61mm. I've not seen them side by side with a crest/arch that i was using before. I don't know that they look loads wider on these rims. its the angle of the side walls - and therefore the shape of the tyre that's noticeably different. much more vertical on the wider rims and less lightbulb shaped. i guess thats why they don't roll or squirm in ways you don't want them too. there's no way I'd run them at 15psi on crests/arch they would burp or deflect to the point where they would feel like they'd roll off the rim!

Cheers Ian

--

to reply to the OP on the last question:

Presta