Silvio and Climbing

[Mark B]

I'd like to hear from other Silvio riders and tell me about your climbing experiences. I've had a few issues off and on with front wheel slippage on steep climbs. I'm not sure if this is a matter of me being too heavy and weighting the back wheel too much, or what.

I'm running a road triple on my Silvio and as much as I would like another gear or two sometimes, I'm already busting the tire loose in my lowest gears. I can't imagine you guys running mountain bike gearing not experiencing the same things, unless, like I said, maybe it's my weight.

The other issue I'm having is more of a front suspension setup issue, I think. Occasionally, I will hit a bump or something and make the front wheel hop and spin just a little. I was running 150# in the front shock and softened that up to about 125# That seemed to help, but I still get the front wheel off the ground from time to time. I have run it softer than 125 and that really does the trick, but if I hit a hard bump, will bottom the shock out. I think I just need to do more experimenting to find the magic spot where I have enough suspension to not bottom out, yet soft enough to keep the wheel on the ground. This, too, could be another weight issue with me and one that might fix itself as I lose weight.

Your thoughts, ideas? No fat jokes, please, I'm sensitive. :lol: :lol:

Mark

 

[defjack]

Do you mean really steep climbs?Under normal road conditions I only break the tire loose if I use too much power starting out on some steeper stuff.I dont get alot of that but do have plenty of lite sand especialy around the corners.I have yet to loose traction no matter how stupid I ride.Thats the main reason im riding a Cruzbike. Jack

 

[Flasharry]

I guess it would be good to know your weight distribution between the two wheels when you are sitting on the bike and then compare it with others so we can determine if you are suffering any more than them or whether you are now so fit, you are now attacking ridiculously step hills.

Perhaps changing the front tyre to something like the 'Continental GP Attack,' which is front wheel specific and made entirely from a sticky compound, rather than the normal racing tyre design which has a hard compound in the centre (and less grip) to cope with wear from skidding the back wheel when braking. We do have good suspension up front, so the smaller sized tyre may not be a problem, although a bigger contact patch would be advantageous and tyre wear may(?) be an issue.

Finally, other than sitting forwards or on the front edge of the seat (if that's possible), lengthening the wheelbase is the only thing that will actually add weight to the front wheel, compared to the Barchetta, the silvio is actually very short. I have wondered whether a couple of upward pointing bar ends on the outside top of the bars to hook the crook of your arm around (is that the right word for the inside of your elbow) to maintain an effortless closed position would help with climbing, but perhaps this is just an impossible fantasy of mine.

Cheers.
Stuart.

 

[Doug Burton]

Mark B wrote:

I'm running a road triple on my Silvio and as much as I would like another gear or two sometimes, I'm already busting the tire loose in my lowest gears. I can't imagine you guys running mountain bike gearing not experiencing the same things

Mark

Hi Mark,

This is one of the reasons we don't go crazy putting low gears on the SR and FR. At some point gearing and traction limit come together, although the traditional bogey of letting the bike speed drop below the minimum balancing speed while pedalling furiously doesn't seem to show up on the Cruzbike.

Another line of experiment that might aid in front traction is looking at the rear elastomer spring. Changing the stiffness in back might give you the very small additional forward transfer you need to smooth out these small discontinuities. An alternative to changing the stifness might be to change the elastomer such that it is progressive rate rather than somewhat linear.

If you pull back the boot covering the elastomer, you'll see it's two front fork elastomers on top of each other. Your LBS may stock alternate spring rate elastomers for tuning MTB front shocks - if you get a couple of different ones from the LBS you can mix and match and put them in different orders to play with the rear spring behavior. The critical dimension for mounting is the hole in the middle, the outer diameter shouldn't matter very much.

Bryan's Silvio (he received it yesterday) has a new progressive elastomer John is evaluating. Intersting to see what he thinks. But it is a large one-piece unit. The existing part can be tuned.

Just a thought...

No sensitivity jokes, please, I'm fat.

 

[Mark B]

Did you hear about the sensitive guy that.... Oh,wait..

I did a crude measurement of my balance fore and aft and it appears I'm about 51% rear and 49% front. I'm a little surprised (pleasantly) by this apparent good balance. I'm going to keep an eye on this as I lose weight, but I don't think it will change much.

