Fat tires on Specialized Sirrus?- Mtbr.com
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  1. #1

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    Fat tires on Specialized Sirrus?

    Newbie here, but lots of experience on asphalt with my road bikes.

    I need a bike to ride well maintained, flat trails. I have a Specialized Sirrus that I don't ride too often. Does anyone know what is the largest wheel/tire I can put on the Sirrus?

    Except for the skinny tires, my Sirrus would be perfect for the rails-to-trails riding I'll do.

    I'd appreciate any help, thanks!

  2. #2

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    I appreciate all the fantastic help I've received on this wonderful forum. Oh, wait, I didn't get any.

  3. #3
    i also unicycle
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    give it some time. there's not much clearance out back on a sirrus. i'd be surprised if you could get larger than a 700x35 out there. sell the sirrus, buy an entry level hardtail if you want to actually ride offroad.
    mtbr says you should know: i work in a bike shop.
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  4. #4
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    Sometimes it takes a little while for someone who knows anything to see your post and be able to answer. You asked a hard question. :P I saw your post on the Specialized forum, and actually also have a Sirrus, but I don't have a clue what the largest tire you can put on it is. That's why I didn't answer. What I can suggest is that you take it to your shop and ask them, also see if they'd be willing to let you "try on" some bigger tires to see just how big you can go. Good luck.
    2008 Specialized Safire Comp

  5. #5
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    Agreed

    Quote Originally Posted by Swthrtsuzy
    Sometimes it takes a little while for someone who knows anything to see your post and be able to answer. You asked a hard question. :P I saw your post on the Specialized forum, and actually also have a Sirrus, but I don't have a clue what the largest tire you can put on it is. That's why I didn't answer. What I can suggest is that you take it to your shop and ask them, also see if they'd be willing to let you "try on" some bigger tires to see just how big you can go. Good luck.
    I don't think you'll get too many responses here because a Sirrus isn't a mountain bike. You could try posting your query in the wheels and tires or commuter forums. But I agree that just hitting a local shop might be the way to go.

  6. #6

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    My apologies for rude behavior on my part. Thanks for the advice. I'll be sure to pass along an answer once I get it, although that will probably be a few weeks.

    Thanks again.

  7. #7
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    I would say a 1.5" wide shouldn't be a problem on that bike. The question is are the brakes going to clear? Let the Bike Shop figure it out.

  8. #8
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    Well, it's 9 months later... do you still need to know...? I just put 37x700C Travel Contacts on my Sirrus. They fit just fine...


  9. #9
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    Max tyre on Sirrus

    Hi Mike
    I read your post re the biggest tyre you can put on a Sirrus and thought great thats what I'll do as I was unsure whether to go for a Crosstrail or Sirrus. My riding is 90% road 10% rough paths not really muddy just small stones and gravel. Problem is the guys in my local shop are saying they doubt that a 37X700 Travel Contact will fit so I thought I'd ask what model and year your Sirrus is?
    Thanks
    Steve

  10. #10
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    Steve,

    I put the 37x700 travel contacts on a 2007 Sirrus Sport (the one with the carbon fork and stays. You can see some pics here...








    Mike...

    Quote Originally Posted by G4fan
    Hi Mike
    I read your post re the biggest tyre you can put on a Sirrus and thought great thats what I'll do as I was unsure whether to go for a Crosstrail or Sirrus. My riding is 90% road 10% rough paths not really muddy just small stones and gravel. Problem is the guys in my local shop are saying they doubt that a 37X700 Travel Contact will fit so I thought I'd ask what model and year your Sirrus is?
    Thanks
    Steve
    Last edited by mikeschn; 04-07-2010 at 02:21 PM.

  11. #11
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    Sirrus tyres

    Thanks Mike, looks like you have a few nice upgrades on yours with the wheels and bars etc. I've been looking again at options and I thought about a Cyclocross bike with a flat bar conversion. Maybe a Tricross or something similar, did you consider going down that route?
    Steve

  12. #12
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    Quote Originally Posted by G4fan
    I've been looking again at options and I thought about a Cyclocross bike with a flat bar conversion.
    NO!!!!

    Cyclocross bikes have pretty much the same geometry as any other road bike. The top tube is quite short, so if you put flat bars on one, you'll have a ridiculously upright position. Think hipster on a fixie. If you put a really long stem on, like 150mm, it would be less bad. But still bad.

    If you have back problems and really need a position like that, fine. But if you think it's going to give you a light, high-performance bike with a comfortable riding position, think again. Something like the Specialized Sirrus or Crosstrail or Trek FX would probably be a lot closer to what you want, and you won't have to buy a whole new cockpit and screw up a perfectly good cyclocross bike to get it. They already have longer top tubes and are designed to be flat bar road bikes. Or just get a mountain bike and some skinny tires or road wheels.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  13. #13
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    Okay, here are the two pics I was looking for... front & rear clearance...






    Mikey

    P.S. I had to get the wider rims to make it work. I don't think the original rims would work with anything over 28mm.

    P.P.S. Check out the BMC in this message... https://forums.roadbikereview.com/sh...01#post2669301

  14. #14
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    Sirrus and other options

    Thanks for the advice AndrewSwitch and the pictures Mikey.
    You can probably tell I'm new to all this, it'd be a real pity to get the 'wrong' bike at the beginning so your help is invaluable.
    That's it then, decision made, Sirrus with A319's rims and bigger tyres for me.
    I've already had a test ride so I'll be ordering a size large in the morning!!
    I'll sleep a lot better tonight now I'm confident of the way forward.
    Thanks again guys
    Steve

  15. #15
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    weight

    Hey, is your sirrus as light as say the allez road bike?

