# Ask PB: Tire Pressure, Ghost Shifting, and Pedals for Bigfoot

Jun 16, 2015

Here at Pinkbike we get inundated with all kinds of questions, ranging from the basic "Can I have stickers" to more in-depth, soul searching types of queries like if you should pop the question or what to name your first child. Ask Pinkbike is an occasional column where we'll be hand picking and answering questions that have been keeping readers up at night, although we'll likely steer clear of those last two and keep it more tech oriented.

Proper PSI

Question: Pinkbike user cryan asked this question in the downhill forum: I'm just wondering if anyone has any good tips when it comes to figuring out the proper pressure to run your tires at when downhilling in different conditions? How much do I run when it's dry? And how much should I run if it's wet and muddy?

 First, there are all sorts of things that can factor in here, including if you're running tubes or not, what type of rider you are (smooth or smashy), how much you weigh, and what you're trying to accomplish on your bike. Then there's also things like rim width, tire volume and casing rigidity, and even the rubber compound to keep in mind. It's a topic we've covered before, with Vittoria's Ken Avery covering the hows and whys of air pressure in a 'To The Point' article a few years back, but it bears going over again. What I can't do is give you an exact number to go with, but I can explain how to figure it out for yourself.One could easily write a few thousand words about what tire pressures work best in each scenario, but there's a much simpler way to figure it out for yourself: since you didn't specify what kind of tire setup you use, try starting at 30 PSI and riding a section of trail that is typical of your usual terrain. Be sure to include difficult corner as well. Do the section over a few times, letting out 3 - 5 PSI before each test run, until you either feel like the there is too much casing roll (it'll feel vague, and like your bike isn't responding to inputs), or you start to bottom out the tires on the rim over roots and rocks. You might also 'burp' the tire if you're using a tubeless system, which is when the casing rolls over so much that it pulls the tire's bead away from the for a spit second and allows a fart of air and sealant to escape. Add a few PSI until those symptoms go away and you should be within the ballpark, and then you can adjust to your preference from there. As for downhilling in wet an muddy conditions, you'll generally want to run your tire's a little lower. This is the opposite approach that a World Cup-level racer takes, as they add pressure to prevent flats since they can't see the rocks and roots hidden under the mud, but more casual racers and riders should be looking for increased traction when things get slippery. - Mike Levy

The ideal air pressure allows the tire to conform to the ground better, thereby improving traction.

Phantom Shifting Woes

Question: Jrcd says in a PM: I'm an ex-bike mechanic and have worked on countless bikes at various shops over the years. Recently, I was working on my wife's bike (a Specialized Stumpjumper FSR 29er), and had the rear shifter's indexing correctly adjusted on the stand. Taking the bike for a test ride, the indexing was revealed to not actually be aligned, and I recalled encountering similar situations from my days in the shop. Further cable tension adjustment solved the problem, but my question is this: Why does the weight of the rider cause a discrepancy between shifting on the stand and shifting during a test ride? A similar phenomenon occurs when truing wheels, but it's easier to see the how the rider's weight would affect the tension of the wheel. What gives?

 Your problem occasionally happens to dual-suspension bikes. The standard cable routing on some models will cause a slight change in length as the suspension settles into its sagged position. I had to run down that issue a few times. Test my theory by running a full-length housing and don't attach it to any part of the frame that will cause it to flex. If that fixes the problem, then reroute the derailleur cable and housing on the frame to minimize flexing. - RC

The 2013 Stumpjumper FSR Expert Carbon EVO 29 has similar under-the-bottom-bracket cable routing as the bike Jrdc was having trouble with.

Pedals for Bigfoot

Question: BigSteve420 asks in the Bikes, Parts and Gear forum: I am curious as to what are some of the biggest pedals available? I have a size 13 foot and the pedals I have seem too small. The Spank Oozy are 110mm x 110mm and the Chromag Scarab are 110mm x 105mm. Are those the biggest or are there some that are biggger?