Today, I reduced the pressure in the front shock. I was running 125# and backed it down to 110# +/-. I didn't pull anything super steep, but I did't get any wheel slip and the wheel hop issue was way, way better. I don't thnk I hit bottom on any big bumps, but I think I was close. I think maybe we're onto something with suspension tweaking, though.

Doug, I guess I'm due an "I told you so" on the gearing issue, but nobody said it was a traction issue. I certainly never gave it a thought as a possibility.

Jack, I'm talking about grades probably in excess of 10 percent. Right now, I don't have the legs or the lungs to pull that for very long, anyway. I'm hoping to get back into some mountain riding eventually, though.

Mark

 

[Kamatu]

See if you can tweak it to a 55/45 f/r with the suspension, because not only can we say that you are getting wheel slip because your power is exceeding your traction, we can also say that you are losing traction because your drive wheel is lifting off the ground.

Of course, if you and I are using the same language when you say "crude", then you might already be there since I'd think 10% error.......

And this from the guy without even a functioning bathroom scale (the batteries are dead :lol: ). :mrgreen:

 

[John Tolhurst]

Mark,
if you are 50-50 on level ground, then you are about 40-60 on a 10%. But roads are deceptive, where it might be 10% over a section, it might be as much as 15% on particular places. On my sofrider outing yesterday I deliberately sat forward on the front of the seat, but stayed leaning back and spinning. Found it was ok that way, was able to regain traction. Also, high torque requires greater traction, so there are two solutions to lower torque, spin much faster but as smooth as you can, or change down and use a much longer duration power stroke. Either can work depending on the situation, because right at the most powerful 'home' cadence, your generate quite a high spike in torque output in the middle of the stroke. Our aim is to keep overall power output high, but remove the spike.

The other obvious but sometimes overlooked option on a high performance bike is to lower tire pressure, which has a direct relationship to traction due to increased contact area. A 700c x 28 will have the same contact area at 120psi as a 700c x 23 at the same pressure - by definition.

On rough pavement, high pressure might not always give lower rolling resistance. Sometimes I suspect a lower pressure will prevent changes of elevation of the frame over rough surfaces. Changes of elevation, i.e. bumps cause higher rolling resistance, as I understand it. On good quality pavement, as high a psi as you like, but on poor surfaces I wonder if a lower psi gives a better all round experience.

I hope this gives you some other angles to consider. We are all very keen to follow your progress.

 

[John Tolhurst]

And Mark,
another obvious thing but worth mentioning in this round up is that as your fitness improves, your speed uphill will improve, and THAT will have a direct bearing on traction. Very difficult wheelspin at higher speeds. So, there is some motivation. Go faster, less wheelspin. I'm sure this ameliorates the wheelspin I would otherwise get around Perth. The hills are generally not that extended, so I am able to keep momentum. No choice really given my 170 crank 39F 27R on 700c x23 lowest gear!!!! :roll:

 

[Brian Lewis]

As you know I did some serious hill climbing recently on my Silvio.

1) I would highly recommend a 30 in front and a 27 in the rear, my 30/23 combination worked but the 27 would have helped keep the cadence higher to reduce stress on the knees

2) I run 125 in my front shock and find its the best for my weight (160-165lbs)

3) I'm running Continental Grand Prix 4 Seasons 700x28 at 85psi. On some of the 12-15 degree hills I had a slight issue if the pavement was wet, in all other cases I had no wheel slippage. The 700x28 allows me to run a lower psi, I'm not in a race, so I don't need a 23c tire.

 

[Mark B]

Brian Lewis wrote: As you know I did some serious hill climbing recently on my Silvio.

1) I would highly recommend a 30 in front and a 27 in the rear, my 30/23 combination worked but the 27 would have helped keep the cadence higher to reduce stress on the knees

I'm running a 30-23, also.

Brian Lewis wrote: 2) I run 125 in my front shock and find its the best for my weight (160-165lbs)

I would think that would be pretty stiff. I go 250 and when I hit a bump with the shock at 125, the front wheel comes off the ground momentarily. Under power on a climb, NOT a good thing. Today, I reduced my pressure to 110 and that really seemed to help. I'm going to run it at that for a few more times before I call it my setting.

