Speed differential between road and mtn bike wheels

I ride a mtn bike with 1.35" tyres and rigid forks and just wondered
approximately what the speed differential was between a road bike and a
mountain bike.

I read somewhere recently that a 10 mile time trial in 30 mins on a
road bike would be a 4th category road race.

So I'm just trying to work out the conversion..


--
dannyfrankszzz

dannyfrankszzz wrote:
I ride a mtn bike with 1.35" tyres and rigid forks and just wondered
approximately what the speed differential was between a road bike and a
mountain bike.

I read somewhere recently that a 10 mile time trial in 30 mins on a
road bike would be a 4th category road race.

So I'm just trying to work out the conversion..

I can't quite give you an exact comparison, but I have done the same
commute on my road bike, hybrid and mtb (with knobblies).
Road bike - ave 35mins, fastest 33mins
Hybrid - ave 38mins, fastest 35mins
MTB - ave 39mins, fastest 37mins

This route has a some lights and traffic, a few hills,
but also some long fast sections.

I reckon over 10 miles you might be 2-3mins quicker with a road bike
than an mtb with slicks

You could also try playing about with the parameters he
http://www.kreuzotter.de/english/espeed.htm

Share and enjoy !

Douglas

Am Tue, 5 Sep 2006 06:35:11 +1000 schrieb dannyfrankszzz:

I ride a mtn bike with 1.35" tyres and rigid forks and just wondered
approximately what the speed differential was between a road bike and a
mountain bike.

I read somewhere recently that a 10 mile time trial in 30 mins on a
road bike would be a 4th category road race.

So I'm just trying to work out the conversion..

The speed difference depends on a lot of factors. If you would use a
similar gear ratio on mtb and racebike and all other conditions are
similar, then you might be 1 or 2 mph faster. With a high pressure slick on
the mtb the difference might even be less. Play around a bit with this
website, and you get an idea:
http://www.kreuzotter.de/english/espeed.htm

Andreas

in message ,
dannyfrankszzz ')
wrote:

I ride a mtn bike with 1.35" tyres and rigid forks and just wondered
approximately what the speed differential was between a road bike and a
mountain bike.

I read somewhere recently that a 10 mile time trial in 30 mins on a
road bike would be a 4th category road race.

It isn't really the wheels, it's really the tyres. Narrow, high pressure
slicks are worth about 10% of total power (on tarmac) over fat, low
pressure knobblies. It's a big difference. Mountain bike hubs typically
have better mud sealing of the bearings, and this adds a little bit of
drag, but not very much.

Your tyres aren't that fat and you don't say whether they're slick or
not. If they are, then, providing you've got them up to at least 80psi
and ideally higher, the improvement you'd get from narrower ones isn't
all that great - probably less than 1%.

Obviously, the other thing with mountain bikes is aerodynamics - the
smaller you can get your frontal area, the less aerodynamic drag you
will have, and this is where road bike geometry and especially drop bars
are a win.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/
;; Generally Not Used
;; Except by Middle Aged Computer Scientists

dannyfrankszzz wrote:
I ride a mtn bike with 1.35" tyres and rigid forks and just wondered
approximately what the speed differential was between a road bike and a
mountain bike.

I read somewhere recently that a 10 mile time trial in 30 mins on a
road bike would be a 4th category road race.



When I moved from a MTB to a road bike, I gained around 2mph average
speed on all my regular rides on road. That was with 2.1" semi slick
tyres at 60psi on the MTB and 25mm tyres at 110psi on the road bike.

Pete

Simon Brooke wrote:
in message ,
dannyfrankszzz ')
wrote:

I ride a mtn bike with 1.35" tyres and rigid forks and just wondered
approximately what the speed differential was between a road bike and a
mountain bike.

I read somewhere recently that a 10 mile time trial in 30 mins on a
road bike would be a 4th category road race.

It isn't really the wheels, it's really the tyres. Narrow, high pressure
slicks are worth about 10% of total power (on tarmac) over fat, low
pressure knobblies. It's a big difference. Mountain bike hubs typically
have better mud sealing of the bearings, and this adds a little bit of
drag, but not very much.

Your tyres aren't that fat and you don't say whether they're slick or
not. If they are, then, providing you've got them up to at least 80psi
and ideally higher, the improvement you'd get from narrower ones isn't
all that great - probably less than 1%.

Obviously, the other thing with mountain bikes is aerodynamics - the
smaller you can get your frontal area, the less aerodynamic drag you
will have, and this is where road bike geometry and especially drop bars
are a win.

