Mt Bike Tire Talk

[AmyPJ]

Tech question: Since I ruined my XR3, and switched back to the XR4 in the back (so, running XR4 front and back, which is what comes stock with the bike) the front and rear suspension feel better matched, for lack of a better description. I've been tinkering with my suspension all summer, because I just haven't been able to get it dialed. Today, it felt really good.

 

[scott43]

Tech question: Since I ruined my XR3, and switched back to the XR4 in the back (so, running XR4 front and back, which is what comes stock with the bike) the front and rear suspension feel better matched, for lack of a better description. I've been tinkering with my suspension all summer, because I just haven't been able to get it dialed. Today, it felt really good.

Sag? How different are the sections/widths between the two tires? Enough to affect weight distribution? The tire might also be acting more (or less) as a suspension component which can change the feel of the suspension.

 

[AmyPJ]

Sag? How different are the sections/widths between the two tires? Enough to affect weight distribution? The tire might also be acting more (or less) as a suspension component which can change the feel of the suspension.

The tires are very similar, the XR4s are just a tad beefier. The tread pattern is essentially the same. Both are 29X2.4.

 

[Tricia]

Tech question: Since I ruined my XR3, and switched back to the XR4 in the back (so, running XR4 front and back, which is what comes stock with the bike) the front and rear suspension feel better matched, for lack of a better description. I've been tinkering with my suspension all summer, because I just haven't been able to get it dialed. Today, it felt really good.

Sag? How different are the sections/widths between the two tires? Enough to affect weight distribution? The tire might also be acting more (or less) as a suspension component which can change the feel of the suspension.

The tires are very similar, the XR4s are just a tad beefier. The tread pattern is essentially the same. Both are 29X2.4.

This is really good tire discussion. Would you mind if we pulled this out for its own thread?

 

[AmyPJ]

This is really good tire discussion. Would you mind if we pulled this out for its own thread?

Go for it!

 

[Tom K.]

This is really good tire discussion. Would you mind if we pulled this out for its own thread?

Great idea, @Tricia. This mtb thread has too many "internal" discussions. Separate tire, suspension, let's ride together, etc. threads would be great.

 

[Tricia]

I asked the question and then let it slip my mind. This discussion pulled from Mountain biking 2018 thread.

 

[AmyPJ]

So, to clarify my original question: Does running different tires front and back change how the suspension handles/works? No changes were made to the suspension settings when the tire swap was made.

 

[cantunamunch]

So, to clarify my original question: Does running different tires front and back change how the suspension handles/works? No changes were made to the suspension settings when the tire swap was made.

I'll rephrase @scott43 's point above - it changes feel far faster than it changes gross mechanical traits and so can easily cue your body to use a different balance point.

 

[scott43]

Yes exactly. I'm looking at the tire specs and one does seem to have more TPI in the casing so perhaps small bumps feel different as a result of the tires..but the actual suspension operation, not unless your position is different or the tires are significantly heavier. So I'm thinking it's just more perception than reality.

 

[martyg]

Tires and their characteristics are an integral part of a bikes suspension equation. You can't really discuss one without the other.

Tires with a higher tpi count tend to be more supple. All things being equal this leads to greater elasticity. Greater elasticity means less change in casing tension at a given psi, and more consistent ride charactoristcs across a range of psi.

Conversely, a tire that is less supple tends to magnify any changes in psi, and provides profoundly different ride charactoristcs with more subtle changes in psi.

 

[Tom K.]

So, to clarify my original question: Does running different tires front and back change how the suspension handles/works? No changes were made to the suspension settings when the tire swap was made.

No, especially since in this case you went from an XR3 to XR4. They have identical casings (assuming both are Team versions), just different knob sizes and patterns. Heck, even the knob patterns are darn near identical. The XR4 does roll a bit slower.

@martyg comments above are spot on with regard to casing thread counts, but in this case, there is no difference.

Maybe you were just having an ON day!

 

[AmyPJ]

No, especially since in this case you went from an XR3 to XR4. They have identical casings (assuming both are Team versions), just different knob sizes and patterns. Heck, even the knob patterns are darn near identical. The XR4 does roll a bit slower.

@martyg comments above are spot on with regard to casing thread counts, but in this case, there is no difference.

Maybe you were just having an ON day!

I think so! And I do prefer the XR4 on the downhill.
I'm afraid that I have been running my pressure lower in the past few years (as in, WAY too low) because my old pump measure inaccurately, and now, I like that squishy feel on the downhill. As a result, I'm having a hard time adapting to running a couple more pounds both front and back and feel like I can't get my suspension dialed in.

 

[Erik Timmerman]

So why not let a little air out if you prefer it that way?

 

[Philpug]

I am still trying to get the feel for running a lower tire pressure. Where I am uncomfortable is when the trail is a bit of a double fall line and I feel the tire flex laterally. Now it is just a matter of finding the pressure I am comfortable with, Kinda like shck pressure needs to be set for the riders weight, weight needs to be considered when setting up tires.

 

[Erik Timmerman]

Yup, sounds like you definitely need to add a pound or two. What tires/rims are you running and what pressure are you at now. Yesterday I was running my carbon wheel set (26 internal) with a Specialized Slaughter grid on the back, very sensitive to pressure, I think I was just one or two pounds below where I need to be, probably need 30 with that tire. On my endure race wheel/tire combo, I am good at 25 or so.

 

[Tom K.]

I am still trying to get the feel for running a lower tire pressure. Where I am uncomfortable is when the trail is a bit of a double fall line and I feel the tire flex laterally. Now it is just a matter of finding the pressure I am comfortable with, Kinda like shck pressure needs to be set for the riders weight, weight needs to be considered when setting up tires.

Tire pressure depends on so many things it's generally a bit hard to give numerical advice (not that you asked, but hey, this IS an internet forum).

Here is the method I use. It's a bit of a PITA -- though nowhere near the level some people go to tuning and waxing a ski!

1. Pump your tire up a bit too high. Say 5 or 6 psi.

2. Ride a quarter mile minimum segment of trail that you feel is representative of your own personal normal.

3. Remove 2 psi and do it again, and repeat until the "pingy" feeling when hitting rocks, etc. is replaced by a slightly muted "thump".

4. Continue downwards until you feel the tire squirm you noted above.

5. Set your pressure somewhere a bit below 3, but above 4.

Ideally, you do this for front and rear tires. Definitely a bit of a PITA, but SO worthwhile. Note that some adjustment will be required when riding trails significantly outside the range of your benchmark. For instance, when I ride high-G flow trails, I need a bit more pressure or it feels like I'm going to roll the tire right off the rim!

 

[Erik Timmerman]

For instance, when I ride high-G flow trails, I need a bit more pressure or it feels like I'm going to roll the tire right off the rim!

That's pretty much the entirety of my find your PSI technique right there. Do laps on flow trail and add psi until the tires stop trying to come off the rim.

 

[Tom K.]

That's pretty much the entirety of my find your PSI technique right there. Do laps on flow trail and add psi until the tires stop trying to come off the rim.

Absolutely, if flow is your focus. After about five years of "can't get enough flow" my personal pendulum of preference seems to have swung back to rugged xc stuff. I've been riding our moto trails a lot this summer, which has been great in many ways, not the least of which being that they are nearly empty, since they are always closed to motos July/Aug/Sept for fire danger.

In fact, I've been having enough fun that I've ordered up a new long travel bike!!!

 

[cantunamunch]

my personal pendulum of preference seems to have swung back to rugged xc stuff. !

Does this mean you're not starting at the minimum? And if so, how do you avoid a Weber's law issue?