Brian Lewis wrote: 3) I'm running Continental Grand Prix 4 Seasons 700x28 at 85psi. On some of the 12-15 degree hills I had a slight issue if the pavement was wet, in all other cases I had no wheel slippage. The 700x28 allows me to run a lower psi, I'm not in a race, so I don't need a 23c tire.

I'm running 25c tires and 28's very well could be the hot ticket. Certainly I can understand how the increased contact patch with the wider tire could make a huge difference.

Thanks for the input!

Mark

 

[Rick Harker]

Hi Guys,
I'm not sure about the compound in the 4 seasons but take a look at the continental 4000 's'.
Its super sticky even compared to the 4000 but the downside is $'s. If it fixes the problem though...

Regards,

Rick.

 

[Mark B]

Rick Harker wrote: Hi Guys,
I'm not sure about the compound in the 4 seasons but take a look at the continental 4000 's'.
Its super sticky even compared to the 4000 but the downside is $'s. If it fixes the problem though...

Regards,

Rick.

Per continental's website:

Quote: But the Grand Prix 4000 S can do more than just look good. With the new Black Chili Compound rolling resistance is reduced by 26%, grip is increased by 30% and mileage is increased by 5%.

It all sounds wonderful, but they only come in 23's. :x

Mark

 

[John Tolhurst]

28s and 23s give identical traction with identical rubber and pressure because the contact area on the road is the same, right? :geek:

 

[Rick Harker]

Stats are a wonderful tool to have if you can back it up. From the factory you will get those from their "testing conditions" for marketing purposes.
If you get to touch one of these though you will immediately feel the difference from other tyres. It feels much like that of motor racing tyres. Rolling resistance. Hmmm! Lasting longer. Hmmm!
If it offers better traction resulting in performance and more importantly the inherent safety and confidence then its worthwhile.
And if you look at the stats... well don't. Put one in your hand first.

Regards,

Rick.

 

[John Tolhurst]

Speed up a constant incline is inversely proportional to total weight, and traction is proportional to speed. So traction is inversely proportional to weight.

Gee I wish I could remember more of my high school physics and maths. :idea:

 

[Flasharry]

johntolhurst wrote: 28s and 23s give identical traction with identical rubber and pressure because the contact area on the road is the same, right? :geek:

Sorry John, you will have to explain that to me as i am a bit thick. Surely a wider tyre will have a slightly wider contact patch than a narrower tyre at the same pressure?

Stuart.

 

[John Tolhurst]

Stuart, I think the physics is that the road resists the force of the tire. If the weight on the front wheel is 60 lbs and the tire is at 120psi, then that means 0.5 square inches will exert a pressure of 60 lbs. That means the contact patch will be 0.5 sq inches. Note that you don't have to know the size of the tire to know the contact area.

Increases in wheel diameter elongate the oval shaped contact path and reduce its width - because the contact area is the same (if pressures and loadings are the same). Reduced width of the oval contact path means less distortion of the tire and this is why larger diameters roll better.

 

[Mark B]

So, correct me if I missed something here. The key to increasing traction, besides dialing in suspension and removing weight from my fat butt, is reducing tire pressure? Currently, I like to run 100 PSI. Perhaps reducing the tire pressure on the front to, say, 90 PSI will increase the contact patch and in theory, the traction? Is that what I'm getting out of this? Would there be any gain by leaving the rear tire at 100 PSI, or even increasing the tire pressure? I'm just thinking that since the rear tire is just a drag tire, maybe you could offset some of the potential increase in rolling resistance. In my pea brain, this makes some sense.

Mark

 

[John Tolhurst]

That also makes sense in my pea brain, Mark.

 

[Mark B]

johntolhurst wrote: That also makes sense in my pea brain, Mark.

Cool, then that's what I'm going to do!

Thanks,

Mark

 

[Flasharry]

Thanks for the physics lesson John, it seems I learn something new every day with a Cruzbike.
Stuart.

johntolhurst wrote: Stuart, I think the physics is that the road resists the force of the tire. If the weight on the front wheel is 60 lbs and the tire is at 120psi, then that means 0.5 square inches will exert a pressure of 60 lbs. That means the contact patch will be 0.5 sq inches. Note that you don't have to know the size of the tire to know the contact area.

Increases in wheel diameter elongate the oval shaped contact path and reduce its width - because the contact area is the same (if pressures and loadings are the same). Reduced width of the oval contact path means less distortion of the tire and this is why larger diameters roll better.