Maximum speed for a mountain bike

stanislavkostov

Hello, I have a question - if a Tour de France competitor rides an average mountain bike on a flat road how fast can he go and what average speed can he achieve?


Sorry if the post is in the wrong section.

The Northern Monkey

depends.

stanislavkostov

On what?

paul.skibum

gearing, wheel size, tyres, weight of the bike etc

paul.skibum

Oh, and what drugs he's on!

The Northern Monkey

ha!

stanislavkostov

I mean average bike, that you can buy in any supermarket, nothing special.

And no drugs

The Northern Monkey

btw, regarding forum, this would be best in the crudcatcher.

A general answer would be - probably not as fast as he would go on a road bike.

paul.skibum

Google search got me this answer as I couldnt be bothered to do the maths myself:

For a gear ratio of 44:11 (front ring 44 tooth, rear cog 11 tooth), a speed of 32.7 mph on a mountain bike (tire diameter 26 inch) corresponds to a cadence (foot speed) of 105-106 rpm.

If you moved your feet faster :
120 rpm = 37.1 mph
150 rpm = 46.4 mph

Or if you changed your gearing (putting a larger ring on the front, for instance) ... for example, using a 48 tooth ring instead of the 44:
105 rpm = 35.6 mph
120 rpm = 40.4 mph
150 rpm = 50.6 mph

My personal best (over a distance of about a mile) is a cadence of 135 at a 44:11 gear ratio, which translates into 41.7 mph ... on low-profile knobbies (not true "mud" tires, but not road slicks either).

But I am suspicious now I re-read it that it is flawed.

paul.skibum

I reckon 35 mph would be a good guess as a top speed on a 2" knobbly tired mtb with standard 9 speed triple gearing

bennett_346

Why does it say that the tyre diameter is 26 inch?

Also it's just wrong, in every way.

The Northern Monkey

supermarket bikes only come with 7 or 8 speed though dont they?

bennett_346

paul.skibum wrote:

I reckon 35 mph would be a good guess as a top speed on a 2" knobbly tired mtb with standard 9 speed triple gearing

Why do the tyres matter?

Chunkers1980

Are these serious questions?

supersonic

Tyres matter because effective diameter influences overall gearing, and the type, tread and pressure influence rolling resistance depending on terrain.

Road bikes can be usually ridden faster on the road because the gearing is higher, and the air resistance and tyre resistance lower. But much can be done to even things out.

bennett_346

supersonic wrote:

Tyres matter because effective diameter influences overall gearing, and the type, tread and pressure influence rolling resistance depending on terrain.

Road bikes can be usually ridden faster on the road because the gearing is higher, and the air resistance and tyre resistance lower. But much can be done to even things out.

A tyre could have x amount of drag compared to another tyre but a more powerful rider could overcome this and add to the top speed, so the only limiting factor on a "supermarket bike" is the gear ratios.

Tyre diameter i'll give you but tread, volume and pressure do not matter, they simply increase the amount of energy needed to reach the top speed the gears will allow.

supersonic

Which is what I was alluding to with comments on resistance. If you cannot output the power required then you'll be slower if there is more resistance ie unable to push a higher gear.

Stu Coops

All about legs and lungs

bennett_346

No it isn't. What utter garbage :roll:

supersonic

cyd190468 wrote:

Then why do they call them 26inch wheels? The outer diameter of the rim is about 22inches so a 2inch tyre round the outside makes 26inches. Please get out a tape measure before replying.

This is correct and is the reason the term was adapted - the nominal diameter of the wheel with tyre fitted. Started a long time ago, and the term has stuck.

bennett_346

cyd190468 wrote:

Then why do they call them 26inch wheels? The outer diameter of the rim is about 22inches so a 2inch tyre round the outside makes 26inches. Please get out a tape measure before replying.

Not denying a rim to rim is 22 inches, im saying calling an average tyre 2 inches is nonsense. Heck, the selection of 5 tyres i have vary by just less than an inch!

paul.skibum

From Wikipedia (and therefore gospel):

26 inch wheel/ISO 559mm

26-inch clincher tires (with inner tubes) are the most common wheel size for mountain bikes. This tradition was started initially because the early mountain bike pioneers procured the wheels for their early bikes from American-made bicycles rather than the larger European standards in use. The typical 26-inch rim has a diameter of 559 mm (22.0") and an outside tire diameter of about 26.2" (665 mm). Increasingly common are tubeless tires conforming to the UST (Universal System Tubeless) standard pioneered by French wheel manufacturer Mavic in conjunction with tire manufacturers Hutchinson and Michelin.

I'd say my tyres are around 2 inches "deep" when inflated (i.e from tread to metal).

paul.skibum

So my quick maths tells me:

26" diameter = 82.3" circumference A mile is 63360".

rotate a tyre 770 times and it travels a mile.

35 miles per hour = 26950 rotations per hour or 450 per minute at a ratio of 1 to 1.

Chuck a 44t front and 11t rear equates to 4 rpm per crank so 112.5 turns of the crank per minute gives 35 mph. So that agrees with the borrowed post I put up earlier. I know in the flat sections of the Tour on their race bikes they average in excess of 50mph over long sections with the pelaton working together.

supersonic

Yep, the maths is correct, I usually use the figure of 120 rpm at the crank and 37mph (for a 26 inch diameter and 44/11 gearing).

Thing is with a road bike, they may have larger rims (622mm compared with 559mm), but the tyres are much less deep. The effective overall diameter can be quite similar, but of course road bikes often have higher gearing (saying that, many use an 12t top gear).

The main reason roadies use narrow tyres is aerodynamics - with weight and potential higher pressures also being an influence.

bennett_346

paul.skibum wrote:

So my quick maths tells me:

26" diameter = 82.3" circumference A mile is 63360".

rotate a tyre 770 times and it travels a mile.

35 miles per hour = 26950 rotations per hour or 450 per minute at a ratio of 1 to 1.

Chuck a 44t front and 11t rear equates to 4 rpm per crank so 112.5 turns of the crank per minute gives 35 mph. So that agrees with the borrowed post I put up earlier. I know in the flat sections of the Tour on their race bikes they average in excess of 50mph over long sections with the peloton working together.

Some sensible maths with no bollocks about tyre drag finally!

supersonic

Tyre drag makes a difference if you cannot push the gear! As does the aerodynamics of the tyre. A roadie jumping on to an MTB with wide tyres and tread will not be able to hit the same speeds than on an equivalently geared road bike.

bennett_346

Like i said that is to do with the power input, ie the rider. It doesn't define the top speed of a particular bicycle, just it's speed when coupled with that rider, and the OP didn't specify a rider!

supersonic

He specified a TdF rider moving to a mountain bike ie the SAME rider. The fact is he will not be able to hit as high a speed nor maintain the same average speed. If the gearing is the same, the reason is DRAG.

bennett_346

He specified a nondescript person and no stats to calculate energy input from therefore the most accurate answer that can be given is the top speed attainable mechanically, hence i assume he specifies no particular rider.

supersonic

A 'nondescript person' who's power output will not change compared to the road bike. This is a constant here. The gearing and drag are variables. We need to look at the variable, which is the bike, as in the question.

cooldad

Time to untwist the knickers ladies because it's an irrelevant question for a mountain bike and becomes redundant as soon as you hit the first wet root.