 Both of the pedals you mention are good options, but for something even bigger I'd recommend the VP Harrier pedals. They measure 120 x 110mm, and are only 12mm thick. When I tested them last year, I found that they were almost too wide for my size 11 feet, but I imagine they would be just about perfect for you, providing plenty of room to avoid having your foot hanging over the edge of the pedal. They're well constructed as well, with an aluminum body that rotates on bushings around a chromoly spindle, and a decent amount of traction provided by the 10 steel pins on each side. - Mike Kazimer

The VP Harrier has plenty of room to accommodate riders with big feet.

Have some unresolved tech questions? Jump in the Pinkbike Forum and we'll look to answer it for next time.

Must Read This Week

### 95 Comments

• 257 6
30 psi in my minions I don't care about your opinions
• 85 3
Crushin' it killin' it all tahm conditions
• 91 1
Riding your trails without your permissions
• 62 2
Mountain bikes are serious business, no flats, I always run tubeless
• 12 83
Just don't be a wanker who put's his tires way down and brag about the psi level...
• 35 112
tetopluz (Jun 16, 2015 at 17:41) (Below Threshold)
I ride mine 40psi ...harder than my cock in a thai whorehouse
• 154 2
I SHALL SING YOU THE SONG OF MY PEOPLE
• 60 1
More sponsors than you'd believe emergency redbull stuffed up my sleeve
• 20 3
Can I have stickers?
• 46 1
We have successfully summoned Matt himself
• 12 3
It was worth it im fanboying
• 11 59
follow me matt follow me please

look at me here
begging on my knees

look how im rhyming
10/10 timing
i promise im not lying
otherwise ill be dying

amen
follo mwe
• 3 1
2-2,5 bar aka 30-35 psi
• 53 0
80 PSI in my Procore, I don't care about all you folk-lore!
• 4 0
Fuck that made me laugh hard out bro
• 5 7
F*ck the haters @mountainbiker-finn! Made me laugh!
• 1 1
I'm fast, i'm faster than you
• 1 1
intense 909 race rubber, 13psi bring it back,and you'll be hitting rocks just for fun.only other tire that came close high roller maxxis @27psi.
• 137 2
If your Aaron Gwinn you don't need tire pressure or even a tire..... or a chain or brakes.
• 11 1
or handlebars, or pedals, or a BB... not even wheels or suspension, God just floats him down the track at 55mph.
• 78 4
Tire pressure: Your weight in lbs., divided by 7. Add 2 PSI for the rear and minus 1 PSI for the front. Works 75% of the time, every time.
• 14 1
Holy shit! I just did your maths and come up with my 'normal' tire pressures. And I care a lot about tire pressure. I may put a little more in if I am racing in rocky terrain, or take a little out when it is wet, but overall - you nailed it.
• 6 3
I've seen this before, and if you're a big guy and/or don't ride hard, sure. It's close, but even with my pack on that equation still comes several psi too low. W/o pack it says 24psi R, 21 psi F. W/ pack says 26psi R, 23 psi F. I'm 155lbs pre-pack, and will destroy a R tire with anything less than 28psi. I typically run 26-28psi F, 28-30psi R. Now this is with Maxxis EXO tires, numbers will vary if running DH tires.
• 24 0
@NMK187 that method is now the Sex Panther method, lol

