Questions about front tyre widths...

Paulus said:

On my mountain bike I can go really fast and feel quite stable (75kph),
My road bike feels a bit flighty at 75 and last weekend when I hit 80, the
front wheel felt like it was half filled with air (it was at 120psi).

That might be because it was spending a lot of time _in_ the air.
At 120psi, its too hard, bouncing off the road too much. On a smoother
road, or with lower pressure, you should get better handling.

Quoted message said:

My moutain bike has 26x1.25? tyres, my racer has 700x20c tyres.

Bigger tyres allow lower pressure, greater contact area, less bounce.

But what about the shock absorbers on your MTB!? They make a BIG
difference to handling at high speed on rough ground.

And frame design is very different. Road bikes are not designed for
stability. Try riding "no hands" on both bikes and compare.

Quoted message said:

So, my questions are:
*if I were to fit a 700x23c tyre to my front wheel, would the stability at
speed improve?

Probably. Try lowering pressure first. If that helps, but you are afraid
of pinch-flats, get the bigger tyre.

Quoted message said:

*do brands make a difference? I use continental grand prix foldable tyres.

I'd think not, in this case.
Some models have softer rubber, which gives better grip at the expense
of wear. But I dont think skidding is your problem.

HTH. These are just opinions - I'm relying on the group to correct any
major errors.

You should try to ask someoone to fix up the road and stop cycling down hill
at top speed if you are too chicken

"Paulus" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

On my mountain bike I can go really fast and feel quite stable (75kph),
My road bike feels a bit flighty at 75 and last weekend when I hit 80, the
front wheel felt like it was half filled with air (it was at 120psi).

My moutain bike has 26x1.25? tyres, my racer has 700x20c tyres.

So, my questions are:
*if I were to fit a 700x23c tyre to my front wheel, would the stability at
speed improve?
*do brands make a difference? I use continental grand prix foldable

tyres.

Quoted message said:

Thanks for any advice
P

Hmmm,
1stly. The rating of the tyres is 120psi. They seem to be fine when I belt
along the flats at 65kph. Slightly rough road surfaces do not phaze me
going downhill, just nasty crosswinds.
2ndly. 75kph is not top speed going down hill...closer to 90 is.

P
P.S. any more views/suggestions/2cents worth?

"Leon" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

You should try to ask someoone to fix up the road and stop cycling down

hill

Quoted message said:

at top speed if you are too chicken

"Paulus" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

On my mountain bike I can go really fast and feel quite stable (75kph),
My road bike feels a bit flighty at 75 and last weekend when I hit 80,

the

Quoted message said:

Quoted message said:

front wheel felt like it was half filled with air (it was at 120psi).

My moutain bike has 26x1.25? tyres, my racer has 700x20c tyres.

So, my questions are:
*if I were to fit a 700x23c tyre to my front wheel, would the stability

at

Quoted message said:

Quoted message said:

speed improve?
*do brands make a difference? I use continental grand prix foldable

tyres.

Quoted message said:

Thanks for any advice
P

Hi paulus.

Wow you go fast..lol

I'm not expert but i hope i can be a little helpfull: Regarding the tyre
widths question, I am wondering if the real issue is not that of
rotating weight of your wheels. Fatter tyres are going to provide for a
heavier rotating weight, and more gyroscopic energy being produced at
speed. Could the increased feeling of stability on the mountain bike
actually be because the mountain bike's rim and tyre set up is heavier
that the racer, therefore, providing more gyroscopic energy to bulldozer
over any irregularities in the road?

I have explored different rims on varous machines, and discovered that a
heavier rim tends to provide more stability at speed, However i dislike
the trade off of lack of respnisvness at low speeds and in climing.

Are you using aerodynamic rims?...if not, perhaps that could prove
usefull trade off between weight, aerodynamics and stability, since they
tend to be a little heavier with a positive design trade off at speed.

I'm a climber, and i prefer low profile rims for that job. And besides
that I'm too much of a fraidy cat to go screaming down a hill at 90
kilometres per hour...*GasP*

Perhaps its a matter of finding the right comprimise to suit your
machine and your riding style.

Also, is the geometry of the frame contibuting to the feel of the bike?
Maybe asking a friend to test ride it might provide some clues.

Anyhow, I'm definitely not an expert. I do hope this helps, however.

good luck, Claire

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Howdy, Paulus here again, looks like I'll not be going down any hills
with my Kronos for a while...I upgraded to a Learsport 8000 on Saturday
and thanks to today's poor weather am chomping at the bit needing a
spin. One thing I forgot to add (not that it'll make much differnece) is
the Kronos is running wolber gtx rim.

P

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Leon <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

You should try to ask someoone to fix up the road and stop cycling down

hill

Quoted message said:

at top speed if you are too chicken

Wow, this guy's a complete [censored], eh!
---
DFM

"Paulus" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

*if I were to fit a 700x23c tyre to my front wheel, would the

stability at

Quoted message said:

speed improve?
*do brands make a difference? I use continental grand prix foldable

tyres.

I have no idea about stability, etc. but I have a couple of points:

1) Almost everything I've read about choosing road tyres indicates
that you should go for 23C. They are common and fast.
http://tinyurl.com/rjuy

2) What is the point choosing a tyre based on its performance
at 75kph+ unless most of your riding is at 75kph+. Is this the
case? Choosing a fast tyre for 75kph+ will probably mean you
lose things like puncture resistance, durability, nice colours :-)

I guess if you commute down a 75kph hill daily, safety on this
hill would be important for you, but is it worth sacrificing other
tyre features for super high speed stability?

hippy
- rather wear out $5 brake pads slowing down than buy more
expensive tyres ;-)

Paulus said:

On my mountain bike I can go really fast and feel quite stable
(75kph), My road bike feels a bit flighty at 75 and last weekend when
I hit 80, the front wheel felt like it was half filled with air (it
was at 120psi).
My moutain bike has 26x1.25? tyres, my racer has 700x20c tyres.
So, my questions are: *if I were to fit a 700x23c tyre to my front
wheel, would the stability at speed improve? *do brands make a
difference? I use continental grand prix foldable tyres.
Thanks for any advice P

Why your road bike feels less attached to the road at high speeds? As
you indirectly pointed out, the main reason is a smaller contact area
with the road. Lighter weight and smaller contact surface, especially at
high psi, results in basically no tolerance for road imperfections. To
get the idea, look at racing cars. Over the time, race engineers have
come up with a balance between the amount of grip gain by increasing the
surface area, aka wider tyres, and its drawbacks such as increased drag
and aquaplaning.

Race bikes have resorted to narrow tyres primarily to save weight and
drag. This has been accomplished by applying high psi and stickier
compounds. However, travelling at speeds and temperatures above the
intended limits is risky. Remember the guy in TDF whose rear tyre blew
at a corner causing him multiple fractures and retirement from this
year's race?

Basically bikes are not designed to travel that fast ( for obvious
reasons!) on a regular basis. So neither your road bike nor the MTB are
the products of R&D with high speeds in mind.

Now as hippy pointed out, if you travel a lot at such high speeds, you
would need to look at more specialised tyres and brake pads.

Cheers,

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