IMHO the tyre makes most difference at slow speeds. If you average
12mph on a MTB with knobs on, then expect to get big gains by changing
tyres as they are one of the major sources of energy loss.

As the speed increases the position becomes more important. I can get a
realtively low and stretched position on both MTB and road bike but
there is still a difference. Road bike on 25mm slicks beats the MTB on
1.3 (37mm) slicks considerably once the speed gets up to the low 20's.
It's worth 5mph on a downhill stretch. On the MTB I do 35/36mph, on the
road bike just about/over 40. With putting my palms on the end of the
bar ends and stretching down I can average19/20 mph on the flat with
the MTB.

So the answer is yes they make a difference , especially in the effort
needed to just keep the bike rolling on the flat, but how much depends
on the differences in position.definitely worth puting slicks on for
road use.

...d

dannyfrankszzz
wrote:

I read somewhere recently that a 10 mile time trial in 30 mins on a
road bike would be a 4th category road race.

That time would be a 'never done it before' time in any TT. 4th Cat RR
would average 23-25mph, maybe more over 40 miles.
I've done the RR series at Mallory Pk, I'm crap at TT's, 26:30 is my
best ever time, yet I was REALLY struggling to keep up with the pack in
a 3 and 4 Cat RR. Someone who could only do a 30 min/10 would never
keep up.
The only race that I wasnt lapped, I did the fastest I have ever done
before, averaging around 27mph.It was the drafting that made me go so
well, I could never average such a speed on my own.
Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.

in message . com, David
Martin ') wrote:


Simon Brooke wrote:
in message ,
dannyfrankszzz
') wrote:

I ride a mtn bike with 1.35" tyres and rigid forks and just wondered
approximately what the speed differential was between a road bike
and a mountain bike.

I read somewhere recently that a 10 mile time trial in 30 mins on a
road bike would be a 4th category road race.

It isn't really the wheels, it's really the tyres. Narrow, high
pressure slicks are worth about 10% of total power (on tarmac) over
fat, low pressure knobblies. It's a big difference. Mountain bike hubs
typically have better mud sealing of the bearings, and this adds a
little bit of drag, but not very much.

Your tyres aren't that fat and you don't say whether they're slick or
not. If they are, then, providing you've got them up to at least 80psi
and ideally higher, the improvement you'd get from narrower ones isn't
all that great - probably less than 1%.

Obviously, the other thing with mountain bikes is aerodynamics - the
smaller you can get your frontal area, the less aerodynamic drag you
will have, and this is where road bike geometry and especially drop
bars are a win.

IMHO the tyre makes most difference at slow speeds.

Then you are this: flat wrong. I'm not sure that the rolling resistance
differential varies with speed, but as speed goes up, what that
difference is worth in energy put in increases.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

my other car is #Subr-Car: #5d480
;; This joke is not funny in emacs.

Simon Brooke wrote:
in David Martin ') wrote:

IMHO the tyre makes most difference at slow speeds.

Then you are this: flat wrong. I'm not sure that the rolling resistance
differential varies with speed, but as speed goes up, what that
difference is worth in energy put in increases.

I think it's ambiguous. The tyre makes most difference at slow speeds
in the sense that at high speeds aerodynamics make more difference
than the tyre and at low speeds aerodynamics they don't.

"Simon Brooke" wrote in message
...
in message ,
dannyfrankszzz ')
wrote:

I ride a mtn bike with 1.35" tyres and rigid forks and just wondered
approximately what the speed differential was between a road bike and a
mountain bike.

I read somewhere recently that a 10 mile time trial in 30 mins on a
road bike would be a 4th category road race.

It isn't really the wheels, it's really the tyres. Narrow, high pressure
slicks are worth about 10% of total power (on tarmac) over fat, low
pressure knobblies. It's a big difference. Mountain bike hubs typically
have better mud sealing of the bearings, and this adds a little bit of
drag, but not very much.

Your tyres aren't that fat and you don't say whether they're slick or
not. If they are, then, providing you've got them up to at least 80psi
and ideally higher, the improvement you'd get from narrower ones isn't
all that great - probably less than 1%.

Obviously, the other thing with mountain bikes is aerodynamics - the
smaller you can get your frontal area, the less aerodynamic drag you
will have, and this is where road bike geometry and especially drop bars
are a win.

My experience of riding a hybrid with road / touring tyres and a mountain
bike with slicks is that there's definately less rolling resistance. I don't
know if this down to MTB rims being wider, the smaller radius of the wheel
or what, but it definately seems that there's a fair rolling resistance
difference between the two.