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I bought a downhill bike from a friend awhile ago when I was considering trying out downhill biking. Currently, I want to use it to do some road biking. The tires read 29 PSI 2 bar, Max of 80 PSI. I pumped them to 29 PSI, and that biking session was pretty tiring. I pumped it up to 40-ish PSI and I can coast, and pedal much better. My friend at work suggests I pump it to the max of 80 PSI, but just want to be sure this is a good idea before I try it.

I'm pretty new to the technical side of biking/bikes.

Cheers.

Update: I forgot to mention that I read this post but it doesn't really mention road biking.

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Your friend sounds right. Try pumping it to 80 and see how you like it. If it's rated to 80psi you'll be ok. It'll probably feel good on the road, but may be a bit hard (= unforgiving) if you go offroading. Typical road pressures will exceed 100psi, but of course that assumes skinnier tyres than you have. –  PeteH Jun 11 at 19:18
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Yep, for road biking you want your tires at their max rated pressure or maybe a little higher. –  Daniel R Hicks Jun 11 at 21:15
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Road tires need to absorb terrain just like MTB tires, the tire pressure should match your weight and use. Unless you're 200+ lbs and your roads are perfect, max pressure is not always the best. –  Fred the Magic Wonder Dog Jun 12 at 14:35
    
Thanks PeteH, DanielRHicks, and @FredtheMagicWonderDog for the advice. One question - how would I figure out what tire pressure matches my weight? I'm about 175lbs. Looks like I'll be pumping these tires up more regardless. –  Adrius Jun 12 at 17:45
    
There is an app for that... vittoria.com/tech/recom-tyre-pressure This web pages is also useful. bikequarterly.com/images/TireDrop.pdf But make sure you note the weight listed is PER wheel, not the entire bike/rider. –  Fred the Magic Wonder Dog Jun 12 at 18:24

2 Answers 2

You will have lower rolling resistance at a higher pressure

A lower pressure puts more tire in contact with the ground for traction.
In the dirt this can be important.

But you are running on the street.
Yes traction on the street is also important.
But your downhill tires are not going to have good traction on the street.

Downhill bike and downhill tires on the street you are looking for low rolling resistance.
So pump them up to the max and no hair pin turns at 20 mph.

If you are going to ride on the street you could mount some street type tires.
And they have tires for a mix of dirt and street.

This is probably a duplicate some where.
I did not search.

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There are certainly threads on here which discuss the merits (or otherwise) of running at high pressures. Good entertainment value but would probably not leave the op any the wiser in this case - there is a certain amount of entrenchment ;-) –  PeteH Jun 11 at 19:31
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As I agree with this answer, I strongly recommend to change your tires to slick ones for road use, or at least ones with very light thread. DH tires or really knobby tires tend to swipe on heavy turns on the road, wich will make you avoid leaning, thus wearing only the center of the thread (wasting tire) and givin a less fun ride. Other than that, any tire should be able to withstand the max pressure on the label without problems. –  Jahaziel Jun 12 at 4:54
    
Thanks for the advice @Blam –  Adrius Jun 12 at 17:46
    
@Jahaziel If I can prove to myself that I can make biking a consistent and fun activity I will definitely be looking into buying new slick narrow tires for road use. It might be a bit of an undertaking since this bike came with front shocks, which makes pedalling even more difficult. Yay. –  Adrius Jun 12 at 17:48
    
If the fork is adjustable, for road use, a stiffer compresssion setting, higher pressure on an air fork, locking (if available) and the slowest rebound setting, all help for pedalling (but not all forks have them). –  Jahaziel Jun 12 at 19:27

Please check the rims manfacturer site for maximum pressure levels depending on the tire width. Putting 80 psi into a 50-60 mm tire needs very stiff and unforgiving rims - NoTubes limits the max. pressure for such tires (2.2") to 38 psi (for the old Flow rim)!

The values on the side of the tires are usually safe zone values, where you couldn't destroy anything. They don't really make sense for outside usage. 80 psi is out of the world for a usual MTB tire, and you won't even notice the difference to 60 psi!

Usually you are good with 7-15 psi above the tire pressure for offroad use. Here is an formula for some starting values: http://www.notubes.com/help/tirepressure.aspx Still, you will have to adapt tire pressure to real life usage.

In addition, i would recommend new tires for road and (just) gravel riding, for example some Schwalbe Fat Frank oder SuperMoto. Kenda also produces some high volume slicks, which will be very comfy at 20-30 psi and won't look to stupid on a downhill bike.

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