| View previous topic :: View next topic |
| Author |
Message |
Scaredy_Cat
Barking
Joined: Sep 21, 2006
Posts: 1,907
Location: Daydreaming...
|
 Posted: Tue 28/Oct/08 8:52am Post subject: |
  |
|
| Roma wrote: | Very, very possibly. But combined with an exaggerated sense of paranoia and wussy descending skills it becomes VERY real  |
From a fellow wussy descender 
I found it depended on the tyre a lot - had some Hutchinson Fusions that if I ran at 100psi my bike felt like Skippy the kangaroo  . I now use Michelins - either pro-grip or pro-race & they stick well beyond my ability to find their limits! I usually run them at around 90psi - but they seem to be quite forgiving if I forget to pump them up or someone overinflates them 
All very much IMHO - and from the point of view of a small person who rides downhill like a chicken. 
|
|
|
| Back to top |
|
 |
ryda
OLD
Joined: Jan 30, 2006
Posts: 6,528
Location: driven' the Church Bus
|
| Posted: Tue 28/Oct/08 10:39am Post subject: |
|
|
| Scaredy_Cat wrote: | or someone overinflates them
|
who would do that ??
|
|
|
| Back to top |
|
|
cyclenutnz
Ridden
Joined: Nov 20, 2006
Posts: 158
Location: Cambridge
|
| Posted: Tue 28/Oct/08 8:53pm Post subject: |
|
|
Roma: Are you sure that what you are feeling is bad? Or just different. Whack it down to the 90 you should be at and give it a try - you won't lose anything by giving it a try for a couple of rides (just take the corners easy at first if you're worried). This is the easiest/cheapest way for you to improve comfort and speed - so why not experiment a bit.
A tyre with higher TPI has less friction between the threads and is thus more flexible - so it deforms more easily. This means that it creates a wider contact patch which gives more area to disperse the pressure over (think of high heels vs flats - much higher pressure from stilletos). However, if you go pumping your tyres to the max (and bear in mind that most clincher rims are only rated to 120psi anyway) you don't give the tyre a chance to deform.
And the larger contact patch gives better traction as Oli mentioned.
110psi does not feel squidgy. Squidgy is 50psi (remembering that I'm over 90kg), which occasionally happens on the commuter and I wonder why it is slow and dodgy in corners.
|
|
|
| Back to top |
|
|
Roma
Scuffed
Joined: Jun 23, 2007
Posts: 489
Location: Mount Maunganui
|
| Posted: Wed 29/Oct/08 7:12am Post subject: |
|
|
Hey cheers for all the advice guys.
But going from consistently being at 120, where it is rock hard and there is absolutely no visible deformation of the tire at all to physically being able to see the tyre deforming at 110, even if just a few mm, looked and felt quite unnerving.
But now that I know it's going to be more beneficial for my riding to be lower I am going to have to do it! I have a couple of pairs of racing tyres (Michelin Prorace and Vittoria Open Corsa) that I've not used much, I might start off using them to give myself the best advantage of a good tire, and slowly lower it in increments of 5 per ride.
Feels like every time I feel like I am riding good and have sorted one thing out, I think of another 5 things that could do with improvement too!
|
|
|
| Back to top |
|
|
Tristan
Scuffed
![]()
Joined: Apr 15, 2003
Posts: 447
Location: Building wheels
|
| Posted: Wed 29/Oct/08 7:58am Post subject: |
|
|
| cyclenutnz wrote: |
A tyre with higher TPI has less friction between the threads and is thus more flexible - so it deforms more easily. |
Just watch out for "fake" TPI ratings; a couple of companies used to lay two layers of 160tpi on top of each other and call it 320tpi which isn't really the truth. My memory is fading but I think Hutchinson were guilty of this, however looking at their recent catalog these claims don't seem to be made.
For example a Veloflex Pave uses a true 300 tpi fabric layered twice...they correctly claim this is 300tpi, not 600tpi.
|
|
|
| Back to top |
|
|
Antho_man
Ridden
Joined: Nov 05, 2007
Posts: 149
|
| Posted: Wed 29/Oct/08 12:11pm Post subject: |
|
|
| Oli wrote: | Less pressure = more traction = more stability = safer descending.
This is not just my opinion but the finding of many many riders as well as innumerable studies.
I repeat, I'm 100 kg and if I don't suffer from "squirming" tyres I would be very surprised if you do...unless you're considerably heavier than I am? |
ok well i dont find this. i run 120psi regradless of what im doing. and find if i run it lower. like lower then 100psi. the rim moves on the tyre. k on a road bike it very little movement.
so to extrment this. i rode my MTB bike with a lower then recmended psi in and poped the tyre right off the rim come down a sharp coner on a hill this happnd twice.
the bike did climb better. but going down it scary.so i allways ride just below max psi rating on tryes now and i find the bike performs well
but in the end it how you ride. and what you feel comfy on.
|
|
|
| Back to top |
|
|
cyclenutnz
Ridden
Joined: Nov 20, 2006
Posts: 158
Location: Cambridge
|
| Posted: Wed 29/Oct/08 10:24pm Post subject: |
|
|
| Tristan wrote: | | Just watch out for "fake" TPI ratings; a couple of companies used to lay two layers of 160tpi on top of each other and call it 320tpi which isn't really the truth. My memory is fading but I think Hutchinson were guilty of this, |
Dear old Conti were notable offenders on this front. I have a vague recollection of hutchy doing the same but never really paid attention to their tyres - it was well known that postal and the other teams weren't actually using the sponsors product.
|
|
|
| Back to top |
|
|
Stun
![]()
Joined: Jan 03, 2003
Posts: 35,546
|
| Posted: Wed 29/Oct/08 10:32pm Post subject: |
|
|
| Antho_man wrote: | | Oli wrote: | Less pressure = more traction = more stability = safer descending.
