Mountain Biking - road bike advantage percent over an MTB

What would be the speed advantage of the same rider on the same flat, paved course, on a road bike verses a mountain bike? Assume the MTB never spins out the gears.

I'm talking a standard, 20 lb. road bike with 90psi slicks vs. a standard, 25 lbs. XC hardtail with 40 psi knobbies and enough air pressure in the fork to keep it from bobbing.

Does the road bike, due to lower rolling resistance, lower rotational weight, and better aerodynamic position have a 5% advantage, assuming the same rider and no hills? 10%? 50%?

I just got dropped BADLY by my wife (a triathlete) on a flat bike-path ride of about 25 miles and am wondering if I should play the "my bike's an MTB, yours is a road bike" card to save my delicate ego.

(the fact is that she's in much better shape than I am, but I'd rather blame the bike ;))

Yes it will. Its a perfectly good card to play...reverse the situation and play. If you still get dropped....enjoy humble pie :D

There's lots & lots of variables here to be dealt with.

1st off has to be the rider. If she runs/bikes/swims and you lay on the couch, who do think will win any race?

2nd: the bike's are totally different, other than having two wheels, a seat, frame, etc. The gearing, weight, air pressure in tires & tire tread are all enormous advantages to the road bike. If both bikes were identical in every way EXCEPT just the tires, you'd be amazed how much slower the knobbies would make the bike.

I could go on & on, but why don't you just settle this the most simple way possible.

SWAP BIKES WITH EACH OTHER.... and race again. Provided you can both ride each others bikes.

Mael and I were thinking the exact same thing @ the same time apparently. He beat me by posting a shorter reply.

yeah there is a big difference on the two. just looking at my own speed differences between my two bikes i'd say I'm around 20% to 25% faster on my road bike. I have a better solution for you though. Just admit she's a faster road rider, but you are more versatile. Challenge her to a race on a trail, same bikes as before. Fastest combined road and trail time time wins.

I use my XC rig on the road a lot. It weighs 21-22 pounds i believe, thats with slicks though. Put some slicks and you can greatly narrow the margin between mtn and road bikes

I ride both of the same bikes you describe. Some days i ride the MTB and other days i ride the road bike. I think my average speed advantage on the road bike is somewhere around 2-3 mph. Doesn't seem like much but in 1 hour, i would obviously be as much as 3 miles ahead on the road bike.

I'm talking about an "average." Some days the difference would be much greater, like today when the wind was gusting to 45 mph. It is much easier to ride a roadbike into a stiff wind. With that said, i still rode my Mountan bike 26 miles this morning, mainly on gravel and dirt roads. ;) I'm also exceptionally tired tonight.

Think it might be time for a day off. I rode nearly 100 miles last weekend (2 days) on the roadie and wasnt near this tired. Maybe it is all just adding up.

Thanks guys; that quantifies it nicely.

For the record, it wasn't a race, per se. We had the rare day when I was home early from work, the kids were in school, and she wasn't working so we hit the local paved bike route (Silver Comet Trail, outside of Atlanta) for a ride. We hadn't ridden together in years and when we did last, I was in top triathlon shape, on my Quintana Roo tri bike and she wasn't riding much.

This time the tables were turned. I just got back on the bike about 6 months ago and she's been riding consistently for years. I stuck with her 21mph pace for about 17 miles but died on the last 7. She enjoyed every bit of :) Payback's a *****.

i would say roughly a 33% advantage with the knobbies and all.
It is about as easy to cruise 20 or my roadie as it is to do 15 on my mtb.

If there was a headwind I would go higher. Tough to go aero on your MTB.

There is a big difference. I'd say something like 15-20% in favour of the road bike. More if you are riding into a wind.

The faster the rider the bigger the difference. If you couldn't hang with her in the draft then it wasn't the bike.

The faster the rider the bigger the difference. If you couldn't hang with her in the draft then it wasn't the bike.

Are you saying that all things equal (i.e. equal rider performance), a mountain bike should be able to hang with a road bike in the draft? If that is what you are implying, you are very mistaken.

Akak, I think keeping an average of 21mph on a mountain bike is fantastic. You have nothing to be ashamed of. I am not sure your wife would be able to do that if the roles were reversed. It all depends how hard it was for her to keep that pace on the road bike.

The faster the rider the bigger the difference. If you couldn't hang with her in the draft then it wasn't the bike.

You are crazier than hell. On my XC Mountain bike rig, I could not hang in the draft of myself on my road bike spinning the 53T chainring at a high cadence.

you can try this speed and power calculator

http://www.kreuzotter.de/english/espeed.htm

Very cool calculator.

Even though it didn't allow me to put in my true tire size (the largest it allows is 1.75 knobbies), it did show a 1 mph difference between it and a bike with medium width slicks.

Bottom line: Yes, she had a bike advantage. No, that wasn't the only advantage she had :)

Akak,
I realize in your 1st post you specified that you never "spun out the gears" but you'd have to realize that although you may have been "spinning" at a similar cadence that she could push a much higher gear (I guess higher/taller would be the right description???) and cover a lot more ground at seemingly the same cadence. I hope that makes since as I sometimes have a hard time putting my thoughts in the correct words! Aside from that all the obvious things such as rolling resistance, weight, aero etc mentioned above would put you at a great disadvantage.
I know years ago I rode w/ one of my regular MTB buddies (who I kept up with on the singletrack) on the road and he broke out his trick road bike and he had to stay an his smaller (of the 2) frt chainrings for us to even think of keeping up w/ him. The smaller frt chainring on a roadie is usually a 34-39 tooth and the larger a 50-53 while the rears are usually 11-23 cassettes. Compared to the usual MTB rings on 24-34-46 (some top out at 44) and the rears at 11-34 range that tallest gear can be a big difference (52/11 vs a 46/11 ratio for instance).
Go ahead and give yourself a break and just say it was the "equipment advantage"!!!!

I avg. about 18-20mph on the road with my road bike, and about 14-16mph on my mountain bike, with 60psi in the knobbies FWIW. Figures out to about a 20% difference, but something of note is I can also ride a lot longer on my road bike at 20mph than I can on my mountain bike at 16mph. One of my friends is slower than molasses on her road bike, so I take the MTB when we go out. By 20mi at a 16mph pace, I'm quite spent, whereas on my roadbike I can do 30-40 at 18mph without much problem at all.

I commute to work with a road bike on nice days, it takes 25 to 35 mins to go the 17km. The difference in time is attributable to the wind, other factors remain constant. On days that threaten not to be so nice (but still may be dry) I use my Mtb. It takes 40 to 50 mins to travel the same distance.

My average speed increased by 2mph going from 60psi 2.1" tires to 100psi 1.5" tires.

I ride both and, let me tell you, there's a HUGE difference between the two with the road bike being an exponentially faster machine. The fact of the matter is, the rider is 90% of the equation. Case and point: I'm a 195 lbs rider who occasionally unleashes the road rig. On a road jaunt through the canyon by my house I caught and past a skinny, very fit guy on a very high-end hardtail who was doing a road section in between trails. I didn't think much of it until I heard this buzzing noise behind me and realized that I hadn't dropped the weight weenie!

At that point, I "turned the screws" thinking "I'm going to leave this cocky bastard in the dust!" Uhhhh...no. Even though I was pushing myself to the limit, this guy was holding my wheel like he was Lance-friggin-Armstrong on a club ride.

Thankfully, the guy turned off to head to his trail after about a mile and a half because I think I would have exploded if I kept pushing that hard for too much longer.

It just goes to show: A good rider will beat a good bike any day of the week.