Road Cycling

Dunks · 29 Jul 2015 at 17:04

Running 28's on my bike, lower rolling resistance than 25's but I'm sure the increased rotating weight penalty doesn't help

I'm sure I read that 25mm GP4000 II's measure up around 28mm though.

uv · 29 Jul 2015 at 17:28

Rode in (and will be riding home) on 35c nobblies. Christ they're slow

slipd · 29 Jul 2015 at 18:28

Right, a new one on me guys, from a MTB background anyway, I've just fitted my new Conti Grand Prix 4000s and although the back one is fine the front one, at anywhere near 120psi, is rubbing against the top of my forks... I lower the pressure - right down, and it stops

The new tyres are exactly the same size as my last ones, any ideas?

Vonhelmet · 29 Jul 2015 at 18:47

The new tyres aren't the same size

What were the last tyres you had? What width were they and the new ones supposed to be? Some tyres measure up big. Decent contis do, as do some michelins.

slipd · 29 Jul 2015 at 18:53

Both the old one's and the new are 700x25c. I made sure of that

Do I just run the new ones with less pressure, is that okay? I think I'm good to about 100 psi.

FrenchTart · 29 Jul 2015 at 18:57

You probably shouldn't be running near 120psi on 25mm tyres. 90-100, depending on your weight.

Even if your new tyres are 25mm and your old were it is likely that they are different sizes...unless you bought the exact same model/revision of tyre.

ShiWarrior · 29 Jul 2015 at 19:01

slipd said:
Right, a new one on me guys, from a MTB background anyway, I've just fitted my new Conti Grand Prix 4000s and although the back one is fine the front one, at anywhere near 120psi, is rubbing against the top of my forks... I lower the pressure - right down, and it stops

The new tyres are exactly the same size as my last ones, any ideas?

They shouldn't be touching or near your forks
25c ones, put 80 psi on them
23c go up to 100

slipd · 29 Jul 2015 at 19:02

No, completely different tyres. Budgets to premiums

Okay then, I'm about 15 stone so less pressure is okay? Thanks chaos, I'm a compete novice on my road bike!

lordrobs · 29 Jul 2015 at 19:04

FrenchTart said:
That's hilarious

Not if you are the owner of the Fiesta who had done nothing wrong. Their car got crunched by the front of the one he was dragging round.

ShiWarrior · 29 Jul 2015 at 19:06

slipd said:
No, completely different tyres. Budgets to premiums

Okay then, I'm about 15 stone so less pressure is okay? Thanks chaos, I'm a compete novice on my road bike!

im 11 stone and I don't have any problems with the tyre pressures, if 80 psi doesn't feel enough, up it by 5 psi

lordrobs · 29 Jul 2015 at 19:20

...or use the widely accepted 15% drop calculation http://www.dorkypantsr.us/bike-tire-pressure-calculator.html to give yourself a starting figure to work to.

I made the same mistake on my hybrid running 40 mm tyres at 80 psi because that was the max and max=fastest - WRONG!

grudas · 29 Jul 2015 at 19:20

lordrobs said:
Not if you are the owner of the Fiesta who had done nothing wrong. Their car got crunched by the front of the one he was dragging round.

Party pooper

Roady · 29 Jul 2015 at 19:46

slipd said:
Okay then, I'm about 15 stone so less pressure is okay? Thanks chaos, I'm a compete novice on my road bike!

lordrobs said:
...or use the widely accepted 15% drop calculation http://www.dorkypantsr.us/bike-tire-pressure-calculator.html to give yourself a starting figure to work to.

120 PSI would be too much for anything unless you were riding track/race circuit on 22mm/23mm's. Or have bawls of steel

For normal road use I found 23mm's are best around 90-95 PSI and 25mm's are best 85-95 PSI depending on comfort levels.

FrenchTart · 29 Jul 2015 at 20:05

15% drop is definitely the pro way to go. Choose the 45/55% split options for front/back weight load however.

PermaBanned · 29 Jul 2015 at 20:07

I mean, let's not pretend that it's universally accurate, the website itself lists several valid criticisms of the method. It's probably a good starting point but it's not going to work for everybody.

FrenchTart · 29 Jul 2015 at 20:16

PermaBanned said:
I mean, let's not pretend that it's universally accurate, the website itself lists several valid criticisms of the method. It's probably a good starting point but it's not going to work for everybody.

Fair point. It's definitely the way to go rather than inflating your tyres to maximum rated pressure and assuming that is right though (at least initially).

tedmaul · 29 Jul 2015 at 20:18

FrenchTart said:
15% drop is definitely the pro way to go. Choose the 45/55% split options for front/back weight load however.

That says I should be running my 25mm GP4000s at 62 front and 77 rear. Surely not?! I'd be bouncing all over the shop and getting pinch flats all the time on our crappy roads.

Vonhelmet · 29 Jul 2015 at 20:32

I think I usually end up at about halfway between the min and max on my tyres.

James07 · 29 Jul 2015 at 20:51

Roady said:
They work but they do flex and make loads of noise banging your tyres and from flexing (boingy clattering!). I found clearance ok with 23mm but really tight with 25mm and saw some rubbing. No matter how much adjusting I did.

Any idea what I could use? Need some sharpish tbh.

Jonny ///M · 29 Jul 2015 at 21:08

Not sure on the defy model but we had a marin that took mudguards but **** all fitted between the tyre and brake.

Portland design works do a nice metal guard that stops before the brake and a metal part about 1mm thick goes under the brake then the guard starts again.

Not cheap but seem good quality.

I don't get all the tyre pressure pish talking. I still think a 23mm feels better to ride hard than a 25mm.

23c gp4000 at 110r 100f for me. Grippy as and notably comfier to ride than an equivalent gatorskin.

Every one I've had has had the tyre sidewall thread thing. Been fine over time. The tread shouldn't be cracked like that, do you keeping it next to a radiator?