I'm Ron Burgundy?
• 6 0
Ya, that equation works well for tubeless. Might be a bit soft for tubes. I'm 195 lbs and it works really well for me. 27F, 30R. And yes, that is in ideal conditions. I take out a few PSI's in the rain, and add a few for a really rough and rocky trail.
• 2 1
Divide by 6 if riding hard on jagged terrain with tubes.
• 3 0
Dude that is spot on! I got 18psi front and 20psi rear which is what I run on my DH bike!
• 1 0
@NMK187 Not bad. Your formula put me within 1 psi front and 2psi rear of what I run.
• 3 2
@mtnbykr05 Your psi seems really high to me.
I'm 155 pounds with gear and run 20 psi front/22 psi rear.
That's tubeless on a mix of Maxxis EXO, Shwalbe and Continental TR.
• 6 4
Wow, that is a nice equation! But I recently started pumping them Big Bettys up. 30 rear 28-29 front. I am 142lbs...
I like my rubber hard, I also ride it very stiff in the front and go hard and slow in the rear, and yes, she did say that
• 1 0
To get to my "usual" pressure through this method I had to divide by 5 instead of 7. Then its very accurate
• 1 0
Wait, why the minuses?
• 1 0
The equation works for tubeless tires on normal rim width. But these new wide rims can allow pressures well below 20.
• 1 1
Good luck with your low tire pressures! I'll save my rims and tires. Just last week I hit a very mild rocky section of trail, with about 23psi rear, and destroyed my rim and tire. Yes, I'm running tubeless w/ a stan's flow ex. Rarely have issues @ mid to high 20's. Even look at the bike check on vitalMTB; m.vitalmtb.com/photos/features/PIT-BITS-Oregon-Enduro-Series-Bend,9030/Curtis-Keenes-Custom-Specialized-XL-S-Works-Stumpjumper-650b,92558/sspomer,2

All pressure's are mid-20's and up. Voreis with a super high 38psi F+R. Most WC DH riders are also running high 20's and into the 30's. I think Fairclough stated to be running 30-32ish.
• 1 0
I can run 25lbs or less in my DH tires (minions) and the same on SG Schwalbe MM's because of the casing./ sidewalls.
On trail bikes it's abou t4- 5lbs more on the single ply sidewalls, even when tubeless, for the same feel.

It's important to state what application it's for to make any sense of it.. DH and Trail tires are worlds apart.
• 6 1
I just give the tire the good 'ol squeeze the sidewall test and call er good
• 1 0
Unless you have one of these new wide rims (28mm+ inner width), you definitely shouldnt be running anything lower than 28 rear 25 front. but with a wide rum, I know guys are running pressures less than 20.
• 22 2
Best pedals for Bigfoot would have velcro surface so that his fur sticks to it.
• 16 0
Size 15 foot. Raceface atlas pedals have been very to me so far. Love em. Tire pressure? Who knows. I gave up like looking at the psi numbers and just sit on the bike and bounce up and down like a wild animal to figure it out.
• 11 0
I have a size 13 and the Chromag Scarabs are amazing pedals. The concave in them hugs your feet exceptionally well. Also the DMR Vaults are a great pedal for big feet.
• 1 0
I have a size 14. The DMR Vaults or the e-Theriteen pedals work quite fine
• 11 0
i find tire pressure is tire specific, with different tire thickness and widths. all the 1 ply i have tried, feel noodly.
• 8 0
Me + bike + some water = about 300lbs. Currently running 26x2.35 Spesh Butcher and Purgatory with Control casing, tubeless on 32mm rims, at 28lbs in the front and 33lbs in the back. Crazy grip, no farts = happy fat guy.
• 49 1
Sometimes fat guys aren't happy unless they fart. -a fellow happy fat guy
• 3 0
East coast rocks are not kind to tubeless control casings, I learned the hard way and moved up to grids. I. Around 250 lbs all trail ready too haha
• 11 0
Pure fantasy! There is no credible proof that bigfoot rides a bicycle
• 1 0
I hear he rips on a unicycle though!
• 5 0
I have size 13's and the best I've found is E*Thirteen LG1's. They're huge! They're wide, but more importantly, long. First thought I had when stepping on them is this is what regular pedals must feel like for the majority of people. Gobs of traction, multiple pin length configurations and replaceable wear plates. They aren't the thinnest, lightest or easiest to spin. But they're the best pedal for big feet by far.
• 2 0
I have regular sized feet but just prefer a large pedal and have been very happy with the e13s.
• 2 0
Yup, just bought a second pair myself. great pedals for those who like a big platform, big feet or no.
• 6 0
I have always thought that under the BB cable routing was a stupid idea (mainly for risk of damage) but this even more reason.
• 10 2
The picture of the tire I would call flat.
• 7 0
Raise pressure for bike park.
• 6 0
Ask PB Sasquatch edition? Large pedals, compressing suspension so much as to compromise shifting, and tire pressure
• 2 0
I have VP harriers and like them. Only downside is they have a little bit of bushing play, but not usually noticeable underfoot. Just as grippy as my spank spikes, but lighter and more supportive. tried to sell them and realized I'd rather just keep them cause they're badass.
• 1 0
I've tried a lot of flats over the years and I'm now on VP Harriers. I only wear size 10.5 shoes but I've always liked wide pedals. The big platform feels just right and offers great support. Grip is fantastic. Recommended.
• 2 0
Size 12 4E, so I end up wearing 13s, since 5-10s don't come in widths. Using Shimano Saint pedals and loving them. Wide enough, lots of pins. Even better, the pins are straight up mini hex bolts, so you can adjust them to be as aggressive as you want them to be. And since they screw in from the other side, tehy're easy to replace. Not that I've lost even one, mind you.
• 2 0
Pressures equation is near enough for me at 155lbs. Pedals gotta be DMR Vaults.....115x115 MASSIVE PLATFORM and available in magnesium for the weight watchers..just watch your shins cause these pedals bite. And they have a concave platform WITH NO PINS so your foot beds in properly for massive grip. The new oil slick Lacondeguy signature pedal is badass
• 4 2
I use to run 22 psi in the front with a bonty XR3 team, then switched to XR4 expert and have to run at 18 to get similar feel. Just goes to show that casing and compound can make a huge difference.
• 6 19
nyles (Jun 16, 2015 at 17:00) (Below Threshold)
You should try a real tire! Those bontragers blow hard.
• 5 0
Not quite sure what tires you tried, I've had great experiences with all their tires
• 2 0
Bontragers are garbage, unless you use them to correct your spelling mistakes, and they still leave an ugly smudge on the paper. I will rename them sphincter rubbers..........
• 3 0
Had a stumpjumper for a few years - thought i was useless at getting cable tension right as always had to adjust it on the fly after a tune! this explains it! chur
• 2 0
Yes i've had to do on the fly adjustments on my '14 trance as well, same routing. A mate with the same bike has it far worse than me though.
• 5 1
I run 50 psi slopestyle fully, on my local buffed out flow trail, with lots of jumps, and flow.. love being fast.
• 4 1
1. vittoria "GOMA" F-28psi, R-32psi
2. So I will be with BB Cable routing upwards.
3. Size 100X105mm pedal seems the best.

