[Westy]

Local DOT seems to be conspiring to make my rides miserable. In the last month they have put a fresh layer of the coarsest chipseal down on two of my favorite routes. Areas where I could cruise at 20mph I am now killing myself to hold 17. I already run fairly low pressure in the tires but was thinking that running some 25's or 27's might roll better. Would a larger tire actually have better rolling resistance on really rough roads?

 

[LordOpie]

I think 20s are just too narrow, but 23 to 25, I think it's far more about the PSI. I think the contact patch is the same area for both widths at the same PSI.

What's your current PSI?

 

[Westy]

I think 20s are just too narrow, but 23 to 25, I think it's far more about the PSI. I think the contact patch is the same area for both widths at the same PSI.

What's your current PSI?

I usually run about 90 psi in 23mm tires.

 

[LordOpie]

You must be pretty skinny to get away with 90?

What happens if you go to 110psi? Too much vibration? Aluminum bike? Can you tires and wheels handle 100+?

 

[luelling]

Where I used to live, they chip sealed everything and it really sucked. I normally had 23s with 110 in em and it worked, but the vibration sucked. The only upside to the chip seal, it will make you stronger as you push to get back to 20 mph.

If you go with a wider tire it may be a more comfortable ride, but it will give more rolling resistance. So....I have no good solution for you, I just felt like babbling on

 

[Westy]

Tires and wheels can handle 120. The bike has carbon fork and stays and was designed more for comfort than speed, it is a Fuji Marseille. Anything over 100psi and things get harsh on the crap roads. When on smoother roads I run 110 and everything is fine.

 

[LordOpie]

Wow, you guys make part Aluminum bikes sound like the devil.

 

[LordOpie]

If you go with a wider tire it may be a more comfortable ride, but it will give more rolling resistance.

Are you sure about that? I forgot where I read it, but someone broke down the physics of it all and if I remember correctly, the summary was: same PSI, same size contact patch.

 

[Westy]

Wow, you guys make part Aluminum bikes sound like the devil.

Actually the bike rides quite nice. I am more concerned with rolling resistance than comfort. On rough roads you actually have less resistance with a lower pressure, I was wondering if the same affect could be said with larger tires. I could actually do a fairly scientific test if I was so inclined.

From a lennard Zinn Q&A

Dear Tom,
I agree with Josh, and yes, there are lots of test numbers to back it up. It is the same reason a suspension bike (or car) is faster over rough ground - less mass must be accelerated when bumps are encountered, thus saving energy and reducing momentum loss. Every little bump that gets absorbed into your tire (another reason that supple, handmade casings roll faster than stiffer, low-thread-count casings) is a bump that does not lift the entire weight of you and the bike.

You feel fast on a rock-hard tire for a similar reason that people like the feel of stiff brakes (V-brakes with the levers set on low leverage). The brake feels good and stiff because you are doing more of the work. If you increase the leverage, the brake feels spongy, because the extra mechanical advantage allows a modest pull to squish the pads.

When you ride a tire at 170psi, the bike feels really lively and fast. That is because you are being bounced all over the place by the surface roughness of the road. However, every time you are bounced, energy you applied to the pedals to get you up to speed is lost. Also, you have less control of the bike, so it feels like it is going faster, even though it isn't. Ever notice how driving down the highway at 75mph in an old Jeep feels crazy fast, and you can cruise smoothly along at 100mph in a nice Saab or BMW and feel like you are going maybe 60mph unless you are looking at stationary objects passing by?

There is simply no question about it; rolling resistance tests conducted with bicycle tires rolling over surfaces akin to normal road surfaces always indicate the lowest rolling resistance at pressures a lot closer to 100psi than to 170psi! Years ago, for example, I saw results like this at the Continental tire factory. I was told of similar results at a number of other tire factories I have visited.
Lennard

 

[LordOpie]

Would chip seal be considered bumps?

 

[luelling]

Lennard Zinn doesn't know what he is talking about j/k I have heard the pressure argument, although I think a wider tire will give more resistance (depending on the shape of the tire)

 

[luelling]

Would chip seal be considered bumps?

hell yes, especially with the way they do it in Southern Oregon

 

[golgiaparatus]

Would chip seal be considered bumps?

I thought it was those clip things that keep your Tato chips from getting stale.

 

[GravityFreakTJ]

I think a wider tire will give more resistance (depending on the shape of the tire)

i'm willing to bet it's round






:biggrin:

 

[luelling]

i'm willing to bet it's round

If is made by Nokian its square :biggrin:

 

[splat]

They just Chipsealed , what used to be my favorite road on my commute

 

[Wumpus]

They just Chipsealed , what used to be my favorite road on my commute

Going to have to give up those 20s with 140psi, eh?

 

[MMcG]

Is chipsealing the same as throwing down that oil stuff and then throwing gravel on top of it and then using cars and maybe a roller to help it all imbed?

If so, that stuff sucks monkey balls.

 

[Serial Midget]

Is chipsealing the same as throwing down that oil stuff and then throwing gravel on top of it and then using cars and maybe a roller to help it all imbed?

If so, that stuff sucks monkey balls.

Yes.

A few years back my group was 20 miles into a fast paced 30 mile ride when we ran into a fresh chipseal project. We were all on the skinnies - I was on 19mm at 170psi. The project was so fresh the gravel had not even been rolled. We were pumping pretty hard and hit the first patch going down hill - at first just large loose gravel but it kept getting deeper up to maybe 1" in spots. We fishtailed at 5 MPH - the most grueling 3 miles I have ever done on a road bike.

Set chipseal doesn't bother me at all - I ride steel.

I say that fat tires will have the same resistance as skinnies if you are running lower PSI.

 

[splat]

Going to have to give up those 20s with 140psi, eh?

No , I'll just go a different route . about a mile longer . and/or take the punishment it puts out.