This is not just my opinion but the finding of many many riders as well as innumerable studies.
I repeat, I'm 100 kg and if I don't suffer from "squirming" tyres I would be very surprised if you do...unless you're considerably heavier than I am? |
ok well i dont find this. i run 120psi regradless of what im doing. and find if i run it lower. like lower then 100psi. the rim moves on the tyre. k on a road bike it very little movement.
so to extrment this. i rode my MTB bike with a lower then recmended psi in and poped the tyre right off the rim come down a sharp coner on a hill this happnd twice.
the bike did climb better. but going down it scary.so i allways ride just below max psi rating on tryes now and i find the bike performs well
but in the end it how you ride. and what you feel comfy on. |
Rolling a tyre or having it move on a road bike has more to do with a worn chamfer on your tyre, than on the pressure. If the tyre has a poor quality or worn chamfer, then yep, you'll see movement. Not a lot... but some.
On a mountain bike, rolling a XC tyre off at low pressures only happens to me if I land sideways, or I'm being stupid and running 15 psi... and burp my UST tyre mid-berm.
I used to run my Michelin DH tyres at 19-23 psi regularly. No popping of tyre beads... BUT I did damage the tyres chamfer, and it popped off on me after about a 8 months of use. From there, the tyre would never re-seat fully and was consigned to the sparc heap. Aparantly it's common on 2.8 Michelin's and 3.0 Gazza's where super low pressures are not only achievable, but also quite common.
|
|
|
| Back to top |
|
|
specializedman
Worn
Joined: Jan 13, 2008
Posts: 799
|
| Posted: Wed 29/Oct/08 11:42pm Post subject: |
|
|
You will struggle to roll a road tyre off.
I rode 10km home the other day on a flat tyre including some big decents and tough grinding up hills. I only weigh 70kg though.
The tyre was still good when I changed the tube and pumped it up!
|
|
|
| Back to top |
|
|
jo
Windy
Joined: Jun 20, 2003
Posts: 4,058
Location: Melbourne
|
| Posted: Thu 30/Oct/08 12:23am Post subject: |
|
|
 you can roll a road tyre off - again if the bead is deformed, such as with a kevlar beaded tyre, perhaps improperly inflated w gas. I have done so and i do not recommend trying it.
After i got my cast off, Tyre was refitted to wheel and could not hold the rim. Tyre was binned. now im paranoid about both gas and kevlar beaded tyres.
|
|
|
| Back to top |
|
|
HamishW
Joined: Feb 11, 2008
Posts: 12
|
| Posted: Thu 30/Oct/08 11:11am Post subject: |
|
|
I cant believe thats all the pressure ppl run in their tubs. I run 160psi in my Vittoria EVO CORSA KXs in the dry, and 140psi in the wet. I would never run anything lower than 140psi.
Although maybe the 808's soak a few of the bumps up.
My training wheels would run 120psi in the Vittoria Rubino clinchers and they are comfortable as.I am 80kgs, so that might help too
|
|
|
| Back to top |
|
|
Oli
Mangled
Joined: Aug 03, 2005
Posts: 32,945
|
| Posted: Thu 30/Oct/08 1:02pm Post subject: |
|
|
|
Tubulars are different - I'd usually run 20-30psi more than I would on a clincher tyre.
|
|
|
| Back to top |
|
|
FLATULENTFRIEND
Scuffed
Joined: Oct 04, 2008
Posts: 439
|
| Posted: Thu 30/Oct/08 7:04pm Post subject: |
|
|
| Oli wrote: | | Tubulars are different - I'd usually run 20-30psi more than I would on a clincher tyre. |
What about tubs that are rated up to 220psi?
Is that realistic? 
|
|
|
| Back to top |
|
|
istepinyards
Wrecked
Joined: Feb 13, 2007
Posts: 6,118
Location: Rooting for the SunDevils
|
| Posted: Thu 30/Oct/08 7:12pm Post subject: |
|
|
| FLATULENTFRIEND wrote: | | Oli wrote: | | Tubulars are different - I'd usually run 20-30psi more than I would on a clincher tyre. |
What about tubs that are rated up to 220psi?
Is that realistic? |
Ever heard the sound of one blowing up in a confined space
Makes a mess in your undergarments 
|
|
|
| Back to top |
|
|
twinshock750
Dusty
Joined: Aug 31, 2007
Posts: 56
Location: Auckland
|
| Posted: Thu 30/Oct/08 9:46pm Post subject: |
|
|
| istepinyards wrote: | | FLATULENTFRIEND wrote: | | Oli wrote: | | Tubulars are different - I'd usually run 20-30psi more than I would on a clincher tyre. |
What about tubs that are rated up to 220psi?
Is that realistic? |
Ever heard the sound of one blowing up in a confined space
Makes a mess in your undergarments |
says the man with an avatar of of devil holding a pitch fork! I found that quite amusing for some reason!
|
|
|
| Back to top |
|
|
|