^^*)
• 1 0
Yes, the Goma is an incredible tire!!! Too bad that the Datura does not come in a 275 version, they are aces in the mud!!
• 1 0
Usually when I tune a der. And there are issues (on dual suspension) I have issues with the front der. Over rear. It issue happens when the height is set on the stand correctly it isn't on the test ride. So I usually get it close and adjust on my test. If it is really giving me a hard time I look at it while really pushing into the susp. Or opposite (depending on my weight vs the customers) and then raise / lower height accordingly.
• 1 0
I always run about 24-28 psi depending on the course. I err towards 24/25 for wet and muddy and I usually run more for dry conditions.
The best trick I've learned is just a good few thumb presses on the tire. Once it feels "right" I know I'm good to go. This takes time and practice to master but I've never had a flat in a race run. I invested in a good digital gauge also. I make up for higher pressures by setting my suspension a tad more soft than most. Not super plush but one or two clicks.
• 1 0
Huge pedals =Speedplay Drillium. Not made anymore, but look here on buy/sell, or e bay. They come up often, and were the largest pedal made. Industructable with chromoly spindle, do it yourself easy greasin, and slight concave. These babies are heavy but take clydesdale crushing abuse and laugh it off.The spindle goes all the way though pedal, where the VP Harier stops short and can fail if your size 15 gunboats hold up alot of girth.
• 1 0
Hahaha size 13? Im guessing thats US sizing too? Hahaha try 16 UK (17 US). My feet overhang dmr vaults by about an inch. Ive been told of the syntace pedals though, apparently the biggest model is about 15mm wider than vaults
• 3 0
Having that exact shifting problem on my 08 specialized pitch right now, thanks for the info on it
• 3 0
Twenty6 pedals have a big platform are low profile the best grip of any flat. Come in many colors.
• 3 0
My simple tyre pressure thoughts...25psi front, 30psi rear, adjust accordingly to conditions on the day
• 1 0
stumpy routing is full length, It doesn't ghost shift. The cure for ghost shifting issues on older long travel bikes like the kona stab is full legth zip tied down. kinda confused about this whole discussion
• 2 0
depends on the frame size even with the Stumpy, its better or worse as the outer flexes during suspension cycling I've cured a lot of customer's bikes by ditching the stock cabling and coming up with a custom cable route using zip ties, stick on cable guides or whatever else is to hand worse bike was the old Big Hit due to the amount of cable movement under compression, we used to cure it by running the rear mech cable along the top of the chainstay with a thick chainstay protector to prevent the outer getting torn by chain slap, and often an Avid Rollamajig on the rear mech to remove the loop at the rear that was vulnerable to getting split
• 1 0
Harrier pedals suck, the bushings blow out real quick mate. Start to develop play way to fast. I've had Deity pedals for six years now with no play and the bearings are still fine!
• 2 0
I wear a size 16 or 17 shoes depending on the maker and i love my Acros A-Flat XL (120 x 110 x 20 mm) largest platform I've been able to find.
• 1 0
Sitting on my road bike (80's ten speed) also tweaks my gear adjustment. I was hoping to be enlightened reading this, but I guess I got my hopes up too much
• 1 2
www.treefortbikes.com/#navbar=pro___333222400807___1471