    Quote Originally Posted by mikeschn
    Okay, here are the two pics I was looking for... front & rear clearance...






    Mikey

    P.S. I had to get the wider rims to make it work. I don't think the original rims would work with anything over 28mm.

    P.P.S. Check out the BMC in this message... https://forums.roadbikereview.com/sh...01#post2669301

  16. #16
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    I bought a Sirrus Expert in the end and had exactly the same wheel and tyre spec as per Mikeys suggestion. I'm only an occasional biker so my experience is very limited but it seems incredibly light to me. The tyres make it easy to stay with my young lad off-road yet I can ride it to work at what seems like effortless speed.
    To be honest it makes me feel a little guilty as my sons small mountain bike (he's 8) looks great but weighs more than my bike!!
    Steve

  17. #17
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    Glad that's working out for you G4Fan!

    Mikey

    Quote Originally Posted by G4fan
    I bought a Sirrus Expert in the end and had exactly the same wheel and tyre spec as per Mikeys suggestion. I'm only an occasional biker so my experience is very limited but it seems incredibly light to me. The tyres make it easy to stay with my young lad off-road yet I can ride it to work at what seems like effortless speed.
    To be honest it makes me feel a little guilty as my sons small mountain bike (he's 8) looks great but weighs more than my bike!!
    Steve

  18. #18
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    The cyclocross bike also has a higher bottom braket hight than the Sirus. I also would not recomend the Sirrus on fireroads or rails to traisl that are not asphalt.
    Some of my happiest memories in life took place on my bicycles. - Me

  19. #19
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    high BB? thats just BS... a hybrid can do pretty much everything a cross bike can do and especially off-road. Plus the sirrus comes with v brakes (or at least my one did) which are better than canti's and enough tyre clearance to get 32s in there. The bottom bracket thing only scares newbies and is made largely irrelevant with clipless pedals unless you ride fixed or REALLY gnarly terrain.

  20. #20
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    weight trimming on a kids' bike

    Quote Originally Posted by G4fan
    To be honest it makes me feel a little guilty as my sons small mountain bike (he's 8) looks great but weighs more than my bike!!
    Steve
    Don't know if you're still following this thread, but...

    The easiest place to lose some weight would be the tires. BMX tires come in many sizes, so you can probably find something decent to fit. I recently figured out that the swing in weight on my MTB from swapping its current all-conditions tires to a racier set when the trails dry out is going to be about a pound. If a width change is in there too, the weight loss can be even more.

    Children's bikes often have a cheap frame. Unfortunately there's not much you can do about that. To make pricepoint, they have some other cheap parts, and sometimes some stupid ones. The suspension fork, for example, is a good candidate for removal and replacement. Replacing might be a little tricky especially if you want a front brake, but between BMX forks, non-suspension-corrected MTB forks, and maybe even forks purpose-built to go on a child's bike, there's something out there.

    Wheels - same deal, kind of, but maybe a little easier to source parts. Depending on wheel size, there are rims available. Building a set of wheels is a fun project, but if you procrastinate at all, do 'em on new hubs so you don't make your son's bike unridable.

    Other things are going to be diminishing returns, and since he's 8, you need to decide how much you want to put into lightening his bike. If he's got a couple younger siblings, maybe it's worth a lot of effort, but if not, you're probably not going to make any more selling it to another parent in a season or two than if you didn't mess around with the build. So this would be because you feel guilty, or as a fun project.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  21. #21
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    FWIW (& for those that land here with google), I just measured the clearance on my 2012 Sirrus Comp with a micrometer. The narrowest clearance is the space between the seatstays: about 52mm wide at about 1cm above the factory 622x28 tire. So with a properly trued wheel I'd guesstimate that a 40C (42mm) would clear but you really wouldn't want to go bigger than that. 35C (37mm) is clearly OK as posted above, 40C might work but would be pushing it (depending on the tire & how much mud you plan on caking up on them). Clearance on the front fork & chainstay is more like 55mm.

    BTW Schwalbe Smart Sam seems to be one of the few 29" MTB tires available in these sizes.

    And yes, the 622x15 ETRTO factory wheels shouldn't be run with anything much bigger than a 28C on them. I put Michelin Mud 2 30C cyclocross tires on mine & they work fine but I haven't had them on anything sloppier than hard-packed dirt trails; I run them at the 36psi minimum recommended pressure.

    In my situation (I've got Open Pro road wheels on the Sirrus for commuting and thus a spare set of factory wheels lying around) looking for an off-road setup, I've come to the conclusion that the extra ~1cm of tire width with custom A319 wheels & 40C tires vs. cyclocross tires on the factory rims isn't worth the trouble of changing the wheels for the few times a year I'll go off-road with it, especially given that I can run the Mud 2s @35psi and the 40C Smart Sam wants 50psi min. I'm guessing it'll be a wash between the two of them. For stuff too loose or sloppy for the Mud 2s, I've decided I'll borrow my riding partner's old MTB instead & buy him some new tires.

    If I were trail commuting or touring on trails it would certainly be different...

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