use the "add to cart at their price" feature to get them at the outside outfitter price

boss pedals, better than the spank spikes i've blown up 3x
• 1 0
• 1 0
Very interesting. I like that nerds out there take the time to apply mathematics to activities that are actually fun(there is partial sarcasm in this statement). There are some qualifying statements that should be made -- these tests were designed and performed with road bikes needs in mind, and the last line of the article reads,"4 For tires mounted on rims of appropriate width for the tire width." This last statement has been the source of much debate lately, so I think the best MTB tire pressures are going to change a lot in the next few years until rims are widened out (an idea which I am all for) until tires are purposely built for the newer, wider rims.
As a consumer, I wish the manufacturers would have solved this problem better when DH and freeride pioneers were experimenting in the late 90's and early 00's so that I wouldn't have to immediately start looking for new rims and tires for my first 29er I bought this spring. I had to go from 2.25 to 2.35 tires after my first semi-fast downhill turn, and 21mm rims are falling to pieces and making my PSI go up to hopefully preserve the rims long enough to get some tough, wide rims.
• 1 0
I took the idea of 15% tire drop and tried to replicate that on my mountain bike. I also tried to apply the 60% 40% weight distribution idea. Took some air pressure measurements and like the setup. This brought me to 23 and 37 psi. I use it as a starting place, scrub air on the trail if I find it too bouncy.
• 1 0
Opposite problem. Try finding shoes for a size 7 EEE width food and pencil skinny heels. Damn my hobbit feet.
• 1 0
is it for real that when it's really dry and dusty you have to ride with really soft tires like 1-2 bar ??
• 1 0
Another size 13 foot here, I like the RF Atlas pedals, I now have them on my DH and AM bikes. All other bikes are Time ATAC.
• 1 0
Anyone know where I can buy some vp harrier pedals?
• 1 0
Try finding mtb shoes for a size 15 foot. B*stard
• 6 0
You can use a shovel with straps.
• 2 1
Size 16 homie, get at me. But for real, DC skate shoes are the only thing big enough with a grippy bottom and stiff sole for riding flats, and Shimano makes some of their clipless shoes big enough.
• 1 0
Di2 is great for FS bikes!
• 1 0
as a big foot I use Scarabs and they are just fine
• 1 1
Meanwhile I can barely find riding shoes for my 5" feet
• 1 0
can we all have stickers

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